(327j) Photosensitive and Stable Hgte Quantum Dot for Mid-Wavelength Infrared Photodetector

Commercially available infrared (IR) imaging devices rely on Hg_1-xCd_xTe made using expensive epitaxial growth processes. Films of colloidal quantum dots (CQDs), also known as ligand-stabilized semiconductor nanocrystals, offer an alternative. The optical absorption of mercury telluride (HgTe) CQDs can across a wide range of energies with size and shape–almost across the entire infrared wavelength ranges. Due to the discrete energy states, thermal transition in CQDs requires multiple phonons in a way to increase relaxation lifetime of hot carriers, which reduces thermal noise and dark current. However, incomplete ligand passivation or ligand exchange processes often generates surface trap states in CQDs, quenching the photoexcited carriers. Therefore, reducing the number of trapped carriers is critical for high performance photodetectors. Here, we show that HgTe CQDs capped with oleylamine, trioctylphosphine oxide, and LiN(SiMe₃)₂ exhibit mid-wavelength infrared (MWIR) absorption with fast carrier transport. The mixture of ligands removes conventional solid-phase ligand exchange steps with small molecules and increases stability of QD films over 6 months without encapsulation techniques. Optoelectronic properties of HgTe CQDs were evaluated by measuring spectroscopic photoconductivity, temperature-dependent lifetime of photoexcited carriers, and temperature-dependent field effect mobility. We also demonstrate that HgTe CQDs deposited on focal plane arrays show real-time MWIR imaging with high detectivity and fast photo-response.