Abstract
Epitaxial AlGaN/GaN/AlGaN-on-Si high-electron mobility structures with and without carbon doping have been studied. By considering the donor density required to suppress a 2D hole gas in the undoped structure, we demonstrate that the $2 \times 10^{19}$ cm−3 substitutional carbon incorporated during metal-organic chemical vapor deposition must be a source of donors as well as acceptors, with a donor to acceptor ratio of at least 0.4. This compensation ratio was determined based on the comparison of substrate bias experiments with TCAD simulations. This value, which was previously unknown, is a key parameter in GaN power switching high- electron- mobility transistors, since it determines the resistivity of the layer used to suppress leakage and increase breakdown voltage.
Highlights
G ALLIUM nitride is a key material system for efficient, high-power electronic devices
Current theoretical results suggest that the key levels for substitutional carbon are an acceptor state for the nitrogen site (CN) with a level of EV + 0.9 eV for GaN increasing to EV + 1.88 eV for AlN [5]–[7], and a donor state in or near the conduction band for the Ga site in Manuscript received December 22, 2017; revised February 1, 2018; accepted February 26, 2018
In the carbon-doped sample, the 2D electron gas (2DEG) density depleted roughly linearly with applied negative substrate bias, very close to that expected for back-gating, if the epitaxial stack were behaving as an insulating dielectric layer
Summary
G ALLIUM nitride is a key material system for efficient, high-power electronic devices. In AlGaN/GaN highelectron-mobility transistors, carbon is inevitably present in low densities as an unintentional dopant [1] but often intentionally incorporated in high densities to suppress buffer conduction and increase breakdown voltage [2], [3]. Current theoretical results suggest that the key levels for substitutional carbon are an acceptor state for the nitrogen site (CN) with a level of EV + 0.9 eV for GaN increasing to EV + 1.88 eV for AlN [5]–[7], and a donor state in or near the conduction band for the Ga site in Manuscript received December 22, 2017; revised February 1, 2018; accepted February 26, 2018.
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