Temperature dependence of the photoreflectance of strained and lattice-matched InGaAs/InAlAs single quantum wells

Temperature dependence of photoreflectance spectra is reported for lattice-matched and strained InxGa1-xAs/In0.52Al0.48As (x = 0.53 or 0.60) single quantum wells with different well widths (L = 5 and 25 nm). Several interband transitions have been observed between heavy-hole and light-hole subbands, and conduction subbands at room temperature and at 5 K. Least-squares fits to an Aspnes third derivative functional form yield the energy, broadening parameter, amplitude and phase of the optical transitions. The evolution of the energetic position versus the temperature is fitted using the Varshni semiempirical relationship. A significative modification of the main optical transition E1H1 is evidenced: as the temperature is decreased below 50 K, E1H1 changes from a free to a bound excitonic transition. The energetic positions of four optical transitions in the strained 25 nm quantum well have been compared with the theoretical values obtained by an envelope function model and yield the conduction band offset parameter Q(c) in the strained InGaAs/InAlAs system with a high accuracy (Q(c) = 0.73 +/- 0.02).