Simultaneous electronic and lattice characterization using coupled femtosecond spectroscopic techniques.

Abstract

High-power electronics are central in the development of radar, solid-state lighting, and laser systems. Large powers, however, necessitate improved heat dissipation as heightened temperatures deleteriously affect both performance and reliability. Heat dissipation, in turn, is determined by the cascade of energy from the electronic to lattice system. Full characterization of the transport then requires analysis of each. In response, this four-month late start effort has developed a transient thermoreflectance (TTR) capability that probes the thermal response of electronic carriers with 100 fs resolution. Simultaneous characterization of the lattice carriers with this electronic assessment was then investigated by equipping the optical arrangement to acquire a Raman signal from radiation discarded during the TTR experiment. Initial results show only tentative acquisition of a Raman response at these timescales. Using simulations of the response, challenges responsible for these difficulties are then examined and indicate that with outlined refinements simultaneous acquisition of TTR/Raman signals remains attainable in the near term.

Invited Review Article: Error and uncertainty in Raman thermal conductivity measurements

“…Equation (2) implies that variations along the radial direction are extremely small in line with the assumption of 1D heat transport. Temperature differences along the radial direction were less than 0.001 K.…”

“…Traditional implementations of Raman thermometry, for example, are capable of specifying temperature to within only ±1 K. 2,6 Similarly, the amount of heat dissipated can be quantified with only a finite level of certainty. Uncertainty can stem from dissipation at the contacts rather than within the nanowire in Joule-heating experiments, for example, or due to ill-quantified reflection or transmittance, rather than absorption, during laser-heating.…”

“…2,5 While precise, the peak position is not a direct measurement of temperature. Rather, it is a probe of the zone center optical phonons, which themselves have an energy that is dependent upon the interatomic potential.…”

“…Raman spectroscopy is capable of meeting each of these challenges due to the technique's ability to perform non-contact thermal measurements with a resolution of ∼1 K in a manner that is unobtrusive to device operation. 2 The technique also provides a spatial resolution that is on par with the structures themselves (∼0.5 µm), coupled with the ability to sample in a materialspecific fashion. For these reasons, Raman thermometry is often utilized to examine self-heating in operating devices [3][4][5][6] but has recently been extended to measure the thermal conductivities of materials ranging from graphene [7][8][9][10][11] and carbon nanotubes [12][13][14] to semiconductor nanowires 15 and silicon.…”

Thermal conductivity of epitaxially grown InP: experiment and simulation

“…Owing to the variations in the equilibrium position of the atomic species, the anharmonicity of the bonds results in a variation of the interatomic forces and therefore in the shift of the phonon frequencies. 28,29 The resulting temperature-dependent peak positions are then recorded as a function of the absorbed power and compared to a calibration curve that allows the estimation of the weighted average temperature rise in the probed volume. The calibration curve is obtained by externally heating the sample and registering the corresponding vibrational frequencies of the optical phonon modes.…”