Frequency-dependent characteristics and trap studies of lattice-matched (x=0.53) and strained (x<0.53) In/sub 0.52/Al/sub 0.48/As/In/sub x/ Ga/sub 1-x/As HEMTs

The low-frequency characteristics of InAlAs/In/sub x/Ga/sub 1-x/As high-electron-mobility transistors (HEMTs) are studied, and trap densities are evaluated. The HEMTs' transductance (g/sub m/) and output resistance (R/sub ds/) dispersion are smallest for 60% indium (In) content and largest for 53% In. The maximum dispersion for the 53% In sample is approximately 6% for g/sub m/ and approximately 13.3% for R/sub ds/ corresponding to lower values than observed in MESFETs. The R/sub ds/ dispersion characteristics are weaker than in AlGaAs/GaAs HEMTs and manifest themselves primarily up to 100 kHz. An analysis of the dispersion results indicates that, unlike in the case of MESFETs, the channel region under the gate rather than the access regions is responsible for the dispersion. Interface state densities were extracted by the AC conductance method and were found to follow the same trend as the g/sub m/ and R/sub ds/ dispersion: maximum values (2.69*10/sup 12/ cm/sup -2//eV/sup -1/) for 53% In and minimum (1.98*10/sup 12/ cm/sup -2//eV/sup -1/) for 60% In.>