Room temperature polarized photoreflectance characterization of GaAlAs/InGaAs/GaAs high electron mobility transistor structures including the influence of strain relaxation

Using room temperature photoreflectance (PR) we have characterized the prop erties of three GaAlAs/InGaAs/GaAs high electron mobility transistor struct ures with two different well widths fabricated by molecular beam epitaxy on (001) GaAs substrates. The samples were denoted as #1, #2, and #3 with wel l widths of 140, 160, and 160 Angstrom, respectively. Samples #2 and #3 wer e grown on substrates with different threading dislocation densities. For t he latter two samples the well width exceeds the pseudomorphic limit so tha t there are some strain relaxation and related misfit dislocations as deter mined from the x-ray measurements. In order to detect the anisotropic strai n of the misfit dislocations related to strain relaxation, the PR measureme nts were performed for incident light polarized along [110] and [<1(1)over bar>0] directions. Evidence for the influence of the strain relaxation upon the relaxed channel was provided by the observed anisotropy of the polariz ed PR signal in the InGaAs channel layer. Signals have been observed from e very region of the sample, making it possible to evaluate the In and Al com positions, channel width and two-dimensional electron gas density, as well as the properties of the GaAs/GaAlAs multiple quantum well buffer layer. (C ) 2000 American Institute of Physics. [S0021-8979(00)04714-9].