Canxing Wang

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.

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.

Comparison on electrically pumped random laser actions of hydrothermal and sputtered ZnO films

Random lasing (RL) in polycrystalline ZnO films is an intriguing research subject. Here, we have comparatively investigated electrically pumped RL behaviors of two metal-insulator-semiconductor structured devices using the hydrothermal and sputtered ZnO films as the semiconductor components, i.e., the light-emitting layers, respectively. It is demonstrated that the device using the hydrothermal ZnO film exhibits smaller threshold current and larger output optical power of the electrically pumped RL. The morphological characterization shows that the hydrothermal ZnO film is somewhat porous and is much rougher than the sputtered one, suggesting that in the former stronger multiple light scattering can occur. Moreover, the photoluminescence characterization indicates that there are fewer defects in the hydrothermal ZnO film than in the sputtered one, which means that the photons can pick up larger optical gain through stimulated emission in the hydrothermal ZnO film. Therefore, it is believed that the stronger multiple light scattering and larger optical gain contribute to the improved performance of the electrically pumped RL from the device using the hydrothermal ZnO film.

Visible and near-infrared electroluminescence from TiO2/p+-Si heterostructured device

We report on visible and near-infrared (NIR) electroluminescence (EL) from the device based on the TiO2/p+-Si heterostructure, in which the TiO2 film is composed of anatase and rutile phases. As the device is applied with sufficiently high forward bias with the positive voltage connecting to p+-Si, the visible EL peaking at ∼600 nm along with the NIR EL centered at ∼810 nm occur simultaneously. It is proposed that the oxygen vacancies in the anatase TiO2 and Ti3+ defect states in the rutile TiO2 are the responsible centers for the visible and NIR EL, respectively.

Electrically pumped random lasing in ZnO-based metal-insulator-semiconductor structured devices: Effect of ZnO film thickness

In our previous report [Ma et al., Appl. Phys. Lett. 91, 251109 (2007)], electrically pumped random lasing (RL) from polycrystalline ZnO films has been realized by means of metal-insulator-semiconductor (MIS) structures based on ZnO films on silicon substrate. Herein, we investigate the effect of ZnO film thickness on the threshold current and output power of RL from the ZnO-based MIS structured devices. It is found that the RL threshold current increases with the increase of ZnO film thickness. Moreover, the output power of RL decreases with the increase of ZnO film thickness at small injection current, while it increases with the ZnO film thickness at large injection current. The mechanisms underlying the above-mentioned results have been tentatively explored in terms of the two ingredients of RL, i.e., multiple light scattering and optical gain.

Electrically pumped random lasing from the light-emitting device based on two-fold-tandem SiO2/ZnO structure

We report on remarkable decrease in threshold current for electrically pumped random lasing (RL) from the light-emitting device based on two-fold-tandem (double-) SiO2/ZnO-structure with respect to that in the case of single-SiO2/ZnO-structured device. Moreover, the former is of higher power conversion efficiency. In the double-SiO2/ZnO-structure, a waveguide is formed by the stacking SiO2/ZnO/SiO2, which enables photon confinement. Moreover, the electrons leaking out of the bottom SiO2/ZnO-structure are collected and partly involved in the radiative recombination in the top one. Furthermore, the RL photons generated in the bottom SiO2/ZnO-structure act as the stimuli to increase the stimulated emission rate in the top one. For the above-mentioned reasons, the RL performance of the double-SiO2/ZnO-structured device is substantially improved.

On the mechanism of carrier scattering at oxide precipitates in Czochralski silicon

Oxygen precipitation (OP) in Czochralski (CZ) silicon has been extensively and intensively studied in the past decades due to its significance for improving manufacturing yield of integrated circuits. Nevertheless, how OP affects the carrier transportation in CZ silicon has hardly been addressed. Here, we report that the carrier mobility is decreased to a certain extent while the carrier concentration is nearly unchanged due to significant OP in CZ silicon. Interestingly, such a decrease in mobility can be offset by copper (Cu) decoration of oxygen precipitates via Cu drive-in anneal at appropriate temperatures. It is clarified that the charges associated with the oxygen precipitate/silicon interface states exert additional scattering effect on the carrier transportation, leading to the decrease of carrier mobility as mentioned above. We believe that the present work gains an insight into OP in CZ silicon from the electrical point of view.