A memory for images

Nano Lett. 15, 259–265 (2015)

Two-dimensional materials such as graphene and transition metal dichalcogenides are being widely investigated for use in electronic and optoelectronic devices because of their flexibility and versatile optical and electronic properties. Now, Antony George, Liehui Ge, Pulickel Ajayan and colleagues at Rice University and Lanzhou University add to the pool of existing optoelectronic devices by creating an imaging sensor made from few-layer CuIn₇Se₁₁.

In these devices, incident light excites photoelectrons in a semiconductor channel made of CuIn₇Se₁₁. When a positive gate voltage is applied, the electrons are then trapped in the channel by a potential well formed by the Schottky barriers at the contacts between the 2D material and the source and drain metal electrodes. The amount of trapped charge is proportional to the exposure dose of light, analogous to conventional charge-coupled device imaging sensors. Information about the photoexcitation is maintained until a negative source–drain voltage is applied, which allows the trapped electrons to be released and for the stored information to be read.

Each device of this kind could form a pixel in a memory array that can capture and store an image, and the researchers demonstrate a three-unit array. They also illustrate the generality of the approach by fabricating sensors in few-layer InSe and monolayer MoS₂. The flexibility of 2D materials means that such sensors are advantageous compared with conventional imaging sensors when it comes to flexible electronic applications, or when integration with other 2D electronic devices is required.