Optoelectronic Properties of Nanocrystalline Silicon-Based Superlattice Structures

Abstract

Superlattice structures consist of alternate layers of two different materials, each having a fixed thickness. These structures thus have an additional periodicity along the growth direction and thus behave like a quasi-crystal with a periodicity much larger than that in single-crystal materials having a periodicity of the order of lattice constant of crystal and exhibit several interesting phenomena. The optical, electrical and other physical properties of these structures are significantly different from those of individual layers. In the present article, we present some interesting experimental results observed for nc-Si/a-Si:H-based superlattice structures. Though the lattice constant and electron affinity of nc-Si/a-Si:H are nearly matched, their structural, electrical and optical properties are significantly different. Our studies show that the electrical transport properties of these structures can be tuned by controlling the thickness of the individual layer. The superlattice structures with thick individual layers show excess conductivity in dark after exposure to light. On the other hand, strong photoluminescence (PL) signal in the visible range is observed for the structures with thin individual layers and the PL peak energy depends upon the thickness of the nc-Si layer. The nc-Si/a-Si:H superlattice structures can be used for silicon-based photonic devices in the integrated circuits.