Low ohmic-contact resistance in recessed-gate normally-off AlGaN/GaN MIS-HEMT with δ-doped GaN Cap Layer

Summary form only given. In this paper, we discuss an ohmic contact resistance (R_c) in a recessed-gate normally-off AlGaN/GaN MIS-HEMT with a δ-doped GaN Cap Layer. This structure ensures high uniformity of a threshold voltage (V_th) by a selective dry-etching of GaN over AlGaN at a gate region. At the δ-doped region of the GaN cap layer, diffusion of electrons toward the surface leaves excess ionized donors, resulting in compensation of negative polarization charges between the GaN cap and the AlGaN barrier. Thanks to this effect, we successfully obtained an low R_c of less than 0.1 Ωmm by reduction of band-barrier at the interface between the GaN cap and the AlGaN barrier.