Research On Field Control Energy-band Mechanism And New Structure Of E-mode GaN-on-Si Power Devices

Due to the advantages of high breakdown voltage,high operating temperature and high operating frequency,Gallium Nitride on Silicon(GaN-on-Si)based power semiconductor devices are ideal semiconductor switches in the field of power electronics,and have become one of the research hotspots in the international semiconductor field.Owing to the great convenience of the enhancement-mode(E-mode)power device,the preparation of high-performance GaN-on-Si E-mode power device is the focus of scholars'attention.In order to reduce the design cycle and cost of power devices,theoretical models of devices are often needed for the design of power devices,but there is little research on physical models of GaN-on-Si E-mode power devices.At the same time,the long-term reliability of GaN-on-Si E-mode power devices needs to be studied in all aspects.In addition,some applications require that GaN-on-Si E-mode power devices not only have excellent forward blocking ability,but also reverse blocking ability.In view of the above problems in the development of GaN-on-Si power semiconductor technology,the theoretical model,novel structure,key process and long-term reliability of GaN-on-Si E-mode power devices are studied in this dissertation.The main innovations of this dissertation are as follows:(1)Field control energy-band model for GaN-on-Si E-mode power devices.The field control energy-band mechanism of GaN-on-Si E-mode power devices is studied,and the influence of the device structure,material structure,trap charge and applied electric field on the energy band structure and two-dimensional electron gas(2DEG)concentration is analyzed.Then the field control energy-band model for GaN-on-Si E-mode power devices has been established.It not only reveals the relationship between constant-density trap charge and 2DEG concentration,but also introduces the relationship between trap charge density and the applied electric field,the trap charge distribution function.(2)Novel field control structure for GaN-on-Si E-mode power devices.Under the guidance of the above model,a reverse blocking GaN-on-Si field control energy-band power device with a Schottky-Metal Insulator Semiconductor(Sch-MIS)mixed Drain used to replace the ohmic Drain and a graded Aluminum component barrier layer used to replace conventional barrier layer is proposed.By combining the high reverse blocking capability of the Sch-MIS mixed Drain and the high forward conduction capability of the graded Aluminum component barrier layer,the turn-on voltage of the device is reduced by 15%,and the reverse blocking voltage is increased by 350%.Based on the above model,a reverse blocking GaN-on-Si field control tunneling power device without ohmic contact is further proposed.The device can be turn on by changing the barrier thickness of Source Schottky junction controlled by the insulated Gate.The proposed device can be fabricated at a lower temperature to avoid oxidation of the surface of the barrier layer.(3)High temperature and low damage etching technique for GaN-on-Si E-mode power devices.Research on etching technology of GaN-on-Si E-mode power devices is carried out.And a high temperature and low damage etching technology is proposed.The proposed etching technology can reduce the etching damage and surface roughness,and reduce the concentration of trap charges,thus reduce the influence of electric field formed by trap charges on the energy-band structure and 2DEG concentration,and improve the2DEG mobility of device.Through the proposed etching technology,a GaN-on-Si E-mode power device with high threshold voltage(3.2V),high channel mobility(180cm~2/V?s)and high conduction current(663 mA/mm)is obtained.(4)Field-induced degradation mechanism of GaN-on-Si E-mode power devicesUnder the guidance of the field control energy-band model,the influence of pulse overcurrent on the long-term reliability of GaN-on-Si E-mode power devices is studied.It is found that the repeated pulse overcurrent can cause the degradation in the device on-resistance and off-state current under certain conditions.Moreover,the field-induced degradation mechanism of GaN-on-Si E-mode power devices is proposed.Under the condition of repetitive pulse overcurrent,the device is subjected to both high transient current and high transient electric field,which lead to the generation of a large amount of heat at the peak point of the device electric field and result in the produce of a large thermal stress,then bringing in the generation of traps.The electric field formed by the ionization trap will raise the energy band of the heterojunction and partially deplete2DEG,resulting in an increase in the on-resistance of the device.