Zinc-hyperdoped silicon nanocrystalline layers prepared via nanosecond laser melting for broad light absorption

Current techniques for hyperdoping of Si wafer surface by femtosecond laser or ion implantation have encountered several problems for device fabrication, such as severe lattice defects, shallow doping depth, poor electrical activity of impurities, difficult collection of charge carriers, or weak compatibility with present complementary metal-oxidesemiconductor processes. To provide a new way to solve these problems, in this study, Zn-hyperdoped Si layers were prepared on polycrystalline Si substrates by vacuum evaporation and nanosecond (ns) laser melting under different conditions of deposition and laser treatment. As a result, the hyperdoped Si layers of up to micron-level thickness with a broad light absorption (above 90% from the ultraviolet to the visible range and up to 54% for the near-infrared spectrum) and good electrical transport properties (electron mobility of up to 88.5 cm2.V- 1s- 1 and sheet resistance of - 100 Omega.square- 1) were obtained. These hyperdoped Si layers can be flexibly superimposed on the existing Si optoelectronic devices: Such tandem structure avoids the damage of substrate and provides both the layers and substrate properties. In addition, the variation in the microstructural characteristics of the Zn-hyperdoped Si layers consisting of surface and cross-section structures, Zn impurity distribution and concentration, and crystallinity were carefully studied to clarify the relationships between their preparation conditions, microstructures, and physical properties. The results show that a matching between the thickness of Si-Zn deposited layer and the ns-laser irradiation fluence is crucial to achieve a full melting process and to obtain excellent Zn-hyperdoped Si layers. Their near-infrared absorption and electrical transport properties are determined by the combined effects of surface antireflection, Zn-hyperdoping, and nanocrystallization.