A conveyor having a plurality of buckets lined up in and fixed to an inner side of a frame is supported so that the conveyor can be circulated in the shape of a loop and substantially horizontally in a substantially vertical plane via rotary shafts. The handle assembly includes a recess formed at a lower end of an upper handle component and a neck portion formed at an upper end of a lower handle component. Multiple dopant sources may be employed to form active diffusion regions of varying doping levels.