Indirect photoreflectance from high-electron-mobility transistor structures

Photoreflectance in sample regions shaded from laser pump illumination reveals a low-level signal attributable to modulation of the two-dimensional electron gas in GaAs/Alₓ{Ga}_{1{{-}}x}As high-electron-mobility transistor structures. Samples with 2--9×{10}⁵$/${cm}²/V s electron mobility (at 4 K) display photoreflectance ΔR/R~5×{10}^{{{-}}6}$ at distances up to 3 mm away from the modulated area of the sample. A rotationlike behavior of the GaAs signature in the 0--1.5-mm region reveals the presence of multiple modulation mechanisms whose lateral ranges differ with temperature and electron mobility.