Room-temperature phototransmittance and photoluminescence characterizationof the AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor structures with varied quantum well compositional profiles

We have studied the effects of the two-dimensional electron gas (2DEG) rind indium surface segregation in four pseudomorphic AlGaAs/InGaAs/GaAs high e lectron mobility transistor structures using room-temperature phototransmit tance (PT) and photoluminescence (PL) measurements. The PT spectra from the InGaAs modulation-doped quantum well channel can be accounted for by a lin eshape function which is the first-derivative of a step-like two-dimensiona l density of states and a Fermi level filling factor. A detailed lineshape fit makes it possible to evaluate the Fermi energy, and hence the concentra tion of 2DEG in addition to the energies of the intersubband transitions. T he lowest-lying intersubband transition has been confirmed by a comparison of the PT and PL spectra. From the difference of intersubband transition en ergies, the surface segregation effects of indium atoms are demonstrated.