Impact of Gamma Radiations on Static, Pulsed <i>I–V</i>, and RF Performance Parameters of AlGaN/GaN HEMT
Ajay Kumar Visvkarma, Khushwant Sehra, Chanchal, Robert Laishram, Amit Malik, Sunil K. Sharma, Sudhir Kumar, D. S. Rawal, Seema Vinayak, Manoj Saxena
Abstract
In this article, the impact of gamma (<inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>) irradiation on passivated and unpassivated AlGaN/GaN HEMT is presented in detail. Passivated and unpassivated GaN-HEMT devices have been exposed to <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-radiations to a total dose of 10 kGy. Post-<inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-irradiation, a refinement in ohmic contact, which makes device source/drain, is recorded. Alteration in Schottky gate electrical characteristics (<inline-formula> <tex-math notation="LaTeX">${C} - {V}$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">${I}\!\!-\!\!{V}$ </tex-math></inline-formula>) along with advances in device drain current and transconductance has been observed in unpassivated HEMT, while it remained almost unaltered in passivated GaN-HEMT after <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-irradiation. The OFF-state gate leakage has deterioration in both types of HEMTs, suggesting a modification in trap concentration beneath the gate and near gate region during <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-exposure. This is confirmed via pulsed <inline-formula> <tex-math notation="LaTeX">${I}\!-\!{V}$ </tex-math></inline-formula> measurements. A strong upswing in drain current recovery after stress bias is recorded post-<inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-irradiation in both types of HEMTs. This confirms that the trapping sites have been altered during <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-exposure. Possible reasons causing this modification are improvement in gate metal barrier inhomogeneities and reduction/rearrangement of crystal defects during <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> <i>-exposure</i>. The effect of <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-radiation on intrinsic/extrinsic device parameters has also been determined using S-parameters measurements. Intrinsic/extrinsic device parameters of passivated HEMT are observed to be less affected by <inline-formula> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula>-irradiation in comparison to unpassivated GaN-HEMT devices, and post-radiation, both the devices have similar device parameters values as it was prior radiation making it suitable for harsh environment applications.