TCAD Investigation of Buffer-free High Electron Mobility Transistors
GaN-based high electron mobility transistors (HEMT) have emerged as a powerful technology with excellent performance in high speed and high power applications. Properties exhibited by GaN, like large bandgap (3.4eV) and high breakdown fields (3.4 MV/cm) and lower dielectric constants (9.5) make it an outstanding candidate compared to other material systems. For switching and RF applications, GaN-on-SiC is a primary choice due to high fT and high breakdown voltages. Various work demonstrates layer thickness engineering to enhance device performance. The buffer layer between the substrate and the channel contributes to the dispersion and isolation phenomenon. Generally, a highly insulated thick buffer, doped with C or Fe is used to increase the breakdown, limit leakage, and various short channel effects. However, the trapping effects in the buffer due to acceptor carriers have been a subject of research. To study this and to obtain a good tradeoff for good device performance, several works have demonstrated that mutating the buffer layer thickness can help in adjusting the lattice mismatch and obtain high performance..
GaN-based devices have shown exemplary performance in space in space electronics and have attracted researchers to study it under harsh environments. As proton is a major species of radiation in low earth orbital, the effects of binary and ternary nitride bonding which is a major phenomenon during proton irradiation are greatly studied. Recently, the proton-induced effects on device performance and reliability have been a topic of intense research. Tremendous research has indicated the strong radiation hardness of GaN technology , however, the implications of proton exposure on RF performance on large-signal applications like power amplifier, is not yet explored much.
In this work, novel device architecture without the conventional buffer layer as proposed by Chen et.al is studied. Understanding the significance of proton irradiation, this work presents a systematic study on the proton radiation effects on various DC, RF and Thermal characteristics. Results demonstrate that the device exhibits extreme radiation hardness as compared to the conventional with-buffer structure which is sensitive to radiation. Further, to understand the device mechanism in real life applications, ASM HEMT Model and MVSG RF HEMT Model calibration is discussed. Project report can be outlined as follows:
Chapter 1 presents a brief introduction of the semiconductor device technologies and the focusing device of the project- The High electron mobility transistors (HEMT). A short introduction to the software used in the study is also covered.
Chapter 2 revolves around the salient features and gives a comparative study of the buffer-free HEMT structure and the conventional with-buffer HEMT model. Various studies like DC, RF and Thermal were carried out to systematically study the buffer-free architecture.
Chapter 3 describes the exhaustive simulation results of the proton irradiation on the two structures and investigates various electrical properties under irradiation.
Chapter 4 presents a glimpse of small-signal modeling of the devices studied in the work and discusses the calibration of ASM-HEMT and MVSG Model done in ADS for future applications.
Appendix in the report covers the various assignments completed during the tenure.