Susceptor - a plate on which wafer may be heated during deposition steps. It used in MOCVD systems. Substrates are placed on top of a rotating susceptor, which is resistively heated. The three-zone heater enables modification of the temperature profile to provide temperature uniformity over the susceptor diameter. Temperature profiling can be modified during each recipe step to allow different profiles to step up for different process temperatures. A transducer on the underside of the susceptor controls the temperature, and the temperature profile can be monitored through optical pyrometer ports on the topside of the susceptor.