Piezoreflectance and photoreflectance study of GaAs/AlGaAs digital alloy compositional graded structures

We have studied the piezoreflectance (PzR) spectra at 300 and 80 K related to the intersubband transitions from two different (001) GaAs/AlGaAs structures, an asymmetric triangular quantum well and a rectangular quantum well, fabricated by molecular beam epitaxy using the digital alloy compositional grading (DACG) method. A comparison of the relative intensity of heavy- and tight-hole related features in the PzR spectra and those in the photoreflectance emphasizes the contribution of the strain dependence of the energies of the confined states which allows us to identify the features associated with the heavy- and light-hole valence bands unambiguously. Comparison of the observed intersubband transitions with the envelope function calculations provides a self-consistent verification that the DACG method generated the desired potential profiles. Furthermore, the temperature dependence of both the energy position and broadening parameter of the fundamental conduction to heavy-hole (11H) and light-hole (11L) excitonic features are investigated in the range of 20-300 K. The anomalous behavior of the temperature dependence of the linewidth of 11H(L) excitonic features of the samples are discussed. (C) 1995 American Institute of Physics.