Bowing of the band gap pressure coefficient in InxGa1−xN alloys

Abstract

The hydrostatic pressure dependence of photoluminescence, dEPL/dp, of InxGa1−xN epilayers has been measured in the full composition range 0<x<1. Furthermore, ab initio calculations of the band gap pressure coefficient dEG/dp were performed. Both the experimental dEPL/dp values and calculated dEG/dp results show pronounced bowing and we find that the pressure coefficients have a nearly constant value of about 25 meV/GPa for epilayers with x>0.4 and a relatively steep dependence for x<0.4. On the basis of the agreement of the observed PL pressure coefficient with our calculations, we confirm that band-to-band recombination processes are responsible for PL emission and that no localized states are involved. Moreover, the good agreement between the experimentally determined dEPL/dp and the theoretical curve of dEG/dp indicates that the hydrostatic pressure dependence of PL measurements can be used to quantify changes of the band gap of the InGaN ternary alloy under pressure, demonstrating that the disorder-related Stokes shift in InGaN does not induce a significant difference between dEPL/dp and dEG/dp. This information is highly relevant for the correct analysis of pressure measurements.