Improvements of surface morphology and sheet resistance of AlGaN/GaN HEMT structures using quasi AlGaN barrier layers

We report the growth and characterization results of AlGaN/GaN heterostructures using quasi AlGaN as a barrier layer, which is formed by AlN/GaN super-lattice. It is found that the surface morphology of the heterostructure is greatly improved, where monolayer steps on the surface are clearly observed. Simultaneously, electric properties in such structures are superior to those using the conventional alloy AlGaN caplayers. Low sheet resistance (less than 200 Ω/□) is obtained from our samples with high Al composition (>40%) in average, which shows the great merit of our growth method to the conventional technique. It is expected that the technique can be applied to the high power and high frequency device applications.