title: Photojunction field-effect transistor based on a colloidal quantum dot absorber channel layer.
abstract: The performance of photodetectors is judged via high responsivity, fast speed of response, and low background current. Many previously reported photodetectors based on size-tuned colloidal quantum dots (CQDs) have relied either on photodiodes, which, since they are primary photocarrier devices, lack gain; or photoconductors, which provide gain but at the expense of slow response (due to delayed charge carrier escape from sensitizing centers) and an inherent dark current vs responsivity trade-off. Here we report a photojunction field-effect transistor (photoJFET), which provides gain while breaking prior photoconductors' response/speed/dark current trade-off. This is achieved by ensuring that, in the dark, the channel is fully depleted due to a rectifying junction between a deep-work-function transparent conductive top contact (MoO3) and a moderately n-type CQD film (iodine treated PbS CQDs). We characterize the rectifying behavior of the junction and the linearity of the channel characteristics under illumination, and we observe a 10 μs rise time, a record for a gain-providing, low-dark-current CQD photodetector. We prove, using an analytical model validated using experimental measurements, that for a given response time the device provides a two-orders-of-magnitude improvement in photocurrent-to-dark-current ratio compared to photoconductors. The photoJFET, which relies on a junction gate-effect, enriches the growing family of CQD photosensitive transistors.
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Toronto , 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
authors.forename: Valerio
authors.initials: V
authors.lastname: Adinolfi
authors.forename: Illan J
authors.initials: IJ
authors.lastname: Kramer
authors.forename: André J
authors.initials: AJ
authors.lastname: Labelle
authors.forename: Brandon R
authors.initials: BR
authors.lastname: Sutherland
authors.forename: S
authors.initials: S
authors.lastname: Hoogland
authors.forename: Edward H
authors.initials: EH
authors.lastname: Sargent
keywords: FET; JFET; colloidal quantum dots; photodetectors; phototransistors