Abstract
Photoluminescence (PL) spectra under pressure have been measured at 80 K for MBE grown (GaAS)m(AlAs)m superlattices (SLS). Two main emission bands have been observed for the (GaAs)12(AlAs)12SL. The higher emission band (1.785 eV) behaves like a Gamma edge under pressure and the lower emission band (1.749 eV), on the other hand, behaves like an X edge. One emission band at 1.664 eV has been observed for (GaAs)18(AlAs)18SL at atmospheric pressure. This band moves to higher energy when pressure is applied, which shows the lowest lying conduction band is Gamma like. The PL emission intensity of this SL decreases abruptly to the order of 10-2 at 7.5 kbar, which is due to the pressure-induced Gamma -X crossover. The pressure-induced change-over from Gamma - to X-like emission has been clearly observed for (GaAs)15(AlAs)15SL. These results give conclusive evidence to verify the finding that, on increasing the number of monolayers, the lowest conduction band edge of (GaAs)m(AlAs)m switches from the X-like to Gamma -like state at a thickness of 14 monolayers.
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