Dopant Incorporation Efficiency in CVD Silicon Carbide Epilayers
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ABSTRACT In order to ensure reproducible and reliable SiC semiconductor device characteristics, controlled dopant incorporation must be accomplished. Some of the many factors which greatly influence dopant incorporation are the site-competition effect, SiC(0001) substrate polarity, substrate temperature, and the dopant-source reactor concentration. In this paper, dopant incorporation is considered and compared for various dopants in the context of dopant incorporation efficiency. By using secondary ion mass spectrometry (SIMS), the relative dopant incorporation efficiencies were calculated by dividing the SIMS determined dopant concentration in the resulting epitaxial layer by the intentional gas phase dopant concentration used during the SiC CVD. Specifically, the relative magnitudes of dopant incorporation efficiencies for nitrogen, phosphorus, and boron in 6H-SiC (0001) Si-face epitaxial layers are compared as a function of the site-competition effect and the dopant-source reactor concentrations. This serves as a first approximation for comparison of the relative "doping potencies" of some common dopants used in SiC CVD epitaxial growth. INTRODUCTION Silicon carbide (SiC) is a high temperature semiconductor material currently being pursued for applications in high temperature, high power, and high frequency electronics 1-5 . SiC electronic devices will find applications in aerospace vehicle control, aerospace power conditioning, space communications, as well as terrestrial control systems 6 -8 . However, in order to ensure reproducible and reliable SiC semiconductor device characteristics, controlled dopant incorporation must be accomplished. Some of the many factors which significantly influence dopant incorporation in SiC epitaxial layer growth include the site-competition effect, the SiC substrate polarity (i.e. Si-face or C-face of the SiC(0001) ), substrate temperature, and the dopant-source reactor concentration. Site-competition epitaxy is a recently reported dopant incorporation control technique which allows control over dopant incorporation by adjusting the silicon-source/carbon-source flow ratio (Si/C ratio) into the CVD reactor during epitaxial layer growth 9 . For example, on both 6H- and 4H-SiC(0001) Si-face substrates, nitrogen dopant incorporation was found to be proportional to the Si/C ratio whereas phosphorus, boron, and aluminum dopant incorporation was inversely proportional to the Si/C ratio used in the CVD reactor during epitaxial growth10, 11. In addition to the site-competition effect, the SiC substrate polarity has also been recently reported to effect dopant incorporation'2, 13. For example, secondary ion mass spectrometry (SIMS) results from aluminum doping studies indicate that aluminum dopant incorporation on C-face substrates is 50X less efficient compared to Si-face 6H-SiC substrates1 3 . In this paper, dopant incorporation efficiency will be considered and discussed for phosphorus (P) and nitrogen (N) as n-type and boron (B) as p-type dopants in context of the sitecompetition eff
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