Photoluminescence studies of ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs strained quantum wells under hydrostatic pressure

The photoluminescence from ${\mathrm{In}}_{\mathit{x}}$${\mathrm{G}}_{1\mathrm{-}\mathit{x}}$As/GaAs strained quantum wells with thickness from 30 to 160 Å have been studied at 77 K under hydrostatic pressure up to 60 kbar. It was found that the pressure coefficients of the exciton peaks corresponding to transitions from the first conduction subband to the heavy-hole subband increased with reduced well width, in contrast to the case of GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells. Calculations revealed that the increased barrier height with pressure was the major cause of the change in the pressure coefficients. Two peaks related to indirect transitions were observed at pressures higher than 50 kbar. They are attributed to type-I transitions from the lowest conduction-band edge, which are the strain splitted ${\mathit{X}}_{\mathit{x}\mathit{y}}$ valleys, to the heavy-hole subband in the ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As well.