Interpretation of transconductance dispersion in GaAs MESFET using deep level transient spectroscopy

The negative transconductance dispersion in a GaAs metal-semiconductor field-effect transistor (MESFET) was interpreted using both surface leakage current and capacitance deep level transient spectroscopy (DLTS) measurements. The transconductance of the device was reduced by 10% in the frequency range of 10 Hz /spl sim/1 kHz. The transition frequency shifted to higher frequency region with the increase of device temperature. The activation energy for the change of the transition frequency was determined to be 0.66/spl plusmn/0.02 eV. It was found that the activation energy for the conductance of electrons on the surface of GaAs was 0.63/spl plusmn/0.01 eV. In the DLTS spectra, two types of hole-like signals with activation energies, 0.65/spl plusmn/0.07 eV (H1) and 0.88/spl plusmn/0.04 eV (H2), were observed. The activation energy of H1 trap agrees well with those obtained from the transconductance dispersion and surface leakage current measurements. This demonstrates that surface state H1 causes the generation of surface leakage current, leading to the transconductance dispersion in the MESFET. Using the experimental results, a model for the evolution of hole-like signal by surface states in the capacitance DLTS is proposed.