For a given semiconductor material, can we consider charge carrier lifetime as a material property? Or does it vary much with processing conditions, doping etc?
several parameters control the carriers lifetime.
the presence of defects limits the lifetime,
for example the radiative lifetime of GaAs can be tuned from several hundred of picoseconds down to the ps by introducing defects (oxygen implantation without annealing)
the doping level and interface quality play can also seriously affect the carriers lifetime
see the basic document:
http://www.iue.tuwien.ac.at/phd/park/node32.html
Lifetime of charge carriers strongly depend on defects present in the semiconductor which act as recombination centers in the band gap. These may be structural defects created during preparation as in case of amorphous semiconductors or may be due to certain impurities introduced in the material to control lifetime. In case of amorphous semiconductors defect density changes many orders of magnitude by preparation condition. For example amorphous silicon prepared by glow discharge technique has much smaller defect density as compared to vacuum evaporated amorphous silicon. The lifetime of charge carriers is also quite different accordingly. In conclusion one can say that lifetime of carriers depends on preparation conditions. Effect may be case dependent. In single crystals it is less as compared to amorphous films of the same semiconductor.
Thank you for your answers.
So in single crystal instances I can more or less presume it to be a material property , but in case of semi crystalline or amorphous instances, it is very much dependent on the processing conditions.
On the same lines, can you provide some examples as to where the carrier lifetime is mainly a property of bulk semiconductor Vs where the carrier lifetime is limited by the contact/interface ?
The bulk minority carrier lifetime is a material property, yes. But even in case of crystalline semiconductor it is influenced by a variety of factor like defect density, doping, etc. These actually have a quite strong effect on it. Even some technological steps, like high temperature annealing can influence it. Take also into account, that it is temperature dependent, too.
So of course you can use it a material property, but to determine it you have to know some other properties of the material (or simply measure it). Take for instance single crystalline silicon: depending on the doping level the minority carrier lifetime can range from ns to ms. So far for the bulk minority carrier lifetime, that is in fact a material property.
When processing devices or structures the minority carrier lifetime is in addition by a broad variety of the properties of the material surfaces/interfaces, as this has been mentioned above.
Using the bulk minority carrier lifetime is for example quite acceptable when dealing with solar cells.
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