(Invited) Effect of Annealing on Electronic Carrier Transport Properties of Gamma-Irradiated AlGaN/GaN High Electron Mobility Transistors

AlGaN/GaN High Electron Mobility Transistors (HEMTs) are the most advanced electronic nitride devices to be used at high temperatures and in harshly radiated environments. A clear understanding of radiation effects on these devices is essential in order to predict their behavior in space and terrestrial applications including military, nuclear and high energy physics. Only a limited amount of insight exists into the behavior of III-N based junction transistor after exposure to gamma irradiation. Investigation of gamma-irradiated device properties will provide important information about the defects in semiconductor heterostructures. Therefore, it is important to understand how defects are created by gamma-rays and how they can be healed by annealing. Here we present the impact of gamma-irradiation on AlGaN/GaN heterostructures fundamental properties including carrier transport and recombination. We also report the effect of annealing at 200^o C over 25 min on gamma-irradiated samples through monitoring of minority carrier diffusion length using Electron Beam Induced Current (EBIC) method.

We found the relationship between dose, diffusion length and its  activation energy after gamma-irradiation and after annealing treatment. Temperature dependent EBIC measurements yielded a decrease in diffusion length with corresponding increase in activation energy after the gamma-irradiation.The increase in activation energy is likely an indication of the creation of deeper gamma irradiation induced defect traps due to nitrogen vacancies. These deep traps reduce the carrier concentration and mobility and increase the activation energy related to carrier recombination. It is evident from our results that annealing of HEMTs that were gamma-irradiated with moderate dose leads to the recovery (depending on dose) of minority carrier diffusion length. The recovery is also reflected in the activation energy returning to its pre-irradiated value. The level of recovery of gamma-irradiated devices after annealing treatment depends on the dose of irradiation. Increase in diffusion length after annealing had been attributed to a reduction in point defects (nitrogen vacancies) induced in AlGaN/GaN by gamma-irradiation.