Optical properties of HgTe colloidal quantum dots
Résumé
Room temperature photodetection with HgTe colloidal quantum films is reported between 2 and 5 µm for particles of sizes between ~5 and ~12 nm diameter, and photodetection extends to 7 µm at 80 K. The size-tuning of the absorption of HgTe colloidal quantum dots, their optical cross section and the infrared absorption depth of films are measured. The tuning with radius is empirically given by ${\lambda }_{\mathrm{BE}}^{\mathrm{QD}}=\frac{30.5}{\sqrt{1+(43/{R}_{\mathrm{QD}})^{2}}-1}$, where R is in nm. The optical cross section of the colloidal dots at 415 nm is approximately proportional to their volume and given by ${\sigma }_{\mathrm{Hg}}^{415}=2.6\pm 0.4\times 1{0}^{-17}~{\mathrm{cm}}^{2}/\mathrm{mercury}$ atom. The size-dependent optical cross section at the band edge ~1.5 × 10−15 cm2 is consistent with the expected oscillator strength of the quantum dots. The absorption depth of HgTe colloidal dot films is short, about 1–2 µm, which is an advantage for thin film devices. These properties agree rather well with the expectation from the k ⋅ p model. HgTe colloidal quantum dot thin films show a strong tuning with temperature with a large positive thermal shift between 0.4 and 0.2 meV K−1, decreasing with decreasing size within the size range studied and this is attributed primarily to electron–phonon effects.
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