2D Oxides Realized via Confinement Heteroepitaxy

Abstract

Novel confinement techniques facilitate the formation of non-layered 2D materials. Here it is demonstrated that the formation and properties of 2D oxides (GaO x , InO x , SnO x ) at the epitaxial graphene (EG)/silicon carbide (SiC) interface is dependent on the EG buffer layer properties prior to element intercalation. Using 2D Ga, it is demonstrated that defects in the EG buffer layer lead to Ga transforming to GaO x with non-periodic oxygen in a crystalline Ga matrix via air oxidation at room temperature. However, crystalline monolayer GaO 2 and bilayer Ga 2 O 3 with ferroelectric wurtzite structure(FE-WZ') can then be formed via subsequent high-temperature O 2 annealing. Furthermore, the graphene/X/SiC (X = 2D Ga or Ga 2 O 3 ) junction is tunable from Ohmic to a Schottky or tunnel barrier depending on the interface species. Finally, using vertical transport measurements and electron energy loss spectroscopy analysis, the bandgap of 2D gallium oxide is identified as 6.6 ± 0.6 eV, significantly larger than that of bulk β-Ga 2 O 3 (≈4.8 eV), suggesting strong quantum confinement effects at the 2D limit. The study presented here is foundational for development of atomic-scale, vertical 2D/3D heterostructure for applications requiring short transit times, such as GHz and THz devices.

Microstructure Evolution and Electrical Behaviors for High-Performance Cu2O/Zr-Doped β-Ga2O3 Heterojunction Diodes

“…Generally, the J – V characteristics can be described by a single-exponential diode model: J = J 0 exp [ q n k T true( V − R J true) ] + G V where V represents the applied voltage, q is the electronic charge, k is the Boltzmann constant, n is the ideality factor, T is the temperature, and G and R represent the parallel conductance and series resistance of the diode, respectively. J 0 is the reverse leakage current density, defined as follows: .25ex2ex J 0 = A * T 2 exp ( − q Φ SB k T ) where A represents the device area, typically defined by the electrodes. A * = 4π qk 2 m * h –3 is the effective Richardson constant, for Cu 2 O is 120 A·K –2 cm –2 , and m * is the effective mass of the holes in Cu 2 O. Φ SB is the barrier height, which can be calculated using the expression involving J 0 : .25ex2ex Φ SB = k T q ln ( A * T 2 J 0 ) …”

“…where V represents the applied voltage, q is the electronic charge, k is the Boltzmann constant, n is the ideality factor, T is the temperature, and G and R represent the parallel conductance and series resistance of the diode, respectively. J 0 is the reverse leakage current density, defined as follows: 54 i k j j j y…”

Elucidating the Mechanism of Large Phosphate Molecule Intercalation Through Graphene-Substrate Heterointerfaces

“…Further inspection and comparison of our XPS core-level spectra to previous reported XPS of indium phosphates suggest that the peaks at 445.8 and 453.3 eV are the In 3d core-levels associated with P–O–In 3d 3/2 and P–O–In 3d 5/2 bonding, respectively. Although the phase of the confined indium phosphate at the graphene-substrate heterointerface was likely in the form of InPO 4 , In­(PO 3 ) 3 and other metastable oxide phases could also form at such confined spaces ,, and therefore are important to investigate in future studies.…”

“…So far, a variety of alloys (Sn 1– x Ge x , Fe 1– x Co x , etc.) and compounds (GaN, − AlN, MoS 2 , PtSe 2 , Ga 2 O 3 , etc.) have been formed at graphene-substrate heterointerfaces via chemical reactions.…”

Stacking Order Effects on the Energetic Stability and Electronic Properties of $N$-Doped Graphene/H-Bn Van Der Waals Heterostructures on Sic(0001)

“…In fact, Al Balushi et al [11] developed an experimental scheme that enhanced the intercalation of Ga and N species below epitaxial graphene on SiC(0001), which allowed for the realization of a 2D-like GaN phase encapsulated between graphene and SiC(0001). This approach has recently been generalized for achieving confined epitaxy of 2D metals as well as oxides at the interface between graphene and SiC(0001) [12,13]. It could in principle also be implemented to controllably create an atomically thin h-BN below epitaxial graphene, which could lead to the electronic decoupling of graphene from the buffer layer/SiC(0001).…”