Using photoluminescence (PL) and photoreflectance (PR) spectroscopy, we report the optical properties of Al0.24Ga0.76As/In0.15Ga0.85As/GaAs delta-doped pseudomorphic high electron mobility transistor structures with various annealing temperatures. In both PL and PR spectra measured at 12 K, a transition from the first electron subband to the second heavy hole (12H) at 1.35 eV is newly observed at above 600degreesC annealing temperature. The presence of 12H transition peak could be explained by the decrease of phase space filling on the first electron subband and the high availability of holes in the second heavy-hole level after rapid thermal annealing. (C) 2002 Elsevier Science B.V. All rights reserved.