Electrical and structural properties of Be- and Si-doped low-temperature-grown GaAs

Excess As is incorporated in GaAs grown at low substrate temperatures by molecular beam epitaxy. Excess As is distributed in the epilayer as defects and the material exhibits considerable strain. When annealed to moderate temperatures, the strain is seen to disappear and the excess As is now in the form of semimetallic clusters. It has been proposed that these As clusters form buried Schottky barriers with the GaAs matrix and are surrounded by spherical depletion regions. In this article, we examine the effects of doping on the material properties and compare our results to the buried Schottky barrier mode. Si-doped GaAs epilayers grown at 250 “C, with doping densities between 5X 1017 and 5X 10” cm-s, were annealed to temperatures between 700 and 1000 “C for 30 s. Be-doped GaAs epilayers grown at 250 “C, with doping densities between 5X 1017 and 5X lOI cm-s, were annealed to temperatures between 700 and 900 “C for 30 s. Using extensive Hall measurements and transmission electron microscopy, we observe that the As precipitates deplete the surrounding GaAs matrix.