Hi Sara, with regard to 2D materials, photogating effect refers to light induced modification in the carrier density and thereby a change in conductance.

Actually, a photogating effect is a special case of the photoconductive effect.

This effect is generally observed in semiconductors with high dislocation or defect density. In this effect, two mechanisms of photo electron-hole (e-h) pair generation are observed.

First, the e-h pairs generated by the incident light serves as the conducting channel. Thereafter, the trap states inside the defective semiconductor or at the surface adsorbates capture either electrons or holes. For instance, in an n-type semiconductor with hole trap states, the holes get trapped by defects and only photogenerated electrons contribute to the photocurrent. However, an extra gate voltage is induced by the trapped holes.

In the second mechanism, the photo excited carriers are generated only in the surface adsorbates and then only one type of charge carrier serves as the conducting channel. The photogating effect therefore generates an extra gate voltage on the conducting channel in both cases that effectively modulates the channel resistance.

I hope this info is useful.

Best regards,

Zia

Hi Zia,

Can you please share some documents regarding your explanations.

Thanking you,

Anirban

Hi Sara

The bottom gate generally used is Silicon (Si) which is a degenerate semiconductor (highly doped so act as metal). Si itself and Si/SiO2 interface contains many defects (traps). Now let see what happens when light is illuminated on the sample (graphene, TMDs,..... above SiO2). Light not only illuminate the sample area, it can penetrate SiO2 and reach to the Si. In Si, e-h pairs will be generate by this light (which generally is unwanted in photocurrent measurement). Among these e-h pair on Si, some will recombine but some will be trapped (either hole or electron) at the defect state at interface. These trapped charges at the interface act as additional gate voltage so called Photo gating effect.

Metal gate can be used to remove the photo gating effect. Lets follow this paper.

In thin film photodetector where the device is composed of a thin semiconductor layer deposited on a substrate consisting of SIO2 on heavily doped silicon. The interfaced between SIO2 and silicon contains silicon defects that can act as traps.

On illuminating the device with light the light penetrate to the silicon and generates electron hole pairs where a part will recombine while some charges will be trapped at interface. These static charges alter the gate voltage and therefore this phenomenon is called photogating.

Best wishes