Toward Air Stability of Thin GaSe Devices: Avoiding Environmental and Laser‐Induced Degradation by Encapsulation

Abstract

Gallium selenide (GaSe) is a novel 2D material, which belongs to the layered III-VIA semiconductors family and attracted interest recently as it displays single-photon emitters at room temperature and strong optical nonlinearity. Nonetheless, few-layer GaSe is not stable under ambient conditions and it tends to degrade over time. Here atomic force microscopy, Raman spectroscopy, and optoelectronic measurements are combined in photodetectors based on thin GaSe to study its long-term stability. It is found that the GaSe flakes exposed to air tend to decompose forming first amorphous selenium and Ga 2 Se 3 and subsequently Ga 2 O 3 . While the first stage is accompanied by an increase in photocurrent, in the second stage, a decrease in photocurrent is observed, which leads to the final failure of GaSe photodetectors. Additionally, it is found that the encapsulation of the GaSe photodetectors with hexagonal boron nitride (h-BN) can protect the GaSe from degradation and can help to achieve long-term stability of the devices.

Solution‐Processed GaSe Nanoflake‐Based Films for Photoelectrochemical Water Splitting and Photoelectrochemical‐Type Photodetectors

“…Additionally, the Raman spectra of GaSe crystals and exfoliated flakes do not present signatures attributed to Ga 2 Se 3 , Ga 2 O 3 , and amorphous/crystalline Se (a‐/c‐Se) modes, which are observed at ≈155, ≈200, and between 135–160 cm −1 , respectively. This indicates that the LPE of GaSe crystals in anhydrous IPA does not cause significant additional surface oxidation of the native material . This conclusion is further supported by X‐ray photoelectron spectroscopy (XPS) analysis (Figures S4 and S5 and Tables S2–S7, Supporting Information).…”

“…Despite these encouraging driving factors, the PEC properties of GaSe are still experimentally uncharted. A certain reluctance to study the (photo)electrochemical properties of GaSe and other group‐III monochalcogenides undoubtedly originated from their tendency to undergo surface oxidation . The latter can occur either in a two‐step reaction: 1) GaSe + 1/4O 2 = 1/3Ga 2 Se 3 + 1/6Ga 2 O 3 followed by Ga 2 Se 3 + 3/2O 2 = Ga 2 O 3 + 3Se; or in a single‐step reaction: 2) GaSe + 3/4O 2 = 1/2Ga 2 O 3 + Se .…”

“…To prove our theoretical predictions, GaSe nanoflakes were prepared in liquid dispersion by means of a viable and environmentally friendly liquid‐phase exfoliation (LPE) of synthetized bulky crystals in anhydrous 2‐Propanol (IPA). Due to its scalability, the LPE method is suitable for applications in which large amounts of material are needed, overcoming the low‐throughput suffered by micromechanical cleavage‐based exfoliation and bottom‐up nanomaterial synthesis (e.g., CVD), which are typically exploited for fundamental studies, including those on photodetectors . The as‐produced GaSe nanoflakes were exploited as solution‐processable materials for PEC water splitting and PEC‐type photodetectors in aqueous electrolytes.…”

Controlling Defects in Continuous 2D GaS Films for High‐Performance Wavelength‐Tunable UV‐Discriminating Photodetectors

“…This also explains why stoichiometric GaS crystals show greatly enhanced stability under laser and UV light. As a conjecture, the degradation could be greatly suppressed by encapsulation or inert gas protection, as have been shown to be effective in GaSe and GaTe . Second, the degradation rate of GaS 0.87 crystals varies with thickness.…”

“…Jannatul et al used Raman spectroscopy to show that both Te metals and tellurium oxides form on the surface of layered GaTe crystals due to rapid oxidation . Recently, Zhao et al demonstrated that GaSe begins to degrade within hours on exposure to air into amorphous selenium, Ga 2 Se 3 , and Ga 2 O 3 . However, the degradation chemistry for each material is different, and more studies are needed for the increasing new members of 2D family.…”