Structural and electronic properties of GaAs : C and Al xGa 1-xAs : C grown by solid-source molecular beam epitaxy

Abstract

C-doped GaAs and Al x Ga 1- x As (0 < x < 0.39) films, grown by solid-source MBE with doping levels beyond 10 19 cm -3, have been investigated by high-resolution X-ray diffraction, Hall-effect measurements and photoluminescence (PL). Comparison of X-ray and Hall data reveals that carbon is substitutionally incorporated on As sites up to C concentration of 3×10 19 cm -3. Sharp excitonic and free-to-bound (e-C 0) transitions on the high-energy side of the PL spectra show the existence of local incorporation of C as interstitial impurity. Both these sharp transitions disappear in samples grown with high As 4 beam fluxes. Moreover, in C-doped Al x Ga 1- x As films grown with the same C concentration and the same As 4 flux, the free-hole density is found to increase with the AlAs mole fraction. A higher Al-C bond strength compared to Ga-C causes an increase of C on As lattice sites with respect to C-incorporated interstitially in the GaAs matrix.