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Effects of Impurity between Epitaxial Layer and Substrate on Current Transient for GaAs Metal-Semiconductor Field-Effect Transistors

The effects of the impurity between the epitaxial layer and substrate (epi/sub) on the current transient were examined by the drain bias pulsed current deep level transient spectroscopy (DLTS) method. Test devices used for evaluation were GaAs metal-semiconductor field-effect transistors (MESFETs) grown by metalorganic chemical vapor deposition (MOCVD). Energy-band diagram simulation of the MESFET structure showed that the drain bias pulsed current DLTS method is suitable for determining the buffer layer quality. Negative DLTS spectra, which were regarded to be caused by the electron emission in the AlGaAs buffer layer, were observed for both the intentionally doped epi/sub sample and purified epi/sub sample. The intensity difference of these DLTS signals could be explained by the quality change of the AlGaAs buffer layers. This electron trap was determined to be the oxygen-related deep level. For the purified epi/sub sample, another positive peak was found. The origin of this “hole trap”-like peak was discussed.