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Deposition of nano-crystalline lead chalcogenide thin films using a simple electrochemical technique

Nillohit Mukherjee 1Sk Faruque Ahmed 3Dipankar Mukherjee 2Kalyan K. Chattopadhyay 3Anup Mondal 1

1. Bengal Engineering and Science University Department of Chemistry, Howrah 711103, India
2. Bengal Engineering and Science University Department of Electronics and Telecomm Engineering, Howrah 711103, India
3. Jadavpur University Department of Physics Thin Film and Nanoscience Laboratory, Kolkata 700032, India

Abstract

Nano-crystalline thin films of lead chalcogenides (PbS, PbSe and PbTe) were deposited on transparent conducting oxide (TCO) coated glass substrates using a simple galvanic technique. The basic electrochemical cell consisted of a Pb strip as a self-decaying anode, with TCO coated glass substrate as the cathode and a Pb(CH3COO)2 solution. Na2S2O3, H2SeO3 and HTeO2+ were introduced in the cell for PbS, PbSe and PbTe thin film depositions, respectively. No external bias was applied for the depositions; instead, the two electrodes were short circuited externally by a copper wire. The deposition potential was achieved from the difference in the electrode potentials. The Pb2+ was complexed to Pb-EDTA in all the cases, so that, no other Pb salts are precipitated through chemical reactions. A pH of 3 for the working solution was found to be optimum for all the depositions. Depositions were carried out at room temperature, without stirring of the solution. The following are the cathode reactions for the three electrochemical processes:

For PbS:

At cathode: Pb2+ + 2e → Pb, S2O32- + 6H+ + 4e → 2S + 3H2O

Overall: 2Pb2+ + S2O32- + 6H+ + 8e → 2PbS + 3H2O

For PbSe:

At cathode: Pb2+ + 2e → Pb, SeO32- + 6H+ + 4e → Se + 3H2O

Overall: Pb2+ + SeO32- + 6H+ + 6e → PbSe + 3H2O

For PbTe:

At cathode: Pb2+ + 2e → Pb, HTeO2+ + 3H+ + 4e → Te + 2H2O

Overall: HTeO2+ + Pb2+ + 3H+ + 6e → PbTe + 2H2O

The anodic reaction Pb → Pb2+ + 2e is the same for all the three cases.

X-ray characterization revealed that PbS, PbSe and PbTe thin films were all of cubic phase. The formation of nano-crystallites with dense and compact surface morphology was detected from FESEM and AFM measurements. EDX analysis showed metal deficient compositions, indicating p-type nature of the films. The nano-crystalline films showed ‘blue shifted’ IR absorption, which changed to bulk values when the crystallites were allowed to grow large. The nature of the n-TCO/p-PbX (X = S, Se, Te) hetero-junction has been studied.

 

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Related papers

Presentation: Oral at E-MRS Fall Meeting 2007, Symposium B, by Nillohit Mukherjee
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 11:56
Revised:   2009-06-07 00:44