From GaAs:N to oversaturated GaAsN: Analysis of the band-gap reduction

Abstract

The composition dependence of the band-gap reduction of ${\mathrm{GaAs}}_{1\ensuremath{-}x}{\mathrm{N}}_{x}$ grown by molecular beam epitaxy and metal organic vapor phase epitaxy was investigated using transmission, reflection, and low-temperature photoluminescence (PL) spectroscopy for N incorporations ranging from doping concentrations up to $x=5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}.$ We identified four different regimes of N incorporation with distinctly different band-gap scaling. N-doped GaAs shows sharp PL lines due to N cluster states, but no significant change in the band gap. In the ultradilute region ${(10}^{\ensuremath{-}5}\ensuremath{\lesssim}x<~1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3})$ a strong band-gap reduction was observed which scales according to x, irrespective of the local distribution of N atoms in the As sublattice. The same band-gap scaling was observed for ultradilute InGaAsN after corrections for strain and In alloying. In an intermediate compositional region $(1.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}<~x<~2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2})$ $\ensuremath{\Delta}{E}_{g}$ scales according to ${x}^{2/3}.$ At higher concentrations $(x>2.5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2})$ $\ensuremath{\Delta}{E}_{g}$ weakens due to effects connected with N oversaturation of the As sublattice.