Abstract
Gradient a-Si1−xGex layers have been deposited by ”one-sample concept” combinatorial direct current (DC) magnetron sputtering onto one-inch-long Si slabs. Characterizations by electron microscopy, ion beam analysis and ellipsometry show that the layers are amorphous with a uniform thickness, small roughness and compositions from x = 0 to x = 1 changing linearly with the lateral position. By focused-beam mapping ellipsometry, we show that the optical constants also vary linearly with the lateral position, implying that the optical constants are linear functions of the composition. Both the refractive index and the extinction coefficient can be varied in a broad range for a large spectral region. The precise control and the knowledge of layer properties as a function of composition is of primary importance in many applications from solar cells to sensors.
Highlights
SiGe thin film research is largely motivated by diverse applications in various semiconductor devices [1,2], such as solar cells, thin film transistors [3], Schottky diodes [4], temperature sensors [5], detectors and bolometers [6,7]
We show that the strictly controlled preparation of a-Si1− x Gex films is possible over the entire range of 0 ≤ x ≤ 1 using magnetron sputtering over a length of 2 cm, but the composition, and even more importantly the refractive index (n) and extinction coefficient (k) all show a linear dependence on the position in most of the wavelength range
The most important feature of the optical properties is that both n and k show a linear dependence on the position in the whole measured photon energy range, as shown by the color stripes with straight edges corresponding to large changes of the optical properties as a function of the photon energy
Summary
SiGe thin film research is largely motivated by diverse applications in various semiconductor devices [1,2], such as solar cells, thin film transistors [3], Schottky diodes [4], temperature sensors [5], detectors and bolometers [6,7]. We show that the strictly controlled preparation of a-Si1− x Gex films is possible over the entire range of 0 ≤ x ≤ 1 using magnetron sputtering over a length of 2 cm, but the composition, and even more importantly the refractive index (n) and extinction coefficient (k) all show a linear dependence on the position in most of the wavelength range. The combinatorial a-Si1− x Gex samples with gradient composition ranging in 0 ≤ x ≤ 1 were deposited onto 25 × 10 mm size Si slabs by DC magnetron sputtering. We followed the “one sample concept” combinatory in order to cover the entire composition range of a binary film within a single specimen This is implemented by means of a scaled-up device originally constructed for the preparation of 3-mm diameter micro-combinatorial TEM samples [20]. As the power of the Si source arrived to zero and, simultaneously, that of the Ge arrived to its maximum, the Si source was switched off and, the Ge section of the sample was deposited at 100% power of the Ge source
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