Temperature-dependent photoreflectance and photoluminescence characterization of the subband structure and built-in electric field of GaAs/GaInAs graded-channel high electron mobility transistor structures

We have measured temperature-dependent photoreflectance (PR) and photoluminescence (PL) spectra of three symmetric linearly graded GaAs/GaInAs high electron mobility transistor (gHEMT) structures with opposite channel-band slopes in the temperature range between 30 and 300 K. Analyses of the PL and PR spectra indicate the existence of two-dimensional electron gas (2DEG) in the graded-channel well of the three gHEMTs in the temperature range of 30-300 K. The comparison of PL and PR spectra facilitates the identification of channel-well transitions in the gHEMTs with different channel-band slopes. Inter-subband transitions, Fermi-level energies, 2DEG and the built-in electric field of the three gHEMTs with dissimilar channel-band slopes are evaluated. The well widths for the gHEMTs of different channel-band slopes are estimated. The temperature dependences of the channel inter-subband transition energy and built-in electric field of the three gHEMTs are analyzed and discussed.