Quasi-ordering of composition fluctuations and their interaction with lattice imperfections in an optical spectra of dilute nitride alloys. (25th August 2016) - Mintairov, A M
Abstract: Using optical spectroscopy experiments, including conventional low-temperature photo-reflectance and photoluminescence (PL) together with time-resolved PL and near-field magneto PL, we distinguish between statistical composition fluctuations (CFs) and nitrogen clusters (Ncl ) in i- and n - type GaAs1− x N x alloys ( x = 0.01–0.03). We measured the size ( l = 3–24 nm), activation energy ( E a = 15–30 meV) and density ( n l ∼ 10 11 cm −2 ) of CFs in i-type material. In n-type material we resolved the emission of nitrogen clusters (Ncl ) having activation energy ∼70 meV and density n cl ∼ 10 12 cm −2 . Analysis of l and E a values in i-GaAs1− x N x revealed a strong interaction between substitutional (N s ) and interstitial (N i ) nitrogen, which results in band gap splitting accompanied by activation of the heavy-hole exciton and Ncl emission. In the optical spectra of i-GaAs1− x N x, we suggest the identification of different N i species and N i -N s arrangements, and in n-GaAs1− x N x we observed activation/suppression of Ncl /CF emission and interference between CFs and ionized donors. Using numerical analysis of amplitude, size and density of CFs we revealed unexpected quasi-ordering which results in modulation of CFs having period 2 l . This is consistent with the high n l values observed. We show that this quasi-ordering, arising from statistical non-uniformity of the CFs, creates a set of latent states, which allows us to probe exciton properties, defect density and the structural homogeneity in GaAs1− x N x .