Electroluminescence Of Silicon-Based TiO₂ Film Devices

As an indirect band gap semiconductor, the inter-band luminescence efficiency of TiO2 is very low at room temperature. However, there exist a number of deep-level defects in TiO2, which may act as the light-emitting centers. In this thesis, the electroluminescence (EL) from TiO2 films on silicon has been investigated. The TiO2/p+-Si and TiO2:B/p+-Si heterostructured devices have been fabricated by means of atomic layer deposition (ALD) and magnetron sputtering, respectively, and their related EL mechanisms have been addressed. The primary results achieved in this thesis are listed in the following.(1) TiO2 films were grown on the heavily boron-doped silicon (p+-Si) substrates by atomic layer deposition. Such TiO2 films were then annealed under certain conditions, thus forming TiO2/p+-Si heterostructures. It is found that the intensity of EL from the TiO2/p+-Si heterostructured device is remarkably reduced as the ALD temperature of TiO2 film exceeds a critical value. Moreover, the annealing ambient for TiO2 film exerts significant effect on the EL intensity of the device. That is, the oxygen ambient is more advantageous for the EL from the device than the nitrogen ambient. Under the same other conditions, the TiO2/p+-Si heterostructured device using the ALD TiO2 film exhibits much higher EL intensity than the counterpart using the sputtered TiO2 film.(2) As for the TiO2/p+-Si heterostructured devices using the ALD TiO2 films deposited at 165℃ and annealed under oxygen ambient, the increase of annealing temperature, the extension of annealing time and the decrease of thickness for the TiO2 film leads to the blue-shift of EL. The aforementioned changes in different factors actually result in the variation of proportions of different deep-level defects in TiO2 film, eventually changing the EL from the TiO2/p+-Si heterostructure to a certain extent.(3) The TiO2/p+-Si and TiO2:B/p+-Si heterostructures were formed by sputtering TiO2 films and boron-doped TiO2(TiO2:B) films on heavily boron-doped silicon (p+-Si) substrates, respectively, followed by annealing at 600 ℃ in oxygen ambient. Compared with the TiO2/p+-Si heterostructured devices, the TiO2:B/p+-Si counterparts exhibit markedly enhanced electroluminescence (EL). This is due to that the doped B atoms in TiO2:B films enter into the interstitial sites of TiO2 lattice, which introduces excessive oxygen vacancies. The increase in the concentration of oxygen vacancies due to B-doping leads to the enhanced EL from the TiO2:B/p+-Si heterostructured devices.