Phase diagram of quantum Hall breakdown and nonlinear phenomena for InGaAs/InP quantum wells

Abstract

We investigate non-linear magneto-transport in a Hall bar device made from a strained In-GaAs/InP quantum well: a material system with attractive spintronic properties. From extensive maps of the longitudinal differential resistance (rxx) as a function of current and magnetic (B-) field phase diagrams are generated for quantum Hall breakdown in the strong quantum Hall regime reaching filling factor ν=1. By careful illumination the electron sheet density (n) is incremented in small steps and this provides insight into how the transport characteristics evolve with n. We explore in depth the energetics of integer quantum Hall breakdown and provide a simple picture for the principal features in the rxx maps. A simple tunneling model that captures a number of the characteristic features is introduced. Parameters such as critical Hall electric fields and the exchange-enhanced g-factors for odd-filling factors including ν=1 are extracted. A detailed examination is made of the B-field dependence of the critical current as determined by two different methods and compiled for different values of n. A simple rescaling procedure that allows the critical current data points obtained from rxx maxima for even-filling to collapse on to a single curve is demonstrated. Exchange-enhanced g-factors for odd-filling are extracted from the compiled data and are compared to those determined by conventional thermal activation measurements. The exchange-enhanced g-factor is found to increase with decreasing n.

Effects of biased and unbiased illuminations on two-dimensional electron gases in dopant-free GaAs/AlGaAs

“…7(b)] are stable for more than 3 days after illumination, thus demonstrating persistent photoconductivity and confirming the sample is in the equilibrium regime. Had a large number of d 0 or DX 0 states decayed to a charged state (d + or DX − ) during that time, the mobility would have decreased, 8 as is indeed observed in modulation-doped GaAs 2DEGs [60]. Thus, neutral metastable states are not the primary cause for the +30% mobility increase observed in sample J in Fig.…”

“…The photoexcited electrons are captured in the GaAs conducting channel. Incremental illumination in small doses (intensity × duration) can be used for precise tuning of the carrier concentration in modulation-doped ungated heterostructures [8]. Aside from acting on DX centers, illumination may also have other effects, such as activating or deactivating unintentional impurity atoms in the transport channel itself.…”

“…In typical modulation-doped 2DEGs, the d 0 state's lifetime depends on the tunneling rate through the AlGaAs barrier separating the impurity from the 2DEG 8. In fact, there is a very small increase (by + 0.6%) in the mobility over 3 days for n 2D ≈ 2.846 × 10 11 cm −2 and n 2D ≈ 2.203 × 10 11 cm −2 (but not for n 2D ≈ 1.557 × 10 11 cm −2 ).…”

Effects of biased and unbiased illuminations on dopant-free GaAs/AlGaAs 2DEGs

“…In both cases, the photo-excited electrons are captured in the GaAs conducting channel. Incremental illumination in small doses (intensity × duration) can be used for precise tuning of the carrier concentration in modulation-doped ungated heterostructures [7]. Aside from acting on the dopants (DX centers), illumination may also have other effects, such as activating or deactivating unintentional impurity atoms, or affecting the overall electric field in the crystal.…”