INP SUBSTRATE-TEMPERATURE MEASUREMENTS IN A HORIZONTAL, LOW-PRESSURE METALORGANIC CHEMICAL VAPOR-DEPOSITION REACTOR BY INFRARED-LASER INTERFEROMETRIC THERMOMETRY

Infrared laser interferometric thermometry was used to measure InP substrate temperatures in a horizontal, low pressure metalorganic chemical vapor deposition (MOCVD) reactor. These measurements were made by using a 1.53 mum distributed feedback laser, demonstrating the use of semiconductor lasers to diagnose an epitaxial crystal growth process. The laser beam was reflected off of 2 inch diameter (100) n-type InP substrates in a commercial low-pressure MOCVD reactor. Substrate. temperature profiles were taken as a function of reactor pressure from 20-1000 mbar and as a function of substrate position on the susceptor. For a constant susceptor set-point temperature of 640-degrees-C, temperatures increase monotonically from 600 to 615-degrees-C at 20 mbar along the substrate in the gas flow direction, increasing to 621 to 655-degrees-C at 1000 mbar for a substrate positioned in the downstream location of a two-well susceptor used for normal epitaxial growth runs. The variation in temperature decreases when the substrate is placed in a center well susceptor. The data shows that improvements in temperature uniformity, and hence compositional uniformity can be achieved by judicious choice of substrate position and reactor pressure. In particular, uniform temperature profiles resulted in improved compositional uniformity obtained for 1.15 mum InGaAsP layers grown on a 2 inch diameter substrate placed in the center well susceptor.