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Transport in GaN-based nanoscale devices is of supreme importance for various applications. While the transport in bulk and two-dimensional (2D) structures is relatively well understood, understanding one-dimensional (1D) transport is still at its nascent stage. More importantly, the nanoscale structures may not operate at an explicit dimension of 2D and 1D. The understanding of the transport becomes limited on such an occasion. Here, we investigate the evolution of lowfield mobility in GaN-based nanostructures for increasing quantum confinement in a uniform framework. We have used a split-gate architecture to change the degree of quantum confinement electrostatically. The low-field mobility is experimentally determined, which is then matched using scattering theory. It is shown that acoustic phonon, polar optical phonon, and scattering from piezoelectric fields dominate these devices. Contrary to intuition, the piezoelectric fields play the most determining role in low-field regimes. In addition, the evolving density of states and 2D phonon confinement, in addition to electron confinement, lead to a non-monotonic change in mobility. A decrease in the number of states near conduction band minima tends to increase mobility by reducing the number of final scattering states for the electrons. A larger overlap between confined electrons and phonons aggravates scattering and reduces mobility. These two competing effects can lead to many possible values for mobility during device operation.

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Herein, Ta2O5 high‐k gate dielectric‐based GaN high electron‐mobility transistors (HEMTs) with a high I ON/I OFF ratio and low gate leakage current are demonstrated without any significant deterioration of the other performance parameters. Ta2O5 with an average surface roughness of 1.8 nm and a dielectric constant of ≈26 are grown by sputtering and annealing in O2. The bandgap, valence, and conduction band offsets with Al0.3Ga0.7 N are 4.85, 0.24, and 0.61 eV, respectively. The reverse gate leakage current at −7 V is observed to be 1.2 ×10−10 A mm−1 for 5 nm and <1.0×10−11 A mm−1 for 20 and 30 nm oxide thickness compared to 5.0 × 10−6 A mm−1 for the control sample. This current is among the lowest ever reported for GaN‐based oxide‐HEMTs without significantly sacrificing other performances. The I ON/I OFF ratio is 2 × 109, 7 × 109, and 1  × 10 for 5, 20, and 30 nm oxide thickness, respectively, as compared to 2 × 108 for the control sample. The interface–state–density is estimated to be 1.5 × 1013 cm−2 eV−1. I DS,sat is measured to be 710, 700, and 690 mA mm−1 for 5, 20, and 30 nm Ta2O5 thickness, respectively, compared to 725 mA mm−1 for the control sample. The presence of oxide does not change the other characteristics much.

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