The Electric Transport Properties Of ZnTe And ZnSe Under High Pressure

Both ZnTe and ZnSe are wide bandgap II VI semiconductors, which aresignificant in semiconductor laser and various luminescent instrument applications.Because high pressure can result in the decrease of atomic spacing and big changes inthe interaction between nucleus and electron orbital, new structures and propertieswill be generated in materials. ZnTe and ZnSe are no exception. To grasp andunderstand new properties of ZnTe and ZnSe under high pressures deeply, in thispaper, we specially select electrical properties of these two materials as our studysubject in the in situ electrical measurements. Related study contents and results arelisted as follows:(1) Using thin film deposition and lithography micromachining techniques, weintegrated metal thin film electrodes on diamond anvil for in situ high pressureelectrical measurements. Successively, we conducted AC impedance and DCresistivity measurements on different grain sizes of ZnTe and ZnSe respectively withdouble electrode and van der Pauw electrode configurations.(2)We studied electrical transport properties of ZnTe by in situ AC impedance andDC resistivity measurements under high pressures. The discontinuous change inresistivity was caused by the structural phase transition of ZnTe from zinc blende tocinnabar phase at8.8and to quadroture phase at12GPa. However, the increase ofresistivity at3GPa was caused by an augment of point defect in lattice.(3) By analyzing the pressure dependence of resistivity of ZnTe in different particlesize, we found that smaller particle size of ZnTe has higher transition pressure andlarger resistivity, which caused by the increase of free energy barrier.(4) We studied the electrical transport properties of ZnSe material under pressuresby in situ electrochemical impedance spectroscopy and DC resistivity measurement, and found that the resistance of ZnSe in size of478nm is smaller than that of ZnSe insize of859nm via the analysis of AC impedance spectra. It is opposite to the generallaw of the smaller the grain size, the larger the resistance.. The most possible reason isthat the cracking of grains generates many defects in grains and (or) grain boundariesin the process of grinding ZnSe grains, which can produce defect energy levels in theenergy gap, and make charge carries jump much more easily from the valence band tothe defect energy level and participate in conducting.(5) From AC impedance spectra, we obtained the pressure dependence of resistanceof ZnSe in859nm and478nm, and found that the resistance suddenly drops4ordersof magnitude at8.9GPa and9.7GPa, respectively, which is caused by the phasetransition of ZnSe sphalerite to cinnabar structure under high pressures.(6) DC resistivity measurement reflected that the phase transition of ZnSe fromcinnabar to rock salt structure starts from13GPa and finishes at16GPa. Upondecompression, the phase transition begins from12.9GPa and ends at10.4GPa. Thewidth of pressure hysteresis region is3GPa. By analyzing the pressure dependence ofresistivity of ZnSe in different size, we found that smaller grain of ZnSe has higherphase transition pressure, which results from the increase of free energy barrier.