Polycrystalline thin films of Hg1-xZnxTe for use in multijunction solar cells

Thin films of Hg_1-xZn_xTe were deposited onto Corning 7059 glass substrates using the coevaporation of HgTe with ZnTe. Layers were produced with bandgaps in the range of 0.6-2.25 eV by altering the alloy composition. The layers had absorption coefficients >10⁵/cm¹ and as high as 6×10⁵ cm¹ in samples with E_g>1.5 eV. The samples were p-type at 300 K with low resistivities (≈0.5 Ωcm) and Hall mobilities in the range 2-12 cm²/V¹s¹ for layers <0.5-μm thick. Arrhenius plots of the resistivities gave two straight lines corresponding to an activation energy, of 50 ±5 meV for temperatures >220 K and an activation energy of 7 ±4 meV for temperatures <220 K. The layers consisted of columnar grains, and the grain size increased with film thickness and with postgrowth annealing in argon. Heterojunctions with CdS and Cd_1-xZn_xS window, layers had I-V characteristics which were rectifying, and these devices exhibited the photovoltaic effect