ATOMIC DISTRIBUTION IN CRYSTALLINE II-IV-V2 SEMICONDUCTOR ALLOYS - P-31 AND CD-113 MAGIC ANGLE SPINNING, SPIN-ECHO, AND P-31-CD-113 SPIN-ECHO DOUBLE-RESONANCE NMR-STUDIES OF THE SYSTEMS ZNGEAS2-XPX AND CDGEAS2-XPX

Anion substitution in the ternary II-IV-V2 semiconductor systems ZnGeAs2-xPx and CdGeAs2-xPx results in homogeneous solid solutions, which crystallize in the chalcopyrite structure. The distribution of local (nearest neighbor) environments in these materials has been examined by a number of complementary solid-state NMR techniques, including Cd-113 and P-31 magic angle spinning (MAS), Cd-113 and P-31 spin-echo, and Cd-113-P-31 spin-echo double-resonance (SEDOR) experiments. Cd-113 and P-31 MAS-NMR spectra show single resonances, whose chemical shifts change monotonically as a function of x. Contrary to the situation in II-VI semiconductor alloys, no chemical shift discrimination attributable to different local nearest neighbor configurations is apparent in either MAS or locally selective SEDOR experiments. These results suggest that the chemical shifts in these compounds are not determined by local bonding configurations and, rather, that a description involving charge delocalization is more appropriate. P-31 spin-echo and P-31-Cd-113 SEDOR decay data reveal that the P-31-P-31 homonuclear dipole coupling is stronger, and that the P-31-Cd-113 dipolar coupling is weaker than expected for a random distribution of P and As over the anionic sublattice of the chalcopyrite structure. These results are qualitatively consistent with a structure in which both the cation and the anion sublattices are disordered, and where the average number of P-Ge and As-Cd bonds is somewhat higher than that of the P-Cd and As-Ge bonds.