Effects of Stoichiometry and Te Concentration on the Deep Levels in Liquid-Phase Epitaxially Grown n-Type Al03Ga07As

Photocapacitance (PHCAP) and Hall effect measurements are applied to liquid—phase epitaxially grown n— Al0 3Ga07As 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 (E5-0.5 eV level and E5-1.1 eV level). The E5-0.5 eV level density increases with applied arsenic vapor pressure during annealing. The Ee_1.1 eV level density increases with increasing arsenic vapor pressure, but de— creases at the highest arsenic vapor pressures. Hall effect measurements show that activation ratio between carrier con-centration and Te concentration is higher when the epitaxial layers are annealed under lower arsenic vapor pressure (0.2 Ton) 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-AlGa1As is discussed in view of deviation from the stoichio-metric composition and Te doping in the M,Ga1As ternary alloy system. Infroduction The deviation from the stoichiometric composition is the most important factor to be controlled in compound semi-conductor materials. Nishizawa and co-workers have sys