Han-Chun Liu

Low-frequency noise gain and photocurrent gain in quantum well infrared photodetectors

We present a theory of the low-frequency noise gain gn and photocurrent gain gp in quantum well infrared photodetectors (QWIPs). Expressions for gn and gp in terms of QW capture probability pc and number of QWs N are obtained. These expressions are valid for any number of QWs N⩾1 and capture probability 0<pc⩽1. The difference of noise gain from photocurrent gain is due to the discrete structure of generation–recombination centers (QWs) in QWIP. The ratio gn/gp ranges from 0.5 (for pc→1) to 1 (for pc→0). QWIP is well described by a conventional photoconductor theory in the case of low capture probability pc→1, which corresponds to practical QWIPs. The assumptions of the model are discussed in detail, and a comparison with previously published results is made.

Combined study of microwave-power/linear-polarization dependence of the microwave-radiation-induced magnetoresistance oscillations in GaAs/AlGaAs devices

We report the results of a combined microwave polarization-dependence and power-dependence study of the microwave-radiation-induced magnetoresistance oscillations in high mobility GaAs/AlGaAs heterostructure devices at liquid helium temperatures. The diagonal resistance was measured with the magnetic field fixed at the extrema of the radiation-induced magnetoresistance oscillations, as the microwave power was varied at a number of microwave polarization angles. The results indicate a nonlinear relation between the oscillatory peak or valley magnetoresistance and the microwave power, as well as a cosine square relation between the oscillatory peak or valley magnetoresistance and the microwave polarization angle. The main features are briefly compared with the predictions of existing models.

Mutual influence between current-induced giant magnetoresistance and radiation-induced magnetoresistance oscillations in the GaAs/AlGaAs 2DES.

Radiation-induced magnetoresistance oscillations are examined in the GaAs/AlGaAs 2D system in the regime where an observed concurrent giant magnetoresistance is systematically varied with a supplementary dc-current, Idc. The Idc tuned giant magnetoresistance is subsequently separated from the photo-excited oscillatory resistance using a multi-conduction model in order to examine the interplay between the two effects. The results show that the invoked multiconduction model describes the observed giant magnetoresistance effect even in the presence of radiation-induced magnetoresistance oscillations, the magnetoresistance oscillations do not modify the giant magnetoresistance, and the magnetoresistance oscillatory extrema, i.e., maxima and minima, disappear rather asymmetrically with increasing Idc. The results suggest the interpretation that the Idc serves to suppress scattering between states near the Fermi level in a strong magnetic field limit.

Frequency-dependent polarization-angle-phase-shift in the microwave-induced magnetoresistance oscillations

Linear polarization angle, θ, dependent measurements of the microwave radiation-induced oscillatory magnetoresistance, Rxx, in high mobility GaAs/AlGaAs 2D electron devices have shown a θ dependence in the oscillatory amplitude along with magnetic field, frequency, and extrema-dependent phase shifts, θ0. Here, we suggest a microwave frequency dependence of θ0(f) using an analysis that averages over other smaller contributions, when those contributions are smaller than estimates of the experimental uncertainty.

Coherent backscattering in quasi-ballistic ultra-high mobility GaAs/AlGaAs 2DES

A small and narrow negative-magnetoresistance (MR) effect that appears about null magnetic field over the interval −0.025 ≤ B ≤ 0.025 T in magnetotransport studies of the GaAs/AlGaAs 2D system with μ ≈ 107cm2/Vs is experimentally examined as a function of the sample temperature, T. The temperature dependent magnetoresistance data were fit using the Hikami et al. theory, without including the spin-orbit correction, to extract the inelastic length, li, which decreases rapidly with increasing temperature. It turns out that li < le, where le is the elastic length, for all T. Thus, we measured the single particle lifetime, τs, and the single particle mean free path ls = vFτs. A comparison between li and ls indicates that li > ls. The results suggest that the observed small and narrow magnetoresistance effect about null magnetic field could be a manifestation of coherent backscattering due to small angle scattering from remote ionized donors in the high mobility GaAs/AlGaAs 2DES.

Evolution of the frequency-dependent polarization-angle phase-shift in the microwave radiation-induced magnetoresistance oscillations

Linear polarization angle,

Millimeter wave radiation-induced magnetoresistance oscillations in the high quality GaAs/AlGaAs 2D electron system under bichromatic excitation

\theta

Study of the angular phase shift in the polarization angle dependence of the microwave induced magnetoresistance oscillations

, dependent measurements of the microwave radiation-induced oscillatory magnetoresistance,

Angular phase shift in polarization-angle dependence of microwave-induced magnetoresistance oscillations

R_{xx}

Interaction of microwave radiation with the high mobility two-dimensional electron system in GaAs/AlGaAs heterostructures

, in high mobility GaAs/AlGaAs 2D electron devices have shown a