| GaN material has shown great potential in the application of high voltage and power devices due to large bandgap,large breakdown field,and two-dimensional-electron-gas(2DEG)with high density and high mobility induced by strong spontaneous and piezoelectric polarization effects in the heterostructure.Meanwhile,the compatible fabrication process between Al GaN/GaN Schottky Barrier Diodes(SBDs)and High Electron Mobility Transistors(HEMTs)shows a great promise for monolithic integration with suppressed parasitics capacitance,parasitic inductance and chip volume.With the gradual maturity of Al GaN/GaN epitaxial technology on large scale Si substrate,it shows a great breakthrough in reducing the cost of devices fabrication,which promotes the commercialization of GaN based power electronics.In order to improve the rectification efficiency and satisfy the application in high power,the SBDs with low turn-on voltage(VON),low leakage current(IR)and high breakdown voltage(BV)are essentials.Basing on the above background,this paper focused on the optimization of structuredesign and fabrication process of lateral AlGaN/GaN SBDs,and the main research work and research results are summarized as follows:1.The etching process of GaN material is optimized to satisfy the fabrication of groove anode with low etching rate and low damage.It shows a relatively stable etching rate and a small surface roughness compared to the conventional etching process,and a low rate etching process is helpful to achieve a smaller leakage current and a higher BV of devices.Basing on the international research results of SBDs with low VON,the AlGaN/GaN SBDs with dual anode metal is studied in this paper.According to the simulation results of groove Schottky anode under different bias and I-V characteristics of SBDs with various length of recessed Schottky metal(LSC),a device structure with a smaller LSC is proposed,which is helpful to obtain a high forward current density and a small leakage current at the same time.2.As for AlGaN/GaN SBDs with groove anode and fully recessed AlGaN barrier layer,the anode metal is contacted with the sidewall of GaN channel which is contributed to an extremely uniformity of devices characteristics.According to the First Principles Calculation in the paper,the theoretical basis about the rectifying effect of AlGaN/GaN SNDs with groove anode is obtained.The conventional anode metal Ni which shows a large work-function is hard to further reduce the VON.Based on the foundation of research,the low work-function metal W(4.6 e V)is proposed as anode metal of SBDs,which shows an extremely uniformity of devices characteristics,a low VON(0.35 V@1 m A/mm),a low IR(1.1?A/mm@-200 V)and a high BV(1900 V@LAC=25?m).In order to further reduce the VON and improve the efficiency of rectification,Mo with a lower work-function of 4.5 e V was proposed.By further optimizing the etching process of the device fabrication,high performance SBDs with a lower VON(0.31 V)and a higher BV(2650 V@LAC=25?m)were obtained.As for the SBD with LAC of 20?m,the power figure-of-merit(PFOM)is up to 2.65 GW/cm2,and it is the first time to get a BV over 2500 V and a PFOM over2.5 GW/cm2 on Si-based Al GaN/GaN epi.3.Generally speaking,SBDs with low VON always show a large IR which will increase the static power.The characteristics of devices whose anode is treated with various condition were studied in detail.The AlGaN barrier layer under anode was removed by the low rate and low damage etching process,also combined with low work-function metal as anode and annealing treatment,high performance GaN SBD with low VON of 0.38 V,low IR of 1.28×10-7 A/mm,high BV greater than 3 k V and low subthreshold slope of 65m V/dec was obtained.The record PFOM is more than 3 GW/cm2,and it is the first time to get a Al GaN/GaN SBD on Si substrate with BV more than 3000 V and PFOM more than 3GW/cm2.The mechanism of SBD with improved performance was obtained by the studying of the microstructure of the interface between anode metal and GaN surface.4.As for dry etching,due to the motion of plasma gas in the groove region will be affected by the sidewall of the GaN material and photoresist,so there will be an etching spike at the edge of anode groove.The thermal oxidation followed by wet etching in hot KOH solution technique is proposed instead of the conventional dry etching process,and the great surface morphology at the etching surface was obtained.Combined with the W anode fabrication process,great performance was achieved,which lays the foundation for the fabrication of high reliability Al GaN/GaN SBDs with groove anode.5.AlGaN material shows larger band gap and higher breakdown field compared with GaN material,so it is more suitable for the application under high voltage and anti-irradiation.Additionally,the 2DEG of AlGaN channel was insensitive to temperature which shows great potential for high temperature applications.However,it is difficult to obtain AlGaN material with excellent crystalline quality due to the significant lattice mismatches between Al GaN material and substrate,and the BV of devices shows negligible improvement.Furthermore,a large barrier height will be formed between anode metal and Al GaN channel,which will lead to serious degradation of VON.In this paper,low work-function metal Mo was proposed as anode,which shows a VON of 0.64 V.The leakage current only increased by 3 times at 425 K than 300 K,which shows a great improvement than GaN channel SBD,meanwhile,the degradation of on-resistance is less. |
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