Abstract
Using room-temperature surface photovoltage spectroscopy (SPS) we have characterized four GaAlAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (pHEMT) structures with varied quantum well compositional profiles fabricated by molecular beam epitaxy. Signals have been observed from every region of the samples. The normalized first derivative of the surface photovoltage (SPV) signal with respect to photon energy from the InGaAs quantum well channel can be accounted for by a line shape function which is the first derivative of a step-like two-dimensional density of states and a Fermi level filling factor. A detailed line shape fit makes it possible to evaluate the Fermi energy, and hence the concentration of two-dimensional electron gas in addition to the energies of the intersubband transitions. The differences of intersubband transition energies are attributed to the surface segregation effects of indium atoms. In addition, other important parameters of the system such as the Al composition and the properties of the GaAs/GaAlAs superlattice (SL) buffer layer also are obtained from the SPV spectra. The results demonstrate the considerable potential of SPS for the contactless and nondestructive characterization of pHEMT structures at room temperature.
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