Department of Electrical Engineering and Computer Science, University of Toronto , 10 King's College Road, Toronto, Ontario M5S 3G4, Canada.
ACS Nano. 2015 Jan 27;9(1):356-62. doi: 10.1021/nn5053537. Epub 2015 Jan 13.
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.
光电探测器的性能通过高响应度、快速响应速度和低背景电流来判断。许多之前报道的基于尺寸调谐胶体量子点（CQD）的光电探测器要么依赖于光电二极管，由于它们是主要的光生载流子器件，缺乏增益；要么依赖于光电导器件，虽然它们提供了增益，但代价是响应速度慢（由于延迟了从敏化中心逃逸的电荷载流子），并且固有暗电流与响应度之间存在权衡。在这里，我们报告了一种光电结场效应晶体管（photoJFET），它提供了增益，同时打破了之前光电导器件的响应/速度/暗电流权衡。这是通过确保在黑暗中，由于深功函数透明导电顶接触（MoO3）和适度 n 型 CQD 薄膜（碘处理的 PbS CQD）之间的整流结，通道完全耗尽来实现的。我们对结的整流行为和光照下通道特性的线性进行了表征，并观察到 10 μs 的上升时间，这是提供增益、低暗电流 CQD 光电探测器的记录。我们使用经过实验测量验证的分析模型证明，对于给定的响应时间，与光电导器件相比，该器件在光电流与暗电流比方面提高了两个数量级。photoJFET 依赖于结栅效应，丰富了不断发展的 CQD 光敏晶体管家族。
