The study of structural, electrical and optical properties of phosphorus doped fewlayer In₆Se₇ for homojunction device

Yu Hung Peng^1*, Ching Hwa Ho¹

¹Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan

* Presenter:Yu Hung Peng, email:D11022604@mail.ntust.edu.tw

This work investigates the characteristic of layered In₆Se₇ with varying phosphorus (P) dopant concentrations (In₆Se₇:P) from P=0, 0.5, 1, to P=5%. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses indicate that the structure and morphology of In₆Se₇:P series compounds remain unchanged, exhibiting a monoclinic structure. Room-temperature micro-Raman (µRaman) result of all the compositions of layered In₆Se₇:P reveals two dominant peaks at 101±3 cm^-1 (i.e. In-In bonding mode) and 201±3 cm^-1 (i.e. Se-Se bonding mode) for each P composition in In₆Se₇. An extra peak at approximately 171±2 cm^-1 is observed and it shows enhancement at the highest P composition of In₆Se₇:P 5%. This mode is attributed to the P-Se bonding caused by the P doping inside In₆Se₇. All the doped and undoped In₆Se₇:P showed n-type conductivity and their carrier concentrations increased with the P dopant is increased. Temperature-dependent resistivity revealed a reduction in activation energy (for donor), as the P content is increased in the In₆Se₇:P samples. Kelvin probe measurement shows a decrease in work function (i.e. an energy increase of Fermi level) of the n-type In₆Se₇ multilayers with the increase of P content. The indirect and direct band gaps for all the multilayer In₆Se₇:P of different P composition are identical. They are determined to be 0.732 eV (indirect) and 0.772 eV (direct) obtained by micro-transmittance and micro-thermoreflectance (μTR) measurements. A rectified n-n⁺ homojunction was formed by stacking multilayered In₆Se₇/In₆Se₇:P 5%. The built-in potential is about V_bi ~ 0.15 V. It agrees well with the work function difference between the two layer compounds.

Keywords: In₆Se₇, Energy compound, n-type semiconductor, P-Se bond, Band gap