# Unveiling the electrical and thermoelectric properties of highly degenerate indium selenide thin films: Indication of In3Se4 phase

## TL;DR

This study investigates how annealing affects the electrical and thermoelectric properties of InSe thin films, revealing a phase transition to a metallic In3Se4 phase with significant implications for optoelectronic applications.

## Contribution

It provides detailed analysis of phase transformation and property changes in InSe thin films induced by annealing, highlighting the emergence of a metallic In3Se4 phase.

## Key findings

- InSe thin films become polycrystalline with In3Se4 phase after annealing.
- Resistivity shows irreversible phase transition stabilizing after several heat cycles.
- Annealed films exhibit highly degenerate n-type metallic behavior with increased optical band gap.

## Abstract

The effects of annealing and variation of temperature on the electrical and thermoelectric properties of e-beam evaporated InSe thin films has been investigated in details. The XRD study demonstrates that the as-deposited InSe thin films are amorphous while they become polycrystalline with the presence of In3Se4 phase after annealing. The SEM micrographs reveal that the surfaces of as-deposited films are smooth whereas they become non-uniform due to annealing. The heating and cooling cycles of the as-deposited films exhibit that the resistivity of the films shows an irreversible phase-transition and become stable after 3-4 successive heat-treatment operations in air. The electrical conductivity of annealed InSe thin films shows a highly degenerate semiconducting (metallic) behavior. The thermopower of the annealed films indicates that InSe thin film is a highly degenerate n-type semiconductor i.e. metallic. Thickness dependence thermopower obeys the Fuchs-Sondheimer theory. The optical band gap of the annealed films increases as compared to the as-deposited films. These results indicate that InSe thin films encounter a phase-transformation from In2Se3 to a new In3Se4 metallic phase with an optical band gap of ~1.8 eV due to heat-treatment.

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Source: https://tomesphere.com/paper/1907.00654