Study Of Vertical GaN Schottky Barrier Diode

Gallium Nitride?GaN?power devices with the inherent material advantages have attracted worldwide attention extensively due to the huge potential for high voltage and power application.Recently,due to the breakthrough of bulk GaN growth,there has been a chance for GaN power devices to be grown homoepitaxially,which accelerates the progress of vertical GaN devices.Compared to lateral devices,achievements can be realized easier in vertical devices including high power in small size,superior thermal management and high reliability.With the merits of low turn-on voltage and high-speed switching,vertical GaN Schottky barrier diodes?SBDs?are highly desired for various high power application in electric circuits.However,vertical SBDs have not fully exerted their advantages but always suffer from high reverse leakage current and premature breakdown voltage.These problems indicate that the development of vertical SBDs still has a long way to go,and the technology of material growth and device fabrication need to be improved.At present,there have been five main challenges to fabricate high-performance vertical GaN SBD:fabricating high-quality Schottky contact;designing edge termination;growing high-quality GaN epilayer with low doping concentration;growing high-quality bulk GaN substrate and fabricating high-stability and low-resistant Ohmic contact.This thesis is focused on several key technologies of vertical GaN SBDs in order to break through challenges which hinder from fabricating high-performance SBDs.The main works are as follows:1.The GaN film homoepitaxially grown by hydride vapor phase epitaxy?HVPE?was demonstrated.The overall characterizations including the surface,crystal quality and impurities were carried out taking advantage of atomic force microscope?AFM?,cathdoluminescence?CL?,X-ray diffraction?XRD?and secondary ion mass spectrometry?SIMS?equipment.These results presented that homoepitaxial GaN layer grown by HVPE was high-quality and smooth with well-controlled impurities,which could be used for device fabrication.2.The edge termination structures of vertical GaN SBDs were presented.A vertical GaN SBD with field plate and a vertical GaN SBD not only with field plate but using fluorine?F?ion implantation treatment were fabricated.Compared with GaN SBD without F implantation,this SBD with F implantation effectively enhanced the breakdown voltage from 155V to 775V and significantly reduced the reverse leakage current by 10⁵ times.A high I_on?I_offratio of 10⁸ and high Schottky barrier height of0.92 eV were also achieved for this diode with F implantation.Meanwhile,the influence of F ion implantation to the device was discussed in detail.3.The thermal stability of GaN N face Ohmic contacts was studies.The difficulty of the low-temperature thermal degradation?about 300??of GaN N face Ohmic contacts was overcome through a suitable surface treatment to N face,and the specific contact resistance was lowered to the level of 10^-4?·cm².Meanwhile,the properties of GaN N surface and formed contacts were characterized taking advantage of atomic force microscope?AFM?,transmission electron microscope?TEM?and energy dispersive spectroscopy?EDS?equipment,and the key of fabricating thermally stable GaN N face Ohmic contacts was concluded.In addition,the influence of carrier density on GaN N face Ohmic contacts was also studied.It was concluded that high carrier density was helpful to form low-resistant and thermally stable Ohmic contacts.