Single-Molecule Photocurrent at a Metal-Molecule-Semiconductor Junction.
Single-Molecule Photocurrent at a Metal-Molecule-Semiconductor Junction.
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DOI：
10.1021/acs.nanolett.7b02762
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发表时间：
2017-05
期刊：
影响因子：
10.8
通讯作者：
A. Vezzoli;Richard J Brooke;S. Higgins;W. Schwarzacher;R. Nichols
中科院分区：
文献类型：
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作者：
A. Vezzoli;Richard J Brooke;S. Higgins;W. Schwarzacher;R. Nichols
我们在这里展示了一个金属分子半导体纳米器件的新概念，该器件采用Au和GaAs触点作为光电二极管。使用STM记录这些结的电流-电压迹线，并使用“闪烁”或“I(t)”方法记录黑暗和照明下单分子水平的电行为，使用低掺杂和高掺杂的GaAs样品以及两种不同类型的分子桥：非共轭的戊二硫醇和更共轭的1,4-苯基（二甲基硫醇）。高掺杂GaAs的结在黑暗中表现出较差的整流和低光电流，而低掺杂GaAs的结在黑暗中表现出特别高的整流比（在1.5 V偏置电位下>103）和高的反向偏置光电流。在低掺杂的砷化镓中，损耗层的厚度越大，不仅减少了反向偏置漏电流，而且增加了产生光电流的体积，这一效应被结的点接触几何放大了。此外，由于光生空穴在分子桥HOMO的帮助下隧穿到金属电极，因此后者的选择对金属-分子-半导体光电二极管的稳态和瞬态响应都有很大的影响。通过光产生的电荷载流子控制结电流为单分子纳米器件增加了新的功能。
We demonstrate here a new concept for a metal-molecule-semiconductor nanodevice employing Au and GaAs contacts that acts as a photodiode. Current-voltage traces for such junctions are recorded using a STM, and the "blinking" or "I(t)" method is used to record electrical behavior at the single-molecule level in the dark and under illumination, with both low and highly doped GaAs samples and with two different types of molecular bridge: nonconjugated pentanedithiol and the more conjugated 1,4-phenylene(dimethanethiol). Junctions with highly doped GaAs show poor rectification in the dark and a low photocurrent, while junctions with low doped GaAs show particularly high rectification ratios in the dark (>103 for a 1.5 V bias potential) and a high photocurrent in reverse bias. In low doped GaAs, the greater thickness of the depletion layer not only reduces the reverse bias leakage current, but also increases the volume that contributes to the photocurrent, an effect amplified by the point contact geometry of the junction. Furthermore, since photogenerated holes tunnel to the metal electrode assisted by the HOMO of the molecular bridge, the choice of the latter has a strong influence on both the steady state and transient metal-molecule-semiconductor photodiode response. The control of junction current via photogenerated charge carriers adds new functionality to single-molecule nanodevices.