Ryuichiro Kamimura

Normally off AlGaN/GaN HEMT on Si substrate with selectively dry-etched recessed gate and polarization-charge-compensation δ-doped GaN cap layer

We demonstrate a recessed-gate normally off AlGaN/GaN high-electron-mobility transistor (HEMT) on a silicon substrate that provides a precisely controllable threshold voltage (Vth). To ensure Vth uniformity, dry-etching of GaN with high etching selectivity between GaN and AlGaN is developed. Furthermore, to introduce selective dry-etching in the HEMT fabrication process, we propose a delta-doped GaN cap structure that enables negative polarization charges between the GaN cap and the AlGaN barrier to be compensated. Combining these two technologies, we fabricate recessed-gate normally off metal–insulator–semiconductor HEMTs with a subthreshold slope of 130 mV/dec and an on–off drain current ratio exceeding 107.

High external quantum efficiency (10%) AlGaN-based deep-ultraviolet light-emitting diodes achieved by using highly reflective photonic crystal on p-AlGaN contact layer

We increased the light-extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) by introducing a highly reflective photonic crystal (HR-PhC) into the surface of the p-AlGaN contact layer, thereby achieving a high external quantum efficiency (EQE). A low-damage HR-PhC with a lattice period of approximately 250 nm was fabricated using nanoimprinting and dry etching. A reflective Ni/Mg p-type electrode was deposited on the HR-PhC layer using a tilted-evaporation method. The EQE of a conventional DUV LED with emission around 283 nm was increased from 4.8 to 10% by introducing the HR-PhC and the reflective Ni/Mg electrode. A simple estimation of the effective reflectance of the HR-PhC p-AlGaN contact layer with the Ni/Mg electrode indicated a value exceeding 90%.

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 (Rc) 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 (Vth) 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 Rc of less than 0.1 Ωmm by reduction of band-barrier at the interface between the GaN cap and the AlGaN barrier.