Raman Spectroscopy

Raman Spectroscopy

Raman Background: The technique involves directing a monochromatic beam of light at a sample, collecting the back-scattered radiation, and passing this through a spectrometer. The vast majority of the light that is scattered from the sample will be at exactly the same wavelength as the incident source, but a very small proportion of it – perhaps a few parts in a million – will be at a slightly different frequency, due to the interactions of photons with atomic vibrations within the material under investigation. This shift in frequency can be correlated with changes in temperature and stress in the material, and can be applied specifically to GaN HEMTs on multiple substrates. This technique can be used to estimate thermal conductivities and thermal interface resistances when temperature measurements are combined with an analytical solution or FEM model. Raman Spectroscopy is a non-destructive technique that requires no sample preparation.

The Heat Lab contains two Raman Spectrometers.

raman

A Renishaw inVia confocal Raman microscope featuring a 1200 or 3000 gr/mm grating selection with 532nm or 488nm wavelength excitation source and a selection of 5x, 20x, 50x, or 100x optical magnification. This system is capable of beam diameters from 0.8 – 5 um. Samples can be packaged or powered using standard needle probes or 125 um spaced G-S-G probes. System contains a temperature controlled Instec heating stage capable of maintaining base temperatures from 300 – 500 K, and x-y-z mapping capabilities.

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A Horiba Jobin Yvon LabRAM HR800 with a back-illuminated-UV coated liquid N2 cooled 2048 x 13.5 um2 pixels CCD featuring an 1800 or 2400 gr/mm grating selection with 325nm, 448nm, or 532nm wavelength excitation source and a selection of 10x, 20x, 50x, and 100x visible objectives, as well as 39x and 40x UV objectives. This system is capable of beam diameters from 0.6 – 5 um. Samples can be packaged and powered via wire bonds. X-Y-Z mapping capabilities with baseplate temperatures from 77 – 500 K are possible.

REFERENCES:

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

The thermal effects of substrate removal on GaN HEMTs using Raman Thermometry

Thermometry of AlGaN/GaN HEMTs Using Multispectral Raman Features

Analysis of the residual stress distribution in AlGaN/GaN high electron mobility transistors