Helicity-dependent photocurrent (HDPC) has been observed in epitaxial thin films of the three-dimensional topological insulator ${\mathrm{Sb}}_2{\mathrm{Te}}_3$ with a thickness of 7, 20, and 30 quintuple layers (QLs). By analyzing the incident angle dependence of the HDPC, we successfully extract the photocurrent induced by the circular photon drag effect (CPDE) of even parity from the HDPC. It is found that the circular photogalvanic effect (CPGE) is larger than the odd parity of CPDE. The CPGEs of the top and bottom surface states are successfully distinguished at room temperature. As the thickness of the ${\mathrm{Sb}}_2{\mathrm{Te}}_3$ film is increased from 7 to 20 QLs, the dominant contribution of the CPGE current switches from the top surface states to the bottom surface states under the front illumination of a 1064-nm laser. Additionally, it is found that the CPGE currents of the 20- and 30-QL samples reverse sign when the temperature is increased from 77 to 300 K, which may be attributed to the HDPC current induced by the combined action of the inverse spin Hall effect and the vertical thermoelectric effect overwhelming the CPGE current at low temperature in the samples. The insights we obtained are significant for engineering optospintronic devices based on three-dimensional topological insulators with a strong thermoelectric effect.

For InAs/GaAs(001) quantum dot (QD) system, the wetting layer (WL) evolution and its temperature dependence were studied using reflectance difference spectroscopy and were analyzed with a rate equation model. WL thicknesses showed a monotonic increase at relatively low growth temperatures but showed an initial increase and then decrease at higher temperatures, which were unexpected from a thermodynamic understanding. By adopting a rate equation model, the temperature dependence of QD formation rate was assigned as the origin of different WL evolutions. A brief discussion on the indium desorption was given. Those results gave hints of the kinetic aspects of QD self-assembly.

The photocurrent spectra of inter-band photoinduced anomalous Hall effect (AHE) in insulating InGaAs/AlGaAs quantum wells have been observed at room temperature. The AHE current changes linearly with longitudinal electric fields. The anomalous Hall conductivity corresponding to excitonic state 1HH-1E (the first valence subband of heavy hole to the first conduction) has the same sign with that of excitonic state 1LH-1E, while the sign inverses when the photon energy is larger than the excitonic state 1LH-1E. The reason for this interesting phenomenon has been discussed. Due to the strong Rashba spin-orbit coupling in this perfect crystal, the photoinduced AHE is supposed to be intrinsic.

Catalyst-free, vertical array of InAs nanowires (NWs) are grown on Si (111) substrate using MOCVD technique. The as-grown InAs NWs show a zinc-blende crystal structure along a < 111 > direction. It is found that both the density and length of InAs NWs decrease with increasing growth temperatures, while the diameter increases with increasing growth temperature, suggesting that the catalyst-free growth of InAs NWs is governed by the nucleation kinetics. The longitudinal optical and transverse optical (TO) mode of InAs NWs present a phonon frequency slightly lower than those of InAs bulk materials, which are speculated to be caused by the defects in the NWs. A surface optical mode is also observed for the InAs NWs, which shifts to lower wave-numbers when the diameter of NWs is decreased, in agreement with the theory prediction. The carrier concentration is extracted to be 2.25 × 10¹⁷ cm^-3 from the Raman line shape analysis. A splitting of TO modes is also observed. PACS: 62.23.Hj; 81.07.Gf; 63.22.Gh; 61.46.Km

X-ray photoelectron spectroscopy has been used to measure the valence band offset of the InN/BaTiO₃ heterojunction. It is found that a type-I band alignment forms at the interface. The valence band offset (VBO) and conduction band offset (CBO) are determined to be 2.25 ± 0.09 and 0.15 ± 0.09 eV, respectively. The experimental VBO data is well consistent with the value that comes from transitivity rule. The accurate determination of VBO and CBO is important for use of semiconductor/ferrroelectric heterojunction multifunctional devices.