Defect engineering and opto electronic property modifications by 1.5 MeV Li⁺ implantation on nano crystalline MgIn₂O₄ thin films

Abstract

Spinel MgIn₂O₄ thin films were deposited on quartz substrates by the chemical spray pyrolysis technique using metal organic precursors at 450°C. Energetic 1.5 MeV Li⁺ ions were implanted to various fluences of 10¹³, 10¹⁴ and 10¹⁵ ions/cm² onto insulating MgIn₂O₄ films using a 9 SDH-2, NEC, 3MV accelerator to modify the material properties and surface nature. X-ray diffraction analysis was carried out to identify the changes in the crystallinity and grain orientations before and after implantations. Before implantation, the grains of polycrystalline MgIn₂O₄ were randomly oriented [(222), (311), (442) and (511)], and after implantation they exhibited a tendency to realign the crystallites along the even (hkl) planes [(222) and (442)]. On the Li⁺-implanted sample, one or more grains combine together and form bigger grains along with shallow pits, as observed through the atomic force micrographs. The as-deposited films have a percentage transmittance of 70–80% in the wavelength range 400–800 nm and the observed optical transmittance was less in Li⁺-implanted MgIn₂O₄ films. The index of refraction and the extinction co-efficient values were respectively n=1.98 and k=10⁻² in the visible region. However, the DC electrical conductivity of Li⁺-implanted films to a fluence of 10¹⁵ ions/cm² was nearly 0.7 S/cm at room temperature. The efficiency of the carrier generation was increased from 13.41% to 26.81% on annealing the implanted sample to lower fluence (10¹³ ions/cm²).

Keywords:

• thin films
• implantation
• X-ray diffraction
• optical property
• electrical conductivity

PACS :

• 77.55.+f
• 78.70.−g
• 61.10.Nz
• 78.20.−e
• 72.20.−i