InGaN/GaN quantum wells studied by high pressure, variable temperature, and excitation power spectroscopy

The energies of photo- and electroluminescence transitions in In_xGa_1-xN quantum wells exhibit a characteristic "blueshift" with increasing pumping power. This effect has been attributed either to band-tail filling, or to screening of piezoelectric fields. We have studied the pressure and temperature behavior of radiative recombination in In_xGa_1-xN/GaN quantum wells with x=0.06, 0.10, and 0.15. We find that, although the recombination has primarily a band-to-band character, the excitation-power induced blueshift can be attributed uniquely to piezoelectric screening. Calculations of the piezoelectric field in pseudomorphic In_xGa_1-xN layers agree very well with the observed Stokes redshift of the photoluminescence. The observed pressure coefficients of the photoluminescence (25-37 meV/GPa) are surprisingly low, and, so far, their magnitude can only be partially explained.