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Characterization of ZnSe Nanolayers by Spectroscopic Ellipsometry

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Šćepanović M., Grujić-Brojčin M., Nesheva D., Levi Z., Bineva I., Popović Z.

Acta Physica Polonica A

2009

vol. 116

issue 4

708-711

Single layers of ZnSe with thicknesses of 30, 40, 50, 70 and 100 nm are deposited at room substrate temperature by thermal evaporation of ZnSe powder in vacuum. The layers surface morphology has been investigated by atomic force microscopy. Structural characterization by the Raman scattering measurement revealed the existence of randomly oriented crystalline ZnSe particles in all layers, and the presence of amorphous phase in layers thinner than 100 nm. The ellipsometric measurements were performed in the range from 1.5 to 5 eV at room temperature in air. To interpret the experimental results, the Bruggeman effective medium approximation of dielectric function of ZnSe layers has been used, representing the layers as different mixtures of crystalline ZnSe (c-ZnSe), amorphous ZnSe (a-ZnSe), and voids. The assumption of polycrystalline ZnSe layers modeled as mixture of porous c-ZnSe (with volume fraction of voids ≈ 0.17) and a-ZnSe gives the best fit of ellipsometric experimental data. Single layer thicknesses similar to those expected from preparation conditions have been obtained by this fitting procedure. It has been also found that decrease in the layer thickness causes an increase of the volume fraction of a-ZnSe. Thus, c-ZnSe/a-ZnSe ratio, porosity and layer thickness obtained by spectroscopic ellipsometry, provides useful information about crystallinity and micro-/nanostructure of ZnSe nanolayers.

Raman Scattering from ZnSe Nanolayers

100%

Nesheva D., Šćepanović M., Aškrabić S., Levi Z., Bineva I., Popović Z.

Acta Physica Polonica A

2009

vol. 116

issue 1

75-77

A series of ZnSe single layers having thickness between 30 nm and 1 μm was deposited on c-Si and glass substrates at room substrate temperature. Thermal evaporation of ZnSe powder in high vacuum has been applied. Moreover, SiO_x/ZnSe periodic multilayers prepared by the same deposition technique and having ZnSe layer thickness of 2 and 4 nm have been studied. Raman spectra were measured at 295 K, using the 442 nm line of a He-Cd laser as well as different lines of the Ar^+ or Ar^+/Kr^+ lasers. The observed Raman features have been related to multiple optical phonon (1LO to 4LO) light scattering and connected with the existence of randomly oriented crystalline ZnSe grains in both ZnSe single layers and ZnSe layers of the multilayers. Relatively large line width ( ≈ 15 cm^{-1}) of the 1LO band has been observed and related to lattice distortion in the crystalline grains and existence of amorphous phase in the layers thinner than 100 nm. The Raman spectra measured on both ZnSe single layers and SiO_x/ZnSe multilayers using the 488 nm line with a gradually increased laser beam power indicate an increased crystallinity at high irradiation levels.

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2 Acta Physica Polonica A

2 2009

2 Bineva I.

2 Levi Z.

2 Nesheva D.

2 Popović Z.

2 Šćepanović M.

1 Aškrabić S.

1 Grujić-Brojčin M.

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Characterization of ZnSe Nanolayers by Spectroscopic Ellipsometry

Raman Scattering from ZnSe Nanolayers