超晶格GaAs/(GaAl)As(100)和GaAs/Ge(100)的电子结构

本文采用经验紧束缚方法,计算了第一类半导体超晶格(GaAs)_(nl)/(Ga_xAl_(1-x)As)_(n2)(100)和(GaAs_n/(Ge)_n(100)的电子结构。对于GaAs/(GaAl)As,得到了能带边随层数(n_1,n_2)变化的关系及带边电子态的空间分布,并得出能隙随n和组分x的变化(n_1=n_2=n≤10),结果与现有实验值和其它理论计算基本相符;对于GaAs/Ge,计算了GaAs和Ge等厚时,间接能隙随层数的变化,考察了(GaAs)_5/(Ge)_5(100)的能带结构。在两种超晶格中,本文都报道了界面态的存在,讨论了超晶格的准二维性质。     

超晶格(Al_xGa_(1-x)As)_m/(GaAs)_m中ГX_z态的混和

首先对(001)及(110)超晶格(Al_xGa_(1-x)As)_m/(GaAs)_m的布里渊区折叠进行了仔细的分析。然后采用紧束缚方法计算了单层超晶格的导带沿晶体生长方向的色散关系,并讨论了FXz态的混和效应。同时也计算了(001)及(110)超晶格(AlAs)_m/(GaAs)_m的直接带隙(或赝直接带隙)随层厚m的变化情况。最后,计算了各超晶格导带底能态的静压力系数,由此确定它们是类г态还是类x态,以及它们的гXz态混和情况。     

超薄层超晶格GaAs/AlAs(001)的电子结构

本文讨论了SU(N.M)的空间对称性和布里渊区经折叠后的特殊性质。使用分区变分法计算了超薄层超晶格(GaAs)_n/(AlAs)_n(n=1,2,3)的能带,运用四个势场调整参数所算出的能带和实验结果基本相符。结果表明,(GaAs)_1—(AlAs)_1为间接能隙半导体,禁带宽度为1.87eV,导带底位于Z_x点(1,0,0)(2π/a)。而(GaAs)_n—(AlAs)(n≥2)则为直接能隙半导体,且禁带宽度E_g随着n的增大而减小。并将计算结果和别的理论结果、实验数据作了比较和分析。     

Znse/GaAs超晶格的电子态和芯态激子

本文用半经验紧束缚法计算了ZnSe/GaAs(001)超晶格的能带结构,研究了其能隙与有效质量随层厚的变化.计算了(ZnSe)_5/(GaAs)_5超晶格中与杂质有关的芯态激子,其结果能说明相应异质结中束缚在Ga上的激子峰.本文还提出了该材料中导带底存在界面态.     

MBE[(AI_xGa_(1-x)As)_l(GaAs)_m]_n/GaAs(001)超晶格结构参数的X射线双晶衍射测量研究

本文根据超晶格结构的台阶模型,利用X射线衍射的运动学模型,导出了超晶格的X射线衍射峰的相对光强比.利用X射线双晶衍射方法测定了MBE[(Al_xGa_(1-x)As)_1(GaAs)_m]./GaAs(001)一维超晶格的衍射迴摆曲线,除超晶格的主衍射峰外,还观察到一级和二级卫星峰.由这些衍射峰之间的角距离和相对光强比,计算出了超晶格的结构参数,其中包括周期D、垒宽L_B、量子阱宽度L_Z和Al含量x值.     

可调能隙的光电器件结构——(AlAs)_ (n_l)/(GaAs)_(m_l)渐变周期超晶格

本文提出了一种具有渐变周期的(AlAs)_(nl)/(GaAs)_(ml)(1=1,2,…)超晶格,并采用递归方法计算了这种渐变周期超晶格的电子结构.其特点是带隙E_g在空间随(n_(?),m_(?))渐变.例如,对(AlAs)_4/(GaAs)_4(AlAs)_4、/(GaAs)_5/(AlAs)_4/(GaAs)_6/(AlAs)_4/(GaAs)_7结构,带隙由短周期一端的1.93eV变到长周期一端的1.78eV.同时导、价带边得到不同的调制,因而提高了电子与空穴电离率比值,有可能应用到作光电探测材料.     

氢在GaAs(110)表面吸附的研究

采用EHMO方法计算了氢在GaAs(110)表面的吸附,确定了氢原子在表面的吸附位置.计算结果表明,Ga与As都能吸附氢原子,最稳定的吸附位置在As的悬键位,其次为Ga的悬键位;氢与表面原子形成共价键,键长均约为1.32A|°.当氢原子吸附于As的悬键位时,禁带中出现由As原子及Ga原子引入的表面态.同时计算表明GaAs(110)表面不能吸附分子态的氢,与已知的实验结果相符.     

应变层超晶格(ZnSe)_(2n)/(ZnS_xSe_(1-x))_(2n)的电子结构

本文用LCAO-Recursion方法研究了应变层超晶格(ZnSe)_(2n)/(ZnS_xSe_(1-x))_(2n)(n=1)的电子结构。计算了两种应变组态(赝晶生长,Free-Standing生长)下超晶格总的态密度,各原子的局域和分波态密度。我们发现:带隙E_g、费米能级E_f和原子价随应变的变化而变化;(ZnSe)_(2n)/(ZnS_xSe_(1-x))_(2n)超晶格中离子键和共价键共存;电子在界面附近发生了转移。     

(Al_xGa_(1-x)As)_m/(GaAs)_m(001)超晶格的能带结构与合金组分x间的关系

采用紧束缚的重整化方法研究了(Al_xGa_(1-x)As)_m/(GaAs)_m(001)超晶格的电子能带结构与合金组分x及层厚间的变化关系。给出了临界组分x_o与层厚m间的变化关系图。并以二次函数形式给出了直接能隙和间接能隙与合金组分x间的变化关系。最后,也用Kronig—Penney模型对超晶格的电子能带结构进行了计算,并与紧束缚的计算结果进行了比较。     

超晶格结构的X射线衍射拟合计算

运用X射线衍射运动学理论研究了[(Ga_(1-x)Al_xAs)_m(GaAs)_n ]_N/GaAs(001)-维超晶格的结构,通过模拟计算,精确确定了超晶格的结构参数.本方法可用于各种超晶格结构,具有普遍意义.另外,还对超晶格卫星峰强度的非称性和超晶格中叠层界面处存在过渡层的影响进行了讨论.     

Far infrared measurements of bulk and surface phonons in GaAs/AlAs superlattices

We have used far-infrared oblique-incidence reflection spectroscopy to study bulk phonon polaritons, and attenuated total reflection (ATR) spectroscopy to study surface phonon polaritons, in long-period GaAs/Al_xGa_1?xAs and short-period GaAs/AlAs superlattices. Results on the former are in good agreement with an effective-medium bulk-slab model of the dielectric tensor of the superlattice; results on the latter are analysed in terms of a model that contains dielectric-tensor contributions from the confined optic phonons.     

Structure of heterointerfaces and photoluminescence properties of GaAs/AlAs superlattices grown on (311)A and (311)B surfaces: Comparative analysis

The photoluminescence properties of type II GaAs/AlAs superlattices grown on the (311) surface are determined by their polarity. Previous HRTEM investigations demonstrated a corrugation (with height of 1 nm and period of 3.2 nm) of both GaAs/AlAs and AlAs/GaAs interfaces in samples grown on the (311)A surface. In the present study, a lateral periodicity of 3.2 nm is also revealed in HRTEM images of a superlattice grown on the (311)B surface and in their Fourier transforms. However, this periodicity is poorly pronounced, which is due to fuzzy corrugation and the presence of a long-wavelength (>10 nm) disorder. Photoluminescence spectra of the GaAs/AlAs superlattice on the (311)A surface are strongly polarized relative to the direction of interface corrugation, in contrast to the (311)B superlattice, in which the corrugation is weakly pronounced. It was found that the strong mixing between the Θ and X minima of the conduction band, occurring only in sublattices with strongly corrugated interfaces, allows generation of bright red luminescence at 650 nm up to room temperature. The distinctions revealed between the superlattices grown on the (311)A and (311)B surfaces confirm that it is precisely the interface corrugation, and not crystallographic orientation, that governs the optical properties of (311) superlattices.     

用静压光致发光研究GaAs/AlAs短周期超晶格的Ⅰ一Ⅱ类超晶格转变点

<正> 近年来,GaAs/AlAs短周期超晶格的研究受到越来越多的重视。在GaAs/AlAs超晶     

Raman study of GaAs quantum wires grown with partial filling of corrugated (311)A AlAs surfaces

Raman spectroscopy powered by theoretical modeling of vibrational modes was shown to be an effective tool to examine interface structure of superlattices (SLs). In this work we studied GaAs_n/AlAs_m (n=1–10 monolayers) corrugated superlattices (CSLs) grown on (311)A GaAs substrates using Raman spectroscopy and high-resolution transmission electron microscopy. The strongest modification of the calculated Raman spectra is found for the finite length of the GaAs-domain in the CSL in the case of partial (<1 nm) GaAs filling of the AlAs surface. This theoretical result is in a very good agreement with the sharp transformation of the experimental Raman spectra observed for this thickness range. Thus, calculated and experimental Raman spectra demonstrated a good agreement for both complete (≥1 nm) and partial (<1 nm) GaAs filling of the AlAs surface.     

杂质和空位对AlAs/GaAs超晶格电学性质的影响

在紧束缚近似基础上,本文采用Recursion方法首次计算了含有杂质和空位的短周期AlAs/GaAs超晶格电子结构。局域态密度和分波态密度的计算结果清楚地反映了少量无序杂质和空位在AlAs/GsAs中的局部细节以及对材料本身电学性质的影响。在具有点缺陷(杂质或空位)的AlAs/GaAs材料能隙中将出现新能级,本文计算了它们的位置。同时利用对原子价的讨论发现体内点缺陷周围存在一个电中心,而界面点缺陷产生一个局域电场,它将导致电荷分布的转移。比较了杂质和空位的影响,并进一步证明在所有情况下它们的作用是高度局域的。     

The form of the profile of heterointerfaces in (311)Ga GaAs/AlAs structures

The steady-state photoluminescence and kinetics of photoluminescence of the (100)-oriented and (311)Ga-oriented type II GaAs/AlAs superlattices are studied under the effect of the electric field of the surface acoustic wave. It is found that, in the (100)-oriented structures, the drop of intensity of steady-state photoluminescence and acceleration of photoluminescence kinetics are independent of the direction of the electric field of the surface acoustic wave with respect to crystallographic directions, while in the (311)Ga-oriented structures these effects are anisotropic. It is shown that all variations in the steady-state photoluminescence and in kinetics of photoluminescence of (100)-oriented and (311)Ga-oriented structures under the effect of the electric field of the acoustic wave are associated with transfer and capture by the nonradiative recombination centers of nonequilibrium charge carriers, which are initially localized in wide quantum wells formed by fluctuations of the thickness of the layers of the structures. From the obtained experimental data, the parameters of the profile of heterointerfaces of the (311)Ga GaAs/AlAs superlattices are determined. It is established that the lateral sizes of microgrooves in the [011] direction on the direct and inverse heterointerfaces of the (311)Ga superlattices exceed 3.2 nm, while the modulation of the thickness of the AlAs layers is from 0.8 to 1.2 nm.     

GaAs/AlAs超晶格中的TO声子限制模

本文报道在室温和非共振散射条件下,GaAs/AlAs 超晶格结构中TO声子限制模的拉曼散射测量结果.超晶格样品用MBE方法生长在<001>晶向的GaAs衬底上.在背散射条件下,具有E对称性的TO 声子是拉曼禁戒的.但是利用近布儒斯特角入射和大孔径的散射光收集透镜,我们观测到分别限制在GaAs和AlAs层中的TO声子模.其中,限制在AlAs层中的TO模是首次报道.从测量的TO声子限制模频率得到的声子色散曲线与GaAs和AlAs体材料的TO声子色散曲线进行比较,二者符合良好.进一步证明,超晶格结构的拉曼散射测量是测定晶体声子色散曲线的有效的实验方法.     

Photoluminescence study of type-II GaAs quantum well wires grown on nano-faced (3 1 1)A surface: Quasi-1D exciton observation?

GaAs/AlAs corrugated superlattices (CSLs) grown on nano-faceted (3 1 1)A GaAs surface were studied using Raman spectroscopy and photoluminescence (PL) techniques. Raman data (splitting of localized transversal optical phonons) have proved structural anisotropy of the CSLs. The structural anisotropy leads to optical anisotropy appeared in strong polarization dependence of PL. Temperature dependence of PL has shown that the CSLs are type-II superlattices. Additional peak in PL spectrum at low (77–100 K) temperatures can be result of quasi-1D exciton appearance in the CSLs.     

Interface structure and growth mode of quantum wire and quantum dot GaAs-AlAs structures on corrugated (311)A surfaces

GaAs-AlAs corrugated superlattices (CSL) are formed on spontaneously nanofaceted (311)A surfaces. Using high-resolution transmission electron microscopy (HRTEM) along the $[\bar 233]$ zone axis with an appropriate image evaluation technique to enhance the contract between GaAs and AlAs we found two distinct lateral periodicities along the $[0\bar 11]$ directions for two different CSL layer thickness regimes. For multilayer deposition with GaAs layer thickness exceeding 1 nm the lateral periodicity of 3.2 nm is clearly revealed. The contrast originates from the thickness modulation of both AlAs and GaAs layers with a period of 3.2 nm in the $[0\bar 11]$ direction. The corrugation height is about 1 nm and it is symmetric for both upper and lower GaAs-AlAs interfaces. Thicker sections of the thickness-modulated AlAs and GaAs layers of the CSL are shifted by a half period with respect to each other. In the regime when the GaAs deposited average thickness is below 1 nm, which is necessary for complete coverage of the AlAs surface, a lateral periodicity of ≈1.5–2 nm is additionally revealed. We attribute this effect to the formation of local GaAs clusters dispersed on a corrugated (311)A AlAs surface resulting in a local phase reversal of the AlAs surface in their vicinity upon subsequent overgrowth. This reversal can be explained by the same effect as the phase shift of the surface corrugation upon heteroepitaxy on (311)A. In our model AlAs does not wet the GaAs cluster surface, unless different more energetically favorable scenario is possible. This causes accumulation of AlAs in the vicinity of the GaAs cluster and, as a result, the local phase reversal of the AlAs surface. The AlAs corrugated surface domains with different phases coexist on the surface resulting in an additional periodicity revealed in the HREM contrast modulation. Additionally HRTEM studies indicate that the AlAs-GaAs interface inclination angles in both regimes are 40° and 140° with respect to the flat (311) surface in an argreement with the {331} facet geometry model proposed by R. Nötzel, N.N. Ledentsov, L. Däweritz, M. Hohenstein, and K. Ploog.