GaN/AlxGa1-xN异质结二维电子气的磁电阻研究

通过对GaN/Al_xGa_1-xN异质结中二维电子气磁输运结果的分析,研究了磁电阻的起因.结果表明,整个磁场范围的负磁电阻是由电子-电子相互作用引起的,而高场下的正磁电阻来源于平行电导的进一步修正.用拟合的方法得到了电子-电子相互作用项以及平行电导层的载流子浓度和迁移率,并用不同的计算方法对拟合结果进行了验证.     

AlxGa1-xN/GaN异质结二维电子气磁输运性质研究

在1.5K低温和0～9T的高磁场下研究了AlGaG/GaN异质结二维电子气的磁输运性质.实验结果在4块样品中都观察到了Shubnikov-da HaSS振荡的双周期行为.表明异质结的三角势阱中有两个子带被电子占据.通过电子子带占据时电子浓度分配的线形行为得到第二子带被占据的阈值浓度为7.2×1012cm-2.通过对不同样品量子散射时间和输运迁移率的研究,说明在1.5K下远程离化施主散射在量子散射时间中起主要作用.     

InAlN/GaN异质结二维电子气波函数的变分法研究

使用变分法推导了InAlN/GaN异质结二维电子气波函数和基态能级的解析表达式,并讨论了InAlN/GaN异质结结构参数对二维电子气电学特性的影响.在假设二维电子气来源于表面态的前提下,使用了一个包含两个变分参数的尝试波函数推导电子总能量期望值,并通过寻找能量期望极小值确定变分参数.计算结果显示,二维电子气面密度随InAlN厚度的增大而增大,且理论结果与实验结果一致.二维电子气面密度增大抬高了基态能级与费米能级,并保持二者之差增大以容纳更多电子.InAlN/GaN界面处的极化强度失配随着In组分增大而减弱,二维电子气面密度随之减小,并导致基态能级与费米能级减小.所建立的模型能够解释InAlN/GaN异质结二维电子气的部分电学行为,并为电子输运与光学跃迁的研究提供了解析表达式.     

N极性GaN/AlGaN异质结二维电子气模拟

通过自洽求解薛定谔方程和泊松方程,较系统地研究了GaN沟道层、AlGaN背势垒层、Si掺杂和AlN插入层对N极性GaN/AlGaN异质结中二维电子气(2DEG)的影响,分析表明,GaN沟道层厚度、AlGaN背势垒层厚度及Al组分变大都能一定程度上提高二维电子气面密度,AlGaN背势垒层的厚度和Al组分变大也可提高二维电子气限阈性,且不同的Si掺杂形式对二维电子气的影响也有差异,而AlN插入层在提高器件二维电子气面密度、限阈性等方面表现都较为突出,在模拟中GaN沟道层厚度小于5nm时无法形成二维电子气,超过20nm后二维电子气面密度趋于饱和,而AlGaN背势垒厚度超过40nm后二维电子气也有饱和趋势,对均匀掺杂和delta掺杂而言AlGaN背势垒层Si掺杂浓度超过5×10~(19)cm~(-3)后2DEG面密度开始饱和,而厚度为2nmAlN插入层的引入会使2DEG面密度从无AlN插入层时的0.93×10~(13)cm~(-2)提高到1.17×10~(13)cm~(-2)。     

窄禁带稀磁半导体二维电子气的拍频振荡

通过对调制掺杂的n型Hg_0.82Cd_0.16Mn_0.02Te/Hg_0.3Cd_0.7Te第一类量子阱中磁性二维电子气磁阻拍频振荡的研究，发现温度、栅压的变化都会引起磁阻拍频节点位置的变化.从对拍频的分析中，可以将依赖于栅压的Rashba自旋-轨道分裂和依赖于温度的巨大塞曼分裂区分开来. 关键词： 磁性二维电子气 自旋分裂 sp-d交换相互作用 拍频     

二维电子气的关联函数

本文在少粒子体系波函数数值解的基础上讨论了强磁场中二维电子气的二体关联函数.在数值计算的意义上给出了有限集团体系二体关联函数的计算公式. 关键词：     

AlxGa1-xN/GaN异质结构中Al组分对二维电子气性质的影响

通过用数值计算方法自洽求解薛定谔方程和泊松方程,研究了Al组分对AlxGa1-xN/GaN异质结构二维电子气性质的影响,给出了AlxGa1-xN/GaN异质结构二维电子气分布和面密度,导带能带偏移以及子带中电子分布随AlxGa1-xN势垒层中Al组分的变化关系,并用AlxGa1-xN/GaN异质结构自发极化与压电极化机理和能带偏移对结果进行讨论分析.     

晶格匹配InAlN/GaN和InAlN/AlN/GaN材料二维电子气输运特性研究

文章研究了InAlN/GaN和引入AlN界面插入层形成的InAlN/AlN/GaN材料的输运性质. 样品均在蓝宝石上以脉冲金属有机物化学气相淀积法生长,霍尔迁移率变温特性具有典型的二维电子气(2DEG)特征. 综合各种散射机理包括声学形变势散射、压电散射、极性光学声子散射、位错散射、合金无序散射和界面粗糙度散射,理论分析了温度对迁移率的影响,发现室温下两种材料中2DEG支配性的散射机理都是极性光学波散射和界面粗糙度散射;AlN插入层对InAlN/GaN材料迁移率的改善作用一方面是免除2DEG的合金无序散射,另外还显著改善异质界面,抑制了界面粗糙度散射. 考虑到2DEG密度也是影响其迁移率的重要因素,结合实验数据给出了晶格匹配InAlN/GaN和InAlN/AlN/GaN材料的2DEG迁移率随电子密度变化的理论上限. 关键词： InAlN/GaN 二维电子气 迁移率     

ZnMgO/ZnO异质结构中二维电子气的研究

论文根据ZnMgO/ZnO异质结构二维电子气的能带结构及相关理论模型, 采用一维Poisson-Schrodinger方程的自洽求解, 模拟计算了ZnMgO/ZnO异质结构中二维电子气的分布及其对ZnMgO势垒层厚度及Mg组分的依赖关系. 研究发现该异质结构中ZnMgO势垒层厚度存在一最小临界值: 当垒层厚度小于该临界值时, 二维电子气消失, 当垒层厚度大于该临界值时, 其二维电子气密度随着该垒层厚度的增加而增大; 同时研究发现ZnMgO势垒层中Mg组分的增加将显著增强其二维电子气的行为, 导致二维电子气密度的明显增大; 论文对模拟计算获得的结果与相关文献报道的实验结果进行了比较, 并从极化效应和能带结构的角度进行了分析和讨论, 给出了合理的解释. 关键词： 氧化锌 二维电子气 异质结构 理论计算     

窄禁带稀磁半导体二维电子气的磁阻振荡研究

通过改变温度和磁场方向对调制掺杂的n型Hg_0.82Cd_0.16Mn_0.02Te/Hg_0.3Cd_0.7Te第一类量子阱中磁性二维电子气磁阻拍频振荡进行了深入的研究，发现不仅温度的变化能够引起磁阻拍频节点位置的变化. 而且改变磁场方向，可以分别调整塞曼分裂和朗道分裂. 从对拍频的分析中，可以将依赖于磁场垂直方向的朗道能级分裂和依赖于整个磁场大小的塞曼分裂区分开来. 关键词： 磁性二维电子气 自旋分裂 塞曼分裂 拍频     

Al0.22Ga0.78N/GaN二维电子气中的弱局域和反弱局域效应

通过磁输运测量研究了Al_0.22Ga_0.78N/GaN二维电子气的电子相干散射中的弱局域和反弱局域化现象.在外加弱磁场的情况下，该系统表现出正-负磁阻的变化，说明在Al_0.22Ga_0.78N/GaN异质结中存在晶体场引起的电子自旋-轨道散射.同时讨论了二维电子气中不同的散射时间对温度的依赖关系，实验得到的非弹性散射时间与温度成反比，表明非弹性散射机理主要来源于小能量转移的电子-电子散射. 关键词： 二维电子气 弱局域 磁阻     

Low-field magnetoresistance of strongly modulated two-dimensional electron gas

The typical form of the low-field magnetoresistance anomaly induced by a strong one-dimensional periodic modulation of the background potential is described. It is shown that the magnetoresistance peak due to the magnetic breakdown is always followed by a resistance increase at higher magnetic fields, for which οcτ > 1.     

The low-temperature mobility of two-dimensional electron gas in AlGaN/GaN heterostructures

To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas （2DEG） in Al- GaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scat- tering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGaN/GaN interface roughness increases due to the stress accumulation in AlGaN layer.     

Degradation mechanism of two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures

This paper finds that the two-dimensional electron gas density in high Al-content AlGaN/GaN heterostructures exhibits an obvious time-dependent degradation after the epitaxial growth. The degradation mechanism was investigated in depth using Hall effect measurements, high resolution x-ray diffraction, scanning electron microscopy, x-ray photoelectron spectroscopy and energy dispersive x-ray spectroscopy. The results reveal that the formation of surface oxide is the main reason for the degradation, and the surface oxidation always occurs within the surface hexagonal defects for high Al-content AlGaN/GaN heterostructures.     

Magnetotransport properties of two-dimensional electron gas in AlGaN/AlN/GaN heterostructures

Magnetotransport measurements are carried out on the AlGaN/AlN/GaN in an SiC heterostructure, which demonstrates the existence of the high-quality two-dimensional electron gas (2DGE) at the AlN/GaN interface. While the carrier concentration reaches 1.32 × 10¹³ cm ^{- 2} and stays relatively unchanged with the decreasing temperature, the mobility of the 2DEG increases to 1.21 × 10⁴ cm²/(V·s) at 2 K. The Shubnikov—de Haas (SdH) oscillations are observed in a magnetic field as low as 2.5 T at 2 K. By the measurements and the analyses of the temperature-dependent SdH oscillations, the effective mass of the 2DEG is determined. The ratio of the transport lifetime to the quantum scattering time is 9 in our sample, indicating that small-angle scattering is predominant.     

Influence of a two-dimensional electron gas on current—voltage characteristics of Al0.3{Ga}0.7 N/GaN high electron mobility transistors

The J-V characteristics of AltGa1 tN/GaN high electron mobility transistors（HEMTs） are investigated and simulated using the self-consistent solution of the Schro dinger and Poisson equations for a two-dimensional electron gas（2DEG） in a triangular potential well with the Al mole fraction t = 0.3 as an example.Using a simple analytical model,the electronic drift velocity in a 2DEG channel is obtained.It is found that the current density through the 2DEG channel is on the order of 10^13 A/m^2 within a very narrow region（about 5 nm）.For a current density of 7 × 10^13 A/m62 passing through the 2DEG channel with a 2DEG density of above 1.2 × 10^17 m^-2 under a drain voltage Vds = 1.5 V at room temperature,the barrier thickness Lb should be more than 10 nm and the gate bias must be higher than 2 V.