Apparatus for vapor phase growing of crystals having a single multi-zone heater arranged to heat a heated zone to give a predetermined temperature profile along the length of the heated zone. A generally U-shaped tube having a first limb, a second limb, and a linkage connecting the first and second limbs is located on the heated zone. The first limb contains a source material. The second limb supports a seed such that the source material and seed are spaced longitudinally within the heated zone to provide a predetermined temperature differential between the source and seed. The crystal is grown on the seed.