Hydrogen Passivation of Shallow Dopants in InP Studied by Photoluminescence Spectroscopy

The effect of hydrogenation on the photoluminescence (PL) of InP : Mg, InP : Zn and undoped n-InP is presented. An increase in the near band edge pl intensity due to passivation of non-radiative centers was observed in all the samples. A donor - acceptor pair transition was observed before hydrogenation in the InP : Mg sample and after hydrogenation in the InP : Zn sample due to the acceptor deactivation. In n-InP the enhancement of donor bound exciton after hydrogenation points to the absence of donor passivation.

Hydrogen passivation of multi-crystalline silicon solar cells

The effects of hydrogen passivation on multi-crystalline silicon (mc-Si) solar cells are reported in this paper. Hydrogen plasma was generated by means of ac glow discharge in a hydrogen atmosphere. Hydrogen passivation was carried out with three different groups of mc-Si solar cells after finishing contacts. The experimental results demonstrated that the photovoltaic performances of the solar cell samples have been improved after hydrogen plasma treatment, with a relative increase in conversion efficiency up to 10.6%. A calculation modelling has been performed to interpret the experimental results using the model for analysis of microelectronic and photonic structures developed at Pennsylvania State University.

Thermodynamical and plasma-driven kinetic growth of high-aspect-ratio nanostructures : effect of hydrogen termination

The results of studies on the growth of high-aspect nanostructures in low-temperature non-equilibrium plasmas of reactive gas mixtures with or without hydrogen are presented. The results suggest that the hydrogen in the reactive plasma strongly affects the length of the nanostructures. This phenomenon is explained in terms of selective hydrogen passivation of the lateral and top surfaces of the surface-supported nanostructures. The theoretical model describes the effect of the atomic hydrogen passivation on the nanostructure shape and predicts the critical hydrogen coverage of the lateral surfaces necessary to achieve the nanostructure growth with the pre-determined shape. Our results demonstrate that the use of a strongly non-equilibrium plasma is very effective in significantly improving the shape control of quasi-one-dimensional single-crystalline nanostructures.

LITHIUM PASSIVATION OF ZN AND CD ACCEPTORS IN P-TYPE GAAS

We report lithium passivation of the shallow acceptors Zn and Cd in p-type GaAs which we attribute to the formation of neutral Li-Zn and Li-Cd complexes. Similar to hydrogen, another group-I element, lithium strongly reduces the concentration of free holes when introduced into p-type GaAs. The passivation is inferred from an increase of both the hole mobility and the resisitivity throughout the bulk of the sample. It is observed most clearly for Li concentrations comparable to the shallow-acceptor concentration. In addition, compensation of shallow acceptors by randomly distributed donors is present in varying degree in the Li-diffused samples. Unlike hydrogenation of n-type GaAs, Li doping shows no evidence of neutralizing shallow donors in GaAs.

Hydrogen-passivated detonation nanodiamond:an impedance spectroscopy study

Detonation nanodiamond (DND) is an attractive class of diamond material, which has a great potential to be used for a wide range of applications. In this paper, untreated DND was employed to perform hydrogen passivation process using microwave plasma enhanced chemical vapor deposition in order to investigate the influence of hydrogen-terminated surface on the DND's electrical properties. Impedance spectroscopy (IS) has been used to characterize the electrical properties of DND samples using a newly-developed measurement set-up. It is found that hydrogen-passivation process has increased the electrical conductivity of the DND by up to four orders of magnitude when compared with the untreated sample. An RC parallel equivalent circuit with a Warburg element has been proposed to model the DND's impedance characteristics. © 2012 Elsevier B.V. All rights reserved.

How to achieve high mobility thin film transistors by direct deposition of silicon using 13.56 MHz RF PECVD?

CMOS nanocrystalline silicon thin film transistors with high field effect mobility are reported. The transistors were directly deposited by radio-frequency plasma enhanced chemical vapor deposition at 150°C The transistors show maximum field effect mobility of 450 cm2/V-s for electrons and 100 cm2/V-s for holes at room temperature. We attribute the high mobilities to a reduction of the oxygen content, which acts as an accidental donor. Indeed, secondary ion mass spectrometry measurements show that the impurity concentration in the nanocrystalline Si layer is comparable to, or lower than, the defect density in the material, which is already low thanks to hydrogen passivation.

Influence of coupling between Er3+, nc-Si and nonradiative centers on photoluminescence from Er3+-doped nc-Si/SiO2 films

Con-elation between nc-Si, Er3+ and nonradiative defects in Er-doped nc-Si/SiO2 films is studied. Upon the 514.5 run laser excitation, the samples exhibit a nanocrystal-related spectrum centered at around 750 nm and an Er3+ luminescence line at 1.54mum. With increasing Er3+ content in the films,the Er3+ emission becomes intense while the photoluminescence at 750 nm decreases. Hydrogen passivation of the samples is shown to result in increases of the two luminescence peaks. However, the effect of hydrogen treatment is different for the samples annealed at different temperatures. The experimental results show that the coupling between Er3+, nc-Si and noradiative centers has a great influence on photoluminescence from nc-Si/SiO2 < Er > films.

Optical and Electrical Properties of GaN.Mg Grown by MOCVD

Mg-doped GaN layers prepared by metalorganic chemical vapor deposition were annealed at temperatures between 550 and 950℃. Room temperature （RT） Hall and photoluminescence （PL） spectroscopy measurements were performed on the as-grown and annealed samples. After annealing at 850℃, a high hole concentration of 8 × 10~(17) cm~(-3) and a resistivity of 0. 8lΩ·cm are obtained. Two dominant defect-related PL emission bands in GaN.. Mg are investigated; the blue band is centered at 2. 8eV （BL） and the ultraviolet emission band is around 3.27eV （UVL）. The relative intensity of BL to UVL increases after annealing at 550℃, but decreases when theannealing temperature is raised from 650 to 850℃, and finally increases sharply when the annealing temperature is raised to 950C. The hole concentration increases with increased Mg doping, and decreases for higher Mg doping concentrations. These results indicate that the difficulties in achieving high hole concentration of 10~(18)cm~(-3) appear to be related not only to hydrogen passivation, but also to self-compensation.

LPCVD of tungsten by selective deposition on silicon

Beta-phase W, selectively grown at 440C had resistivity 20 micro-ohm cm and maximum layer thickness 100nm. Hydrogen passivation proved essential in this process. Higher deposition temperatures resulted in increased layer thickness but incorporated WSi2 and alpha- phase W. Self limiting W grown on polycrystalline and heavily doped silicon yielded reduced thickness. Boron is involved in the WF6 reduction reaction but phosphorus is not and becomes incorporated in the W layer. The paper establishes an optimised and novel CVD process suited to IC contact technology. A funded technology transfer contract with National Semiconductor Greenock (M Fallon) resulted from this work.

Low temperature magneto-photoluminescence characterization of high purity gallium arsenide and indium phosphide

Low-temperature magneto-photoluminescence is a very powerful technique to characterize high purity GaAs and InP grown by various epitaxial techniques. These III-V compound semiconductor materials are used in a wide variety of electronic, optoelectronic and microwave devices. The large binding energy differences of acceptors in GaAs and InP make possible the identification of those impurities by low-temperature photoluminescence without the use of any magnetic field. However, the sensitivity and resolution provided by this technique rema1ns inadequate to resolve the minute binding energy differences of donors in GaAs and InP. To achieve higher sensitivity and resolution needed for the identification of donors, a magneto-photoluminescence system 1s installed along with a tunable dye laser, which provides resonant excitation. Donors 1n high purity GaAs are identified from the magnetic splittings of "two-electron" satellites of donor bound exciton transitions 1n a high magnetic field and at liquid helium temperature. This technique 1s successfully used to identify donors 1n n-type GaAs as well as 1n p-type GaAs in which donors cannot be identified by any other technique. The technique is also employed to identify donors in high purity InP. The amphoteric incorporation of Si and Ge impurities as donors and acceptors in (100), (311)A and (3ll)B GaAs grown by molecular beam epitaxy is studied spectroscopically. The hydrogen passivation of C acceptors in high purity GaAs grown by molecular beam epitaxy (MBE) and metalorganic chemical vapor deposition (MOCVD) 1s investigated using photoluminescence. Si acceptors ~n MBE GaAs are also found to be passivated by hydrogenation. The instabilities in the passivation of acceptor impurities are observed for the exposure of those samples to light. Very high purity MOCVD InP samples with extremely high mobility are characterized by both electrical and optical techniques. It is determined that C is not typically incorporated as a residual acceptor ~n high purity MOCVD InP. Finally, GaAs on Si, single quantum well, and multiple quantum well heterostructures, which are fabricated from III-V semiconductors, are also measured by low-temperature photoluminescence.

Hydrogen in plasma-nanofabrication : selective control of nanostructure heating and passivation

The possibility of independent control of the surface fluxes of energy and hydrogen-containing radicals, thus enabling selective control of the nanostructure heating and passivation, is demonstrated. In situ energy flux measurements reveal that even a small addition of H2 to low-pressure Ar plasmas leads to a dramatic increase in the energy deposition through H recombination on the surface. The heat release is quenched by a sequential addition of a hydrocarbon precursor while the surface passivation remains effective. Such selective control offers an effective mechanism for deterministic control of the growth shape, crystallinity, and density of nanostructures in plasma-aided nanofabrication. © 2010 American Institute of Physics.

THE EFFECT OF PASSIVATION OF BORON DOPANTS BY HYDROGEN IN NANO-CRYSTALLINE AND MICROCRYSTALLINE SILICON FILMS

It is well known that the value of room-temperature conductivity sigma(RT) of boron-doped silicon films is one order lower than that of phosphorus-doped silicon films, when they are deposited in an identical plasma-enhanced chemical vapour deposition system. We use surface acoustic wave and secondary-ion mass spectrometry techniques to measure the concentration of total and electrically active boron atoms. It is shown that only 0.7% of the total amount of incorporated boron is electrically active. This is evidence that hydrogen atoms can passivate substitutional B-Si bonds by forming the neutral B-H-Si complex. By irradiating the boron-doped samples with a low-energy electron beam, the neutral B-H-Si complex converts into electrically active B-Si bonds and the conductivity can be increased by about one order of magnitude, up to the same level as that of phosphorus-doped samples.

The effect of microscopic texture on the direct plasma surface passivation of Si solar cells

Textured silicon surfaces are widely used in manufacturing of solar cells due to increasing the light absorption probability and also the antireflection properties. However, these Si surfaces have a high density of surface defects that need to be passivated. In this study, the effect of the microscopic surface texture on the plasma surface passivation of solar cells is investigated. The movement of 105 H+ ions in the texture-modified plasma sheath is studied by Monte Carlo numerical simulation. The hydrogen ions are driven by the combined electric field of the plasma sheath and the textured surface. The ion dynamics is simulated, and the relative ion distribution over the textured substrate is presented. This distribution can be used to interpret the quality of the Si dangling bonds saturation and consequently, the direct plasma surface passivation.

Passivation of surface and bulk defects in p-GaSb by hydrogenated amorphous silicon treatment

Passivation of point and extended defects in GaSb has been observed as a result of hydrogenated amorphous silicon (a-Si:H) treatment by the glow discharge technique. Cathodoluminescence (CL) images recorded at various depths in the samples clearly show passivation of defects on the surface as well as in the bulk region. The passivation of various recombination centers in the bulk is attributed to the formation of hydrogen-impurity complexes by diffusion of hydrogen ions from the plasma a-Si:H acts as a protective cap layer and prevents surface degradation which is usually encountered by bare exposure to hydrogen plasma. An enhancement in luminescence intensity up to 20 times is seen due to the passivation of nonradiative recombination centers. The passivation efficiency is found to improve with an increase in a-Si:H deposition temperature. The relative passivation efficiency of donors and acceptors by hydrogen in undoped and Te-compensated p-GaSb has been evaluated by CL and by the temperature dependence of photoluminescence intensities. Most notably, effective passivation of minority dopants in tellurium compensated p-GaSb is evidenced for the first time. (C) 1996 American Institute of Physics.

Optical and electrical properties of hydrogen-passivated gallium antimonide

The effect of hydrogen-plasma passivation on the optical and electrical properties of gallium antimonide bulk single crystals is presented. Fundamental changes of the radiative recombination after hydrogenation in undoped, zinc-doped, tellurium-doped, and codoped (with Zn and Te) GaSb are reported. The results of optical measurements indicate that passivation of acceptors is more efficient than that of the donors and, in general, the passivation efficiency depends on the doping level. Passivation of deep nonradiative centers is reflected by the gain of photoluminescence intensity and decrease in deep-level transient spectroscopy peak height. Extended defects like grain boundaries and dislocations have also been found to be passivated. The thermal stability of the passivated deep level and extended defects is higher than that of the shallow level. The kinetics of thermally released hydrogen in the bulk has been studied by reverse-bias annealing experiments.