Electronic Properties of Nitrogen Delta-Doped Silicon Carbide Layers
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Electronic Properties of Nitrogen Delta-Doped Silicon Carbide Layers Toshiya Yokogawa, Kunimasa Takahashi, Takeshi Uenoyama, Osamu Kusumoto, Masao Uchida, and Makoto Kitabatake Advanced Technology Research Laboratories, Matsushita Electric Industrial Co. Ltd., Hikaridai 3-4, Seika-cho, Kyoto 619-0237, Japan. ABSTRACT Nitrogen delta-doped silicon carbide (SiC) layers were grown by a new pulse doping method in a chemical vapor deposition. Doping distribution with high peak concentration (1 1018 cm-3) and narrow distribution width (12 nm) was fabricated in the nitrogen delta-doped structure of SiC. Mobility enhancement due to spatial separation of electrons and their ionized parent donors was observed for the delta-doped structure. Metal-semiconductor field-effect transistors with a nitrogen delta-doped channel and a recess gate structure were fabricated. The devices had large source-drain breakdown voltages, high drain current capability and easy control of the threshold voltage with a good pinch-off characteristics.
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INTRODUCTION Silicon carbide (SiC) is one of the reliable candidate for high power, high frequency, and high temperature devices due to its large energy bandgap, high breakdown voltage, high saturated electron velocity and high thermal conductivity.1-4 Single crystalline SiC has been successfully grown on the off-oriented SiC substrates by a chemical vapor deposition (CVD).5, 6 These SiC homoepitaxial layers enable us to develop the SiC-based devices.7 Much attention has been paid to delta-doping, in which the doping impurities are uniformly distributed within a two-dimensional thin layer, in III-V compound semiconductors for high-performance device applications. Achievement of well-controlled crystal growth However, it had been difficult to grow a techniques enabled to make delta-doped profiles.8-10 well-defined doping profile because of an extremely high temperature of SiC CVD growth.11 Instability of the dopant gas flow at the high temperature ( 1500 ) makes it difficult to form an abrupt doping profile. Recently, a new pulse doping method was developed using a pulse valve, which realized well-defined and well–controlled doped layers.11 In this paper, we demonstrate a nitrogen delta-doped SiC by the pulse-doping method in CVD. We report structural and electrical behavior of the nitrogen delta-doped SiC and propose application for a delta-doped channel field-effect transistor (FET). MATERIAL GROWTH AND CHRACTERIZATION A vertical hot-wall type CVD reactor was used in this study. The reactor was equipped with a crucible made of graphite in the quartz chamber. Out side of the crucible was surrounded by heat insulators made of carbon felt. The substrate was set surface-down in the crucible heated by a radio frequency induced current. Source gases (SiH4 and C3H8) and carrier gas (H2) flowed in from the bottom of the crucible and out from the top in consideration of the buoyancy of the gas flow at the high temperature above 1600 .
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Commercially available 6H-SiC(0001) 3.5 off-axis wafers were u
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