Improved AlGaN/GaN HEMTs Grown on Si Substrates Using Stacked AlGaN/AlN Interlayer by MOCVD

AlGaN/GaN high electron mobility transistors (HEMTs) are grown on 2-inch Si (111) substrates by MOCVD. The stacked AlGaN/AlN interlayer with different AlGaN thickness and indium surfactant doped is designed and optimized to relieve the tensile stress during GaN epitaxial growth. The top 1.0μm GaN buffer layer grown on the optimized AlGaN/AlN interlayer shows a crack-free and shining surface. The XRD results show that GaN(002) FWHM is 480 arcsec and GaN(102) FWHM is 900 arcsec. The AGaN/GaN HEMTs with optimized and non-optimized AlGaN/AlN interlayer are grown and processed for comparison and the dc and rf characteristics are characterized. For the dc characteristics of the device with optimized AlGaN/AlN interlayer, maximum drain current density I_dss of 737mA/mm, peak transconductance G_m of 185mS/mm, drain leakage current density I_ds of 1.7μA/mm, gate leakage current density I_gs of 24.8 μA/mm and off-state breakdown voltage V_BR of 67 V are achieved with L_g/W_g/L_gs/L_gd = 1/10/1/1 μm. For the small signal rf characteristics of the device with optimized AlGaN/AlN interlayer, current gain cutoff frequency f_T of 8.3 GHz and power gain cutoff frequency f_max of 19.9 GHz are achieved with L_g/W_g/L_gs/L_gd = 1/100/1/1 μm. Furthermore, the best rf performance with f_T of 14.5 GHz and f_max of 37.3 GHz is achieved with a reduced gate length of 0.7μm.