This article presents a comprehensive simulation analysis of a normally-off AlGaN/GaN HEMT with recessed p-GaN gate. Based on a conventional p-GaN HEMT, the structure of the device is achieved by selectively etching the AlGaN barrier layer beneath the gate and depositing a p-GaN cap layer. The TCAD tool was used to analyze transfer characteristics, output characteristics, transconductance, and breakdown voltage of the device. Besides, the large-signal power performance was also studied. The results indicate that the normally-off HEMT exhibits great performance with a threshold voltage of 2.7 V, saturation drain current at 1.52 A/mm, peak transconductance reaching 326 mS/mm, and a breakdown voltage of 610 V. When the device is driven with large-signal operation at the gate, the output power and power output efficiency increase with the increasing input power, while the power gain decreases.
With the development of high-speed RF circuits and high-voltage switches, the enhancement-mode (E-mode) GaN-based high electron mobility transistors (HEMTs) have become a hot topic in those fields. In this work, to improve the device performance of E-mode HEMT, p-GaN gate combined with recessed-gate was proposed. Moreover, the influence of structure parameters such as Al component and thickness of AlGaN barrier layer and the depth of recessed gate on device performance were investigated systematically by theoretical simulation. The results show that the saturation current increases and threshold voltage decreases with the increasing of Al component and thickness of AlGaN barrier layer. In addition, the saturation current decreases and threshold voltage increases with the increasing of the recessed gate depth. So, to obtain relative larger threshold voltage and saturation current, the Al component and thickness of the AlGaN barrier layer and the recessed gate depth for the p-GaN gate HEMT combined with recessed-gate structure should be moderate.
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 Al0.1Ga0.9N back barrier and with graded back barrier are simulated by adding surface charges on HEMT sensing area. The results indicate that the current sensitivity ΔID of 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.
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