Optimization of AlGaN/GaN HEMT performance

Performance optimization of AlGaN/GaN HEMTs on sapphire or silicon substrates is presented. Firstly, 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 (I_dss=130-360 mA/mm and g_m,ext=79-132 mS/mm) is obtained on structures with nearly identical 2DEG properties (G_ch≅1 mS). An improvement of the DC behavior is obtained for RF-optimized i.e. linear HEMTs (I_dss=603 mA/mm and g_m,ext=236 mS/mm). High-frequency measurements show a f _T=35 GHz and f_max=70 GHz for L_G=300 nm and W_G=100 μm. 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 110 mS/mm. The highest saturation current reported so far for AlGaN/GaN/Si HEMTs and static output characteristics up to 20 V demonstrate that the devices are capable of handling 16 W/mm of static heat dissipation without any degradation of their performance