Chapter 3 - Quantum Dot Infrared Photodetectors

Mid- and far-infrared detectors operating at elevated temperatures (T>150K) are critical for imaging applications. In(Ga)As/GaAs quantum dots, grown by self-organized epitaxy, are an important material for the design and fabrication of high-temperature infrared photodetectors. Quantum dot infrared photodetectors (QDIPs) allow normal-incidence operation, in addition to low dark currents and multispectral response. The long intersubband relaxation time of electrons in quantum dots improves the responsivity of the detectors, contributing to better high-temperature performance. These devices also exhibit photoconductive gain. The characteristics of state-of-the-art lateral and vertical QDIPs will be described. We have achieved peak responsivity for wavelengths ranging from 3.7-18micrometers . We have also obtained extremely low dark currents (Idark=27pA,T=100K,Vbias=0.5V), high detectivities (D*=2.9x108 cmHz½/W, T=100K, Vbias=0.2V), and high operating temperatures (T=150K) for these quantum-dot detectors. The excellent performance of these devices at low bias voltages indicates the compatibility of high temperature QDIPs with commercially available silicon read- out circuits for imaging focal plane arrays. These results, as well as infrared imaging with QDIP arrays, will be described and discussed.

Quantum Dot Infrared Photodetectors

In this review article, the current status of quantum dot infrared photodetectors (QDIPs) compared to competitive infrared (IR) technologies will be evaluated. Carrier generation and some of the other important physical properties of quantum dots (QDs) will be discussed. Recent design improvements of epitaxial and colloidal QDIPs are presented, followed by a thorough discussion on the growth techniques for both types of QDs. Important figures of merit for QDIPs, including dark current, responsivity, detectivity, and noise equivalent differential temperature (NEDT), will be explained, and a comparison will be made between QDIPs performance and other IR technologies in terms of their figures of merit.


Keywords:

quantum dot;
colloidal quantum dot;
epitaxial quantum dot;
self-assembled quantum dot;
infrared photodetector;
quantum dot infrared photodetector;
QDIP ;
responsivity;
detectivity;
dark current

Colloidal and Epitaxial Quantum Dot Infrared Photodetectors: Growth, Performance, and Comparison

Quantum dot infrared photodetectors (QDIPs) have made significant progress after their early demonstration about a decade ago. We review the progress made by QDIP technology over the last few years and compare QDIPs with quantum well infrared photodetectors (QWIPs). It is shown that the performance of QDIPs has significantly improved using novel architectures such as dots-in-a-well designs, and large-format (1 K × 1 K) focal plane arrays have been realized. However, even though there are significant reports of performance parameters better than QWIPs from single-pixel devices, QDIP-based focal plane arrays are still a factor of 3–5 worse in terms of noise equivalent temperature difference. We discuss the reasons for the performance gap and the key scientific and technological challenges that need to be addressed to achieve the full potential of QD-based technology.

Review of current progress in quantum dot infrared photodetectors

Infrared pixel detectors sensitive to radiation in the wavelength range 8 to 9 µm have been fabricated and evaluated. The detectors have 320 × 240 pixels and consist of two parts. One is the infrared sensitive part with a quantum well structure based on n-doped AlGaAs/GaAs. The other part is a readout circuit in standard CMOS technology. The two parts are hybridized by a flip-chip technique using indium bumps. Optical coupling into the detectors is performed by using optimized, etched, two-dimensional gratings combined with GaAs substrate thinning down. The thinning removes the problem with thermal mismatch, enhances the absorption and eliminates optical crosstalk between pixels. The intended operating temperature range is 70–73 K, achievable by a miniature Stirling cooler. Excellent wafer uniformities resulting in responsivity uniformities of 3.3% across an array are found, and a temperature resolution NETD (noise equivalent temperature difference) = 20 mK is achieved.

https://iopscience.iop.org/article/10.1238/Physica.Topical.079a00138/pdf

A 320 × 240 pixels quantum well infrared photodetector array for thermal imaging

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A 320 × 240 pixels quantum well infrared photodetector array for thermal imaging