Studies of Hg(1-x)CdxTe formation by electrochemical atomic layer deposition and investigations into bandgap engineering
Films of Hg(1-x)CdxTe (MCT) were grown using electrochemical atomic layer deposition, the electrochemical analog of atomic layer epitaxy, and atomic layer deposition (ALD). The present study describes the growth of MCT via electrochemical ALD, using an automated electrochemical flow cell deposition system. The system allows potential control and solution exchange as desired. Deposits were characterized using X-ray diffraction, electron probe microanalysis, and reflection absorption Fourier transform infrared spectroscopy. The as-deposited films showed strong (111) preferred orientation. No postdeposition annealing was required. Changes in deposit composition showed the expected trend in bandgaps: the more Hg the lower the bandgap, but with some significant deviations. Deposit composition was controlled using a superlattice deposition program. Hg0.5Cd0.5Te and Hg0.8Cd0.2Te deposits resulted in bandgaps of 0.70 and 0.36 eV, respectively. Electrochemical quartz crystal microbalance studies, using an automated flow cell, indicated that some deposited Cd was stripping at potentials used to deposit Hg. In addition, redox replacement of Cd for Hg was evident, a function of the greater stability of Hg than Cd. (c) 2007 The Electrochemical Society.