Wafer‐Scale Two‐Dimensional Semiconductors for Deep UV Sensing

Abstract

Abstract2D semiconductors (2SEM) can transform many sectors, from information and communication technology to healthcare. To date, top‐down approaches to their fabrication, such as exfoliation of bulk crystals by “scotch‐tape,” are widely used, but have limited prospects for precise engineering of functionalities and scalability. Here, a bottom‐up technique based on epitaxy is used to demonstrate high‐quality, wafer‐scale 2SEM based on the wide band gap gallium selenide (GaSe) compound. GaSe layers of well‐defined thickness are developed using a bespoke facility for the epitaxial growth and in situ studies of 2SEM. The dominant centrosymmetry and stacking of the individual van der Waals layers are verified by theory and experiment; their optical anisotropy and resonant absorption in the UV spectrum are exploited for photon sensing in the technological UV‐C spectral range, offering a scalable route to deep‐UV optoelectronics.

Review of Nanolayered Post-transition Metal Monochalcogenides: Synthesis, Properties, and Applications

“…54 Recently, a novel γ′-GaSe with a centrosymmetric space group of D 3d and a γ-type stacking sequence has been experimentally observed by Grzonka et al 29 Its inversion symmetry makes it particularly useful in optoelectronic applications. 55 GaS has a unit cell of a = b = 3.587 Å and c = 15.492 Å. 27 There is only one polytype of GaS, β-GaS, which has a similar P6 3 /mmc space group to β-GaSe.…”

“…Due to the poor wettability of Ga atoms on sapphire, Yu et al 86 proposed a three-step growth method to improve the quality of atomically thin GaSe films (≤3 layers). In addition, Shiffa et al 55 obtained the pure γ′-GaSe polytype on a sapphire substrate using MBE. This is the first experimental report of the synthesis of this polytype using any synthesis method.…”

“…The recently reported γ′-GaSe with a centrosymmetric unit cell shows resonant ultraviolet (UV) absorption and optical anisotropy, making it effective for deep UV (200−280 nm) sensing. 55 GaSe can not only serve as a photodetector for visible and UV light, but also as an excellent material for nonlinear optical devices due to its large nonlinear optical coefficient of 54 pmV −1 . 97 Finally, GaTe nanosheetbased photodetectors show high sensitivity and high photoresponsivity in the 254−700 nm range, reaching a peak value of 274.1 AW −1 at 490 nm with a comparable specific photodetectivity of 10 12 Jones.…”

“…AB stacking has been found to be more stable than AA′ stacking, so ε-GaSe (ABAB) is the most widely studied type, followed by γ-GaSe (ABCABC) . Recently, a novel γ′-GaSe with a centrosymmetric space group of D 3d and a γ-type stacking sequence has been experimentally observed by Grzonka et al Its inversion symmetry makes it particularly useful in optoelectronic applications …”

“…Additionally, Yuan et al grew GaSe flakes on n-type Si substrates using MBE, forming a p-n heterojunction to fabricate photodiodes with stable rectifying performance and high photoresponsivity. The recently reported γ′-GaSe with a centrosymmetric unit cell shows resonant ultraviolet (UV) absorption and optical anisotropy, making it effective for deep UV (200–280 nm) sensing . GaSe can not only serve as a photodetector for visible and UV light, but also as an excellent material for nonlinear optical devices due to its large nonlinear optical coefficient of 54 pmV –1 .…”