The linear and circular photogalvanic effects (CPGEs), induced by ultraviolet (325nm) radiation, have been observed in the (0001)-oriented Al0.15Ga0.85N∕GaN superlattices. The CPGE current changes sign upon reversing the radiation helicity, and it is up to two orders of magnitude larger than that obtained by far-infrared radiation. This result suggests the existence of a sizeable Rashba spin splitting in AlGaN∕GaN superlattices. It also provides a possibility for the generation of spin orientation-induced current at room temperature.

Circular and linear photogalvanic effects are experimentally demonstrated in ͑0001͒-oriented Al 0.25 Ga 0.75 N / GaN heterostructures. By changing the incident angle of the pumping light beam, it is possible to manipulate the relative strength between the circular and linear photogalvanic effects. The spin-dependent signal is evidenced by the sign change upon reversing the radiation helicity. Its consistency with the strength of the Rashba-type spin splitting as determined from the beating of Shubnikov-de Haas oscillations reveals the underlying mechanism responsible for the observed effect. The measured spin-dependent photocurrent is larger than that of the intersubband transition by two orders of magnitude at room temperature. AlGaN / GaN heterostructures therefore provide an excellent opportunity for the generation of spin polarized current to be used in spintronics.

Low-temperature magnetotransport measurements were performed on AlxGa1−xN∕GaN two-dimensional electron systems. By studying the beating pattern in the Shubnikov–de Haas oscillations in a perpendicular magnetic field, we are able to measure the zero-field spin-splitting energies in our systems. Our experimental results demonstrate that the Rashba term due to structural inversion asymmetry is the dominant mechanism which gives rise to the measured zero-field spin splitting in our wurzite AlGaN∕GaN structures. By utilizing the persistent photoconductivity (PPC) effect, we are able to increase the carrier density n in our AlGaN∕GaN two-dimensional electron system. It is found that the Rashba spin-orbit splitting parameter α decreases with increasing n. We suggest that the formation of long-lived electron-hole pairs induced by the PPC effect decreases the large electric field near the AlGaN∕GaN interface, causing α to decrease with increasing n.

The admixture of linear and circular photogalvanic effects and (CPGEs) in AlxGa1−xN∕GaN heterostructures has been investigated quantitatively by near-infrared irradiation at room temperature. The spin-based photocurrent that the authors have observed solidly indicates the sizable spin-orbital interaction of the two-dimensional electron gas in the heterostructures. Further analysis shows consistency between studies by optical and magnetic (Shubnikov de-Haas) measurements on the spin-orbital coupling effects among different AlxGa1−xN∕GaN heterostructures, indicating that the CPGE measurement is a good way to investigate the spin splitting and the spin polarization in semiconductors.

The electron effective mass in n-type InN x As 1Ϫx ͑with x up to 3.0%͒ grown by gas-source molecular-beam epitaxy was obtained from infrared reflectivity and Hall-effect measurements. The large increase of the effective mass due to the incorporation of nitrogen is attributed mainly to the nitrogen-induced modification on the electronic states near the conduction-band edge. The well-known band anticrossing ͑BAC͒ model for the electronic structure of the III-N-V alloys cannot well describe the experimental data, especially in the region of higher electron concentration. This result provides an opportunity to examine the ''universality'' of the BAC model.