In indirect band gap semiconductors, the carrier lifetime strongly depends on the concentration of recombination centers.
[1] In practical applications, the electronic band structure of a semiconductor is typically found in a non-equilibrium state.
Therefore, processes that tend towards thermal equilibrium, namely mechanisms of carrier recombination, always play a role.
As a result of this, the carrier lifetime plays a vital role in many semiconductor devices that have dopants.
[3] As opposed to this, Langevin recombination plays a major role in organic solar cells, where the semiconductors are characterized by low mobility.
Electrons are either excited through the absorption of light, or if the band-gap energy of the material can be bridged, electron-hole pairs are created.
[6] Additionally, the same method of layering different semiconductor materials is used to reduce the capture probability of the electrons, which results in a decrease in trap-assisted SRH recombination, and an increase in carrier lifetime.
Radiative (band-to-band) recombination is negligible in solar cells that have semiconductor materials with indirect bandgap structure.
Auger recombination occurs as a limiting factor for solar cells when the concentration of excess electrons grows large at low doping rates.
Otherwise, the doping-dependent SRH recombination is one of the primary mechanisms that reduces the electrons’ carrier lifetime in solar cells.
A BJT uses a single crystal of material in its circuit that is divided into two types of semiconductor, an n-type and p-type.
Additionally, in order to prevent high rates of recombination, the base is only lightly doped with respect to the emitter and collector region.
For other modes of operation, like that of fast switching, a high recombination rate (and thus a short carrier lifetime) is desirable.
The desired mode of operation, and the associated properties of the doped base region must be considered in order to facilitate the appropriate carrier lifetime.
Because the efficiency of a semiconductor device generally depends on its carrier lifetime, it is important to be able to measure this quantity.
This means that the carrier lifetime of a solar cell can be calculated by studying its voltage decay rate.
In practice, this generally implies reducing structural defects within the semiconductors, or introducing novel methods that do not suffer from the same recombination mechanisms.
[14] Reducing the amount of damage done during this process is therefore important to increase the efficiency of the solar cell, and a focus of current research.
Modern advancements suggest that there is still ample room to improve on the carrier lifetime of this solar cell, with most of the issues surrounding it being construction-related.
Current problems include the structural defects that appear when semiconductor devices are manufactured with the material, as the dislocation density associated with the crystals is a detriment to their carrier lifetime.