Naslov
Refined analysis of absorption spectra of CdS thin films

Autori
Novkovski, Nenad ; Tanusevski, Atanas ; Gracin, Davor

Izvornik
Journal of physics. D, Applied physics (0022-3727) 48 (2015); 395105-1

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
cadmium sulfide; optical absorption spectra; interband electronic transitions; fundamental absorption edge

Sažetak
We demonstrate that optical absorption spectra of CdS thin flms in the visible/near ultraviolet range can be precisely described by four different contributions of electron transitions from Γ points of three branches of the valence band maxima (Γ7, Γ in the conduction band (Γe, Γe′), in accordance with the theoretical results of the work (Lew Yan Voon et al 1996 Phys. Rev. B 53 10703). By using the method of successive extractions of different contributions in the absorption coeffcient (α), four contributions have been found, attributed to the following electron transitions: (Γ7′ → Γe), (Γ9 → Γe), (Γ7 → Γe) and (Γ → Γ Corresponding bandgaps for flms annealed at 400 °C in CdCl2 obtained in this work are Printed in the UK 9, Γ 7′, ) to the lowest two minima JPD 10.1088/0022-3727/48/39/395105 Papers 7 e′). 2.20 eV, 2.30 eV, 2.43 eV and 3.88 eV, that are close to the theoretical values for bulk CdS 2.24 of the confnement effect in microcrystals of a smaller size. For the flms annealed in air due to creation of Cd vacancies, the bandgap decreases down from the bulk values ; thus, the values of bandgaps for flms annealed at 400 °C in air are: 1.82 eV, 2.11 eV, 2.25 eV and 3.87 eV. eV, 2.28 eV, 2.43 eV and 3.8 eV. Bandgaps for as grown flms are somehow higher because 0022-3727 39 Strong absorption onset, considered as the fundamental absorption edge, corresponds to direct allowed transitions (Γ7 → Γe′) at photon energies of about 3.8 eV. Absorption due to direct allowed transitions (Γ7 → Γe) at photon energies of about 2.3 eV are usually reported as the optical bandgap of CdS saturates at relatively low values α ≈ 5 × 10 cm −1 4 .

Izvorni jezik
Engleski

Znanstvena područja
Fizika

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