Design and characterization of colloidal quantum dot photoconductors for multi-color mid-infrared detection

This report paves the way for low cost, multi-color, room-temperature, and easily-feasible mid-IR photodetector with distinct output currents. The proposed device is designed and simulated to be fabricated by the solutionprocess technology thanks to its simplicity and fabrication ease, room-temperature operation capability, low production cost, and excellent photoelectric properties. In this approach, the proposed structure is composed of an array of n x n pixels, where each pixel is designed to enable multi-wavelength detection. The absorber layer consists of different sized quantum dots that absorb distinct wavelengths simultaneously through interband transitions in the mid-infrared region. Selective energy contacts based on quantum well structures are designed to be deposited on interdigitated contacts as a means of extracting the stimulated carriers from the absorber layers to the metal contacts. Through resonant tunneling, the excited carriers are transferred, which generates the output photocurrent and significantly reduces the dark current. In order to model the designed multi-color photoconductor, coupled rate equations and three-dimensional Schrodinger-Poisson equations have been developed and solved self-consistently. As a way of demonstrating the validity of the introduced model, a experimentally fabricated photoconductor and a theoretically modeled photodetector using the nonequilibrium Green's function (NEGF) model have been simulated; the comparison between the simulation results is quite satisfactory. In order to simplify the theoretical model, two different sizes of InSb/ZnSe core/shell quantum dots have been considered in the theoretical model to detect two MIR wavelengths (3 mu m and 4 mu m) of the incident light. Simulation results indicate that the peak responsivities are about 3.3(A/W) and 6(A/W), and the high specific detectivities D* are about 9 x 1010(cm.Hz1/2W- 1) and 15 x 1010(cm.Hz1/2W- 1) for the wavelengths of 4 mu m and 3 mu m, respectively.