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 intrinsic silicon has been used to model Si devices, regardless of the doping level. This approximation may not be satisfactory for the emitter and back surface field regions of Si solar cells. Therefore, the authors measured the DOS by performing 4.2 K tunnel spectroscopy measurements on Schottky diodes fabricated on heavily doped silicon. They extracted the DOS from this data by calculating the quantum-mechanical tunnel probability through the Schottky barrier, using a standard theory based on the WKB approximation and the two-band model. They find that this theory adequately describes the change of the DOS within the conduction band. However, below the conduction band edge, they show that the determination of the DOS requires the inclusion of phononic effects.