Optimization of AlGaN/GaN HEMT performance

Performance optimization of AlGaN/GaN HEMTs on sapphire or silicon substrates is presented. At first, the Round-HEMT technology, which is simple in processing and allows fast feedback between structure growth and device properties, is presented. It is shown that different device performance (L-dss=130-360mA/mm and g(m,ext) =79-132mS/mm) is obtained on structures with nearly identical 2DEG properties (G(ch)congruent to 1mS). An improvement of the dc behavior is obtained on rf-optimized i.e. linear HEMTs (I-dss=603mA/mm. and g(m,ext)=236 mS/mm). High-frequency measurements show a f(T)=35GHz and f(max) =70GHz for L-G=300nm and W-G=100mum. Finally, first results we obtained on AlGaN/GaN HEMTs grown on Si substrates are presented. The Round-HEMTs with 300 nm gate length exhibit a saturation current of 820 mA/mm, a good pinch-off and a peak extrinsic transconductance of 110mS/mm. Highest saturation current reported so far on AlGaN/GaN/Si HEMTs and static output characteristics up to 20V demonstrate that the devices are capable of handling 16W/mm of static heat dissipation without any degradation of their performance.