PHOTOREFLECTANCE OF ALXGA1-XAS AND ALXGA1-XAS/GAAS INTERFACES AND HIGH-ELECTRON-MOBILITY TRANSISTORS

Photoreflectance is used to measure AlxGa1-xAs composition, and to determine carrier concentrations in Si-doped AlGaAs epilayers capped with GaAs. Undoped caps are generally depleted, and do not show a usual GaAs photoreflectance. However, photoreflectance from the cap/(doped AlGaAs) interface produces a broad signal which distorts the entire spectrum, making it hard to locate the GaAs and AlGaAs band edges precisely. A similar broad signal from modulation-doped heterostructures is apparently associated with samples that show the presence of two-dimensional electron gas.