The Density of States in Heavily Doped Regions of Silicon Solar Cells

The density of states (DOS) of crystalline silicon changes with the introduction of dopants due to the formation of an impurity band and band tails. Until now, the DOS of undoped silicon has been used to model silicon devices, regardless of the doping level. This approximation may not be satisfactory for the emitter and back surface field regions of silicon solar cells. Therefore, we measured the DOS by performing tunnel spectroscopy measurements on Schottky diodes fabricated on heavily doped silicon. We extracted the DOS from this data by calculating the quantum-mechanical tunnel probability through the Schottky barrier. The goal is to use silicon samples with varying phosphorus doping density in order to determine the DOS as a function of the phosphorus doping density. The use of this parameterisation (instead of the DOS of undoped silicon) is expected to improve the calculation of the minority carrier density in the emitter and back surface field region of crystalline silicon solar cells.