Optical Characterization of CdSe Colloidal Quantum Dot/ MEH-PPV Polymer Nanocomposites Spin-Cast on GaAs Substrates
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0939-O02-04
Optical Characterization of CdSe Colloidal Quantum Dot/ MEH-PPV Polymer Nanocomposites Spin-Cast on GaAs Substrates Adrienne D. Stiff-Roberts, Abhishek Gupta, and Zhiya Zhao Electrical and Computer Engineering, Duke University, Box 90291, Durham, NC, 27708-0291
ABSTRACT The motivation and distinct approach for this work is the use of intraband transitions within colloidal quantum dots for the detection of mid- (3-5 µm) and/or long-wave (8-14 µm) infrared light. The CdSe colloidal quantum dot/MEH-PPV conducting polymer nanocomposite material is well-suited for this application due to the ~1.5 eV difference between the corresponding electron affinities. Therefore, CdSe colloidal quantum dots embedded in MEH-PPV should provide electron quantum confinement such that intraband transitions can occur in the conduction band. Further, it is desirable to deposit these nanocomposites on semiconductor substrates to enable charge transfer of photogenerated electron-hole pairs from the substrate to the nanocomposite. In this way, optoelectronic devices analogous to those achieved using Stranski-Krastanow quantum dots grown by epitaxy can be realized. To date, there have been relatively few investigations of colloidal quantum dot nanocomposites deposited on GaAs substrates. However, it is crucial to develop a better understanding of the optical properties of these hybrid material systems if such heterostructures are to be used for optoelectronic devices, such as infrared photodetectors. By depositing the nanocomposites on GaAs substrates featuring different doping characteristics and measuring the corresponding Fourier transform infrared absorbance, the feasibility of these intraband transitions is demonstrated at room temperature. INTRODUCTION The detection of infrared (IR) radiation is critical for many applications, such as situational awareness sensors and thermal imaging. Commercial technologies, such as Si microbolometers and HgCdTe narrow-bandgap photodiodes, are widely used; yet, significant improvements in device performance can be realized by using a quantum dot (QD) active region. In particular, the low dark current resulting from three-dimensional quantum confinement enables high-operating temperature IR photodetection (≥ 150 K). In addition, quantum dot infrared photodetectors (QDIPs) possess two important characteristics that motivate their investigation and distinguish them from available, state-of-the-art technologies. First, despite room temperature operation in thermal detectors, IR photodetectors are preferred for applications requiring fast modulation response. Secondly, QDIPs are well-suited for high spectral resolution due to multiple tuning parameters (material composition, shape, size, and carrier occupation).
Stranski-Krastanow (S-K) QDs are synthesized using strained-layer epitaxy in ultra-high vacuum crystal growth systems, such as molecular beam epitaxy or metal-organic chemical vapor deposition. QD growth is a consequence of the lattice mismatch between the widerbandgap matrix material
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