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AlGaN-based light-emitting diodes (LEDs) are attractive candidates for next-generation light sources in the deep ultraviolet (DUV) region because they can cover the spectral range of 210 – 365 nm through control of the Al content in the epitaxial layers. Moreover, they are environmentally friendly, having zero mercury content and a long lifetime. These excellent properties of AlGaN-based DUV LEDs are suitable for sterilization and polymer curing applications, however, their output power is not yet sufficient for practical applications. One method to improve output power of DUV LEDs is the enhancement of the light extraction efficiency from the LEDs chips to the air by connecting graded refractive index medium outside the chips. The refractive index medium should have the long-term reliability against DUV. We designed and fabricated the hemispherical lensmade of inorganic materials as a refractive index medium, and bonded the hemispherical lenses to the LEDs using room temperature bonding methods. We demonstrated high output power 255 nm and 280 nm LEDs with lenses [M. Ichikawa et al., APEX, to be contributed]. For this study, the excellent properties of fabricated LEDs with lenses are reviewed in connection with the bonded interface structure in light of new experimental data. The following figures (A) and (B) show schematic illustrations of LED chips and hemispherical lenses. We fabricated AlGaN-based 255 nm and 280 nm LEDs on sapphire substrates with a size of 1 mm square. A flip-chip type LED was produced to extract DUV light through the sapphire substrate. A simulation study predicted that the refractive index of the hemispherical lens was optimum when the lens was made of sapphire, which was the same material as that of LED substrates. Moreover, the light extraction efficiency was most enhanced when the lens diameter exceeded 3 mm. Therefore, we fabricated hemispherical lenses made of sapphire, with diameters of 3 or 5 mm. The LED chips were bonded to sapphire lenses at room temperature using two different bonding methods as shown in figure (C). One was surface activated bonding (SAB). In this method, the bonding surfaces of sapphire are sputter-etched and activated using an Ar fast ion beam. Transmission Electron Microscopy (TEM) images revealed that the surfaces of sapphire are consisted of several nanometer-thick amorphous layers, which were the damaged layers of the sapphire by the Ar ion beam irradiation. A large loading force was necessary to bond sapphire to sapphire. However, no light absorption was observed at the SAB interface. Another bonding method was atomic diffusion bonding (ADB). In this method, metal films are fabricated on two flat sapphire surfaces using sputter deposition with subsequent bonding of the two films on the sapphire in vacuum. Very thin Al films were used as the metal films for this study because the extinction coefficient of aluminum is small. A light absorption was slightly observed at the bonded interface in the DUV region. However, sapphire could be bonded without applying too high loading pressures. Moreover, ADB is applicable to bonding any mirror-polished substrates, in addition to sapphire, which is expected to extend the applications. The LEDs with lenses had higher light extraction efficiency than conventionally structured LEDs without lenses. In SAB devices, the maximum external quantum efficiency of the 255 nm LED was 4.56% at 100 mA, and that of the 280 nm LED was 10.1% at 1 A. As a result, at a forward current of 350 mA, the output power of a 255 nm LED with a lens increased by a factor 2.8, reaching 73.6 mW. Furthermore, that of the 280 nm LED increased by a factor of 2.3, reaching 153 mW. The output powers of ADB devices were also significantly higher than those of conventionally structured LEDs without lenses but were slightly lower than those of SAB devices because of a light absorption at the bonding interface. A further enhancement of output powers of ADB devices can be expected by tuning bonding process. The findings in this study would contribute not only to the research in DUV LEDs but also to the research of visible light LEDs. Figure 1

High output power deep-ultraviolet light-emitting diodes (LEDs) are reported. First, two series devices were operated at a forward current of 350 mA. We measured powers of 45.2, 93.3, and 65.8 mW for 255, 280, and 310-nm LEDs, respectively. Next, single-chip devices with a modified epitaxial structure and electrode pattern were evaluated. Peak wavelengths, output powers, forward voltages, and external quantum efficiencies were respectively 258.0 nm, 34.8 mW, 8.25 V, 2.07% for the 255-nm LED, 282.8 nm, 40.5 mW, 5.69 V, 2.64% for the 280-nm LED, and 312.3 nm, 40.1 mW, 6.36 V, 2.89% for the 310-nm LED. The 70% lifetime of the 280-nm LED was estimated to be over 3000 h at a junction temperature of 45°C.

We demonstrate the fabrication of blue, green, and amber InGaN/GaN light-emitting diodes (LEDs) on semipolar {11-22} bulk GaN substrates. The {11-22}GaN substrates used in this study are produced by cutting out from a c-oriented GaN bulk crystal grown by hydride vapor epitaxy. The LEDs have a dimension of 320 ×320 µm2 and are packed in an epoxide resin. The output power and external quantum efficiency (EQE) at a driving current of 20 mA are 1.76 mW and 3.0%, respectively, for the blue LED, 1.91 mW and 4.1% for the green LED, and 0.54 mW and 1.3% for the amber LED. The maximum output powers obtained with a maximum current of 200 mA are 19.0 mW (blue), 13.4 mW (green), and 1.9 mW (amber), while the maximum EQEs are 4.0% at 140 mA (blue), 4.9% at 0.2 mA (green), and 1.6% at 1 mA (amber). It is confirmed that the emission light is polarized along the [1-100] direction, reflecting the low crystal symmetry of the {11-22} plane.

欧州ではオゾン層保護の観点から発泡断熱材中のフロンの回収が既に行われている所がある。一方, わが国では現時点で断熱材中のフロンの回収までは行われていないが, 回収の必要性は高まっている。そのため筆者らは, これまで実験プラント等を用いて, わが国で廃棄されるような大形冷蔵庫 (内容積300lクラス) も処理できる廃冷蔵庫断熱材からのフロン回収装置の開発を進めてきた。そしてこれらの成果をもとに平成8年, 実証プラント (冷蔵庫処理量50台/h) を (財) 家電製品協会の環境特別事業として神奈川県秦野市に建設し, 実証試験を行った。その結果, フロン回収量は廃冷蔵庫1台あたり400g程度であること, フロン含有率が既知の標準パネル実験ではフロン回収率は90%以上であることが明らかになり, 断熱材フロンの回収装置の実用化が図られた。

We fabricated high-output-power 255 and 280 nm light-emitting diodes (LEDs) using direct bonding. The LED chips were bonded to sapphire lenses at room temperature using either atomic diffusion bonding or surface-activated bonding. The LEDs with lenses had a higher light extraction efficiency than conventionally structured LEDs. As a result, at a forward current of 350 mA, the output power of the 255 nm LED increased by a factor of 2.8, reaching 73.6 mW, while that of the 280 nm LED increased by a factor of 2.3, reaching 153 mW.

255/280/310 nm deep ultraviolet light-emitting diodes (DUV LEDs) suitable for high-current operation are reported. Newly developed 1 mm sized chips are installed in a commercial package with a two-series configuration. At a forward current of 350 mA, we measured powers of 45.2, 93.3, and 65.8 mW for the 255, 280, and 310 nm LEDs, respectively. The corresponding external quantum efficiencies per serial circuit were 1.3, 3.0, and 2.4%, and successful chip scalability was demonstrated. The 50% lifetime of the 280 nm LED die was estimated to be 3000 h at a junction temperature of 30 °C.

We realized room-temperature lasing of blue and green GaN-based vertical-cavity surface-emitting lasers (VCSELs), for the first time, by current injection. The blue GaN-based VCSEL had a threshold current of 1.5 mA and a threshold voltage of 3.3 V under continuous-wave operation. Its maximum output power was 0.70 mW and its laser emission wavelength was 451 nm. The green GaN-based VCSEL had a threshold current of 22 mA and a threshold voltage of 6.3 V under pulsed current operation. Its maximum output power was estimated to be over 0.80 mW and the laser emission wavelength was 503 nm.

The purpose of this study is to investigate the relation between the fluctuation of sizing degree of StOckigt method and the factors which might have some influence to it. In this report, the measuring condition in many factors were investigated and the data obtained were analyzed by the statistic means. The factors in the measuring condition are the temperature of solution, the concentration of solution, the concentration of reagent's soln., the dropping time of reagent's soln., the content of water in paper, two sided difference of paper and the individual difference, etc. Examples of some information obtained are shown as follow : -There is a linier relation between the sizing effect (y) and viscosity (x) of water. y=a+bx (1) And there is another relation between the viscosity and the temperature (t) of water. x=17.16-0.438t+0.0044t2 (2) Therefore, the relation between the sizing degree and the temperature has been shown as next equation. y=a+b (17.16-0.438t+0.0044t2) (3) The a and b are the constants settled by a sort of paper. The supplement value of the sizing degree at t°C given by the next equation. y'=b (-0.438+0.0088t) (4)