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Highly conductive Ge-doped GaN epitaxial layers were grown by low-temperature pulsed sputtering, and their fundamental structural and electrical properties were investigated. The room-temperature (RT) electron concentration was increased to 5.1 × 1020 cm−3 by the Ge doping, and the atomically flat stepped and terraced surface and the crystalline quality of the layers were maintained. Consequently, the RT resistivity was reduced to 0.20 mΩ·cm, which is comparable to that for typical transparent conductive oxides such as indium tin oxide. The contact resistance of Ge-doped GaN with a Ti/Al/Ti/Au metal stack prepared without annealing was as low as 0.087 Ω·mm. Furthermore, the selective formation of a Ge-doped region using an SiO2 mask was demonstrated. The results clearly indicate the strong potential of pulsed sputtering Ge-doped GaN growth for forming low-parasitic-resistance contact layers of various electrical and optical devices. [ABSTRACT FROM AUTHOR]

We investigated the potential of low-temperature pulsed sputtering deposition (PSD) for the fabrication of high-In-composition thick InGaN multiple quantum wells (MQWs). Low-temperature PSD growth allowed the growth of a 100-period 1.2-nm-thick In0.3Ga0.7N MQW on GaN bulk crystals without apparent lattice relaxation. We fabricated a nitride-based photovoltaic device using 100-period In0.3Ga0.7N MQW absorption layers and obtained a clear photovoltaic response with an open-circuit voltage of 1.24 V, a short-circuit current density of 1.76 mA·cm−2, and a maximum output power density of 1.10 mW·cm−2 under 1 sun with air mass 1.5 illumination. [ABSTRACT FROM AUTHOR]

We grew In-rich InxGa1-xN films on yttria-stabilized zirconia (YSZ) substrates at low temperatures by pulsed sputtering deposition. It was found that single-crystal InxGa1-xN (0.63 ≤ x ≤ 0.82) films can be prepared without significant compositional fluctuations at growth temperatures below 500 °C. It was also found that the electrical properties of InGaN are strongly dependent on In composition, growth temperature, and film polarity. N-channel operation of the metal–insulator–semiconductor field-effect transistor (MISFET) with an ultrathin InGaN channel on the YSZ substrates was successfully demonstrated. These results indicate that an InGaN-based MISFET is a promising device for next-generation high-speed electronics. [ABSTRACT FROM AUTHOR]

We investigated basic characteristics of InN films grown on glass substrates and fabricated thin-film transistors with them. It was found that highly c-axis oriented InN films can be obtained by the surface modification of glass substrates with amorphous HfO2 layers. The electron mobility of the c-axis-oriented InN on HfO2/glass reached 330 cm² V-1 s-1. We demonstrated that a field effect transistor based on the ultrathin film of highly c-axis-oriented InN exhibited an on/off current ratio as high as 106; in addition, this InN-on-glass device supported current densities greater than 14mA mm-1. The results indicate that InN-based ultrathin-film transistors are promising electronic devices that enable high-current densities to be achieved on glass substrates. [ABSTRACT FROM AUTHOR]

To investigate the interfacial charge-transfer phenomena between perovskite transition metal oxides LaNiO3 (LNO) and LaMnO3 (LMO), we have performed in situx-ray absorption spectroscopy(XAS) measurements on LNO/LMO multilayers. The Ni-L2,3 and Mn-L2,3 XAS spectra clearly show the occurrence of electron transfer from Mn to Ni ions in the interface region. Detailed analysis of the thickness dependence of these XAS spectra has revealed that the spatial distribution of the transferred charges across the interface is significantly different between the two constituent layers. The observed spatial distribution is presumably described by the charge spreading model that treats the transfer integral between neighboring transition metal ions and the Coulomb interaction, rather than the Thomas-Fermi screening model. [ABSTRACT FROM AUTHOR]