Study and characterization of GaN MOS capacitors: planar versus trench topographies

TL;DR

This study compares planar and trench GaN MOS capacitors, revealing how etching and trench formation influence dielectric robustness, trapping behavior, and device performance, providing insights for optimizing GaN-based power transistors.

Contribution

It offers a detailed analysis of how etching and trenching affect GaN MOS capacitor interfaces, trapping, and breakdown, guiding improved device fabrication.

Findings

Blanket etching does not degrade dielectric robustness.

Trench etching improves reproducibility but reduces breakdown voltage.

Trench structures maintain >20 V for 10-year lifetime.

Abstract

Developing high quality GaN/dielectric interfaces is a fundamental step for manufacturing GaN vertical power transistors. In this paper, we quantitatively investigate the effect of planar etching treatment and trench formation on the performance of GaN-based MOS (metal oxide semiconductor) stacks. The results demonstrate that (i) blanket etching the GaN surface does not degrade the robustness of the deposited dielectric layer; (ii) the addition of the trench etch, while improving reproducibility, results in a decrease of breakdown performance compared to the planar structures. (iii) for the trench structures, the voltage for a 10 years lifetime is still above 20 V, indicating a good robustness. (iv) To review the trapping performance across the metal-dielectric-GaN stack, forward-reverse capacitance-voltage measurements with and without stress and photo-assistance are performed. Overall, as-grown planar capacitors devoid of prior etching steps show lowest trapping, while trench capacitors have higher interface trapping, and bulk trapping comparable to the blanket etched capacitors. (v) The nanostructure of the GaN/dielectric interface was characterized by high resolution scanning transmission electron microscopy (HR-STEM). An increased roughness of 2-3 monolayers at the GaN surface was observed after blanket etching, which was correlated to the higher density of interface traps. The results presented in this paper give fundamental insight on how the etch and trench processing affects the trapping and robustness of trench-gate GaN-MOSFETs, and provide guidance for the optimization of device performance.