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

The hydrostatic pressure dependence of photoluminescence, dE(PL)/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 dE(G)/dp were performed. Both the experimental dE(PL)/dp values and calculated dE(G)/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 dE(PL)/dp and the theoretical curve of dE(G)/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 dE(PL)/dp and dE(G)/dp. This information is highly relevant for the correct analysis of pressure measurements. (C) 2008 American Institute of Physics.