Low-Pressure Fast Growth and Characterization of 4H-SiC Epilayers

Abstract

Fast and thick 4H-SiC epitaxial growth is demonstrated in a vertical-type reactor under a low system pressure within the range 13-40 mbar. A very fast growth rate of up to 250 m/h is obtained. The material quality of the epilayers grown in the reactor is evaluated by low-temperature photoluminescence, deep level transient spectroscopy, microwave photoconductive decay, synchrotron topography and room temperature PL imaging. The carrier lifetime of thick epilayers with or without the application of the C+-implantation/annealing method and extended defects in the epilayers grown on 8º and 4º off substrates are discussed.

Impacts of recombination at the surface and in the substrate on carrier lifetimes of n-type 4H–SiC epilayers

“…Tsuchida and co-workers utilized carbon ion implantation followed by high-temperature annealing at 1700-1800°C to eliminate the Z 1/2 center below the detection limit ͑5 ϫ 10 cm −3 ͒ and demonstrated remarkable improvement of carrier lifetimes. [25][26][27] The authors have succeeded in similar elimination of the Z 1/2 center and lifetime improvement by thermal oxidation. 28 Two-step thermal treatment, namely thermal oxidation and inert ͑Ar͒ annealing at high temperature, has been proposed for further defect elimination and lifetime improvement.…”

“…Since the carrier lifetimes of n-type 4H-SiC epilayers have been remarkably improved by elimination of the Z 1/2 center in recent years, [25][26][27][28][29] much care has to be paid for accurate lifetime measurements. As described above, the measured carrier lifetime can be severely limited by the surface recombination, and the recombination in the substrate can also dominate the measured lifetime when the epilayers are not thick enough.…”

Mechanisms of growth and defect properties of epitaxial SiC

“…There are different ways to overcome this issue: a higher growth temperature can be employed which is the "chimney reactor concept" developed by Ellison et al; 41 a significantly lower pressure and/or higher carrier gas flow can be used when growing the material which is a method used by Tsuchida et al; 42 and finally a different chemistry can be used which reduces or eliminates the formation of Si-Si bonds in the gas phase replacing them by other species that can be used for deposition.…”

“…This method was followed by Tsuchida et al 42 who reduced the pressure to below 40 millibars while maintaining a high flow rate of hydrogen of 50-70 standard litre per minute (slm). In doing so, the growth rate could gradually be increased up to 250 lm/h by increasing the silane and propane flow rates.…”

Epitaxial Growth of Silicon Carbide

“…The typical impurity density in CVD-grown 4H-SiC epitaxial layers is about (1-5) × 10 13 cm −3 for boron and (0.5-5) × 10 12 cm −3 for titanium. The densities of Z 1∕2 and EH6/7 centers are strongly dependent on the C/Si ratio and growth temperature; however, the growth rate only has a minor effect on defect generation, even if the growth rate is changed from 5 to 80 μm h −1 [83,[162][163][164]. Figure 4.34 shows the C/Si ratio dependence of the densities of Z 1∕2 and EH6/7 centers in as-grown n-type 4H-SiC(0001) and (0001) epitaxial layers [165].…”