**Proton Irradiation E** ff**ects on the Time-Dependent Dielectric Breakdown Characteristics of Normally-O** ff **AlGaN**/**GaN Gate-Recessed Metal-Insulator-Semiconductor Heterostructure Field E** ff**ect Transistors**

#### **Dongmin Keum and Hyungtak Kim \***

School of Electronic and Electrical Engineering, Hongik University, Seoul 04066, Korea; rmaehdalf@hanmail.net **\*** Correspondence: hkim@hongik.ac.kr; Tel.: +82-2-320-3013

Received: 14 September 2019; Accepted: 23 October 2019; Published: 26 October 2019

**Abstract:** In this work, we investigated the time-dependent dielectric breakdown (TDDB) characteristics of normally-o ff AlGaN/GaN gate-recessed metal–insulator–semiconductor (MIS) heterostructure field e ffect transistors (HFETs) submitted to proton irradiation. TDDB characteristics of normally-o ff AlGaN/GaN gate-recessed MISHFETs exhibited a gate voltage ( *V*GS) dependence as expected and showed negligible degradation even after proton irradiation. However, a capture emission time (CET) map and cathodoluminescence (CL) measurements revealed that the MIS structure was degraded with increasing trap states. A technology computer aided design (TCAD) simulation indicated the decrease of the vertical field beneath the gate due to the increase of the trap concentration. Negligible degradation of TDDB can be attributed to this mitigation of the vertical field by proton irradiation.

**Keywords:** AlGaN/GaN; proton irradiation; time-dependent dielectric breakdown (TDDB); reliability; normally o ff
