Electrical and Photo-Induced Effects in Graphene Channels When Interfaced with Quantum Dots
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Figure 1. The device configuration: QDs were imbedded in the substrate pores. RESULTS and DISCUSSION First, we ascertained that our method works well for flat surfaces. The samples were 150 nm thick oxide on the same silicon wafers albeit with the Al removed by etching. Contacts to the graphene were made with two Cu tapes. As demonstrated by Fig. 2a, the Ids-Vds curve was linear. The curve for Ids-Vgs exhibited the familiar upward inclination typical of graphene channels. 0.4
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(a) (b) Figure 2. (a) Drain-Source current as a function of drain-source voltage, Ids-Vds on a flat oxidized Si surface at a given source-gate voltage, Vgs=0 V. (b) drain-source current as a function of gate-source voltage, Ids-Vgs for a given drain-source voltage, Vds=0.1 V
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The Ids-Vds curve for graphene on AAO was linear, as well. It was similar to the flat samples shown in Fig. 2a. The Ids-Vgs curve, however, exhibited a reverse trend as shown in Fig. 3. One may observe some asymmetry in the curve, as well. Ids (microAmp)
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Figure 3. Ids-Vgs at Vds=0.1 Volts
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Under white light illumination, the current generally rose a bit. Nevertheless, the Ids-Vgs curves exhibited a decrease as a function of Vgs. In Fig. 4 we show maps of these trends. While not so apparent, the curves as a function of Vgs exhibited the downfall trend of Fig. 3. The larger voltage range is attributed to a thicker alumina layer under the graphene.
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(a) (b) Figure 4. Maps of Ids-Vds-Vgs. (a) Without white light illumination on the sample. (b) Under 50 mW/cm2 of white light illumination. The drain-source current has decreased as a function of Vgs. Fig. 4 may be better understood in terms of the difference and the relative difference in the Ids response to light. In Fig. 5 we show the current difference map between the illuminated and non-illuminated cases. Resonance may be seen at Vds~0.3 V. A clearer picture is obtained when we plot the relative differential current under illumination. The relative differential current is directly related to the relative differential channel resistance: specifically, Ids/Ids=R/R. The white light accentuated the relatively small effect noted in Figure 3a even further. One may identify the effect as related to negative differential resistance [5,6]. The effect may be attributed to charge localization under channel illumination.
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(a) (b) Figure 5. (a) Differential current [(Ids under light) – (Ids in dark)]. (b) Relative differe
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