PIEZOREFLECTANCE AND PHOTOREFLECTANCE STUDY OF GAAS ALGAAS DIGITAL ALLOY COMPOSITIONAL GRADED STRUCTURES/

We have studied the piezoreflectance (PzR) spectra at 300 and 80 K rel ated to the intersubband transitions from two different (001) GaAs/AlG aAs structures, an asymmetric triangular quantum well and a rectangula r quantum well, fabricated by molecular beam epitaxy using the digital alloy compositional grading (DACG) method. A comparison of the relati ve intensity of heavy- and tight-hole related features in the PzR spec tra and those in the photoreflectance emphasizes the contribution of t he strain dependence of the energies of the confined states which allo ws us to identify the features associated with the heavy- and light-ho le valence bands unambiguously. Comparison of the observed intersubban d transitions with the envelope function calculations provides a self- consistent verification that the DACG method generated the desired pot ential profiles. Furthermore, the temperature dependence of both the e nergy position and broadening parameter of the fundamental conduction to heavy-hole (11H) and light-hole (11L) excitonic features are invest igated in the range of 20-300 K. The anomalous behavior of the tempera ture dependence of the linewidth of 11H(L) excitonic features of the s amples are discussed. (C) 1995 American Institute of Physics.