Structure and Properties of Quasi-Monocrystalline Silicon Thin-Films

ABSTRACTThis contribution describes the preparation of a single crystalline Si thin-film separable from a reusable Si wafer. The method relies on: i) etching of a porous silicon layer ii) high-temperature annealing and iii) transfer of the recrystallized film to a foreign substrate. As a result of the process we obtain 1 to 30 μm thick monocrystalline Si films that contain voids with a size of several 100 nm. Due to its “swiss-cheese-like” structure the material is termed as “quasi-monocrystalline Si”. Sub micrometer thin layers are almost compact, while in several micron thick films voids cause scattering of incident light. This effect increases the effective absorption coefficient by light trapping and seems promising for the application of our quasi-monocrystalline films in thin film solar cells. Quasi-monocrystalline p-type silicon reaches a hole mobility of 78 cm2/ Vs measured by room-temperature Hall-effect. High carrier mobility and adjustable optical characteristics make these films suitable for display and photovoltaic applications. Quasi-monocrystalline films are processed using conventional high-temperature Si processing; finished devices can be transferred to a foreign substrate such as glass, while the starting wafer can be reused several times.