Nagoya University · Physics and Astronomy
Professor Maki Kushimoto's research lab specializes in the development and optimization of wide-bandgap semiconductor devices, with a primary focus on AlGaN-based deep ultraviolet (DUV) laser diodes. The lab investigates fundamental challenges in epitaxial growth, device fabrication, and material defects—such as dark line defects, hexagonal-pyramid-shaped hillocks (HPHs), and stress-induced dislocations—aiming to improve device performance and reliability. Key research directions include advanced epitaxial engineering, low-threshold lasing through innovative mirror fabrication (e.g., on-wafer etched mirrors with atomic layer deposition), and the enhancement of electroluminescence uniformity and efficiency on foreign substrates like Si and AlN. The lab also explores functional oxide semiconductors, particularly MgZnO, for transparent and conductive oxide applications in optoelectronic devices.
Figures are computed from collected data and may differ slightly.
We have demonstrated an on-wafer fabrication process for AlGaN-based UV-C laser diodes (LDs) with etched mirrors and have achieved lasing for 100 ns pulsed current injection at room temperature. A combined process of dry and wet etching was employed to achieve smooth and vertical AlGaN (11¯00) facets. These etched facets were then uniformly coated with a distributed Bragg reflector by atomic layer deposition. A remarkable reduction of the lasing threshold current density to 19.6 kA/cm2 was obtai
We demonstrated lasing action and investigated the optical properties of multiquantum-well (MQW) stripe crystals on patterned (001) Si substrates. Longitudinal and higher order transverse modes were observed from a ridge waveguide structure. These results strongly suggest the possibility of fabricating InGaN MQW laser diodes on (001) Si.
Previously reported UV-C laser diode (LD) structures have been subject to design constraints owing to dark line defects at the edge of the mesa stripe after device fabrication. To address this issue, a detailed analysis revealed that the dark line defects were dislocations generated by local residual shear stresses associated with mesa formation on highly strained epitaxial layers. A technique for controlling the local concentration of shear stress using a sloped mesa geometry was proposed based
Abstract The electroluminescence (EL) uniformity of AlGaN-based deep UV laser diodes on AlN substrate was analyzed by using the EL imaging technique. Although nonuniform EL patterns were observed, the uniformity was improved by changing the position of the p-electrode. The threshold current density was also reduced by suppressing the inhomogeneity of the EL. Cathodoluminescence analysis revealed that the cause of the non-uniformity is the degradation of the active layer and the nonuniformity emi
Abstract The presence of hexagonal-pyramid-shaped hillocks (HPHs) in AlGaN epitaxial films affects device characteristics; this effect is significant in DUV laser diodes (LDs) on AlN substrates, where the presence of HPHs under the p-electrode increases the threshold current density and inhibits the lasing. In this study, we investigated the difference between the lasing characteristics of LDs with and without HPHs. It was found that in the presence of HPHs, the threshold excitation power densit
The properties of phase‐separated MgZnO induced by heat treatment are investigated, because the electrical conductivity of MgZnO deposited by sputtering can be improved by heat treatment. The absorption edge shows a red shift, but the transmittance in the ultraviolet (UV)‐C region increases after heat treatment. This is due to the formation of wurtzite (WZ) MgZnO with a high Zn content and a rock salt (RS) structure with a low Zn content induced by phase separation. This suggests that the curren
Abstract Low-toxity high-In-content InGaN is an attractive option for short-distance communications through plastic optical fibers because its performance is only slightly affected by temperature. However, its fabrication on the c -plane is impaired by In droplets and V pits, which form at low-growth temperature. On the other hand, unlike the c -plane, <?CDATA $(1\bar{1}01)$?> InGaN relaxes with tilting. Therefore, in this study, we first grew a high-In-content InGaN single layer, and then we fa
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