Dielectric function of ZnTe nanocrystals by spectroscopic ellipsometry

Abstract

We have studied the optical properties of ZnTe nanocrystals (ZnTe-nc) by spectroscopic ellipsometry. The ZnTe-nc are embedded in a SiO2 matrix by an ion implantation technique. Two doses of 1 x 10(16) and 5 x 10(15) cm(-2) of tellurium and zinc ions are implanted in a 250 nm thick SiO2 layer thermally grown on silicon with respective implantation energies of 180 and 115 keV. Subsequent thermal treatments at 800 degrees C lead to the formation of ZnTe-nc. Their sizes are characterized by transmission electron microscopy. The ZnTe-nc obtained with the 1 x 10(16) cm(-2) dose are self-organized into two layers parallel to the surface. Their mean radius ranges between 4-17 nm and 7-17 nm. The ZnTe-nc obtained with the 5 x 10(15) cm(-2) dose are self-organized into one layer with a mean radius between 4-17 nm. A critical points (CPs) dispersion model is used to extract the optical responses of the ZnTe-nc. The optical properties such as the dielectric function and the second derivative of the dielectric function are presented and analyzed. The dielectric function spectra reveal distinct structures attributed to band gap and optical transitions at higher energy. The correlation between the optical responses and the size of the nanocrystals is also given.

Oxygen Induced Enhanced Photoanodic Response of ZnTe:O Thin Films: Modifications in Optical and Electronic Properties

“…Further transition at energy values ∼3.78, 4.34, and 5.23 eV are denoted by E 1 , E 1 + Δ 1 , and E 2 , respectively, and occur at L 4,5 , L 6 , and X points of the BZ, respectively. The values of dielectric constants and features in ε­( E ) spectra of ZnTe nanocrystalline films in the present study are in agreement with the existing literature. , …”

“…The values of dielectric constants and features in ε(E) spectra of ZnTe nanocrystalline films in the present study are in agreement with the existing literature. 20,50 Nonzero values of ε 2 for ZnTe:O (0.2%, 0.02%) thin films below the band edge of ZnTe (<2.24 eV) show the absorption due to the sub band gap states. In comparison to ZnTe (0.02%), ZnTe:O (0.2%) samples show appreciable value of ε 2 at about 1.…”

Dielectric function of colloidal lead chalcogenide quantum dots obtained by a Kramers-Krönig analysis of the absorbance spectrum

“…Considering its importance, surprisingly few experimental reports on ⑀ for colloidal Qdots exist in literature. Data are mainly collected using spectroscopic ellipsometry and results are reported for II-VI ͓ZnTe, 15 CdTe, 16 and HgTe ͑Ref. 17͔͒, IV-VI ͓PbSe ͑Refs.…”

Time-Resolved Spectroscopy of ZnTe Photocathodes for Solar Fuel Production

“… The brownish-red ZnTe films exhibited a broad absorption in the visible region with several weak absorption bands at ∼530, ∼625 and 730 nm and a tail extending to ∼800 nm (Figure S3), following with onset of the band edge absorption at approximately 560 nm confirming the bandgap to be approximately 2.2 eV. The optical absorption at ∼530 nm (2.34 eV) corresponds to the direct transitions along the Γ direction from the valence band to conduction band, − and the absorption peaks at ∼630 and 750 nm, with the transition energy lower than the bandgap value of ZnTe, possibly involved with the electronic transition in the mid-bandgap states. The SEM pattern of thin ZnTe films shows that the films are uniform and have an average grain size of 120 ± 50 nm (Figure S4).…”