Crystalline BeO Grown on 4H-SiC via Atomic Layer Deposition: Band Alignment and Interface Defects

Abstract

A crystalline beryllium oxide (BeO) film was grown on 4H-silicon carbide (4H-SiC) via thermal atomic layer deposition (ALD). Diethylberyllium and water were used as key precursors. The growth rate of BeO corresponded to 0.8 Å/cycle over the temperature range of 150–200 °C. Transmission electron microscopy and X-ray diffraction of BeO/4H-SiC demonstrated that wurtzite BeO (0002) was grown on 4H-SiC (0001) substrate. The average crystallite sizes of BeO were 15–16 nm, and the compressive strain was applied to the BeO film in the out-of-plane direction. The band alignment and interface defects of BeO/4H-SiC were determined by using internal photoemission spectroscopy (IPE), ultraviolet photoelectron spectroscopy (UPS), and reflection electron energy loss spectroscopy (REELS). The conduction band offset (CBO), valence band offset (VBO), and energy bandgap of 4H-SiC and BeO corresponded to 2.28 ± 0.1 eV, 2.53 ± 0.01 eV, 3.16 ± 0.1 eV, and 8.3 ± 0.05 eV, respectively. The calculated bandgap (7.97 eV) of a thin BeO film was obtained from the sum of CBO (2.28 eV), VBO (2.53 eV), and the SiC bandgap (3.16 eV). The difference between the calculated (7.97 eV) and REELS (8.3 eV) bandgaps of BeO film is due to the error bars between the analysis methods. Interface defect levels, as determined via IPE analysis, corresponded to 3.53 ± 0.1 eV (graphitic carbon) and 4.46 ± 0.1 eV (π-bonded carbon) and were formed during the ohmic annealing process.

Determination of the interface band alignment of Mg2Si/4H‐SiC heterojuction for potential photodetector application

“…This value coincides exactly with the result of 4H‐SiC reported by Ashrafi 23 . Because the optical bandgap of 4H‐SiC is almost the same (3.25 eV) in the literatures, 6,24–26 it is not measured in this work. According to the bandgap of 4H‐SiC, the Fermi level is near the bottom of conduction band, suggesting that unintentionally doped 4H‐SiC exhibits n‐type conduction.…”

“…One can solve the Poisson equation of the barrier region (depletion region) on both sides of the interface to obtain the contact potential difference (band bending) of Mg 2 Si/4H‐SiC heterojunction. Assuming that Mg 2 Si/4H‐SiC is a mutant heterojunction and the Poisson equations on both sides of the interface are, respectively, the following: where , , , and 28 denote the barrier width, potential, carriers concentration, and static dielectric constant in the Mg 2 Si side, respectively; , , , and 26 denote the corresponding parameter in the 4H‐SiC side. Solving Equations () and () will yield the following: where and are the values of band bending in Mg 2 Si and 4H‐SiC sides, respectively.…”

X‐ray photoelectron spectroscopy characterization of band offsets of MgO/Mg2Si and SiO2/Mg2Si heterojunctions

“…The intensity is in arbitrary units (a.u.) many high k dielectric materials to choose, it seems that MgO (k = 9.8) 11 and SiO 2 (k = 3.9) 12,13 should be given priority because MgO and SiO 2 are natural oxidizing layers on the surface of Mg 2 Si, [14][15][16] and normally, a native oxide would be useful for manufacturability and reliability. 17 If the heterojunction formed by the natural oxide layer and Mg 2 Si meets the required band offset, the effort to find other suitable dielectric materials can be reduced.…”