Optical and Electrical Properties of Type-II GaAsSb/GaAs Multiple Quantum Wells

• Main Authors: Tzung-Te Chen, 陳宗德
• Other Authors: Yang-Fang Chen
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/95542280029012252650

碩士 === 國立臺灣大學 === 物理學研究所 === 92 === In this thesis we report the studies of optical and electrical properties on type-II GaAs0.7Sb0.3/GaAs multiple quantum wells. Photoluminescence (PL), photoluminescence excitation (PLE), photoconductivity (PC), and persistent photoconductivity (PPC) have been performed. Some peculiar results have been obtained from our studies which very useful for the understanding as well as application of these materials. They are presented as follows. I. Optical studies of strained type-II GaAs0.7Sb0.3/GaAs multiple quantum wells We report a detailed investigation on the optical transitions of strained type-II GaAs0.7Sb0.3/GaAs (100) multiple quantum wells. For the theoretical calculations, both of the elastic deformational potential of intrinsic compressive biaxial strain, and quantum confinement effects are included. The asymmetric photoluminescence spectra reveal the features of excited state transition and quantum confinement Stark effect (QCSE) at high and low temperatures, respectively. The asymmetry features have also been investigated and confirmed by low-temperature photoluminescence experiments under different excitation power. From polarized photoluminescence excitation and photoconductivity spectra, both of the type-I and type-II optical transitions can also be clearly identified. II. Persistent photoconductivity in GaAs0.7Sb0.3/GaAs multiple quantum wells The optoelectronic properties of undoped type-II GaAs0.7Sb0.3/GaAs (100) multiple quantum wells has been investigated by photoluminescence (PL), and photoconductivity (PC) measurements. Interestingly, persistent photoconductivity (PPC) has been discovered in this novel material. The decay kinetics of the PPC effect can be well described by a stretched-exponential function Ippc(t)= Ippc(0)exp[-(t/τ)β], (0<β<1). Through the study of the PPC effect under various condition, and combining with the characteristics of the PL spectra, we identify that the origin of the PPC effect arises from the spatial separation of photoexcited electrons and holes, in which electrons fall into the GaAs layer, and holes are trapped by defects in the GaAsSb layer. In order to return to the initial states, photoexcited electrons have to overcome the energy barrier between the type-II transition and the band gap of the GaAsSb layer.