LOW-TEMPERATURE GROWTH OF GAAS AND ALGAAS BY MBE AND EFFECTS OF POSTGROWTH THERMAL ANNEALING

GaAs and Al0.3Ga0.7As films were grown by molecular beam epitaxy (MBE) using substrate temperatures between 350 and 620-degrees-C. These samples were produced under otherwise identical conditions using either elemental As (tetrameric As) or GaAs (dimeric As) as the arsenic source, and using fixed fluxes of either Si or Sn, corresponding to an atomic dopant concentration of approximately 3 x 10(18) cm-3. The samples were characterized by Hall effect measurements at 300 and 77 K, and by photoluminescence measurements at 300 K. In the as-grown samples, the free carrier concentration, n, the Hall mobility, mu, and the luminescence intensity all decrease as the substrate temperature decreases below 450-degrees-C The lower values of n, mu, and luminescence intensity can, however, be improved by thermally annealing the films at 850-degrees-C for between 5 and 30 s. After the anneal, values of n, mu, and photoluminescence intensity are comparable to those observed in unannealed films grown at 620-degrees-C. For a given growth temperature, the measured electrical and optical properties and the annealing behavior of these samples are very similar, whether Si or Sn is used as the dopant, and whether a tetrameric or dimeric As source is used.