Abstract
In this paper, several epitaxial variations influencing the two-dimensional electron gas (2DEG) in AlGaN/AlN/GaN heterostructures are investigated. The effects of an n-doped AlGaN barrier and of the AlN spacer thickness are studied by examining the sheet electron density (ns) and the mobility (µs) of the 2DEG using ID(VG) and C(VG) measurements, and 1D Schrödinger-Poisson (1DSP) simulations. Specifically, the correlations between the resistance, µs, ns and the polarization interface charges (σ) are studied. Besides the well-reported benefits of the AlN spacer on ns, we show that a thicker AlN spacer leads to larger ns due to the enhancement of the AlN polarization. In addition, we prove experimentally that an n-doped AlGaN barrier does not significantly improve the 2DEG density but leads to the formation of a second channel in the AlGaN barrier for negative gate voltage (VG ≤ 0 V), driving the overall improvement of the resistance.
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