Laser power-induced Fermi-level shift in graphene/Al₂O₃ under ambient atmosphere: Toward neutralizing unintentional graphene doping

Manipulating unintentional doping in graphene layers, which is influenced by environmental factors and supporting substrates, is of significant concern for the performance and advancement of graphene-based devices. In this context, laser-induced tuning of charge carriers in graphene facilitates the exploration of graphene’s properties in relation to its surroundings and enables laser-assisted functionalization. This has the potential to advance optoelectronic devices that utilize graphene on transparent dielectric substrates, such as Al₂O₃. In this work, laser power (P_L) in Raman spectroscopy is used as a convenient contactless tool to manipulate and control unintentional carrier concentration and Fermi level position (E_F) in graphene/α-Al₂O₃ (G/Al₂O₃) under ambient conditions. Samples are annealed at 400 °C for two hours in an (Ar + H₂) atmosphere to remove any chemical residues. Analysis of the peak frequency (ω) and full width at half maximum (Γ) of the G and 2D bands show that G/Al₂O₃ layers initially exhibit p-type doping, with E_F located at ∼ 100 meV below its Dirac charge-neutral point (DCNP). Increasing P_L results in effective carrier manipulation and raises E_F above DCNP. No significant internal stress is produced due to P_L, as inferred from the strain-sensitive G* band of graphene. Raman analysis of three successive cycles reveals hysteretic behavior from cycle to cycle, which is commonly reported to be limited by the type and density of the existing unintentional doping. Because of the ubiquitous nature of unintentional doping in graphene, manipulating it using contactless laser power to realize the desired graphene properties would be one of the best available practical approaches.