FULL-BAND-STRUCTURE CALCULATION OF 1ST-HARMONIC, 2ND-HARMONIC, AND 3RD-HARMONIC OPTICAL-RESPONSE COEFFICIENTS OF ZNSE, ZNTE, AND CDTE

We report full-band-structure calculations of the frequency-dependent second- and third-harmonic response functions of ZnSe, ZnTe, and CdTe, as well as our results for the dielectric function of these semiconductors. We use a linear combination of Gaussian orbitals technique, in conjunction with the X-alpha-method, to obtain the energy band structures and optical matrix elements of each material. The expressions for epsilon <--> (omega) and chi <--> (2)(-2-omega; omega,omega) are evaluated utilizing a linearized sampling method for integrating over an irreducible segment of the Brillouin zone; the expression for chi <--> (3)(-3-omega; omega,omega,omega) is evaluated using a random-sampling method. The results of our calculations of epsilon-2 <--> (omega) are in good agreement with experimental results. Our calculated value of chi-14(2)(0) = 24.8 x 10(-8) esu for CdTe is in excellent agreement with the measured value [G. H. Sherman and P. D. Coleman, J. Appl. Phys. 44, 238 (1973)] of chi-14(2)(lambda = 28-mu-m) = (28 +/- 11) x 10(-8) esu. We argue that the experimental results for chi-14(2)(lambda = 10.6-mu-m) of ZnSe and ZnTe [C. K. N. Patel, Phys. Rev. Lett. 16, 613 (1966)] are likely to be inaccurate and that there is a need for additional measurements. Our calculations show that both chi <--> (2)(0) and chi <--> (3)(0) are positive for the materials considered in this work. We analyze the prominent features of epsilon-2 <--> (omega), chi <--> (2)(-2-omega; omega,omega), and chi <--> (3)(-3-omega; omega,omega,omega) over a wide range of frequencies. Our results indicate that the effects of weak optical transitions are much more pronounced in the second- and third-order optical response functions than in the linear-response functions.