Optical thickness monitoring in dielectric multilayer deposition for surface-emitting laser reflectors

To operate a GaInAsP surface-emitting laser diode (SELD) at room temperature, it is important to reduce the cavity loss by increasing the reflectivity of the mirrors. Reflectivity of 95 percent was achieved by using a dielectric multilayer deposited by electron-beam evaporation for the major. However, it was difficult to achieve high reproducibility in the layer thickness. To achieve precise control in layer thickness for an Si/SiO2 dielectric multilayer mirror designed for the 1.3 to 1.55-μm, wavelength region, optical thickness control during layer deposition was attempted instead of using the conventional crystal thickness monitor. As a result, the reflectivity of about 99 percent in the Si/SiO2 multilayer for 1.3-μm and 1.55-μm wavelength band SELD with excellent reproducibility was obtained. The optical film thickness control technique was used to form multilayer reflectors on GaInAsP surface-emitting lasers and the threshold current was reduced drastically. If this film thickness control technique and the technique for high-quality crystal growth such as a chemical beam epitaxial method are used together, the room-temperature operation of a GaInSaP surface-emitting laser diode will be realized.