Characterization and modeling of AlGaN/GaN MOS capacitor with leakage for large signal transistor modeling

Dual mode AlGaN/GaN metal oxide semiconductor (MOS) heterostructure field-effect transistor (HFET) devices were fabricated and characterized. In HFET mode of operation the devices showed an f_T/spl middot/L/sub g/ product of 12GHz/spl middot/μm at Vgs=-2 V. The AlGaN devices showed formation of an accumulation layer under the gate in forward bias and a f_T/spl middot/L/sub g/ product of 6GHz/spl middot/μm was measured at Vgs=5 V. A novel piecewise small signal model for the gate capacitance of MOS HFET devices is presented and procedures to extract the capacitance in presence of gate leakage are outlined. The model accurately fits measured data from 45MHz to 10GHz over the entire bias range of operation of the device.

I. Introduction

Algan/gan heterostructure field-effect transistors (HFETs) have generated a lot of interest because of the extremely high power densities that have been demonstrated using these transistors. Recently, a field plated AlGaN/GaN HFET was demonstrated with 30W/mm power density in the X band [1]. However, RF dispersion continues to plague the microwave power performance and surface passivation has been identified as a way to alleviate dispersion [2]. Various oxides and nitrides have been investigated for surface passivation and have shown varying degrees of success [3].