Field emission measure of the time response of individual semiconducting nanowires to laser excitation

Abstract

International audienceA simple technique is explored to determine the temporal photo-response, s, of individual semiconducting SiC and Si nanowires (NWs), with a high time resolution. Laser-assisted field emission (LAFE) from the NWs is first shown to be highly sensitive to continuous laser illumination. Pulsed illumination is then combined with measurements of the total energy distributions to determine s which were rather large, 4-200 ls. The time response scaled roughly with the square of the NWs length and could be attributed to laser-induced heating. LAFE is thus a new tool for quantifying rapid thermo-optical effects in such nano-objects

Current Saturation in Field Emission from H-Passivated Si Nanowires

“…We have recently explored the effect of such laser heating on other NWs and found that temperature increases in the tens to hundreds of degrees were easily generated in similar structures. 18 Extrapolating data in Figure 3, the optical excitation of the Si NW at 7 mW corresponds to an increase in temperature K. This temperature is too for desorbing the oxide layer, but the interface is expected to be free of all silicon hydride species at ∼850 K. 19 Therefore, temperatures induced here by the laser were high enough to eliminate the H-passivation, thereby creating a large concentration of dangling bonds at the Si/SiO 2 interface. Evidently, the heating here has transformed the H-passivated interface into a highly conductive surface "channel", with its overall importance in NW FE probably enhanced due to their high surface/bulk ratios.…”

“…Moreover, the FN I ( V ) plot in Figure becomes less sensitive to temperature (the blue curve is at room temperature and the red curve at 365 K). We have recently explored the effect of such laser heating on other NWs and found that temperature increases in the tens to hundreds of degrees were easily generated in similar structures . Extrapolating data in Figure , the optical excitation of the Si NW at 7 mW corresponds to an increase in temperature of ∼900 K. This temperature is too low for desorbing the oxide layer, but the interface is expected to be free of all silicon hydride species at ∼850 K .…”

“…FE measurements were performed in an UHV system (2 × 10 –10 Torr) that has been described in detail elsewhere. ,, The polyvalent setup allows one to carry out a wide range of measurements. An electron counter permits low current measurements starting at 10 –20 A.…”

Negative differential resistance in photoassisted field emission from Si nanowires

“…We tested other conditions that could induce a significant temperature gradient across the NW, but we reached the same conclusion. It was, for instance, possible to generate a non-uniform temperature gradient across the NW using laser heating on one side of the NW and thermal contact on the other side with the W tip acting as a heat sink 32 . Figure 3-c presents a direct comparison of two NDR shapes obtained when the W tip is placed at 100K and room temperature.…”