Fig. 4: Structural analysis of GaSe on Al₂O₃ and GaP/Si.

a 15 × 15 µm² AFM image of 175 nm-high, out-of-plane GaSe sheets on GaP/Si. b 2 × 2 µm² AFM image of planar GaSe on Al₂O₃, showing screw dislocations and hexagonal/trigonal edges, with a 1.5× magnified inset of an individual screw dislocation. c SEM image of GaSe on GaP/Si showing sheet-like out-of-plane growth in 〈111〉 directions of GaP substrate. EDX analysis verifies the stoichiometry, yielding a Ga:Se ratio of 1:1, as shown in Fig. S9. d Raman spectra for (a) and (b) show vibrational modes consistent with GaSe, including an additional out-of-plane mode (marked in orange), as reported in literature^{13,24,61,62,63}. Substrate peaks are not marked for clarity but are consistent with reported spectra^{68,69,70,71,72,73}, and the corresponding Raman spectra of the substrates are provided in the Supplementary Information (Fig. S7). e A high-resolution STEM image of the GaP/GaSe interface. The red and cyan squares indicate the regions of GaP and GaSe, respectively, from which FFTs were generated. The FFTs of GaP and GaSe are shown in (f) and (h), respectively. The FFT of the full field of view is shown in (g). The corresponding simulated diffraction patterns are depicted in (i)–(k). To highlight the epitaxial orientation relation, the (002) diffraction spots of each material are marked.