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Diode device structure. (a) Scanning electron micrograph of a vertical as-grown InAs nanowire on a substrate showing the hexagonal cross section and absence of tapering. Scale bar is 200 nm and viewing angle is 45°. (b) Schematic cross section of a Si–InAs heterojunction diode.
characteristics of a Si–InAs heterojunction diode. (a) Temperature dependence of a diode with a substrate doping of . The device exhibits a forward thermal current with ideality factor close to two. In the reverse direction, breakdown occurs at 4–8 V, depending on temperature. (b) Breakdown voltage vs temperature. An increasing breakdown voltage is observed as a function of increasing temperature, indicating an avalanche breakdown mechanism. The dashed line is only a guide for the eye. (c) Barrier height vs applied voltage. The temperature-dependent measurements were used to extract a potential barrier of 275 meV for thermal injection across the Si–InAs interface. (d) Band diagram of the Si–InAs device in (a). The potential barrier extracted in (c) yields a valence band offset of and results in an effective band gap of .
Effect of doping. (a) Current density vs applied voltage for a substrate doping of , , and (two topmost curves). As the substrate doping is increased to , the reverse interband tunnel current increases almost six orders of magnitude, reaching current densities of around at 0.5 V. At the highest doping level, an NDR region in the forward characteristics is sometimes observed with peak-to-valley current ratios up to 1.4, an explicit sign of an Esaki diode. (b) Temperature dependence of a Si–InAs diode with substrate doping of . (c) Current density vs applied voltage for increasing disilane concentrations and a substrate doping of . Changing the disilane/TMIn ratio (0, , and ) during InAs growth by several orders of magnitude has limited effect on the overall current levels.
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