Effect of a step quantum well structure and an electric-field on the Rashba spin splitting

Spin splitting of conduction subbands in Al_(0.3)Ga_(0.7)As/GaAs/Al_xGa_(1-x)As/Al_(0.3)Ga_(0.7)As step quantum wells induced by interface and electric field related Rashba effects is investigated theoretically by the method of finite difference. The dependence of the spin splitting on the electric field and the well structure, which is controlled by the well width and the step width, is investigated in detail. Without an external electric field, the spin splitting is induced by an in terface related Rashba term due to the built-in structure inversion asymmetry. Applying the external electric field to the step QW, the Rashba effect can be enhanced or weakened, depending on the well structure as well as the direction and the magnitude of the electric field. The spin splitting is mainly controlled by the interface related Rashba term under a negative and a stronger positive electric field, and the contribution of the electric field related Rashba term dominates in a small range of a weaker positive electric field.A method to determine the interface parameter is proposed.The results show that the step QWs might be used as spin switches.

Si_(0.75)Ge_(0.25)虚衬底上应变补偿Si/Si_(0.62)Ge_(0.38)量子阱发光

由于Si/SiGe异质结构的带阶差主要发生在价带,为实现高效率的发光,本文从理论上设计了在硅基Si_(1-x) Ge_x虚衬底上外延应变补偿的Si/S_(1-y) Ge_y(y>x)量子阱的能带结构,将量子阱对电子的限制势垒提高到100meV以上.在实验上,采用300℃生长的Ge量子点插入层,制备出薄的SiGe驰豫缓冲层(虚衬底),表面Ge组份达到0.25,表面粗糙度小于2nm,驰豫度接近100%.在我们制备的SiGe缓冲层上外延了应变补偿SiGe/Si多量子阱结构,并初步研究了其发光特性.

Growth of 0.55eV-GaInAsSb Quaternary Alloy Films for a Thermophotovoltaic Device by Liquid Phase Epitaxy

Lattice matched Ga_(1-x)In_xAs_ySb_(1-y) quaternary alloy films for thermophotovoltaic cells were successfully grown on n-type GaSb substrates by liquid phase epitaxy. Mirror-like surfaces for the epitaxial layers were achieved and evaluated by atomic force microscopy. The composition of the Ga_(1-x)In_xAs_ySb_(1-y) layer was characterized by energy dispersive X-ray analysis with the result that x = 0.2, y = 0.17. The absorption edges of the Ga_(1-x)In_xAs_ySb_(1-y) films were determined to be 2. 256μm at room temperature by Fourier transform infrared transmission spectrum analysis, corresponding to an energy gap of 0.55eV. Hall measurements show that the highest obtained electron mobility in the undoped p-type samples is 512cm2~/(V·s) and the carrier density is 6. 1×10~(16)cm~(-3) at room temperature. Finally, GaInAsSb based thermophotovoltaic cells in different structures with quantum efficiency values of around 60% were fabricated and the spectrum response characteristics of the cells are discussed.

AlGaN／GaN异质结紫外探测器

采用p-AlGa1-xN／i-GaN／n-GaN异质结构成功制备了含铝组分分别为0．1和0．07的正照射可见盲紫外探测器，并分别测试了它们的伏安特性曲线和光电响应光谱。对于Al组分为0．1的器件，在零偏压处出现了板低的暗电流密度，表明器件具有非常高的信噪比。高分辨率X射线衍射仪对材料的测试结果表明，高铝组分（0．1）窗口层薄膜材料的晶体质量较差，导致暗电流增大，而其窗口层的窗口选择作用则可以得到较高的响应率和较宽的响应波段。

数值分析渐变DBR对垂直腔面发射激光器谐振腔模的影响

通过数值分析研究了含线性渐变层的Al_(0.9)Ga_(0.1)As/Al_yGa_(1-y)As/GaAs/Al_xGa_(1-x)As DBR的光学特性及其对VCSEL谐振腔光学特性的影响,建立了渐变型DBR渐变层厚度与折射率的关系,通过特征矩阵法计算了突变GaAs/Al_(0.9)Ga_(0.1)As DBR和渐变型DBR的反射谱和反射相移,分析了渐变层对DBR反射率和反射相移的影响.对渐变型DBR,要使VCSEL谐振腔满足中心波长相位匹配条件,还需要在DBR靠近谐振腔一侧的最前面增加一定厚度的渐变层,称为相位匹配层.通过计算,我们得到了使VCSEL谐振腔满足相位匹配条件时均匀层和相位匹配层的厚度.

具有非均匀渐变界面DBR的光学特性分析

应用特征矩阵法研究了非均匀渐变界面Al_(0.9)Ga_(0.1)As/AlyGa_(1-y)As/GaAs/Al_xGa_(1-x)As DBR的光学特性.建立了非均匀渐变界面AlyGa1-yAs的折射率模型，并得到了渐变界面特征矩阵的解析解，通过特征矩阵法分别计算了突变GaAs/Al_(0.9)Ga_(0.1)As DBR和渐变DBR的反射谱和反射相移，分析了非均匀渐变层对DBR光学特性的影响，对渐变DBR，需要在DBR前面再增加一定厚度的非均匀渐变相位匹配层才能使整个DBR满足中心波长相位匹配条件，并通过光学厚度近似方法求出相位匹配层厚度.

Resonant Raman Scattering and Photoluminescence Emissions from Above Bandgap Levels in Dilute GaAsN Alloy

The transitions of E0 ,E0 ＋A0, and E＋ in dilute GaAs（1-x） Nx alloys with x = 0.10% ,0.22% ,0.36% ,and 0.62% are observed by micro-photoluminescence. Resonant Raman scattering results further confirm that they are from the intrinsic emissions in the studied dilute GaAsN alloys rather than some localized exciton emissions in the GaAsN alloys. The results show that the nitrogen-induced E E＋ and E0 ＋ A0 transitions in GaAsN alloys intersect at a nitrogen content of about 0.16%. It is demonstrated that a small amount of isoelectronic doping combined with micro-photoluminescence allows direct observation of above band gap transitions that are not usually accessible in photoluminescence.

HCl/HF/CrO3溶液对 InGaAs/InGaAsP的选择性湿法刻蚀--应用于楔形结构的制备

利用动态掩膜湿法腐蚀技术,研究了HCl/HF/CrO3溶液对与InP衬底晶格匹配的InxGa1-xAs1-yPy(y=0,0.2,0.4,0.6)材料的腐蚀特性.对于HCl(36wt%)/HF(40wt%)/CrO3(10wt%)的体积比为x∶0.5∶1的溶液,随着x由0增加到1.25,相应的腐蚀液对In0.53Ga0.47As/In0.72Ga0 28As06P0.4的选择性由42.4降到1.4;通过调节腐蚀液的选择性,在In072Ga0.28As06P0.4外延层上制备出了倾角从1.35°到35.9°的各种楔形结构;当x为0.025和1.25时,相应的In0.72Ga0.28As0.6P0.4腐蚀表面的均方根粗糙度分别为1.1nm和1.6nm.还研究了溶液的组分与InxGa1-xAs1-yPy(y=0,0.2,0.4)的腐蚀速率间的关系,并对腐蚀机理进行了分析.

Si被注入Gd后的磁性及其整流特性的研究

采用离子束技术,在n型硅基片中注入稀土元素钆,制备了磁性-非磁性p-n结.磁性层Gd_xSi_(1-x)表现出优良的磁学性能,高居里温度,高原子磁矩(利用RKKY模型可以得到解释),低矫顽力,并保持着半导体的属性,磁性-非磁性p-n结具有整流特性,但没有观察到明显的磁电阻效应.

HF/CrO_3溶液对AlGaAs的选择性湿法刻蚀应用于楔型结构的制备

利用动态掩膜腐蚀技术，研究了HF/CrO_3腐蚀液对各种不同组分的Al_xGa_(1-x)As (x = 0.3, 0.5, 0.65)的腐蚀速率及腐蚀表面形貌。随着HF(48wt%)/CrO_3(33wt%)的体积比由0.01变化到0.138，相应的腐蚀液对Al_(0.8)Ga_(0.2)As/Al_(0.3)Ga_(0.7)As的选择性由179降到8.6；通过调节腐蚀液的选择性，在Al_(0.3)Ga_(0.7)As外延层上制备出了倾角从0.32°到6.61°的各种斜面。当HF(48wt%)/CrO_3(33wt%)的体积比为0.028时，Al组分分别为0.3、0.5和0.65时，相应的腐蚀表面的均方根粗糙度为1.8、9.1和19.3nm。另外，还分析了腐蚀机理与腐蚀表面形貌之间的关系。

InGaAs/GaAs自组织量子点光致发光特性研究

用PL谱测试研究了GaAs和不同In组份In_xGa_(1-x)As(x=0.1,0.2,0.3)覆盖层对分子束外延生长的InAs/GaAs自组织量子点发光特性的影响。用In_xGa_(1-x)As外延层覆盖InAs/GaAs量子点，比用GaAs做覆盖层其发光峰能量向低能端移动，发光峰半高宽变窄，量子点发光峰能量随温度的红移幅度变小。理论计算证实这是由于覆盖层In_xGa_(1-x)As减小了InAs表面应力导致发光峰红移，而In元素有效抑制了InAs/GaAs界面组份的混杂，量子点的均匀性得到改善，PL谱谱半高宽变窄。用InGaAs覆盖的In_(0.5)Ga_(0.5)As/GaAs自组织量子点实现了1.3μm发光，室温下PL谱半高宽为19.2meV，是目前最好的实验结果。

立方相InGaN的稳态和瞬态光学特性研究

用光荧光和时间分辨光谱技术研究了MEB生长立方In_(1-x)Ga_(1-x)N(x=0.150.26)外延材料的稳态和瞬态发光特性。实验表明InGaN发光主要来自局域激子发光，局域化是由合金无序造成的，相应局域化能量为60meV左右。荧光衰退呈现双指数特性，快过程(50ps,12K)是自由激子的快速驰豫引起的，而慢过程(200～270ps,12K)则对应局域激子发光，其荧光寿命随温度缓变反映了激子发光的强局域性质。

C离子注入Si中Si-C合金的形成及其特征

利用离子注入和高温退火的方法在Si中生长了C含量为0.6%-1.0%的Si_(1-x)C_x合金，研究了注入过程中产生的损伤缺陷，注入C离子的剂量及退火工艺对合金形成的影响，探讨了合金的形成机理及合金产生的应变分布的起因，如果注入的C离子剂量小于引起Si非晶化的剂量，退火过程中注入产生的损伤缺陷容易与C原子结合形成缺陷团簇，难于形成Si_(1-x)C_x合金，而预先利用Si离子注入引进损伤有利于Si_(1-x)C_x合金的形成；但如果注入的C离子可以引起Si的非晶化，预先注入产生的损伤缺陷不利于Si_(1-x)C_x合金的形成。与慢速退火工艺相比，快速热退火工艺有利于Si_(1-x)C_x合金的形成。离子注入的C原子在空间分布不均匀，退火过程中将形成应变不同的Si_(1-x)C_x合金区域。

弛豫SiGe衬底上SiGe/Si Ⅱ型量子阱

采用UHV/CVD系统，在Si衬底上生长了具有渐变Si_(1-x)Ge_x缓冲层结构的弛豫Si_(0.76)Ge_(0.24)虚衬底和5个周期的Si_(0.76)Ge_(0.24)/Si多量子阱。在渐变Si_(1-x)Ge_x缓冲层生长过程中引入原位退火，消除了残余应力，抑制了后续生长的SiGe中的位错成核。透射电子显微照片显示，位错被有效地限制在组份渐变缓冲层内，而SiGe上层和SiGe/Si量子阱是无位错的。在样品的PL谱中，观察到跃迁能量为0.961eV的Ⅱ型量子阱的无声子参与(NP)发光峰。由于Ⅱ型量子阱中电子和空穴不在空间同一位置，较高光功率激发下引起的高浓度载流子导致能带弯曲严重。NP峰随激发功率增加向高能方向移动，在一定激发条件下，电子跃迁或隧穿至弛豫SiGe层弯曲的导带底后与处于同一位置的空穴复合发光，所以NP峰积分强度随光激发功率先增加后减小。

快速退火对SiGe/Si多量子阱p-i-n光电二极管的影响（英文）

利用光电流谱，结合X射线双晶衍射研究了快速退火对Si_(1-x)Ge/Si多量子阱p-i-n光电二极管的影响。由于应变SiGe的部分弛豫和Si-Ge互扩散，退火后的二极管的截止波长有显著的减小。但是，在750-850℃范围内，波长蓝移量随着退火温度的增加而变化缓慢，而样品的光电流强度却随温度是先减弱而后又增强，这可能主要是由于在不同温度退火过程中失配位错的产生和点缺陷的减小造成的。