Dependence of the Al_xGa_1-xAs band edge on alloy composition based on the absolute measurement of x

The absolute determination of the Al concentration, x, in epitaxial layers of AlxGa1-xAs was carried out using a nuclear reaction technique. This technique utilizes the narrow resonances found in the 27Al (p,γ)Si28 reaction, together with Rutherford backscattering measurements, to obtain accurate values of the alloy composition. The AlxGa1-xAs band edge was measured on these samples through low-temperature photoluminescence (2 K) measurements. An improved value of the direct edge (Γ) on composition was determined to be EΓg =1.512 +1.455x(eV) within a ±0.3% limit. The direct-to-indirect transition was found to occur at an Al concentration of x≅0.37±0.015, lower than previously reported for He temperatures.