Fumitsugu Fukuyo

Fabrication of Deep-Ultraviolet-Light-Source Tube Using Si-Doped AlGaN

An ultraviolet (UV)-light-source tube using a Si-doped AlGaN film as a target of electron beam excitation was fabricated. The Si-doped AlGaN was grown on an AlN/sapphire substrate by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE), and its optical properties were evaluated by excitation with a 10 kV electron beam (EB). Emission intensity was significantly improved by Si doping and optimization of the growth conditions. 247 nm deep-UV light was observed from the tube, and the lifetime of the light tube until 50% emission output of the initial strength was approximately 2000 h at an EB acceleration voltage of 10 kV with a current of 100 µA.

Growth and Characterization of AlGaN Multiple Quantum Wells for Electron-Beam Target for Deep-Ultraviolet Light Sources

The structure of Si-doped AlGaN multiple quantum well (MQW) targets has been optimized for application to electron-beam (EB)-pumped deep-ultraviolet (UV) light sources. The deep-UV light emission from Si-doped AlGaN MQW targets pumped by a 10 kV EB has been evaluated. The targets exhibited a deep-UV light output power of over 15 mW at a peak wavelength of 256 nm for an EB input power of 2.0 W, and the conversion efficiency was estimated to be over 0.75%. These results demonstrate the advantageousness of using p-type-AlGaN-free AlGaN MQW targets as a material for application to EB-pumped deep-UV light sources.

Growth of High-Quality Si-Doped AlGaN by Low-Pressure Metalorganic Vapor Phase Epitaxy

In this paper we report the growth of Si-doped AlGaN on an AlN/sapphire substrate by low-pressure metalorganic vapor phase epitaxy (LP-MOVPE) with an in situ monitoring system to fabricate a high-quality film with controlled thickness. The AlN mole fraction in AlGaN can be controlled by adjusting the growth temperature. We also discuss the quality and growth mechanism of AlGaN on AlN. GaN and AlGaN with an AlN mole fraction of 0.28 were free from stress because of the occurrence of three-dimensional (3D) growth. The lattice constant a of AlGaN with an AlN mole fraction of 0.40 was larger than that at an AlN mole fraction of 0.28 despite the two-dimensional (2D) growth mode. This indicates that the lattice mismatch between AlGaN and the underlying AlN adversely affects the crystal quality. AlGaN with an AlN mole fraction of over 0.60 was coherently grown on AlN owing to the fact that the AlN/sapphire template used in this work was subjected to compression. For this reason, in the samples with an AlN mole fraction of over 0.6, the crystal quality was high because of the coherent growth on the underlying AlN. Moreover, Si doping was performed for AlGaN. The carrier concentration increased linearly up to a Si concentration of 2 ×1018 cm-3, indicating that the activation rate was approximately 1.

Modified-layer formation mechanism into silicon with permeable nanosecond laser

The purpose of this study is to clarify the formation mechanism of modified layer. A coupling problem composed of focused laser propagation in a silicon single crystal is examined, considering laser absorption, temperature rise and heat conduction, with particular attention to an experimental result that the absorption coefficient varies with temperature. Simple thermal stress analysis was also conducted based on those results. As a result, the formation mechanism of the modified layer could be explained clearly. It was seen that the temperature dependence of absorption coefficient is the most important factor of the modified layer formation. This present analysis can be applied to find the optimum laser irradiation condition for Stealth Dicing (SD) method, and it is a future subject to confirm it experimentally. It was supported by this present analysis that the problem of thermal effect on the device region can be solved by the SD method. [Received 7 May 2006; Accepted 2 February 2007]