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 480arcsec and GaN(102)FWHM is 900arcsec.The AGaN/GaN HEMTs with optimized and nonoptimized 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 Ids of 1.7μA/mm,gate leakage current density I_(gs)of 24.8μA/mm and off-state breakdown voltage VBR of 67V are achieved with L_(g)/W_(g)/L_(g)/L_(g)=1/10/1/1μm.For the small signal rf characteristics of the device with optimized AlGaN/AlN interlayer,current gain cutoff frequency fT of 8.3 GHz and power gain cutoff frequency fmax of 19.9GHz are achieved with L_(g)/W_(g)/L_(g)/L_(g)=1/100/1/1μm.Furthermore,the best rf performance with fT of 14.5 GHz and fmax of 37.3 GHz is achieved with a reduced gate length of 0.7μm.