An InAs/GaAs quantum dot infrared photodetector with strong, multicolor, broadband (5-20 lm) photoresponse is reported. Using a combined quaternary In 0.21 Al 0.21 Ga 0.58 As and GaAs capping that relieves strain and maintains strong carrier confinement, we demonstrate a four color infrared response with peaks in the midwave-(5.7 lm), longwave-(9.0 and 14.5 lm), and far-(17 lm) infrared regions. Narrow spectral widths (7% to 9%) are noted at each of these wavelengths including responsivity value $95.3 mA/W at 14.5 lm. Using strain field and multi-band k Á p theory, we map specific bound-to-bound and bound-to-quasibound transitions to the longwave and midwave responses, respectively. V
An InAs/GaAs quantum dot infrared photodetector (QDIP) based on p-type valence-band intersublevel hole transitions as opposed to conventional electron transitions is reported. Two response bands observed at 1.5–3 and 3–10 μm are due to transitions from the heavy-hole to spin-orbit split-off QD level and from the heavy-hole to heavy-hole level, respectively. Without employing optimized structures (e.g., the dark current blocking layer), the demonstrated QDIP displays promising characteristics, including a specific detectivity of 1.8×109 cm·Hz1/2/W and a quantum efficiency of 17%, which is about 5% higher than that of present n-type QDIPs. This study shows the promise of utilizing hole transitions for developing QDIPs.
We report experimental results showing how the noise in a Quantum-Dot Infrared photodetector (QDIP) and Quantum Dot-in-a-well (DWELL) varies with the electric field and temperature. At lower temperatures (below $100 K), the noise current of both types of detectors is dominated by generation-recombination (G-R) noise which is consistent with a mechanism of fluctuations driven by the electric field and thermal noise. The noise gain, capture probability, and carrier life time for bound-to-continuum or quasi-bound transitions in DWELL and QDIP structures are discussed. The capture probability of DWELL is found to be more than two times higher than the corresponding QDIP. Based on the analysis, structural parameters such as the numbers of active layers, the surface density of QDs, and the carrier capture or relaxation rate, type of material, and electric field are some of the optimization parameters identified to improve the gain of devices.
The n-type quantum dot (QD) and dots-in-well (DWELL) infrared photodetectors, in general, display bias-dependent multiple-band response as a result of optical transitions between different quantum levels. Here, we present a unique characteristic of the p-type hole response, a wellpreserved spectral profile, due to the much reduced tunneling probability of holes compared to electrons. This feature remains in a DWELL detector, with the dominant transition contributing to the response occurring between the QD ground state and the quantum-well states. The biasindependent response will benefit applications where single-color detection is desired and also allows achieving optimum performance by optimizing the bias. V C 2014 AIP Publishing LLC.
Terahertz (THz) response observed in a p-type InAs/In0.15Ga0.85As/GaAs quantum dots-in-a-well (DWELL) photodetector is reported. This detector displays expected mid-infrared response (from ∼3 to ∼10 μm) at temperatures below ∼100 K, while strong THz responses up to ∼4.28 THz is observed at higher temperatures (∼100–130 K). Responsivity and specific detectivity at 9.2 THz (32.6 μm) under applied bias of −0.4 V at 130 K are ∼0.3 mA/W and ∼1.4 × 106 Jones, respectively. Our results demonstrate the potential use of p-type DWELL in developing high operating temperature THz devices.
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