Study On The InAlN/GaN Heterojunction Schottky Diode

As the core device of rectifying circuit,limiting circuit,etc.,high-power GaN Schottky Barrier Diode(SBD)has attracted much attention in recent years.In the research of gan-based SBD,the main material used is Al GaN/GaN heterostructure material,which has obtained excellent device performance.Yet In GaN heterostructure,InAlN/GaN has better performance than InAlN/GaN in many aspects,especially the lattice matching between In Al N and GaN at an indium content is 17%.However,the quality of In Al N barrier layer is not as good as Al GaN barrier layer,it will bring great challenges to the SBD devices,so there are few studies.In order to make up for the lack of this research,the InAlN/GaN heterojunction schottky diode has been studied in this paper.The major achievements are listed as following:1.High quality InAlN/GaN heterostructures are successfully grown on c-plane sapphire substrate by proposed pulsed metal organic chemical vapor deposition(PMOCVD)and combined with Al N dislocation blocking layer.Atomic force microscope(AFM)test showed that the epitaxial material surface root mean square(rms)roughness is 0.2nm,GaN(002)and(102)planes full widths of half maximum of rocking curves tesed by XRD were220arcsec and 325arcsec respectively corresponding to the screw dislocation and edge dislocation density were 4.3×10⁷(88)^-2and2.3×10⁸(88)^-2,two dimensional electron gas(2DEG)sheet carrier density at room temperature is 1.9×10¹³(88)^-2.2.Lattice matched InAlN/GaN heterojunction schottky diodes with turn on voltage(V_on)of0.8V and on-resistance(R_on)of 10??mm were fabricated and investigated by their current-voltage characteristics measured at various temperatures(300k-500k),it was found that the schottky barrier height(SBH)was lower than the theoretical value due to SBH inhomogeneity.When the temperature increases,the donor ion ionization in the barrier layer enlarges the depletion region,resulting in the increase of the barrier height?₍(7) as the temperature increases.At high temperatures the electrons have more energy to cross the barrier,so the ideality factor(n)decreases as the temperature increases.The IV characteristics of the device showed strong temperature correlation,which did not conform to the ideal thermionic emission mechanism(TE).In-depth analysis shows that the forward-low-bias current is dominated by the trap assisted tunneling model(TAT),while the forward-high-bias current is governed by the thermionic emission mechanism with a significant series resistance effect;the reverse leakage current under low bias the reverse current is mainly carried by the Frenkel-Poole emission electrons(FP),while at higher bias the Fowler-Nordheim tunneling mechanism(FN)dominates due to the formation of a triangular barrier.3.The fabrication process and anode structure of InAlN/GaN heterojunction schottky diode were optimized,which significantly improved the performance of the device.By adopting ohmic contact area etching process,make the device on-resistance reduced to14?from 23?which anode radius of 120?m,the anode–cathode distance(L_AC)of 3?m,forward current reached 0.1A@2.2v;The device V_on is reduced from 0.8V to 0.55V by using the recessed anode structure.Ammonium sulfide passivation reduced the reverse leakage of InAlN/GaN heterojunction schottky diode by an order of magnitude.4.Double channel InAlN/GaN heterojunction schottky diode with low on-resistance was developed.It showed better forward properties than single channel InAlN/GaN heterojunction schottky diode.Its forward current reached 0.1A@2.7v which anode radius of 120?m and the L_AC of 6?m,and the R_ondecreased 1.9??mm than the single channel device.but it suffers a high reverse leakage current.In order to solve this problem,two methods were proposed,namely,inserting Al₂O₃ medium layer between anode metal and In Al N barrier layer by ALD to form MOS anode structure and thermal oxidation treatment of In Al N barrier layer.Experimental results showed that both methods can significantly reduce the reverse leakage of double channel InAlN/GaN heterojunction schottky diode.