Emissivity-correcting near-UV pyrometry for group-III nitride OMVPE

We developed a pyrometer that operates near the high-temperature bandgap of GaN, thus solving the transparency problem once a ∼1 μm thick GaN epilayer has been established. The system collects radiation in the near-UV (380–415 nm) and has an effective detection wavelength of ∼405 nm. By simultaneously measuring reflectance we also correct for emissivity changes when films of differing optical properties (e.g. AlGaN) are deposited on the GaN template. We recently modified the pyrometer hardware and software to enable measurements in a multiwafer Veeco D-125 OMVPE system. A method of synchronizing and indexing the detection system with the wafer platen was developed; so signals only from the desired wafer(s) could be measured, while rejecting thermal emission signals from the platen. Despite losses in optical throughput and duty cycle we are able to maintain adequate performance from 700 to 1100 °C.