Optimization of Te Solution Chemistry in the Electrochemical Atomic Layer Deposition Growth of CdTe

Abstract

The deposition of CdTe using the electrochemical form of atomic layer deposition (ALD) is discussed as a function of the Te solution chemistry. 100 cycle CdTe deposits were formed using both acidic and basic solutions of TeO2, with and without a reductive Te stripping step. The resulting films were characterized using electron probe microanalysis (EPMA), X-ray diffraction (XRD), microRaman, spectroscopic ellipsometry (SE), and photoelectrochemistry (PEC). EPMA indicated stoichiometric deposits, XRD a strong (111) preferred orientation and pole figures suggested the deposits were epitaxial on an Au(111) single crystal substrate. MicroRaman results evidenced the transvers optical (TO) mode of CdTe. SE results showed the E-ALD CdTe had an index of refraction of 2.98 and a growth rate dependent on the Te deposition potential. Both EPMA and SE showed the growth to be linear versus the number of cycles. PEC indicated that the 100 cycle CdTe deposits (40 nm thick) were p-type and displayed an external quantum efficiency of 10%, with a direct bandgap of 1.5 eV.