Hexagonal Silicon Carbide Substrates Research Articles

Hot Filament CVD epitaxy of 3C-SiC on 6H and 3C-SiC substrates

ABSTRACTFor the first time, we are reporting the growth of high quality single crystalline 3C-SiC epitaxially on hexagonal silicon carbide substrates using Hot Filament Chemical Vapor Deposition (HF-CVD) on full 4” wafers. Rocking curve X-Ray diffraction (XRD) measurements resulted in a full width at half maximum (FWHM) as low as 88 arcsec for a 40 µm thick layer. We achieved this quality using a carefully optimized process making use of the additional degrees of freedom the hot filaments create. The filaments allow for precursor pre-cracking and a tuning of the vertical thermal gradient, which creates an improved thermal field compared to conventional Chemical Vapor Deposition. Growth rates of up to 8 µm/h were achieved with standard silane and propane chemistry, and further increased to 20 µm/h with chlorinated chemistry. The use of silicon carbide substrates promises superior layer quality compared to silicon substrates due to their better match in lattice parameters and thermal expansion coefficients. High resolution scanning electron microscopy, X-Ray rocking measurements, and micro-Raman allow us to assess the crystalline quality of our material and to compare it to layers grown on low-cost silicon substrates. Hall measurements reveal a linear increase of the charge carrier density in the material with the flow of nitrogen gas as a dopant. Electron densities above 10-18 cm-3 have been reached.

Investigation of the Metal–Insulator Transition in n-3C-SiC Epitaxial Films

n-type 3C-SiC films have been grown by sublimation epitaxy on hexagonal silicon carbide substrates. The low-temperature conductivity and magnetoresistance of the films have been studied in relation to their doping level and structural perfection. It was found that a metal--insulator transition occurs in the n-3C-SiC layer at concentrations Nd - Na ≤ 3 1017 cm-3.

Metal-insulator transition in n-3C-SiC epitaxial films

n-Type 3C-SiC films have been grown by sublimation epitaxy on hexagonal silicon carbide substrates. The low-temperature conductivity and magnetoresistance of the films have been studied in relation to their doping level and structural perfection. It was found that a metal-insulator transition occurs in the n-3C-SiC layer at uncompensated donor concentrations N d − N a ≤ 3 × 1017 cm−3.

Bulk crystal growth of cubic silicon carbide by sublimation epitaxy

Cubic silicon carbide has a potential for high power, high frequency and high temperature devices. Sublimation growth is an established technique to prepare silicon carbide wafers, due to the possibility to obtain high quality crystals with high growth rates. However, the sublimation growth of cubic silicon carbide has not been very successful owing to the poor temperature stability of the polytype. In this study, bulk crystal growth of cubic silicon carbide on hexagonal silicon carbide substrates was tried by sublimation epitaxy. In previous work, the (0 0 0 1) basal plane of hexagonal silicon carbide have been used as substrate for cubic silicon carbide growth by the sublimation method. In this study, crystal growth was carried out not on the (0 0 0 1) basal plane but on the off-axis (0 0 0 1) plane tilted towards 11 2 ̄ 0 . This tilted plane was used in order to form step-free (0 0 0 1) basal plane and to grow cubic silicon carbide on this step-free plane. A step-free surface was formed on the off-axis oriented seed crystal by limiting the growth area and single crystal cubic silicon carbide could be successfully grown. Cubic silicon carbide with a size of 4.0 mm×4.0 mm and 2.0 mm thick was obtained.

Gallium Nitride Films

The thermal decomposition of a gallium tribromide‐ammonia complex in an ammonia, argon, or nitrogen atmosphere has been used for the deposition of gallium nitride films on silicon and hexagonal silicon carbide substrates in a gas flow system. The substrate temperature and the nature of the ambient are the most important parameters of the deposition process. Adherent and transparent films of gallium nitride have been deposited at substrate temperatures up to about 600°C in an ammonia atmosphere and up to about 750°C in a nitrogen or argon ambient. At higher temperatures, the deposit became contaminated with gallium. The gallium nitride films deposited on {111} oriented silicon substrates at 600°–700°C were found to show a (110) fiber orientation. Epitaxial, single crystalline gallium nitride films have been grown successfully on the basal plane of hexagonal silicon carbide substrates at 520°–600°C. These films are of high resistivity indicating that the thermal decomposition of gallium nitride is negligible. Thus, the thermal decomposition of the gallium tribromide‐ammonia complex provides a new promising technique for the crystal growth of gallium nitride.

Crystals and Epitaxial Layers of Boron Phosphide

The thermal decomposition of diborane-phosphine mixtures in a hydrogen atmosphere and the thermal reduction of boron tribromide-phosphorus trichloride mixtures with hydrogen have been used for the deposition of boron phosphide on the basal plane of hexagonal silicon carbide substrates. In the thermal decomposition process, the substrate must be maintained at temperatures below 900°C to minimize the contribution of gas-phase reactions, and the boron phosphide layers showed only preferred orientations. The thermal reduction process was carried out over a wide temperature range, and the boron phosphide layers deposited on the silicon face of silicon carbide substrates at 1050°–1150°C were found, by optical microscopy and reflection electron diffraction examinations, to be single crystalline and epitaxial with respect to the substrate. Epitaxial boron phosphide layers prepared by the halide reduction reaction without intentional doping are p type with a room-temperature carrier concentration of approximately 1019 cm−3. Resistivity measurements in the temperature range 300°–1000°K indicated the presence of two impurity states with activation energies of approximately 0.22 and 0.66 eV, respectively. Needle-shaped boron phosphide crystals have also been obtained by the halide reduction reaction. They are single crystals with the elongated axis along a 〈111〉 direction and are p type with a room-temperature resistivity of approximately 20 Ω cm.

Epitaxial Growth of Silicon Carbide by the Thermal Reduction Technique

The epitaxial growth of silicon carbide on the basal plane of hexagonal silicon carbide substrates has been accomplished by the thermal reduction of carbon and silicon tetrachlorides, and experimental parameters of the growth process have been studied. Using good in situ etching techniques and inert susceptor materials, epitaxial silicon carbide layers with structural perfection similar to that of the substrate were grown at a substrate temperature of 1700°C and a deposition rate of 0.5 µ/min. Doped silicon carbide layers were prepared using nitrogen, arsine, or phosphine as n‐type dopants and diborane as a p‐type dopant, and the electrical properties of these layers were evaluated by Hall measurements in the temperature range 78°–900°K. Preliminary junction structures prepared by doping techniques were found to be capable of supporting up to 50v at 500 °C.

Directional growth of single-crystal silicon films across silicon carbide by a moving deposition-zone technique

Epitaxial silicon films deposited on foreign substrates by conventional chemical deposition techniques always exhibited structural imperfections due to the lattice mismatch or the occurrence of more than one epitaxial orientation. To improve the structural perfection of these films, a moving deposition-zone technique was used to control the nucleation and growth of silicon films on hexagonal silicon carbide substrates. This technique was found to be capable of promoting the growth of silicon films of a {110} orientation with considerably increased crystal size.

Epitaxial Growth of Silicon on Hexagonal Silicon Carbide

The epitaxial growth of silicon on the basal plane of hexagonal silicon carbide substrates has been studied using the pyrolysis of silane in a flow system. The effects of deposition variables on the properties of grown films were evaluated using chemical etching and optical microscope techniques. The films were found to have almost exclusively {111} and {110} orientations and were found to be different in appearance on the carbon and silicon faces of the substrate. The epitaxial orientations were confirmed by reflection electron diffraction. The device quality of these films was established by preparing small diffused and epitaxial p-n junctions and MOS transistors.