4.6 Some optical properties of thin Cd 3As 2 films

Abstract

The transmission of vacuum deposited Cd 3As 2 films has been measured in the spectral range 0.6–15 ωm. The absorption coefficient α has been calculated from the data for crystalline films obtained at substrate temperature T s = 440 K and also for amorphous films obtained on substrates at T s = 300−393 K. The position of the low-energy absorption edge in the spectral range 0.1–0.3 eV is discussed and the value Δ g opt = 0.06 eV for indirect transion Γ → Γ 15 is obtained for crystalline films. For amorphous films, a shift of the minimum absorption edge to Δ E g opt ⋍ 0.4−0.5 eV was observed. For higher energies two direct transitions have been established: the first at E 1 = 0.9 eV in the photon energy range 0.9–1.2 eV.and the second at E 2 = 1.2−1.3 eV in the photon energy range 1.3−1.6 eV. The last value is in good agreement with the value calculated by Lin Chung and with reflectivity data; it corresponds to the transition Γ 15 → X 1 in the hypothetical band model of Lin Chung. Differences in the reflective index values for crystalline and amorphous Cd 3 As 2 are also discussed.