In Situ Reflectance Monitoring of Overgrowth of InGaAs Gratings in Laser Diode Manufacture

We report on the use of a commercially available spectral reflectance (SR) unit and its application to grating overgrowth on a Rotating Disk Reactor (RDR). Spectral reflectance measurements for in situ thickness measurements of critical layers allow for an improvement in process control in the fabrication of InP based laser diodes. We show that reflectance measurements are applicable to InP overgrowth of continuous 50% duty cycle, InGaAs gratings as well as patterned gratings. A correlation between post growth XRAY and SEM measurements and SR determined thickness show good agreement for layer thickness between 2500 and 7500 A as shown in figure 1. In the fabrication of laser diodes, control of this layer thickness is important because it determines the coupling coefficient (K) of the active part of the laser to the grating.