Giant conductivity enhancement: Pressure-induced semiconductor-metal phase transition in $\mathrm{C}{\mathrm{d}}_{0.90}\mathrm{Z}{\mathrm{n}}_{0.1}\mathrm{Te}$

Element doping and pressure compression may change material properties for improved performance in applications. We report pressure-induced metallization in the semiconductor $\mathrm{C}{\mathrm{d}}_{0.90}\mathrm{Z}{\mathrm{n}}_{0.1}\mathrm{Te}$. Transport measurements showed an overall resistivity drop of 11 orders of magnitude under compression up to 12 GPa, which is indicative of a metallization transition. X-ray diffraction measurements revealed that the sample underwent a structural transition from a cubic-$F4\overline{3}m$ phase (zinc blende) to a cubic-$Fm\overline{3}m$ phase (rock salt) at about 5.5 GPa, followed by another transition to an orthorhombic $Cmcm$ structure at 13 GPa. A huge volume collapse of about 18% was observed during the first phase transition, suggesting a first-order phase transition. The disappearance or weakening of Raman modes, temperature-dependent resistivity, and $abinitio$ calculation results depict the metallic nature of both the rock-salt and $Cmcm$ phases. The band structure changes and increased carrier density (especially at the first structural transition) are likely a consequence of the structural transition.

Figure 1

(a) The variation of resistivity as a function of pressure for $\mathrm{C}{\mathrm{d}}_{0.9}\mathrm{Z}{\mathrm{n}}_{0.1}\mathrm{Te}$. Closed symbols represent compression data, while open symbols are for decompression data. (b) The isobaric temperature-dependent resistance of the sample at a few representative pressure values.

Figure 2

Calculated band structure of $\mathrm{C}{\mathrm{d}}_{0.9}\mathrm{Z}{\mathrm{n}}_{0.1}\mathrm{Te}$ at (a) 0 GPa, (b) 7 GPa, and (c) 14 GPa for the ZB, RS, and Cmcm structure, respectively. (d) Pressure dependence of the band gap in the LP region.

Figure 3

(a) Angle-dispersive XRD patterns for $\mathrm{C}{\mathrm{d}}_{0.9}\mathrm{Z}{\mathrm{n}}_{0.1}\mathrm{Te}$ at selected pressures at room temperature $(\lambda =0.4959\AA )$. Arrows indicate the appearance of new peaks. (b) Pressure-dependent enthalpies of all three phases computed by first-principles calculations.

Figure 4

(a) Rietveld refinements for the ambient pressure and new HP-1 and HP-2 phases at 7.0 and 17 GPa, respectively $(\lambda =0.4959\AA )$. (b) A comparison between the cubic-$F4\overline{3}m$, cubic-$Fm\overline{3}m,$ and orthorhombic-Cmcm crystal structures.

Figure 5

Unit-cell volume as a function of pressure for cubic-$F4\overline{3}m$, cubic-$Fm\overline{3}m,$ and orthorhombic-Cmcm phase.

Figure 6

(a) Raman spectra of $\mathrm{C}{\mathrm{d}}_{0.9}\mathrm{Z}{\mathrm{n}}_{0.1}\mathrm{Te}$ from 0 to 40 GPa showing Raman modes disappearing at the first phase transition (HP-1) and reappearing modes at the second phase transition (HP-2). (b) Deconvoluted spectra with Lorentzian fitting for the Raman modes at 0.5 GPa. (c) Pressure dependence of the Raman modes at different pressures from 0 and 40 GPa, where solid lines show the linear fits corresponding to the specific modes.