ELECTROMODULATION SPECTROSCOPY STUDY OF A GAAS GAALAS ASYMMETRIC TRIANGULAR QUANTUM-WELL STRUCTURE/

Using the contactless electromodulation methods of photoreflectance an d contactless electroreflectance we have studied the intersubband tran sitions from a (001) GaAs/GaAlAs asymmetric triangular quantum well (A TQW) structure at 300 and 80 K. The sample was fabricated by molecular beam epitaxy using a digital alloy composition grading (DACG) method. Comparison of the observed intersubband resonances with a theoretical calculation (envelope function method) provided a self-consistent ver ification that the DACG produced the intended result, i.e. an effectiv e linearly graded profile. An external uniaxial stress along [100] was used to confirm the heavy- or light-hole nature of some of the spectr al features. Furthermore, the temperature dependence of both the energ y and broadening parameter, GAMMA(T), of the fundamental conduction to heavy-hole exciton feature were investigated in the wide temperature range 10 K < T < 450 K. These observations, particularly the anomalous behaviour of GAMMA(T), will be compared to recent results for GaAs/Ga AlAs symmetric rectangular quantum wells of comparable dimensions.