Density functional theory based study of effects of heterojunction and oxide interface traps on III-V FETs

Abstract

To overcome the limits of conventional MOSFETs, various types of III-V FETs have been considered as a promising replacement for them. III-V heterojunction TFETs, which have a broken/staggered gap, particularly exhibit a steep slope and a comparably higher on-state current in comparison to those of Si TFETs. However, the high trap density at III-V/oxide interfaces is still an obstacle to achieving the desired device performance. To investigate heterojunctions or defects, the effects of individual atoms must be considered, but only limited simulation studies have been conducted by using empirical Hamiltonians. Thus in this thesis, first-principles based device-level simulations were studied. We investigated the performance of GaSb/InAs heterojunction-based UTB TFETs and the effects of trap states on III-V FETs, by performing NEGF quantum transport simulations with DFT Hamiltonians. We found that for relatively short channel devices, (001)/[110] GaSb/InAs exhibits high off-state leakage. To reduce the off-state leakage, we designed (110)/[001] GaSb/InAs which shows superior performance for the short channel devices. Also, we revealed that device performance is significantly affected by types of trap states. As dangling bonds decreas the on-state current of PFETs, As antisites degrade the SS of TFETs.