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Momentum relaxation due to polar optical phonons in AlGaN/GaN heterostructures

The momentum relaxation time is a key parameter for semiconductor device performance optimization. The approximation of bulk semiconductor values is used regularly to analyse the experimental performance data from devices such as HFETs and HEMTs to extract parameters such as mobility, cut-off frequency etc. While this is valid for wide channel devices we show for the first time that this approximation is completely inaccurate for narrow channel devices at electron energies close to the LO phonon energy. We also predict a preference for forward scattering, an effect hitherto limited to quantum wires and one source of their superior conductive properties.