An apparatus and method for manufacturing thin-film CdS/CdTe photovoltaic modules in a vacuum environment. The apparatus deposits CdS and CdTe layers onto a substrate using heated pocket deposition, a form of physical vapor deposition (PVD) in which a material thermally sublimes from a thermal sublimation source block and is deposited onto a substrate. The thermal sublimation source block includes a pocket having a lower surface into which an array of holes is formed to house plugs of deposition material. Upon heating, deposition material sublimes from a surface of each plug of deposition material, and the surface of each plug regresses into its corresponding hole while maintaining a constant surface area. The sublimation surface area of deposition material across the pocket remains substantially constant during an extended deposition process, and the deposition material is substantially free of undesired thermal radiation from the substrate. As such, the thermal sublimation source block provides a temporally- and spatially-uniform thin film deposition rate across the lower surface of the substrate.