Sage Bauers1,Theodore Culman1,Rachel Woods-Robinson2,John Mangum1,Rebecca Smaha1,Chris Rom1,Andriy Zakutayev1
National Renewable Energy Laboratory1,Lawrence Berkeley National Laboratory2
Sage Bauers1,Theodore Culman1,Rachel Woods-Robinson2,John Mangum1,Rebecca Smaha1,Chris Rom1,Andriy Zakutayev1
National Renewable Energy Laboratory1,Lawrence Berkeley National Laboratory2
Conventional II-VI and III-V compound semiconductors can be roughly split into two structural categories: zincblende and wurtzite. Both are tetrahedral systems and furthermore, their crystal structures are polytypes with only slight modification to the stacking pattern of honeycomb cation/anion planes. Controlling zincblende–wurtzite polytypism within a single material is a promising way to design semiconductor functionality. In this talk we show that nitrogen doping induces a zincblende-to-wurtzite structural transition in ZnSe<sub>1-x</sub>Te<sub>x</sub> when grown as sputter deposited thin films. N-doped ZnSe<sub>1-x</sub>Te<sub>x</sub> is prepared from ZnSe and ZnTe source targets with gaseous N<sub>2</sub> as a N source. In some doped films, there is a structural transformation from the usual zincblende to wurtzite. Depending on the temperature and N<sub>2</sub> flow rate during growth, wurtzite can be synthesized across most of the composition range explored, ranging from Te-rich (x ≈ 0.7) to nearly pure ZnSe (x ≈ 0.1). Grazing-incidence, wide-angle synchrotron x-ray scattering (GIWAXS) data show that the N-doped ZnSe<sub>0.5</sub>Te<sub>0.5</sub> alloy forms as phase-pure wurtzite. Temperature-dependent electronic transport measurements collected from N-doped ZnSe<sub>0.5</sub>Te<sub>0.5</sub> indicate the material is a p-type semiconductor and low-temperature resistivity data are well fit by a transport model dominated by 3D variable range hopping. Scanning electron microscopy reveals voids in the N-doped films that are not present in undoped films. We attribute these microstructural features to N<sub>2</sub> gas trapped during growth, which is confirmed by signals from molecular nitrogen in x-ray absorption spectroscopy data. 0 K formation enthalpy calculations do not completely describe the stability of the wurtzite phase, so we hypothesize that the open microstructure plays a role by increasing the surface energy contribution. This work highlights unexpected polytypism in one of the most studied II-VI semiconductor systems and thus motivates a closer look at other well-studied semiconductor alloys for similar structural diversity.