Observations of backgate impedance dispersion in GaAs isolation structures

Low frequency reactive, resonant and negative resistance effects have been observed in backgate current flow in monolithic GaAs integrated circuits. Comparisons have been made between structures prepared by MBE on undoped buffer layers at high and low temperatures and by ion implantation. The study employed GaAs MESFETs which were similarly prepared on the three substrates. Backgate admittance spectroscopy measurements were performed between adjacent isolated n-type mesa structures on the different isolation materials in the range 10 Hz to 10 kHz, at temperatures ranging from 80 K to 340 K. In the case of the ion implanted and normally buffered structures the form of the susceptance frequency spectra depended on cathode size, dc bias and temperature and could include capacitive relaxation as well as inductive and capacitive behaviors separated by a resonance. The form of the variation of the conductance was closely associated and frequently included a frequency region within which there was negative small signal resistance. These effects were not present when the buffer layer was prepared at low temperatures. The results are summarized to make explicit the requirements of an explanatory model.