Modeling of hydrogen diffusion in p-type GaAs:Zn

Experimental hydrogen diffusion profiles are reported in undoped and zinc doped GaAs. Hydrogen was introduced by exposure to a hydrogen plasma. The hydrogen profiles are fit using a diffusion model which assumes that hydrogen has a donor level in the band gap and diffuses as H⁺ and H⁰ in the material. It is also assumed that H⁺ can be trapped by ionized acceptors to form neutral complexes. Good simulations are obtained in p-type GaAs for various doping levels. We find that neutral hydrogen is present with high concentration in the diffusion process and the hydrogen molecule formation is absent. The hydrogen donor level, the diffusivities of H⁺ and H⁰, the associated activation energies and the dissociation energy of the acceptor-hydrogen pairs are determined.     

Hydrogen diffusion in crystalline semiconductors

The diffusion of hydrogen in semiconductors is complicated by the existence of several charge states (notably H⁺ in p-type material and H^- or H⁰ in n-type material, at least for Si) and also that hydrogen is present in a number of different forms, namely atomic, molecular or bound to a defect or impurity. Since the probability of formation of these different states is dependent on the defect or impurity type and concentration in the material and on the hydrogen concentration itself, then the apparent hydrogen diffusivity is a function of the sample conductivity and type and of the method of hydrogen insertion. Under conditions of low H⁺ concentration in p-type Si, for example, the diffusivity is of the order of 10^-10 cm² · s^-1 at 300 K and is consistent with the value expected from an extrapolation of the Van Wieringen and Warmoltz expression D_H = 9.4 × 10^-3 exp[-0.48 eV/kT] cm² · s^-1. The characteristics of hydrogen diffusion in n- and p-type Si and GaAs are reviewed in this paper, and the retardation of hydrogen permeation by molecular formation and impurity trapping is discussed. The measurement of several key parameters, including the energy levels for the hydrogen donor and acceptor in Si and the diffusivity of the H⁰ and H^- species, would allow a more quantitative treatment of hydrogen diffusion in semiconductors.     

High sensitivity Hall devices with AlSb/InAs quantum well structures

AlSb/InAs quantum well (QW) structures and InAs films on GaAs (001) substrates were grown by molecular beam epitaxy (MBE). We investigated the dependence of electron mobility and two-dimensional electron gas (2DEG) concentration on the thickness of an InAs channel. It is found that electron mobility as high as 19050 cm2·V-1·s-1 has been achieved for an InAs channel of 22.5 nm. The Hall devices with high sensitivity and good temperature stability were fabricated based on the AlSb/InAs QW structures. Their sensitivity is markedly superior to Hall devices of InAs films.     

Combined effects of hydrostatic pressure and electric field on the donor binding energy and polarizability in laterally coupled double InAs/GaAs quantum-well wires

This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38 kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a nonlinear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum well wires.     

The effects of hydrogen dose and thermal treatment on the formation of microsplits in hydrogen implanted GaAs

Transmission electron microscopy has been used to study the effect of thermal treatment on the formation of microsplits and damage rafts in hydrogen implanted (1 × 10¹⁶ and 5 × 10¹⁶ H⁺ cm^-2) and annealed (700 and 800°C) GaAs. The results show that microsplit and damage raft formation in implanted samples may be prevented if the samples are first given a pre-anneal heat treatment for 15 minute intervals at 300, 350, 400 and 450°C, during which the hydrogen concentration is reduced without allowing vacancy coalescence to take place.     

Pressure dependence of electron scattering by DX centres in GaAs and AlGaAs

Abstract

The electron mobility of heavily n-dopped GaAs and AlGaAs increases rapidly with applied hydrostatic pressure as carriers are trapped at DX centres. This has been taken as evidence against the Chadi and Chang (CC) negative charge state model of the DX centre. We argue that DX^? centres are formed close to d⁺ centres in highly doped samples, and that the mobility data is in fact fully consistent with the CC model, when such dipole-like correlations are included.     

静水压力对Al14Mn2P16磁光性质影响的密度泛函理论研究

采用第一性原理，研究不同静水压力（0~20 GPa）下Al₁₄Mn₂P₁₆的弹性与磁光性质.计算得到基态是铁磁态.弹性稳定性判据表明该体系是稳定的.研究发现磁矩随静水压力的增加而减小.静水压力低于5 GPa时，居里温度达到184 K，随着静水压力的增加略有下降；有趣的是，当静水压力高于5 GPa时，随着静水压力的增加，居里温度急剧下降，在18 GPa时消失.同时还发现随静水压力的增加可见光范围的吸收峰有明显的蓝移，当静水压力达到20 GPa时，可见光范围的吸收峰消失.     

Hydrogen-induced missing-row reconstructions of Pd(110) studied by scanning tunneling microscopy

The effect of hydrogen adsorption on the Pd(110) surface structure at room temperature has been studied by scanning tunneling microscopy. Depending on the partial pressure of hydrogen two different reconstructions of Pd(110) have been observed: a (1 × 3) phase at hydrogen pressures in the 10⁻⁹ mbar range and an additional (1 × 2) phase at p_H2 ≥ 5 × 10⁻⁸ mbar. Both reconstructions are found to be of the missing-row type. The evolution of the surface reconstructions has been followed in situ.     

Photoreflectance spectroscopy of semiconductor structures at hydrostatic pressure: A comparison of GaInAs/GaAs and GaInNAs/GaAs single quantum wells

The pressure dependence of optical transitions in Ga_0.64In_0.36As/GaAs and Ga_0.64In_0.36N_0.01As_0.99/GaAs single quantum well (SQW) structures were studied in photoreflectance (PR) spectroscopy. In order to apply high hydrostatic pressure, up to ∼11 kbar, the liquid-filled clamp-pressure cell with a sapphire window for optical access has been adopted in the PR set-up with the so called ‘bright configuration’. It has been found that the linear hydrostatic pressure coefficient for the ground state transition are equal to 8.6 and 7.3 meV/kbar for the GaInAs/GaAs and GaInNAs/GaAs SQWs, respectively. This result shows that the incorporation of only 1% of N atoms into GaInAs/GaAs leads to ∼15% decrease in the pressure coefficient. In addition, a non-linearity in the pressure dependence of the ground state transition has been resolved for the GaInNAs/GaAs SQW.     

The effect of annealing under hydrostatic pressure on the visible photoluminescence from si-ion implanted SiO2 films

We have studied the influence of the hydrostatic pressure during annealing on the intensity of the visible photoluminescence (PL) from thermally grown SiO₂ films irradiated with Si⁺ ions. Post-implantation anneals have been carried out in an Ar ambient at temperatures T_a of 400°C and 450°C for 10 h and 1130°C for 5 h at hydrostatic pressures of 1 bar–15 kbar. It has been found that the intensity of the 360, 460 and 600 nm PL peaks increases with rising hydrostatic pressure during low-temperature annealing. The intensity of the short-wavelength PL under conditions of hydrostatic pressure continues to rise even at T_a=1130°C. Increasing T_a leads to a shift in the PL spectra towards the ultraviolet range. The results obtained have been interpreted in terms of enhanced, pressure-mediated formation of ≡Si–Si≡ centres and small Si clusters within metastable regions of the ion-implanted SiO₂.     

First-principles calculations of hydrogen in bulk GaAs

We present the results of first-principles calculations of the properties of neutral (H⁰) and charged (H⁺ and H^-) hydrogen in bulk GaAs. The equilibrium sites are determined, and the electronic properties for the equilibrium positions are studied. H⁺ behaves as a deep donor and prefers to stay in a high valence charge region which includes the bond center. H^- behaves as a deep acceptor and prefers the low valence charge region near a tetrahedral site. H⁰ has an amphoteric behaviour depending on the site it occupies. We compare our results with the results of calculations for H in Si.     

Hydrostatic pressure effects on impurity states in InAs/GaAs quantum dot

Within the framework of effective-mass approximation, the hydrostatic pressure effects on the donor binding energy of a hydrogenic impurity in InAs/GaAs self-assembled quantum dot(QD) are investigated by means of a variational method. Numerical results show that the donor binding energy increases when the hydrostatic pressure increases for any impurity position and QD size. Moreover, the hydrostatic pressure has a remarkable influence on the donor binding energy for small QD. Realistic cases, including the impurity in the QD and the surrounding barrier, are considered.     

Evaluation of the diffusion length of minority carriers in bulk GaAs

The diffusion length of minority charge carriers has been investigated in LEC GaAs, silicon-doped with doping density N_D - N_A ranging from 10¹⁶ to 10¹⁸ cm^-3, by surface photovoltage (SPV) and electron-beam-induced current (EBIC) of scanning electron microscopy (SEM) measurements. Au Schottky diodes have been evaporated along the diameter of wafers cut from different doping density ingots to determine the variation of minority carrier diffusion length with both the radial position on the slice and the carrier concentration. The diffusion length values obtained by optical and electron excitation enhance systematic differences, which can be explained by the different surface recombination weight in the carrier generation volume and by the injection level, too. In all the examined samples an M-shaped radial variation of the diffusion length has been observed; on the other hand, the mean value of L_p increases from 0.5 to 7 μm when the doping concentration increases. The authors correlate this distribution to the electrical inhomogeneity induced by native defects and associated recombination centres. The role of the dislocations, which induce two competitive effects, i.e. an enhanced recombination probability and a precipitate condensation, is here discussed.     

InOOH压致氢键对称化及其弹性性质

利用第一性原理研究了InOOH在高压下的氢键对称化行为及其对InOOH弹性等性质的影响.结果表明约在18 GPa时InOOH中的氢键发生了对称化转变,导致轴比率b/c对压力的斜率由负值变为正值;压缩弹性常数、非对角弹性常数、体积模量和纵波波速出现异常增加,如体积模量增加了20%—40%.高压下InOOH弹性性质呈现出更加明显的各向异性.常压下InOOH呈现韧性,且伴随着氢键对称化韧性异常增加.对畸变金红石型MOOH(M=Al,In,Ga,Fe,Cr)化合物在高压下的弹性性质转变与氢键性质转变的耦合规律进行了初探.     

Raman characterization of passivated GaAs surfaces

The technique of Raman scattering at room temperature, is used to investigate the effect of H₂S passivation of the surface of n-type GaAs. Well-defined LO, L^- and L⁺ features are distinguished in spectra which have been recorded in z(x, y)[ovbar|zovbar] scatte ring orientation. It is observed that the ratio of the LO to L^- peak is reduced by the effects of the passivation process and that the shift of the L⁺ feature from the laser line is decreased. This latter effect, it is suggested, is caused by a decrease in free-carrier concentration due to donor neutralization by hydrogen during passivation. This neutralization effect will also affect the LO to L^- ratio and so complicate a quantitative analysis of the influence of passivation on the surface barrier potential.     

TEM study of the origin of the surface microroughness in DSL photoetched Si-implanted GaAs wafers

TEM has been used to study the origin of the surface microroughness that formed in both ²⁹Si as-implanted and rapid thermal annealed LEC undoped GaAs wafers after DSL photoetching. The degree of microroughness increased as the implant dose increased from 3 × 10¹² to 3 × 10¹⁴ atoms/cm². It has been found that such a microroughness is due to the fine-scale damage induced by the implantation in the as-implanted wafers and to interstitial dislocation loops in the implanted and then annealed wafers. Microroughness appears during DSL etching because such defects are effective recombination centres for the holes involved in the dissolution of the GaAs surface so that the wafers etch slower at the point-defect clusters and dislocation loops.     

FIRST-PRINCIPLE SELF-CONSISTENT PSEUDOPOTENTIAL CALCULATION OF THE ELECTRONIC STRUCTURES OF SHORT-PERIOD (GaAs)m(AlAs)n SUPERLATT1CES

With the local density approximation, the band structares of the short-period (GaAs)₁(AlAs)₁ and (GaAs)₂(AlAs)₁ superlattices are calculated by using the first-principle self-consistent pseudopotential method. The results show that the (GaAs)₁(AlAs)₁ superlattice is an indirect semiconductor, and the lowest conduction band state is at point R in the Brillouin zone; the (GaAs)₂(AlAs)₁ superlattice is a direct semiconductor and the lowest conduction band state is at point Γ. The squared matrix elements of transition are calculated. The pressure coefficients of energy gaps of the (GaAs)₁(AlAs)₁ and (GaAs)₂(AlAs)₁ superlattices are calculated and compared with those obtained by hydrostatic pressure experiments.     

Identification of the double and single acceptor state of isolated NiGa in GaAs

The question of the exact energy positions of isolated Ni_Ga as well as their optical and electrical properties have not yet been fully clarified in GaAs. We present a systematic study by deep-level transient spectroscopy, deep-level optical spectroscopy and optical absorption performed on several Ni-doped GaAs materials: n- and p-type LEC (liquid-encapsulated Czochralski) grown and p-type layers grown by liquid-phase epitaxy (LPE). All the electrical and optical results are up to now relatively coherent with the following identifications: (i) the double-acceptor charge state (Ni⁺ /Ni²⁺) is at E_c - 0.4 eV, (ii) the single-acceptor charge state (Ni²⁺ / Ni³⁺) is at E_v + 0.2 eV. However, when Ni is introduced during LPE in p-type materials we do not detect the Ni²⁺ /Ni³⁺ level which suggest a very low solubility of Ni in the LPE growth conditions.     

Simultaneous effects of hydrostatic pressure and electric field on impurity binding energy and polarizability in coupled InAs/GaAs quantum wires

This work is concerned with the theoretical study of the combined effects of applied electric field and hydrostatic pressure on the binding energy and impurity polarizability of a donor impurity in laterally coupled double InAs/GaAs quantum-well wires. Calculations have been made in the effective mass and parabolic band approximations and using a variational method. The results are reported for different configurations of wire and barriers widths, impurity position, and electric field and hydrostatic pressure strengths. Our results show that for symmetrical structures the binding energy is an even function of the impurity position along the growth direction of the structure. Also, we found that for hydrostatic pressure strength up to 38 kbar, the binding energy increases linearly with hydrostatic pressure, while for larger values of hydrostatic pressure the binding energy has a non-linear behavior. Finally, we found that the hydrostatic pressure can increase the coupling between the two parallel quantum-well wires.     

High pressure photoluminescence and resonant Raman study of GaAs

Photoluminescence and resonant Raman scattering have been studied in GaAs under hydrostatic stress up to 72 kbar. From the pressure dependence of the photoluminescence intensity the pressure coefficient of the X₆ conduction band minimum in GaAs has been determined. The pressure dependence of zone edge phonon energies in GaAs is also reported.