Fast photoresponse and high detectivity in copper indium selenide (CuIn₇Se₁₁) phototransistors

The fast and sensitive detection of light can lead to a variety of optoelectronics and/or photonic-based applications in fields ranging from fast optical switching devices to health and environmental monitoring systems. Although several systems based on organic and inorganic materials show high sensitivity to visible light, in general they suffer from slow response times. Here we show that phototransistors fabricated using multilayers of CuIn₇Se₁₁ exhibit response times of ∼ tens of with responsivity (R) values > 10 AW^-1 and with external quantum efficiencies reaching beyond 10³ % when excited with a 658 nm wavelength laser. These devices also show high specific detectivity (D ^∗) values of ∼10¹² Jones. The responsivity and detectivity exhibited by these phototransistors are at least an order of magnitude better than commercially available conventional Si-based photodetectors, coupled with response times that are orders of magnitude better than several other families of layered materials investigated so far. The properties of the CuIn₇Se₁₁ phototransistor can be further tuned and enhanced by applying a back-gate voltage. Our investigations indicate that such layered ternary compounds can potentially be used as components in opto-electronics-related applications.