Chunyan Lv

Electroluminescence from metal-oxide-semiconductor devices with erbium-doped CeO2 films on silicon

We report on erbium (Er)-related electroluminescence (EL) in the visible and near-infrared (NIR) from metal-oxide-semiconductor (MOS) devices with Er-doped CeO2 (CeO2:Er) films on silicon. The onset voltage of such EL under either forward or reverse bias is smaller than 10 V. Moreover, the EL quenching can be avoidable for the CeO2:Er-based MOS devices. Analysis on the current-voltage characteristic of the device indicates that the electron transportation at the EL-enabling voltages under either forward or reverse bias is dominated by trap-assisted tunneling mechanism. Namely, electrons in n+-Si/ITO can tunnel into the conduction band of CeO2 host via defect states at sufficiently high forward/reverse bias voltages. Then, a fraction of such electrons are accelerated by electric field to become hot electrons, which impact-excite the Er3+ ions, thus leading to characteristic emissions. It is believed that this work has laid the foundation for developing viable silicon-based emitters using CeO2:Er films.

Multicolor and near-infrared electroluminescence from the light-emitting devices with rare-earth doped TiO2 films

We report on multicolor and near-infrared electroluminescence (EL) from the devices using rare-earth doped TiO2 (TiO2:RE) films as light-emitting layers, which are ascribed to the impact excitation of RE3+ ions, with the EL onset voltages below 10 V. The devices are in the structure of ITO/TiO2:RE/SiO2/Si, in which the SiO2 layer is ∼10 nm thick and RE includes Eu, Er, Tm, Nd, and so on. With sufficiently high positive voltage applied on the ITO electrode, the conduction electrons in Si can tunnel into the conduction band of SiO2 layer via the trap-assisted tunneling mechanism, gaining the potential energy ∼4 eV higher than the conduction band edge of TiO2. Therefore, as the electrons in the SiO2 layer drift into the TiO2:RE layer, they become hot electrons. Such hot electrons impact-excite the RE3+ ions incorporated into the TiO2 host, leading to the characteristic emissions.

Color-tunable electroluminescence from Eu-doped TiO(2)/p(+)-Si heterostructured devices: engineering of energy transfer.

We report on color-tunable electroluminescence (EL) from TiO(2):Eu/p(+)-Si heterostructured devices using different TiO(2):Eu films in terms of Eu content and annealing temperature. It is found that the Eu-related emissions are activated by the energy transferred from TiO(2) host via oxygen vacancies, at the price of weakened oxygen-vacancy-related emissions. Both the higher Eu content and the higher annealing temperature for TiO(2):Eu films facilitate the aforementioned energy transfer. In this context, the dominant EL from the TiO(2):Eu/p(+)-Si heterostructured devices can be transformed from oxygen-vacancy-related emissions into Eu-related emissions with increasing Eu-content and annealing temperature for TiO(2):Eu films, exhibiting different colors of emanated light. We believe that this work sheds light on developing silicon-based red emitters using the Eu-doped oxide semiconductor films.

Near-infrared electroluminescence from light-emitting devices based on Nd-doped TiO2/p+-Si heterostructures

We report on near-infrared (NIR) electroluminescence (EL) from the light-emitting devices based on Nd-doped TiO2/p+-Si heterostructures. NIR emissions peaking at ∼910, 1090, and 1370 nm, originated from intra-4f transitions in Nd3+ ions, can be activated by a forward bias voltage as low as ∼5 V. Such NIR EL is triggered by the energy transferred from TiO2 host to Nd3+ ions. It is found that the coexistence of anatase and rutile phases in the TiO2 host enables the device to exhibit pronounced Nd-related EL without concurrent emission from the TiO2 host itself, quite other than the case of existing only anatase phase in TiO2 host. We tentatively suggest that the anatase/rutile interface states play important role in the energy transfer from TiO2 host to Nd3+ ions.

Green electroluminescence from Tb4O7 films on silicon: Impact excitation of Tb3+ ions by hot carriers

We report on green electroluminescence (EL) due to the intra-4f transitions of the trivalent terbium (Tb3+) ions inherent in a Tb4O7 film that is sandwiched between the ITO film and heavily phosphorous- or boron-doped silicon (n+-Si or p+-Si) substrate, thus forming the so-called metal-oxide-semiconductor (MOS) device. The onset voltage of such EL is below 10 V. From the current-voltage characteristic and voltage-dependent EL spectra of the aforementioned MOS device, it is derived that the Tb-related green EL results from the impact excitation of Tb3+ ions by the hot electrons (holes), which stem from the electric-field acceleration of the electrons (holes) injected from the n+-Si (p+-Si) substrate via the trap-assisted tunneling mechanism.

Ultraviolet-visible electroluminescence from metal-oxide-semiconductor devices with CeO2 films on silicon

We report on ultraviolet-visible (UV-Vis) electroluminescence (EL) from metal-oxide-semiconductor (MOS) devices with the CeO2 films annealed at low temperatures. At the same injection current, the UV-Vis EL from the MOS device with the 550 °C-annealed CeO2 film is much stronger than that from the counterpart with the 450 °C-annealed CeO2 film. This is due to that the 550 °C-annealed CeO2 film contains more Ce3+ ions and oxygen vacancies. It is tentatively proposed that the recombination of the electrons in multiple oxygen-vacancy–related energy levels with the holes in Ce 4f1 energy band pertaining to Ce3+ ions leads to the UV-Vis EL.