Microcrystalline silicon p–i–n photodetectors for telecommunications and photovoltaic applications

Very-high-frequency plasma enhanced chemical vapor deposition was used to fabricate microcrystalline silicon p–i–n photodetectors. Optical simulation of reflectance measurements was used to monitor the crystalline fraction, which determines the quantum efficiency in the near infrared range, relevant for telecommunication applications. To improve the i/p interface quality, a variable silane concentration was used in the early stages of the i-layer deposition. It is observed that a 50% large-grain fraction in the initial (200 nm) region of the i-layer results in a microcrystalline material well beyond the transition region between the amorphous and microcrystalline phase. The large-grain concentration in such initial layer is correlated with the open circuit voltage of the final p–i–n device. We suggest that the total elimination of the amorphous component in the heterophase transition region would result in excessive crystallization of the i-layer in the p–i–n device, which is to be technologically hindered by an on-time modulation of the deposition parameters.