Study Of Blocking Performances In Vertical GaN-based HEMT Devices

Recently,the vertical GaN-based HEMT has attracted much attention in fields of high power electronics due to its excellent characteristics.Studies of the methods for improving the blocking and turn-on characteristic has been one of the hot topics.With the introduction of the P_doping_Buried-layer,superjunction,SiO₂ CBL techniques,the performance of the vertical device has been improved significantly,which is a foundation for the current wider applications.However,the contradiction between the breakdown voltage and on-resistance in device is still obvious in existing technologies.Therefore,how to solve the above problems and further improve the performance of power devices is the focus of studies for many researchers at home and abroad,which is also the forcus of this thesis.The main researches and achievements are presented as following.?1?A kind of ladder current blocking layer technology is proposed.Based on this technology,the blocking characteristics and conduction characteristics of vertical GaN-based HEMT device with different kinds of ladder current blocking structure are studied.The results show that compared with the traditional vertical GaN-based HEMT device,the ladder current blocking layer vertical GaN-based HEMT devices could form additional electric field peaks inside the device so as to more efficiently modulate the electric field distribution near the current blocking layer and improve the breakdown characteristics of device.Since the ladder current barrier layer is far away from the current aperture,the depletion region is far from the conduction current path,the on-resistance of the device can be reduced more effectively.?2?Two kinds of vertical GaN-based HEMT devices based on P_doping_embeded_layer structure in buffer layer are proposed and studied.The results show that with the increase of the depth of P_doping_embeded_layer,the device can form several electric field peaks by optimizing the corresponding doping concentration,which can effectively modulate the electric field distribution in the buffer layer and improve the device breakdown characteristics.And the depletion region of the double vertical P_doping_embeded_layer structure is far away from the current path,which could decrease the on-resistance.?3?Four kinds of novel structures,namely,half superjunction,T-type superjunction,high-k insultor and the current blocking layer growing on high-k insultor vertical GaN-based HEMTs are proposed and studied based on the ideal of semi-superjunction and high-k insultor in vertical Si-based MOSFET devices.And the operation mechanism of these devices is analyized in-depth.The results reveal that all the four device structures can effectively modulate the device electric field distribution and obviously improve the breakdown voltage.In the half superjunction device,an extra electric field peak is formed near the half superjunction,which improves the device breakdown characteristics and reduces the on-resistance.In the T-type half superjunction,by optimizing the corresponding doping concentration with the change of half superjunction length,an additional electric field peak can be formed to realize the vertical GaN-based HEMT device with different half superjunction length for the same breakdown voltage and on-resistance.This could increase the freedom of the impurity doping in the device design.In the high-k insultor HEMT,the breakdown voltage is approximately equal to that of the superjunction HEMT,while the on-resistance will decrease significantly and is even lower than that of the traditional device.This indicates an improvement of the turn-on performance in the high-k insultor HEMT,and a FOM value,as high as 2.8GW/cm²,could be achieved.In order to further realize the high-k enhancement device,the method of regrowing the P-type current blocking layer on high-k layer is utilized,which can improve the enhancement effect and modulate the electric field in the buffer and thus lead to a higher breakdown voltage.