Strong effect of scandium source purity on chemical and electronic properties of epitaxial ScxAl1−xN/GaN heterostructures

Abstract

Epitaxial multilayer heterostructures of ScxAl1−xN/GaN with Sc contents x = 0.11–0.45 are found to exhibit significant differences in structural quality, chemical impurity levels, and electronic properties depending on the starting Sc source impurity levels. A higher purity source leads to a 2–3 orders of magnitude reduction in the carbon, oxygen, and fluorine unintentional doping densities in MBE-grown ScxAl1−xN/GaN multilayers. Electrical measurements of ScxAl1−xN/n+GaN single heterostructure barriers show a 5–7 orders of magnitude reduction in the electrical leakage for films grown with a higher purity Sc source at most Sc contents. The measured chemical and electrical properties of epitaxial ScxAl1−xN highlight the importance of the starting Sc source material purity for epitaxial device applications that need these highly piezoelectric and/or ferroelectric transition-metal nitride alloys.

Enhanced AlScN/GaN Heterostructures Grown with a Novel Precursor by Metal–Organic Chemical Vapor Deposition

“…Impurities in the Sc source were proven to have a strong negative effect on the chemical and electronic properties of AlScN/GaN heterostructures grown by MOCVD [ 17 ] and MBE [ 27 ] . In MOCVD growth, impurities can be introduced not only by a poorly purified source material but also by the precursor molecule itself.…”

“…High impurity concentrations in the precursor, such as oxygen or metal traces, lead to high , low and low μ in HEMT structures grown by MOCVD, especially at low growth temperatures of 900 and 1000 °C, [ 17 ] as well as to the degradation of the electrical properties of AlScN/n‐GaN heterostructures grown by MBE. [ 27 ] Furthermore, the interface abruptness affects the electrical performance. This is directly related to the growth temperature.…”

“…A passivated MBE‐grown structure with very high of 6.2 × 10 13 and low μ of 340 was demonstrated, [ 11 ] as well as an unpassivated structure with very high μ of 1556 and moderate of 2.4 × 10 13 . [ 27 ] The sheet resistances were 294 and 167 Ω sq −1 , respectively. With as Sc precurser, we managed to achieve a very low sheet resistance of 172Ω sq −1 at both high and μ.…”

Effect of AlN and AlGaN Interlayers on AlScN/GaN Heterostructures Grown by Metal–Organic Chemical Vapor Deposition

“…46 We speculate that the oxygen content was considerably reduced with respect to the research grade (rg) Cp 3 Sc we used so far and will refer to it as electronic grade (eg) Cp 3 Sc. Considering that the Sc source was found to introduce considerable amounts of nonintentional oxygen into the AlScN films grown by MBE 47 and that the scandium source purity was found to have a strong effect on chemical and electronic properties of AlScN/ GaN heterostructures, 48 we expect an increased performance of the grown AlScN HEMT structures. Both 4-in.…”

Direct Observation of Al Migration Enhancement by Changing the Al and N Source Relative Position in the Molecular Beam Epitaxy of AlGaN Nanowires

“…Epitaxial compound semiconductors have been the driving force for the development of modern electronic and photonic devices, with examples including InGaAs-based III–V materials by MBE and their application to near-infrared (IR) photonic devices that have become the backbone of modern optical communication technologies, GaN-based III-nitride materials by metal–organic vapor phase epitaxy (MOVPE) and their application to blue LEDs and lasers that have changed how we illuminate our world today, and so on. − On the other hand, the past decade has witnessed rapid growth in the study of the epitaxy of technologically important Al-containing nitride semiconductors, including AlGaN, AlN, and AlScN. − AlN is the material of choice for a wide range of applications such as radio frequency (RF) electronics, light emission, and buffer layers for AlGaN-based ultraviolet (UV) LEDs. − On the other hand, AlGaN has become an irreplaceable material in the development of high-efficiency, compact, far-UVC light sources that are able to deactivate viruses and in the meantime are safe for human exposure. − More intriguingly, by incorporating scandium (Sc) into AlN, it can further lead to novel ferroelectric properties; − ,− in fact, AlScN is an extremely appealing material platform for the development of multifunctional ferroelectric, electronic, and photonic devices in a single semiconductor platform.…”