Rashba Spin Orbit Coupling And Circular Photogalvanic Effect Of Two-dimensional Electron Gas In Al_xGa_1-xN/GaN Heterostructures

The research about GaN-based wide-band gap semiconductors in semiconductor spintronics has been attracting more and more attentions. In this dissertation, we introduce the semiconductor spintronics and current research state of GaN-based semiconductors in this field. The most attention has been paid on the two-dimensional electron gas (2DEG) in AlxGa1-xN/GaN heterostructures. The Rashba spin orbit splitting of the 2DEG has been investigated systemically using circular phototgalvanic effect (CPGE), an anomalous CPGE current has been observed firstly and its relationship with reverse spin Hall effect (RSHE) has been discussed. The major contents and results are as follows:1. We introduce the semiconductor spintronics briefly and the major issues in this field have been discussed, demonstrating that the Rashba spin orbit coupling makes important effects on spin manipulation and spin relaxation. The current research state of GaN-based semiconductors in this area has been introduced. The spin orbit coupling induced by structure inversion symmetry (SIA) and bulk inversion symmetry (BIA) of semiconductors with wurtzite lattice has been discussed in detail.2. The CPGE of the 2DEG in AlxGa1-xN/GaN heterostructures under near infrared irradiation with the wavelength of 1060 nm has been observed. The mechanism of the optical transition in this situation has been discussed, and the relationship between CPGE and Rashba spin splitting of the first subband of the 2DEG has been analyzed. In addition, we compared the CPGE experiments with Shubnikov-de Hass (SdH) magneto-resistance measurements at low temperatures, demonstrating that the CPGE is a more convenient and sensitive way for the research of Rashba spin splitting.3. The differentiation of SIA and BIA spin splitting of the 2DEG in AlxGa1-xN/GaN heterostructures has been discussed. The linear increase of the CPGE current with additional uniaxial strain has been observed firstly. Based on the experimental results, the contribution of BIA and SIA spin splitting of the 2DEG to the CPGE current have been separated, and the S/B ratio is estimated to be about 13.2/1, indicating that the SIA is the dominant mechanism to induce the k-linear spin splitting of the sub-bands in the triangular quantum well (QW) at AlxGa1-xN/GaN heterointerfaces.4. A swirly current named anomalous CPGE has been observed firstly by moving the incident light spot. A physical model which has established a relationship between anomalous CPGE and the RSHE was built to explain the origin of this novel phenomenon. Based on the experimental data , the spin transverse force and Hall voltage for the light spot with a given size has been estimated to be about 2.4×10-19 N and 2.4μV,respectively. We believe that the anomalous CPGE is an universal phenomenon of electron spin dynamics in semiconductors and suggest a new way to investigate the RSHE and spin current on the macroscopic scale and at room temperature.