Correlation Between Epitaxial Layer Quality and Drain Current Stability of GaN/AlGaN/GaN Heterostructure Field-Effect Transistors

Stability of current-voltage characteristics was investigated for GaN/AlGaN/GaN heterostructure field-effect transistors, which were fabricated using epiwafers with different yellow luminescence (YL)-to-band edge (BE) ratios in photoluminescence spectrum and full-width at half-maximum (FWHM) values of X-ray rocking curves. After application of a long-term high-voltage OFF-state stress, they exhibited a temporary reduction of drain current (I_d) accompanied by a positive threshold voltage shift with a long recovery time (>1 h at room temperature). To study the mechanism of this instability, transient of Id just after removing the stress was measured under the subthreshold condition for different ambient temperatures (-20 °C to 200 °C). An isothermal capacitance transient spectroscopy-like analysis applied to the transient signal indicated that electron traps with an activation energy of 0.3-0.5 eV and a density of the order of 10¹¹ cm^-2 are responsible for this phenomenon. The emission rate of these electron traps increased when the YL/BE ratio was reduced, while the trap density decreased when the FWHM values were reduced. These results suggest that the long-term Id transient can be minimized by reducing both of these parameters.