Nearest-Neighbor Distributions in Ga1xInxNyAs1y and Ga1xInxNyAs1yzSbz Thin Films upon Annealing
Journal Article - Open Access
Stanford University Stanford United States
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We examine the distribution of N-In nearest-neighbor bonds in GaInNAsSb 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 blue shift 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 AXVbetween these levels is found to be considerably smaller for GaInNAsSb 18 meV than for GaInNAs 35 meVd. 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.
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- Solid State Physics