Comparison of vacancy and antisite defects in GaAs and InGaAs through hybrid functionals

The formation energies and charge transition levels of vacancy and antisite defects in GaAs and In(0.5)Ga(0.5)As are calculated through hybrid density functionals. In As-rich conditions, the As antisite is the most stable defect in both GaAs and InGaAs, except for n-type GaAs for which the Ga vacancy is favored. The Ga antisite shows the lowest formation energy in Ga-rich conditions. The As antisite provides a consistent interpretation of the defect densities measured at mid-gap for both GaAs/oxide and InGaAs/oxide interfaces.     

表面悬挂键对GaAs纳米线掺杂的影响及其钝化

利用第一性原理计算方法研究了表面悬挂键对GaAs纳米线掺杂的影响及其钝化．计算结果显示,不论是闪锌矿结构还是纤锌矿结构,GaAs纳米线表面Ga原子上带正电荷的表面悬挂键都是一类稳定的缺陷,并且这种稳定性不会随着纳米线直径的变化而变化．这种表面悬挂键会形成载流子陷阱中心从而从p型掺杂的GaAs纳米线俘获空穴,使得纳米线的掺杂效率下降．和NH₃相比,NO₂ 具有足够的电负性来俘获GaAs纳米线表面悬挂键上的未配对电子,从而有效地钝化GaAs纳米线的表面悬挂键,提高纳米线的p型掺杂效率,并且这种钝化特性不会随着纳米线直径的变化而改变．     

Effects of strain and local charge on the formation of deep defects in III-V ternary alloys

The effects of external and internal strains and of defect charges on the formation of gallium vacancies and arsenic antisites in GaAs and In0.5Ga0.5As have been investigated by ab initio density functional methods. Present results show that a proper understanding of strain and defect charge permits the development of a defect engineering of semiconductors. Specifically, they predict that arsenic antisites in InGaAs ternary alloys can form, upon p-type doping in the presence of an arsenic overpressure, even in the case of high-temperature epitaxial growths.     

Spatial correlations in GaInAsN alloys and their effects on band-gap enhancement and electron localization

In contrast to pseudobinary alloys, the relative number of bonds in quaternary alloys cannot be determined uniquely from the composition. Indeed, we do not know if the Ga0.5In0.5As0.5N0.5 alloy should be thought of as InAs+GaN or as InN+GaAs. We study the distribution of bonds using Monte Carlo simulation and find that the number of In-N and Ga-As bonds increases relative to random alloys. This quaternary-unique short range order affects the band structure: we calculate a blueshift of the band gap and predict the emergence of a broadband tail of localized states around the conduction band minimum.     

GaAs表面硫化学钝化,CH3CSNH2处理新探

应用同步辐射光电子谱（SRPES）和光致荧光（PL）方法探讨不同钝化条件对GaAs表面键合状态和电子态的影响．发现无论在酸性溶液或碱性溶液条件下，经过CH₃CSNH₂处理的GaAs表面S都与Ga和As成键，形成硫化物钝化层；钝化层形成后，PL谱的强度明显增强，表明GaAs表面复合中心的减少和缺陷态密度的降低 关键词：     

Photon stimulated ion desorption of H+ ions from GaAs (110)/H2O

The photon stimulated ion desorption yield of H⁺ ions from a H₂O dosed GaAs (110) surface has been measured in the range 18eV ? hυ ? 30eV. There is a direct correspondence between the PSID H⁺ yield, reflectance, and the secondary electron yield spectrum of GaAs (110). The data provides evidence that the initial stages of PSID involve core level (Ga(3d), O(2s)) → conduction band excitation followed by Auger decay.     

Influence of Ga(Al)As substrates on surface morphology and critical thickness of InGaAs quantum dots

Influence of Ga(Al)As substrates on surface morphology of InGaAs quantum dots and critical thickness of In_0.5Ga_0.5As film grown by molecular beam epitaxy is investigated. The In_0.5Ga_0.5As quantum dots are grown on (001) surfaces of GaAs and Al_0.25Ga_0.75 A at 450 °C, scanning tunneling microscope images show that the size of quantum dots varied slightly for 10 ML of In_0.5Ga_0.5As grown on GaAs and Al_0.25Ga_0.75As surfaces. Reflection high energy electron diffraction (RHEED) is used to monitor the growth of 4 monolayers (ML) In_0.5Ga_0.5As on Al_0.25Ga_0.75As and GaAs surfaces during deposition. The critical thickness is theoretically calculated by adding energy caused by surface roughness and heat from substrate. The calculations show that the critical thickness of In_0.5Ga_0.5As grown on GaAs and Al_0.25Ga_0.75As are 3.2 ML and 3.8 ML, respectively. The theoretical calculation agrees with the experimental results.     

Study of n type porous GaAs by photoluminescence spectroscopy: Effect of the etching time on the deep levels

Photoluminescence (PL) analysis is used to study porous layers elaborated by electrochemical etching of n⁺ Si-doped GaAs substrate with different etching times. Temperature and power dependence photoluminescence (PL) studies were achieved to characterize the effect of the etching time on the deep levels of the n⁺ Si-doped GaAs. The energy emission at about 1.46 eV is attributed to the band-to-band (B-B) (e-h) recombination of a hole gas with electrons in the conduction band. The emission band is composed of four deep levels due to the complex of (V_AsSi_GaV_Ga), a complex of a (Ga vacancy - donor - As vacancy), a (Si_Ga-V_Ga³⁻) defect or Si clustering, and a (gallium antisite double acceptor-effective mass donor pair complex) and which peaked, respectively, at about (0.94, 1, 1.14, and 1.32 eV). The PL intensity behavior as function of the temperature is investigated, and the experimental results are fitted with a rate equation model with double thermal activation energies.     

The study of the optical properties of the GaAs with point defects

GaAs is a common material for negative electron affinity photoelectric cathodes. It has a widely application in night vision. It is unavoidable to produce point defects in the process of the GaAs growth. In this article, the first principle method is used to calculate the formation energy and the optical properties of six types familiar point defects in GaAs. Three types of point defects (Ga vacancy defect, As antisite defect and As interstitial defect) are easier to be formed in these six types according to the formation energy calculation. In fact, crystal GaAs is grown in an As-rich environment. The Ga vacancy, As antisite and As interstitial defects are easier to be formed in reality. Hence the theoretical calculation results are in keeping with the experiments. In this article, the optical properties of these three types are compared with that of perfect GaAs. The electron structures are changed as a result of the point defects. Some of the defect levels enter into the band gap and the electron transitions become easier. It makes the optical spectra move to the low-energy region. Additionally, GaAs with Ga vacancy defect and that with As interstitial defect shows similar optical properties. Therefore both of the two types of defects can be considered as the same in the later experiments. The theoretical results in this article provide the basis for experimental study for photoelectric emission of the real GaAs material related to the optical properties and electronic structures.     

Photoemission from α and β phases of the GaAs(0 0 1)-c(4 × 4) surface

We prepared α- and β surface phases of GaAs(0 0 1)-c(4 × 4) reconstruction by molecular beam epitaxy (MBE) using As₄ and As₂ molecular beams, respectively, and examined them by angle-resolved ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation as an excitation source. The UPS valence band spectra and the XPS 3d core level data show pronounced differences corresponding to the surface composition and the atomic structure of the two phases, as proposed in the literature. In UPS, the β phase is characterized by an intensive surface state 0.5 eV below the top of the valence band at low photon energy, while an analogous peak in the α phase spectra is missing. The surface state is interpreted in terms of dangling bonds on As dimers. The As3d and Ga3d core level photoelectron lines exhibit phase-specific shapes as well as differences in the number, position and intensity of their deconvoluted components. The location of various atoms in the surface and subsurface layers is discussed; our photoemission results support models of the β phase and the α phase with As-As dimers and Ga-As heterodimers, respectively.     

High-k Al2O3 MOS structures with Si interface control layer formed on air-exposed GaAs and InGaAs wafers

This paper attempts to realize unpinned high-k insulator-semiconductor interfaces on air-exposed GaAs and In_0.53Ga_0.47As by using the Si interface control layer (Si ICL). Al₂O₃ was deposited by ex situ atomic layer deposition (ALD) as the high-k insulator. By applying an optimal chemical treatment using HF acid combined with subsequent thermal cleaning below 500 °C in UHV, interface bonding configurations similar to those by in situ UHV process were achieved both for GaAs and InGaAs after MBE growth of the Si ICL with no trace of residual native oxide components. As compared with the MIS structures without Si ICL, insertion of Si ICL improved the electrical interface quality, a great deal both for GaAs and InGaAs, reducing frequency dispersion of capacitance, hysteresis effects and interface state density (D_it). A minimum value of D_it of 2 × 10¹¹ eV⁻¹ cm⁻² was achieved both for GaAs and InGaAs. However, the range of bias-induced surface potential excursion within the band gap was different, making formation of electron layer by surface inversion possible in InGaAs, but not possible in GaAs. The difference was explained by the disorder induced gap state (DIGS) model.     

Competition in the carrier capture between InGaAs/AlGaAs quantum dots and deep point defects

The presence of an extrinsic photoluminescence (PL) band peaked at 1.356 eV at low temperature is observed, on a large number of self-assembled InAs and In_0.5Ga_0.5As quantum dot (QD) structures, when exciting just below the GaAs absorption edge. A detailed optical characterization allows us to attribute the 1.356 eV PL band to the radiative transition between the conduction band and the doubly ionized Cu _Ga acceptor in GaAs. A striking common feature is observed in all investigated samples, namely a resonant quenching of the QD-PL when exciting on the excited level of this deep defect. Moreover, the photoluminescence excitation (PLE) spectrum of the 1.356 eV emission turns out to be almost specular to the QD PLE. This correlation between the PL efficiency of the QDs and the Cu centers evidences a competition in the carrier capture arising from a resonant coupling between the excited level of the defect and the electronic states of the wetting layer on which the QDs nucleate. The estimated Cu concentration is compatible with a contamination during the epitaxial growth. Received 13 November 2001 / Received in final form 28 May 2002 Published online 19 July 2002     

Charge transport diagnosis by: I-V (resistivity), screening and Debye length, mean free path, Mott effect and Bohr radius in InAs, In0.53Ga0.47As and GaAs MBE epitaxial layers

We propose using collected galvano-magnetic data on MBE samples of n-type undoped epi-layers of InAs, In_0.57Ga_0.47As and GaAs on InP semi-insulating and GaAs semi-insulating substrates to characterize their charge transport properties. Hall concentration and resistance measurements vs. temperature were carried out, and these results allowed us to calculate the mean free path and magnetic length. However, they are mono-crystalline, they present multi-component charge transport structures. The characterization of these layers by means of a combined analysis of galvano-magnetic properties, I-V (resistivity), screening and Debye length, mean free path, Mott effect and Bohr radius characteristics gave new and very interesting results.The application of a previously described method of analysis also allows for the presence of a Mott transition to be determined. The presence of a Mott transition leads to the hypothesis that a part of conductance in such layers, especially at low temperatures may be due to an impurity band.We suppose either that during their epitaxial growth all of the investigated layers were unintentionally doped with excess atoms of one component, vacancies of other or that dangling bonds are present. Therefore, in the range of low temperatures, the possible and dominant conduction mechanism is conduction via such defects, with electrons moving by thermally activated hopping.     

XPS analysis of surface chemistry of near surface region of epiready GaAs(1 0 0) surface treated with (NH4)2Sx solution

In this work we analyze the effect of (NH)₂S_x wet treatment on the GaAs(1 0 0) covered with “epiready” oxide layer without any pretreatment in order to check the removal of oxides and carbon-related contamination, and the formation of sulfur species. The sulfidation procedure consisted of epiready sample dipping (at room and 40 °C temperatures) in an ammonium polysulfide solution combined with a UHV flash annealing up to 500 °C.The inspection of the XPS As 2p_3/2 and Ga 2p_3/2 spectra taken at surface sensitive mode revealed: (i) the temperature-dependent reduction of the amount of GaAs oxides and carbon contamination after sulfidation, and almost their complete removal after subsequent annealing, (ii) the creation of sulfur bonds with both Ga and As, with more thermally stable Ga-S bonds, and (iii) the slight reduction in elemental arsenic amount.     

Structural and optical properties of In0.5Ga0.5As/GaAs quantum dots in an In0.1Ga0.9As well using repeated depositions of InAs/GaAs short-period superlattices for the application of optical communication

We report structural and optical properties of In_0.5Ga_0.5As/GaAs quantum dots (QDs) in a 100 Å-thick In_0.1Ga_0.9As well grown by repeated depositions of InAs/GaAs short-period superlattices with atomic force microscope, transmission electron microscope (TEM) and photoluminescence (PL) measurement. The QDs in an InGaAs well grown at 510 °C were studied as a function of n repeated deposition of 1 monolayer thick InAs and 1 monolayer thick GaAs for n=5–10. The heights, widths and densities of dots are in the range of 6–22.0 nm, 40–85 nm, and 1.6–1.1×10¹⁰/cm², respectively, as n changes from 5 to 10 with strong alignment along [1 −1 0] direction. Flat and pan-cake-like shape of the QDs in a well is found in TEM images. The bottoms of the QDs are located lower than the center of the InGaAs well. This reveals that there was intermixing—interdiffusion—of group III materials between the InGaAs QD and the InGaAs well during growth. All reported dots show strong 300 K-PL spectrum, and 1.276 μm (FWHM: 32.3 meV) of 300 K-PL peak was obtained in case of 7 periods of the QDs in a well, which is useful for the application to optical communications.     

Optical characteristics of highly ordered gallium oxide nano-islands on GaAs

A periodic array of Ga oxide islands was obtained by annealing the highly ordered Ga nano-droplets on GaAs surface at 400°C under an oxygen atmosphere for 7 hours. These Ga oxides are a mixture of α-Ga₂O₃ and β-Ga₂O₃ confirmed by Raman spectroscopy study. Enhanced optical transmission of GaAs with such ordered Ga oxide nano-islands was obtained. Both dielectric and dimensional confinement effects were considered in analysis of the electromagnetic characteristics of the nanostructured materials. Finite-difference time-domain method was used to numerically study the light transmission through the patterned Ga oxide on GaAs surface. Based on the calculated results, the light transmission enhancement is attributed to the formation of the ordered nano Ga oxides.     

Molecular dynamics simulation comparison of atomic scale intermixing at the amorphous Al2O3/semiconductor interface for a-Al2O3/Ge, a-Al2O3/InGaAs, and a-Al2O3/InAlAs/InGaAs

The structural properties of a-Al₂O₃/Ge, a-Al₂O₃/In_0.5Ga_0.5As and a-Al₂O₃/In_0.5Al_0.5As/InGaAs interfaces were investigated by density-functional theory (DFT) molecular dynamics (MD) simulations. Realistic a-Al₂O₃ samples were generated using a hybrid classical-DFT MD “melt and quench” approach. The interfaces were formed by annealing at 700 K/800 K and 1100 K with subsequent cooling and relaxation. The a-Al₂O₃/Ge interface demonstrates pronounced interface intermixing and interface bonding exclusively through Al–O–Ge bonds generating high interface polarity. In contrast, the a-Al₂O₃/InGaAs interface has no intermixing, Al–As and O–In/Ga bonding, low interface polarity due to nearly compensating interface dipoles, and low substrate deformation. The a-Al₂O₃/InAlAs interface demonstrated mild intermixing with some substrate Al atoms being adsorbed into the oxide, mixed Al–As/O and O–Al/In bonding, medium interface polarity, and medium substrate deformation. The simulated results demonstrate strong correlation to experimental measurements and illustrate the role of weak bonding in generating an unpinned interface for metal oxide/semiconductor interfaces.     

Si中深能级T2对称波函数理论

木文在文献[5,6]所发展的在位缺陷势格林函数方法基础上,进一步讨论Si中短程缺陷势引入的T₂对称深能级波函数性质。第一次给出了Si禁带中部很宽能量范围之内T_2对称波函数的完整数据。波函数在缺陷最近邻四个格点的占据几率P₁有一高达50％以上峰值。该部分相当于四个最近邻格点指向缺陷的杂化轨道准悬键的T₂组合。第0,1,2三个格点壳层波函数占据几率之和约为70％。波函数其余部分较平缓地分布在一相当大空间。波函数的以上特征与禁带中部能量位置关系不灵敏。但在靠近导带E_c和满带E_v的浅能量区,以上P₁峰趋于消失,整个波函数在空间的分布趋于平坦。Si空位在禁带引入一个T₂对称深能级,位于E_v以上0.51eV处。 关键词：     

Theoretical study of the optical absorption and refraction index change in a cylindrical quantum dot

Analytical expressions of the optical absorption coefficient and the change in refractive index associated with intraband relaxation in a cylindrical quantum dot are obtained by using the density matrix formalism. Energy levels in conduction band were calculated with finite confining potential in the framework of the effective-mass envelope-function theory. Numerical calculations on a typical GaAs/AlβGa1−βAs QD are performed. It is found that the absorption and refraction index change sensitively depend not only on the incident optical wave but also on the dot size and the Al mole fraction β in the AlβGa1−βAs material.     

Photoemission studies of the electronic structure of III–V semiconductor surfaces

The photoemission technique using synchroton radiation in the photon energy range 5–450 eV has been applied to the study of the electronic structure of some III–V semiconductor surfaces, prepared by cleavage in situ under ultrahigh vacuum conditions, ? 10^?11 Torr. For p-type GaAs(110), the Fermi level is pinned at the top of the valence band and thus no filled surface states extend into the band-gap. The situation is more complicated for n-type GaAs(110), where band bending easily can be introduced by extrinsic effects (impurities, cleavage quality, etc.) and push the Fermi level down to about midgap. Chemical shifts of inner core levels (3d for Ga and As) are used to obtain information on the bonding site of oxygen on the (110) surface. GaAs(110) can be exposed to atmospheric pressure of molecular oxygen without breaking the bonds between the surface atoms and the bulk. Oxygen is predominantly bonded to the As atoms on the surface. The oxidation behavior is strikingly different for GaSb(110) with formation of gallium and antimony oxides on the surface directly upon oxygen exposure. Heavier oxidation of GaAs(110) and breaking of the surface bonds will also be reported.