Low Leakage Ferroelectric Heteroepitaxial Al$_{0.7}$Sc$_{0.3}$N Films on GaN

TL;DR

This study demonstrates that high-quality epitaxial Al0.7Sc0.3N ferroelectric films on GaN exhibit significantly lower leakage currents than previously reported, challenging the assumption that crystalline mosaicity directly correlates with leakage.

Contribution

It reveals that crystalline mosaicity does not dominate leakage current in Al0.7Sc0.3N stacks and reports record low leakage currents in high-quality epitaxial ferroelectric films.

Findings

Leakage current is not dominated by crystalline mosaicity.

Record low leakage current of 0.07 A/cm² achieved.

Structural quality on InGaN buffers affects leakage characteristics.

Abstract

Wurtzite (Al,Sc)N ferroelectrics are attractive for microelectronics applications due to their chemical and epitaxial structural compatibility with wurtzite semiconductors such as GaN and (Al,Ga)N. However, the leakage current in epitaxial stacks reported to date should be reduced for reliable device operation. Following the tradition of other semiconductor heterostructures, crystalline structural quality, as measured by breadth of diffraction peaks and correlating with dislocation density, is commonly used as a proxy for leakage current, but we demonstrate here that the crystalline mosaicity that dominates the broadening of diffraction peaks in epitaxial Al$_{0.7}$Sc$_{0.3}$N stacks does not dominate leakage current. We report here well-saturated ferroelectric hysteresis loops and orders of magnitude lower leakage current (0.07 A cm$^{-2}$) compared to values reported in literature (1 ~ 19 A cm$^{-2}$) for sputter-deposited epitaxial Al$_{0.7}$Sc$_{0.3}$N/GaN of comparable crystalline quality to prior reports. Further, we show Al$_{0.7}$Sc$_{0.3}$N on lattice-matched InGaN buffers with improved structural characteristics exhibits increased leakage characteristics. This demonstration and understanding can help to guide further efforts towards reliable wurtzite ferroelectric devices and prioritize approaches targeting further leakage current reduction.