Events and Announcements

Jun J. Morihara,^1,* Mao Bando,¹ Junya Yoshinaga,^2,3 Yoshinao Kumagai,² and Masataka Higashiwaki^1,4,*

¹Department of Physics and Electronics, Osaka Metropolitan University, Sakai, Osaka 599-8531, Japan

²Department of Applied Chemistry, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan

³TAIYO NIPPON SANSO CORPORATION, Yokohama, Kanagawa 220-8561, Japan

⁴National Institute of Information and Communications Technology, Koganei, Tokyo 184-8795, Japan

Low-pressure hot-wall metalorganic chemical vapor deposition (MOCVD) can provide high-purity Ga₂O₃ homoepitaxial films even at a high growth rate of over 16 µm/h and thus is one of the most promising techniques for the future mass production of high-quality Ga₂O₃ epitaxial wafers [1]. In this work, we investigated electrical properties of Si-doped Ga₂O₃ thin films grown by the novel MOCVD technique and effects of post-growth high-temperature annealing on them…

Degradation of far-ultraviolet light emitting diodes on AlN substrate

3. Optical devices
Shashwat Rathkanthiwar¹ , Maki Kushimoto², Yudai Shimizu³, Kazutada Ikenaga³, Mayank Bulsara³, Keitaro Ikejiri³, Hiroshi Amano⁴, Leo J. Schowalter^1
1 Lit Thinking, Orlando, Florida 32826, USA
² Graduate School of Engineering, Nagoya University, Aichi 464-8603, Japan
³ Taiyo Nippon Sanso, Innovation Unit, Yokohama, Kanagawa 220-8561, Japan
⁴ Center for Integrated Research of Future Electronics, Institute of Materials Research and System for Sustainability, Nagoya University, Nagoya, 464-8601, Japan

Abstract:
The safety and efficacy of far-UVC radiation (<240 nm) for indoor pathogen inactivation has spurred research on far-UVC light sources.  While nitride LED technology promises to replicate the advantages of visible and near-UV LEDs like compact size, low operating power, and tunable wavelength, a major challenge is the sharp decrease in efficiency and lifetime (at practical current densities) at shorter wavelengths (high Al content). Perhaps this degradation is linked to the increased point defect incorporation during high Al-content AlGaN growth or to a greater susceptibility of point defects (or point defect complexes) to be activated by high current at high Al composition. The precise mechanism is unknown, and, in this study, we are investigating the impact of multi-quantum well (MQW), electron blocking layer (EBL), and graded-AlGaN hole injection layer (HIL) variations on 240-nm LED lifetimes. The LEDs were grown on AlN substrates using a low-pressure, resistive-heated, horizontal-flow metalorganic chemical vapor deposition (MOCVD) which achieved step-flow morphology and pseudomorphic growth. Cross-sectional transmission electron microscopy corroborated the high-quality epitaxial growth. The Si-doped Al_0.79Ga_0.21N n-contact layer exhibited a sheet resistance of 405 Ω/□. TLM contacts on the p+ GaN contact layer showed a linear I-V behavior confirming an Ohmic contact formation. LEDs exhibited a sharp electroluminescence with FWHM of ~11 nm. Accelerated constant-current degradation tests [1] were conducted in the range of 0.7 to 4 kA/cm² (corresponding to a forward voltage ranging from 7.9 to 11.3 V, respectively, at the start of the test). A 12-fold reduction (from 520 to 42 seconds) in L50 lifetime (50% drop from the initial output power) was observed for the 6-fold increase in current density. Notably, increasing the HIL start composition from 90% to 95% Al led to 2.5 and 5 times decrease in the L50 lifetime at 0.7 and 4 kA/cm², respectively, which supports the hypotheses that point defects at higher Al content are susceptible to higher degradation rates for far-UVC LEDs.

[1] Zhang et al., physica status solidi (a), 221 (2024) 2300946.

Advanced High-Flow-Velocity Horizontal MOCVD Technology for Nitride Semiconductor Growth
Keitaro Ikejiri¹ , Yudai Shimizu¹, Mizuki Yamanaka¹, Kenichi Eriguchi¹, Kazutada Ikenaga¹, Hiroki Tokunaga^1
1 TAIYO NIPPON SANSO Corporation, 10 Okubo, Tsukuba, Ibaraki 300-2611 Japan

Abstract:

The expansion of nitride semiconductor applications, such as LEDs, lasers, and high-power electronics, requires MOCVD systems that can precisely control crystal growth while maintaining high throughput. In this context, the MOCVD process has conflicting requirements. For high-quality GaN or high-indium-content InGaN deposition, relatively high pressures are necessary. However, increasing pressure leads to enhanced parasitic growth, resulting in deteriorated crystal quality and uniformity. Conversely, lower pressures improve the thickness and composition uniformity of AlGaN and control the carbon concentration in GaN. The optimal MOCVD system for flexible control of nitride semiconductors must handle pressures from low to atmospheric while maintaining high-flow velocities through narrow channels. The challenge is to meet these requirements effectively in both R&D and mass production. Taiyo Nippon Sanso’s MOCVD system achieves this with a high-flow-velocity system using triple gas injectors in a horizontal reactor with a flow channel height under 10 mm, and a gas control system operating from low to atmospheric pressure. In addition, zone-divided resistive heating technology allows the system to accurately regulate temperatures even for large diameter wafers as well as wafers that deform into concave or convex shapes during high-temperature processes.

The system’s effectiveness was demonstrated with AlGaN growth. Using the SR4000 MOCVD system for a single 4-inch substrate, we controlled the Al composition in AlGaN by adjusting the TMA to total MO supply ratio (TMG + TMA) linearly. This method maintained a favorable Al composition distribution (in-plane max-min ≤ 1.5%) and thickness distribution (in-plane max-min/average < 5.0%) for 40% to 80% Al composition. The same approach applies to the UR26K MOCVD system, a large-scale production system for 6 x 8-inch substrates. Optimizing growth conditions achieved an Al composition distribution (in-plane and inter-plane max-min ≤ 0.2%) and thickness distribution (in-plane and inter-plane max-min ≤ 1.0 nm, average: 18.1 nm) in the AlGaN barrier layer of AlGaN/GaN HEMT on Si. We will also discuss the flow channel effectiveness using numerical simulations and InGaN crystal growth characteristics.