Shedding Light on Electrochemically Doped Semiconductors

Abstract

To utilize the full potential of semiconductor materials in device applications including solar cells, LEDs, and lasers, the ability to precisely and controllably tune the charge carrier concentration and hence the doping density is crucial. The conventional methods such as impurity doping with thermal diffusion or ion implantation, have been successfully implemented for doping bulk semiconductors for decades. In spite of the maturity of doping with traditional methods, it has remained a long-standing challenge to introduce impurity doping successfully into organic and new generation of semiconductors, such as conducting polymers and quantum dots. Additionally, the prospect of new technologies and the shrinkage in the device dimensions to nanoscale have stimulated researchers to search for alternative methods for achieving doping of such semiconductor materials reliably.

Electrochemical doping is arguably the most powerful and versatile method for doping porous semiconductor materials, in which the charge carrier concentration can be precisely and controllably modulated as a function of applied potential by an external voltage source. Unfortunately, when the doped semiconductor film is disconnected from the voltage source, the electrochemically injected charges leave the film spontaneously in a matter of seconds to few minutes.

In that regard, the stability of injected charges as well as the immobilization of external dopant ions need to fixed for achieving stable electrochemical doping of such semiconductor films to be used in device applications. The research carried out in this thesis is aimed to enhance the stability of injected charges and the fixation of dopant ions with photopolymerization treatment at room temperature in electrochemically doped quantum dots and conducting polymers. This was attempted by understanding the underlying mechanism of electrochemical doping in such porous films and eliminating or minimizing possible causes for instability with the final goal of producing stable doped of semiconductor films.