We have investigated the transport properties of a field-effect transistor (FET) with a composite quantum well, which consists of two adjacent semiconductor quantum wells, GaSb and InAs, sandwiched by AlSb barriers. This FET shows a novel V-shaped transfer characteristic, which is a direct result of the switching between electron and hole channels.

The mechanism of the negative persistent photoconductivity (NPPC) in InAs/AlSb single quantum wells is discussed. The molecular beam epitaxy grown single InAs quantum well sample is made into Hall bars with the substrate as the backgate. Using the newly designed buffer, the gate bias can deplete or enhance the two-dimensional electrons in the InAs quantum well without substantial gate leakage current. Based on the 4.2 K magnetoresistance data, and the fact that the trapped electrons can be redistributed by gate bias, we conclude that the NPPC effect at low temperatures is a result of the capture of photoexcited electrons by ordinary, deep donors in AlSb. Numerical modeling using physical assumptions can quantitatively explain our experimental observation, and the calculated AlSb donor energy is 0.41±0.05 eV above the AlSb valence band maximum, with 4×1016/cm3 to 1017/cm3 in concentration. The previously discussed DX-center-like characteristic of deep levels in AlSb, i.e., lattice-relaxation with a relatively high activation energy, is not evidenced in this work.

This study employed the approach of non-linear autoregressive moving average model with exogenous inputs (NARMAX) to analyze the dynamics of a Permanent Magnet Synchronous Motor (PMSM). The non-linearity in PMSM including cogging force, reluctance force and force ripple is difficult to estimate. By using the NARMAX approach, thrust-speed relationship and thrust-position relationship could be analyzed by identifying both time and frequency domain models of the system. The frequency domain analysis is studied by mapping the discrete-time NARMAX models into generalized frequency response functions (GFRFs) to reveal the non-linear coupling between the various input spectral components and the energy transfer mechanisms in the system. From the results, the interpretation of the higher-order GFRFs has been comprehensively studied and non-linear effects have been related to the physical models of the systems.