Photosensitivity of the PbS Colloidal Quantum Dot-Based Nanostructures with an Energy Barrier

Yuan Y., Xu J., Zhang J., Gao X., Zhong Y., Wang S.

A simple and effective strategy, that is the use of 2-Methoxyethanol rather than anhydrous ethanol as the ZnO precursor solvent, is developed to greatly improve the photoresponsivity in the PbS colloidal quantum dot (CQD)/ZnO heterojunction short-wavelength infrared (SWIR) photodiodes. This approach significantly modifies the PbS/ZnO interface through an increase of electron concentration and a reduction of surface defects in the ZnO layer, which is critical to suppressing carrier recombination at the PbS/ZnO interface. The optimized photodiodes show superior figures of merit, including low dark current density of 1.28 $\times \,\,10^{-{8}}$ A/cm 2 at −0.5 V, high photoresponsivity of 0.47 A/W and high specific detectivity of 2.22 $\times \,\,10^{{12}}$ Jones at 1413 nm, and fast response/recovery time of 6.8/8.6 $\mu \text{s}$ .

Pejovic V., Georgitzikis E., Lee J., Lieberman I., Cheyns D., Heremans P., Malinowski P.E.

Quantum dots (QDs) have been explored for many photonic applications, both as emitters and absorbers. Thanks to the bandgap tunability and ease of processing, they are prominent candidates to disrupt the field of imaging. This review article illustrates the state of technology for infrared image sensors based on colloidal QD absorbers. Up to now, this wavelength range has been dominated by III–V and II–VI imagers realized using flip-chip bonding. Monolithic integration of QDs with the readout chip promises to make short-wave infrared (SWIR) imaging accessible to applications that could previously not even consider this modality. Furthermore, QD sensors show already state-of-the-art figures of merit, such as sub-2- $\mu \text{m}$ pixel pitch and multimegapixel resolution. External quantum efficiencies already exceed 60% at 1400 nm. With the potential to increase the spectrum into extended SWIR and even mid-wave infrared, QD imagers are a very interesting and dynamic technology segment.

Gregory C., Hilton J.A., Violette K., Shefte S., Procida C., Tessema T., Bond M., Klem E.J.

Shortwave IR (SWIR) sensors made using colloidal quantum dot photodiodes offer CMOS-like opportunities for highly scalable, small pixel pitch sensors, owing to their straightforward, monolithic integration with silicon circuitry. SWIR Vision Systems began to realize this potential when it introduced its 2.1 MP Acuros cameras to the industrial, scientific, and commercial imaging markets in 2018. Other opportunities for this detector technology can be found in the need for new sensor technologies in the development of cost and resolution scalable direct time of flight depth sensing systems for consumer and automotive applications. But to realize this potential, this relatively new detector system must also be shown to meet thermal and environmental conditions found in consumer and automotive devices. This paper will provide an overview of the performance of our high definition sensors; and show <3 ns rise/fall time results from testing the response time of the photodiode structure using a pulsed laser sources. It will also present data demonstrating stable device operation at elevated temperature and humidity conditions.

Zhang J., Wang W., Li Z., Ye H., Huang R., Hou Z., Zeng H., Zhu H., Liu C., Yang X., Shi Y.

A 1280 × 1,024 In0.53Ga0.47As short wave infrared (SWIR) focal plane array (FPA) detector with a planar-type back-illuminated process has been fabricated. With indium bump flip-chip bonding techniques, the InGaAs photodiode arrays were hybrid-integrated to the CMOS readout integrated circuit (ROIC) with correlated double sampling (CDS). The response spectrum is 0.9–1.7 μm. The test results show that the dark current density is 2.25 nA/cm2 at 25 °C, the detectivity D* is up to 1.1 × 1013 cm · Hz1/2/W, the noise electron is as low as 48 e− under correlated double sampling mode, the quantum efficiency is 88% at 1550 nm, and the operability is more than 99.9%. Moreover, the dark current and noise electron have been studied theoretically in depth. The results indicate that the diffusion current is the main contribution of the dark current, and the readout integrated circuit noise electron is the main source of FPA noise.

The architecture and main parameters of photosensor structures and devices based on colloidal quantum dots (CQDs) of II, IV and VI group elements of the Periodic Table of D. Mendeleev are considered. Hybrid structural schemes of photoresistor, photodiode and phototransistor with absorbing layers based on HgTe, HgSe, PbS, PbSe CQDs and 2D materials for operation in various spectral ranges are com-prehensively discussed.

Hinds S., Klem E., Gregory C., Hilton A., Hames G., Violette K.

We present, for the first time, solution processed colloidal quantum dot extended short wavelength infrared (eSWIR) 1920 x 1080 format cameras sensitive from 300 nm to 2100 nm wavelengths at a pitch of 15 microns. We describe the performance of this high-definition imager using EMVA1288 machine vision testing and demonstrate pixel detectivities of 1 x1012 Jones and 32 fA of dark current when operating at room temperature [1]. These results show this monolithically integrated detector technology has sensitivity superior to most traditional epitaxial IR sensors employed in the 1700 to 2100 nm band [2]. The straightforward and scalable fabrication processes employed have enabled the first commercially available room temperature 2.1 MP camera with sensitivity out to 2.1 um.

Shuklov I.A., Razumov V.F.

The review concerns the state of the art in methods of synthesis of colloidal lead chalcogenide quantum dots (QDs). The most recent data on the mechanisms of chemical transformations involving various precursors are discussed. Particular attention is paid to the influence of (i) trace impurities in the reactants used and (ii) post-synthesis treatment on the physicochemical properties of QDs used in photoelectric devices. The bibliography includes 129 references.

Reich K.V.

Brittman S., Colbert A.E., Brintlinger T.H., Cunningham P.D., Stewart M.H., Heuer W.B., Stroud R.M., Tischler J.G., Boercker J.E.

The size of a quantum-confined nanocrystal determines the energies of its excitonic transitions. Previous work has correlated the diameters of PbS nanocrystals to their excitonic absorption; however, we observe that PbS quantum dots synthesized in saturated dispersions of PbCl2 can deviate from the previous 1Sh-1Se energy vs diameter curve by 0.8 nm. In addition, their surface differs chemically from that of PbS quantum dots produced via other syntheses. We find that these nanocrystals are coated in a shell that is measurable in transmission electron micrographs and contains lead and chlorine, beyond the monatomic chlorine termination previously proposed. This finding has implications for understanding the growth mechanism of this reaction, the line width of these quantum dots' photoluminescence, and electronic transport within films of these nanocrystals. Such fundamental knowledge is critical to applications of PbS quantum dots such as single-photon sources, photodetectors, solar cells, light-emitting diodes, lasers, and biological labels.

Zandian M., Farris M., McLevige W., Edwall D., Arkun E., Holland E., Gunn J.E., Smee S., Hall D.N., Hodapp K.W., Shimono A., Tamura N., Carmody M., Auyeung J., Beletic J.W.

We present the test results of science grade substrate-removed 4K×4K HgCdTe H4RG-15 NIR 1.7 μm and SWIR 2.5 μm sensor chip assemblies (SCAs). Teledyne’s 4K×4K, 15 μm pixel pitch infrared array, which was developed for the era of Extremely Large Telescopes, is first being used in new instrumentation on existing telescopes. We report the data on H4RG-15 arrays that have achieved science grade performance: very low dark current (<0.01 e-/pixel/sec), high quantum efficiency (70-90%), single CDS readout noise of 18 e-, operability >97%, total crosstalk <1.5%, well capacity >70 ke-, and power dissipation less than 4 mW. These SCAs are substrate-removed HgCdTe which simultaneously detect visible and infrared light, enabling spectrographs to use a single SCA for Visible-IR sensitivity. Larger focal plane arrays can be constructed by assembling mosaics of individual arrays.

Klem E.J., Gregory C., Temple D., Lewis J.

RTI has developed a photodiode technology based on solution-processed PbS colloidal quantum dots (CQD). These devices are capable of providing low-cost, high performance detection across the Vis-SWIR spectral range. At the core of this technology is a heterojunction diode structure fabricated using techniques well suited to wafer-scale fabrication, such as spin coating and thermal evaporation. This enables RTI’s CQD diodes to be processed at room temperature directly on top of read-out integrated circuits (ROIC), without the need for the hybridization step required by traditional SWIR detectors. Additionally, the CQD diodes can be fabricated on ROICs designed for other detector material systems, effectively allowing rapid prototype demonstrations of CQD focal plane arrays at low cost and on a wide range of pixel pitches and array sizes.

Klem E.J., Lewis J., Gregory C., Temple D., Wijewarnasuriya P.S., Dhar N.

RTI has developed a novel photodiode technology based on solution-processed PbS colloidal quantum dots (CQD) capable of providing low-cost, high performance detection across the Vis-SWIR spectral range. The most significant advantages of the CQD technology are ease of fabrication, small pixel size, and extended wavelength range. The devices are fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. We will discuss recent advances in device architecture and processing that result in measured dark currents of 15 nA/cm 2 at room temperature and enhanced SWIR responsivity from the UV to ~1.7 μm, compare these results to InGaAs detectors, and present measurements of the CQD detectors temperature dependent dark current.

Langley D., Giusti G., Mayousse C., Celle C., Bellet D., Simonato J.

The class of materials combining high electrical or thermal conductivity, optical transparency and flexibility is crucial for the development of many future electronic and optoelectronic devices. Silver nanowire networks show very promising results and represent a viable alternative to the commonly used, scarce and brittle indium tin oxide. The science and technology research of such networks are reviewed to provide a better understanding of the physical and chemical properties of this nanowire-based material while opening attractive new applications.

Klem E., Lewis J., Gregory C., Cunningham G., Temple D., D'Souza A., Robinson E., Wijewarnasuriya P.S., Dhar N.

While InGaAs-based focal plane arrays (FPAs) provide excellent detectivity and low noise for SWIR imaging applications, wider scale adoption of systems capable of working in this spectral range is limited by high costs, limited spectral response, and costly integration with Si ROIC devices. RTI has demonstrated a novel photodiode technology based on IR-absorbing solution-processed PbS colloidal quantum dots (CQD) that can overcome these limitations of InGaAs FPAs. The most significant advantage of the CQD technology is ease of fabrication. The devices can be fabricated directly onto the ROIC substrate at low temperatures compatible with CMOS, and arrays can be fabricated at wafer scale. Further, device performance is not expected to degrade significantly with reduced pixel size. We present results for upward-looking detectors fabricated on Si substrates with sensitivity from the UV to ~1.7 µm. We further show devices fabricated with larger size CQDs that exhibit spectral sensitivity that extends from UV to 2 µm.

Beek W.J., Wienk M.M., Kemerink M., Yang X., Janssen R.A.

Bulk heterojunction photovoltaic devices based on blends of a conjugated polymer poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) as electron donor and crystalline ZnO nanoparticles (nc-ZnO) as electron acceptor have been studied. Composite nc-ZnO:MDMO-PPV films were cast from a common solvent mixture. Time-resolved pump-probe spectroscopy revealed that a photoinduced electron transfer from MDMO-PPV to nc-ZnO occurs in these blends on a sub-picosecond time scale and produces a long-lived (milliseconds) charge-separated state. The photovoltaic effect in devices, made by sandwiching the active nc-ZnO:MDMO-PPV layer between charge-selective electrodes, has been studied as a function of the ZnO concentration and the thickness of the layer. We also investigated changing the degree and type of mixing of the two components through the use of a surfactant for ZnO and by altering the size and shape of the nc-ZnO particles. Optimized devices have an estimated AM1.5 performance of 1.6% with incident photon to current conversion efficiencies up to 50%. Photoluminescence spectroscopy, atomic force microscopy, and transmission electron microscopy have been used to gain insight in the morphology of these blends.

Ponomarenko Vladimir P., Popov Victor, Shuklov Ivan, Ivanov Victor V., Razumov Vladimir F.

Photosensing based on colloidal quantum dots (CQDs) is a rapidly developing area of infrared photoelectronics. The use of colloidal quantum dots markedly simplifies the manufacture, decreases the restrictions to the pixel pitch of the photosensitive elements, and reduces the production cost, which facilitates the wide use of IR sensors in various technological systems. This paper is the first exhaustive overeview of the architectures, methods of manufacturing and basic properties of photonic sensors based on colloidal quantum dots of compounds of Group II, IV and VI elements. Characteristic features of the synthesis and roles of the ligands and CQD morphology in the design of photosensors are considered in detail. The structures of photoresistive, photodiode and phototransistor elements based on HgTe, HgSe, PbS and PbSe CQDs, which are sensitive in various spectral ranges, are described. The main parameters of the most advanced optoelectronic devices based on colloidal quantum dot structures are presented. The key trends in the development of this area are analyzed.The bibliography includes 361 references.