Theory of terahertz-photocurrent resonances in miniband superlattices

The currents of de and ac components and their phase-angle cosines for a superlattice under a direct bias and alternating field are calculated with the balance equations. It is found that the de currents as functions of the direct field show resonance peaks at the fields corresponding to the Bloch frequency equal to n omega. With increasing alternating field intensity the resonance peaks of higher harmonic increase, and simultaneously the first peak caused by the de field decreases. The results are in good agreement with the experimental results, indicating that this resonance can be understood in terms of electron acceleration within the miniband, i.e., it is a bulk superlattice effect, rather than caused by the electric-field localization mechanism (Wannier Stark ladder). The phase-angle cosine for the first harmonic cos phi(1) becomes negative when the Bloch frequency increases to be larger than the frequency of the ac field omega, and it also shows resonance peaks at the resonance frequencies n omega. The negative cos phi(1) may cause the energy transferred to the alternating field, i.e., oscillation of the system.

CONTINUUM-THEORIES OF OPTICAL PHONONS AND POLARITONS IN SUPERLATTICES - A BRIEF CRITIQUE - COMMENT

The so-called hydrodynamic (HD) model on optical-phonon modes in superlattices is critically examined. Contrary to the HD model, a comparison between TM polaritons and the Fuchs-Kliewer-type interface modes has shown that the Fuchs-Kliewer interface modes do possess Frohlich potentials.

WANNIER LOCALIZATION IN GAAS/GAALAS SUPERLATTICES UNDER ELECTRIC-FIELD

We have studied the Wannier-Stark effect in GaAs/GaAlAs short-period superlattices under applied electric field perpendicular to the layers by room- and low-temperature photocurrent measurements. The changes in the transition intensities with biasing are well fitted to a theoretical calculation based on the finite Kronig-Penney model on which the potential of an applied electric field is superposed. With increasing electric field, the 0h peak grows to a maximum while the -1h and +1h peaks monotonousely decrease. By a comparison of the spectra measured at different temperatures, the two peaks in the room temperature photocurrent spectra at relatively low electric field (1.0 X 10(4) V/cm) are identified to be caused by the Wannier localization effect instead of saddle-point excitons.

Effective-mass theory for InAs/GaAs strained superlattices

By using the recently developed exact effective-mass envelope-function theory, the electronic structures of InAs/GaAs strained superlattices grown on GaAs (100) oriented substrates are studied. The electron and hole subband structures, distribution of electrons and holes along the growth direction, optical transition matrix elements, exciton states, and absorption spectra are calculated. In our calculations, the effects due to the different effective masses of electrons and holes in different materials and the strain are included. Our theoretical results are in agreement with the available experimental data.

A voltage-controlled tunable two-color infrared photodetector using GaAs/AlAs/GaAlAs and GaAs/GaAlAs stacked multiquantum wells

A voltage-controlled tunable two-color infrared detector with photovoltaic (PV) and photoconductive (PC) dual-mode operation at 3-5 mu m and 8-14 mu m using GaAs/AlAs/AlGaAs double barrier quantum wells (DBQWs) and bound-to-continuum GaAs/AlGaAs quantum wells is demonstrated. The photoresponse peak of the photovoltaic GaAs/AlAs/GaAlAs DBQWs is at 5.3 mu m, and that of the photoconductive GaAs/GaAlAs quantum wells is at 9.0 mu m. When the two-color detector is under a zero bias, the spectral response at 5.3 mu m is close to saturate and the peak detectivity at 80 K can reach 1.0X10(11) cmHz(1/2)/W, while the spectral photoresponsivity at 9.0 mu m is absolutely zero completely. When the external voltage of the two-color detector is changed to 2.0 V, the spectral photoresponsivity at 5.3 mu m becomes zero while the spectral photoresponsivity at 9.0 mu m increases comparable to that at 5.3 mu m under zero bias, and the peak detectivity (9.0 mu m) at 80 K can reach 1.5X10(10) cmHz(1/2)/W. Strictly speaking, this is a real bias-controlled tunable two-color infrared photodetector. We have proposed a model based on the PV and PC dual-mode operation of stacked two-color QWIPs and the effects of tunneling resonance with narrow energy width of photoexcited electrons in DBQWs, which can explain qualitatively the voltage-controlled tunable behavior of the photoresponse of the two-color infrared photodetector. (C) 1996 American Institute of Physics.

DETERMINATION OF THE X-CONDUCTION-SUBBAND ENERGIES IN TYPE-II GAAS/ALAS/GAAS QUANTUM-WELL BY DEEP-LEVEL TRANSIENT SPECTROSCOPY

Using deep level transient spectroscopy (DLTS) the X conduction-subband energy levels in an AlAs well sandwiched by double GaAs layers were determined. Calculation gives eight subbands in the well with well width of 50 Angstrom. Among them, five levels and the other three remainders are determined by using the large longitudinal electron effective mass m(1)(1.1m(0)) and transverse electron effective mass m(t)(0.19m(0)) at X valley, respectively. Two subbands with the height energies were hardly detectable and the other six ones with lower energies are active in the present DLTS study. Because these six subbands are close to each other, we divided them into three groups. Experimentally, we observed three signals induced from the three groups. A good agreement between the calculation and experiment was obtained. (C) 1995 American Institute of Physics.

GaAs、AlAs、DBR反应离子刻蚀速率的研究

采用BCl_3和Ar作为刻蚀气体对GaAs、AlAs、DBR反应离子刻蚀的速率进行了研究，通过控制反应的压强、功率、气体流量和气体组分达到对刻蚀速率的控制。实验结果表明

流体静压力下窄势垒GaAs/AlAs超晶格的低温纵向输运

研究了77K温度下掺杂弱耦合GaAs/AlAs窄垒超晶格在流体静压力下的垂直输运，发现其输运性质与宽垒超晶格有很大不同。当在压力下AlAs垒层中的X基态子能级降至E_(Γ1)子能级和E_(Γ2)子能级中间或更低能量位置时，未观察到Γ-Γ共振隧穿到Γ-X共振隧穿的转 变,I-V曲线上的平台并未随压力增大而收缩，反而稍有变宽。同时，平台电流随压力增大而增加，直到与E_(Γ1)-E(Γ1)共振峰电流相当。认为，由于垒层很薄，Γ电子隧穿通过垒层的几率很高，E_(Γ1)-E_(Γ1)共振峰显著高于E_(Γ1)-E_(X1)共振峰，因此，高场畴区内的输运机制在压力下仍由Γ-Γ级联共振隧穿控制。但由于X子级能随压力升高而降低，导致隧穿通过Γ-X垒的几率增加，非共振背景电流增大。由于电流连续性条件的要求，高场区的电场强度增强，导致在高压力下平台宽度随压力稍微变宽。

GaAs／AlAs超晶格纵向电流与阱间偏压的动态关系

于2010-11-23批量导入

低温和高压条件对GaAs/AlAs弱耦合超晶格电场畴形成的影响

于2010-11-23批量导入

GaAs/AlAs脊形量子线的光学研究

利用分子束外延技术，在GaAs两个(113)晶面的脊形交接处制备了量子线。在低温PL谱上，观测到量子线的发光峰。通过微区、变温和偏振的发光测量，证实了量子限制效就和一维量子线在上述结构中的存在。

GaAs/AlAs超晶格室温下的输运机制及自维持场畴振荡

在GaAs/AlAs(10nm/2n,)弱耦合掺杂超晶格I-V曲线的第一个平台上，首先观测到了直流偏压下的室温微波振荡。观测到的最高振荡频率可达142MHz。这种由级联隧穿引起的振荡在测试温度范围14～300K内始终存在。经 分析发现，由于垒怪公有2nm,电子隧穿通过垒层的几率很高，相比之下，电子越过势垒而产生的热离子发射电流要小得多。在温度低于300K时，超晶格内的纵向输运机制是级联共振隧穿和声子辅助隧穿。这是室温仍然能观测到自维持振荡的主要原因，由于实现振荡所施加的偏压比较低(在室温下偏压范围大约为0.5～2V),有利于抑制室温下通过X谷的热离子发射电流。