| Industrial semiconductors based on Silicon(Si)materials have made unprecedented progress.However,their smaller band gaps can not meet the requirements of semiconductor devices for high-voltage,high-frequency,high-power,and short-wavelength emission and detection.As a new type of ultra-wide band gap(UWBG)semiconductor,Gallium Oxide(?-Ga2O3)has received more and more advantages by virtue of its ultra-wide band gap,extremely high breakdown field strength and high electron saturation drift speed.People pay more attention to it.In recent years,there has been endless reports on?-Ga2O3 based field effect transistor(FET)devices at home and abroad.Its low cost single crystal growth technology,controllable donor doping,and low loss characteristics during switching are very suitable for making FET power Device.However,there are still some problems of the research of?-Ga2O3 FET devices.The excessively wide band gap makes it difficult for?-Ga2O3 materials to form a lower contact resistance,which increases the on-state resistance and power loss of the device during operation.The preparation of thermally stable ohmic contact is so significant that it can improve the performance of the device under high temperature and high pressure.In addition,the realization of enhanced devices is conducive to take advantage of?-Ga2O3 in high-power power electronics.However,due to the lack of acceptor doping,there are few reports on enhanced(E-MODE)?-Ga2O3 FETs.In response to the above problems,thesis first starts with the simulation of?-Ga2O3structure of metal-oxide-semiconductor field effect transistor(MOSFET)device,and has deep understanding of the work mechanism of the device,and then obtains a single crystal?-Ga2O3 nanometer by means of mechanical peeling.Thesis fabricates MOSFET devices with back gate structure,optimizes the contact resistance of the device through rapid annealing,and finally studies the electrical properties of nano belts with different thicknesses as a function of thickness,and obtains an enhanced device with a minimum thickness of 27nm.The summary of thesis is as follows:1.First,in this paper,the device models and electrical simulation of?-Ga2O3 MOSFET with lateral back-gate structure are carried out.The mobility model,carrier generation-recombination model,etc.We describe the carrier,electric field and potential distribution of the?-Ga2O3 channel in the switching state,and theoretically verify that?-Ga2O3 can regulate the different thickness of the channel to realize depletion and enhancement devices.Simulation of breakdown characteristics shows that the carrier concentration is 2×1017cm-3.The channel length is 4?m,and the thickness is 150 nm.The reverse breakdown voltage of the device with no termination structure reaches 234 V,and the critical breakdown field at the drain reaches 4.8 MV/cm,which proves the convincing voltage capability of?-Ga2O3 as a FET power device.In addition,the simulation of temperature characteristics shows that when the operating temperature is increased from 25°C to 225°C,the carrier mobility increases and the device saturation current increases About 20%.2.Secondly,the preparation and process optimization of UID(1.21×1017 cm-3)?-Ga2O3MOSFET with back-gate structure are carried out.We use mechanical lift-off method to obtain?-Ga2O3 single crystal nano belts and transfer to Si O2/Si insulating substrate,locate by electron beam lithography,complete ohmic pattern;by increasing the thickness of deposited metal and rapid annealing,the contact resistance of the device was reduced by other means.The transmission line model method(TLM)test results of the device after annealing at 470°C shows that the metal-semiconductor contact type changes from Schottky characteristics to Ohmic characteristics,and the saturation current increases from 0.091m A/mm to 5.5 m A/mm.The calculated Rc is 16.52?·mm,which is close to the mainstream data indicators at home and abroad.After process optimization,the sub-threshold swing of the 303 nm thick MOSFET device is 0.71 m V/dec,and the saturation current reaches 6.22m A/mm;at high temperature of 200°C,the switching ratio can still reach 105,and the saturation current can reach 12.5 m A/mm.It proves the advantages of the wide band gap material of Gallium Oxide material in high temperature environment.In addition,this article also explores an inductively coupled plasma(ICP)etching process suitable for?-Ga2O3 nano belts,and the surface roughness of the material after etching is 0.23 nm.3.Finally,this work obtains the experimental rule of?-Ga2O3 MOSFET device threshold voltage changing with thickness,and realizes the transition of the device from depletion mode to enhancement mode.Tape stripping obtains multiple groups of?-Ga2O3 single crystals with different thicknesses(300-27 nm)and fabricates MOSFET devices with threshold voltage range from-95 V to 60 V.When the thickness of?-Ga2O3 MOSFET is reduced to 110 nm,the device is changed from D-MODE to E-MODE.The breakdown voltages of the 110 nm E-MODE and 204 nm D-MODE devices reach 128 V and 263 V,respectively,which fully prove the convincing voltage capability of the?-Ga2O3 MOSFET structure three-terminal device.In particular,the experiment also prepares an ultra-thin?-Ga2O3 MOSFET device with a thickness of 27 nm.Its off-state current is as low as 10-7m A/mm,and the switching ratio reaches 6 orders of magnitude.This thickness is the lowest thickness of?-Ga2O3 device obtained by mechanical peeling in recent years. |
PDF Full Text Request