Crystallization of silicon–germanium by aluminum-induced layer exchange

Abstract

We have studied the crystallization of amorphous silicon-germanium (a-SiGe) by aluminum (Al)-induced layer exchange (ALILE) with a starting structure of glass/Al/Al oxide/a-SiGe. We examined ALILE at 450 °C, which is slightly higher than the eutectic temperature of Ge and Al, in order to shorten the ALILE time. We successfully produced c-SiGe films oriented in the (111) direction for 16 h without significant alloying. The thickness of Al layers should be 2800 Å or more to complete the ALILE for the a-SiGe layers of 2000-2800 Å thickness. When the Al layer is as thick as the a-SiGe layer, almost uniform c-SiGe is formed on the glass substrate. On the other hand, the islands of c-SiGe are formed on the glass substrate when the Al layer is thicker than the a-SiGe layer. The islands become smaller with thicker Al layers because more excess Al remains between the SiGe islands. The results indicate that the configuration of c-SiGe can be altered from a uniform structure to island structures of various sizes by changing the ratio of a-SiGe thickness to Al thickness.

Epitaxial growth of SiGe films by annealing Al–Ge alloyed pastes on Si substrate

“…Lattice-matching with upper cells and narrow gap can be realized by increasing Ge content higher than 82% 17 . Moreover, SiGe is low-cost and environmentally friendly and can be fabricated by chemical vapor deposition (CVD) or molecular beam epitaxy (MBE) 18 , 19 . However, they need toxic gasses such as SiH 4 and GeH 4 20 – 22 or ultra-high vacuum and take much time.…”

Epitaxial growth of SiGe on Si substrate by printing and firing of Al–Ge mixed paste

“…Silicon-germanium (SiGe) has a lattice constant and band gap close to that of Ge while also being relatively low cost and environmentally friendly. [2][3][4][5][6][7] Also, because SiGe is an all-fractional solid solution whose composition can be freely controlled, its lattice constant and band gap can be widely controlled. Therefore, SiGe could serve as a template for high-performance tandem solar cells.…”