PHOTOMODULATED REFLECTANCE OF TENSILELY STRAINED INGAAS INGAASP QUANTUM-WELL STRUCTURES/

Room-temperature photomodulated reflectance (PR) has been performed on a series of tensilely strained In1-xGaxAs undoped multiple quantum we ll (QW) structures with In0.80Ga0.20As0.43P0.57 barriers, which were l attice matched to an InP substrate. The nominal QW Ga composition vari ed from x = 0.467 to 0.684 corresponding to tensile strains between ze ro and 1.5%, respectively. In this range of strain, the QW heavy-hole (HH) and light-hole (LH) ground-state zone-centre excitonic transition s increase in energy, with the HH varying more rapidly, with the resul t that it moves from energies below that of the LH, in the unstrained wells, to above the LH, at the highest strain. The variation in the LH and HH energies with strain is measured using PR which is able to res olve these two transitions even when they are almost degenerate, which occurs at (0.39 +/- 0.02)% tensile strain. The results from the PR me asurements are also compared with room-temperature photoluminescence a nd photovoltage measurements on samples from the same wafers. The expe rimental results are shown to compare well with theoretical QW calcula tions based on an effective mass formalism.