Temperature Dependence of The Thermo-Optic Coefficient In 4H-SiC and GaN Slabs At The Wavelength of 1550 nm

The refractive index and its variation with temperature, i.e. the thermo-optic coefficient, are basic optical parameters for all those semiconductors that are used in the fabrication of linear and non-linear opto-electronic devices and systems. Recently, 4H single-crystal Silicon Carbide (4H-SiC) and Gallium Nitride (GaN) have emerged as excellent building materials for high power and high temperature electronics, and wide parallel applications in photonics can be consequently forecasted in the near future, in particular in the infrared telecommunication band of λ=1500-1600 nm.In this paper, the thermo-optic coefficient (dn/dT) is experimentally measured in 4H-SiC and GaN substrates, from room temperature to 480 K, at the wavelength of 1550 nm. Specifically, the substrates, forming natural Fabry-Perot etalons, are exploited within a simple hybrid fiber–free space optical interferometric system to take accurate measurements of the transmitted optical power in the said temperature range. It is found that, for both semiconductors, dn/dT is itself remarkably temperature dependent, in particular quadratically for GaN and almost linearly for 4H-SiC.