An Extrinsic Approach Toward Achieving Fast Response and Self‐Powered Photodetector

Abstract

An extrinsic approach toward achieving fast response and self‐powered photodetector is reported. It is shown that an organic–inorganic hybrid device (SnSe2/PEDOT:PSS) not only operates in self‐powered mode for infra‐red photodetection but also improves the response time with respect to inorganic (SnSe2) linear devices. Fast response and recovery time constants of ≈1.33 and 1.22 s, respectively, are obtained. Furthermore, the sensitivity is highest at zero bias and the device is stable for over 6 months stored in open air condition. The observed photo‐current, faster response and recovery time constants are ascribed to the formation of a strong built‐in electric field at the interface between SnSe2 and PEDOT:PSS. In a broader view of these findings, the device proves its potential as a self‐powered photo‐detector and the results reported here can pave the way to design self‐powered and fast response for other wavelengths.

Device Architecture for Visible and Near-Infrared Photodetectors Based on Two-Dimensional SnSe2 and MoS2: A Review

“…When the device is illuminated with photons of energy greater than the band gap, as shown in Figure 2 b, electron-hole pairs are generated (excitons) and are separated by an applied bias. For a linear (Ohmic) photoconductor based on a metal-semiconductor-metal structure, the transit time (considered as the charge lifetime from generation until recombination or extraction), a measure of the response time of the photodetector is defined by a mathematical relation below [ 5 , 6 , 59 ]; where µ is the mobility, L is the electrode spacing, and E is the applied field separating the free carriers. The consequence of this equation is the response time of a photoconductor highly depends on the carrier mobility of the semiconductor and electrode spacing.…”

“…In photoconductive mode, the external electric field is in the same direction as the built-in electric field which increases the separation efficiency of the electron-hole pairs and the response time. The charge carrier transit time for a p–n or Schottky junction depends on the width of the depletion region as well as charge carrier mobility, as depicted in Figure 1 b, and is defined as [ 5 , 59 ] where is the width of the depletion region, V bi , V a , N a , N d , μ drift , and E o are built-in potential, applied potential, concentration of acceptor atoms, concentration of donor atoms, electron-hole drift mobility and built-in electric field, respectively. The consequence of Equation (4) is that the transit time highly depends on the depletion width which is in the order of few nm and electron/hole mobility and as a result, the transit time is much faster for p–n or Schottky junction.…”

“…It is interesting to note that the response time is in accordance with Equation (1) for a photoconductor. We further fabricated a hetero-structure based on SnSe 2 and PEDOT:PSS on soda lime glass substrate ( Figure 8 c) in order to utilize the built-in potential and narrow depletion width for fast response/recovery speed [ 5 ]. The response/recovery time improved to 1.33 and 1.22 s respectively with the device operating at zero-bias ( Figure 8 d) but the improve in response time resulted into a reduction in responsivity to 1.4–2.6 μA/W [ 5 ].…”

“…We further fabricated a hetero-structure based on SnSe 2 and PEDOT:PSS on soda lime glass substrate ( Figure 8 c) in order to utilize the built-in potential and narrow depletion width for fast response/recovery speed [ 5 ]. The response/recovery time improved to 1.33 and 1.22 s respectively with the device operating at zero-bias ( Figure 8 d) but the improve in response time resulted into a reduction in responsivity to 1.4–2.6 μA/W [ 5 ]. The fact that PEDOT:PSS and SnSe 2 suffer from low interfacial mobility, the response/recovery time was further improved to 57 ± 25/34 ± 15 μs by fabricating a hetero-structure based on n-SnSe 2 /p-Si substrate ( Figure 8 e,f) and a responsivity of 120 mA/W was obtained [ 66 ].…”

“…The transit time strongly depends on mobility and bias for a photoconductor where as it strongly depends on the width of the depletion region and mobility for a photodiode. ( a , b ) are reproduced with permission from reference [ 5 ].…”