Abstract
The optical parameters of hydrogenated amorphous a-hbox {Si}_{1-x},hbox {Ge}_{{x}}:H layers were measured with focused beam mapping ellipsometry for photon energies from 0.7 to 6.5 eV. The applied single-sample micro-combinatorial technique enables the preparation of a-hbox {Si}_{1-x},hbox {Ge}_{{x}}:H with full range composition spread. Linearly variable composition profile was revealed along the 20 mm long gradient part of the sample by Rutherford backscattering spectrometry and elastic recoil detection analysis. The Cody-Lorentz approach was identified as the best method to describe the optical dispersion of the alloy. The effect of incorporated H on the optical absorption is explained by the lowering of the density of localized states in the mobility gap. It is shown that in the low-dispersion near infrared range the refractive index of the a-hbox {Si}_{1-x},hbox {Ge}_x alloy can be comprehended as a linear combination of the optical parameters of the components. The micro-combinatorial sample preparation with mapping ellipsometry is not only suitable for the fabrication of samples with controlled lateral distribution of the concentrations, but also opens new prospects in creating databases of compounds for optical and optoelectonic applications.
Highlights
Until now, a great number of integrated circuit applications have been introduced, which can operate in the infrared wavelength region, e.g. at 4.5 μ m and even beyond, toward the longer wavelengths[10,14,15,16,17,18,19,20]
In this article we show that the strictly controlled preparation of a-Si1−x Gex :H films is possible over the entire range of 0 ≤ x ≤ 1 using magnetron sputtering over a length of 2 cm, but—for wavelength ranges we identify in the study—the composition, and even more importantly the optical gap ( Eg ) and n all show an accurately linear dependence on the position
Preparation of a‐Si1−x Gex :H using “single‐sample” micro‐combinatory. a-Si1−x Gex :H samples were prepared on 10 mm × 25 mm size Si wafers by “single-sample” micro-combinatory that resulted in gradient composition of a-Si1−x Gex with x ranging in 0 ≤ x ≤ 1
Summary
A great number of integrated circuit applications have been introduced, which can operate in the infrared wavelength region, e.g. at 4.5 μ m and even beyond, toward the longer wavelengths[10,14,15,16,17,18,19,20]. Dispersion s haping[8] can improve the conventionally used optical structures These advantages of Ge-rich SiGe offer new directions in improvement for generation spectroscopic methods operating at the infrared range, e.g. for mid-IR interferometers[23]. There are some inevitable hardship during the fabrication of SiGe wafers with reliable quality, since there is a large splitting of the solid/liquid phase boundary[30] This means that the availability of data on the optical properties of high-quality bulk SiGe (especially around x = 0.5 ) is very limited. In spite of this fact, systematic data for the amorphous compositions in the whole range of x have been published for amorphous silicon-germanium (a-Si1−x Gex)[31].
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