Dielectric function and electric properties of germanium thin films prepared by gold mediated crystallization

Abstract

Crystallization of hydrogenated amorphous germanium (a-Ge:H) thin films deposited by plasma enhanced chemical vapor deposition using the GeH4 and H2 precursors has been investigated. A comparative analysis of the kinetics of the thermal crystallization by annealing to 650°C and of the gold-mediated crystallization (Au-MMC) is carried out. The impact of the Au-MMC on the microcrystalline Ge film microstructure and electrical properties is discussed. The Au thin layer results in a more dense and ordered structure with lower roughness of the microcrystalline Ge films. In order to describe the Ge crystallization kinetics, the dielectric functions of a-Ge:H and microcrystalline germanium μc-Ge have also been determined by spectroscopic ellipsometry in the range of 0.75−6.0eV and parametrized using the Tauc-Lorentz dispersion equation.

Formation of high quality nano-crystallized Ge films on quartz substrates at moderate temperature

“…They attributed the conversion of conduction type to the formation of oxygen vacancy, which leaded to the pinning of E F near the valence bands. 16,19 But this is not the case in our samples. From the results of FTIR, no Ge-O bonds are found.…”

“…19 Recently, Zhang et al 16 also reported that holes were the major carriers in ncGe films embedded in SiO 2 matrix according to Hall measurements and thermoelectric power results. They attributed the conversion of conduction type to the formation of oxygen vacancy, which leaded to the pinning of E F near the valence bands.…”

Ellipsometric study of crystallization of amorphous Ge thin films embedded in SiO2

“…1. At first sight, the largest difference is a reduced intensity of the E 1 transitions, which is correlated to the nanocrystalline structure of the Ge layer [11][12][13][14]. To determine the volume fractions of crystallized and amorphous Ge in every sample it is necessary to use as input the characteristic ε of the components.…”

Ellipsometric study of thermally induced redistribution and crystallization of Ge in Ge:SiO2 mixture layers

“…They are determined by minima of the second derivative of ε 2 [7][8][9]. In this case it is proper to use ε 2 dispersion obtained from wavelength by wavelength analysis because otherwise CPs positions could be imposed by the used dispersion model.…”

“…However, using optical constants of bulk Ge in EMA for characterization of a mixture containing Ge quantum dots can fail because the optical constants of dots can be quite different than those of material as bulk. Solutions proposed to solve this problem are finding volume fraction and optical constants of the quantum dots by direct inversion [6,7], using dispersion model [8] or using splines [9]. These approaches were applied always to the homogeneous thin films, where Ge was homogeneously distributed through the film.…”