Atomically thin GaSe has been predicted to have a non-parabolic, Mexican hat-like valence band structure due to the shift of the valence band maximum (VBM) near the Γ point which is expected to give rise to novel, unique properties such as tunable magnetism, high effective mass suppressing direct tunneling in scaled transistors, and an improved thermoelectric figure of merit. However, the synthesis of atomically thin GaSe remains challenging. Here, we report on the growth of atomically thin GaSe by molecular beam epitaxy (MBE) and demonstrate the high quality of the resulting van der Waals epitaxial films. The full valence band structure of nominal bilayer GaSe is revealed by photoemission electron momentum microscopy (k-PEEM), confirming the presence of a distorted valence band near the Γ point. Our results open the way to demonstrating interesting new physical phenomena based on MBE-grown GaSe films and atomically thin monochalcogenides in general.

由于价带最大值（VBM）在Γ点附近的移动，已预测原子薄GaSe具有非抛物线形，墨西哥帽状的价带结构，这有望产生新颖，独特的特性，例如可调谐磁性，抑制大规模晶体管中直接隧穿的高效质量以及改进的热电性能。然而，原子上薄的GaSe的合成仍然具有挑战性。在这里，我们报道了通过分子束外延（MBE）原子上薄的GaSe的生长，并证明了所得范德华外延膜的高质量。标称双层GASE的全价电子带结构由光电发射电子动量显微镜（揭示ķ-PEEM），确认在Γ点附近存在扭曲的价带。我们的研究结果为展示基于MBE生长的GaSe薄膜和一般来说原子薄的单硫族化物的有趣的新物理现象开辟了道路。