Measurement of ultra-low photocurrents in metal-semiconductor-metal nanostructures: noise and sensitivity aspects

Capability of generating electric currents and charges via direct driving free carriers of metal-semiconductor-metal nanostructures by electric field of few-cycle laser pulses promises breakthrough developments in PHz electronics, fundamental material science, characterization of laser pulses, and many other areas [1-3]. One of major challenges of this research area is the need to detect extremely low levels of laser-generated charges (about few femto-Coulombs) and currents (pico-Amps). Traditional methods of photocurrent detection fail in this case. Novel advanced approaches based on accurate analysis of noise and sensitivity of detecting units and electronic circuits are required.

Here, we report simulations of thermal noise of Au-GaN-Au planar structures with parameters very similar to those reported in available publications [1-3]. We compare simulation results with resistance and noise analysis of fabricated Au-GaN-Au devices. We demonstrate feasibility of substantial reduction of noise level by increase of resistivity of the structure. However, increase of resistivity reduces the laser-induced current required to detect and can drive it below the detection threshold. In the search for a non-trivial balance between reduction of noise and increase of photocurrent, we consider several combinations of geometrical and electric parameters of the structures.

[1] A. Schiffrin, et al, Nature, 493, 70-74 (2013).

[2] T. Paasch-Colberg, et al, Nature Photonics, 8, 214-218 (2014).

[3] S. Yu. Kruchinin, et al, Rev. Mod. Phys. 90, 021002 (2018).