Method of low-temperature optical measurements with diamond anvil cells

Abstract

Constructions of a cryogenic diamond anvil system with mechanical clamping press and helium pressure medium for microscopic optical studies are described. Low temperature nonmagnetic cells ø40 and ø20 mm have been developed. GaP samples doped with S, Te and isoelectronic impurities N, NN have been investigated up to 20 GPa at 1.5-300K.     

ODMR of bismuth and sulphur in GaP

Optically detected magnetic resonance (ODMR) of bismuth and sulphur impurities in GaP is reported. The results are compared to previous measurements by Cavenett et al. on GaP:N and further confirm the model proposed by these authors to explain the observed decrease in photoluminescence.     

Intensity variations in the near-band-edge recombination of GaP epitaxial layers, grown on (111) and (001) oriented substrates, as observed by cathodoluminescence imaging

In this study a comparison between GaP layers, grown by metalorganic vapour phase epitaxy on either (111) oriented GaP substrates or (001) oriented GaP substrates, is made with respect to the near-band-edge luminescence. Spectrally resolved cathodoluminescence, CL, images were recorded at ˜ 25 K with detection on either the bound exciton emission or the donor-to-acceptor pair emission. The intensity variations observed in the CL images are interpreted in terms of aggregation of impurities around threading dislocations. Contrary to the layers grown on (001) oriented substrates, the layers grown on (111) oriented substrates show a segregation effect of the acceptor constituent involved in the donor-to-acceptor pair emission.     

ESR identification of the iron double electron trap state in GaP

By Electron Spin Resonance (ESR) it has been found that neutral substitutional iron impurities in gallium phosphide can trap two electrons. The 3d⁷-character of the two-electron trap state of iron in GaP was inferred from the characteristic angular dependence of the Zeeman-splitting of its Γ₈-ground state.     

Features of the Percolation Scheme of Vibrational Spectrum Reconstruction in the Ga1 – xAl x P Alloy

Specific features of the properties of Ga–P lattice vibrations have been investigated using the percolation model of a mixed Ga_{1 – x}Al _x P crystal (alloy) with zero lattice mismatch between binary components of the alloy. In contrast to other two-mode alloy systems, in Ga_{1 – x}Al _x P a percolation splitting of δ ~ 13 cm^–1 is observed for the low-frequency mode of GaP-like vibrations. An additional GaP mode (one of the percolation doublet components) split from the fundamental mode is observed for the GaP-rich alloy, which coincides in frequency with the gap corresponding to the zero density of one-phonon states of the GaP crystal. The vibrational spectrum of impurity Al in the GaP crystal has been calculated using the theory of crystal lattice dynamics. Upon substitution of lighter Al for the Ga atom, the calculated spectrum includes, along with the local mode, a singularity near the gap with the zero density of phonon states of the GaP crystal, which coincides with the mode observed experimentally at a frequency of 378 cm^–1 in the Ga_{1 – x}Al _x P (x < 0.4) alloy.

     

Determination of shallow traps in n-type GaP

The effect of shallow trapping centers on the electron life time (τ_η) in n-type (S doped) GaP has been investigated by photoconductivity measurements. The values of τ_η as a function of temperature and light intensity give information on the centers acting as traps. The basic assumption of the theory, that there is only one type of trap, is verified by the two types of experiments. There is also indication that S impurities act as traps.     

Crystalline to amorphous transformations in ion implanted GaP

Abstract

The amorphization process of GaP by ion implantation is studied. The samples of 〈111〉 oriented GaP were implanted at 130 K with various doses 5 × 10¹³-2 × 10¹⁶ cm^?2 of 150 keV N⁺ ions and with the doses of 6 × 10¹²-1.5 × 10¹⁵ cm^?2 of 150 keV Cd⁺ ions. Room temperature implantations were also performed to see the influence of temperature on defect production. Rutherford backscattering and channelling techniques were used to determine damage in crystals. The damage distributions calculated from the RBS spectra have been compared with the results of Monte-Carlo simulation of the defect creation.

The estimated threshold damage density appeared to be independent on ion mass and is equal 6.5 × 10²⁰ keV/cm³. It is suggested that amorphization of GaP is well explained on the basis of a homogenous model.     

Calculation of distribution coefficients of donors in III-V semiconductors

The techniques recently developed for the calculation of III-V ternary phase diagrams have been extended to the calculation of distribution coefficients of impurities in III-V semiconductors. The distribution coefficients are calculated with no adjustable parameters, the calculation requiring only the temperatures and entropies of fusion, binary phase diagrams and lattice parameters of the relevant III-V compounds, and the tetrahedral covalent radii, electronegativities, molar volumes and atomization energies of the donor impurities and group III and V elements concerned.The calculation is carried out for common donors S, Se, Te and Sn at the melting points of the III-V compounds GaP, GaAs, GaSb, InP, InAs and InSb, and the results compared with experimental results where available. In GaAs and GaP, the distribution coefficients are calculated vs temperature for solidification from the group III rich melt.     

Surface corrosion as an apparent cause of degradation of GaP : N LED’s

The effect of heat treatment and subsequent current stressing was studied and compared on passivated and non-passivated VPE GaP∶N LED’s. It was found that the drastically increased degradation rate of the non-protected diodes is due completely to increased surface leakage current, no structural change or contamination of the semiconductor-bulk was observed.

     

DLTS investigation of GaP under hydrostatic pressure

Abstract

Deep Level Transient Spectroscopy (DLTS) was applied to nitrogen related deep electron trap 0.4 eV in green emitting diodes of GaP under hydrostatic pressure. The pressure coefficient of the level energy is determinated as equal -31 meV/kbar with respect to the valence band edge.     

Detection of hydrogen in nominally pure GaP:Zn by optically detected electron nuclear double resonance

Optically detected electron nuclear double resonance (ODENDOR) measurements of the triplet antisite center P_Ga³⁺ in GaP:Zn have revealed the presence of hydrogen atom impurities in a nominally pure sample. Strong ligand ³¹P signals have also been observed. Assuming a uniform distribution of hydrogen the intensity ratio of the ³¹P to ¹H lines sets a rough lower limit of between 1–10 ppm on the hydrogen concentration. The possibility that the H¹ atoms form part of the antisite defects is also discussed.     

光测磁共振及其在研究Ⅲ-Ⅴ族半导体材料中的应用

光测磁共振技术是一种研究半导体中的杂质缺陷的有效工具,它可以提供有关杂质缺陷的电子结构及与辐射复合过程的关系的信息。这篇文章对光测磁共振的原理和技术进行了讨论,着重评述了最近几年来新的认识和进展。对光测磁共振技术在Ⅲ-V族半导体材料的辐射过程的研究中的应用也进行了评述,比较详细地介绍了对l_np:M_n及G_ap:O的研究工作。     

Liquid-metal field electron source based on porous GaP

We have reported on a new method for obtaining a liquid-metal field emitter. The treatment of a porous crystal of GaP binary semiconducting compound with high-voltage pulses in a vacuum has made it possible to obtain stable structures on its surface in the form of discrete gallium clusters. These structures exhibit high emission properties, including stable currents at a level of a few microamperes, as well as the high uniformity of the distribution of emission nanocenters over the surface.

     

GaP:(Bi,N)晶体中束缚激子的辐射复合及能量转移

本文研究了在4.2K—147K温度范围内GaP:(Bi,N)晶体的光致发光光谱的精细结构,积分强度及其随温度的变化,并将它们与GaP:Bi,GaP:N光谱进行比较。首次发现在GaP:(Bi,N)晶体中激发能量从孤立N中心和NNi对(i≥3)中心到Bi中心的转移,增大了Bi束缚激子态的浓度,使Bi发射带增强。     

Dynamique de reseau et frequences des modes de vibration pour des impuretes substitutionnelles dans InP,GaP et ZnS

The model used is a rigid-ion model with an effective ionic charge including general interactions for nearest and next nearest neighbours and long range Coulomb interactions. It provides a good fit with available neutron data and with IR absorption results for InP. In this model, no hypothesis is made apriori on the interatomic forces and the eleven parameters given by the model are used. A mathematical model which employs a Green's function technique in the mass defect and the nearest neighbour force constant defect approximation is used to calculate the lattice dynamics of the imperfect crystal. The frequencies of the local modes, the gap modes and the band modes, are given for isolated substitutional impurities. The same calculation is achieved for GaP and ZnS and the results are compared with IR data.     

Ⅲ-Ⅴ族化合物半导体中的深能级杂质缺陷

本文综述了近十多年以来对Ⅲ-Ⅴ族化合物半导体中深能级杂质缺陷的研究工作。讨论了深能级杂质缺陷对Ⅲ-Ⅴ族化合物材料与器件的性能的重要影响。介绍了结谱法、光致发光与电子自旋共振等几种研究深中心的方法在研究Ⅲ-Ⅴ族化合物时的某些特点。评述了对砷化镓、磷化镓和磷化铟及某些Ⅲ-Ⅴ族混晶中的一些深中心所取得的研究成果。     

Electron beam epitaxy of alloy semiconductors

Abstract

It was investigated that, when an Al evaporated layer on a GaP (GaAs, GaAs_1?y P _y ) substrate was bombarded with total fluences of 0.1?1.0 × 10¹⁸ electrons cm^?2 at 7 MeV and at 50°C, a thin heteroepitaxial layer of Al _x Ga_1?x P (Al _x Ga_1?x As, Al _x Ga_1?x As_1?y P _y ) crystal was grown on S-doped (111), (100) and (110) GaP [(110) Cr, O-doped GaAs, (100) Te-doped GaAS_1?y P _y ] substrates.

Evidence for the creation of the epilayers before annealing was obtained from measurements using an X-ray diffractometer, an X-ray photoelectron spectrometer, a reflection high-energy electron diffractometer, a transmission electron microscope and a scanning transmission electron microscope. In the case of Al/GaP, the epitaxial layers of Al_～0.25Ga_～0.75P, Al_～0.5Ga_～0.5P and Al_～0.75Ga_～0.25P were grown on (111), (100) and (110) GaP substrates, respectively. Their compositions did not vary with the total electron fluence.     

Radiation damage by implanted ions in GaAs and GaP

Abstract

The production of lattice disorder in GaAs and GaP by Te ions up to 40 keV has been investigated. For GaAs the build up of damage with implanted ion dose is linear until a saturation level is reached. For Gap, two linear regions are evident; a slow build up of damage to ?15 per cent of the saturation level, followed by a faster rate of increase up to the final 100 per cent level. Radiation annealing, for GaP samples, both by the heavy ion beam during implantation and by the helium beam during back-scattering measurements has been observed. The annealing temperatures required for re-ordering the lattice depend on the percentage of damage present. Samples damaged up to the saturation level require annealing at ?500°C, whilst 300°C is sufficient for samples damaged to ?50 per cent of the saturation value.     

The role of phase-matching and nanocrystal-size effects in three-wave mixing and CARS processes in porous gallium phosphide

Nonlinear-optical interactions, such as second-harmonic and sum-frequency generation and coherent anti-Stokes Raman spectroscopy (CARS), are investigated in porous GaP for the first time by means of a novel laser source based on mode-locked picosecond Nd³⁺:YVO₄ laser and subsequent continuum generation in an optical fiber. The efficiency of the former two nonlinear optical processes is shown to be strongly dependent on the wavelengths of the interacting waves and tends to increase with the decrease of the excitation wavelength. The power of the generated second-harmonic and sum-frequency increases by a factor of 2 and 30, respectively, compared to the crystalline GaP. In contrast, the CARS signal in porous GaP is found to be less efficient than one in crystalline GaP. The observed results are explained in terms of competition of the phase-matching effects in GaP nanocrystals and the enhanced photon lifetime in scattering porous GaP layers. PACS 42.25.Dd; 42.65.Ky; 42.70.Nq; 81.07.Bc     

X ray absorption spectroscopy investigation of phase transition in Ge,GaAs and GaP

Abstract

The phase transitions of GaAs, GaP and Ge under pressure have been investigated by x-ray absorption spectroscopy (XAS). At the onset of the transition the Debye-Waller factor increases and the x-ray absorption near edge structure (XANES) is progressively modified. A mixing of the low and high pressure phase can be determined by XAS as well as amorphization of the sample on pressure release.