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Lee Kwang Hong

Nanyang Technological University, School of Electrical & Electronic Engineering, Graduate Student

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Krishnamurthy Prabhakar

Central University of Jammu, Jammu, J&K, India

Obafemi Awolowo University

José Francisco Pessanha

UERJ - Universidade do Estado do Rio de Janeiro / Rio de Janeiro State University

International Journal of Science and Management

Syed Fida Hussain Shah

COMSATS Institute of Information Technology,Abbottabad,Pakistan

Obafemi Awolowo University

RANA ZAMIN Abbas

University of Management and Technology

Muhammad Akram Akhund

Mehran University of Engineering and Technology

CENTRAL UNIVERSITY OF TECHNOLOGY FREE STATE

Muhammad Imran Rasheed

COMSATS Institute of Information Technology

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Papers by Lee Kwang Hong

Curvature evolution of 200 mm diameter GaN-on-insulator wafer fabricated through metalorganic chemical vapor deposition and bonding

Japanese Journal of Applied Physics, 2018

Crack-free 200 mm diameter N-polar GaN-on-insulator (GaN-OI) wafers are demonstrated by the trans... more Crack-free 200 mm diameter N-polar GaN-on-insulator (GaN-OI) wafers are demonstrated by the transfer of MOCVD-grown Ga-polar GaN layers from Si(111) wafers onto SiO 2 /Si(100) wafers. The wafer curvature of the GaN-OI wafers after the removal of the original Si(111) substrate is correlated with the wafer curvature of the starting GaN-on-Si wafers and the voids on the GaN-on-Si surface evolve into cracks on the GaN-OI wafers. In crack-free GaN-OI wafers, the wafer curvature during the removal of the AlN nucleation layer, AlGaN strain-compensation buffer layers and GaN layers is correlated with the residual stress distribution within individual layers in the GaN-OI wafer.

Geometry and Thermal Stress Analysis of In-plane Outgassing Channels in Al2O3-Intermediated InP (Die)-to-Si (Wafer) Bonding

ECS Journal of Solid State Science and Technology, 2015

Geometry and thermal stress analysis of in-plane outgassing channels in Al2O3-intermediated InP (... more

Layer-Transferred Gallium Arsenide Heterojunction Bipolar Transistor on Insulator Substrate

SSRN Electronic Journal

Enhanced Light Emission of Germanium Light-Emitting-Diode on 150 mm Germanium-On-Insulator (GOI)

Germanium-on-insulator (GOI) has become a novel platform for Ge-based electronic and photonic app... more Germanium-on-insulator (GOI) has become a novel platform for Ge-based electronic and photonic applications. Discrete photonic devices such as waveguides, photodetectors, modulators, and optical pumping lasers have been successfully demonstrated on this platform. To realize electric injection emitting is highly desirable towards integrated photonics. In this work, we report for the first time the Ge p−i−n light-emitting-diodes (LEDs) on the GOI substrate. The high-quality Ge LED on a 150-mm diameter GOI substrate was fabricated via direct wafer bonding followed by ion implantations. As a tensile strain of 0.19% has been introduced during the GOI fabrication process resulting from thermal mismatch, the LED devices exhibit a dominant direct bandgap transition peak near 0.785 eV (~1,580nm) at room temperature. In sharp contrast to conventional III-V LEDs, we found that the electroluminescence/photoluminescence (EL/PL) spectra show enhanced intensities as raising the temperature from 300...

Metal-Semiconductor-Metal Photodetectors on a GeSn-on-Insulator Platform for 2 µm Applications

IEEE Photonics Journal

In this work, the metal-semiconductor-metal photodetectors were demonstrated on the Ge 0.91 Sn 0.... more In this work, the metal-semiconductor-metal photodetectors were demonstrated on the Ge 0.91 Sn 0.09-on-insulator (GeSnOI) platform. The responsivity was 0.24 and 0.06 A/W at wavelengths of 1,600 and 2,003 nm, respectively. Through a systematic study, it is revealed that the photodetectors can potentially detect wavelength beyond 2,200 nm. The dark current density was measured to be 4.6 A/cm 2 for GeSnOI waveguide-shaped photodetectors. The 3 dB bandwidth was observed to be 1.26 and 0.81 GHz at 1,550 and 2,000 nm wavelengths, respectively. This work opens up an opportunity for low-cost 2 µm wavelength photodetection on the GeSn/Ge interface-free GeSnOI platform. Index Terms-Germanium-tin alloys, germanium-tin on insulator, metal-semiconductor-metal photodetector. I. INTRODUCTION G ERMANIUM-tin (GeSn) alloys have been promising for silicon (Si)-based photonic-integrated circuits (PICs), leading to the technological advances in 5G, Internet of Things, fiber-optic telecommunication, and Light Detection and Ranging operating in the near-and mid-infrared (MIR) range. Ge itself is a quasi-direct bandgap material with the direct bandgap at the wavelength of 1550 nm. Alloying of Ge with Sn allows a shrinkage of the Ge bandgap, extending the photodetection range beyond 2000 nm wavelength [1]. Especially including hollow-core fiber optics, sensing, and imaging applications, the 2000 nm photodetection is desirable, but III-V material systems have received much attention for that wavelength [2], [3].

Strain relaxation of germanium-tin (GeSn) fins

AIP Advances, 2018

Strain relaxation of biaxially strained Ge 1-x Sn x layer when it is patterned into Ge 1-x Sn x f... more Strain relaxation of biaxially strained Ge 1-x Sn x layer when it is patterned into Ge 1-x Sn x fin structures is studied. Ge 1-x Sn x-on-insulator (GeSnOI) substrate was realized using a direct wafer bonding (DWB) technique and Ge 1-x Sn x fin structures were formed by electron beam lithography (EBL) patterning and dry etching. The strain in the Ge 1-x Sn x fins having fin widths (W Fin) ranging from 1 µm down to 80 nm was characterized using micro-Raman spectroscopy. Raman measurements show that the strain relaxation increases with decreasing W Fin. Finite element (FE) simulation shows that the strain component in the transverse direction relaxes with decreasing W Fin , while the strain component along the fin direction remains unchanged. For various Ge 1-x Sn x fin widths, transverse strain relaxation was further extracted using micro-Raman spectroscopy, which is consistent with the simulation results.

Heteroepitaxial growth of In In[subscript 0.30]Ga[subscript 0.70]As high-electron mobility transistor on 200 mm silicon substrate using metamorphic graded buffer

We report on the growth of an In 0.30 Ga 0.70 As channel high-electron mobility transistor (HEMT)... more We report on the growth of an In 0.30 Ga 0.70 As channel high-electron mobility transistor (HEMT) on a 200 mm silicon wafer by metal organic vapor phase epitaxy. By using a 3 µm thick buffer comprising a Ge layer, a GaAs layer and an In-AlAs compositionally graded strain relaxing buffer, we achieve threading dislocation density of (1.0 ± 0.3) × 10 7 cm −2 with a surface roughness of 10 nm RMS. No phase separation was observed during the InAlAs compositionally graded buffer layer growth. 1.4 µm long channel length transistors are fabricated from the wafer with I DS of 70 µA/µm and g m of above 60 µS/µm, demonstrating the high quality of the grown materials.

PIC-integrable, uniformly tensile-strained Ge-on-insulator photodiodes enabled by recessed SiNx stressor

Photonics Research, 2021

Mechanical strain engineering has been promising for many integrated photonic applications. Howev... more Mechanical strain engineering has been promising for many integrated photonic applications. However, for the engineering of a material electronic bandgap, a trade-off exists between the strain uniformity and the integration compatibility with photonic-integrated circuits (PICs). Herein, we adopted a straightforward recess-type design of a silicon nitride ( SiN x ) stressor to achieve a uniform strain with enhanced magnitude in the material of interest on PICs. Normal-incidence, uniformly 0.56% tensile strained germanium (Ge)-on-insulator (GOI) metal-semiconductor-metal photodiodes were demonstrated, using the recessed stressor with 750 MPa tensile stress. The device exhibits a responsivity of 1.84 ± 0.15 A / W at 1550 nm. The extracted Ge absorption coefficient is enhanced by ∼ 3.2 × to 8340 cm − 1 at 1612 nm and is superior to that of In 0.53 Ga 0.47 As up to 1630 nm limited by the measurement spectrum. Compared with the nonrecess strained device, additional absorption coeffi...

Strain-enabled ultra-broadband Ge-based photonic devices for low-cost integration in PICs

Photonic-integrated circuits (PICs) have become one of the most promising solutions to the burgeo... more Photonic-integrated circuits (PICs) have become one of the most promising solutions to the burgeoning global data communication and are being envisioned to have revolutionary impact in many other emerging fields. This outlook requires future PICs to be significantly more broadband and cost-effective. The current germanium (Ge)-based active photonic devices in PICs are thus facing a new bandwidth-cost trade-off. Here, we demonstrate ultra-broadband, high-efficiency Ge photodetectors up to 1,630 nm operation wavelength and Ge0.99Si0.01 electro-absorption (EA) modulator arrays with an operating range of ~100 nm from 1,525 to 1,620 nm, using a CMOS-compatible recess-type silicon nitride (SiNx) stressor. The broadband operation could facilitate a wide (>100 nm) window for low-cost Ge modulator-detector co-integration, requiring only a single step of Ge epitaxy and two different SiNx depositions. The broad modulation and co-integration coverage can be entirely shifted to shorter (~1,30...

High-efficiency normal-incidence vertical p-i-n photodetectors on a germanium-on-insulator platform

Photonics Research, 2017

In this paper, normal incidence vertical p-in photodetectors on a germanium-on-insulator (GOI) pl... more In this paper, normal incidence vertical p-in photodetectors on a germanium-on-insulator (GOI) platform were demonstrated. The vertical p-in structure was realized by ion-implanting boron and arsenic at the bottom and top of the Ge layer, respectively, during the GOI fabrication. Abrupt doping profiles were verified in the transferred high-quality Ge layer. The photodetectors exhibit a dark current density of ∼47 mA∕cm 2 at −1 V and an optical responsivity of 0.39 A/W at 1550 nm, which are improved compared with state-of-the-art demonstrated GOI photodetectors. An internal quantum efficiency of ∼97% indicates excellent carrier collection efficiency of the device. The photodetectors with mesa diameter of 60 μm exhibit a 3 dB bandwidth of ∼1 GHz, which agrees well with theoretical calculations. The bandwidth is expected to improve to ∼32 GHz with mesa diameter of 10 μm. This work could be similarly extended to GOI platforms with other intermediate layers and potentially enrich the functional diversity of GOI for near-infrared sensing and communication integrated with Ge CMOS and mid-infrared photonics.

Low-threshold optically pumped lasing in highly strained germanium nanowires

Nature communications, Jan 29, 2017

The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key t... more The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system. Here we demonstrate a low-threshold, compact group IV laser that employs a germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently overcome optical losses at 83 K, thus allowing the observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm-2. Our demonstration opens new possibilities for group IV lasers for photonic-i...

AlN-AlN Wafer Bonding and Its Thermal Characteristics

ECS Transactions, 2014

Homogeneous bonding was successfully demonstrated on 150 mm Si wafers by face-to-face fusion bond... more Homogeneous bonding was successfully demonstrated on 150 mm Si wafers by face-to-face fusion bonding of two clean and smooth aluminum nitride (AlN) layers. Characterization result from XPS confirms the layer composition and reveals that approximately 5 nm of the layer surface was partially oxidized during processing. The as-bonded wafer pair is nearly void and particle free with a high bonding strength of 1263.0 mJ/m2, enabling it to withstand the subsequent process steps. In addition, the AlN-AlN bonded wafers appear to have the best heat dissipation capability when compared with other bonded wafers, which used SiO2 or Al2O3 as the bonding layer.

The role of AsH3 partial pressure on anti-phase boundary in GaAs-on-Ge grown by MOCVD – Application to a 200mm GaAs virtual substrate

Journal of Crystal Growth, 2015

The role of AsH[subscript 3] partial pressure on antiphase boundary in GaAs-on-Ge grown by MOCVD ... more

Decoupling two-step anodization in anodic aluminum oxide

Journal of Applied Physics, 2009

It is well known that ordered anodic aluminum oxide ͑AAO͒ can be fabricated by a two-step anodiza... more It is well known that ordered anodic aluminum oxide ͑AAO͒ can be fabricated by a two-step anodization process, but in the current approach, pore size and interpore spacing are coupled because the ordering mechanism is expected to be the same in both steps. Here, we demonstrate that, by using a different approach during the second anodization step, we can vary the pore size independently ͑either shrunk or enlarged͒, while preserving the ordering of AAO inherited from the first step. This approach is based on changing the electrolyte in the second step, while applying the same voltage as the first step. These results imply that ordering in AAO is strongly dependent on the coupled effect of electrolyte and voltage in the first step, whereas ordering in the second step is only affected by the voltage, quite independent of the electrolyte used. With this decoupling, AAO template processing should become more versatile.

$Research paper thumbnail of $\hbox{Al}_{2}\hbox{O}_{3}$ Interface Engineering of Germanium Epitaxial Layer Grown Directly on Silicon$

$\hbox{Al}_{2}\hbox{O}_{3}$ Interface Engineering of Germanium Epitaxial Layer Grown Directly on Silicon

IEEE Transactions on Electron Devices, 2013

The quality of germanium (Ge) epitaxial film grown directly on silicon (Si) substrate is investig... more The quality of germanium (Ge) epitaxial film grown directly on silicon (Si) substrate is investigated based on the electrical properties of a metal-oxide-semiconductor capacitor (MOSCAP). Different thermal cycling temperatures are used in this study to investigate the effect of temperature on the Ge film quality. Prior to high-k dielectric deposition, various surface treatments are applied on the Ge film to determine the leakage current density using scanning tunneling microscopy. The interface trap density (D it) and leakage current obtained from the C-V and I-V measurements on the MOSCAP, as well as the threading dislocation density (TDD), show a linear relationship with the thermal cycling temperature. It is found that the Ge epitaxial film that undergoes the highest thermal cycling temperature of 825 • C and surface treatment in ultraviolet ozone, followed by germanium oxynitride (GeO x N y) formation, demonstrates the lowest leakage current of ∼ 2.3 × 10 −8 A/cm 2 (at −2 V), D it ∼ 3.5 × 10 11 cm −2 /V, and TDD < 10 7 cm −2 .

In0.49Ga0.51P/GaAs heterojunction bipolar transistors (HBTs) on 200 mm Si substrates: Effects of base thickness, base and sub-collector doping concentrations

AIP Advances, 2018

We report performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) fabricated on epita... more We report performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) fabricated on epitaxial films directly grown onto 200 mm silicon (Si) substrates using a thin 100% germanium (Ge) buffer layer. Both buffer layer and device layers were grown epitaxially using metalorganic chemical vapor deposition (MOCVD). With the assistance of numerical simulation, we were able to achieve high performance GaAs HBTs with DC current gain of ∼100 through optimizing the base doping concentration (C-doped, ∼ 1.9×10 19 /cm 3), base layer thickness (∼55 nm), and the sub-collector doping concentration (Te-doped, > 5×10 18 /cm 3). The breakdown voltage at base (BV ceo) of higher than 9.43 V was realized with variation of < 3% across the 200 mm wafer. These results could enable applications such as power amplifiers for mobile phone handsets and monolithic integration of HBTs with standard Si-CMOS transistors on a common Si platform.

Improved thin film quality and photoluminescence of N-doped epitaxial germanium-on-silicon using MOCVD

Optical Materials Express

This paper addresses one of the key issues in the scientific community of Si photonics: thin-film... more This paper addresses one of the key issues in the scientific community of Si photonics: thin-film quality and the light emission properties of band-engineered n+ Germanium-on-Silicon (Ge-on-Si). Compared to the traditional delta doping approach, which was utilized in the first electrically-pumped Ge-on-Si lasers, we offer an n+ Ge-on-Si thin film with better material quality and higher carrier injection efficiency grown by metal-organic chemical vapor deposition (MOCVD). The impacts of thermal cycle annealing and Si substrate offcut on the thin film quality were investigated, including surface roughness, strain, threading dislocation density, Si-Ge interdiffusion, and dopant diffusion. It was revealed that: 1) MOCVD overcomes the outdiffision issue of n-type dopants by having the dopant peaks at the bottom of the Ge films; 2) the characterization of the light emission properties of these MOCVD n+ Ge-on-Si samples (1.0 × 1019 cm−3 doped) compared to delta-doped ultra-high vacuum chem...

Dark Current Analysis of Vertical p-i-n Photodetectors on a Germanium-on-Insulator Platform

2019 IEEE 16th International Conference on Group IV Photonics (GFP)

Dark current of vertical p-i-n photodetectors on a germanium-on-insulator platform was analyzed. ... more Dark current of vertical p-i-n photodetectors on a germanium-on-insulator platform was analyzed. The activation energy was found to be from 0.15 to 0.36 eV under reserve bias. The dark current generation was interpreted by Shockley-Read-Hall and trap-assisted-tunneling effects. This work provides the interpretation on germanium-on-insulator photodetectors and suggests the alternative to suppress the dark current generation for Si-based Ge photodetectors.

Germanium-on-silicon nitride: A promising platform for mid-IR sensing applications

2017 IEEE Photonics Conference (IPC), 2017

A new germanium-on-silicon nitride platform is fabricated and tested for mld-lR sensing applicati... more A new germanium-on-silicon nitride platform is fabricated and tested for mld-lR sensing applications. Waveguides with low bending loss are demonstrated allowing one to design compact on-chip sensors. Spiral waveguide sensors have been studied for potential drug detection and food processing applications.

Monolithic Integration of InSb Photodetector on Silicon for Mid-Infrared Silicon Photonics

ACS Photonics, 2018

The InSb photodetector on a Si substrate acts a signal receiver for the mid-infrared silicon phot... more The InSb photodetector on a Si substrate acts a signal receiver for the mid-infrared silicon photonics application to overcome the limitation of group IV semiconductors. In this paper, we demonstrated an InSb p-in photodetector with an InAlSb barrier layer grown on (100) silicon substrates via a GaAs/Ge buffer by molecular beam epitaxy. The lattice mismatch between InSb and GaAs was accommodated by an interfacial misfit (IMF) array. The 50% cutoff detectable wavelength of this detector increased from 5.7 µm at 80 K to 6.3 µm at 200 K. An 80 K detectivity of 8.8×10 9 cmHz 1/2 W-1 at 5.3 µm was achieved with a quantum efficiency of 16.3%. The dark current generating mechanism of this detector is both generation-recombination and surface leakage above 140 K, while it is only surface leakage from 120 K to 40 K.

Curvature evolution of 200 mm diameter GaN-on-insulator wafer fabricated through metalorganic chemical vapor deposition and bonding

Japanese Journal of Applied Physics, 2018

Crack-free 200 mm diameter N-polar GaN-on-insulator (GaN-OI) wafers are demonstrated by the trans... more Crack-free 200 mm diameter N-polar GaN-on-insulator (GaN-OI) wafers are demonstrated by the transfer of MOCVD-grown Ga-polar GaN layers from Si(111) wafers onto SiO 2 /Si(100) wafers. The wafer curvature of the GaN-OI wafers after the removal of the original Si(111) substrate is correlated with the wafer curvature of the starting GaN-on-Si wafers and the voids on the GaN-on-Si surface evolve into cracks on the GaN-OI wafers. In crack-free GaN-OI wafers, the wafer curvature during the removal of the AlN nucleation layer, AlGaN strain-compensation buffer layers and GaN layers is correlated with the residual stress distribution within individual layers in the GaN-OI wafer.

Geometry and Thermal Stress Analysis of In-plane Outgassing Channels in Al2O3-Intermediated InP (Die)-to-Si (Wafer) Bonding

ECS Journal of Solid State Science and Technology, 2015

Geometry and thermal stress analysis of in-plane outgassing channels in Al2O3-intermediated InP (... more

Layer-Transferred Gallium Arsenide Heterojunction Bipolar Transistor on Insulator Substrate

SSRN Electronic Journal

Enhanced Light Emission of Germanium Light-Emitting-Diode on 150 mm Germanium-On-Insulator (GOI)

Germanium-on-insulator (GOI) has become a novel platform for Ge-based electronic and photonic app... more Germanium-on-insulator (GOI) has become a novel platform for Ge-based electronic and photonic applications. Discrete photonic devices such as waveguides, photodetectors, modulators, and optical pumping lasers have been successfully demonstrated on this platform. To realize electric injection emitting is highly desirable towards integrated photonics. In this work, we report for the first time the Ge p−i−n light-emitting-diodes (LEDs) on the GOI substrate. The high-quality Ge LED on a 150-mm diameter GOI substrate was fabricated via direct wafer bonding followed by ion implantations. As a tensile strain of 0.19% has been introduced during the GOI fabrication process resulting from thermal mismatch, the LED devices exhibit a dominant direct bandgap transition peak near 0.785 eV (~1,580nm) at room temperature. In sharp contrast to conventional III-V LEDs, we found that the electroluminescence/photoluminescence (EL/PL) spectra show enhanced intensities as raising the temperature from 300...

Metal-Semiconductor-Metal Photodetectors on a GeSn-on-Insulator Platform for 2 µm Applications

IEEE Photonics Journal

In this work, the metal-semiconductor-metal photodetectors were demonstrated on the Ge 0.91 Sn 0.... more In this work, the metal-semiconductor-metal photodetectors were demonstrated on the Ge 0.91 Sn 0.09-on-insulator (GeSnOI) platform. The responsivity was 0.24 and 0.06 A/W at wavelengths of 1,600 and 2,003 nm, respectively. Through a systematic study, it is revealed that the photodetectors can potentially detect wavelength beyond 2,200 nm. The dark current density was measured to be 4.6 A/cm 2 for GeSnOI waveguide-shaped photodetectors. The 3 dB bandwidth was observed to be 1.26 and 0.81 GHz at 1,550 and 2,000 nm wavelengths, respectively. This work opens up an opportunity for low-cost 2 µm wavelength photodetection on the GeSn/Ge interface-free GeSnOI platform. Index Terms-Germanium-tin alloys, germanium-tin on insulator, metal-semiconductor-metal photodetector. I. INTRODUCTION G ERMANIUM-tin (GeSn) alloys have been promising for silicon (Si)-based photonic-integrated circuits (PICs), leading to the technological advances in 5G, Internet of Things, fiber-optic telecommunication, and Light Detection and Ranging operating in the near-and mid-infrared (MIR) range. Ge itself is a quasi-direct bandgap material with the direct bandgap at the wavelength of 1550 nm. Alloying of Ge with Sn allows a shrinkage of the Ge bandgap, extending the photodetection range beyond 2000 nm wavelength [1]. Especially including hollow-core fiber optics, sensing, and imaging applications, the 2000 nm photodetection is desirable, but III-V material systems have received much attention for that wavelength [2], [3].

Strain relaxation of germanium-tin (GeSn) fins

AIP Advances, 2018

Strain relaxation of biaxially strained Ge 1-x Sn x layer when it is patterned into Ge 1-x Sn x f... more Strain relaxation of biaxially strained Ge 1-x Sn x layer when it is patterned into Ge 1-x Sn x fin structures is studied. Ge 1-x Sn x-on-insulator (GeSnOI) substrate was realized using a direct wafer bonding (DWB) technique and Ge 1-x Sn x fin structures were formed by electron beam lithography (EBL) patterning and dry etching. The strain in the Ge 1-x Sn x fins having fin widths (W Fin) ranging from 1 µm down to 80 nm was characterized using micro-Raman spectroscopy. Raman measurements show that the strain relaxation increases with decreasing W Fin. Finite element (FE) simulation shows that the strain component in the transverse direction relaxes with decreasing W Fin , while the strain component along the fin direction remains unchanged. For various Ge 1-x Sn x fin widths, transverse strain relaxation was further extracted using micro-Raman spectroscopy, which is consistent with the simulation results.

Heteroepitaxial growth of In In[subscript 0.30]Ga[subscript 0.70]As high-electron mobility transistor on 200 mm silicon substrate using metamorphic graded buffer

We report on the growth of an In 0.30 Ga 0.70 As channel high-electron mobility transistor (HEMT)... more We report on the growth of an In 0.30 Ga 0.70 As channel high-electron mobility transistor (HEMT) on a 200 mm silicon wafer by metal organic vapor phase epitaxy. By using a 3 µm thick buffer comprising a Ge layer, a GaAs layer and an In-AlAs compositionally graded strain relaxing buffer, we achieve threading dislocation density of (1.0 ± 0.3) × 10 7 cm −2 with a surface roughness of 10 nm RMS. No phase separation was observed during the InAlAs compositionally graded buffer layer growth. 1.4 µm long channel length transistors are fabricated from the wafer with I DS of 70 µA/µm and g m of above 60 µS/µm, demonstrating the high quality of the grown materials.

PIC-integrable, uniformly tensile-strained Ge-on-insulator photodiodes enabled by recessed SiNx stressor

Photonics Research, 2021

Mechanical strain engineering has been promising for many integrated photonic applications. Howev... more Mechanical strain engineering has been promising for many integrated photonic applications. However, for the engineering of a material electronic bandgap, a trade-off exists between the strain uniformity and the integration compatibility with photonic-integrated circuits (PICs). Herein, we adopted a straightforward recess-type design of a silicon nitride ( SiN x ) stressor to achieve a uniform strain with enhanced magnitude in the material of interest on PICs. Normal-incidence, uniformly 0.56% tensile strained germanium (Ge)-on-insulator (GOI) metal-semiconductor-metal photodiodes were demonstrated, using the recessed stressor with 750 MPa tensile stress. The device exhibits a responsivity of 1.84 ± 0.15 A / W at 1550 nm. The extracted Ge absorption coefficient is enhanced by ∼ 3.2 × to 8340 cm − 1 at 1612 nm and is superior to that of In 0.53 Ga 0.47 As up to 1630 nm limited by the measurement spectrum. Compared with the nonrecess strained device, additional absorption coeffi...

Strain-enabled ultra-broadband Ge-based photonic devices for low-cost integration in PICs

Photonic-integrated circuits (PICs) have become one of the most promising solutions to the burgeo... more Photonic-integrated circuits (PICs) have become one of the most promising solutions to the burgeoning global data communication and are being envisioned to have revolutionary impact in many other emerging fields. This outlook requires future PICs to be significantly more broadband and cost-effective. The current germanium (Ge)-based active photonic devices in PICs are thus facing a new bandwidth-cost trade-off. Here, we demonstrate ultra-broadband, high-efficiency Ge photodetectors up to 1,630 nm operation wavelength and Ge0.99Si0.01 electro-absorption (EA) modulator arrays with an operating range of ~100 nm from 1,525 to 1,620 nm, using a CMOS-compatible recess-type silicon nitride (SiNx) stressor. The broadband operation could facilitate a wide (>100 nm) window for low-cost Ge modulator-detector co-integration, requiring only a single step of Ge epitaxy and two different SiNx depositions. The broad modulation and co-integration coverage can be entirely shifted to shorter (~1,30...

High-efficiency normal-incidence vertical p-i-n photodetectors on a germanium-on-insulator platform

Photonics Research, 2017

In this paper, normal incidence vertical p-in photodetectors on a germanium-on-insulator (GOI) pl... more In this paper, normal incidence vertical p-in photodetectors on a germanium-on-insulator (GOI) platform were demonstrated. The vertical p-in structure was realized by ion-implanting boron and arsenic at the bottom and top of the Ge layer, respectively, during the GOI fabrication. Abrupt doping profiles were verified in the transferred high-quality Ge layer. The photodetectors exhibit a dark current density of ∼47 mA∕cm 2 at −1 V and an optical responsivity of 0.39 A/W at 1550 nm, which are improved compared with state-of-the-art demonstrated GOI photodetectors. An internal quantum efficiency of ∼97% indicates excellent carrier collection efficiency of the device. The photodetectors with mesa diameter of 60 μm exhibit a 3 dB bandwidth of ∼1 GHz, which agrees well with theoretical calculations. The bandwidth is expected to improve to ∼32 GHz with mesa diameter of 10 μm. This work could be similarly extended to GOI platforms with other intermediate layers and potentially enrich the functional diversity of GOI for near-infrared sensing and communication integrated with Ge CMOS and mid-infrared photonics.

Low-threshold optically pumped lasing in highly strained germanium nanowires

Nature communications, Jan 29, 2017

The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key t... more The integration of efficient, miniaturized group IV lasers into CMOS architecture holds the key to the realization of fully functional photonic-integrated circuits. Despite several years of progress, however, all group IV lasers reported to date exhibit impractically high thresholds owing to their unfavourable bandstructures. Highly strained germanium with its fundamentally altered bandstructure has emerged as a potential low-threshold gain medium, but there has yet to be a successful demonstration of lasing from this seemingly promising material system. Here we demonstrate a low-threshold, compact group IV laser that employs a germanium nanowire under a 1.6% uniaxial tensile strain as the gain medium. The amplified material gain in strained germanium can sufficiently overcome optical losses at 83 K, thus allowing the observation of multimode lasing with an optical pumping threshold density of ~3.0 kW cm-2. Our demonstration opens new possibilities for group IV lasers for photonic-i...

AlN-AlN Wafer Bonding and Its Thermal Characteristics

ECS Transactions, 2014

Homogeneous bonding was successfully demonstrated on 150 mm Si wafers by face-to-face fusion bond... more Homogeneous bonding was successfully demonstrated on 150 mm Si wafers by face-to-face fusion bonding of two clean and smooth aluminum nitride (AlN) layers. Characterization result from XPS confirms the layer composition and reveals that approximately 5 nm of the layer surface was partially oxidized during processing. The as-bonded wafer pair is nearly void and particle free with a high bonding strength of 1263.0 mJ/m2, enabling it to withstand the subsequent process steps. In addition, the AlN-AlN bonded wafers appear to have the best heat dissipation capability when compared with other bonded wafers, which used SiO2 or Al2O3 as the bonding layer.

The role of AsH3 partial pressure on anti-phase boundary in GaAs-on-Ge grown by MOCVD – Application to a 200mm GaAs virtual substrate

Journal of Crystal Growth, 2015

The role of AsH[subscript 3] partial pressure on antiphase boundary in GaAs-on-Ge grown by MOCVD ... more

Decoupling two-step anodization in anodic aluminum oxide

Journal of Applied Physics, 2009

It is well known that ordered anodic aluminum oxide ͑AAO͒ can be fabricated by a two-step anodiza... more It is well known that ordered anodic aluminum oxide ͑AAO͒ can be fabricated by a two-step anodization process, but in the current approach, pore size and interpore spacing are coupled because the ordering mechanism is expected to be the same in both steps. Here, we demonstrate that, by using a different approach during the second anodization step, we can vary the pore size independently ͑either shrunk or enlarged͒, while preserving the ordering of AAO inherited from the first step. This approach is based on changing the electrolyte in the second step, while applying the same voltage as the first step. These results imply that ordering in AAO is strongly dependent on the coupled effect of electrolyte and voltage in the first step, whereas ordering in the second step is only affected by the voltage, quite independent of the electrolyte used. With this decoupling, AAO template processing should become more versatile.

$Research paper thumbnail of $\hbox{Al}_{2}\hbox{O}_{3}$ Interface Engineering of Germanium Epitaxial Layer Grown Directly on Silicon$

$\hbox{Al}_{2}\hbox{O}_{3}$ Interface Engineering of Germanium Epitaxial Layer Grown Directly on Silicon

IEEE Transactions on Electron Devices, 2013

The quality of germanium (Ge) epitaxial film grown directly on silicon (Si) substrate is investig... more The quality of germanium (Ge) epitaxial film grown directly on silicon (Si) substrate is investigated based on the electrical properties of a metal-oxide-semiconductor capacitor (MOSCAP). Different thermal cycling temperatures are used in this study to investigate the effect of temperature on the Ge film quality. Prior to high-k dielectric deposition, various surface treatments are applied on the Ge film to determine the leakage current density using scanning tunneling microscopy. The interface trap density (D it) and leakage current obtained from the C-V and I-V measurements on the MOSCAP, as well as the threading dislocation density (TDD), show a linear relationship with the thermal cycling temperature. It is found that the Ge epitaxial film that undergoes the highest thermal cycling temperature of 825 • C and surface treatment in ultraviolet ozone, followed by germanium oxynitride (GeO x N y) formation, demonstrates the lowest leakage current of ∼ 2.3 × 10 −8 A/cm 2 (at −2 V), D it ∼ 3.5 × 10 11 cm −2 /V, and TDD < 10 7 cm −2 .

In0.49Ga0.51P/GaAs heterojunction bipolar transistors (HBTs) on 200 mm Si substrates: Effects of base thickness, base and sub-collector doping concentrations

AIP Advances, 2018

We report performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) fabricated on epita... more We report performance of InGaP/GaAs heterojunction bipolar transistors (HBTs) fabricated on epitaxial films directly grown onto 200 mm silicon (Si) substrates using a thin 100% germanium (Ge) buffer layer. Both buffer layer and device layers were grown epitaxially using metalorganic chemical vapor deposition (MOCVD). With the assistance of numerical simulation, we were able to achieve high performance GaAs HBTs with DC current gain of ∼100 through optimizing the base doping concentration (C-doped, ∼ 1.9×10 19 /cm 3), base layer thickness (∼55 nm), and the sub-collector doping concentration (Te-doped, > 5×10 18 /cm 3). The breakdown voltage at base (BV ceo) of higher than 9.43 V was realized with variation of < 3% across the 200 mm wafer. These results could enable applications such as power amplifiers for mobile phone handsets and monolithic integration of HBTs with standard Si-CMOS transistors on a common Si platform.

Improved thin film quality and photoluminescence of N-doped epitaxial germanium-on-silicon using MOCVD

Optical Materials Express

This paper addresses one of the key issues in the scientific community of Si photonics: thin-film... more This paper addresses one of the key issues in the scientific community of Si photonics: thin-film quality and the light emission properties of band-engineered n+ Germanium-on-Silicon (Ge-on-Si). Compared to the traditional delta doping approach, which was utilized in the first electrically-pumped Ge-on-Si lasers, we offer an n+ Ge-on-Si thin film with better material quality and higher carrier injection efficiency grown by metal-organic chemical vapor deposition (MOCVD). The impacts of thermal cycle annealing and Si substrate offcut on the thin film quality were investigated, including surface roughness, strain, threading dislocation density, Si-Ge interdiffusion, and dopant diffusion. It was revealed that: 1) MOCVD overcomes the outdiffision issue of n-type dopants by having the dopant peaks at the bottom of the Ge films; 2) the characterization of the light emission properties of these MOCVD n+ Ge-on-Si samples (1.0 × 1019 cm−3 doped) compared to delta-doped ultra-high vacuum chem...

Dark Current Analysis of Vertical p-i-n Photodetectors on a Germanium-on-Insulator Platform

2019 IEEE 16th International Conference on Group IV Photonics (GFP)

Dark current of vertical p-i-n photodetectors on a germanium-on-insulator platform was analyzed. ... more Dark current of vertical p-i-n photodetectors on a germanium-on-insulator platform was analyzed. The activation energy was found to be from 0.15 to 0.36 eV under reserve bias. The dark current generation was interpreted by Shockley-Read-Hall and trap-assisted-tunneling effects. This work provides the interpretation on germanium-on-insulator photodetectors and suggests the alternative to suppress the dark current generation for Si-based Ge photodetectors.

Germanium-on-silicon nitride: A promising platform for mid-IR sensing applications

2017 IEEE Photonics Conference (IPC), 2017

A new germanium-on-silicon nitride platform is fabricated and tested for mld-lR sensing applicati... more A new germanium-on-silicon nitride platform is fabricated and tested for mld-lR sensing applications. Waveguides with low bending loss are demonstrated allowing one to design compact on-chip sensors. Spiral waveguide sensors have been studied for potential drug detection and food processing applications.

Monolithic Integration of InSb Photodetector on Silicon for Mid-Infrared Silicon Photonics

ACS Photonics, 2018

The InSb photodetector on a Si substrate acts a signal receiver for the mid-infrared silicon phot... more The InSb photodetector on a Si substrate acts a signal receiver for the mid-infrared silicon photonics application to overcome the limitation of group IV semiconductors. In this paper, we demonstrated an InSb p-in photodetector with an InAlSb barrier layer grown on (100) silicon substrates via a GaAs/Ge buffer by molecular beam epitaxy. The lattice mismatch between InSb and GaAs was accommodated by an interfacial misfit (IMF) array. The 50% cutoff detectable wavelength of this detector increased from 5.7 µm at 80 K to 6.3 µm at 200 K. An 80 K detectivity of 8.8×10 9 cmHz 1/2 W-1 at 5.3 µm was achieved with a quantum efficiency of 16.3%. The dark current generating mechanism of this detector is both generation-recombination and surface leakage above 140 K, while it is only surface leakage from 120 K to 40 K.