Temperature dependence of the thermo-optic coefficient in 4H-SiC and GaN slabs at the wavelength of 1550 nm

Abstract

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.

Experimental characterization of the thermo-optic coefficient vs. temperature for 4H-SiC and GaN semiconductors at the wavelength of 632 nm

“…The sample, containing into a U-bench (Thorlabs, FBC-1550-FC), is heated through a ceramic-resistive heater at a desired temperature and the actual temperature is monitored by a high-sensitive PT-100 sensor glued into its surface. More information about the measurement technique and the experimental setup can be retrieved in [21].…”

“…In our previous work, we measured both the thermo-optic coe cient (TOC) of a 4H-SiC and GaN at 1550 nm [21], the most common wavelength used in optical communications due to the exceptionally low absorption losses shown by silica optical bers, and the TOC dependence on temperature in a wide temperature range from RT to T = 480 K. However, both semiconductors are transparent in the shorter wavelength range of visible, which could favor the conception of new communication or sensory applications based on these materials, including biosensing [22], nonlinear optics [23], and quantum photonics [24]. For this reason, in this paper, we extend the data of [21] with new measurements run at a wavelength close to 630 nm.…”

Experimental characterization of the thermo-optic coefficient vs. temperature for 4H-SiC and GaN semiconductors at the wavelength of 632 nm

“…The sample, contained in a U-bench (Thorlabs, FBC-1550-FC), is heated through a ceramic-resistive heater at a desired temperature, precisely monitored by a high-sensitive PT-100 sensor glued onto its surface. More information about the measurement technique and the experimental setup can be retrieved in 26 .

Figure 1 Schematic diagram of the experimental setup used for characterization of TOC as a function of temperature.

…”

“…In our previous work, we measured both the thermo-optic coefficient (TOC) of a 4H-SiC and GaN at 1550 nm 26 , the most common wavelength used in optical communications due to the exceptionally low absorption losses shown by silica optical fibers, and the TOC dependence on temperature in the wide temperature range from RT to T = 480 K. However, both semiconductors are transparent in the shorter wavelength range of visible, which could favor the conception of new communication or sensory applications based on these materials, including biosensing 27 , nonlinear optics 28 , and quantum photonics 29 . For this reason, in this paper, we extend the data of 26 with new measurements run at a wavelength close to 630 nm.…”

In Situ TEM Characterization and Modulation for Phase Engineering of Nanomaterials

“…71 The 4H structure is also found in some ceramic materials, noble metal alloy nanocrystals, and epitaxially grown transition metals (mainly noble metals). 72 Its characteristics are preserved in hexagonal lattices, such as SiC, 73 Ag, 10 Pd, and PdAg. 74 The hexagonal cell undergoes a phase transition and changes from a 2H structure to different interlayer stacking orders along the ⟨100⟩ direction, i.e., 4H (ABCB), 6H (ABCACB), and 8H (ABCBCBAB).…”