Possibility of a quasi-liquid layer of As on GaAs substrate grown by MBE as observed by enhancement of Ga desorption at high As pressure

The As vapor pressure dependence of the Ga desorption rate during molecular beam epitaxy (MBE) growth on GaAs(n11)A (n = 1-4 hereafter) substrates was studied by photoluminescence (PL) measurements at 12 K for undoped AlGaAs/ GaAs asymmetric double quantum wells (ADQWs). Reflection high energy electr on diffraction (RHEED) oscillation measurements on a GaAs(100) surface were also used. Two K-cells of As solid sources (corresponding to beam equivale nt pressures (BEPs) of 9.0 x 10(-6) and 4.5 x 10(-5) Torr) were used to cha nge the As pressure rapidly. The Ga flux and substrate temperature were kep t constant at 0.76 ML/s and 12 K, respectively, while the As flux changed f rom 7.6 (BEP 9.0 x 10(-6) Tow) to 32 ML/s (4.5 x 10(-5) Ton). With increasi ng As pressure, two separated PL peaks for the wide well (WW) of high index substrates were observed. This peak separation is attributed to a reduced well depth from an increasing Ga desorption rate. The energy differences of the PL peak depending on the off-angle from (111)A to (100) plane indicate s an orientation-dependent Ga desorption rate. Moreover, amongst all (n11)A and (100) planes, the Ga desorption rate was smallest from the (111)A surf ace. The increase of Ga desorption from the surface at high As pressures pr obably arose from an increasing coverage with a quasi-liquid layer (QLL). ( C) 2000 Elsevier Science B.V. All rights reserved.