基于肖特基电流输运模型和扫描分布电阻显微术的窄量子阱载流子浓度表征（英文）

目前对于纳米尺度半导体材料的局域电导与对应载流子浓度关系的描述主要以参数拟合为主。其关系模型主要依赖人工拟合参数,例如理想因子。所以无法从测得局域电导分布来推出载流子浓度分布。为此,提出了一种获取量子阱中载流子浓度的模型。通过小于10nm分辨的截面扫描分布电阻显微术,测得了GaAs/AlGaAs量子阱(110)截面的局域电导分布。基于实验设置,提出了只含有掺杂浓度参量的实验描述模型。通过模型,由测得的量子阱(掺杂浓度从10~(16)/cm~3到10~(18)/cm~3)局域电导分布,推导出了其载流子分布。相对误差在30%之内。     

Ge/Si量子阱结构的C-V特性的模拟

采用有限深对称方势阱近似模型求解薛定谔方程得到Ge/Si量子阱中的子能级分布,并基于迭代法数值求解泊松方程模拟计算了量子阱结构样品在不同偏压下的载流子浓度分布和C-V特性.C-V曲线上电容平台的存在是量子阱结构C-V特性的显著特征,它与量子阱结构参数有密切的关系.随着覆盖层厚度的减小,C-V曲线上平台起始点的电容值增加,并且向低电压方向移动直至其消失.随着量子阱中的掺杂浓度提高,阱中的载流子浓度也会相应增加,那就需要更高的外加电压才能耗尽阱中的载流子,因此平台宽度也就随着掺杂浓度的增加而增加.当覆盖层厚度增加时,由于电压的分压作用,使得降在量子阱上的分压相应减少,因此需要更大的外加偏压才能使阱中载流子浓度全部耗尽,这就使平台的宽度增大.同样地,当覆盖层掺杂浓度增加时,覆盖层中更多的载流子转移到阱内,也就需要更高的外加偏压才能使阱中载流子全部耗尽,平台的宽度也就随之增大.     

Ge/Si量子阱结构的C-V特性的模拟

采用有限深对称方势阱近似模型求解薛定谔方程得到Ge/Si量子阱中的子能级分布,并基于迭代法数值求解泊松方程模拟计算了量子阱结构样品在不同偏压下的载流子浓度分布和C-V特性.C-V曲线上电容平台的存在是量子阱结构C-V特性的显著特征,它与量子阱结构参数有密切的关系.随着覆盖层厚度的减小,C-V曲线上平台起始点的电容值增加,并且向低电压方向移动直至其消失.随着量子阱中的掺杂浓度提高,阱中的载流子浓度也会相应增加,那就需要更高的外加电压才能耗尽阱中的载流子,因此平台宽度也就随着掺杂浓度的增加而增加.当覆盖层厚度增加时,由于电压的分压作用,使得降在量子阱上的分压相应减少,因此需要更大的外加偏压才能使阱中载流子浓度全部耗尽,这就使平台的宽度增大.同样地,当覆盖层掺杂浓度增加时,覆盖层中更多的载流子转移到阱内,也就需要更高的外加偏压才能使阱中载流子全部耗尽,平台的宽度也就随之增大.     

GaAs/AlGaAs量子阱中电子浓度的自洽计算

应用波函数展开方法,自洽计算了调制掺杂AlGaAs/GaAs/AlGaAs量子阱中电势能分布、子能级位置、2DEG浓度分布和2DEG面浓度n_s,以及这些参数与量子阱宽度、不掺杂AlGaAs厚度等材料参数的关系.计算表明,量子阱中2DEG n_s比单异质结n_s大2倍左右,量子阱宽度在200-300A之间n_s有个最大值;量子阱太宽时,2DEG主要集中在两边异质结界面附近,变为双异质结.     

结区中存在量子阱结构样品的C—V特性分析

对不同组分、阱宽和垒宽的锗硅单量子和多量子阱样品的Ｃ－Ｖ特性及其与温度的关系进行了测量，并用数值方法解泊松方程模拟计算了单量子阱样品的Ｃ－Ｖ特性及其Ｃ－Ｖ载流子浓度分布，实验和模拟计算的结果均表明，Ｃ－Ｖ载流子浓度分布在量了阱位置有一个深度 高的峰值，它反映了被限制在阱中的载流子的积累，峰高随着量子阱异质界面的能带偏移的增加而增另，低温由于阱中载流子的热发射几率变小，阱中载流子深度的变化跟不上测试     

量子阱红外探测器掺杂阱中能级的计算

量子阱中能级位置的确定是获得量子阱红外探测器其它设计参数的基础。为了提供足够的载流子跃迁,阱层一般为重掺杂层。重掺杂使半导体材料禁带宽度变窄,从而改变量子阱中能级的位置。通过对不同温度、量子阱区不同掺杂浓度条件下的量子阱材料PL 谱进行测量,得出PL 谱峰值波长对应的电子跃迁峰值能量,它与阱中基态能级的位置有关。分别计算了考虑和不考虑禁带变窄效应时的电子跃迁峰值能量,并与实验结果相比较,可以看出考虑禁带变窄效应时与实验结果相吻合,因此掺杂量子阱区能级的计算需要考虑禁带变窄效应,这样可以较为精确的得出阱中能级的位置。     

GaAs/AlGaAs量子阱的输运特性

本文研究了低迁移率GaAs/AlGaAs量子阱的散射机制。由电导测量和Shubnikov de-Haas振荡曲线分别得到输运散射时间τ_0和弛豫时间τ_q(量子散射时间)。在GaAs/AlGaAs量子阱中,τ_0≈τ_q;而在调制掺杂的异质结中,τ_0》τ_q。用量子阱、异质结中起支配作用的散射机构不同很好地解释了实验结果。本文还研究了弱磁场下量子阱的负磁阻效应,这是磁场抑制了电子局域态的结果。     

结区中存在量子阱结构样品的C－V特性分析

对不同组分、阱宽和垒宽的锗硅单量子阱和多量子阶样品的Ｃ－Ｖ特性及其与温度的关系进行了测量，并用数值方法解油松方程模拟计算了单量子阱样品的Ｃ－Ｖ特性及其Ｃ－Ｖ载流于浓度分布．实验和模拟计算的结果均表明，Ｃ－Ｖ载流子浓度分布在量子阱位置有一个浓度较高的峰值，它反映了被限制在阱中的载流子的积累，峰高随着量子阶异质界面的能带偏移的增加而增加．低温时由于阱中载流子的热发射几率变小，阱中载流于浓度的变化跟不上测试电压的频率，造成电容值显著变小．     

GaAs/Al_xGa_(1-x)As量子阱红外探测器光谱特性的研究

采用MBE法制备了不同结构参数及不同阱中掺杂浓度的GaAs/AlxGa1-xAs量子阱红外探测器外延材料。通过对量子阱红外探测器材料特性和器件特性的实验测试及理论分析,研究了量子阱红外探测器的响应光谱特性,并通过薛定谔方程和泊松方程的求解,对掺杂对量子阱能级的影响做了研究。结果表明,由于应力导致的能带非抛物线性使得阱中能级发生了变化,从而引起吸收峰向高能方向发生了漂移,而阱中进行适度的掺杂没有对量子阱能级造成影响,光致发光谱实验结果与之吻合较好。在光电流谱的实验分析基础之上,分析了量子阱阱宽、Al组分与峰值探测波长λ的关系,为量子阱红外探测器的设计优化提供了参考。     

2 μm半导体激光器有源区量子阱数的优化设计

利用LASTIP软件理论分析了有源区量子阱数目对不同组分的InGaAsSb/AlGaAsSb 2 m半导体激光器能带、电子与空穴浓度分布以及辐射复合率等性能参数的影响。研究表明: 量子阱的个数是影响激光器件性能的关键参数, 需要综合分析和优化。量子阱数太少时, 量子阱对电子束缚能力弱, 电子在p层中泄漏明显, 辐射复合率低。量子阱数过多时, 载流子在阱内分配不均匀, p型层中电子浓度升高, 器件内损耗加大, 辐射复合率下降。结合对外延材料质量的分析, InGaAsSb/AlGaAsSb 半导体激光器有源区最优量子阱数目为2~3。该研究结果可合理地解释已有实验报道, 并为2 m半导体激光器结构设计提供理论依据。     

Carrier heating in quantum wells under optical and current injection of electron-hole pairs

Carrier heating in GaAs/AlGaAs quantum wells (QWs) under optical interband pumping in the spontaneous-emission mode has been studied. The electron temperature was determined as a function of the pumping intensity. The effect of the electric field on the photoluminescence spectrum was examined. The change in the carrier concentration with the drive current in the spontaneous- and stimulated-emission modes in InGaAsSb/InAlGaAsSb QWs was determined from electroluminescence spectra. The rise in the temperature of hot carriers, which results in the increase in the carrier concentration with the drive current, was roughly estimated.     

Super-flat (411)A interfaces and uniformly corrugated (775)B interfaces in GaAs/AlGaAs and InGaAs/InAlAs heterostructures grown by molecular beam epitaxy

Extremely flat interfaces, i.e. effectively atomically flat interfaces over a wafer-size area were realized in GaAs/AlGaAs quantum wells (QWs) grown on (411)A GaAs substrates by molecular beam epitaxy (MBE). These flat interfaces are called as “(411)A super-flat interfaces”. Besides in GaAs/AlGaAs QWs, the (411)A super-flat interfaces were formed in pseudomorphic InGaAs/AlGaAs QWs on GaAs substrates and in pseudomorphic and lattice-matched InGaAs/InAlAs QWs on InP substrates. GaAs/AlGaAs resonant tunneling diodes and InGaAs/InAlAs HEMT structures with the (411)A super-flat interfaces were confirmed to exhibit improved characteristics, indicating high potential of applications of the (411)A super-flat interfaces. High density, high uniformity and good optical quality were achieved in (775)B GaAs/(GaAs)_m(AlAs)_n quantum wires (QWRs) self-organized in a GaAs/(GaAs)_m(AlAs)_n QW grown on (775)B GaAs substrates by MBE. The QWRs were successfully applied to QWR lasers, which oscillated at room temperature for the first time as QWR lasers with a self-organized QWR structure in its active region. These results suggest that MBE growth on high index crystal plane such as (411)A or (775)B is very promising for developing novel semiconductor materials for future electron devices.     

High quality GaAs/AlGaAs quantum wells grown on (111)A substrates by metalorganic vapor phase epitaxy

Growth of GaAs and AlGaAs epitaxial layers on both (111)A and (111)13 faces of GaAs substrates was studied by the atmospheric metalorganic vapor phase epitaxy (MOVPE) technique. We show that GaAs and AlGaAs layers with excellent surface quality can be grown at relatively low temperatures and V/III ratios (600°C, 15) on the (111)A face, whereas for layers on the (111)13 face a higher growth temperature (720°C) was required. GaAs/AlGaAs quantum well (QW) structures were successfully grown for the first time on the (111)A GaAs face by the MOVPE technique. The effects of various growth conditions on the surface morphology of the epilayers were studied. For the (111)A surface a wide growth window with temperatures in the range 600°-660°C and V/III ratios varying from 15 to 45 was established for obtaining excellent surface morphology. The properties of the QWs were investigated by high resolution X-ray diffractometry, photoluminenscence and photoreflectance measurements. These measurements indicate that the QWs are of very high structural and optical quality.     

Optical properties and defects in GaAsN and InGaAsN films and quantum well structures

Photoluminescence and microcathodoluminescence spectra of thick-film GaAsN and InGaAsN structures and GaAs/InGaAsN, AlGaAs/InGaAsN quantum wells (QWs) were studied for InGaAsN layers with low nitrogen concentration of 0.35–0.5%. It is shown that in thick-film structures the bandedge luminescence intensity is strongly decreased in the row homoepitaxial GaAs, GaAsN on GaAs buffer, GaAsN, GaAs on GaAsN buffer, InGaAsN which correlates with the increasing concentration of electron traps with activation energy 0.53–0.55 eV. The type of defect bands in the thick-film structures was found to strongly depend on composition of the layers. For the GaAs/InGaAsN QW structures the intensity of luminescence was found to be more than an order of magnitude higher than in InGaAsN single films.     

Effect of GaAs/AlGaAs quantum-well structure on refractive index

We investigate the refractive index difference between the GaAs/AlGaAs quantum wells (QWs) and bulk AlGaAs. We find the refractive index difference is smaller when the electric field in the nominally intrinsic MQW region is larger, or when the well (GaAs) thickness of the QW's is larger, or when the Al fraction of the QWs is smaller. The maximum refractive index difference between the 100 Å GaAs/100 Å Al_0.2Ga_0.8As QWs at zero electric filed and bulk Al_0.1Ga_0.9As is about 0.044. Even with a small refractive index difference of 0.0132, the OFF-state reflectance of a normally-off MQW modulator at the designed photon wavelength will increase from the desired value of 0% to 90% when the reflectivity of the bottom mirror is 0.99     

GaAs异质面太阳电池光谱响应和暗J-V特性的拟合分析

本文用LPE法制备了GsAs异质面太阳电池,测量了电池的光谱响应(SR)和暗J—V特性,推导了它们的理论公式,用这些理论公式对测量值进行了曲线拟合。从SR拟合求得三个区的少子扩散长度、AlGaAs层厚度、结深、前表面和界面复合速度等七个结构参数。从暗∫—V特性拟合求得扩散电流密度分量、复合电流密度分量、结品质因子和串并联电阻等五个电学参数。最后分析拟合结果,讨论了这些参数对电池效率的影响,提出提高效率的方法。     

注入Ga离子的GaAs／AlGaAs量子阱中界面混合的光荧光研究

用注入Ｇａ离子ＧａＡｓ／ＡｌＧａＡｓ量子阱在快速热退火中大大加快了异质结界面的互扩散，表现在ＰＬ光谱中量子阱峰值能量有３０～９０ｍｅＶ的兰移．发现兰移大小同注入损伤程度、退火的温度及时间有关，并得到快速退火中的互扩散系数Ｄ约为１０－１５～１０－１７ｃｍ２／ｓ     

Room-temperature electroreflectance and reflectance of a GaAs/AlGaAs single quantum well structure

The room-temperature electroreflectance and reflectance of a GaAs/AlGaAs single quantum well (QW) structure are studied. An oscillatory behavior of the electroreflectance signal as a function of the thickness of the top AlGaAs barrier layer is observed. The experimental data are analyzed using a dielectric function of QWs and the transfer matrix method for multilayer systems. This analysis allows the determination of the parameters of the QW and the barrier layers.     

量子阱平面光学各向异性的偏振差分反射谱研究

在室温下用偏振差分反射谱技术观察到了 Ga As/Al Ga As、In Ga As/Ga As和 In Ga As/In P三种量子阱材料的平面光学各向异性。我们发现 Ga As/Al Ga As量子阱 1 h→ 1 e跃迁的偏振度与阱宽成反比 ,与 In Ga As/In P量子阱的报道结果类似。 Ga原子偏析引起的界面不对称可以很好地解释这种行为。与之相反 ,In Ga As/Ga As量子阱的光学各向异性倾向于与阱宽成正比。目前还不能很好地解释这种现象。     

MOVPE growth of AlGaAs/GaInP diode lasers

GaAs-based diode lasers for emission wavelengths between 800 nm and 1060 nm with AlGaAs-cladding and GaInP-waveguide layers were grown by MOVPE. For wavelengths above 940 nm broad area devices with InGaAs QWs show state-of-the-art threshold current densities. Ridge-waveguide lasers fabricated by selective etching achieve 200 mW CW monomode output powers. (In)GaAsP QW-based diode lasers with an emitting wavelengths around 800 nm suffer from problems at the upper GaInP/AlGaAs interface. Asymmetric structures with a lower AlGaAs/GaInP and an upper AlGaAs/AlGaAs waveguide not only avoid this interface but also offer better carrier confinement. Such structures show very high slope efficiencies and a high T₀. Maximum output powers of 7 W CW are obtained from 4 mm long devices.