Formation of carbon vacancy in 4H silicon carbide during high-temperature processing

• As-grown and pre-oxidized silicon carbide (SiC) samples of polytype 4H have been annealed at temperatures up to 1950 degrees C for 10 min duration using inductive heating, or at 2000 degrees C for 30 s using microwave heating. The samples consisted of a n-type high-purity epitaxial layer grown on 4 degrees off-axis < 0001 > n(+)-substrate and the evolution of the carbon vacancy (V-C) concentration in the epitaxial layer was monitored by deep level transient spectroscopy via the characteristic Z(1/2) peak. Z(1/2) appears at similar to 0.7 eV below the conduction band edge and arises from the doubly negative charge state of V-C. The concentration of V-C increases strongly after treatment at temperatures >= 1600 degrees C and it reaches almost 10(15)cm(-3) after the inductive heating at 1950 degrees C. A formation enthalpy of similar to 5.0 eV is deduced for V-C, in close agreement with recent theoretical predictions in the literature, and the entropy factor is found to be similar to 5 k (k denotes Boltzmann's constant). The latter value indicates substantial lattice relaxation around V-C, consistent with V-C being a negative-U system exhibiting considerable Jahn-Teller distortion. The microwave heated samples show evidence of non-equilibrium conditions due to the short duration used and display a lower content of V-C than the inductively heated ones. Finally, concentration-versus-depth profiles of V-C favour formation in the "bulk" of the epitaxial layer as the prevailing process and not a Schottky type process at the surface.

Nyckelord

4H silicon carbide

Boltzmann's constant

Conduction band edge

Formation enthalpy

High-temperature processing

Lattice relaxation

Nonequilibrium conditions

Silicon carbides (SiC)

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