Experimental Evidence of Large Bandgap Energy in Atomically Thin AlN

Abstract

Ultrathin III-nitrides beyond BN, such as GaN and AlN, have attracted much research interest due to their potential applications in 2D optoelectronic devices. Taking advantage of the atomic thickness, the bandgap is expected to be widened in these thin films due to quantum confinement. As a promising intrinsic dielectric and tunneling layer for optoelectronic devices, ultrathin freestanding AlN structures have not been systematically studied, and the band structure still remains in the theoretical description. In this work, atomically thin hexagonal AlN nanotubes with controllable wall thickness have been fabricated via selective thermal evaporating the GaN/AlN core/shell nanowires, where the GaN cores entirely decomposed and are removed from the bottom open end while the robust AlN shells remain and form tubular structures. The bandgap energy of 9.2±0.1 eV is confirmed through spectrally resolved X-ray photoelectron spectroscopy and spatially resolved electron energy loss spectroscopy measurements on AlN nanotubes with the wall thickness of two monolayers.

Giant excitonic absorption and emission in two-dimensional group-III nitrides

“…Measurements of GaN sheets encapsulated in graphene seem to suggest a fundamental optical gap of about 5 eV 10 . Gaps even larger than in BN have been found for low-dimensional AlN structures 9 . These successful experiments pave the way to new photovoltaic and optical nanodevices based on 2D nitrides 11 .…”

“…Only monolayer BN can, in principle, be easily prepared by exfoliation from hexagonal bulk BN 6 . Promising experimental attempts to obtain 2D AlN and GaN recently appeared [7][8][9] . Measurements of GaN sheets encapsulated in graphene seem to suggest a fundamental optical gap of about 5 eV 10 .…”

Research development of 2D materials based photodetectors towards mid‐infrared regime

“…Secondly, the introduction of a novel gain mechanism that is different from the photogating effect could be an optional method so as to reduce the negative impact on the device operating speed and to promote mid‐infrared band light absorption. Thirdly, it has been demonstrated that by introducing external modifications, such as quantum confinement, [ 101–105 ] pressure, [ 106–109 ] mechanical strain [ 110–118 ] , and chemical doping means, [ 119–123 ] can significantly extend the spectral response of 2D materials, and tune the performance of 2D materials based photodetectors.…”

Infinite possibilities of ultrathin III-V semiconductors: Starting from synthesis

“…Taking advantage of the atomic-thin thickness, the generation of quantum confinement effect in ultrathin III-V semiconductors leads to a wider band gap, such as GaN, AlN, InN, InP, and InSb ( Brus, 1984 ). It has been reported that the band gap of 2D AlN is about 9.2 eV while the band gap of its bulk counterparts is only 6.2 eV, which endows it with the ability to be used in UV photoelectric devices ( Wang et al., 2019a , 2019b ). The band gap of 2D GaN is wider than that of bulk counterparts which have also been discovered in the experiment ( Al Balushi et al, 2016 ).…”