HgTe/HgCdTe量子阱中巨大电子Rashba自旋分裂

主要研究具有倒置能带结构的n-HgTe/HgCdTe第三类量子阱Shubnikov-de Haas（SdH）振荡中的拍频现象.发现在量子阱中电子存在强烈的Rashba自旋分裂,通过对SdH振荡进行三种不同方法的分析：SdH振荡对1/B关系的快速傅里叶变换、SdH振荡中拍频节点分析和对SdH振荡拍频数值拟合,得到了完全一致的电子Rashba自旋分裂能量（28—36 meV）.关键词：n-HgTe/HgCdTeShubnikov-de Haas振荡Rashba自旋分裂     

HgCdTe薄膜的输运特性及其应力调控

窄禁带直接带隙半导体材料碲镉汞(Hg1–xCdxTe)是一种在红外探测与自旋轨道耦合效应基础研究方面都具有重要应用意义的材料.本文对单晶生长的体材料Hg0.851Cd0.149Te进行阳极氧化以形成表面反型层,将样品粘贴在压电陶瓷上减薄后进行磁输运测试,在压电陶瓷未加电压时观察到了明显的SdH振荡效应.对填充因子与磁场...     

HgCdTe反型层的磁输运性质

利用成本低廉的液相外延技术, 成功制备了具有金属-绝缘体-半导体结构的HgCdTe场效应管器件. 在该器件中, 观察到清晰的Shubnikov-de Hass振荡和量子霍尔平台, 证明样品具有较高的质量. 测量零场附近的磁阻曲线, 在HgCdTe-基器件中观察到反弱局域效应, 表明样品中存在较强的自旋-轨道耦合作用. 利用Iordanskii-Lyanda-Pikus理论, 很好地拟合了反弱局域曲线. 由拟合得到的自旋分裂能随电子浓度的增大而增大, 最大达到9.06 meV. 根据自旋分裂能得到的自旋-轨道耦合系数同样随电子浓度的增大而增大, 与沟道较宽的量子阱中所得到的结果相反.     

AlGaN/AlN/GaN结构中二维电子气的输运特性

对使用金属有机物汽相沉积法生长的AlGaN/AlN/GaN结构进行的变温霍尔测量,测量结果指出在AlN/GaN界面处有二维电子气存在且迁移率和浓度在2K时分别达到了1.4×10⁴cm²·V^-1·s^-1和9.3×10¹²cm^-2,且在200K到2K范围内二维电子气的浓度基本不变,变磁场霍尔测量发现只有一种载流子(电子)参与导电.在2K温度下,观察到量子霍尔效应,Shubnikov-de Haas (SdH) 振荡在磁场约为3T时出现,证明了此结构呈现了典型的二维电子气行为.通过实验数据对二维电子气散射过程的半定量分析,推出量子散射时间为0.23ps,比以往报道的AlGaN/GaN结构中的散射时间长,说明引入AlN层可以有效减小合金散射,进一步的推断分析发现低温下以小角度散射占主导地位.     

不同量子阱宽度的InP基In0.53GaAs/In0.52AlAs高电子迁移率晶体管材料二维电子气的性能研究

用Shubnikov-de Haas(SdH)振荡效应,研究了在1.4 K下不同量子阱宽度(10—35 nm)的InP基高电子迁移率晶体管材料的二维电子气特性.通过对纵向电阻SdH振荡的快速傅里叶变换分析,得到不同阱宽时量子阱中二维电子气各子带电子浓度和量子迁移率.研究发现,在Si掺杂浓度一定时,阱宽的改变对于量子阱中总的载流子浓度改变不大,但是随着阱宽的增加,阱中的电子从占据一个子带到占据两个子带,且第二子带上的载流子迁移率远大于第一子带迁移率.当量子阱宽度为20 nm时,处在第二子能级上的电子数与处在关键词：量子阱宽二维电子气Shubnikov-de Haas振荡高电子迁移率晶体管     

含带隙石墨烯纳米带的自旋筛选输运

利用Landauer-Büttiker公式和非平衡格林函数方法,研究了在电荷和自旋偏压共同作用下的扶手椅型石墨烯纳米带的自旋相关的电子输运性质. 当系统存在两种偏压时,不用自旋的电子具有不同的偏压窗口. 同时,含带隙石墨烯纳米带具有与自旋无关的导电电压阈值. 通过设置适当的两种偏压值,系统可以产生易于调节的单一自旋的电流.     

GeFe2O4晶体的基态能级和零场分裂参量

GeFe2O4是一种单晶化合物,考虑到由3个〈111〉方向之一的一个轴,从一个中心位置到另一个中心位置之间,以Fe2+离子为中心离子和O2-为配体构成了三角(C3v)对称体系.利用不可约张量理论,建立了3d4/3d6离子三角(C3v)对称的晶体场和自旋相互作用哈密顿矩阵,因此,由完全对角化的晶体场和自旋-轨道相互作用哈密顿矩阵和电子顺磁共振理论公式求出单晶GeFe2O4中Fe2+离子的电子顺磁共振零场分裂参量D和F-a.并研究了自旋三重态对电子顺磁共振(EPR)零场分裂的贡献.结果显示自旋三重态对基态零场分裂的贡献是较强的,理论计算结果与实验值相符.     

GeFe2O4晶体的基态能级和零场分裂参量

GeFe₂O₄是一种单晶化合物,考虑到由3个〈111〉方向之一的一个 轴,从一个中心位置 到另一个中心位置之间,以Fe²⁺离子为中心离子和O^2-为配体构 成了三角（C 3v）对称体系.利用不可约张量理论,建立了3d⁴/3d⁶离子三角（C3 v）对称的晶体场和 自旋相互作用哈密顿矩阵,因此,由完全对角化的晶体场和自旋-轨道相互作用哈密顿矩阵 和电子顺磁共振理论公式求出单晶GeFe₂O₄中Fe²⁺离子 的电子顺磁共振零场分 裂参量D和F-a.并研究了自旋三重态对电子顺磁共振（EPR）零场分裂的贡献.结果显示自旋 三重态对基态零场分裂的贡献是较强的,理论计算结果与实验值相符.关键词：自旋三重态晶体场低自旋态高自旋态零场分裂     

分子束外延HgCdTe材料的光致发光研究

报道了分子束外延生长 Ｈｇ０．６８ Ｃｄ０．３２ Ｔｅ 材料的光致发光测量结果。研究了原生样品和退火处理样品、以及氮离子注入样品的低温光致发光特征。对光致发光的测试结果进行拟合得到的禁带宽度, 与用红外透射谱得到的薄膜禁带宽相近; 其半峰宽和带尾能量较小, 显示了较高的薄膜质量。样品经过退火后带尾能量降低, 双晶衍射的半峰宽也有明显的变窄     

掺入Mg2+对CsNiCl3晶体的基态能级、零场分裂参量及Jahn-Teller效应的影响

应用不可约张量理论构造了三角对称晶场中3d²/3d^８态离子的45阶可完全对角化的微扰哈密顿矩阵,在考虑了以前工作中被忽略的自旋-自旋耦合作用的基础上计算了CsNiCl₃晶体和CsNiCl₃:Mg²⁺晶体的基态能级、晶体结构、零场分裂参量和Jahn-Teller效应,研究了掺入Mg²⁺对CsNiCl₃晶体的光谱、零场分裂参量及Jahn-Teller效应的影响和自旋单重态对基态能级的贡献,发现掺杂使得晶体结构产生畸变,从而改变晶体光谱的精细结构和零场分裂参量,不改变Jahn-Teller效应的分裂规律但改变分裂的大小.关键词：基态能级掺杂零场分裂自旋-自旋耦合     

Magneto-transport study of Landau level broadening in a gated AlGaAs/GaAs parabolic quantum well structure

We study the Landau level broadening by analyzing the Shubnikov-de Haas oscillations in a gated AlGaAs/GaAs parabolic quantum well structure when only one electronic subband is occupied. Small-angle scattering is determined to be important in this system. The Shubnikov-de Haas oscillations are described equally well by employing Gaussian or Lorentzian broadening of the Landau levels at low magnetic field where the quantum localization effect is not important. A possible explanation is that the electron-electron interactions lead to the overlapping of adjacent Landau levels and one can not distinguish between the two broadening types.     

Transport studies of localized and extended states of a two-dimensional electron gas in low magnetic fields

We have observed the quantum Hall effect in a high mobility two-dimensional electron gas to filling factors up to 80 at 0.3 K. This demonstrates the presence of both localized and extended states at low field, and explains the failure of the standard semi-classical analysis of Shubnikov–de Haas (SdH) oscillations in this regime. We go on to derive a general expression for the conductivity due to rectangular bands of extended states, and show that the observed temperature dependence of the SdH oscillations is consistent with this picture. An analysis of the oscillations using this expression reveals the predicted levitation of the extended states as the magnetic field is reduced.     

Temperature dependent energy relaxation time in AlGaN/AlN/GaN heterostructures

The two-dimensional (2D) electron energy relaxation in Al_0.25Ga_0.75N/AlN/GaN heterostructures was investigated experimentally by using two experimental techniques; Shubnikov-de Haas (SdH) effect and classical Hall Effect. The electron temperature (T_e) of hot electrons was obtained from the lattice temperature (T_L) and the applied electric field dependencies of the amplitude of SdH oscillations and Hall mobility. The experimental results for the electron temperature dependence of power loss are also compared with the current theoretical models for power loss in 2D semiconductors. The power loss that was determined from the SdH measurements indicates that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. In addition, the power loss from the electrons obtained from Hall mobility for electron temperatures in the range T_e > 100 K is associated with optical phonon emission. The temperature dependent energy relaxation time in Al_0.25Ga_0.75N/AlN/GaN heterostructures that was determined from the power loss data indicates that hot electrons relax spontaneously with MHz to THz emission with increasing temperatures.     

Rashba spin-splitting in narrow gap III–V semiconductor quantum wells

Using Kane's 8-band k·p theory and the envelope function approximation we derive a tight binding Hamiltonian for III–V semiconductor quantum well structures, which accurately models band structure and spin–orbit coupling. By applying a potential difference across the well we have calculated the Rashba spin-splitting in the lowest conduction subband. For identical well widths the Rashba splitting in InSb is shown to be approximately twice that of InAs and, in all cases, passes through a weak maximum with increasing quasimomentum.     

Fast-electron optical spectrum of a two-dimensional electron gas in the presence of the Rashba effect

We examine how the Rashba spin-orbit interaction (SOI) affects the fast-electron optical spectrum of a two-dimensional electron gas (2DEG). It is found that for a spin-split 2DEG, the spectrum of optical absorption is mainly induced by plasmon excitation via inter-SO electronic transition. From the width and position of the spectrum, the Rashba spin-splitting can be identified optically and, therefore, important spintronic properties can be measured though optical experiments.