Light-induced quantum tunnelling current in graphene

Abstract

In the last decade, advancements in attosecond spectroscopy have allowed researchers to study and manipulate electron dynamics in condensed matter via ultrafast light fields, offering the possibility to realise ultrafast optoelectronic devices. Here, we report the generation of light-induced quantum tunnelling currents in graphene phototransistors by ultrafast laser pulses in an ambient environment. This tunnelling effect provides access to an instantaneous field-driven current, demonstrating a current switching effect (ON and OFF) on a ~630 attosecond scale (~1.6 petahertz speed). We show the tunability of the tunnelling current and enhancement of the graphene phototransistor conductivity by controlling the density of the photoexcited charge carriers at different pump laser powers. We exploited this capability to demonstrate various logic gates. The reported approach under ambient conditions is suitable for the development of petahertz optical transistors, lightwave electronics, and optical quantum computers.

Fig. 1. Light-induced quantum current tunnelling in graphene phototransistor.

a The optical microscope (and zoom in) images of the graphene-silicon (Si)-graphene phototransistor and illustration of its band structure, the black dashed line presents the Fermi level. b The measured current-voltage (I–V) curve in case of laser ON (blue line) and laser OFF (red line). The inset shows the switching ON and OFF the photocurrent signal by the laser beam. c the tunnelling characteristics I–V curve for the Gr-Si-Gr transistor and the redline is an eye guide. The error bars present the calculated standard deviation error of three scans.

Fig. 2. Attosecond current switching.

a Cross-correlation current measurement setup. The pump laser beam splits into two beams by beam splitter. The two beam are focused into the transistor and generate current signals. The delay between these two generated signals is controlled by a delay stage implemented in one of the beam paths. b Instantaneous field-induced current (I_E) (average of three measurements), shown as black dots connected by red line. The error bars present the calculated standard deviation error of three scans. The calculated current is plotted in dashed black line. c Absolute I_E measured signal modulation in time, obtained from (b), is plotted in diamond shape points connected with black line. The inset in (c) (a zoom in delay ranges from −1.5 to 1.5 fs) shows the switching of the current ON and OFF with a periodicity of 630 as.

Fig. 3. Controlling the light-induced current signal.

a Experimental setup illustration for controlling the light induced current in a graphene-silicon-graphene transistor. The laser beam of the pump pulse is focused by a parabolic mirror into a transistor channel. The power is controlled by a neutral density filter. b the measured light-induced current I_L (black dots connect by red line) and the calculated excited carriers’ populations (blue line) as a function of the pump laser field intensity. c calculated carrier distribution in the reciprocal space (K) of graphene excited by 1.2 V/nm laser field.

Fig. 4. Photoconductivity enhancement in the graphene phototransistor.

a Acquired I–V curves (average of three measurements) at different pump field intensities. b, c The change of resistance (R) and conductivity as function of the laser field intensities obtained from the measured I–V curves in (a), respectively. The red line in (b) is an eye guide and the blue line in (c) represents the calculated conductivity from our simulation model.