Contrasting properties of free carriers in $n$- and $p$-type Sb$_2$Se$_3$

Abstract

We report persistent photoconductivity in $p$-type Sb$_2$Se$_3$ single crystals doped with Cd or Zn, where enhanced conductivity remains for hours after illumination ceases at temperatures below $\sim$25~K. Comparative transport and infrared absorption measurements, including on $n$-type Cl-doped counterparts, reveal strong indications that hole transport in Sb$_2$Se$_3$ is more strongly affected by intrinsic carrier scattering than electron transport. These results point to a fundamental asymmetry in charge carrier dynamics and highlight the potential role of polaronic effects in limiting hole mobility in this quasi-one-dimensional semiconductor.

Figures (4)

• Figure 1: Semi-logarithmic $I$--$V$ characteristics of $p$-type Cd-doped (left panel) and $n$-type Cl-doped (right panel) Sb$_2$Se$_3$ single crystals measured at low temperature ($\sim$22 K), before and after 1-minute illumination with an XBO lamp. The inset shows the temporal evolution of the sample conductance (measured at 4 V) for the Cd-doped crystal, highlighting the persistent nature of the photoconductivity.
• Figure 2: Arrhenius plots of sample conductance during heat-up for Cl-, Cd-, Zn-, and nominally undoped Sb$_2$Se$_3$ crystals after a 1-minute illumination with a XBO lamp at 18 K. Measurements were performed in the dark under a 5 V bias with a heating rate of approximately 2 K/min.
• Figure 3: Top panel: IR absorbance spectra obtained on a Cd-doped Sb$_2$Se$_3$ single crystal after cooling down to 18 K in dark, measured before (red) and after (blue) 10 s of illumination using an XBO light source. Bottom panel: "differential" absorbance spectra with the spectra measured before and after illumination cross-subtracted. Inset: Temporal evolution of conductance (blue) and photo-induced absorption (red) of the Cd-doped Sb$_2$Se$_3$ sample, measured during a series of short illumination steps at 18 K after cooling down in dark.
• Figure 4: Polarization-resolved differential PIA spectra of Cd- and Cl-doped Sb$_2$Se$_3$ single crystals, obtained by subtracting the dark spectra from those measured after illumination. Blue and red curves correspond to light polarized along the $c$ and $a$ axes, respectively, while green curves represent measurements with unpolarized light. Data below 630 cm$^{-1}$ were recorded using a Mylar beam splitter and bolometer detector combination; for frequencies above 630 cm$^{-1}$, a KBr beam splitter and MCT detector setup was used.