Band Structure and Photoelectric Characterization of GeSe Monolayers

Germanium selenide monolayer is promising in photoelectric applications for its natural p-type semiconductor and complicated band structures. Basic experimental investigations of few-to-monolayer germanium selenide are still absent; major scientific challenge is to develop of techniques for controllably thinned monolayers. In this study laser thinned monolayer germanium selenide on SiO2/Si substrates is demonstrated. A broad photoluminescence spectrum with eight continues peaks is observed from visible to infrared wavebands centered at approximate to 589, 655, 737, 830, 1034, 1178, 1314, and 1456 nm, respectively. First-principle calculations based on density functional theory illuminate the band structures of few-to-monolayer germanium selenide. Photoluminescence investigation combined with first-principle calculations indicates that the indirect to direct bandgap transition happens at few layers of N = 3. Current-voltage and photoresponse characteristics of monolayer based devices show 3.3 times the photosensitivity and much faster falling edges compared with those of the pristine nanosheet based devices. The present results provide useful insight into deep understanding of thickness dependent performances of germanium selenide monocrystalline.