Band Alignment of Sc_xAl_1–xN/GaN Heterojunctions

Abstract

ScAlN is an emergent ultrawide-band-gap material with both a high piezoresponse and demonstrated ferroelectric polarization switching. Recent demonstration of epitaxial growth of ScAlN on GaN has unlocked prospects for new high-power transistors and nonvolatile memory technologies fabricated from these materials. An understanding of the band alignments between ScAlN and GaN is crucial in order to control the electronic and optical properties of engineered devices. To date, there have been no experimental studies of the band offsets between ScAlN and GaN. This work presents optical characterization of the band gap of molecular beam epitaxy grown Sc x Al1–x N using spectroscopic ellipsometry and measurements of the band offsets of Sc x Al1–x N with GaN using X-ray photoemission spectroscopy, along with a comparison to first-principles calculations. The band gap is shown to continuously decrease as a function of increasing ScN alloy fraction with a negative bowing parameter. Furthermore, a crossover from straddling (type-I) to staggered (type-II) band offsets is demonstrated as Sc composition increases beyond approximately x = 0.11. These results show that the ScAlN/GaN valence band alignment can be tuned by changing the Sc alloy fraction, which can help guide the design of heterostructures in future ScAlN/GaN-based devices.

Estimation of the band alignment of metal/AlScN interfaces by hard X-ray photoelectron spectroscopy

“…These values are slightly larger than the results of previous studies. 32) From these results, the energy difference from the binding energy of the Sc 2p core level to the upper edge of the VB of sample #1-2 (AlScN) and sample #1-3 (AlScON) were 398.10 eV and 397.86 eV, respectively. These values are slightly smaller than the results of previous studies, but we believe that they are reasonable considering the small composition of Sc in our sample, i.e., the large bandgap.…”

An Epitaxial Ferroelectric ScAlN/GaN Heterostructure Memory

“…Besides, the conduction band offset between ScAlN with 18% Sc content and GaN is predicted to be ≈1.74 eV from first-principle calculations and ≈2.09 eV by X-ray photoelectron spectroscopy (XPS) measurements. [60,61] Those wide-bandgap characteristics, carrying over to ScAlN from IIInitrides, are expected to help suppress the thermally activated current at high temperatures. Figure 5a first compares the P-V loops at room temperature and at 670 K. A drastic drop of coercive field is observed at 670 K, while the remnant polarization keeps steady, in accordance with previous reports.…”

Strain-Controlled Formation Energy and Migration of Nitrogen Vacancy in Al1–xScxN: A First-Principles Study

“…The continuous advancement of information technology demands the development of storage technologies that can efficiently manage the ever-increasing amount of data. In contrast to conventional semiconductor storage methods, ferroelectric memory storage presents a multitude of advantages including high charge density, low power consumption, rapid access speeds, and nonvolatility. − As a result, ferroelectric memory storage has emerged as a field of great potential for further investigation and development. The key part of ferroelectric memory is the ferroelectric material.…”