Cation-anion vacancy complexes in semiconducting compounds

Esa Korhonen

Research output: ThesisDoctoral ThesisCollection of Articles

Abstract

In this work, positron annihilation spectroscopy was used to study complex, optically relevant semiconductor materials. The interpretation of the experimental results was assisted by theoretical modeling. Most of the measured samples were grown using epitaxial growth methods such as MOVPE or MBE. These techniques produce thin-film material, which is markedly different from bulk crystals. The distance from the substrate to the surface may be in the 100 nm range, in which lattice strains may not completely relax. The growth itself introduces lattice defects to the material due to atoms not arranging optimally on the growth surface. In many of the samples, vacancy complexes were detected instead of only monovacancies. The existence of complexes was deduced based on the correlation between the Doppler broadening results and the growth parameters of the samples. For CuGaSe2, more vacancies were detected as Cu-concentration decreased and the trend of the change was a mix between cation and anion vacancies. For CuInSe2, most of the samples seemed to be dominated by monovacancies while the samples with least Cu gave results hinting towards larger vacancies. With SnO2, the high S-values detected in the least doped samples hint towards the existence of clusters. In the case of In2O3 vacuum annealing increases the size of the detected vacancies. The effects of these various vacancy complexes on the electrical properties vary. In Cu(In,Ga)Se2, the detected divacancies may be the cause of metastability by introducing more holes when illuminated. In SnO2, the vacancies seem to have no effect as Sb-doping is fully efficient. This is not the case in In2O3, where increasing the size of the vacancies coincides with increase of conduction electron concentration and is likely caused by donor type VO being added to VIn. Finally, in Ga2O3 the detected high concentration of compensating acceptor-like VGa is the most likely cause for the failure of n-doping with Si in the studied samples.
Translated title of the contributionKationi-anioni-vakanssikompleksit seospuolijohteissa
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
Supervisors/Advisors
  • Tuomisto, Filip, Supervising Professor
Publisher
Print ISBNs978-952-60-6741-4
Electronic ISBNs978-952-60-6742-1
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)

Keywords

  • semiconductor
  • transparent conducting oxide
  • positron spectroscopy

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