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Investigation Of ?-Ga2O3 Schottky Barrier Diodes

Posted on:2022-02-07Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z Z HuFull Text:PDF
GTID:1488306605989109Subject:Microelectronics and Solid State Electronics
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Gallium oxide,as an emerging ultra-wide band semiconductor material,has drawn much attention due to its ultra-wide band and high theoretical critical breakdown electric field.With the progress of material growth research,the low growth cost of bulk single crystals and the ever-increasing epitaxial technology have made the large-scale production of gallium oxide take shape and have huge development potential.The advantages in cost combined with a larger band gap make it have lower power loss and higher conversion efficiency in the application of power electronic devices,which has led to rapid development to the gallium oxide based power devices.Gallium oxide Schottky barrier diodes have become one of the research focuses and hotspots of gallium oxide power devices in recent years because of their faster switching speed,reliable high-temperature and high-voltage operation and lower off-state loss.Based on the above research background,this dissertation starts from the study of the material characteristics of gallium oxide,and investigates the Schottky contact characteristics of metal and gallium oxide.On this basis,horizontal and vertical Schottky diodes are fabricated and their forward and reverse current transport mechanisms are studied.Finally,combined with 2-D theoretical simulation,a gallium oxide Schottky diode with high breakdown voltage and high power density with edge terminal structure was designed and fabricated.Starting with materials,combining theoretical analysis,mechanism research,and finally realizing Schottky diode devices with high breakdown voltage and high power,this dissertation consolidates the theoretical foundation for the research of gallium oxide Schottky diodes and highlights its broad application prospects in power devices.The main research contents and results of this dissertation are as follows:1.The material properties of gallium oxide and the adjustment engineering of the bandgap of gallium oxide doped with aluminum are studied.The method of segmented fitting ellipsometer test results is used for the first time to study the optical bandgap width,extinction coefficient and absorption coefficient of gallium oxide material epitaxially on sapphire.The experimental results are compared and analyzed by transmission spectrum.Good consistency results were obtained.At the same time,pulsed laser deposition was used to epitaxial high-quality aluminum gallium oxide thin film layers with different Al components on sapphire,and the optical properties were characterized in the same way.2.The characteristics of metal/Gallium Oxide Schottky contact including Schottky contact barrier and its inhomogeneity,the forward,reverse current transport mechanism and interface state of Schottky junction were studied.For the first time,a high-quality gallium oxide flake was obtained by mechanical peeling off from the substrate,and for the first time,a Schottky diode was prepared using Mo/Au as Schottky contact.The forward and reverse IV,variable temperature IV,variable frequency CV,and continuous stress in the on and off states of the fabricated Schottky diodes were tested.By analyzing the test results,the Schottky contact barrier and ideality factor of Mo and Ni,the current transport mechanism,the inhomogeneity of Schottky barrier and the interface state of metal-semiconductor contact were investigated.It is finally verified that the Schottky diode has a Gaussian Schottky barrier with an average barrier height of 1.55 e V and a standard deviation of 0.186 e V,and has an interface state with a density of 1.24×1012cm-2e V-1-1.71×1013 cm-2e V-1 where the energy level lies 0.87-0.90 e V below the conduction band edge.At the same time,the Schottky barrier inhomogeneity of the Schottky diodes fabricated on the(Al0.11Ga0.89)2O3 film epitaxially on gallium oxide were investigated.3.Fabricated and studied lateral gallium oxide-based Schottky diodes with a high breakdown voltage.For the first time,a lateral nano-membranes gallium oxide Schottky barrier diode on sapphire substrate was prepared.Without any terminal structure to improve the electric field concentration effect,devices with a cathode-anode spacing of 4?m,6?m,11?m,and 15?m have breakdown voltages of 0.64 k V,0.85 k V,1.2 k V and 1.7k V,respectively.Furthermore,a lateral Schottky diode with a field plate was fabricated on a sapphire substrate,and a power density of up to 500 MW/cm2 was obtained.For the first time,a gallium oxide Schottky diode with a breakdown voltage more than 3 k V was obtained at an anode-cathode spacing of 24?m.The reliability of the device has been initially explored.The device with a breakdown voltage of 2.26 k V and a cathode-anode spacing of 26?m is subjected to a reverse high voltage stress of-600 V for up to 104ms,and the device only exhibited only a 15%increase in forward on-resistance.The increase in on-resistance indicates the broad application prospects of gallium oxide materials in power devices.4.Fabricated and studied vertical gallium oxide based Schottky diodes with high breakdown voltage.A variety of terminal structures are proposed and fabricated to alleviate the edge concentration effect of the electric field,thereby increasing the breakdown voltage of Schottky diode devices.The Schottky diode with a floating metal ring fabricated has the highest breakdown voltage of 188 V when the distance between the metal ring and the anode is 3?m,which is 57.98%higher than the reverse breakdown voltage of the device without the terminal structure.The fabricated vertical gallium oxide Schottky diode with N-injection guard ring has an on-resistance value of 8 m?·cm2 and a breakdown voltage of1420 V.Because it is difficult to achieve p-type doping of gallium oxide,a Metal/Ti O2/?-gallium oxide MDS junction diode with Ti O2 as the insulating layer has also been proposed and investigated.Without the need for high-temperature annealing,high-energy ion implantation,plasma etching and other complex processes,the prepared MDS diode exhibits an high quality power pefermance with a on-resistance of 3.3 m?·cm2 and a breakdown voltage of 1010 V.5.For the first time,a vertical bevel fluoride ion plasma treatment terminated gallium oxide Schottky diode was proposed and fabricated.The RIE plasma shallow low-energy fluoride ion treatment was used,and combined with the bevel mesa terminal method,a breakdown voltage of 1050 V was obtained with a on-resistance of 2.5 m?·cm2.Compared with the device without a terminal structure,the bevel fluoride ion plasma treatment termination increases the breakdown voltage of the device from 200 V to 1050 V,and finally achieves a power density of 0.44 GW/cm2.Using Silvaco to simulate the influence of the device structure parameters of the vertical bevel fluoride ion plasma treatment terminated gallium oxide Schottky diode on the breakdown voltage and optimize the structure.The breakdown voltage of the optimized Schottky diode is about 2450 V,which is about 5 times that of the unterminal structure.The theoretical simulation of the device not only gives the structural parameters of the optimized BFPT Schottky diode,but also shows the broad prospects for the development of gallium oxide Schottky diode.
Keywords/Search Tags:Gallium Oxide, Schottky diode, mechanism analysis, high breakdown voltage, power device, two-dimensional simulation
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