Photoluminescence-linewidth-derived reduced exciton mass for ${\mathrm{In}}_y{\mathrm{Ga}}_{1-y}{\mathrm{As}}_{1-x}{\mathrm{N}}_x$ alloys

We report the measurement of the variation of the value of the linewidth of an excitonic transition at 4 K in ${\mathrm{In}}_y{\mathrm{Ga}}_{1-y}{\mathrm{As}}_{1-x}{\mathrm{N}}_x$ alloys (1% and 2% nitrogen) as a function of hydrostatic pressure using photoluminescence spectroscopy. We find that the value of the excitonic linewidth increases as a function of pressure until about 100 kbar after which it tends to saturate. This change in the excitonic linewidth is used to derive the pressure variation of the exciton reduced mass using a theoretical formalism based on the premise that the broadening of the excitonic transition is caused primarily by compositional fluctuations in a completely disordered alloy. The variation of this derived mass is compared with the results from a nearly first-principles approach in which calculations based on the local-density approximation to the Kohn-Sham density-functional theory are corrected using a small amount of experimental input.