Influence of graded back barrier on AlGaN/GaN HEMT and HEMT-based sensor

Abstract

The influence of AlGaN (Al=0.1) back barrier layer and graded back barrier layer on AlGaN/GaN high electron mobility transistor (HEMT) and HEMT based sensor was investigated by Silvaco TCAD. The results show that, both the AlGaN (Al=0.1) back-barrier HEMT and the graded AlGaN back-barrier HEMT can improve drain current and transconductance compared with conventional AlGaN/GaN HEMT. The HEMT with graded back barrier layer shows larger drain current and higher transconductance than that with AlGaN back barrier, which can be attributed to that the introduction of graded AlGaN back barrier layer increases the carrier concentration at the heterojunction interface and greatly reduces the effect of the parasitic channel. Correspondingly, the device performance should exhibit stronger dependence on surface charge. To confirm the inference, the sensing performance of the HEMTs without back barrier, with Al_0.1Ga_0.9N back barrier and with graded back barrier are simulated by adding surface charges on HEMT sensing area. The results indicate that the current sensitivity ΔI_Dof the graded back-barrier HEMT caused by surface charge is largest, so the HEMT with a graded back barrier layer is more suitable for ion sensor than that conventional AlGaN/GaN HEMT and fixed Al-content back barrier.