Carrier behavior of HgTe under high pressure revealed by Hall effect measurement

Abstract

We investigate the carrier behavior of HgTe under high pressures up to 23 GPa using in situ Hall effect measurements. As the phase transitions from zinc blende to cinnabar, then to rock salt, and finally to Cmcm occur, all the parameters change discontinuously. The conductivity variation under compression is described by the carrier parameters. For the zinc blende phase, both the decrease of carrier concentration and the increase of mobility indicate the overlapped valence band and conduction band separates with pressure. Pressure causes an increase in the hole concentration of HgTe in the cinnabar phase, which leads to the carrier-type inversion and the lowest mobility at 5.6 GPa. In the phase transition process from zinc blende to rock salt, Te atoms are the major ones in atomic movements in the pressure regions of 1.0–1.5 GPa and 1.8–3.1 GPa, whereas Hg atoms are the major ones in the pressure regions of 1.5–1.8 GPa and 3.1–7.7 GPa. The polar optical scattering of the rock salt phase decreases with pressure.

Colossal variations in the thermopower and n–p conductivity switching in topological tellurides under pressure

“…Recent Hall-coefficient studies of the zinc-blende phase of HgTe reported a pressure-driven decrease in an effective carrier concentration and an increase in their mobility. 106 These findings confirmed a pressure-driven reduction of the overlap of the valence and conduction bands, thereby suggesting that at a certain pressure they should be completely separated. 79,80,106 Note here that the band structure of HgTe is very sensitive to many factors, like small strains or defects, and hence, the fine details of the band structure can vary a bit from sample to sample.…”

“…106 These findings confirmed a pressure-driven reduction of the overlap of the valence and conduction bands, thereby suggesting that at a certain pressure they should be completely separated. 79,80,106 Note here that the band structure of HgTe is very sensitive to many factors, like small strains or defects, and hence, the fine details of the band structure can vary a bit from sample to sample. 168 The rising in the electrical resistance with the pressure we observed in the zinc-blende phase of HgTe [Fig.…”

“…Earlier studies found that the NaCl phase in HgTe is metallic and has a p-type conductivity. 106 Above 4-6 GPa, after the smooth negative extremum, the Seebeck coefficients of these three HgTe 1−x S x samples showed an apparent tendency to decreasing of their absolute values, followed by an n-p sign inversion (Fig. 2).…”

“…96,97 The zinc-blende → cinnabar phase transition in HgTe was established to result in a bandgap opening. [98][99][100] Binary HgTe was the focus of many experimental high-pressure studies, which investigated its structural, optical, and electronic transport properties, 69,76,77,80,[82][83][84]87,88,95,[98][99][100][101][102][103][104][105][106] whereas its solid solutions, like HgTe 1−x S x , were considered in a few works only. [89][90][91]105,[107][108][109] It was found that a certain critical concentration of sulfur of about x c ∼ 0.15-0.2 turns HgTe 1−x S x from a gapless semiconductor to a semimetal.…”

“…[76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94] The pressure dependencies of the electrical resistance and the thermopower of HgTe 1−x S x indicated that above the phase transition point of 1-4 GPa, the cinnabar phase of all the samples is a p-type semiconductor, in agreement with previous works. 80,101,103,106 The thermopower in the cinnabar phase of HgTe 1−x S x can be well described by a formula for an intrinsic semiconductor with a two-band electrical conductivity as follows: 171…”