GaAs/AlAs短周期超晶格的静压光致发光研究

在室温和液氮温度下对不同层厚的GaAs/AlAs短周期超晶格在0—50kbar范围内进行了静压光致发光研究。在导带最低能级为类Γ态能级(Ⅰ类超晶格)和类X态能级(Ⅱ类超晶格)两种情况下都得到了类Γ态能级与类X态能级差随层厚的变化。首次直接观察到室温、常压下(GaAs)_(11)(AlAs)_(11)超晶格中类Γ态能级与类X态能级发生交叉。从发光峰的强度随压力的变化求得室温下在类Γ态能级与类X态能级恰好交叉的压力下类X态电子和类Γ态电子到价带空穴的跃迁几率之比从(GaAs)_(17)(AlAs)_(17)的1.4×10~(-4)逐渐增加到(GaAs)_6(AlAs)_6的4.6×10~(-3)。表明类Γ态和类X态间的混合较弱。对实验结果进行了简短的讨论。     

50周期的In_(0.3)Ga_(0.7)As/GaAs应变超晶格的生长

在本文，我们用一个低组分的InxGa(1-x)As缓冲层（x～0．01），有效地限制了50周期的In0.3Ga0．7As／GaAs应变超晶格本身弛豫所产生的位错，X射线双晶衍射测量结果表明使用这样缓冲层的超晶格质量明显改善，可以观察到12级卫星峰，而在没有这个缓冲层的样品上只能观察到3个衍射卫星峰．透射电子显微镜上观察到产生的位错被限制在这个缓冲层中或弯曲进入了衬底而没有进入所需要的外延层。     

非对称GaAs／Al0.3Ga0.7As双量子阱的光学特性和光学非线性

报道用光调制反射谱和光致发光方法对非对称的GaAs/Al_(0.3)Ga_(0.7)As耦合双量子阱研究的实验结果。在300K和77K下测量了光调制反射谱,对实验结果的线形拟合确认了在双量子阱中分别对应子能级11H、11L、13H、22H等的跃迁,并与理论计算结果作了比较。以氩离子激光器488nm激发测量了双量子阱中基态(n=1)荧光峰强度随激发光密度的变化,研究了其非线性效应。用632.8nm激光在弱激发下测量了3.8～300K范围内相应荧光峰随温度的变化,对实验结果作了分析讨论。     

GaAs/Ga_(0.7)Al_(0.3)As超晶格中场致激子峰展宽机制的研究

我们利用光电流谱在10—300K温度范围内研究了GaAs/Ga_(0.7)Al_(0.3)As(35A/35A)短周期超晶格中的Wannier-Stark效应,实验发现0h激子峰随电场的增加而展宽。我们把激子峰的场致展宽归因于:Wannier-Stark局域化使界面的涨落对电子态的散射增加而使激子峰展宽。这种与电场有关的散射机制会使L.Esaki和Tsu所预期的超晶格的负微分电阻效应减小。     

δ掺杂GaAs超晶格的辐射跃迁

低温下观察了弱耦合δ掺杂ＧａＡｓ超晶格的辐射复合发光．实验结果表明：除观察到基态的复合发光外,还观察到激发态的复合发光．基于有效质量近似理论,计算了能带结构和发光光谱,理论结果与实验结果符合得很好．     

InAs/GaSb Ⅱ型超晶格的拉曼和光致发光光谱

采用分子束外延(MBE)技术,在GaSb(100)衬底上外延生长晶体结构完整和表面平整的Ⅱ型超晶格InAs(1.2 am)/GaSb(2.4 am).拉曼光谱表明:随着温度从70 K升高至室温,由于热膨胀作用和光声子散射过程中的衰减,超晶格纵光学声子拉曼频移向低波数方向移动5 cm-4,频移温度系数约为0.023 cm-1/K.光致发光(PL)峰在2.4～2.8 μm,由带间辐射复合和束缚激子复合构成,2.55 μm PL峰随温度变化(15～150 K)发生微小红移,超晶格中InAs电子带与GaSb空穴带带间距随温度变化比体材料的禁带宽度小.PL发光强度在15～50 K随温度升高而升高,在60～150 K则相反,并在不同温度段表现出不同的温度依赖关系.     

ZnSe_(1-x)S_x-ZnSe应变超晶格结构光致发光研究

本文研究了ZnSe_(1-x)S_x-ZnSe应变超晶格结构在77K时自由激子的光致发光的线型随激发光密度、势阱涨落、势垒高度的涨落及各层厚对超晶格发光峰E_(?)的影响,并利用Kronig-Penney模型计算了n=1的激子峰值能量与势阱宽度、势垒高度涨落的关系.首次从实验上分析了77-250K温度范围内ZnSe_(1-x)S_x-ZnSe应变超晶格激子发光的线型与各参量的密切关系.     

Characteristics of Si3N4/GaAs metal-lnsulator-semiconductor interfaces with coherent Si/Al0.3Ga0.7As interlayers

Si₃N₄/GaAs metal-insulator-semiconductor (MIS) interfaces with Si(10Å)/ Al_0.3Ga_0.7As (20Å) interface control layers have been characterized using capacitance-voltage (C-V) and conductance methods. The structure was in situ grown by a combination of molecular beam epitaxy and chemical vapor deposition. A density of interface states in the 1.1 × 10¹¹ eV^-1 cm^-2 range near the GaAs midgap as determined by the conductance loss has been attained with an ex situ solid phase annealing of 600°C in N₂ ambient. A dip quasi-static C-V demonstrating the inversion of the minority-carrier verifies the decent interface quality of GaAs MIS interface. The hysteresis and frequency dispersion of the MIS capacitors were lower than 100 mV, some of them as low as 50 mV under a field swing of about ±2 MV/cm. The increase of the conductance loss at higher frequencies was observed when employing the surface potential toward conduction band edge, suggesting the dominance of faster traps. Self-aligned gate depletion mode GaAs metal-insulator-semiconductor field-effect transistors with Si/Al_0.3Ga_0.7As interlayers having 3 μm gate lengths exhibited a transconductance of about 114 mS/mm. The present article reports the first application of pseudomorphic Si/ Al_0.3Ga_0.7As interlayers to ideal GaAs MIS devices and demonstrates a favorable interface stability.     

掺杂GaAs／AlGaAs超晶格的激发态向受主中心跃迁的发光

在室温下测量了GaAs／Al0.28Ga0.72As超晶格的光致发光，发现在波长λ=764nm处存在一较强的发光峰。理论分析表明，此峰是量子阱阱口附近能级上的电子与受主杂质上的空穴复合发光。实验还观测到在λ=824nm和829nm处分别存在一发光峰。分析表明，λ=829nm和λ=824mn处的发光峰分别为激子发光和量子阱中基态电子与基态重空穴的复合发光；理论计算值与实验结果符合得很好。     

Photoluminescence studies of In0.7Al0.3As/In0.75Ga0.25As/In0.7Al0.3As metamorphic heterostructures on GaAs substrates

The influence of the design of the metamorphic buffer of In_0.7Al_0.3As/In_0.75Ga_0.25As metamorphic nanoheterostructures for high-electron-mobility transistors (HEMTs) on their electrical parameters and photoluminescence properties is studied experimentally. The heterostructures are grown by molecular-beam epitaxy on GaAs (100) substrates with linear or step-graded In _x Al_{1 ? x} As metamorphic buffers. For the samples with a linear metamorphic buffer, strain-compensated superlattices or inverse steps are incorporated into the buffer. At photon energies ?ω in the range 0.6–0.8 eV, the photoluminescence spectra of all of the samples are identical and correspond to transitions from the first and second electron subbands to the heavy-hole band in the In_0.75Ga_0.25As/In_0.7Al_0.3As quantum well. It is found that the full width at half-maximum of the corresponding peak is proportional to the two-dimensional electron concentration and the luminescence intensity increases with increasing Hall mobility in the heterostructures. At photon energies ?ω in the range 0.8–1.3 eV corresponding to the recombination of charge carriers in the InAlAs barrier region, some features are observed in the photoluminescence spectra. These features are due to the difference between the indium profiles in the smoothing and lower barrier layers of the samples. In turn, the difference arises from the different designs of the metamorphic buffer.     

High uniformity of Al0.3Ga0.7As/ln0.15Ga0.85As doped-channel structures grown by molecular beam epitaxy on 3″ GaAs substrates

Al_0.3Ga_0.7As/ln_0.15Ga_0.85As doped-channel structures were grown by molecular beam epitaxy on 3″ GaAs substrates. The uniformities of electrical and optical properties across a 3″ wafer were evaluated. A maximum 10% variation of sheet charge density and Hall mobility was achieved for this doped-channel structure. A1 μm long gate field-effect transistor (FET) built on this layer demonstrated a peak transconductance of 350 mS/mm with a current density of 470 mA/mm. Compared to the high electron mobility transistors, this doped-channel FET provides a higher current density and higher breakdown voltage, which is very suitable for high-power microwave device applications.     

Investigation of DX centers in modulation-doped field-effect transistor-type Al0.3Ga0.7As/GaAs heterostructures using a fourier-transform deep level transient spectroscopy system

Al_0.3Ga_0.7As:Si/GaAs modulation-doped field-effect transistor-type heterostructures were grown using two different growth temperatures (500 and 620°C) and three doping modes (δ-doping, pulse-doping, and uniform-doping). Deep level transient spectroscopy (DLTS) measurements were performed on these structures using a new Fourier-analysis method. Up to four DLTS peaks, related to the different possible configurations of the nearest Al and Ga neighbors around each DX site, were observed. Both the growth temperature and the doping-mode are found to affect the DLTS spectra, in particular the number of observed peaks and their width. These results are interpreted in terms of the different mobilities of the Si doping atoms on the surface during growth.     

Hydrogen plasma passivation of bulk GaAs and Al0.3Ga0.7As/GaAs multiple-quantum-well structures on Si substrates

Hydrogen (H) plasma passivation effects on GaAs grown on Si substrates (GaAs on Si) are investigated in detail. H plasma exposure effectively passivates both the shallow and deep defects in GaAs on Si, which improves both the electrical and optical properties. It was found that the minority carrier lifetime is increased and the deep level concentration is decreased by the H plasma exposure. In addition, after H plasma exposure, room temperature photoluminescence (PL) for Al_0.3Ga_0.7As/GaAs multiple-quantum-well (MQW) on Si is enhanced with a decrease in the spectral width.     

Electrical characteristics of low temperature-Al0.3Ga0.7As

In this work, we present electrical characterizations of n⁺ GaAs/low temperature (LT)-Al_0.3Ga_0.7As/n⁺ GaAs resistor structures in which the LT layers are grown at nominal substrate temperatures of 250 and 300°C. The resistivity and V_tfl parameters of these LT-Al_0.3Ga_0.7As layers are compared with those of LT-GaAs and Al_0.3Ga_0.7As grown at a normal growth temperature of 720°C. Low-temperature Al_0.3Ga_0.7As layers exhibit resistivities as high as 10¹² ohm-cm, nearly four orders of magnitude higher than that of LT-GaAs, and V_tfl values as high as 45 V, over twice that of LT-GaAs. We also find that the LT-Al_0.3Ga_0.7As materials grown at 250 and 300°C appear to show opposite and contradictory trends with respect to resistivity and V_tfl. We propose that this result can be explained by residual hopping conduction in the 250°C material. Temperature dependent conductivity measurements confirm the presence of a hopping mechanism in LT-Al_0.3Ga_0.7As grown at 250°C and yield activation energies of 0.77 and 0.95 eV for LT-GaAs and LT-Al_0.3Ga_0.7As, respectively.     

GaAs/Al0.3Ga0.7As 量子阱红外探测器光谱特性研究

采用金属有机物化学气相沉积法(MOCVD)生长GaAs/Al0.3Ga0.7As量子阱材料,制备300 m300 m台面,内电极压焊点面积为20 m20 m,外电极压焊点面积为80 m80 m单元量子阱器件两种。利用傅里叶光谱仪对1#,2#样品进行77K液氮温度光谱响应测试。实验结果显示1#,2#样品峰值响应波长分别为8.43 m,8.32 m,与根据薛定谔方程得到器件理论峰值波长8.5 m间误差分别为1.0%,2.1%。实验结果说明MOCVD技术可以满足QWIP生长制备工艺要求,且器件电极压焊点位置与面积大小对器件峰值波长影响不大,而对峰值电流有一定影响。     

Hot-hole lateral transport in a two-dimensional GaAs/Al0.3Ga0.7As structure

A narrow peak at the leading edge of the current pulse was found in samples of p-GaAs/Al_0.3Ga_0.7As structures subjected to a high electric field. An analysis of the shape and height of the peak as a function of the electric field, as well as the field redistribution along the sample, allows us to conclude that domain instability exists under these conditions. It is also shown that the energy of holes heated in moderate electric fields can significantly exceed the optical phonon energy.     

Persistent photo-conductance and photoquenching of selectively doped Al0.3Ga0.7As GaAs/heterojunctions

The dependence on photon energy of the persistent photoconductivity (PPC) in selectively doped high mobility Al_0.3Ga_0.7As—GaAs heterostructures has been measured at temperatures below 80 K. A decrease in conductivity due to light exposure at one wavelength after exposure to light at another wavelength — photo-quenching — is also found. It is concluded that deep centers in GaAs and AlGaAs other than the DX center in AlGaAs are mainly responsible for PPC.