Direct bonding of gallium nitride to silicon carbide: Physical, and electrical characterization

The direct bonding method is applied to the GaN/SiC system, and the processing conditions for successful direct bonding are clarified. Direct bonding of GaN/SiC is achieved at 900°C. The direct bonding of GaN to Si-face SiC is very dependent on the choice of chemical treatments, but the bonding of GaN to C-face SiC is less dependent on surface preparation. If a native oxide is present when the bonded interface is prepared, the current through the interface is decreased, which is attributed to an energy barrier due to the presence of charged interface states. TEM images indicate 10nm spaced dislocations at the interface for the GaN/SiC (Si-face), and ∼6nm for the GaN/SiC (C-face), which form to accommodate the lattice mismatch (3.4%) and twist (1∼2°) and tilt misfit (0.2° for Si-face SiC and 3° for C-face SiC). In some regions (∼30%) an amorphous oxide layer forms at the interface, which is attributed to inadequate surface preparation prior to bonding. The strain of the GaN film with a Ga/C interface was ∼0.1%, tensile strain, and that of GaN with a Ga/Si interface was ∼0.2%, tensile strain. Our analysis indicates that the GaN/SiC thermal misfit dominates the strain of the GaN after bonding. The electrical characteristics of n-p GaN/SiC heterojunctions display diode ideality factors, saturation currents, energy barrier heights, and band offsets of 1.5 ± 0.1, 10−13 A/cm 2, 0.75 ± 0.10 eV, and ΔE_C = 0.87 ± 0.10 eV for the Ga/Si interface and 1.2 ± 0.1, 10 −16 A/cm2, 0.56 ± 0.10 eV, and Δ E_C = 0.46 ± 0.10 eV for the Ga/C interface.