van der Waals Epitaxy of GaSe/Graphene Heterostructure: Electronic and Interfacial Properties

Abstract

Stacking two-dimensional materials in so-called van der Waals (vdW) heterostructures, like the combination of GaSe and graphene, provides the ability to obtain hybrid systems which are suitable to design optoelectronic devices. Here, we report the structural and electronic properties of the direct growth of multilayered GaSe by Molecular beam Epitaxy (MBE) on graphene. Reflection high-energy electron diffraction (RHEED) images exhibited sharp streaky features indicative of high quality GaSe layer produced via a vdW epitaxy. Micro-Raman spectroscopy showed that, after the vdW hetero-interface formation, the Raman signature of pristine graphene is preserved. However, the GaSe film tuned the charge density of graphene layer by shifting the Dirac point by about 80 meV toward lower binding energies, attesting an electron transfer from graphene to GaSe. Angle-resolved photoemission spectroscopy (ARPES) measurements showed that the maximum of the valence band of few layers of GaSe are located at the Γ point at a binding energy of about -0.73 eV relatively to the Fermi level (p-type doping). From the ARPES measurements, a hole effective mass defined along the ΓM direction and equal to about m*/m0 = -1.1 was determined. By coupling the ARPES data with high resolution X-ray photoemission spectroscopy (HR-XPS) measurements, the Schottky interface barrier height was estimated to be 1.2 eV. These findings allow deeper understanding of the interlayer interactions and the electronic structure of GaSe/graphene vdW heterostructure.

Large-grain MBE-grown GaSe on GaAs with a Mexican hat-like valence band dispersion

“…Our results clearly show the sharp interface without indication of inter-diffusion which is in line with the reported in situ XPS experiments 16 and a recent study of MBEgrown GaSe on graphene. 17,19 In a high-magnification crosssectional STEM image, Fig. 2c, we have measured an interlayer spacing c/2 of~0.8 nm, which is consistent with the height measurements obtained using an AFM.…”

“…12 Although the synthesis of GaSe by molecular beam epitaxy (MBE) can be traced back to early 1990's, [13][14][15][16] the atomically thin nature of GaSe has been much less studied, and the studies of electronic properties were mostly based on the bulk material. 17 Here, we address the main difficulties related to the growth of atomically thin and high-quality GaSe. First is the random orientation of as-grown films, which can take place during the growth.…”

Single‐Crystal Hybrid Perovskite Platelets on Graphene: A Mixed‐Dimensional Van Der Waals Heterostructure with Strong Interface Coupling

“…Since G and 2D band positions are sensitively dependent on the carrier concentration, they can be used to probe the graphene doping level 33–37. Clearly, compared to the uncovered graphene, the covered one displays blue‐shifted G and 2D bands.…”

“…Clearly, compared to the uncovered graphene, the covered one displays blue‐shifted G and 2D bands. The blue‐shifted 2D band indicates p ‐type doping to graphene after the growth of MAPbBr 3 platelets 35,36. Furthermore, the Fermi level of graphene ( E F ) can be derived from the shift of the G band wavenumber (ω G ) based on the formula of ω G − 1580 = | E F | × 42 cm −1 eV −1 35,36.…”

“…The carrier density can be estimated from the corresponding Fermi energies. The relationship between the carrier density N and the Fermi level E F of graphene is | E F | = ℏ v F (π | N |) 1/2 , where v F is the Fermi velocity of the linear band and ℏ is the reduced Planck constant 35,36. Using a Fermi velocity of v F = 1.1 × 10 6 m s −1 , the hole densities for graphene with and without the growth of MAPbBr 3 platelets are 4.9 × 10 11 and 8.0 × 10 12 cm −2 , respectively.…”