Jiaming Sun

Bright green electroluminescence from Tb3+ in silicon metal-oxide-semiconductor devices

Bright green electroluminescence with luminance up to 2800cd∕m2 is reported from indium-tin-oxide∕SiO2:Tb∕Si metal-oxide-semiconductor devices. The SiO2:Tb3+ gate oxide was prepared by thermal oxidation followed by Tb+ implantation. Electroluminescence and photoluminescence properties were studied with variations of the Tb3+ ion concentration and the annealing temperature. The optimized device shows a high external quantum efficiency of 16% and a luminous efficiency of 2.1lm∕W. The excitation processes of the strong green electroluminescence are attributed to the impact excitation of the Tb3+ luminescent centers by hot electrons and the subsequent crossrelaxation from D35 to D45 energy levels. Light-emitting devices with micrometer size fabricated by the standard metal-oxide-semiconductor technology are demonstrated.

Switchable two-color electroluminescence based on a Si metal-oxide-semiconductor structure doped with Eu

A Si metal-oxide-semiconductor electroluminescent device structure is reported which emits two colors, while being doped with a single rare-earth element. Thermally grown SiO2 oxide layers were implanted with Eu and subseqently annealed. Depending on the electrical excitation current, the luminescence is red or blue, which can be ascribed to electronic transitions in tri- and divalent europium (Eu3+ and Eu2+), respectively.

Efficient ultraviolet electroluminescence from a Gd-implanted silicon metal-oxide-semiconductor device

Strong ultraviolet electroluminescence with an external quantum efficiency above 1% is observed from an indium-tin oxide/SiO2:Gd∕Si metal–oxide–semiconductor structure. The SiO2:Gd active layer is prepared by thermal oxidation followed by Gd+ implantation and annealing. The electroluminescence spectra show a sharp peak at 316nm from the P7∕26 to S7∕28 transition of Gd3+ ions. Micrometer-sized electroluminescent devices are demonstrated.

Light emission and charge trapping in Er-doped silicon dioxide films containing silicon nanocrystals

The processes of electro- (EL) and photoluminescence (PL) and charge trapping in Er-implanted SiO2 containing silicon nanoclusters have been studied. It is shown that in Er-doped SiO2 with an excess of silicon nanoclusters of 10 at. %, a strong energy transfer from silicon nanoclusters results in a ten-fold increase of the PL peak at 1540 nm from Er luminescent centers, whereas the EL is strongly quenched by the excess silicon nanoclusters. It is further shown that the implantation of Er creates in the oxide positive charge traps with a giant cross section (σh0>10−13cm2). Introducing subsequent silicon nanocrystals in the oxide leads to the formation of negative charge traps of a giant cross section (σe0>10−13cm2). The possible reason for the EL quenching in the Er-doped SiO2 by silicon nanoclusters is discussed.

Electrical and optical properties of Al-doped ZnO and ZnAl2O4 films prepared by atomic layer deposition

ZnO/Al2O3 multilayers were prepared by alternating atomic layer deposition (ALD) at 150°C using diethylzinc, trimethylaluminum, and water. The growth process, crystallinity, and electrical and optical properties of the multilayers were studied with a variety of the cycle ratios of ZnO and Al2O3 sublayers. Transparent conductive Al-doped ZnO films were prepared with the minimum resistivity of 2.4 × 10−3 Ω·cm at a low Al doping concentration of 2.26%. Photoluminescence spectroscopy in conjunction with X-ray diffraction analysis revealed that the thickness of ZnO sublayers plays an important role on the priority for selective crystallization of ZnAl2O4 and ZnO phases during high-temperature annealing ZnO/Al2O3 multilayers. It was found that pure ZnAl2O4 film was synthesized by annealing the specific composite film containing alternative monocycle of ZnO and Al2O3 sublayers, which could only be deposited precisely by utilizing ALD technology.

Origin of anomalous temperature dependence and high efficiency of silicon light-emitting diodes

Efficient electroluminescence with power efficiency up to 0.12% is observed from silicon pn diodes prepared by boron implantation with boron concentrations above the solubility limit at the postimplantation annealing temperature. The electroluminescence spectra exhibit a transition from two bound-exciton bands towards the free electron-hole pair recombination with an anomalous increase in the total intensity with increasing temperature. The implantation dose and temperature dependences of the relative peak intensities provide evidence for the relevance of excitonic traps as a supply for free electron-hole pairs and thus for the origin of the enhanced electroluminescence at elevated temperatures.

Increase of blue electroluminescence from Ce-doped SiO2 layers through sensitization by Gd3+ ions

Efficient blue electroluminescence peak at around 440nm with a maximum output power density of 34mW∕cm2 was obtained from Ce and Gd coimplanted metal-oxide-semiconductor light emitting devices. Energy transfer from Gd3+ to Ce3+ ions was observed during the excitation process, leading to a more than threefold increase of the external quantum efficiency of the blue Ce3+ luminescence up to 1.8%. This is evidenced by the increase of the excitation cross section of Ce3+ ions from 4.8×10−13to3.5×10−12cm2 and the simultaneous reduction of the decay time and the impact cross section of Gd3+ ions.Efficient blue electroluminescence peak at around 440nm with a maximum output power density of 34mW∕cm2 was obtained from Ce and Gd coimplanted metal-oxide-semiconductor light emitting devices. Energy transfer from Gd3+ to Ce3+ ions was observed during the excitation process, leading to a more than threefold increase of the external quantum efficiency of the blue Ce3+ luminescence up to 1.8%. This is evidenced by the increase of the excitation cross section of Ce3+ ions from 4.8×10−13to3.5×10−12cm2 and the simultaneous reduction of the decay time and the impact cross section of Gd3+ ions.

Giant stability enhancement of rare-earth implanted SiO2 light emitting devices by an additional SiON protection layer

The electrical stability of rare-earth implanted SiO2 light emitting devices was improved by using a SiON dielectric buffer layer in an indium tin oxide/SiON∕SiO2:Tb∕Si device structure. At the expense of a small increase of the electroluminescence threshold voltage, a large increase of the breakdown electric field from 7.5to10.5MV∕cm was obtained in the SiO2:Tb layer, and the maximum injection current density was increased by three orders of magnitude from 4mA∕cm2to4A∕cm2. The operation time of the electroluminescence devices was increased by more than three orders of magnitude at an injection current density of ∼4mA∕cm2. Our experimental results are consistent with a theoretical model proposed for designing a stable and efficient thin-film light emitting device containing double-stacked dielectric layers.

Electroluminescence properties of the Gd3+ ultraviolet luminescent centers in SiO2 gate oxide layers

Electroluminescence (EL) properties in the ultraviolet (UV) range were studied on Gd-implanted indium tin oxide/SiO2:Gd∕Si metal-oxide-semiconductor light emitting devices. The efficient UV line at 316nm from Gd3+ centers shows a maximum power density of 2mW∕cm2 and a quantum efficiency above 5%. The Gd3+ luminescent center has an excitation cross section above 7.4×10−15cm2 with an EL decay time around 1.6ms at a Gd concentration of 3%. A decrease of the EL efficiency is observed by a cross relaxation at a high Gd concentration and by clustering of Gd atoms at an annealing temperature of 1000°C. A strong quenching of the UV EL due to electron trapping around optically active Gd3+ centers is observed during the injection of hot electrons.

Flash Lamp Annealing vs Rapid Thermal and Furnace Annealing for Optimized Metal-Oxide-Silicon-Based Light-Emitting Diodes

Conventional annealing processes such as furnace annealing (FA) and rapid thermal annealing (RTA) are compared to the more advanced technique of flash lamp annealing (FLA) regarding the electroluminescence (EL) efficiency, electrical stability, defect formation, and rare-earth nanocluster (RE-nc) creation in metal-oxide-silicon-based light-emitting diodes with Gd implanted SiO 2 layers. We observed strong correlation between the electroluminescence efficiency, the nanocluster size, and the annealing technique for Gd implanted oxides. The increase of the annealing temperature and time leads to an increase of the RE-nc size and decreases the EL efficiency. Therefore, short-pulse high-temperature annealing (FLA) has a large advantage over the different annealing techniques (FA and RTA) from the point of view of stable and efficient metal oxide semiconductor light emitters.