Solid phase epitaxy of germanium compounds

Future developments of micro-and nano-electronics are to a great extent dependent on high mobility semiconductor materials and their integration in device structures. Thin films with high structural quality are required to achieve excellent electronic and optical properties. The fabrication of high mobility thin films is however challenging since relatively high temperatures are needed to obtain excellent structural and physical properties. At these temperatures several problems arise. The limited solubility of Ge and Sn prohibits for example the formation of GexSn1-x alloys with high Sn content [1,2,3]. This material system is however very interesting because of its high carrier mobility and excellent absorption in the infrared (IR) [3,4]. We demonstrate a new methodology for the fabrication of high mobility semiconductors, that overcomes the problems related to heteroepitaxial growth. This methodology is novel in applying solid phase crystallization for the fabrication of high mobility semiconductor materials. Solid phase crystallization is commonly used for large scale and low cost applications [5,6], and roughly consists of two steps: (1) low temperature deposition of a layer and (2) crystallization by thermal or laser annealing. In general, this approach leads to poly-crystalline layers, with the presence of significant concentrations of impurities [6]. Our methodology consists of deposition of an amorphous layer by suppressing ad-atom diffusion and initiation of crystallization at the amorphous layer/crystalline substrate interface by thermal annealing, see Fig. 1. We will show the possibilities of plasma enhanced chemical vapor deposition (PECVD) and inert gas fluxes during molecular beam epitaxy (MBE) to lower the ad-atom diffusion and decrease the structural order of amorphous semiconductor layers. Single crystalline Ge on Si with excellent crystalline and electrical properties is obtained, even for very thin layers (< 100 nm) [7]. Furthermore we demonstrate that this approach can be used to obtain single crystalline GeSn on Si with 4 % of Sn.status: publishe