Characterization of deep levels in semi-insulating gallium arsenide

Two traps with activation energies ofE _c – 0·47 eV andE _v + 0·79 eV have been detected in semi-insulating GaAs:Cr through optical transient current spectroscopy (otcs) in the temperature range 300–450 K. The latter trap gives rise to rising current transients which result in a negative peak in theotcs spectrum. The theoretical expressions for current transients have been derived.     

Subsurface burnout mechanisms in gallium arsenide (GAAS) electronic devices

This paper reviews the present knowledge on subsurface burnout mechanisms in Gallium Arsenide (GaAs) electronic devices. The results of the work should assist in the creation of more reliable devices with greater radiation hardness.     

Solid-state gallium NMR characterization of cubic gallium nitride prepared by the reaction of gallium arsenide with ammonia

The reaction of cubic gallium arsenide (GaAs) with ammonia yielded gallium nitride (GaN). Powder X-ray diffraction patterns of the GaN products showed that they are a mixture of c- and w-GaN, while their Ga MAS NMR spectra revealed that they have the other phase of GaN besides c- and w-GaN and the high reaction temperature (≥900 °C) induces nitrogen deficiency in GaN. The peaks at 353 and 347 ppm in the ⁷¹Ga MAS NMR spectra were tentatively assigned to c-GaN and an intermediate of w- and c-GaN in the stacking order, respectively. The observed ⁷¹Ga chemical shifts of GaN, GaP, GaAs and GaSb in cubic phase were well correlated with the reciprocal of their band gaps.     

Characterization of deep level defects in Si irradiated with MeV Ar+ ions using constant capacitance time analyzed transient spectroscopy

An isothermal spectroscopic technique called time analyzed transient spectroscopy (TATS) in the constant capacitance (CC) mode has been used to characterize electrically active defects in the MeV Ar⁺ implanted silicon. The problems associated with high defect density and the presence of damaged region in the as-implanted material are overcome by CC-TATS method. The CC-TATS spectra of the as-implanted sample shows two positive peaks and an attendant negative peak. Two distinct traps have also been identified using thermally stimulated capacitance method modified to operate in constant capacitance mode. Variable pulse width measurements using CC-TATS show exponential capture kinetics in contrast to extremely slow capture observed in conventional deep level transient spectroscopy (DLTS) experiment. The results indicate that trapping behaviour is due to point-like defects associated with extended defects such as dislocation and stacking fault.     

Point defects and diffusion mechanisms pertinent to the Ga sublattice of GaAs

For the Ga sublattice of GaAs, the recent understanding of the impurity and self-diffusion mechanisms and the nature of the point defects responsible are discussed. Analyses of doping enhanced AlAs/GaAs superlattice disordering data and impurity diffusion data have led to the conclusion that, under thermal equilibrium and intrinsic conditions, the triply-negatively-charged Ga vacancy ((V_Ga³⁻) governs Ga self-diffusion and Al---Ga interdiffusion in As-rich crystals, while the doubly-positively-charged Ga self-interstitial (I_Ga²⁺) dominates in Ga-rich crystals. When doped sufficiently, dominates in n-type crystals, while I_Ga²⁺ dominates in p-type crystals, irrespective of the crystal composition. The V_Ga³⁻ species also contributes to the diffusion of the main donor species Si, while I_Ga²⁺ also governs the diffusion of the main acceptor species Zn and Be via the kick-out mechanism. The thermal equilibrium concentration of V_Ga³⁻ (C_VGa³⁻) has been found to exhibit a temperature independence or even a small negative temperature dependence in that, when the temperature is lowered, C_VGa³⁻; is either unchanged or even slightly increases. This C_VGa³⁻ behavior is consistent with many outstanding experimental results.     

SI-GaAs晶片的PL mapping表征技术

研究了扫描光致发光光谱（ＰＬｍａｐｐｉｎｇ）在表征半绝缘砷化镓（ＳＩ－ＧａＡｓ）材料中的应用,实验结果表明ＳＩ－ＧａＡｓ晶片的强度及ｍａｐｐｉｎｇ均匀性对器件性能有着十分密切的关系,所以在为制备器件筛选优质的ＳＩ－ＧａＡｓ材料时,除了电阻率、迁移率、位错密度,碳含量,ＥＬ２浓度及其均匀性,晶片表面质量上,ＰＬｍａｐｐｉｎｇ也是表征材料质量的一个重要参数。     

Hydrogen effects on deep level defects in proton implanted Cu(In,Ga)Se2 based thin films

Hydrogen effects on deep level defects and a defect generation in proton implanted Cu(In,Ga)Se₂ (CIGS) based thin films for solar cell were investigated. CIGS films with a thickness of 3 μm were grown on a soda-lime glass substrate by a co-evaporation method, and then were implanted with protons. To study deep level defects in the proton implanted CIGS films, deep level transient spectroscopy measurements on the CIGS-based solar cells were carried out, these measurements found 6 traps (including 3 hole traps and 3 electron traps). In the proton implanted CIGS films, the deep level defects, which are attributed to the recombination centers of the CIGS solar cell, were significantly reduced in intensity, while a deep level defect was generated around 0.28 eV above the valence band maximum. Therefore, we suggest that most deep level defects in CIGS films can be controlled by hydrogen effects.     

Characterization of defects in hydrogenated amorphous silicon deposited on different substrates by capacitance techniques

Hydrogenated amorphous silicon (a-Si:H) thin films deposited on crystalline silicon and Corning glass substrate were analyzed using different capacitance techniques. The distribution of localized states and some electronic properties were studied using the temperature, frequency and bias dependence of the Schottky barrier capacitance and deep level transient spectroscopy. Our results show that the distribution of the gap states depends on the type of substrate. We have found that the films deposited on c-Si substrate represent only one positively charged or prerelaxed neutral deep state and one interface state, while the films deposited on glass substrate have one interface state and three types of deep defect states, positively or prerelaxed neutral, neutral and negatively charged.     

Hydrogen trapping by defects in semiconductors studied by anelastic spectroscopy

We review some results obtained by anelastic spectroscopy on H-related defects in III–V semiconductors. Anelastic measurements on InP lead to the formulation of a model explaining the conversion to the semi-insulating (SI) state. Moreover, in GaAs:Zn an extraordinarily fast relaxation rate has been measured and a possible explanation has been suggested. This results are reviewed and discussed in the light of new experiments on InP:Zn, whose spectrum shows a relaxation process similar to the one in GaAs:Zn.     

Growth and defects of GaAs and InGaAs films on porous GaAs substrates

We investigated the opportunities to increase the electric uniformity of GaAs and InGaAs films grown by molecular-beam epitaxy (MBE) technique on monocrystalline (single crystal) GaAs: both on porous and conventional so-called “monolithic” (without pores) GaAs (100) substrates. The basic attention was given to study the electrically active defects in films by using scanning electron microscope (SEM) with new technique which is called “Rau-detector” [E.I. Rau, A.N. Zhukov and E.B. Yakimov, Solid-State Phenomena, 1998, v. 53-54, 327.]. We compared the main properties of epitaxial GaAs and InGaAs films grown on above mentioned substrates. The films grown on porous substrates had higher structural perfection including the following advantages: (a) smoother surface due to lateral growth mechanism; (b) less density of structural defects (without dislocation walls), the density of pyramidal defects was ∼ 2 × 10⁵ cm^− 2 as compared with the density 2 × 10⁷ cm^− 2 in the films grown on monolithic substrates; (c) less electrical activity of various structural defects and increased electric uniformity of grown films. The electrical activity of defects in films grown on porous substrates was essentially lowered due to gettering properties of porous substrate.     

Observation and analysis of epitaxial growth with reflectance-difference spectroscopy

Reflectance-difference (RD) (-anisotropy) spectroscopy has developed into an established diagnostic tool for semiconductor epitaxy. Major advantages include the simplicity of the approach and the capability of performing measurements in real time during growth. Studies to date have emphasized understanding the origin of RD spectra, relating them to electronic and atomic structure of growth surfaces, and using them to obtain information about fundamental mechanisms of epitaxy. The observation of RD oscillations during organometallic chemical vapor deposition, oscillations that are analogous to those seen in reflection high energy electron diffraction intensities during molecular beam epitaxy, is providing new opportunities for growth control. Using (001) GaAs as an example, principles, representative results, and current critical issues are discussed.     

A photoluminescence study of defects in non-stoichiometric gallium arsenide using concurrent electrical and structural characterization

Photoluminescence has been used to identify centres associated with point defects and impurities in single crystal gallium arsenide, and this has been correlated with electrical and structural characterization of the same samples. Five different types of defect centre have been identified by this technique in material grown under different conditions of stoichiometry. These studies show systematic differences between the photoluminescence data obtained from stoichiometric and non-stoichiometric gallium arsenide. Precision lattice parameter and density measurements on the same gallium arsenide specimens indicate a deviation from stoichiometry on the arsenic-rich side of the gallium arsenide phase and it is suggested that defects primarily responsible for this stoichiometric deviation are arsenic interstitials in concentrations up to 3×10¹⁸ cm^?3. Photoluminescence measurements associate these defects in arsenic-rich gallium arsenide with an energy level of 0.036 eV.     

高阻In掺杂CdZnTe晶体缺陷能级的研究

利用低压垂直布里奇曼法制备了不同In掺杂量的CdZnTe晶体样品, 采用低温光致发光谱(PL)、深能级瞬态谱(DLTS)以及霍尔测试等手段研究了In掺杂CdZnTe晶体中的主要缺陷能级及其可能存在的补偿机制. PL测试结果表明, 在In掺杂样品中, In原子占据了晶体中原有的Cd空位, 形成了能级位于E_c-18meV的替代浅施主缺陷[In_Cd^+], 同时 [In_Cd⁺]还与[V_Cd^2-]形成了能级位于E_v+163meV的复合缺陷[(In_Cd⁺-V_Cd^2-)^-]. DLTS分析表明, 掺In样品中存在导带以下约0.74eV的深能级电子陷阱能级, 这个能级很可能是Te反位[Te_Cd]施主缺陷造成的. 由此, In掺杂CdZnTe晶体的电学性质是In掺杂施主缺陷、Te反位深能级施主缺陷与本征受主缺陷Cd空位和残余受主杂质缺陷补偿的综合结果.     

Characterization of oxidized gallium droplets on silicon surface: An ellipsoidal droplet shape model for angle resolved X-ray photoelectron spectroscopy analysis

Deposition and oxidation of metallic gallium droplets on Si(111) were studied by angle resolved X-ray photoelectron spectroscopy. Two gallium peaks - Ga 3d and Ga 2p - were simultaneously measured in order to get an advantage of different inelastic mean free paths of photoelectrons from these two energy levels differing in binding energy by 1100 eV. Together with the angular dependent data it enhances the precision of the size characterization of Ga droplets and oxide thickness determination. A model for the calculation of theoretical intensities based on an ellipsoidal shape of droplets is presented and a simple procedure for estimation of droplet height and actual surface coverage based on measurement on a single emission angle is suggested.     

Extended deep level defects in Ge-condensed SiGe-on-Insulator structures fabricated using proton and helium implantations

SiGe-on-Insulator (SGOI) structures were created using the Ge condensation method, where an oxidation process is performed on the SiGe/Si structure. This method involves rapid thermal chemical vapor deposition and H⁺/He⁺ ion-implantations. Deep level defects in these structures were investigated using deep level transient spectroscopy (DLTS) by varying the pulse injection time. According to the DLTS measurements, a deep level defect induced during the Ge condensation process was found at 0.28 eV above the valence band with a capture cross section of 2.67 × 10^− 17 cm², two extended deep levels were also found at 0.54 eV and 0.42 eV above the valence band with capture cross sections of 3.17 × 10^− 14 cm² and 0.96 × 10^− 15 cm², respectively. In the SGOI samples with ion-implantation, the densities of the newly generated defects as well as the existing defects were decreased effectively. Furthermore, the Coulomb barrier heights of the extended deep level defects were drastically reduced. Thus, we suggest that the Ge condensation method with H⁺ ion implantation could reduce deep level defects generated from the condensation and control the electrical properties of the condensed SiGe layers.     

Influence of deposition parameters on hole mobility in polymorphous silicon

Time-of-flight transient photoconductivity measurements reveal a monotonic increase with the deposition pressure in the hole mobility in polymorphous silicon for samples deposited under hydrogen dilution. With helium dilution, a maximum mobility that matches the highest value from H-dilution samples is measured at the intermediate pressure of 1.4 Torr. The deposition rate of those samples is twice the rate for the H-dilution ones. For the samples with the best hole mobilities, the valence-band tail is comparable to the one of standard hydrogenated amorphous silicon.     

Investigation on the role of indium in the removal of metallic gallium from soft and hard sputtered GaN (0001) surfaces

Cleaning of GaN by argon sputtering and subsequent annealing introduces metallic gallium on the GaN surface. Once formed, this metallic gallium can be difficult to remove. It has a strong influence on the Fermi level position in the band gap and poses a problem for subsequent epitaxial growth on the surface. We present a method of removing metallic gallium from moderately damaged GaN surfaces by deposition of indium and formation of an In-Ga alloy that can be desorbed by annealing at ~ 550 °C. After the In-Ga alloy has desorbed, photoemission spectra show that the Ga3d bulk component becomes narrower indicating a smoother and more homogeneous surface. This is also reflected in a sharper low energy electron diffraction pattern. On heavily damaged GaN surfaces, caused by hard sputtering, larger amount of metallic gallium forms after annealing at 600 °C. This gallium readily alloys with deposited indium, but the alloy does not desorb until a temperature of 840 °C is reached and even then, traces of both indium and metallic gallium could be found on the surface.     

RBS-C and ellipsometric investigations of radiation damage in hot-implanted GaAs layers

Semi-insulating (1 0 0) GaAs single crystalline substrates have been doubly Al⁺-implanted using ion beams of the 250 keV energy and the fluence F = 3.5 × 10¹⁶ cm⁻², and 100 keV with F = 9.6 × 10¹⁵ cm⁻² at six target temperatures ranging from 250 to 500 °C. The radiation damage introduced by such “hot implantation” was subsequently investigated by Rutherford Backscattering Spectrometry with Channeling (RBS-C) and Variable Angle Spectroscopic Ellipsometry (VASE) techniques. Using these experimental methods we determined a degree of lattice disorder. With the increasing implantation temperature the degree of disorder substantially decreases. No evidence of full amorphization of the implanted GaAs layers has been found in the present studies. The results of non-destructive ellipsometric characterization are in good agreement with the RBS-C investigations.     

空间微重力条件下生长LiIO3、GaAs晶体的研究进展

综述了空间微重力环境下生长GaAs、α-LiIO3晶体的研究进展,展望了其应用前景.     

Influence of the As/Ga flux ratio on diffusion of Be in MBE GaAs layers

Beryllium (Be) diffusion after rapid thermal annealing experiments is studied in heavily doped GaAs structures grown by MBE. SIMS measurements show that in p/p⁺ structures, Be diffusion is reduced by increasing the As₄/Ga flux ratios. In contrast, no effect is observed in p/p⁺/p structures. Furthermore, Be concentration profiles measured after annealing experiments performed at 770 and 850°C for 30 s indicate that Be redistribution is almost independent of the annealing temperature. These results are discussed in terms of a substitutional interstitial diffusion mechanism.