We report simultaneous measurements and ab initio calculations of the secon
d-order nonlinear coefficients for SiC polytypes. Our measured values for c
hi(zzz) (chi(zxx)) are 18 (-4) pm/V for 4H SiC and 24 (-4) pm/V for 6H SiC.
They are in good agreement with our theoretical results. (C) 1999 American
Institute of Physics. [S0003-6951(99)00531-8].