Photoreflectance of Zn:AlxGa1-xAs at the E1 Transition Energy as a Function of Carrier Concentration and Aluminum Composition
The photoreflectance (PR) spectra of MOCVD grown Zn:AlxGa1-xAs with 0 < x < 0.55 and carrier concentration, N, of 5 × 1017 to 1 × 1019 cm-3 was studied at the E1 transition energy. Of particular interest was the effect of varying N and x on E1, the broadening of the Γ1 structure. Within the experimental error, Γ1 was found to increase as x increases. The slope of Γ1 with log(N) initially decreases as x is increased to 0.29, which is possibly due to a decrease in the translational periodicity of the sample. For 0.30 < x < 0.39, the slope increases sharply which may be due to an increase in the near-surface field with increasing N and decrease in the static dielectric constant, s. The drop of the slope in the region 0.40 < x < 0.49 is probably due to the “crossover region” behavior of AlxGa1-xAs from direct to indirect band. After the transition is crossed over, the slope again shows an upward trend in the range 0.50 < x < 0.55, as expected.