Discrete and continuous spectrum of nitrogen-induced bound states in heavily dopedGaAs1−xNx

We perform a spectroscopic study on ${\mathrm{GaAs}}_{1-x}{\mathrm{N}}_x$ samples with N concentrations near an important value of $x=0.1\%,$ an intermediate concentration between the impurity limit and the alloy region. We find that near $x\sim 0.1\%,$ samples exhibiting seemingly different spectra as reported in the literature and observed in our measurements actually have the same underlying electronic structure. Namely, the shallow N-induced bound states have already formed an impurity band and thus led to an observable band-gap reduction, but deeper N-related bound states persist as discrete levels below the newly formed band edge. The role of these discrete states in the formation of the new band edge on further increasing the N doping levels is discussed. We point out that although the nitrogen bound states form an impurity band in heavily N-doped GaAs, the states constituting such a newly formed band continue to retain certain localization characteristics of the impurity in the dilute limit. We observe that the impurity band gives rise to strong resonant Raman scattering, which makes it possible to obtain the resonant Raman profile near the direct band edge of this direct-gap semiconductor.