Small signal and pulse characteristics of AlN/GaN MOS-HEMTs

AlN/GaN HEMT technology has made rapid progress over the past decade with problems such as high contact resistance and leakage currents being overcome to a certain degree. This paper presents DC and RF results for a short gate length, in-house fabricated AlN/GaN MOS-HEMT. The results indicate that problems with growth and passivation still exist. An extraction technique for small signal equivalent circuit model values is also described which is based on on-wafer S-parameter measurements, and is the first detailed report providing insight to this new device technology. The approach taken is based on an accurate estimate of all the equivalent circuit elements followed by optimisation of these to get the actual element values. This way, element variations due to fabrication tolerances, measurement uncertainties such as probe tip placement accuracy and variations in material across a wafer are accounted for. Excellent fit between measured and modelled S-parameters as well as the physically realistic extracted equivalent circuit elements demonstrate the validity of the approach.