Molecular beam epitaxy of 2D-layered gallium selenide on GaN substrates

Abstract

Large area epitaxy of two-dimensional (2D) layered materials with high material quality is a crucial step in realizing novel device applications based on 2D materials. In this work, we report high-quality, crystalline, large-area gallium selenide (GaSe) films grown on bulk substrates such as c-plane sapphire and gallium nitride (GaN) using a valved cracker source for Se. (002) While six-fold symmetry was maintained in the two step growth, β-GaSe phase was observed in addition to the dominant ε-GaSe in cross-sectional scanning transmission electron microscopy images. This work demonstrates the potential of growing high quality 2D-layered materials using molecular beam epitaxy and can be extended to the growth of other transition metal chalcogenides.

Atomistic study of GaSe/Ge(111) interface formed through van der Waals epitaxy

“…Since the positions of the new streaks compared with those of the Ge(111) streaks are consistent with the lattice constant difference between GaSe(0001) and Ge(111), which are 3.75 Å and 4.00 Å, respectively, it indicates that the GaSe thin film is growing on Ge(111) with the epitaxial relationship GaSe(0001) // Ge (111) and GaSe [11][12][13][14][15][16][17][18][19][20] // Ge [1][2][3][4][5][6][7][8][9][10]. As the growth proceeds, the Ge(111)-(1 × 1) streaks fade out and, in contrast, the GaSe(0001)-(1 × 1) streaks gradually become clearer and sharper ( Figure 1D).…”

“…So far, GaSe has been used in metal‐oxide‐semiconductor field‐effect transistors and photodetectors . By vdWE, the growth of GaSe has been reported on many substrates including WS 2 , MoSe 2 , Si(111), Si(110), Si(100), GaAs(111), GaAs(110), GaAs(100), c‐sapphire, and GaN(0001) …”

“…We investigated the growth of GaSe on Ge(111) by MBE and determined the atomistic structure of the thin film near the interface using HAADF-STEM and EELS. It was revealed that GaSe thin films can be grown on Ge(111) with GaSe(0001) // Ge(111) and GaSe [11][12][13][14][15][16][17][18][19][20] // Ge [1][2][3][4][5][6][7][8][9][10], and the Ge(111) surface is terminated by a half GaSe monolayer, on which the GaSe thin film is grown through vdWE. The grown layers adopt predominantly the expected wurtzite-like structure but monolayers with a zinc blende-like structure are locally observed near the film-substrate interface, which has not been reported previously.…”

“…No growth temperature dependence was observed up to 525°C, while at 550°C, only the Ge(111)-(1 × 1) pattern is visible during the growth which suggests that at this substrate temperature, the growth of GaSe does not occur. GaSe [11][12][13][14][15][16][17][18][19][20] // Ge [1][2][3][4][5][6][7][8][9][10] between the thin film and the substrate (Figure 2A). In addition to the expected ε-type stacking which is the most thermodynamically stable one 17 (Figure 2B), we found that other stacking types of GaSe monolayers can be formed near the interface.…”

“…5,8 By vdWE, the growth of GaSe has been reported on many substrates including WS 2 , 9 MoSe 2 , 10 Si(111), Si(110), Si(100), 11 GaAs(111), 12,13 GaAs(110), 14 GaAs(100), 13 c-sapphire, 15 and GaN(0001). 16 In the present study, we investigated the growth of GaSe on Ge(111) by molecular beam epitaxy (MBE). The atomistic structure of the film-substrate interface and the surface was investigated in order to understand the effects of the interface on the structure of thin films formed through vdWE.…”