Photoluminescence of GaAsSb/AlAsSb superlattices for investigating band structure

Abstract

To study the band structure of GaAsSb/AlAsSb systems grown on InP substrates, optical absorption and photoluminescence (PL) measurements were performed. The measurements utilized GaAsSb/AlAsSb superlattice (SL) samples to investigate the optical properties of the system. By comparing optical absorption and photoluminescence (PL) measurements, it was determined that the non-radiative transition occurred at lower energy levels than the PL transition energy in the sample with the narrowest well width. The excitation power dependence of PL measurements exhibited an almost linear power law of peak intensity, suggesting high-quality luminescence properties of GaAsSb/AlAsSb SLs. In addition, the sample with the narrowest well width exhibited a blueshift of the PL transition energy as a function of the excitation power between square and cubic root laws. To explain these experimental observations, quantized energies in SLs were calculated using the band structures that were suggested and modified using an established band parameter. The most plausible band structure was revealed by comparing experimental observations with the calculations. PL from the SL samples was found to occur within the GaAsSb well (type I) in between the gamma point (Γ) of the conduction band and the heavy hole (HH) energy level in the valence band. To understand the underlying causes of the blueshift phenomenon, a self-consistent calculation that solves the Schrödinger and Poisson equations was performed iteratively as a function of carrier density. As a result, the blueshift of transition energy with an increase in the carrier density was confirmed in the type-I transition between Γ and HH bands if the lowest transition was type II between L for AlAsSb and HH for GaAsSb bands. The Hartree potential due to the separately confined electrons and holes in the SLs slightly narrowed the GaAsSb well width by modifying the conduction band.