The Crystal Quality and Surface Wettability of Various Tellurium-Based Chalcopyrite Layers Grown by the Closed Space Sublimation

AgGaTe₂, AgAlTe₂, CuGaTe₂, and Ag(Ga,Al)Te₂ layers were deposited by the close spaced sublimation method. The surface morphology and crystal quality of these Te-based chalcopyrite layers were systematically evaluated. Controlling the stoichiometry of these layers grown by the closed space sublimation was very difficult because Te preferentially detached from the source materials during the sublimation process and then Te vapor leaked out from the reactor. To solve this problem, the gap between the lid and reactor boat was minimized, and the vapor was encapsulated. As a result, the crystal quality of the AgGaTe₂ and AgAlTe₂ was improved. However, the controlling stoichiometry of CuGaTe₂ remained difficult even after the Te vapor leakage was minimized. This behavior was attributed to the large vapor pressure difference between Cu and Te. The surface morphology of the grown AgGaTe₂ and CuGaTe₂ layers exhibited scattered grain structure, while that of AgAlTe₂ possessed a continuous film structure. These different surface structures contributed to differing wettability between the chalcopyrite materials and substrates. It was found that AgAlTe₂ exhibited a high wettability against a sapphire substrate, which promoted continuous film formation.