Metal site disorder in zinc tin phosphide

The optoelectronic properties of the II-IV-V₂ semiconductor ZnSnP₂ are studied as a function of the cooling rate of the crystal growth melt. The structure of the material, as studied by x-ray diffraction, is seen to change from chalcopyrite to sphalerite as the cooling rate is increased. Photoelectrochemical measurements show that the bandgap of the material decreases from 1.64 eV for the chalcopyrite to 1.25 eV as the structure approaches sphalerite. The ¹¹⁹Sn Mössbauer spectroscopy shows both an isomer shift and a broadening of the ¹¹⁹Sn resonance as a result of new tin environments produced by disordering of zinc and tin sites at the faster cooling rates. The ³¹P solid-state nuclear magnetic resonance spectroscopy clearly shows new resonances associated with the additional phosphorus environments produced by metal site disordering. A model based on zinc and tin site exchange with the introduction of compensating donor and acceptor states is proposed and discussed.