In this paper, low-frequency noise characteristics of commercial AlGaN/GaN high electron mobility transistors with different substrates and devices with and without a p-GaN gate layer are measured and discussed. The noise power spectral density (PSD) of various devices are compared and analyzed under linear-region operation. The 1/f noise behavior exhibits carrier number fluctuation as the dominant cause. Devices with p-GaN gate layer fabricated on Si substrate show the highest normalized noise PSD. Results show that not only flicker noise (1/f noise) exists but that it also accompanied by generation–recombination noise (g–r noise) in the device on SiC substrate. The extracted g–r noise related traps show an activation energy of ∼0.37 eV, which is mostly caused by spatial charges trapping/detrapping with the deep acceptor in the GaN buffer layer.

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