| Summary: | 碩士 === 國立成功大學 === 物理學系 === 88 === This work uses photoreflectance (PR) to investigate the band gap, built-in electric field, and surface Fermi level of a series of lattice-matched In0.52Al0.48As surface intrinsic-n+ structures having different undoped layer thickness. Experimental results indicate that the surface Fermi level is weakly pinned. By converting the dependence of built-in electric field on undoped layer thickness into the dependence of surface state density on the surface Fermi level, this study defines the energy spectrum of the surface state density of InAlAs surface using a Gaussion distribution function.
Next, room temperature photoreflectance was used to investigate the surfcae state density of GaAs and In0.52Al0.48As surface intrinsic-n+ structures. The built-in electric field and thus the surface barrier height are evaluated using the observed Franz-Keldysh oscillation in PR spectra. Based on thermionic emission theory and current-transport theory, the surface state density as well as pinning position of the Fermi level can be determined from the dependence of the surface barrier height on the pump beam intensity. Even though this method is significantly simpler, easier to perform, and time efficient compared with other approaches, the results obtained agree with the literature.
|
|---|
