Local phonon analysis in InGaN film by mapping of Raman peak energy

Since heat generation in electronic devices induces the degradation of performance, the understanding of their thermal properties is required. InGaN and AlInN alloys are possibly the key materials for optical devices in green gap and high power transistors. Characteristic properties of local strain, fluctuation of energy gap, carrier dynamics, and so forth due to spatial nonuniformity of alloy composition are now under investigation, while nonuniform thermal conduction remains unclear. In this report we show nonuniform heat or phonon conductance in the nonuniform field of InGaN alloy composition. An In
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Ga
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N (110nm) film grown on GaN grown on a sapphire substrate was characterized by micro Raman spectroscopy with controlling spot positions of two color lasers: 325nm for electronic excitation and phonon generation and 532nm for Raman probe. Thermal properties were analyzed by two-dimensional mapping of Raman signal by 532 nm line and its energy shift by introducing the 325nm line. It is found that the phonon transport mainly takes place along the region with low GaN mole fraction or low phonon energy, while some of phonons are transported through narrow regions with higher GaN mole fraction. This pump and probe Raman method gives us phonon transport properties in semiconductors.