Photoreflectance Studies of Zinc-Doped Aluminum(x) GALLIUM(1-X) Arsenide at the E(1) Transition Energy.

The photoreflectance (PR) spectra of metalorganic chemical vapor deposition (MOCVD) grown p-type Zn:Al _{x}Ga_{1-x}As with 0 < x < 0.55 and carrier concentration, N, of ~ 5times 10^{17} to ~ 1times 10^{19}cm^{-3 } was studied at the E_1 transition energy. Of particular interest was the effect of varying the carrier concentration and the aluminum composition, x, on the broadening parameter, Gamma_1 , at this energy. By dividing our samples into a set of 6 groups, a linear relation was observed to exist between Gamma_1 and the logarithm of the carrier concentration for each set of the samples. Gamma_1 was also found to increase as x increases at any carrier concentration except for 0.40 < x < 0.49 where Gamma_1 was observed to have values less than those for 0.30 < x < 0.39. The slope of Gamma_1 with the logarithm of the carrier concentration (log N) was observed to initially decrease as x is increased from 0.08 to 0.29. For 0.30 < x < 0.39, the slope increases drastically, then drops for 0.40 < x < 0.49, and finally shows an increase for 0.50 < x < 0.55. Our possible explanation to the observed behaviors was based on: (a) changes in the surface field of the sample due to changes in the carrier concentration and aluminum composition and (b) lattice defects and a decrease in the translational symmetry of the sample and changes in the alloy scattering as a result of the introduction of Al into GaAs.