Aluminum-induced layer exchange (ALILE) was used to crystallize amorphous silicon–germanium (a-Si1−xGex) alloys. A bilayer structure of aluminum (Al) and a-Si1−xGex was deposited on quartz substrates and annealed below the eutectic temperature of the binary Al–Ge alloy (420°C). The annealing process results in an almost complete exchange of the two layers and leads to the crystallization of the initially amorphous Si1−xGex thin films. Elastic recoil detection and Raman spectroscopy were used for structural characterization. The polycrystalline Si1−xGex (poly-Si1−xGex) samples show good structural properties over the entire composition range. In particular, no significant phase segregation was observed. Thus, ALILE has a high potential for the fabrication of polycrystalline Si1−xGex layers.
Recent results concerning the aluminium-induced crystallization of thin SiGe alloy films are reviewed. This crystallization process can be employed throughout the entire alloy range and results in polycrystalline material without a significant amount of phase separation. The structural, optical, and electronic properties of the polycrystalline SiGe films have been determined by a variety of techniques and for different Ge contents. The use of such films in thin film solar cells is discussed.
Large-grained polycrystalline silicon–germanium (poly-Si1−xGex) thin films have been obtained by the aluminum-induced layer exchange (ALILE) process. The optical and electrical properties of these layers have been investigated as a function of the alloy composition. Optical reflection spectra and Hall effect mobility measurements indicate a high structural quality of the recrystallized thin films, which is comparable to bulk crystalline silicon–germanium (c-Si1−xGex) samples prepared by more sophisticated methods. Due to the increasing solubility of aluminum as a substitutional shallow acceptor with increasing germanium content, the room temperature carrier density of holes is found to increase from 1.5×1018cm−3 in poly-Si to 5×1020cm−3 in poly-Ge produced by ALILE.
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