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 low-field 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.
Keywords: 2D to 1D; HEMT; density of states; low-field mobility; nanowire; phonon confinement; quantum confiment.
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