Effects of proton irradiation and thermal annealing on off-state step-stressed AlGaN/GaN high electron mobility transistors

Abstract

The effects of proton irradiation doses on dc characteristics of reference, electrically stressed under off-state conditions and stressed/annealed AlGaN/GaN high electron mobility transistors (HEMTs) were investigated. The HEMTs were irradiated with protons at a fixed energy of 5 MeV and doses ranging from 1013 to 1015 cm−2. As expected, in all three types of HEMTs, more degradation of the device dc characteristics was observed for higher doses due to the larger displacement damage in two-dimensional electron gas channel of the HEMTs. The electrically stressed HEMTs after proton irradiation showed more degradation compared with reference and stressed/annealed HEMTs. After proton irradiation at a dose of 1015 cm−2, the drain saturation current and maximum transconductance of stressed HEMTs were decreased by 28.5% and 15%, respectively, compared to 24% and 11.5%–12%, respectively, for reference and stressed/annealed devices. The dc characteristics of stressed/annealed HEMTs after proton irradiation showed similar degradation trends compared with those of reference HEMTs, confirming that annealing is effective in removing defects created by the off-state stressing. In some cases, the authors also annealed stressed/irradiated HEMTs after the proton irradiation step. The drain current and transconductance of stressed/irradiated HEMTs were slightly increased after subsequent thermal annealing at 450 °C for 10 min, while reverse gate leakage current after annealing was decreased more than an order of magnitude. The interface trap density of stressed HEMTs after proton irradiation at a dose of 1015 cm−2 increased from 3.05 × 1012 to 1.37 × 1013/cm2 V and were reduced to 6.01 × 1012/cm2 V following thermal annealing. Our results are consistent with the notion that off-state stressing creates defects that have a common origin with those created by proton irradiation, and thus, irradiation of off-state stressed devices leads to more defects than in unstressed devices that are subsequently irradiated. Annealing the stressed devices prior to irradiation makes them behave the same as unstressed HEMTs when both are irradiated with protons.