Vertically Stacked Intraband Quantum Dot Devices for Mid-Wavelength Infrared Photodetection

Abstract

Intraband quantum dots are degenerately doped semiconductor nanomaterials that exhibit unique optical properties in mid- to long-wavelength infrared. To date, these quantum dots have been only studied as lateral photoconductive devices, while transitioning toward a vertically stacked structure can open diverse opportunities for investigating advanced device designs. Here, we report the first vertical intraband quantum dot heterojunction devices composed of Ag2Se/PbS/Ag2Se quantum dot stacks that bring the advantage of reduced dark conductivity with a simplified device fabrication procedure. We discuss the improvement in the colloidal synthesis of Ag2Se quantum dots that are critical for vertical device fabrication, identify an important process that determines the mid-wavelength infrared responsivity of the quantum dot film, and analyze the basic device characteristics and key detector performance parameters. Compared to the previous generation of Ag2Se quantum dot-based photoconductive devices, approximately 70 times increase in the mid-wavelength responsivity, at room temperature, is observed.

Midwavelength Infrared p–n Heterojunction Diodes Based on Intraband Colloidal Quantum Dots

“…First, to prepare the CQD materials, Ag 2 Se and PbS CQDs were synthesized following previously reported hot-injection protocols. 16 Figure 2a shows the midinfrared optical absorption of films made from as-synthesized Ag 2 Se, PbS, and mixed (optimized mixture ratio of N Ag2Se /N PbS = 0.04, see more details in Figure 4b) CQDs obtained using Fourier transform infrared (FTIR) spectroscopy. The PbS CQDs capped with oleic acid show an absence of absorption in a 3.5−6 μm spectral range, which makes them a good candidate for use in the binary CQD approach to modify the film's electrical property.…”

“…Devices fabricated from pure Ag 2 Se CQDs, in contrast, showed a narrow temporal window that exhibits the maximum MWIR responsivity. 16 This can be understood by reflecting the fact that the majority component of our binary CQD film is PbS CQDs. To form a p−n junction, ZnO nanoparticles were synthesized following the literature report 25,26 and spin-casted on top of a binary CQD layer with a thickness of 80 nm (see the Supporting Information S2 for optical absorption of ZnO in the mid-infrared).…”

“…This is a 30 times increase over our previous generation of barrier devices. 16 This improvement is mainly attributed to the reduced dark current and noise current density, an advantageous device property offered by reverse-biased p−n junction diodes.…”

“…11−13 The primary advantage of utilizing a p−n diode design lies in the fact that, under a typical reverse-biased operation, the dark current is fed by the minority carriers. 14 Compared to photoconductive 15,3 and barrier device 16,17 designs, where the majority carriers are responsible for the dark current, the p−n junction diode is hence expected to show significant reductions in the magnitudes of the dark current and noise current density. However, the intraband CQDs also present a new and unique challenge when they are used to construct p−n junction devices.…”

Nanostructured Materials and Architectures for Advanced Optoelectronic Synaptic Devices

“…At the nanoscale, energy bands can be adjusted with size and geometry. Thanks to 3D tunability, 0D materials exhibit many unique electronic and optoelectronic properties, in particular for laser, [222][223][224] photodetectors, [225][226][227][228][229][230][231][232] photonic memories, [233,234] etc. Aside from the tunable bandgap, such materials have a large surface area, making them better suited for efficient light absorption than 1D and 2D nanostructured materials.…”