Add carrier concentrations calculation algorithm (#4791)

* added carrier concentrations algorithm

* Add more references

Added more references to the carrier concentrations file

* Update electronics/carrier_concentration.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

* Update electronics/carrier_concentration.py

Co-authored-by: John Law <johnlaw.po@gmail.com>

Co-authored-by: John Law <johnlaw.po@gmail.com>