First-principles study of the thickness-dependent shift current in γ-GeSe thin layers

We investigate the stable structure and optoelectronic properties of thin γ-GeSe layers through first-principles calculations. We examine three stacking configurations (A-A, A-B, and A-C) of adjacent quadruple layers (QLs), revealing the structural stability of A-C stacking. Due to broken inversion symmetry in atomically thin γ-GeSe layers, shift currents are generated, which are very sensitive to their stacking order and thickness. Despite similar optical absorption trends in A-B and A-C stackings, their shift current responses differ significantly. The shift current is notably decreased at odd-number stackings for all cases, attributed to opposite generated flows between the top and bottom surfaces. The analysis of orbital contributions reveals the charge shift's origin in γ-GeSe. We also explore mechanical modifications, such as sliding and strain, demonstrating the tunability of the shift current spectrum in γ-GeSe. This research enhances our understanding of the optoelectronic response in atomically thin materials, providing valuable insights for future applications.