Recently progress of LPP EUV light source is remarkable. Ten years ago, power level is only several 10 W level. At present 250W power level is realized in semiconductor mass production factories1) by ASML. On the other hand, pioneer of this Unique technologies including; combination of pulsed CO2 laser and Sn droplets, dual wavelength pico second laser pulses for shooting and debris mitigation by magnetic field have been applied by Gigaphoton2). They have demonstrated high average power >300W EUV power with CO2 laser more than 27kW at output power in cooperation with Gigaphoton and Mitsubishi Electric3). In near future more higher power (>600W) EUV source is required to fit High NA (>0.55) lithography of semiconductor industry.
In this paper we will discuss about the Sn plasma dynamics which dominate the EUV emission by using Tomson scattering (TS) measurement4. Recent TS results have revealed whole profiles of electron temperature and ion density in the EUV sources. These results mention that there is still sufficient potential to increase EUV output power and conversion efficiency in near future.
In this study, we discuss the potential advantages of a new ZnO-based semiconductor, ZnInON (ZION), for application in multi quantum-well (MQW) photovoltaics. ZION is a pseudo-binary alloy of ZnO and InN, which has direct and tunable band gaps over the entire visible spectrum. It was found from simulation results that owing to the large piezoelectric constant, the spatial overlap of the electron and hole wave functions in the QWs is significantly small on the order of 10-2, where the strong piezoelectric field enhances the separation of photo generated carriers. As a result, ZION QWs have low carrier recombination rate of 1014–1018 cm-3s-1, which is much lower than that in conventional QWs such as InGaAs/GaAs QW (1019 cm-3s-1) and InGaN/GaN QW (1018–1018 cm-3s-1). The long carrier life time in ZION QWs (∼1μs) should enable the extraction of photo-generated carriers from well layers before the recombination, and thus increase Voc and Jsc. These simulation results are consistent with our experimental data showing that both Voc and Jsc of a p-i-n solar cell with strained ZION MQWs and thus the efficiency were increased by the superimposition of laser light with lower photon energy than the band gap energy of the QWs. Since the laser light contributed not to carrier generation but to the carrier extraction from the QWs, and no increase in Voc and Jsc was observed for relaxed ZION MQWs, the improvement in the efficiency was attributed to the long carrier lifetime in the strained ZION QWs.
High-quality epitaxial ZnO films on c-plane sapphire substrates have been obtained by utilizing an off-axis sputtering configuration together with buffer layers prepared via nitrogen-mediated crystallization (NMC). The role of NMC buffer layers is to provide high density of nucleation site and, thus, to reduce the strain energy caused by the large lattice mismatch (18%) between ZnO and sapphire. The NMC buffer layers allow two-dimensional growth of subsequently grown ZnO films, being particularly enhanced by employing an off-axis sputtering configuration in which the substrate is positioned out of the high-energy particles, such as negative oxygen ions originating from the targets. As a result, ZnO films with smooth surfaces (root-mean-square roughness: 0.76 nm) and a high electron mobility of 88 cm2/V·s are fabricated. Photoluminescence spectra of the ZnO films show strong near-band-edge emission, and the intensity of the orange-red defect emission significantly decreases with increasing horizontal distance between the target and the substrate. From these results, we conclude that off-axis sputtering together with NMC buffer layers is a promising method for obtaining high-quality epitaxial ZnO films.
High-quality epitaxial ZnO films on c-plane sapphire substrates have been obtained by utilizing off-axis sputtering configuration together with buffer layers prepared via nitrogen mediated crystallization (NMC). The role of NMC buffer layers is to provide high density of nucleation site and thus to reduce the strain energy caused by the large lattice mismatch (18%) between ZnO and sapphire. The NMC buffer layers allow two dimensional (2D) growth of subsequently grown ZnO films, being particularly enhanced by employing off-axis sputtering configuration, in which the substrate is positioned out of the high-energy particles such as negative oxygen ions originating from the targets. As a result, ZnO films with smooth surfaces (root-mean-square roughness: 0.76 nm) and high electron mobility of 88 cm2/V⋅sec are fabricated. Photoluminescence spectra of the ZnO films show strong near-band-edge emission, and the intensity of the orange-red defect emission significantly decreases with increasing the horizontal distance between the target and the substrate. From these results, we conclude that off-axis sputtering together with NMC buffer layers is a promising method for obtaining high quality epitaxial ZnO films.
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