First principle investigation and substrate temperature dependent structural and electrical transport characterizations of pulsed laser deposited (PLD) cadmium indium Selenide (α-CdIn2Se4) ternary semiconducting compound thin films

The theoretical investigations on CdIn<inf>2</inf>Se<inf>4</inf>, a ternary semiconducting compound belonging to the II-III<inf>2</inf>-VI<inf>4</inf> family, were accomplished using the SIESTA code. Using density functional theory, the band structure of the CdIn₂Se₄ was proposed. Its semiconducting nature was highlighted by the direct band gap of ≃1.6700 eV. The values of the Fermi energy, the highest occupied molecular orbital, the lowest unoccupied molecular orbital, and Mulliken atomic charges of individual atoms in CdIn₂Se₄ were inferred. A pulsed laser deposition technique deposited CdIn<inf>2</inf>Se<inf>4</inf> thin films on various substrates at different substrate temperatures (T<inf>s</inf>). Electron microscopy and an X-ray diffractometer were used to study the morphology and/or crystal structure of CdIn<inf>2</inf>Se<inf>4</inf> films. The CdIn<inf>2</inf>Se<inf>4</inf> films were found to be amorphous when synthesized at lower T<inf>s</inf> (< 425 K), single-phase-polycrystalline-stoichiometric when synthesized between 425 K ≤ T<inf>s</inf> < 675 K, and polyphase when synthesized at higher T<inf>s</inf> (> 550 K). The additional reflection observed in CdIn<inf>2</inf>Se<inf>4</inf> films at higher T<inf>s</inf> (> 550 K) is identified due to the characteristic peak of the hexagonal β-phase In<inf>2</inf>Se<inf>3</inf>. The ICDD card 01-089-2388 was used to index the electron diffraction and X-ray diffraction results of the tetragonally structured and P-42 m (1 1 1) crystallographic space group α-phase CdIn<inf>2</inf>Se<inf>4</inf> films. The lattice constant and unit cell volume for the (1 1 1) reflection of CdIn<inf>2</inf>Se<inf>4</inf> films have been inferred. For the most substantial (1 1 1) reflection, the stacking fault (5.7992 × 10⁻³) and unity value of the texture coefficient for the CdIn<inf>2</inf>Se<inf>4</inf> film are extracted. No element/s other than Cd, In, and Se are evident in the CdIn<inf>2</inf>Se<inf>4</inf> thin films’ energy dispersive analysis of X-ray spectra, which revealed the purity of the CdIn<inf>2</inf>Se<inf>4</inf> films. The Raman investigation demonstrates the effective formation of nanocrystalline, strain-influenced CdIn<inf>2</inf>Se<inf>4</inf> films with a prominent Raman mode at 137 cm⁻¹. The DC electrical resistivity, thermal activation energies, band gap energies, Hall coefficient, carrier concentration, and Hall mobility were deduced for CdIn<inf>2</inf>Se<inf>4</inf> films. The implications are addressed.