High Carrier Mobility in HgTe Quantum Dot Solids Improves Mid-IR Photodetectors

Abstract

Improved mid-infrared photoconductors based on colloidal HgTe quantum dots are realized using a hybrid ligand exchange and polar phase transfer. The doping can also be controlled n and p by adjusting the HgCl 2 concentration in the ligand exchange process. We compare the photoconductive properties with the prior "solid-state ligand exchange" using ethanedithiol, and we find that the new process affords a ∼100-fold increase of the electron and hole mobility, a ∼100-fold increase in responsivity, and a ∼10-fold increase in detectivity. These photodetector improvements are primarily attributed to the increase in mobility (μ) because the optical properties are mostly unchanged. We show that the specific detectivity (D*) of a photoconductive device is expected to scale as μ . The application potential is further verified by long-term device stability.

Advances of Sensitive Infrared Detectors with HgTe Colloidal Quantum Dots

“…Over the past decade, CQDs have been widely used in a variety of applications, including solar cells [24], spectrometers [25], phototransistors [26], FPA imagers [27], lasers [28], LEDs [29]. Among all the CQDs systems, mercury telluride (HgTe) CQDs have demonstrated the highest infrared spectral absorption tunability covering main important atmospheric windows including short-wave infrared (SWIR, 1.5-2.5 µm) [30][31][32][33], mid-wave infrared (MWIR, 3-5 µm) [34][35][36][37][38][39][40][41][42], long-wave infrared (LWIR, 8-12 µm) [43,44] and even the terahertz (THz) [45,46], appearing as promising candidates to substitute conventional semiconductors to achieve good detection performance with low cost. This review will be described from the following aspects, including: synthesis of infrared CQDs, infrared CQDs photodetectors, multispectral CQDs photodetectors and CQDs FPA.…”

“…The performance of CQDs photoconductors can be improved by using compact ligands, which allows higher mobility state. The hybrid ligand exchange and polar phase transfer technology were used to realize the improved mid-infrared photoconductors based on HgTe CQDs, which improved the mobility of carriers and accurately tuned the doping level of HgTe CQDs, so that the D* of detector was increased to 4.5 × 10 10 Jones at 80 K and 500 Hz, and a 5 µm cutoff wavelength [42].…”

Bringing Colloidal Quantum Dots to Detector Technologies

“…Thus, two small companies-Episensors and QDIR-are working independently to commercialize HgTe CQD photodetector arrays for IR imaging. HgTe CQD-based photoconductors, 10 phototransistors, 11 and photodiodes 12,13 have been reported, showing figures-of-merit rapidly approaching commercial semiconductor alloys' levels. EQE often is lower for CQD detectors than for bulk detectors, the D* of CQDs quickly is approaching bulk detector performances.…”

“…Unless otherwise specified, the data presented are for a detector operating at room temperature. Green circle = HgTe CQD photodiodes; 12 , 13 green triangle = phototransistors; 11 green square = photoconductors; 10 blue circle = PbS CQD photodiodes; 8 blue triangle = phototransistors; 7 blue square = photoconductors; 6 red circle = HgCdTe photodiodes; 14 , 15 orange circle = InGaAs photodiodes; 16 , 17 and yellow circle = InSb photodiodes 18…”

“…Consequently, CQD films often are optimized with submicron thicknesses for efficiency charge collection, but at the cost of absorbing only a fraction of the incident light. Two approaches employed to solve this problem include increasing the charge carrier mobility with ligand chemistry engineering and coupling more light into the films using optical microstructures 10 , 13 . Even as we see efficiencies improve, additional work is needed to ensure they are maintained over the detector's lifetime.…”