63 research outputs found
Carrier Mobility, Lifetime, and Diffusion Length in Optically Thin Quantum Dot Semiconductor Films
No full textWe propose a method to measure the fundamental parameters that govern diffusion transport in optically thin quantum dot semiconductor films and apply it to quantum dot materials with different ligands. Thin films are excited optically, and the profile of photogenerated carriers is modeled using diffusion-based transport equations and taking into account the optical cavity effects. Correlation with steady-state photoluminescence experiments on different stacks comprising a quenching layer allows the extraction of the carrier diffusion length accurately from the experimental data. In the time domain, the mapping of the transient PL data with the solutions of the time-dependent diffusion equation leads to accurate calculations of the photogenerated carrier mobility. These findings allow the estimation of the speed limitations for diffusion-based transport in QD absorbers.sponsorship: The results reported in this paper have been realized with the funding of Agentschap Innoveren & Ondernemen (VLAIO) in the framework of project MIRIS (IWT/150029). (Agentschap Innoveren & Ondernemen (VLAIO)|IWT/150029)status: Publishe
Optoelectronic design of thin-film infrared sensitive photodiodes based on lead-sulfide quantum dots
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Determining charge carrier extraction in lead sulfide quantum dot near infrared photodetectors
No full textColloidal quantum dots (QDs) based on lead sulfide (PbS) have acquired scientific interest for infrared optoelectronic devices with potential bandgap tunability and ease of fabrication on arbitrary substrates. In this work, we show how device analysis data feed back into process optimization, towards the realization of high performance QD NIR photodetectors. Using the combination of transient PL, carrier transport and CV measurements we obtain the carrier density, lifetime and diffusion length in the layers. From the measured short diffusion length of the minority carriers, we deduce the need to achieve a wide depletion region to minimize recombination and thus enhance the carrier harvesting. Process optimization lead to a depletion region of more than 150 nm, resulting in high photon to carrier conversion. Furthermore, the complex index of refraction of all layers is characterized using ellipsometry and reflection/transmission, and these values are used as input for a transfer matrix method. Using the first interference peak, we show that a maximum EQE of 25% can be expected from optical modeling, a value that we almost reach experimentally (20%). Combining all of the above, we demonstrate 1450-nm photodetectors with dark current in the range of μA and specific detectivity (D*) of 10^11 Jones
Photodetectors Based on Lead Sulfide Quantum Dot and Organic Absorbers for Multispectral Sensing in the Visible to Short-Wave Infrared Range
No full textstatus: Publishe
Optimization of charge carrier extraction in colloidal quantum dots short-wave infrared photodiodes through optical engineering
No full textColloidal quantum dots (QDs) have attracted scientific interest for infrared (IR) optoelectronic devices due to their bandgap tunability and the ease of fabrication on arbitrary substrates. In this work, short-wave IR photodetectors based on lead sulfide (PbS) QDs with high detectivity and low dark current is demonstrated. Using a combination of time-resolved photoluminescence, carrier transport, and capacitance-voltage measurements, it is proved that the charge carrier diffusion length in the QD layer is negligible such that only photogenerated charges in the space charge region can be collected. To maximize the carrier extraction, an optical model for PbS QD-based photodiodes is developed, and through optical engineering, the cavity at the wavelength of choice is optimized. This universal optimization recipe is applied to detectors sensitive to wavelengths above 1.4 mu m, leading to external quantum efficiency of 30% and specific detectivity (D*) in the range of 10(12) Jones
Ligand termination impact on the optoelectronic properties of PbS quantum dots for next-generation infrared photodetectors
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