PRESSURE-DEPENDENCE OF THE ELECTRONIC SUBBAND STRUCTURE OF STRAINED IN0.2GA0.8AS GAAS MQWS/

We have measured low-temperature photoluminescence (PL) and optical ab sorption spectra of an In0.2Ga0.8As/GaAs multiple quantum well (MQW) s tructure at pressures up to 8 GPa. Below 4.9 GPa, PL shows only the em ission of the n = 1 heavy-hole (HH) exciton. Three new X-related PL ba nds appear at higher pressures. They are assigned to spatially indirec t (type-II) and direct (type-I) transitions from X(Z) states in GaAs a nd X(XY) valleys of InGaAs, respectively, to the HH subband of the wel ls. From the PL data we obtain a valence band offset of 80 meV for the strained In0.2Ga0.8As/GaAs MQW system. Absorption spectra show three features corresponding to direct exciton transitions in tile quantum w ells. In the pressure range of 4.5 to 5.5 GPa an additional pronounced feature is apparent in absorption, which is attributed to the pseudo- direct transition between a HH subband and the folded X(Z) states of t he wells. This gives the first clear evidence for an enhanced strength of indirect optical transitions due to the breakdown of translational invariance at the heterointerfaces in MQWs.