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.

Effects of AlGaN/AlN Stacked Interlayers on GaN Growth on Si （111）

We report the growth of high quality and crack-free GaN film on Si （111） substrate using Al0.2Ga0.8N/AlN stacked interlayers. Compared with the previously used single AlN interlayer, the AlGaN/AlN stacked interlayers can more effectively reduce the tensile stress inside the GaN layer. The cross-sectional TEM image reveals the bending and annihilation of threading dislocations （TDs） in the overgrown GaN film which leads to a decrease of TD density.

Improved breakdown voltage of AlGaN/GaN HEMTs grown on Si substrates using partially Mg-doped GaN buffer layer by MOCVD

AlGaN/GaN high electron mobility transistors(HEMTs) were grown on Si substrates by MOCVD.In the HEMT structure,a 1 μm GaN buffer layer was partially doped with Mg in an attempt to increase the resistivity and minimize the buffer leakage.The AlGaN/GaN HEMTs grown on undoped and partially Mg-doped GaN buffer layers were processed and the DC characteristics of the devices were characterized for comparing the effect of Mg doping.For the device with the partially Mg-doped GaN buffer layer,a lower drain leakage current density of 55.8 nA/mm,a lower gate leakage current density of 2.73 μA/mm,and a higher off-state breakdown voltage of 104 V were achieved with device dimensions Lg/Wg/Lgs/Lgd=1/10/1/1 μm,better than the device with the undoped GaN buffer layer,which has a higher drain leakage current density of 9.2 μA/mm,a higher gate leakage current density of 91.8 μA/mm,and a lower off-state breakdown voltage of 87 V with the same device dimensions.