Electrodeposition of lead chalcogenide thin films, superlattices and photovoltaics by electrochemical atomic layer deposition (EC-AID)

Abstract

This dissertation mainly presents how electrochemical atomic layer deposition (EC-ALD) was used to grow thin films and superlattices of lead chalcogenides and photovoltaics. EC-ALD is the electrochemical analog of atomic layer deposition. It is an electrodeposition technique based on the use of surface limited reactions known as under potential deposition (UPD). UPD is a phenomenon where an atomic layer is deposited on the second at a potential prior to its formal potential to form deposits with atomic level control. EC-ALD is carried out at room temperature, thus considerably reducing interdiffusion in layers of the deposits. EC-ALD has been used successfully to deposit compound semiconductors and metal nanofilms on metallic substrates such as Au, Cu and Pt. The goal of the research investigation was to optimize the deposition of Pb chalcogenides (PbSe, PbTe, and their subsequent superlattices) as they are of interest for their optical and electronic properties, which make them useful in thermoelectric device structures, infrared sensors and in photovoltaics. The formation of PbTe/CdTe superlattices was also pursued as PbTe, being an excellent material for IR laser can be improved by the insertion of a barrier material that has a sufficient electrical and optical confinement such as CdTe. The low lattice mismatch of 0.3 % between PbTe and CdTe could also promote the superlattice growth by electrochemical ALD. Studies on the electrodeposition of CuInSe2 (CIS) and CuIn1-xGaxSe2 (CIGS) photovoltaic cells were undertaken and will also be reported as these materials are one of the promising thin film candidates for the advancement of photovoltaic solar cell technology due to their high conversion efficiency.