Nitrogen-induced increase of the maximum electron concentration in group III-N-V alloys

The maximum free-electron concentration is observed to increase dramatically with the nitrogen content $x$ in heavily Se-doped ${\mathrm{Ga}}_{1\ensuremath{-}3x}{\mathrm{In}}_{3x}{\mathrm{N}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}$ $(0<~x<0.033)$ films. For example, an electron concentration of $7\ifmmode\times\else\texttimes\fi{}{10}^{19} {\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ was observed at $x=0.033;$ a value more than 20 times larger than that observed in GaAs films grown under similar conditions. It is shown that the increase is caused by a combination of two effects: (1) a downward shift of the conduction band and (2) an increase of the electron effective mass caused by flattening of the conduction-band minimum. Both these effects are due to modifications to the conduction-band structure caused by an anticrossing interaction of a localized $N$ state and the conduction band of the III-V host.