Study On Growth Of High Quality InAlGaN/GaN Heterostructures And Devices

III group nitride is one of the most important semiconductor to fabricate electric power devices and photoelectric devices because of its wide and direct bandgap.GaN based high mobility transistors can get high critical breakdown voltage due to its wide bandgap.They have high electron saturation drift velocity due to the exist of two-dimensional electron gas at the interface of the heterostructure induced by its strong spontaneous polarization and piezoelectric effect.It also suitable to work in high temperature because of its stable chemical properties.These superior properties made them great application potential in aerospace,radar and communication field.AlGaN/GaN heterojunction is the most widely used structure in III-V nitride heterosturctures and quite a lot of remarkable achievements have been made based on it.But,AlGaN/GaN based devices also have some problems that it can not overcome,such as lattice mismatch between the AlGaN barrier and GaN channel,inverse piezoelectric effect and so on.Using InAlGaN quaternary alloy instead of AlGaN as the barrier layer of the heterostructure can solve the above problems very well and further enhance GaN based device performances.Base on the background mentioned above,this dissertation mainly investigated the composition design of InAlGaN barrier layer,epitaxial growth of high quality InAlGaN quaternary barrier and analysis of related HEMT device performences.The major work and research results are listed as follows:1.Two kinds of InAlGaN/GaN heterostructures（lattice mach and polarization match）were designed for HEMT application through the 2DEG density analytical model of nitride.For the lattice matched In AlGaN/GaN heterostructure（Al/In ratio is about 4.56）,even though there is no piezoelectric polarization,it still can induce high density 2DEG at the heterostructure interface by strong spontaneous polarization.As the Ga composition of the barrier layer is decreasing（InAlGaN barreir layer and GaN channel keep lattice mateching）,the donduction band offset increased and the density 2DEG is increasing.The electrical properties of the polarization matched InAlGaN/GaN heterostructure can be used for the preparation of enhanced mode HEMT by rational design of the barrier compositions.2.High quality InAlGaN quaternary alloy PMOCVD growth method has been established through process optimization.Influence of substrate temperature,reaction chamber pressure and TEGa flow on PMOCVD growth InAlGaN alloy has been studied.The Ga composition of the barrier layer increased by increasing the TEGa flow.When the TEGa flow is 3.6?mol/min,the sample get the minimum RMS value and the highest2DEG mobility.As the reaction chamber pressure increased from 150 Torr to 250 Torr,Al composition of the barrier layer gradually reduce,growth rate gradually increased,the surface of the film morphology has the minimum RMS values at 200 Torr.At 680℃to760℃temperature range,there is no signs of phase separation in the barrier layer.The electrical characteristics of the heterostrcture is good and has the highest 2DEG mobility which is as high as 1378 cm²/V?s when the growth temperature is 760℃.3.Combined the advantages of InAlGaN barrier and AlGaN layer,InAlGaN/AlGaN/GaN heterostructure with composite barrier layer has been innovative designed and realized.Compared with InAlGaN/GaN heterostructure,the 2DEG transport properties of InAlGaN/AlGaN/GaN heterostructure get obvious improvement,2DEG mobility is 1889 cm²/V?s and square resistance is 201?/?.4.High quality nearly-lattice matched InAlGaN/GaN heterostructure was grown by PMOCVD technology,HEMTs based on this heterostructure was prepared and the device characteristics have been tested.Electrical properties of the heterostructure was measured by Hall effect at room temperature.2DEG mobility is 1668 cm²/V?s,square resistance value is 262?/?.The device test results shown that the biggest saturation output current is760 mA/mm,maximum transconductance is 147 mS/mm,characteristic frequency f _T and maximum oscillation frequency f_max is 11 GHz and 21 GHz respectively.The results above revealed that the PMOCVD is feasible in high quality InAlGaN quaternary growth.5.Nearly polarization matched InAlGaN/GaN heterostructure was grown by PMOCVD based on InAlGaN/GaN heterostructure polarization control theory for the preparation of enhance mode HEMT devices.The components of the In AlGaN barrier layer was measured by SIMS.Hall effect was measured at room temperature shown that the 2DEG mobility is 1129 cm²/V?s which is much higher than the reported results,2DEG density is6.0?10¹¹ cm^-2.Through standard HEMT preparation process,enhanced HEMTs device was prepared.Device’s threshold voltage is as high as+0.7 V,maximum transconductance is 69mS/mm and the maximum saturation current is 172 mA/mm.