The chamber has a lenticular cross-section with a horizontal support plate extending between sides of the chamber. A rectangular aperture is formed in the support plate for positioning a rotatable susceptor. A temperature compensation ring surrounds the susceptor and is supported by fingers connected to the support plate. The ring may be circular or may conform to the shape of the support plate aperture. The ring may extend farther downstream from the susceptor than upstream. A sacrificial quartz plate may be provided between the circular ring and the rectangular aperture. The quartz plate may have a horizontal portion and a vertical lip in close abutment with the aperture to prevent devitrification of the support plate. A gas injector abuts an inlet flange of the chamber and injects process gas into an upper region and purge gas into a lower region.