Impact of Gamma Radiations on Static, Pulsed I–V, and RF Performance Parameters of AlGaN/GaN HEMT

In this article, the impact of gamma ( $\gamma $ ) irradiation on passivated and unpassivated AlGaN/GaN HEMT is presented in detail. Passivated and unpassivated GaN-HEMT devices have been exposed to $\gamma $ -radiations to a total dose of 10 kGy. Post- $\gamma $ -irradiation, a refinement in ohmic contact, which makes device source/drain, is recorded. Alteration in Schottky gate electrical characteristics ( ${C} - {V}$ and ${I}\!\!-\!\!{V}$ ) 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 $\gamma $ -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 $\gamma $ -exposure. This is confirmed via pulsed ${I}\!-\!{V}$ measurements. A strong upswing in drain current recovery after stress bias is recorded post- $\gamma $ -irradiation in both types of HEMTs. This confirms that the trapping sites have been altered during $\gamma $ -exposure. Possible reasons causing this modification are improvement in gate metal barrier inhomogeneities and reduction/rearrangement of crystal defects during $\gamma $ -exposure. The effect of $\gamma $ -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 $\gamma $ -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.

I. Introduction

Gallium nitride high-electron-mobility transistors (GaN-HEMTs) are well-known and established devices because of their incredible device quality and performance parameters via delivering high power with low noise performance at high frequencies [1]–[3]. This can be credited to GaN material’s intrinsic properties [4]–[7]. Although gallium (Ga), as the metal, has a very low melting point, GaN crystal, due to its strong covalent bonding between Ga and N atoms, makes it nearly inert and stable against chemicals and can sustain in harsh environmental conditions, including radiations [8], [9]. The high cohesive energy between Ga–N and Al–N atoms of GaN and its derivative AlGaN leads to low thermal carrier generation rates making it a good choice for space and nuclear reactor device applications [10]. GaN-based RF high-power transistors and switch diodes are already in the industry. Furthermore, the research on GaN devices has moved toward its reliability exploration. Quality literature is published on device reliability with thermal and various radiation analyses. Numerous researchers have reported the effect of the electron [11], proton [12], neutron [13], and ions on GaN and devices fabricated on GaN [14]. The after-effects of high-energy -radiations are still under observation as the available spectrum reports improvements as well as degradation of GaN material and devices. Vitusevich et al. [15] showed a minor improvement in static and dynamic performance of large gate length GaN-HEMT devices post--exposure of 10 MGy and also in a separate study [16] and observed refinement in interfacial properties of AlGaN/GaN epitaxial structure under -irradiation through cathodoluminescence (CL) spectral analysis. Vitusevich et al. [16] reported almost no major changes after 6 MGy of ⁶⁰Co -irradiation on GaN-HEMT dc, pulsed , and RF characteristics. In the low dose range of -radiations, Aktas et al. [17] exposed AlGaN/GaN HEMTs to a dose of 1 kGy and observed degradation in GaN material and devices with the creation of deep traps. Hwang et al. [18] also presented the generation of defects close to the surface in the access region of GaN-HEMTs after a -dose exposure of 700 Gy. On the other hand, Lee et al. [19] showed an improvement in AlGaN/GaN heterostructure transport properties for a dose of 250 Gy of ⁶⁰Co. Recently, an increase in dynamic of metal insulator semiconductor (MIS)-HEMT is demonstrated after -rays exposure to a dose of 37 kGy; this increase in dynamic is due to degradation of gate dielectric during exposure [20]. Degradation of gate dielectric after -irradiation was studied by Chang et al. [21].