ABSTRACTPhotoionization spectroscopy (PS) measurements, previously carried out for the GaN MESFET, have been extended to the more complicated AlGaN/GaN HEMT structures. In all cases, the spectra revealed that the same two traps causing current collapse in the high resistivity (HR) GaN buffer layer of the MESFET were also responsible for current collapse in the HEMT structures. The HR buffer layers supporting the HEMT structures were prepared by MOVPE at varying growth pressures, in order to vary the incorporation of deep trapping centers. Lower growth pressures were observed to correlate with more severe current collapse and with an enhanced incorporation of carbon. Detailed analysis of the PS data suggests that one of the two responsible traps is related to carbon, while the other may be associated with structural defects in the material.
CURRENT COLLAPSE MEASUREMENTS IN PULSED GAN TRANSISTORS