Theory of absorption in doping superlattices

Investigation of the Absorption Spectrum of InAs Doping Superlattice Solar Cells

“…In order to present the device performance clearly, the relevant dark current was extracted by fitting the curves with the dual diode dark current equation [18]:…”

“…The existence of an electric field-dependent absorption is explained as the photo-assisted tunneling of electrons from the valence to the conduction band. The electric field is a function of position in the growth axis z, which is described by the following equations [18,24]: The occurrence of this subband gap peak in EQE can be explained by the combination of two different effects. The first effect is the confined states within the wells, which is originated from minibands and was formed in the forbidden gap of the semiconductor.…”

Subbandgap current collection through the implementation of a doping superlattice solar cell

“…This mechanism will have the strongest effect near the band edge of the semiconductor since formation of these states within the forbidden gap requires the least energy. 3 It is evident that the absorption is achieved through this mechanism since the peak in EQE closely matches with the subband peak in PL. This indicates that a confined state exists where the exitonic peak in EQE exists.…”

“…A theoretical analysis of absorption in a DSL has been demonstrated elsewhere, 3 and we expect that the absorption can be increased by modifying the DSL. To achieve the desired increase in subband absorption, it is necessary to thin the nipi periods and increase the doping levels to maximize the built-in field for each junction while minimizing the flatband region within the doped layers.…”

“…1 The device design intrinsically results in longer carrier lifetimes, increased radiation tolerance, and the formation of sub-bandgap energy states. 2,3 It is also believed that DSL structures can be used as an intermediate band solar cell (IBSC) through the inclusion of quantum dots within the structure to form a miniband coupled with the confined states of the DSL. 4 The IBSC has been proposed to allow dramatic increases in efficiency due to the ability to simultaneously reduce thermalization and transmission losses by absorbing three distinct energy levels through the thickness of the active region.…”