Selected area crystallization of amorphous Si and Ge thin films on glass substrates for solar cell and 3D-optoelectronic applications

Abstract

Selected area crystallization of amorphous Si and Ge thin films on glass and silicon substrates were performed. The crystalized areas are used as templates for III-V solar cells and 3D-optoelectroinc devices. Building these devices on inexpensive flexible substrate is in great demand. At best these templates can be polycrystalline thin films with large grains. Moreover, if these films are patterned into areas comparable in size to the films' grains, then the patterns would be a single crystal structure. Devices can be built on these patterns selectively. To illustrate this concept, thin films of Si and Ge were prepared on glass and silicon substrates. The fabricated films were capped with an aluminum thin layer for processing. The selected areas in the films were patterned using wet lithography and deep reactive ion etching. An oxide layer was intentionally deposited between the aluminum layer and the amorphous film to enhance the large grain crystallization in amorphous films. The films were annealed at 500°C for 17 hours. Optical and scanning electron microscope images showed morphology similar to those on polycrystalline films. The micro-Raman spectroscopy indicated the single crystal structure in the patterned regions was obtained.