Semiconductors by Roland Van Meirhaeghe
The extended English form of my book on evolution and its relationship with information. Can be ... more The extended English form of my book on evolution and its relationship with information. Can be downloaded here .
Applied Physics A, 2009
The effects of deposition conditions on the physical and electrical performance of the n-ZnO/p-Si... more The effects of deposition conditions on the physical and electrical performance of the n-ZnO/p-Si heterojunction were systematically investigated. ZnO films were deposited on the Si and glass substrates using direct current (DC) magnetron sputtering with various ambients and substrate temperatures. The results showed that increasing the O 2 content and substrate temperature during the deposition process could improve the crystallinity and stoichiometry of the ZnO film, resulting in a lower carrier concentration and higher resistivity. The electrical properties of the n-ZnO/p-Si heterojunctions were also affected by the deposition parameters. For the junctions fabricated in the pure Ar ambient, the sample deposited at room temperature (RT) showed Ohmic behavior, while the one deposited at 300°C exhibited poor rectifying behavior. On the other hand, the junctions fabricated in the O 2 /Ar ambient possessed ideal rectifying behaviors. The different carrier transport mechanisms for the heterojunctions under forward and reverse bias were systematically studied using a high temperature current-voltage (I-V) measurement. The recombination-tunneling current showed temperature insensitive performance while the space-charge limited current (SCLC) changed with the measurement temperature.
Vanadium pentoxide was deposited by atomic layer deposition ͑ALD͒ from vanadyl-tri-isopropoxide ͑... more Vanadium pentoxide was deposited by atomic layer deposition ͑ALD͒ from vanadyl-tri-isopropoxide ͑VTIP͒. Water or oxygen was used as a reactive gas in thermal and plasma-enhanced ͑PE͒ processes. For PE ALD, there was a wide ALD temperature window from 50 to 200°C. Above 200°C, VTIP decomposed thermally, resulting in the chemical vapor deposition ͑CVD͒ of vanadium pentoxide. The PE ALD reactions saturated much faster than during thermal ALD, leading to a growth rate of approximately 0.7 Å/cycle during PE ALD using H 2 O or O 2. Optical emission spectroscopy showed combustion-like reactions during the plasma step. X-ray diffraction was performed to determine the crystallinity of the films after deposition and after postannealing under He or O 2 atmosphere. Films grown with CVD at 300°C and PE O 2 ALD at 150°C were ͑001͒-oriented V 2 O 5 as deposited, while thermal and PE H 2 O ALD films grown at 150°C were amorphous as deposited. The crystallinity of the PE O 2 ALD could be correlated to its high purity, while the other films had significant carbon contamination, as shown by X-ray photoelectron spectroscopy. Annealing under He led to oxygen-deficient films, while all samples eventually crystallized into V 2 O 5 under O 2 .
Atomic layer deposition ͑ALD͒ of TiO 2 thin films using Ti isopropoxide and tetrakis-dimethylamid... more Atomic layer deposition ͑ALD͒ of TiO 2 thin films using Ti isopropoxide and tetrakis-dimethylamido titanium ͑TDMAT͒ as two kinds of Ti precursors and water as another reactant was investigated. TiO 2 films with high purity can be grown in a self-limited ALD growth mode by using either Ti isopropoxide or TDMAT as Ti precursors. Different growth behaviors as a function of deposition temperature were observed. A typical growth rate curve-increased growth rate per cycle ͑GPC͒ with increasing temperatures was observed for the TiO 2 film deposited by Ti isopropoxide and H 2 O, while surprisingly high GPC was observed at low temperatures for the TiO 2 film deposited by TDMAT and H 2 O. An energetic model was proposed to explain the different growth behaviors with different precursors. Density functional theory ͑DFT͒ calculation was made. The GPC in the low temperature region is determined by the reaction energy barrier. From the experimental results and DFT calculation, we found that the intermediate product stability after the ligand exchange is determined by the desorption behavior, which has a huge effect on the width of the ALD process window.
It is emphasized that, under certain conditions, the frequency dependences of the real and imagin... more It is emphasized that, under certain conditions, the frequency dependences of the real and imaginary parts of an electrical impedance are correlated by the Kramers-Kronig relations. The importance of these relations in electrochemistry is illustrated by the examples of certain electrochemical impedance types. Some misapprehensions appearing in the electrochemical literature are pointed out.
Applied Physics Letters, 2010
The solid-state reaction and agglomeration of thin nickel-silicide films was investigated from sp... more The solid-state reaction and agglomeration of thin nickel-silicide films was investigated from sputter deposited nickel films (1–10 nm) on silicon-on-insulator (100) substrates. For typical anneals at a ramp rate of 3 °C/s, 5–10 nm Ni films react with silicon and form NiSi, which agglomerates at 550–650 °C, whereas films with a thickness of 3.7 nm of less were found to form an epitaxylike nickel-silicide layer. The resulting films show an increased thermal stability with a low electrical resistivity up to 800 °C.
The growth of epitaxial layers of hexagonal -nickel-silicide on Si͑100͒ and Si͑111͒ substrates is... more The growth of epitaxial layers of hexagonal -nickel-silicide on Si͑100͒ and Si͑111͒ substrates is reported. They form at 370°C on Si͑100͒ and 360°C on Si͑111͒, from codeposited Ni/Si mixtures, containing 37 to 42 atom % Si and the equivalent of a 50 nm Ni layer. These codeposited layers model the Ni/Si mixing layer at the interface in sputter-deposited films. The occurrence and stability at room temperature conflict with the phase diagram for bulk Ni/Si. Congruent crystallization is shown to initiate the growth of this metastable phase.
Solid-State Electronics, 2005
By covering amorphous silicon (a-Si) with a thin metal film, it is possible to lower the crystall... more By covering amorphous silicon (a-Si) with a thin metal film, it is possible to lower the crystallization temperature of the a-Si (typically around 800°C when using ramp anneals) to levels which can be used in a manufacturing process. This phenomenon of Metal Induced Crystallization (MIC) has been reported previously for Ni, Au and Al. In this work, in-situ X-ray Diffraction was used to study the MIC process for 20 different metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Al). The 7 metals which lower the crystallization temperature the most are Ni, Pt, Pd, Cu, Au, Al and Ag. The crystallization kinetics were studied in detail for these 7 materials. In order to explain the MIC process, two models where used depending on the interaction of the metal with Si (eutectic or compound forming).
Metal induced crystallization ͑MIC͒ is a technique that lowers the crystallization temperature of... more Metal induced crystallization ͑MIC͒ is a technique that lowers the crystallization temperature of amorphous semiconductors. The process has mainly been used to influence the crystallization of amorphous silicon ͑a-Si͒ and multiple studies on this subject have already been performed. The research of the MIC of amorphous Ge ͑a-Ge͒ has been mostly limited to the use of a Ni or Al film. This paper focuses on the characterization of the crystallization behavior of aGe films in the presence of 20 transition metals ͑Ti,
The change in barrier height caused by sputter metallization of contacts on both GaAs and InP sub... more The change in barrier height caused by sputter metallization of contacts on both GaAs and InP substrates, and using evaporated contacts as a reference, is investigated. It has been found that by annealing, the reference barrier height can be restored. A model is proposed, wherein sputter metallization leads, to passivation of interfacial defects by hydrogen. Accordingly, the Fermi level pinning caused by these defects is removed and the barrier height changes .and is determined by other mechanisms. Annealing produces a removal of hydrogen and reactivates the amphoteric defects. Additional evidence is given for the assumption that sputter metallization leads to passivation, by hydrogen, of dopants and defects in the semiconductor.
Electrochimica Acta, 1976
It is emphasized that, under certain conditions, the frequency dependences of the real and imagin... more It is emphasized that, under certain conditions, the frequency dependences of the real and imaginary parts of an electrical impedance are correlated by the Kramers-Kronig relations. The importance of these relations in electrochemistry is illustrated by the examples of certain electrochemical impedance types. Some misapprehensions appearing in the electrochemical literature are pointed out.
Ultrathin oxide layers, 2-5 nm thick, have been grown on (100) n-Si by Rapid Thermal Oxidation (R... more Ultrathin oxide layers, 2-5 nm thick, have been grown on (100) n-Si by Rapid Thermal Oxidation (RTO) at 900°C. RTO is an effective method to control the oxide thickness in this range to within 10%. The direct tunnelling through these ultrathin layers is examined with current-voltage and impedance measurements on Al/SiO,/n-Si structures with an oxide layer thickness between 2 and 4 nm. After the determination of the surface potential vs bias relation and the oxide layer capacitance from the capacitance-voltage measurements, a quantitative analysis of the current-voltage characteristic based on electron tunnelling from a degenerate accumulation layer through the SiO, barrier into the metal is made. A very good agreement with the theory is obtained assuming a simple trapezoidal tunnel barrier for the SiO,, from which the tunnel barrier height and the electron effective mass in the SiO, bandgap are derived. The density of interface traps at the Si/SiO, interface is determined using the conductance method. Only a very small increase of interface trap density with decreasing oxide layer thickness is found. The very high density of interface traps (more than 3 x 1O'l crne2 eV-') can be reduced to the 1O'O cme2 eV-' level by application of a conventional Post Metallization Anneal (PMA).
Oxide layer growth on GaAs, kept in methanol and without applying an external voltage, up to a th... more Oxide layer growth on GaAs, kept in methanol and without applying an external voltage, up to a thickness of about 20 nrn is reported. A growth law is found indicating that diffusion (with a diffusion constant = 1O-22 m's"), probably of a water or a water related species, is the dominating growth mechanism. The observed light-dependence of the growth on n-type material can be explained by t h e participation of holes in the first reaction step. Auger depth profiles show that the As-content of the layers grown in methanol is higher than that of layers grown in water, explaining the observed difference in the layers conductivity.
We investigate Co silicide phase formation when extra amorphous Si is added within an as deposite... more We investigate Co silicide phase formation when extra amorphous Si is added within an as deposited 50nm Co film. The addition of Si is investigated for both the Co/SiO2 and Co/Si(100) system. A series of 10 Co-Si mixed films with a Si content varying from 20 to 58at.% was prepared and investigated with in situ X-ray diffraction. The oxide system is used as reference system to identify phases that initially crystallize out in an amorphous mixture of a given composition. Multiple phases can nucleate, and the temperature of crystallization depends on the Co-Si atomic ratio. Upon heating of the Co(Si)/Si system, the first reaction is a similar crystallization reaction of the amorphous mixture. Once the first phase is formed, one has the normal system of a silicide phase in contact with an unlimited amount of Si from the substrate, and the sequential phase formation towards CoSi2 is established. In the Co(43-49%Si) layer composition range where CoSi is the first phase to form, increasing the amount of Si leads to a remarkable improvement of the thermal stability of CoSi on Si(100). CoSi2 nucleation was extensively delayed by 150 • C compared to the reaction in a pure Co/Si(100) film. Electron Back Scatter Diffraction measurements reveal that in this range, the gradual Si increase systematically leads to gradually bigger CoSi grains (up to 20µm). This shows that the grain size of the CoSi precursor strongly affects the nucleation of the following CoSi2 daughter phase. Laser Light Scattering measurements suggest that adding more than 38%Si reduces the roughness of the CoSi2 layer.
Silicides are a very useful group of materials which can be used to make electrical contacts to c... more Silicides are a very useful group of materials which can be used to make electrical contacts to circuits in electronic devices with an extremely high performance. The stress in thin films is an increasingly important technological issue from the standpoint of reliability and performance in IC processing. Manufacturers of micro electronic devices have to control the stress levels in the contact films to avoid device failures. Phase transitions such as silicidation or even a simple rearrangement of atoms like relaxation in the metal film cause a difference in the volume of the film from its starting value. This volume change produces stress inside the film. In this work we analyzed the stress evolution during the silicidation reaction of some metals such as W and Mo by using a home built in situ stress system at the University of Ghent.
A comparative study was made of d.c. magnetron sputtered and evaporated Ti/p-InP Schottky barrier... more A comparative study was made of d.c. magnetron sputtered and evaporated Ti/p-InP Schottky barriers. By means of measuring the barrier height increase, the shift of the Mott-Schottky lines and the change of the ideality factor due to sputtering, it could be shown that donor-type defects were introduced by this deposition technique. An electrostatic model based on a rectangular defect concentration profile enabled to calculate both the depth (0.06-0.4 pm) and the doping concentration (102'-1023 m-') of the n-type layer formed beneath the surface. Both quantities were found to depend on the original substrate doping concentration. The model was supported by the observed changes in the photovoltaic behaviour caused by sputtering. An important increase of the open circuit voltage occurred (0.35-0.70 V) together with a decrease of the spectral response in the short-wavelength region. It could be concluded that magnetron sputtering increases the photovoltaic efficiency (from 3.5 to 9.5%) and leads to a Schottky barrier height increase (0.2 eV) which is comparable to that obtained by more elaborate techniques (e.g. ion implantation).
Journal of Applied Physics, 2009
In this paper, we investigated Ni silicide phase formation when Si is added within an as deposite... more In this paper, we investigated Ni silicide phase formation when Si is added within an as deposited 50 nm Ni film. A series of 22 samples with a Si content varying from 0 to 50 at. % was prepared and systematically investigated with in situ x-ray diffraction. The inert oxide substrate was used to identify the phases which first crystallize
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Semiconductors by Roland Van Meirhaeghe