Si调制掺杂AlGaN/GaN异质结磁阻拍频现象

在低温（15K—25K）和强磁场（0—10T）条件下，对二维电子气占据两个子带的Si调制掺杂AlGaN/GaN异质结构进行磁输运测量.在一定温度范围内观察到磁阻拍频现象.根据Sander等人和Raikh等人给出的磁阻振荡的具体表达式，拟合实验结果表明磁阻拍频是由第一子带S dH振荡和磁致子带间散射引起的磁阻振荡导致的. 关键词： AlGaN/GaN异质结构 SdH振荡 磁致子带间散射 磁阻拍频     

二维原子层谷电子学材料和器件

人为操控电子的内禀自由度是现代电子器件的核心和关键.如今电子的电荷和自旋自由度已经被广泛地应用于逻辑计算与信息存储.以二维过渡金属硫属化合物为代表的二维原子层材料由于其具有独特的谷自由度和优异的物理性质,成为了新型谷电子学器件研究的优选材料体系.本文介绍了能谷的基本概念、谷材料的基本物理性质、谷效应的调控和谷电子学器件...     

激光能量对气体等离子体产生太赫兹波的影响

双色激光脉冲激励气体等离子体产生太赫兹波是得到高强度宽频带太赫兹波的重要方法,本文利用光电流模型研究了该方法中激光能量对产生太赫兹波的影响。理论计算表明,太赫兹波随激光能量的增大而增强,而太赫兹波的频谱结构不受激光能量的影响。分析了双色激光能量影响太赫兹波强度的原因,并利用自由电子浓度和电子电流密度诠释了该影响的内在物理机制。该研究为提高太赫兹辐射强度提供了一种有效的途径。     

Leakage current reduction by thermal oxidation in Ni/Au Schottky contacts on lattice-matched In0.18Al0.82N/GaN heterostructures

By using temperature-dependent current–voltage, variable-frequency capacitance–voltage, and Hall measurements,the effects of the thermal oxidation on the electrical properties of Ni/Au Schottky contacts on lattice-matched In0.18Al0.82N/GaN heterostructures are investigated. Decrease of the reverse leakage current down to six orders of magnitude is observed after the thermal oxidation of the In0.18Al0.82N/GaN heterostructures at 700oC. It is confirmed that the reverse leakage current is dominated by the Frenkel–Poole emission, and the main origin of the leakage current is the emission of electrons from a trap state near the metal/semiconductor interface into a continuum of electronic states associated with the conductive dislocations in the InxAl1-xN barrier. It is believed that the thermal oxidation results in the formation of a thin oxide layer on the InxAl1-xN surface, which increases the electron emission barrier height.     

AlGaN-Based Deep-Ultraviolet Light Emitting Diodes Fabricated on AlN/sapphire Template

We report on the growth and fabrication of deep ultraviolet （DUV） light emitting diodes （LEDs） on an AIN template which was grown on a pulsed atomic-layer epitaxial buffer layer. Threading dislocation densities in the AlN layer are greatly decreased with the introduction of this buffer layer. The crystalline quality of the AlGaN epilayer is further improved by using a low-temperature GaN interlayer between AlGaN and AlN. Electroluminescences of different DUV-LED devices at a wavelength of between 262 and 317nm are demonstrated. To improve the hole concentration of p-type AlGaN, Mg-doping with trimethylindium assistance approach is performed. It is found that the serial resistance of DUV-LED decreases and the performance of DUV-LED such as EL properties is improved.     

银-氯化钾-吡啶甲酸体系的表面增强Raman光谱

测试了吡喃甲酸的固体, 溶液和配合物的普通Raman光谱及其SERS光谱, 用 冲极谱测量吡啶甲酸在汞电极上的极谱氢催化波, 取得了半波电位数据, 估计了吡啶甲酸各个异构体的吸附能力, 结果指出吡啶甲酸的增强因子和吸附能力间有平行关系.     

梨小食心虫信息素的合成

以环辛酮,醇混合物为原料,经八步反应,合成了梨小食心虫性信素.总得率为16%,纯度98%,Z-式与E-式之比为95:5,这是生物活性最佳的组成.     

Optimization of a solar-blind and middle infrared two-colour photodetector using GaN-based bulk material and quantum wells

This paper calculates the wavelengths of the interband transitions as a function of the Al mole fraction of Al_xGa_1-xN bulk material. It is finds that when the Al mole fraction is between 0.456 and 0.639, the wavelengths correspond to the solar-blind (250~nm to 280~nm). The influence of the structure parameters of Al_yGa_1-yN/GaN quantum wells on the wavelength and absorption coefficient of intersubband transitions has been investigated by solving the Schr?dinger and Poisson equations self-consistently. The Al mole fraction of the Al_yGa_1-yN barrier changes from 0.30 to 0.46, meanwhile the width of the well changes from 2.9~nm to 2.2~nm, for maximal intersubband absorption in the window of the air (3~μm <λ <5~μm). The absorption coefficient of the intersubband transition between the ground state and the first excited state decreases with the increase of the wavelength. The results are finally used to discuss the prospects of GaN-based bulk material and quantum wells for a solar-blind and middle infrared two-colour photodetector.     

Thermal stability of tungsten and tungsten nitride Schottky contacts to AlGaN/GaN

Thin tungsten nitride (WNx) films were produced by reactive DC magnetron sputtering of tungsten in an Ar-N2 gas mixture. The films were used as Schottky contacts on AlGaN/GaN heterostructures. The Schottky behaviours of WNx contact was investigated under various annealing conditions by current-voltage (I-V ) measurements. The results show that the gate leakage current was reduced to 10-6 A/cm2 when the N2 flow is 400 mL/min. The results also show that the WNx contact improved the thermal stability of Schottky contacts. Finally, the current transport mechanism in WNx/AlGaN/GaN Schottky diodes has been investigated by means of I-V characterisation technique at various temperatures between 300 K and 523 K. A TE model with a Gaussian distribution of Schottky barrier heights (SBHs) is thought to be responsible for the electrical behaviour at temperatures lower than 523 K.     

AlxGa1-xN/GaN双量子阱的结构和掺杂浓度对子带间跃迁波长和吸收系数的影响

用薛定谔方程和泊松方程自洽计算的方法研究了Al0.75Ga025N/GaN对称双量子阱(DQWs)中子带间跃迁(ISBT)的波长和吸收系数对中间耦合势垒高度、中间耦合势垒宽度、势阱宽度和势垒掺杂浓度的依赖关系.研究发现,第一奇序子带S1ood与第二偶序子带S2evenISBT波长随着中间耦合势垒高度的降低而变短.当中间耦合势垒高度高于0.62 eV时,Slotld-S:一ISBT吸收系数随着中间耦合势垒的降低而增加.当减小AlxGa1-xN/GaN的DQWs中间耦合势垒宽度时,S1odd-S2evenISBT波长将变短,其吸收系数变大.另一方面,当对称DQWs的势阱宽度大于1.9 nm时,S1odd-S2evenISBT波长随着势阱的变窄而减小,S1odd-S2evenISBT吸收系数随着势阱的变窄而增加.当势垒中的掺杂浓度小于1018/cm3时,S1odd-S2evenISBT波长基本不随掺杂浓度变化,而吸收系数随掺杂浓度的增加而增加.这些结果对于利用DQWs实现工作于光纤通信波段超快的、基于三能级或四能级系统的双色光电子器件的应用具有指导意义.