Photoluminescence under pressure of ultrathin AlAs layers grown on GaAs vicinal surfaces: A search for lateral confinement effects

In ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As/GaAs quantum wells bordered by ultrathin (one or two monolayers) AlAs layers, the AlAs layer has been shown to provide a well for electrons at high pressure [Phys. Rev. B 45, 11 846 (1992)]. In this work, the same type of structures, but grown on (001) substrates misoriented towards (111)Ga, are studied by photoluminescence as a function of pressure, and a comparison is made with those grown on nominal substrates in order to investigate the influence of surface steps on electronic levels. Particular emphasis is given to indirect type-II transitions. An important blueshift of indirect transitions is observed in the case of two AlAs monolayers grown on a vicinal substrate. The size of this shift may be explained considering diffusion of carriers by the interface steps, or also lateral confinement. Inversely, a redshift is observed in the one AlAs monolayer sample. We suggest that this last point may be due to terrace length fluctuations.