Influence of pressure on photoluminescence and electroluminescence in GaN/InGaN/AIGaN quantum wells

We have measured photoluminescence and electroluminescence in two different types of high-brightness single-quantum-well light emitting diodes manufactured by Nichia Chemical Industries with In_xGa_1-xN active layers (x=0.45 and x=0.15), under hydrostatic pressures up to 8 GPa. We discovered that the pressure shift of the primary luminescence peak in each diode is very small: 12 and 16 meV/GPa for the green and blue diodes, respectively. The observed pressure coefficients are much lower than those characteristic of the energy gap in GaN (≈40 meV/GPa) or the energy gap in InN (≈33 meV/GPa). This kind of behavior is usually associated with recombination processes involving localized states. These localized states may be associated either with band tails (arising from In fluctuations in the active layer or from high density of defects), and/or with localized excitons of various types.