Effects of stoichiometry and Te concentration on the deep levels in liquid-phase epitaxially grown n-type Al_0.3Ga_0.7As

Photocapacitance (PHCAP) and Hall effect measurements are applied to liquid-phase epitaxially grown n-Al_0.3Ga_0.7As crystals, followed by an annealing at 900°C for 1 h under controlled arsenic vapor pressure. Photocapacitance measurements reveal two deep levels in relatively lightly Te-doped samples, the optical activation energy of which are 0.5 and 1.1 eV, respectively (E_c-0.5 eV level and E_c-1.1 eV level). The E_c-0.5 eV level density increases with applied arsenic vapor pressure during annealing. The E_c-1.1 eV level density increases with increasing arsenic vapor pressure, but decreases at the highest arsenic vapor pressures. Hall effect measurements show that activation ratio between carrier concentration and Te concentration is higher when the epitaxial layers are annealed under lower arsenic vapor pressure (0.2 Torr) than the samples annealed under higher arsenic pressure (310 Torr), and decreases in the heavily Te-doped samples. From these results, the origin of the defects detected in n-Al_xGa_1-xAs is discussed in view of deviation from the stoichiometric composition and Te doping in the Al_xGa_1-xAs ternary alloy system.