Photopolarization Effect and Photoelectric Phenomena in Layered GaAs Semiconductors

The studies of transport properties in semiconductors have made great progresses for the past decades. This is mainly due to the advanced technologies for development of new materials and the application of nonlinear dynamics to the fundamental well-known materials. In particular, the discipline of nonlinear dynamics grows fast, which is due to the cooperation of theoretical background and experimental findings. Among systems considered, semiconductors represent interesting and highly productive examples of the experimental investigation of nonlinear dynamics. One of the typical findings observed in nonlinear semiconductors is the dynamics of propagating electrical solitary waves which could be periodic or chaotic. Many of these phenomena have been studied in bulk semiconductors as well as superlattices, and can be successfully explained by means of theoretical as well as numerical approaches (Amann & Scholl, 2005; Bonilla & Grahn, 2005; Cantalapiedra et al., 2001; Gaa & Scholl, 1996; Wack, 2002). Of particular interest is that GaAs semiconductors have been shown to generate microwave radiation. The generation was attributed to propagating space-charge waves (or high-field domains). The domain shape parameters such as the maximum fields and the domain size are controllable with changing the concentration of ionized donors that are doped in the semiconductor substrate. It is known that nonlinear electro-optic characteristics can be observed in an n+-n−-n-n+ GaAs sandwich structure under optical excitation, where potential applications including optical control of microwave output, ultrafast electric switches, memory cells and other areas. The key factor in such a system is that propagating space-charge waves (SCWs) were formed at the cathode and destroyed at (or before) the anode being due to a balance of the diffusion of carriers and the nonlinearity in the velocity-field characteristic, where it can be realized that propagating SCWs are equivalent to the case of the laser beam propagation in Kerr-type nonlinear optical media. Besides, the notch profile (i.e., the n− layer) will be strongly influenced by the optical illumination, which will result in the tuning traveling-distance of SCWs. Owing to that, optical control of microwave output can be expected, and this phenomenon is related to the photopolarization effect. In addition, the interesting phenomena including optically induced hysteresis and long-lived transient behaviors can be observed in a layered semiconductor. In the meanwhile, the development of multiple sandwich structures has been known to be helpful for the high-power microwave generation; however, electro-optic characteristics are less known in this system. Concerning on multiple sandwich