Study On The Novel Structure And Analytical Models Of GaN-based FP-HEMT

Recently, the Ga N-based HEMT has attracted wide attention in fields of high power, high temperature, high frequency and anti-radiation due to its excellent characteristics. With the introduction of the field-plate techniques, the performance of the Ga N-based HEMT has been improved significantly, which is fundamental for the device to satisfy the current more applications. Field-plates have the priorities in enhancing the breakdown voltage and output power as well as the improvement of reliability of the Ga N-based HEMT. However, many practical problems, such as the design and process implementation of high breakdown field-plated devices, the design of the field-plated devices with high reverse breakdown voltage, the optimization and design of the devices with complex field-plate, are still the focus of many researchers home and abroad. Systemic and deep studies have been carried out aiming at the critical problems above in this thesis. The main researches and results are presented as following.(1) A T-shaped gate field-plated Ga N-based HEMT with simple process and high breakdown voltage is proposed. The characteristics and laws of the channel electric field distribution are studied based on numerical simulations. The results show that, compared with the traditional gate field-plated Ga N-based HEMT, extra channel electric field peak can be formed with the T-shaped gate field-plate, leading to a better modulation of the channel electric field between gate and drain as well as a higher forward breakdown voltage.(2) Two kinds of novel structures, namely, shocktty-drain multiple drain field-plated Ga N-based HEMT(SD-MFP HEMT) and shocktty-drain compound field-plated Ga N-based HEMT(SD-CFP HEMT), are proposed to improve the reverse blocking characteristics. The mechanisms of both structures are studied in depth. The results reveal that the two structures can effectively modulate the channel electric field distribution and improve obviously the reverse breakdown voltage. In the SD-MFP HEMT, the breakdown voltage can be raised with the increase of the number of the field-plate. And in the SD-CFP HEMT, it is an effective way to improve the reverse blocking characteristics with the number of the floating FP and the fabrication processing is more simplified. Besides, some practical and valuable research results are achieved, which is considered as a certain reference for future devices fabrications.(3) The two-dimensional analytical models of the conventional gate field-plated HEMT and the floating gate field-plated HEMT are studied based on Poisson equations, respectively. The significant factors, including the polarization effect, the horizontal expansion of the depletion region and the coupling capacitance are taken into account in the models. The influence of the main device parameters on the distributions of the channel potential and the channel electric field is analyzed in detail in terms of these models established, in which some laws with practical value are obtained. And these models are verified by numerical simulations with Silvaco-TCAD. The study results show that the device models are consistent well with the numerical simulations. These models can be utilized to design and optimize the field-plated HEMT conveniently and to analyze the physical mechanisms in devices. What's more, the method to establish device analytical models can be used in other field-plated HEMTs conveniently, which is of good transplantation.