Study On The Fabrication Of Recessed-gate Enhancement-mode InAlN Barrier HEMT

GaN semiconductor materials have the advantages of wide band gap,high breakdown electrical field,high electron saturation velocity,corrosion resistance,anti-radiation and high-temperature stability,a promising material for high-frequency and high-power devices.The mainstream structure of GaN electronic devices is the high electron mobility transistor(HEMT)based on heterostructures,and the conventional GaN HEMTs are depletion-mode due to the existence of high-density two-dimensional electron gas at the interface of GaN heterostructures.However,in some applications of high-voltage switch,power electronics and high-power switch system,enhancement-mode devices enable to provide safer operating conditions and reduce the complexity and cost of the circuits.Therefore,the realization of reliable and stable enhancement-mode GaN HEMT devices is one of the research hotspots in GaN devices.In this context,this paper focuses on the structural design,fabrication process and performance analysis of recessed-gate structure enhancement-mode InAlN barrier HEMT devices.The main achievements are listed as follows:1.Planar-gate structure depletion-mode single-channel InAlN/GaN HEMT devices were fabricated.Compared with Schottky gate device,the output current density is increased by43%by adopting Al₂O₃gate dielectric,and the gate leakage current is decreased by 6orders of magnitude.Also,the gate control ability of the device is reduced and the threshold voltage shift negatively by 4.8 V.2.Recessed-gate enhancement-mode single-channel InAlN/GaN MOS-HEMT devices were fabricated.The threshold voltage of the device can be shifted positively by etching the barrier layer,and the threshold voltage is increased to 2.9 V for the single-channel InAlN/GaN MOS-HEMT with an etching depth of 17 nm.Compared with planer-gate depletion-mode single-channel InAlN/GaN MOS-HEMT,the threshold voltage is increased by 11.7 V.3.A low etching rate and smooth etched surface morphology are obtained by changing the parameters and the pulse period in the etching process,and recessed-gate enhancement-mode dual-channel InAlN/GaN MOS-HEMT devices were fabricated with gate slot depth of 33 nm.Due to high ohmic contact resistance,the threshold voltage is+0.2 V and the maximum saturation output current density is 200 m A/mm.Besides,the gate leakage current is about 10^-1 m A/mm due to the thin Al₂O₃ gate dielectric.4.The performance of the recessed-gate enhancement-mode dual-channel InAlN/GaN MOS-HEMT is enhanced by improving the processes of ohmic contact and gate dielectric deposition together with repairing etching damage.By increasing the ohmic contact annealing temperature to 850?and using the in-situ etching damage repair process based on plasma enhanced atomic layer deposition(PEALD),in conjunction with increasing the thickness of gate dielectric Al₂O₃ to 15 nm,an recessed-gate enhancement-mode dual-channel InAlN/GaN MOS-HEMT with gate length of 1.0?m and gate slot depth of40 nm was fabricated with a threshold voltage of+1.0 V and output current density of 282m A/mm as well as gate reverse leakage current of 10^-11 m A/mm.