Papers by Kiran Kumar Kovi
Source Source Gate 50nm Drain E-MRS 2010 Spring Meeting June 7-11 Strasbourg, France Contents Ap... more Source Source Gate 50nm Drain E-MRS 2010 Spring Meeting June 7-11 Strasbourg, France Contents Applications of CVD Diamond Intrinsic Single Crystal CVD Diamond Doping CVD Diamond Electronic Devices in Single crystal CVD Diamond E-MRS 2010 Spring Meeting June 7-11 Strasbourg, France Why diamond? Besides extreme mechanical and optical properties, also outstanding electronic properties Diamond is an outstanding material in many applications − extreme mechanical hardness − high resistance to wear and chemical corrosion − broad optical transparency − high refractive index − lowest thermal expansion coefficient − highest thermal conductivity − good electrical insulator / semiconductor if doped − wide bandgap − biologically compatible / tissue like
In1963,Gunn[1]observedastrangeeffectinindiumphosphideandgalliumarsenide:withahighelectricfield(af... more In1963,Gunn[1]observedastrangeeffectinindiumphosphideandgalliumarsenide:withahighelectricfield(afewkV/cm)appliedacrossasample,thecurrentshowedhighfrequency(GHz)oscillations.Aftersomeinitialattempts,thenowgenerallyacceptedexplanationwasfoundtobethepresenceofnegativedifferentialmobility(NDM),i.e.,anelectrondriftvelocitythatdecreaseswithincreasedappliedelectricfield.NegativeelectronmobilityorNDM[2]isnormallyassociatedwithIII-VorII-VIsemiconductorswithanenergydifferencebetweendifferentconductionbandvalleys.
ABSTRACT Diamond is a promising semiconductor material for high power, high voltage, high tempera... more ABSTRACT Diamond is a promising semiconductor material for high power, high voltage, high temperature and high frequency applications due to its remarkable material properties: it has the highest thermal conductivity, it is the hardest material, chemically inert, radiation hard and has the widest transparency in the electromagnetic spectrum. It also exhibits excellent electrical properties like high breakdown field, high mobilities and a wide bandgap. Hence, it may find applications in extreme conditions out of reach for conventional semiconductor materials, e.g. in high power density systems, high temperature conditions, automotive and aerospace industries, and space applications. With the recent progress in the growth of high purity single-crystalline CVD diamond, the realization of electronic devices is now possible. Natural and HPHT diamonds inevitably have too high a concentration of impurities and defects for electrical applications. To develop efficient electronic devices based on diamond, it is crucial to understand charge transport properties. Time-of-flight is one of the most powerful methods used to study charge transport properties like mobility, drift velocity and charge collection efficiency in highly resistive semiconductors, such as diamond. For commercial diamond devices to become a reality, it is necessary to have an effective surface passivation since the passivation determines the ability of a device to withstand high surface electric fields. Surface passivation studies on intrinsic SC-CVD diamond using materials like silicon oxide, silicon nitride and high-k materials have been conducted and observations reveal an increase in measured hole mobilities. Planar MOS capacitor structures form the basic building block of MOSFETs. Consequently, the understanding of MOS structures is crucial to make MOSFETs based on diamond. Planar MOS structures with aluminum oxide as gate dielectric were fabricated on boron doped diamond. The phenomenon of inversion was observed for the first time in diamond. In addition, low temperature hole transport in the range of 10-80 K has been investigated and the results are used to identify the type of scattering mechanisms affecting hole transport at these temperatures. To utilize the potential of diamonds properties and with diamond being the hardest and most chemically inert material, new processing technologies are needed to produce devices for electrical, optical or mechanical applications. Etching of diamond is one of the important processing steps required to make devices. Achieving an isotropic etch with a high etch rate is a challenge. Semi-isotropic etch profiles with smooth surfaces were obtained by using anisotropic etching technique by placing diamond samples in a Faraday cage and etch rates of approximately 80 nm/min were achieved. Valleytronics, which is a novel concept to encode information based on the valley quantum number of electrons has been investigated for the first time in diamond. Valley-polarized electrons with the longest relaxation time ever recorded in any material (300 ns) were observed. This is a first step towards demonstrating valleytronic devices.
Mater. Res. Soc. Symp. Proc. Vol. 1591
Diamond is a unique material in many respects. One of the most well-known extreme
properties of ... more Diamond is a unique material in many respects. One of the most well-known extreme
properties of diamond is its ultrahardness. This property of diamond actually turns out to have
interesting consequences for charge transport, in particular at low temperatures. In fact, the
strong covalent bonds that give rise to the ultrahardness results in a lack of short wavelength
lattice vibrations which has a strong impact on both electron and hole scattering. In some sense
diamond behaves more like a vacuum than other semiconductor materials. In this paper we
describe some interesting charge transport properties of diamond and discuss possible novel
electronic applications.
Applied Physics Letters
The synthesis of new materials for thermal infrared (IR) detection has been an intensive research... more The synthesis of new materials for thermal infrared (IR) detection has been an intensive research area in recent years. Among new semiconductor materials, synthetic diamond has the ability to function even under very high temperature and high radiation conditions. In the present work, diamond Schottky diodes with boron concentrations in the range of 1014<B<1017cm-3 are presented as candidates for IR thermal sensors with an excellent temperature coefficient of resistance (-8.42%/K) and very low noise levels around 6.6 x10-15 V2/Hz. This enables huge performance enhancements for a wide variety of systems, e.g., automotive and space applications.
Diamond & Related Materials, Aug 2015
Etching of diamond is one of the most important process steps to realize diamond based devices. I... more Etching of diamond is one of the most important process steps to realize diamond based devices. Isotropic etching in diamond yielding a high etch rate is challenging owing to its material properties. In the current study, single-crystalline diamond is etched using a Faraday cage that acts as the mask to attain semi-isotropic etching. An oxygen/chlorine plasma discharge with a pressure of 10 mTorr is used. The etching process is optimized by varying the applied plasma power and the substrate bias and also by varying parameters such as the thickness of the mask, the mask-to-diamond surface distance, and the diameter of the holes in the mask. After optimization, the diamond substrates are etched to achieve semi-isotropic profile up to depths of 5 um with an etch rate of 80 nm/min and surface roughness close to that of the unetched surface
IEEE Electron Device Letters, Jun 2015
For the advancement of diamond-based electronic devices, the fabrication of metal-oxide-semicondu... more For the advancement of diamond-based electronic devices, the fabrication of metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial, as this device finds applications in numerous fields of power electronics and high-frequency systems. The MOS capacitor forms the basic building block of the MOSFET. In this letter, we describe planar MOS capacitor structures fabricated with atomic layer deposited aluminum oxide as the dielectric on oxygen-terminated boron-doped diamond substrates with different doping levels. Using capacitance-voltage measurements, we have, for the first time, observed inversion behavior in MOS structures on boron-doped diamond, with a doping concentration of 4.1 × 10E19/cm3.
The electronic properties of diamond, e.g. a high band-gap and high carrier mobilities,
together ... more The electronic properties of diamond, e.g. a high band-gap and high carrier mobilities,
together with material properties such as a very high thermal conductivity, chemical inertness and
a high radiation resistance makes diamond a unique material for many extreme electronic
applications out of reach for silicon devices. This includes, e.g. microwave power devices, power
devices and high temperature electronics. It is important to have an effective passivation of the
surface of such devices since the passivation determines the ability of the device to withstand high
surface electric fields. In addition, the passivation is used to control the surface charge which can
strongly influence the electric field in the bulk of the device. It is possible to measure sample
parameters such as electron and hole drift mobilities, charge carrier lifetimes or saturation
velocities using Time-of-flight (ToF) method. The ToF technique has also been adapted for
probing the electric field distribution and the distribution of trapped charge. In this paper we
present new data from lateral ToF studies of high-purity single crystalline diamond with different
surface passivations. Silicon oxide and silicon nitride are used as passivation layers in the current
study. The effect of the passivation on charge transport is studied, and the results of different
passivation materials are compared experimentally.
Solid State Sciences 13 (2011) 1065-1067, Feb 3, 2011
Carrier transport in a high-purity single-crystalline CVD diamond sample was studied using the Ti... more Carrier transport in a high-purity single-crystalline CVD diamond sample was studied using the Time-of-
Flight technique with optical UV excitation. By varying the intensity of the optical excitation over four
orders of magnitude, the transition between space-charge-free and space-charge-limited hole conduction
in diamond is directly observed. Experimentally, we find that even a relatively small injected charge
appreciably affects the drift velocity measurements. To achieve a relative error in drift velocity less than 1%,
the injected charge has to be less than 0.01 CU, where C is the sample capacitance and U the applied bias.
Applied Physics Letters, Nov 17, 2014
Applied Physics Letters, Oct 20, 2014
The stability of valley polarized electron states is crucial for the development of valleytronics... more The stability of valley polarized electron states is crucial for the development of valleytronics. A long relaxation time of the valley polarization is required to enable operations to be performed on the polarized states. Here we investigate the stability of valley polarized states in diamond, expressed as relaxation time. We have found that the stability of the states can be extremely long when we consider the symmetry determined electron-phonon scattering. By Time-of-Flight measurements and Monte Carlo simulations, we determine electron-phonon coupling constants and use these data in order to map out the relaxation time temperature dependency. The relaxation time can be microseconds or longer below 100K and 100 V/cm for diamond due to the strong covalent bond, which is highly encouraging for valleytronic applications.
Applied Physics Letters, Apr 18, 2013
Investigating the effects of local scattering mechanisms is of great importance to understand cha... more Investigating the effects of local scattering mechanisms is of great importance to understand charge transport in semiconductors. This article reports measurements of the hole transport properties of boron-doped (100) single-crystalline chemical vapor deposited diamond. A Time-of-Flight measurement using a 213 nm, pulsed UV laser for excitation, was performed on high-purity single-crystalline diamonds to measure the hole drift velocity in the low-injection regime. The measurements were carried out in the temperature range 10-80 K. The results obtained are directly applicable to low-temperature detector applications. By comparing our data to Monte-Carlo simulations, a detailed understanding of the dominating hole scattering mechanisms is obtained.
ECS Solid state letters, Mar 21, 2014
The excellent material properties of diamond make it highly desirable for many extreme electronic... more The excellent material properties of diamond make it highly desirable for many extreme electronic applications that are out of reach of conventional electronic materials. For commercial diamond devices to become a reality, it is necessary to have an effective surface passivation since the passivation determines the ability of the device to withstand high surface electric fields. In this paper we present data from lateral Time-of-Flight studies on SiO2-passivated intrinsic single-crystalline CVD diamond. The SiO2 films were deposited using three different techniques. The influence of the passivation on hole transport was studied, which resulted in the increase of hole mobilities. The results from the three different passivations are compared.
Nature materials, 2013
controlling the amount of electric charge in the circuits. Alternatively, it is possible to make ... more controlling the amount of electric charge in the circuits. Alternatively, it is possible to make devices that rely on other properties of electrons than their charge. For example, spintronic devices make use of the electron spin angular momentum as a carrier of information. A novel concept is valleytronics in which information is encoded by the valley quantum number of the electron 1-3 . The analogy between the valley and spin degrees of freedom also implies the possibility of valley-based quantum computing 4,5 . Utilizing the valley degree of freedom requires that the material has two or more conduction band valleys with the same energy minima but located at different positions in momentum space. This is the case for, e.g., graphene and several other semiconductor materials such as silicon and diamond. For useful devices to be possible, electrons residing in the valleys must retain their valley polarization long enough to allow for specific operations to be performed on Note: This is an unedited preprint version of the article. The published full version (Nature Materials 12, (2013) 760-764) can be found at doi:10.1038/nmat3694 2 them. It is also necessary to be able to detect the resulting valley polarized currents. Recently, it has been shown 6-8 that it is possible to create and detect electrons in a given valley in monolayer MoS 2 by pumping and detecting circularly polarized light. The valley polarization was retained longer than 1 ns 7 .
Solid State Sciences, 2011
Carrier transport in a high-purity single-crystalline CVD diamond sample was studied using the Ti... more Carrier transport in a high-purity single-crystalline CVD diamond sample was studied using the Time-of-Flight technique with optical UV excitation. By varying the intensity of the optical excitation over four orders of magnitude, the transition between space-charge-free and space-charge-limited hole conduction in diamond is directly observed. Experimentally, we find that even a relatively small injected charge appreciably affects the drift velocity measurements. To achieve a relative error in drift velocity less than 1%, the injected charge has to be less than 0.01 CU, where C is the sample capacitance and U the applied bias.
More Papers by Kiran Kumar Kovi
By performing Time-of-Flight measurements on high-purity single-crystalline chemical vapor deposi... more By performing Time-of-Flight measurements on high-purity single-crystalline chemical vapor deposited diamond we are able to extract the electron drift velocity of valley-polarized electrons in the low-injection regime. The aim of this study is to improve the understanding of the mechanisms involved in the conduction-band transport of valley-polarized electrons. The measurements were carried out within the temperature range 10 to 80 K and the experimental results are systematically compared with Monte Carlo charge transport simulations. We observe a rapid enhancement of the electron mobility with decreasing temperature, which reveals that inelastic effects in electron-phonon scattering become important below ~40 K. In addition, we obtain the momentum relaxation rate for electrons with different valley polarizations.
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Papers by Kiran Kumar Kovi
properties of diamond is its ultrahardness. This property of diamond actually turns out to have
interesting consequences for charge transport, in particular at low temperatures. In fact, the
strong covalent bonds that give rise to the ultrahardness results in a lack of short wavelength
lattice vibrations which has a strong impact on both electron and hole scattering. In some sense
diamond behaves more like a vacuum than other semiconductor materials. In this paper we
describe some interesting charge transport properties of diamond and discuss possible novel
electronic applications.
together with material properties such as a very high thermal conductivity, chemical inertness and
a high radiation resistance makes diamond a unique material for many extreme electronic
applications out of reach for silicon devices. This includes, e.g. microwave power devices, power
devices and high temperature electronics. It is important to have an effective passivation of the
surface of such devices since the passivation determines the ability of the device to withstand high
surface electric fields. In addition, the passivation is used to control the surface charge which can
strongly influence the electric field in the bulk of the device. It is possible to measure sample
parameters such as electron and hole drift mobilities, charge carrier lifetimes or saturation
velocities using Time-of-flight (ToF) method. The ToF technique has also been adapted for
probing the electric field distribution and the distribution of trapped charge. In this paper we
present new data from lateral ToF studies of high-purity single crystalline diamond with different
surface passivations. Silicon oxide and silicon nitride are used as passivation layers in the current
study. The effect of the passivation on charge transport is studied, and the results of different
passivation materials are compared experimentally.
Flight technique with optical UV excitation. By varying the intensity of the optical excitation over four
orders of magnitude, the transition between space-charge-free and space-charge-limited hole conduction
in diamond is directly observed. Experimentally, we find that even a relatively small injected charge
appreciably affects the drift velocity measurements. To achieve a relative error in drift velocity less than 1%,
the injected charge has to be less than 0.01 CU, where C is the sample capacitance and U the applied bias.
More Papers by Kiran Kumar Kovi
properties of diamond is its ultrahardness. This property of diamond actually turns out to have
interesting consequences for charge transport, in particular at low temperatures. In fact, the
strong covalent bonds that give rise to the ultrahardness results in a lack of short wavelength
lattice vibrations which has a strong impact on both electron and hole scattering. In some sense
diamond behaves more like a vacuum than other semiconductor materials. In this paper we
describe some interesting charge transport properties of diamond and discuss possible novel
electronic applications.
together with material properties such as a very high thermal conductivity, chemical inertness and
a high radiation resistance makes diamond a unique material for many extreme electronic
applications out of reach for silicon devices. This includes, e.g. microwave power devices, power
devices and high temperature electronics. It is important to have an effective passivation of the
surface of such devices since the passivation determines the ability of the device to withstand high
surface electric fields. In addition, the passivation is used to control the surface charge which can
strongly influence the electric field in the bulk of the device. It is possible to measure sample
parameters such as electron and hole drift mobilities, charge carrier lifetimes or saturation
velocities using Time-of-flight (ToF) method. The ToF technique has also been adapted for
probing the electric field distribution and the distribution of trapped charge. In this paper we
present new data from lateral ToF studies of high-purity single crystalline diamond with different
surface passivations. Silicon oxide and silicon nitride are used as passivation layers in the current
study. The effect of the passivation on charge transport is studied, and the results of different
passivation materials are compared experimentally.
Flight technique with optical UV excitation. By varying the intensity of the optical excitation over four
orders of magnitude, the transition between space-charge-free and space-charge-limited hole conduction
in diamond is directly observed. Experimentally, we find that even a relatively small injected charge
appreciably affects the drift velocity measurements. To achieve a relative error in drift velocity less than 1%,
the injected charge has to be less than 0.01 CU, where C is the sample capacitance and U the applied bias.