Abstract
Two-dimensional AIIIBVI layered semiconductors have recently attracted great attention due to their potential applications in piezo-phototronics and optoelectronics. Here, we report the temperature-dependent photoluminescence (PL) of strained and unstrained GaSe flakes. It is found that, as the temperature increases, the PL from both the strained (wrinkled) and unstrained (flat) positions show a prominent red-shift to low energies. However, for the flat case, the slope of PL energy versus temperature at the range of 163–283 K is about −0.36 meV/K, which is smaller than that of the wrinkled one (−0.5 meV/K). This is because more strain can be introduced at the freestanding wrinkled position during the temperature increase, thus accelerates the main PL peak (peak I, direct band gap transition) shift to lower energy. Additionally, for the wrinkled sheet, three new exciton states (peaks III, IV, and V) appear at the red side of peak I, and the emission intensity is highly dependent on the temperature variation. These peaks can be attributed to the bound exciton recombination. These findings demonstrate an interesting route for optical band gap tuning of the layered GaSe sheet, which are important for future optoelectronic device design.
Highlights
Two-dimensional (2D) layered crystals such as graphene have been intensively investigated in the past decade due to their attractive mechanical, electrical, optical, and chemical properties that are absent in the corresponding bulk counterparts [1,2,3,4,5]
It has been shown that the electronic band structures and PL intensity of layered Gallium selenide (GaSe) can be effectively tuned via the elastic strain engineering [18,19,20]
Wecentral assumelayer that within the GaSe remains unstrained, while unstrained, the outer curved of the sheetsurface is stretched the central layerstack within the GaSe stack remains whilesurface the outer curved of the by ε and the inner by curved is compressed by −ε
Summary
Two-dimensional (2D) layered crystals such as graphene have been intensively investigated in the past decade due to their attractive mechanical, electrical, optical, and chemical properties that are absent in the corresponding bulk counterparts [1,2,3,4,5]. Gallium selenide (GaSe) is a representative layered AIII BVI binary chalcogenides, and is an intriguing semiconductor with an indirect band gap of 2.11 eV and a direct band gap of only 25 meV higher [11,12,13] It demonstrates interesting electrical and optical properties, such as a high on/off ratio [7,14], large anisotropic Hall mobility [7,15], good gas sensibility [16], and strong second-harmonic generation [17]. It has been shown that the electronic band structures and PL intensity of layered GaSe can be effectively tuned via the elastic strain engineering [18,19,20] These flexible electrical and optical properties make it an appealing candidate for mechanically compliant optoelectronics with applications in piezo-phototronics, optoelectronics, wearable devices and human–machine interfaces [21,22,23,24].
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