Proceedings of Online nanoGe Fall Meeting 20 (OnlineNFM20)
Publication date: 4th October 2020
Fast nonradiative relaxation in narrow gap semiconductor quantum dots (QDs) is a major bottleneck for their application in mid-infrared detection, LEDs and lasing. Nonradiative decay in the mid-IR is widely attributed to relaxation to surface vibrations via a Forster-type near-field energy transfer [1][2][3]. Given the extremely low photoluminescence quantum yields (PLQY) of mid-IR QDs ~10-4 [3] and the long range of Forster coupling, it is necessary to grow a giant shell (>~5nm in thickness) with type-I alignment to observe a significantly slowed relaxation. Though efforts have been made in growing shells of wide-gap material on HgTe and HgSe QDs [4][5][6], limited success has been observed in growing thick shells, largely due to the poor thermal stability of the cores.
We have recently developed the synthesis of giant HgSe/CdS QDs (>15 layers) to slow the nonradiative decay. The use of single-source precursors allows the growth of thick shells at a relatively low temperature, without independent nucleation or interface alloying. The synthetic strategy provides a uniform shell coverage, along with a Cd-rich surface that is necessary for observing mid-IR intraband PL. Preliminary results on PLQY and PL lifetime measurements show that the giant HgSe/CdS QDs exhibit a nonradiative decay rate 2 orders of magnitude slower than the cores. The PLQY at 5µm is ~1%, which is 10 times brighter than previous reports of mid-IR emitting QDs. These results shed light on the nonradiative relaxation processes in HgSe-based QDs, and pave the path for developing solution-processed mid-IR LEDs and lasers.
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