Unconventional carrier-mediated ferromagnetism above room temperature in ion-implanted (Ga,Mn)P:C

Ion implantation of Mn ions into hole-doped GaP has been used to induce ferromagnetic behavior above room temperature for optimized Mn concentrations near 3 at. %. The magnetism is suppressed when the Mn dose is increased or decreased away from the 3 at. % value, or when n-type GaP substrates are used. At low temperatures the saturated moment is on the order of 1 Bohr magneton, and the spin wave stiffness inferred from the Bloch-law T(3/2) dependence of the magnetization provides an estimate T(c)=385 K of the Curie temperature that exceeds the experimental value, T(c)=270 K. The presence of ferromagnetic clusters and hysteresis to temperatures of at least 330 K is attributed to disorder and proximity to a metal-insulating transition.     

Electron-damage studies in GaP at low temperature

The defects introduced in p-type Zn doped GaP by beta particle irradiation, of 1 MeV average energy, at low temperatures are monitored by bridge measurements of capacitance and delectric losses of a capacitor. The results of measurements, between 15 and 65 K, are attributed, in two different temperature regimes, to a GaP capacitor with losses arising from (a) an a.c hopping conduction process, below 45 K, and (b) a band conduction, above 45 K. Electron irradiation affects both hopping and band conduction as well as the transition temperature.     

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。     

Some optical properties of (ZnS)−(GaP) alloys and their interpretation

Optical measurements on the single crystals of the pseudobinary (ZnS)?(GaP) alloy were carried out. The band gap energy decreased more rapidly with increase in GaP concentration than that reported previously. The analysis of the absorption spectra for the crystals of up to 70 mole % GaP indicated a direct transition characteristic, and that the band gap becomes nearly equal to that of pure GaP at about 30 mole % GaP. The photoluminescence spectra observed at liquid nitrogen temperature could first be resolved into three kinds of emission band with Gaussian distribution. The peak energy of these bands were found to be independent of the band gap variation. Thus the observed peak energy shift with alloy composition was attributed to the variation of the emission intensity of each band. The band gap shrinkage and the origin of the photoluminescence spectra on the basis of a molecular orbital method were discussed.     

A theoretical investigation of the band alignment of type-I direct band gap dilute nitride phosphide alloy of GaN_xAs_yP_(1-x-y)/GaP quantum wells on GaP substrates

The GaP-based dilute nitride direct band gap material Ga（NAsP） is gaining importance due to the monolithic integra- tion of laser diodes on Si microprocessors. The major advantage of this newly proposed laser material system is the small lattice mismatch between GaP and Si. However, the large threshold current density of these promising laser diodes on Si substrates shows that the carrier leakage plays an important role in Ga（NAsP）/GaP QW lasers. Therefore, it is necessary to investigate the band alignment in this laser material system. In this paper, we present a theoretical investigation to optimize the band alignment of type-I direct band gap GaNxAsyP1-x-y/GaP QWs on GaP substrates. We examine the effect of nitrogen （N） concentration on the band offset ratios and band offset energies. We also provide a comparison of the band alignment of type-I direct band gap GaNxAsyP1-x-y/GaP QWs with that of the GaNxAsyP1-x-y/Al2Ga1-2P QWs on GaP substrates. Our theoretical calculations indicate that the incorporations of N into the well and AI into the barrier improve the band alignment compared to that of the GaAsP/GaP QW laser heterostructures.     

Size effect on parameters characteristic of polar GaP crystals

All the parameters characteristic of the GaP crystal doped with O_p and Zn_Ga are investigated and compared to those of the same crystal but doped with S_p and Zn_Ga, basing on a deformation potential model related to the size effect. It is shown that the dilatation resulting from this effect decreases not only the band gap but also the other values of the parameters characteristic of the pure crystal. The band gap of the GaP crystal doped with O and Zn is found to be 1.556eV and it is thus equal approximately to that of the pure CdTe crystal at low temperatures.     

Electronic surface properties of uhv-cleaved III–V compounds

Combined CPD and photoemission measurements were performed on uhv-cleaved surfaces of the III–V compounds InAs, GaSb, GaAs and GaP with moderate p-type and n-type dopings. Except for n-type GaP these materials show practically no band bending. N-type GaP exhibits surface Fermi level stabilization at 0.55 eV below the conduction band edge. This is ascribed to an intrinsic empty surface state band in the forbidden zone. On the basis of our experiments together with available data from literature we propose an empirical model for the (110) plane of III–V compounds containing In or Ga as metal and Sb, As or P as non-metal atoms from which the lower edge of the empty surface state band can be predicted. The model indicates that for any of these compounds except for GaP no empty surface state band exist in the band gap on the (110) surface.     

Reevaluation of bandgap and free exciton binding energy of GaP

Very sensitive measurements on the spectral behaviour of the free-to-bound excitation σ_pl^°(hν) from the valence band to the deep 0 donor in GaP at low temperatures are presented. Evaluation of the threshold energy for the electronic transition, together with the known value of the 0 binding energy, provides a simple and accurate way to determine the indirect bandgap E_g of GaP. Our new value is E_g = 2.3525 ± 0.003 eV at 1.5 K, which gives an exciton binding energy E_x = 24 ± 3 meV, considerably larger than previously used values. These data also imply an upward revision of acceptor binding energies in GaP with 10 ± 2 meV.     

纳米磷化镓粉体中混杂石墨和金刚石微晶的拉曼光谱分析

利用Raman光谱并结合能量色散X射线显微分析(EDX)和X射线衍射图谱(XRD)对混杂于纳米磷化镓粉体内的石墨和金刚石纳米微晶进行了分析。结果表明,在纳米GaP粉体Raman光谱中,位于1324 cm-1和1572 cm-1的两个宽强散射谱带分别归属于金刚石的F2g模和石墨的E2g模振动。EDX结果证实纳米GaP粉体材料中含有碳元素。XRD图谱中出现了石墨和金刚石的低晶面指数衍射峰。     

Formation and crystal structure of GaSb/GaP quantum dots

The atomic structure of GaSb/GaP quantum dots grown via molecular beam epitaxy on a (100) GaP surface at epitaxy temperatures of 420–470°C is investigated. It is established that, depending on morphology of the GaP growth surface, the deposition of 1 ML of GaSb leads to the formation of strained Ga(Sb, P)/GaP or fully relaxed GaSb/GaP quantum dots. The obtained heterostructures exhibit high photoluminescence efficiency.     

Hopping and band transport in amorphized semiconductors

Crystalline samples of Si, GaAs, GaP, InP, and CdTe have been rendered amorphous by bombardment with rare gas ions. DC conductivity and thermopower have been measured as a function of temperature in the interval between 15–500 K. In all cases, electron transport at low temperatures is characterized by non-simply activated processes of the hopping type transport, whereas band transport is observed at higher temperatures. The common and individual features of the different amorphous systems are discussed within the framework of existing transport theories.     

Photoionization of electrons and holes at oxygen donors in gallium phosphide

The spectral dependence of the photoionization cross-section for the oxygen donor in GaP is studied in the temperature range between 90 and 410°K by steady state photocurrent measurements using two different radiation sources. From a fit of Lucovsky's model to the experimental results, accurate information is obtained about the energy position of the oxygen donor at all temperatures. It is found that the oxygen level is pinned to the valence band for temperatures above 295 K and that at these temperatures the Franck-Condon shift is very small. This may indicate that there is little interaction between the impurity level and the surrounding lattice.     

Optical spectra and electronic transitions in gallium phosphide crystals

Analysis of the long-wave edge of the self-absorption spectrum of gallium phosphide crystals not distorted by line structure at low temperatures enabled us to determine the characteristic parameters of indirect transitions. In GaP crystals of a different type the appearance of a discrete structure in the long-wave absorption edge is related to the localization of excitons near impurities of an unknown nature. This is confirmed by the appearance in these crystals of an intense green electroluminescence band at low temperatures.The authors are grateful to I. Ryzhikov, A. Kruchinin, and Yu. Il'in for providing the crystals used in the experiments.     

Electronic structure and optical gain of InAsPN/GaP(N) quantum dots

The electronic structure and optical gain of InAsPN/GaP(N) quantum dots (QDs) are investigated in the framework of the effective-mass envelope function theory. The strain distribution is calculated using the valence force field (VFF) method. With GaP barrier, for smaller InAsPN QDs, the minimum transition energy may occur at a lower phosphorous (P) composition, but for larger QDs, the transition energy increases as P composition increases due to the increased bandgap of alloy QDs. When the nitrogen (N) composition increases, the transition energy decreases due to the stronger repulsion between the conduction band (CB) and the N resonant band, and the transition matrix element (TME) is more affected by the transition energy rather than N–CB mixing. To obtain laser materials with a lattice constant comparable to Si, we incorporated 2% of N into the GaP barrier. With this GaP_0.98N_0.02 barrier, the conduction band offset is reduced, so the quantum confinement is lower, resulting in a smaller transition energy and longer wavelength. At the same time, the TME is reduced and the optical gain is less than those without N in the barrier at a low carrier density, but the peak gain increases faster when the carrier density increases. Finally it can surpass and reach a greater saturation optical gain than those without N in the barrier. This shows that incorporating N into GaP barriers is an effective way to achieve desirable wavelength and optical gain.     

Oxidation and annealing of GaP and GaAs (111)-faces studied by AES and UPS

The annealing behaviour after argon sputtering and the first steps of oxidation of the polar GaP and GaAs (111)-faces are studied by AES and UPS. The Auger spectrum of GaP is briefly discussed. In contrast to GaAs, the GaP surfaces show a gallium accumulation after argon sputtering, but they become stoichiometric by annealing. The photoemission spectra show an additional emission due to oxygen with its maximum at about 5 eV below the valence band edge. The decrease of the emission near the valence band edge by oxidation shows the existence of surface sensitive states. Comparing the results of the two polar faces and for different surface compositions, it is concluded that these states are mainly As- and P-derived, respectively. A linear relationship is found between the UPS and Auger signal of oxygen.     

老化产生的深能级对GaP纯绿发光二极管发光效率的影响

测量了GaP纯绿发光二极管老化前后的可见和近红外发光光谱,研究了老化产生的深能级的来源及其对二极管发光效率的影响.在老化后的发光光谱中观测到650nm和1260nm发光带,发现1260nm发光带的发光强度随老化时间的增加而增强.实验结果表明老化产生的与磷相关的深能级严重地影响了GaP纯绿LED的发光效率.     

TM掺杂的Ⅲ-Ⅴ族稀磁半导体电磁性质的第一原理计算

使用基于自旋局域密度泛函理论的第一性原理方法对3d过渡金属(TM=V，Cr，Mn，Fe，Co和Ni)掺杂的Ⅲ-Ⅴ族半导体(GaAs和GaP)的电磁性质进行了计算.结果发现：用V，Cr和Mn掺杂时体系将出现铁磁状态，而Fe掺杂时将出现反铁磁状态，Co和Ni掺杂时，其磁性则不稳定.其中，Cr掺杂的GaAs和GaP将可能是具有较高居里温度的稀磁半导体(DMS).在这些DMS系统中，V离子的磁矩大于理论期待值，Fe，Co和Ni离子的磁矩小于理论期待值，Cr和Mn离子的磁矩与期待值的差距取决于晶体的对称性以及磁性离子的能带分布.此外，使用Si和Mn共同对Ⅲ-Ⅴ族半导体进行掺杂，将有利于DMS表现为铁磁状态，并可以使体系的T_C进一步提高. 关键词： 稀磁半导体 过渡金属 掺杂 共掺杂     

Specific features of the effect of annealing on the transmission spectra of GaP:N light-emitting diodes

The effect of annealing in a hydrogen atmosphere on the transmission spectra of GaP:N light-emitting diodes at temperatures of 550, 570, and 590 °C has been investigated. Temperature-induced rearrangement of defects has been observed. The band gap of the material studied is determined. The dependence of the transmission and difference transmission spectra on the annealing temperature and the effect of annealing on the electroluminescence spectra are shown.     

Competition between band and hopping carrier transport in Ge : Mn thin films

Regularities of hole transport and its correlation with percolation magnetism caused by localized carriers simultaneously involved in the formation of the magnetic and electrical properties of Ge: Mn thin films are investigated. It is established that at temperatures of T > 22 K the activationless band carrier transport occurs in the Ge: Mn samples (2 at % Mn). At low temperatures, the hopping mechanism with a variable hopping length works.     

Fabrication and characterization of GaP/polymer nanocomposites for advanced light emissive device structures

GaP nanoparticles have been prepared using white P and a mild aqueous synthesis at decreased temperature followed by ultrasonication and stored as the suspension in water–ethanol mixture. They were characterized by standard methods of X-ray diffraction, transmission electron microscopy, Raman light scattering, and photoluminescence. Properties of GaP nanoparticles were compared with industrial and specially grown perfect GaP single crystals. It was shown that the GaP nanoparticles in suspension are the most suitable for high quality GaP/polymers nanocomposites because only they are uniform with dimensions of about 10 nm which is optimal for appearance of the pronounced quantum confinement effect. Polyglycidyl methacrylate (PGMA), polyglycidyl methacrylate-co-polyoligoethyleneglycol methacrylate (PGMA-co-POEGMA), and biphenyl vinyl ether (BPVE) polymers were used to prepare GaP polymer nanocomposites. The thickness of the polymer nanocomposite film was about 250–300 nm defined from AFM scratch experiment. The resulting nanocomposites yielded a bright luminescence at room temperature in a broad band with the maximum ranging from 2.5 to 3.2 eV and showed pronounced quantum confinement effects and other interesting and important for application phenomena leading to dramatic 1 eV expansion of GaP luminescence to the UV spectral region.