Query: Fast, sensitive and spectrally  tuneable colloidal quantum-dot photodetectors

Candidate papers:

abstract: Solution processed semiconductors are compatible with a range of substrates, which enables their direct integration with organic circuits, microfluidics, optical circuitry and commercial microelectronics. Ultrasensitive photodetectors based on solution process colloidal quantum dots operating in both the visible and infrared have been demonstrated, but these devices have poor response times (on the scale of seconds) to changes in illumination, and rapid response devices based on a photodiode architecture suffer from low sensitivity. Here, we show that the temporal response of these devices is determined by two components electron drift, which is a fast process, and electron diffusion, which is a slow process. By building devices that exclude the diffusion component, we are able to demonstrate a >1,000 fold improvement in the sensitivity bandwidth product of tuneable colloidal quantum dot photodiodes operating in the visible and infrared.
author_names: Jason Paul Clifford

Gerasimos Konstantatos

Keith William Johnston

Sjoerd Hoogland

Larissa Levina

Edward H Sargent
title: Fast, sensitive and spectrally tuneable colloidal quantum dot photodetectors.
venue: Nature nanotechnology
year: 2009

abstract: Summary Fast and sensitive infrared (IR) photodetection is of interest for depth imaging that is fundamental to machine vision, augmented reality, and autonomous driving. Colloidal quantum dots (CQDs) are appealing candidates for this goal: in contrast with III V semiconductors, they offer facile tuning of IR absorption and enable ease of integration via solution processing. So far, the best short wave IR CQD photodetectors have been limited to 70 ns response time and quantum efficiency of 17% at 1,450 nm. To advance the field using CQDs, large diameter CQDs are needed that combine passivation with efficient charge transport. Here, we report an efficient ligand exchange route that tailors the halide passivants and introduces an added exchange step crucial to efficient passivation, removal of unwanted organics, and charge transport. In devices, the CQD solids give rise to external quantum efficiency greater than 80% at 1,550 nm, a measured detectivity of 8 x 1011 Jones, and a 10 ns response time.
author_names: Maral Vafaie

James Z Fan

Amin Morteza Najarian

Olivier Ouellette

Laxmi Kishore Sagar

Koen Bertens

Bin Sun

F Pelayo Garcia de Arquer

Edward H Sargent
title: Colloidal quantum dot photodetectors with 10 ns response time and 80% quantum efficiency at 1,550 nm
year: 2021

abstract: Colloidal quantum dots (CQDs) are emerging solution processed materials combining low cost, easy deposition on large and flexible substrates, and bandgap tunability. The latter feature, which allows spectral tuning of the absorption profile of the semiconductor, makes these materials particularly attractive for light detection applications. Lead sulfide (PbS) CQDs, in particular, have shown astonishing performance as a light sensitive material operating at visible and infrared (IR) wavelengths. Early studies of PbS CQDs used as a photosensitive resistor (photoconductor) showed an impressive responsivity exceeding 1000 A/W and a detectivity (D* higher then 10^13 Jones. This impressive D* was preserved in the successive development of the first PbS CQD photodiode, showing the possibility to realize fast f_3db 1Mhz and sensitive IR detectors. Currently, the field is moving toward the development of hybrid devices and phototransitors. PbS CQDs have been combined in field effect transistors (FETs) with graphene and MoS2 channels, showing ultra high gain (exceeding 10^8 electrons/photons) and high D* Recently a photo junction FET (photo JFET) has been reported that breaks the inherent dark current/gain/bandwidth compromise affecting photoconductive light detectors. With this presentation we offer a broad overview on CQD photodetection highlighting the past achievements, the benefits, the challenges and the prospects for the future research on this field.
author_names: Valerio Adinolfi

Edward H Sargent
title: Colloidal quantum dot photodetectors (Presentation Recording)
venue: SPIE NanoScience Engineering
year: 2015

abstract: Abstract Infrared light detection enables diverse technologies ranging from night vision to gas analysis. Emerging technologies such as low cost cameras for self driving cars require highly sensitive, low cost photodetector cameras with spectral sensitivities up to wavelengths of 10 um. For this purpose, colloidal quantum dot (QD) graphene phototransistors offer a viable alternative to traditional technologies owing to inexpensive synthesis and processing of QDs. However, the spectral range of QD/graphene phototransistors is thus far limited to 1.6 um. Here, HgTe QD/graphene phototransistors with spectral sensitivity up to 3 um are presented, with specific detectivities of 6 x 108 Jones at a wavelength of 2.5 um and a temperature of 80 K. Even at kHz light modulation frequencies, specific detectivities exceed 108 Jones making them suitable for fast video imaging. The simple device architecture and QD film patterning in combination with a broad spectral sensitivity manifest an important step toward low cost, multi color infrared cameras.
author_names: Matthias J Grotevent

Claudio U Hail

Sergii Yakunin

Dominik Bachmann

Michel Calame

Dimos Poulikakos

Maksym V Kovalenko

Ivan Shorubalko
title: Colloidal HgTe Quantum Dot/Graphene Phototransistor with a Spectral Sensitivity Beyond 3 um
venue: Advanced science
year: 2021

abstract: Colloidal quantum dots (CQDs) are promising materials for IR light detection due to 15 their tunable bandgap and solution processing; but to date, the time response of CQD IR 16 photodiodes has been inferior to that provided by Si and InGaAs. We reasoned that the high 17 permittivity of II VI CQDs leads to slow charge extraction due to screening and capacitance; 18 whereas III Vs if their surface chemistry could be mastered offer a strong covalent character for 19 low permittivity and fast operation. In initial studies, we found that existing covalent character led 20 to imbalanced charge transport in InAs, the result of unpassivated surfaces and uncontrolled heavy 21 doping. We report surface management using amphoteric ligand coordination and find that it 22 addresses simultaneously the In and As surface dangling bonds. The new InAs CQD solids combine 23 high mobility (0.04 cm2 V 1 s 1) with a 4x reduction in permittivity compared to PbS CQDs. The 24 resulting photodiodes achieve a response time faster than 300 ps a more than 100x improvement 25 compared to the best previously reported CQD photodiodes combined with an external quantum 26 efficiency (EQE) of 30% at 940 nm. 27 Infrared photodetection underpins applications in medicine and bioimaging, information technology, 28 machine vision, and security1,2. Emerging technologies such as autonomous driving and augmented reality 29 rely on Light Detection and Ranging (LiDAR) based on time of flight (ToF)3. This requires sensitive and 30 ultrafast photodetection of infrared light with sub ns resolution4. Today, this is achieved in the near31 infrared (NIR) using indirect bandgap silicon detectors limited by silicon's low absorption coefficient 32 and, at longer wavelengths, using epitaxially grown semiconductors such as III Vs and Hg1 xCdxTe. 33 Colloidal quantum dots (CQDs) are of interest by their low temperature solution processing, which 34 allows them to be integrated in post processing with a silicon electronics front end7 10. Their bandgap is 35 size tuned over a wide range of wavelengths. PbS, for example, has a widely programmable absorption 36 onset covering the visible and short wavelength infrared (SWIR)11,12; however, its high permittivity, 37 stemming from its ionic character er =180 for bulk PbS13 slows charge extraction both for bulk14 and 38 CQD photodiodes15 due to screening and capacitance effects. 39 Indium arsenide (InAs) CQDs can be tuned in a similar spectral range as PbS CQDs, and offer the 40 prospective advantage of a covalent lattice and hence lower permittivity16,17. This, however, comes with a 41 challenge: the surface in InAs CQDs is charge imbalanced, leading to poor passivation and heavy doping, 42 as surface states pin the Fermi level near the conduction band minimum. Much effort has been paid to 43 improving mobility by decreasing interdot distance via ligand exchanges and surface treatments in CQD 44 solids18,19, but III V CQDs require a new approach in order to neutralize CQD charge surface states and 45 reduce trap density. 46 Trap states in InAs semiconductors originate from surface In and As dangling bonds20. Growing 47 epitaxially matched inorganic shells on CQDs passivates surface defects, but it hinders CQD coupling 48 and carrier transport21,22. Using molecular metal chalcogenide complexes (MCCs, e.g. Sn2S6 and 49 In2Se4) enhances carrier mobility in III V CQD solids, leading to an impressive mobility of 15 cm2V 1s50 1, but introduces undesired in gap states19,23. Etching As sites using strong acids facilitates In site 51 passivation but leads to low mobility (10 3 cm2V 1s 1)18,20,24. 52 Here we present a new surface passivation strategy that addresses charge imbalance and passivation 53 in InAs CQD solids for infrared photodetectors. We introduced InBr3 passivants to replace native insulating 54 oleic acid ligands, thereby providing surface passivation and charge transport simultaneously. We found 55 that InBr3 is amphoteric, dissociating into an X type ligand (Br that passivates In dangling bonds; and 56 into a Z type (InX2) ligand25 that passivates As dangling bonds. We incorporate N,N dimethylformamide 57 (DMF) as a coordinating agent to stabilize otherwise unstable Brand InX2passivants. We assess the co58 passivated InAs surfaces using a suite of spectroscopies and density functional theory (DFT) calculations. 59 The resulting InBr3 InAs CQD solids achieve a mobility value of 0.04 cm2V 1s 1, >10 times higher than in 60 halide exchanged InAs solids18; and a low dielectric constant of 6.3 a near 4x advance compared to PbS 61 CQD solid counterparts. The corresponding photodiode devices achieve a 30% external quantum 62 efficiency (EQE) a responsivity of 0.22 A W 1, and measured detectivity of 1011 cmHz1/2W 1 at the 63 excitonic peak (940 nm) Ultrafast transient photocurrent (TPC) experiments reveal a fall time of 300 ps, 64 equivalent of >1 GHz bandwidth. This is the first demonstration of efficient III V CQD photodiodes and 65 the fastest solution processed infrared photodiode reported, with over a 100 fold improvement compared 66 to the best CQDs photodiodes15,26. 67
author_names: B Sun

najarian Am

Chong Zheng

Laxmi Kishore Sagar

M Choi

Xubiao Li

Larissa Levina

Se-Woong Baek

Song-ee Lee

Kirmani Ar

Jehad Abed

M Liu

P Li

Lee J Richter

Oleksandr Voznyy

Z Lu

Arquer FPGd

Edward H Sargent
title: Sub nanosecond Infrared Photodetection using III V Colloidal Quantum Dots
year: 2020

abstract: The ability to detect near infrared and mid infrared radiation has spawned great interest in colloidal HgTe quantum dots (QDs) In contrast to the studies focused on extending the spectral range of HgTe QD devices, the temporal response, another fi gure of merit for photodetectors, is rarely investigated. In this work, a single layer, aqueous HgTe QD based photoconductor structure with very fast temporal response (up to 1 MHz 3 dB bandwidth) is demonstrated. The device is fabricated using a simple spray coating process and shows excellent stability in ambient conditions. The origin of the remarkably fast time response is investigated by combining light intensity dependent transient photocurrent, temperature dependent photocurrent, and fi eld effect transistor (FET) measurements. The charge carrier mobility, as well as the energy levels and carrier lifetimes associated with the trap states in the QDs, are identifi ed. The results suggest that the temporal response is dominated by a fast bimolecular recombination process under high light intensity and by a trap mediated recombination process at low light intensity. Interestingly, it was found that the gain and time response of aqueous HgTe QD based photoconductors can be tuned by controlling the QD size and surface chemistry, which provides a versatile approach to optimize the photodetectors with selectable sensitivity and operation bandwidth.
author_names: Mengyu Chen

Huijie Yu

Stephen V Kershaw

Haihua Xu

Shuchi Gupta

Frederik Hetsch

Andrey L Rogach

Ni Zhao
title: Fast, Air Stable Infrared Photodetectors based on Spray Deposited Aqueous HgTe Quantum Dots
year: 2014

abstract: Herein, we report the first solution processed broadband photodetectors to break the past compromise between sensitivity and speed of response. Specifically, we report photodiodes having normalized detectivity (D* 10 Jones and a 3dB bandwidth of 2.9 MHz. This finding represents a 170,000 fold improvement in response speed over the most sensitive colloidal quantum dot (CQD) photodetector reported and a 100,000 fold improvement in sensitivity over the fastest CQD photodetector reported. At the outset of this study, sensitive, solution processed IR photodetectors were severely limited by low response speeds. Much faster response speeds had been demonstrated by solution processed photodetectors operating in the visible, but these devices offered no benefits for extending the spectral sensitivity of silicon. No available solution processed
author_names: Jason Paul Clifford
title: COLLOIDAL QUANTUM DOT SCHOTTKY BARRIER PHOTODIODES
year: 2008

abstract: Graphene is an appealing material for optoelectronics and photodetection applications. It has various extraordinary properties, including ultrahigh mobility at room temperature, which enables fast response times. Colloidal quantum dots exhibit unique optical properties of spectral tunability and high absorption coefficients. We combine the favourable electronic properties of graphene with the optical characteristics of colloidal quantum dots to realize a novel hybrid graphene quantum dot photodetector for visible and short wave infrared frequencies. [1] The unique electronic properties of graphene offer a gate tunable carrier density and polarity that enable us to tune the sensitivity and operating speed of the detector. Here, we exploit this to maximize the photoconductive gain or to fully reduce it to zero, which is useful for pixelated imaging applications, while the implementation of nanoscale local gates enables a locally tunable photoresponse. We also demonstrate our novel approach to fully suppress dark currents in graphene based photodetectors and increase operation speed of our devices. At the current state our singleand multipixel photodetectors can operate at 30, 60 and up to 90 frames per second. The resulting technology is extremely promising for visible and, more importantly, short wave infrared (SWIR) imaging applications. Sensing and imaging in SWIR range lies at the heart of safety and security applications in civil and military surveillance, night vision applications, automotive vision systems for driver safety, food and pharmaceutical inspection and environmental monitoring. Operation of a prototype device sensitive to visible and IR light in the auditorium will be demonstrated during the talk.
author_names: A M Goossens

Gabriele Navickaite

Juan Piqueras

Gerasimos Konstantatos

L F H
title: Hybrid graphene quantum dot phototransistors for IR imaging applications
year: 2014

abstract: Heterostructures can be assembled from liquid phase exfoliated (LPE) layered materials (LMs) [1] via inkjet printing with tens m [1] resolution and controllable thickness [2] to make photodetectors (PDs) [2] However, LPE materials are unfavourable compared to chemical vapor deposited and mechanically exfoliated LMs, due to the presence of traps [1] which results in low responsivities ~mA/W [1,2] Here, we fabricate printable PDs based on graphene and black phosphorus (BP) inks (Fig. 1) showing high responsivity >300A/W) and broadband (0.4 2.8 m) detection (Fig. 2) LPE BP is used due to its broadband optical absorption (400 3500nm) [3] and its tuneable layer dependent direct bandgap [3] Photoexcited holes from BP are injected into graphene, leaving behind uncompensated electrons, resulting in photogating. We achieve a photoconductive gain (ratio of carrier life time measured from the device response time to transit time [4]~107 ,broadband (400 2800nm) and fast ~50ms) response time. The dark current shows a 1/f component, with a noise equivalent power~1.88x10 10W/Hz, and a detectivity~107 Jones. The responsivity is at least three orders of magnitude higher than previously reported ink jet printed BP PDs operating at the same spectral range [5] and the operating wavelength range (up to 2.8 m) is ~0.5 m longer compared to state of the art hybrid LMs colloidal quantum dots PDs [6,7]
author_names: Alfonso Ruocco

Giancarlo Soavi

T A

Ioannis Paradisanos

Konstantinos Dimos

E J

Hannah F Y Watson

Lucia Lombardi

Stephen A Hodge

Andrea C Ferrari

Ilya Goykhman
title: Graphene 2019 June 25 28 2019 Rome Italy Graphene black phosphorus photodetectors
year: 2019

abstract: Silicon technology is dominant in electronics and optoelectronics. The cut off wavelength of silicon is less than 1.1m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin} 69pt} \begin{document}\upmu$\end{document}m due to the bandgap, limiting applications of silicon in communication, sensing, and light harvesting. A new strategy for infrared photodetection is presented by integrating silicon and PbSe colloidal quantum dots (CQDs) which combines advantages of silicon devices and PbSe CQDs. In this study, we introduce a silicon based photodetector that is sensitive to infrared light with spectral response from 405 nm to 1550 nm. The device can deliver a high responsivity of 648.7AW 1 and a fast response of 32.3m\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin} 69pt} \begin{document}\upmu$\end{document}s at 1550 nm. Besides, the detectivity and the external quantum efficiency of the device reached 7.48 x 1010 Jones and 6.47 x 104% respectively. The performance of the device originates from the photovoltage generated at the interface between the silicon and the quantum dots. This photovoltage changed the width of the depletion layer to realize detection. These results indicate that the silicon based quantum dot infrared photodetectors prepared by this method have application prospects in the field of optoelectronics.
author_names: Pengyu Chen

Zhiming Wu

Yuanlin Shi

Chunyu Li

Jinquan Wang

Jun Yang

Xiang Dong

Jun Gou

Jun Wang

Yadong Jiang
title: High performance silicon based PbSe CQDs infrared photodetector
venue: Journal of Materials Science: Materials in Electronics
year: 2021