Photoreflectance of Zn : AlxGa1-xAs at the E-1 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 similar to 5 x 10(17) to similar to 1 x 10(19) cm(-3) was studied at the E-1 transition energy. Of particular i nterest was the effect of varying N and x on E-1, the broadening of the Gam ma (1) structure. Within the experimental error, Gamma (1) was found to inc rease as x increases. The slope of Gamma (1) with log(N) initially decrease s as x is increased to 0.29, which is possibly due to a decrease in the tra nslational periodicity of the sample. For 0.30 < x < 0.39, the slope increa ses sharply which may be due to an increase in the near-surface field with increasing N and decrease in the static dielectric constant, epsilon (s). T he 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. Afte r the transition is crossed over, the slope again shows an upward trend in the range 0.50 < x < 0.55, as expected.