Micro-Transfer-Printing of Al₂O₃-Capped Short-Wave-Infrared PbS Quantum Dot Photoconductors

Abstract

Quantum dots (QDs) have attracted considerable attention in the development of various optoelectronic applications. The scalable heterogeneous integration of high quality, yet stable QD films is required for low-cost devices based on these materials. Here, we demonstrate the transfer printing of microscale patterns of Al2O3-passivated PbS QD films to realize large-scale integrated photodetector arrays with a 1 st excitonic absorption peak at 2.1 µm wavelength. The process provides a facile approach to selectively pick-and-print passivated QDs assemblies on device structures with high precision. Transfer-printed photoconductor devices were realized and characterized at low bias voltage and optical power. Under 10 nW surface normal illumination at 2.1 µm wavelength, the responsivity of our devices obtained at 1 V bias reached a maximum value of 25 A/W and 85 A/W for PbS QD films of 88 nm and 140 nm thick, respectively. Introduction:The short-wave infrared (SWIR: 0.9 -3µm) spectral range enables a wide range of applications, including hyperspectral imaging, sensing based on spectral signatures derived from molecular vibrations, night time surveillance, communications, etc. Detector arrays based on III-V semiconductors, such as InGaAs, are currently driving these applications due to their high quantum efficiency and low dark current at room temperature 2 . Unfortunately, the high material and fabrication cost per unit area prohibit the penetration of the technology into consumer applications.Moreover, monolithic integration on low-cost Si electronics is difficult due to the lattice mismatch between IR materials such as InGaAs and silicon 3 , requiring a hybrid integration through flip-chip bonding. Ideally, a good photodetector has to address the challenge of mass fabrication by realizing a relatively cheap material with high photoresponse and ease of integration on commercial silicon read-out integrated circuits.Colloidal quantum dots (CQDs) are a promising, new material for optical sensing applications due to their unique optical properties. The broad addressable spectrum with a sharp and tunable absorption onset based on size control, the high quantum efficiency and photostability make CQDs a suitable alternative to epitaxially grown semiconductors 4 . Moreover, colloidal synthesis is a lowcost fabrication approach that enables the QD size, shape and surface chemistry to be tuned, thereby optimizing the opto-electronic properties of the QDs for the envisioned application 5,6 .

Quantum Dots and Their Applications: What Lies Ahead?

“…36 Printing techniques were also applied to PbS QD-based devices, such as broadband photoconductors 37 and photodetector arrays. 38 Photodetectors operating in the ultraviolet spectral range have been fabricated using a WS 2 QD−graphene nanocomposite, 39 while phototransistors with balanced photo-detection were obtained based on CsPbBr 3 colloidal QDs and few-layer MoS 2 . 40…”

“…Midwavelength IR photoconductive photodetectors with high responsivity were fabricated from Ag 2 Se QDs . Printing techniques were also applied to PbS QD-based devices, such as broadband photoconductors and photodetector arrays …”

Atomic layer deposition for quantum dots based devices

“…At the end, prospects of ALD applications on QDs based devices are discussed from the aspects of ALD materials, process parameters, in-situ characterization and device simulations. 86,88 CdSe/ZnS 61,66,77,87 ZnCdSSe/ZnS 68 CdSe@ZnS/ZnS 63 CdSe/CdS/ZnS 69,71 PbS 56,67,72,78,81,[83][84][85]89 PbSe 55,57,74,79,80 APbX3 60,65,70,75 Sphere 65 Film 57,58,66,69,70,73,74,77 FET 55,62,76,[78][79][80]83,86,88 Solar cell 56,82,84,85 Photodetector 67,…”

“…II-VI and IV-VI traditional QDs are easy to fail since surface atoms are very sensitive to oxygen. The ultra-thin and highly dense barrier layer via ALD served as a shield preventing QDs from the damage of ambient air and moisture 67,73 (Fig. 3(b)) 70 .…”

High-yield parallel transfer print integration of III-V substrate-illuminated C-band photodiodes on silicon photonic integrated circuits

“…Transfer printing is a novel pick-and-place technology whereby devices processed in a dense array on the III-V wafer can be selectively picked using a polydimethylsiloxane (PDMS) stamp and printed on a silicon photonics wafer with high alignment accuracy (better than ±1 μm, 3σ [5]). Recently, several demonstrations of this technology have been reported, including transfer printing III-V photodiodes [6] and lasers [7][8][9] but also PbS quantum dot films [10], Si-Ge devices [11], etc., showcasing the versatility of the technology.…”