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 ns1–4 hereafter.substrates was studied by photoluminescence PL.measurements at 12 K for undoped AlGaAsrGaAs asymmetric double quantum wells ADQWs.. Reflection high energy electron diffraction RHEED. oscillation measurements on a GaAs 100.surface were also used. Two K-cells of As solid sources corresponding to beam equivalent pressures BEPs.of 9.0=10y6 and 4.5=10y5 Torr. were used to change the As pressure rapidly. The Ga flux and substrate temperature were kept constant at 0.76 MLrs and 12 K, respectively, while the As flux changed from 7.6 BEP 9.0=10y6 Torr.to 32 MLrs 4.5=10y5 Torr.. With increasing 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 indicates an orientation-dependent Ga desorption rate. Moreover, amongst all n11.A and 100.planes, the Ga desorption rate was smallest from the 111.A surface. The increase of Ga desorption from the surface at high As pressures probably arose from an increasing coverage with a quasi-liquid layer QLL.. q2000 Elsevier Science B.V. All rights reserved.