ROOM-TEMPERATURE PHOTOREFLECTANCE CHARACTERIZATION OF PSEUDOMORPHIC GAALAS INGAAS/GAAS HIGH-ELECTRON-MOBILITY TRANSISTOR STRUCTURES INCLUDING THE 2-DIMENSIONAL ELECTRON-GAS DENSITY/

Using contactless photoreflectance at 300 K we have characterized thre e pseudomorphic GaAlAs/InGaAs/GaAs high electron mobility transistor s tructures. The spectra from the InGaAs modulation-doped quantum well ( MDQW) channel can be accounted for on the basis of a step-like two-dim ensional density of states (screened exciton) and a Fermi level fillin g factor. A detailed lineshape fit makes it possible to evaluate the F ermi energy, and hence the two-dimensional electron gas concentration. Furthermore, other important parameters of the system such as built-i n electric fields, In composition and well width of the InGaAs MDQW ch annel can be evaluated.