Preparation and characterization of monolithic HgCdTe/CdTe tandem cells

ABSTRACTA prototype monolithic HgCdTe/CdTe superstrate tandem cell has been fabricated by RF sputtering, comprising a CdTe/CdS top cell, a ZnTe:N/ZnO:Al interconnect junction and a HgCdTe/CdS bottom cell. The Hg1−xCdxTe film as the bottom absorption layer was deposited by RF sputtering with 70% or 85% Cd content in the Hg1−xCdxTe magnetron target. Hg1−xCdxTe films with band gap from 0.98 eV to 1.45 eV were obtained by controlling the deposition temperature. CdCl2 thermal treatments were used to improve the Hg1−xCdxTe film electrical properties. A nitrogen-doped ZnTe film combined with an aluminium (Al) doped ZnO film formed a good interconnect junction. Results of Voc = 0.99 V and Jsc = 2.1 mA/cm2 were obtained in the best such tandem cell at one sun (AM1.5).

INTERACTION BETWEEN Zn AND Cd ATOMS DURING THE ATOMIC LAYER EPITAXY GROWTH OF CdZnTe/ZnTe QUANTUM WELLS

Layers of 6 and 16 Cd–Te–Zn–Te periods were grown by atomic layer epitaxy (ALE) within ZnTe thin films. Different samples were grown at substrate temperatures of 260 and 290°C. Information about the kinetics of growth and surface reconstruction during the ALE growth of CdTe and ZnTe films, and Cd–Te–Zn–Te periods was obtained by means of reflection high-energy electron diffraction (RHEED) experiments and through the analysis of the temporal behavior of the intensities of several features of the RHEED patterns. The photoluminescence of the sample grown at 260°C presents two narrow and intense peaks corresponding to emission from quantum wells (QWs). However, the spectrum of the samples grown at 290°C does not show any feature associated with QWs, the spectrum resembling that of a ZnTe film. Cd replacement by Zn atoms explains the absence of the CdZnTe QWs at 290°C and a lower Cd content than expected at 260°C. The replacement of Cd atoms by Zn atoms in the CdTe surface was clearly demonstrated by Auger experiments.