半导体技术

TN301 99050357应变异质结Znse/512(110)的价带带阶的第一原理计算/李开航,张志绷乌,黄美纯(厦门大学)11量子电子学·一1999,16(2)一130一133文中从第一原理出发,用Linearized一M“ffin-Tin(LMTO)能带方法对应变超晶格(Znse)。/(512)。(110)(n=2一7)进行自洽计算.在此基础上采用冻结势方法计算了应变异质结Znse/SiZ(110)的价带带阶,得到其理论值为。.93eV,说明该异质结的价带带阶值较大,由其构成的量子阱对空穴运动有较强的限制作用.图2表1参11(许)理国家重点实验室)井真空科学与技术学报.一1 999,19(3)一177一181利用X射线光电子谱…     

Si/GaAs异质结界面态及其价带不连续性

本文报道用自洽EHT方法研究Si/GaAs异质结界面态分布和价带不连续性。用准共度晶格模型处理晶格失配问题,并对晶格常数作了修正。通过对Si/GaAs(111)、Si/GaAs(111)和Si/GaAs(110)异质结中Si应变和GaAs应变的情况,分别进行计算,得到界面态分布和价带不连续值等物理量,结果表明:它们不仅依赖于组成异质结的两种材料的体性质,而且还依赖于界面晶向和材料应变。文中给出了这些计算结果,并作了初步的讨论。     

GaN、AlN的形变势和应变层GaN/AlN异质结带阶的计算

本文采用混合基矢从头赝势能带计算方法研究了（００１）界面应变对ＧａＮ、ＡｌＮ应变层的能带、平均键能Ｅｍ和带阶参数Ｅｍｖ的影响．借助于带阶参数形变势的计算,预言了不同生长厚度情况下ＧａＮ／ＡｌＮ应变层异质结价带带阶和导带带阶．     

应变层异质结ZnS／ZnSe的价带带阶

采用基于ＬＭＴＯ－ＡＳＡ的平均结合能计算方法，研究了在ＺｎＳｘＳｅ１－ｘ衬底上沿（００１）方向外延生长的应变层异质结ＺｎＳ／ＺｎＳｅ的价带带阶值。研究表明，应变的结果使价带带阶随衬底组分（ｘ）的变化呈非线性且单调的关系；与其他理论计算和实验结果比较，本文的计算结果比较理想。     

Si/GaP(111)和(■)界面的研究

本文报道用EHT方法计算Si/GaP(111)、(111)和(110)界面的电子结构,得到它们的价带不连续值△E_v分别为:0.88eV、0.97eV和0.87eV,这和Si/GaP的实验结果:△E_v=0.80eV和0.95eV相符合.不同晶向△E_v相差达0.1eV.分析Si和GaP价带顶位置的变化情况,发现对Si/GaP(111),界面态对价带顶的影响不大.但对于Si/GaP(111)异质结,由于界面态的影响,使Si价带顶明显上移.此时,界面态对△E_v的非线性影响不可忽略。     

Si/GaP(111)和(-1-1-1)界面的研究

本文报道用EHT方法计算Si/GaP(111)、(111)和(110)界面的电子结构,得到它们的价带不连续值△E_v分别为:0.88eV、0.97eV和0.87eV,这和Si/GaP的实验结果:△E_v=0.80eV和0.95eV相符合.不同晶向△E_v相差达0.1eV.分析Si和GaP价带顶位置的变化情况,发现对Si/GaP(111),界面态对价带顶的影响不大.但对于Si/GaP(111)异质结,由于界面态的影响,使Si价带顶明显上移.此时,界面态对△E_v的非线性影响不可忽略。     

Si基外延Ca_2Si电子结构的计算

采用基于第一性原理的赝势平面波方法,对异质外延关系为Ca2Si(001)//Si(100),取向关系为Ca2Si[100]//Si[110]立方相的Ca2Si平衡体系下能带结构、态密度等进行了理论计算。计算结果表明:当原胞的晶格常数a取值为0.490nm时,立方相Ca2Si处于稳定状态并且是具有带隙值为0.6402eV的直接带隙半导体;其价带主要是由Si的3s、3p态电子和Ca的3s、3p态电子构成,导带主要是由Ca的3d态电子构成。     

Si／Ge应变层异质结价带偏移的剪裁与设计

讨论应变层异质结价带偏移的剪裁、设计方法，研究Ｓｉ／Ｇｅ应变层异质结价带偏移设计参数与应变条件的关系，基于异质结中平均键能“对齐”，得到适用于Ｓｉ／Ｇｅ异质结价带偏移剪裁与设计的计算公式和图表。     

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。     

(ZnSe)_n/(Ge_2)_n(110)超晶格的电子结构和光学性质

用线性Muffin－Tin轨道（LMTO）能带计算方法对匹配超晶格（Znse）n／（Ge2）n（n=2－5）系统进行超元胞自洽计算。在此基础上，用冻结势方法计算该超晶格系统的价带带阶（bandoff－set）；用四面体方法计算了该系统的联合态密度，由此计算了该系统的光学介电函数应部ε2（ω）。计算结果表明，该超晶格系统的价带带阶约为1．44eV。（Znse）n／（Ge）n（110）超晶格的光吸收峰结合了体材料Znse和Ge光吸收峰的特点。     

p型半导体量子阱的有效计算方法

提出一种p型半导体量子阱中二维空穴气的有效计算方法。它使用半轴向近似把Luttinger哈密顿简约成3*3矩阵,而仍保留价带的扭曲性和重空穴、轻空穴和自旋-轨道耦合带间的能带混合。使用这种方法和简化的有限差分算出了p型半导体量子阱的价带结构和二维空穴气。研究了量子阱中的价带混合、能带扭曲和阱间空穴气的耦合。该方法计算量少,计算结果满足价带特性,适用于p型异质结器件的优化设计。     

A Unified Model for Gate Capacitance–Voltage Characteristics and Extraction of Parameters of Si/SiGe Heterostructure pMOSFETs

A unified model for gate capacitance-voltage characteristics of Si/SiGe heterostructure pMOSFETs is presented. This model is applicable to buried-channel, surface-channel, and dual-channel Si/SiGe heterostructure pMOSFETs. The results from the model are compared with the experimental results and are found to be in excellent agreement. A simple and accurate method for the extraction of parameters such as the valence band offset, Si cap layer thickness, threshold voltages, and substrate doping is also presented in this paper.     

Blue/green luminescence based on Zn(S)Se/GaAs heterostructures

Substantial advances have been realized in the aim to achieve blue–green light emitting devices based on Zn(S)Se wide band gap II–VI semi-conductor materials. Two light emitting diodes p on n and n on p heterostructures were grown on GaAs substrate by molecular beam epitaxy. The active layer was a single ZnCdSe quantum well, with ZnSSe guiding layers and ZnSe cladding layers. p-GaInP, p-AlGaAs and p-CdZnSe buffer layers were deposited at the p-ZnSe/GaAs interface to reduce the valence band offset in the case of n on p heterostructures. Electrical and optical properties were investigated using current voltage, capacitance voltage, electroluminescence, photoluminescence and photocurrent measurements at room temperature. Blue–green luminescence centered at 516.7 nm is observed. The highest luminescence intensity is observed under 7 V forward bias. Photoluminescence spectrum shows two wide peaks at 2.2 and 1.9 eV energies. These energies are attributed to the transitions between ZnSe and GaAs conduction bands and the deep level at E_v−0.6 eV. Absorption process from ZnSe and ZnSSe conduction bands to the shallow nitrogen acceptor level (2.6 and 2.8 eV, respectively) have been observed using photocurrent measurements. From these results we present a band alignment diagram which confirms the presence of the two levels at 0.1 and 0.6 eV from the valence band of ZnSe.     

Deep level electronic structure of ZnSe/GaAs heterostructures

We performed 1—2 keVcathodoluminescence measurements and He-Ne and HeCd excited photoluminescence studies of ZnSe/GaAs( 100) heterostructures grown by molecular beam epitaxy. Our goal was to investigate the deep level electronic structure and its connection with the heterojunction band offsets. We observed novel deep level emission features at 0.8, 0.98, 1.14, and 1.3 eV which are characteristic of the ZnSe overlayer and independent in energy of overlayer thickness. The corresponding deep levels lie far below those of the near-bandedge features commonly used to characterize the ZnSe crystal quality. The relative intensity and spatial distribution of the deep level emission was found to be strongly affected by the Zn/Se atomic flux ratio employed during ZnSe growth. The same flux ratio has been shown to influence both the quality of the ZnSe overlayer and the band offset in ZnSe/GaAs heterojunctions. In heterostructures fabricated in Se-rich growth conditions, that minimize the valence band offset and the concentration of Se vacancies, the dominant deep level emission is at 1.3 eV. For heterostructures fabricated in Zn-rich growth conditions, emission by multiple levels at 0.88,0.98, and 1.14 eV dominates. The spectral energies and intensities of deep level transitions reported here provide a characteristic indicator of ZnSe epilayer stoichiometry and near-interface defect densities.     

GaAs衬底上（ZnS）n／（ZnSe）n（001）超晶格的光学性质

本文用Ｌｉｎｅａｒｉｚｅｄ－Ｍｕｆｆｉｎ－Ｔｉｎ Ｏｒｂｉｔａｌｓ能带方法，计算ＧａＡｓ衬底上（ＺｎＳ）ｎ／（ＺｎＳｅ）ｎ（００１）超晶格的能带结构。计算中采用外加调整势进行带隙修正，从而得到较准确的能带结构和波函数。在此基础上计算了超晶格系统的光学介电函数虚部ε２（ω）。结果表明，该超晶格系统的光学性质结合了ＺｎＳ和ＺｎＳｅ体材料光学性质的特点，在相当宽的能量范围内有较好的光谱响应，并且该超晶格     

Origin of the anomalous trends in band alignment of GaX/ZnGeX_2(X = N,P, As,Sb) heterojunctions

Utilizing first-principles band structure method, we studied the trends of electronic structures and band offsets of the common-anion heterojunctions GaX/ZnGeX_2(X = N, P, As, Sb). Here, ZnGeX_2 can be derived by atomic transmutation of two Ga atoms in GaX into one Zn atom and one Ge atom. The calculated results show that the valence band maximums(VBMs) of GaX are always lower in energy than that of ZnGeX_2, and the band offset decreases when the anion atomic number increases. The conduction band minimums(CBMs) of ZnGeX_2 are lower than that of GaX for X = P, As, and Sb, as expected. However, surprisingly, for ZnGeN2, its CBM is higher than GaN. We found that the coupling between anion p and cation d states plays a decisive role in determining the position of the valence band maximum, and the increased electronegativity of Ge relative to Ga explains the lower CBMs of ZnGeX_2 for X = P, As, and Sb. Meanwhile, due to the high ionicity, the strong coulomb interaction is the origin of the anomalous behavior for nitrides.     

Formation of a thin III-VI compound interfacial layer at ZnTe/znse heterojunction and its effect on energy band discontinuity

Interfacial layers were inserted at the interface of ZnSe and ZnTe in order to reduce both (1) the effect of strain and (2) the valence band discontinuity. The interfacial layer adapted in this study is the III-VI compound (Ga,Se). The layered structure GaSe is favorable for the present work, because it can be a buffer layer to relax the lattice mismatch at the interface. All layers including ZnTe, (Ga,Se) and ZnSe were grown on (100) GaAs substrate by conventional molecular beam epitaxy. The crystal structure of the (Ga,Se) on ZnSe was investigated. The growth of the layered structure GaSe layer on (100) ZnSe was very difficult, though the defect zinc-blende structure Ga₂Se₃ layer could be easily grown. The defect zinc-blende structure Ga₂Se₃ was inserted at the interface of ZnSe and ZnTe so that the valence band discontinuity could be modified. The discontinuity was decreased to about 0.1 eV when the thickness of the interfacial layer was about 8Å. The current-voltage characteristics were measured for the sample with Ga₂Se₃ interfacial layer. The structure with Ga₂Se₃ exhibited the ohmic property. These results suggest that the valence band discontinuity between ZnTe and ZnSe can be reduced by introducing the Ga₂Se₃ interfacial layer.     

AlGaN/GaN异质结构中的极化工程

从自洽求解薛定谔方程和泊松方程出发,研究了AlGaN/GaN量子阱电子气密度随Al组份比、势垒层厚度和栅压的变化,比较了能带带阶和极化电荷对沟道阱能带和电子气特性的影响,研究了在势垒层和缓冲层中夹入AlN及InGaN薄层的作用,计算了AlGaN/GaN/AlGaN双异质结的能带,最后探讨了势垒层能带的优化设计,提出了剪裁势垒层能带来钝化表面的新方法。     

Low temperature grown be-doped InAIP band offset reduction layer to p-type ZnSe

To solve the difficulty of achieving low resistance ohmic contact to p-type ZnSe, the use of an intermediate p-type InAlP layer to p-type ZnSe as a valence band offset reduction layer is studied by gas source molecular beam epitaxy. It is found that hole concentrations as high as 2 × 10¹⁸ cm⁻³ are easily obtained for p-type InAlP layers grown on GaAs even at low temperature of 350°C, although a higher Be cell temperature is required than that for a 500°C grown p-type InAlP due to the decreased electrical activity of Be in InAlP. Despite the very high Be concentrations, the Be precipitation/segregation is not observed. It was difficult to obtain the same hole concentration of InAlP layers grown on ZnSe as that on GaAs. However, the insertion of only several monolayers of GaAs between ZnSe and InAlP makes it possible to avoid faceting growth of InAlP and to improve the electrical properties of Be-doped InAlP grown on ZnSe. These results suggest that the Be-doped InAlP layer can be used as an intermediate layer to form the low resistance ohmic contact to p-type ZnSe.