Analysis of electrical properties of insulators (Si₃N _4, SiO_2, AlN, and Al₂O₃)/0.5 nm Si₃N₄/AlGaN/GaN heterostructures

The electrical properties in AlGaN/GaN heterostructures with Si- and Al-based insulators (Si₃N_4, SiO_2, AlN, and A1₂O₃) have been examined and analyzed. By insulators deposition, significant increase in the two-dimensional electron gas (2DEG) density (N_s) was observed with the order of N_S(Al ₂O₃) > N_S(AlN) ̃ N_s(SiO ₂) > N_s(Si₃N₄) > N_o (N_o: N_s without insulators). As the result, the decrease in the sheet resistance (R) was observed; the smallest order of R was R(Al ₂O₃) > R(AlN) > R(Si₃N₄) > R_o ̃ R(SiO₂) (R_o: R without insulator). The insulators deposition effect has thus been shown to be significant and different among insulators. The increase in N_s was analyzed in terms of the change in the potential profile, and the observed differences in N _s among insulators have been interpreted. The band engineering including insulators is indispensable in understanding and designing AlGaN/GaN HFETs, since insulators are commonly used for the surface passivation as well as for the gate insulators, and the insulators deposition is to alter the essential device parameters such as the source resistance.