Nearest-neighbor distributions inGa1−xInxNyAs1−yandGa1−xInxNyAs1−y−zSbzthin films upon annealing

Abstract

We examine the distribution of N-In nearest-neighbor bonds in GaInNAs(Sb) quantum wells (QWs) and observe quantitatively the evolution of the distribution during thermal annealing. We use near-edge x-ray absorption fine structure to compare the behavior of compressively strained quantum wells with relaxed thick-film samples, and find no significant effect of strain on the nearest-neighbor bonding. Photoluminescence (PL) and electroreflectance (ER) spectroscopies are used to quantitatively measure the distribution of N-In nearest-neighbor states for a series of variously annealed GaInNAsSb QW samples. We find that increased annealing temperature or time leads to a blueshift of the band gap that saturates after sufficient annealing. This saturation is related to a thermodynamic equilibration of the N-In nearest-neighbor bonding in the material toward highly In-coordinated states, from an as-grown material having a nearly random bonding arrangement dominated by N-Ga bonds. The different N-In nearest-neighbor states form a fine splitting of the band gap of the material. The average spacing between these levels is found to be considerably smaller for GaInNAsSb $(\ensuremath{\sim}18\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$ than for GaInNAs $(\ensuremath{\sim}35\phantom{\rule{0.3em}{0ex}}\mathrm{meV})$. Furthermore, we present absorption measurements that reveal an increased optical efficiency of the higher In-coordinated N states that form upon annealing. Additionally, the line shape observed at room temperature in all of the spectroscopic measurements is Gaussian, indicating a strong exciton-phonon coupling in these alloys.