Ching-Wu Wang

Gamma-ray-irradiation effects on the leakage current and reliability of sputtered TiO2 gate oxide in metal–oxide–semiconductor capacitors

The leakage current and reliability characteristics of γ-ray-irradiated sputtered titanium dioxide (TiO2) thin films have been systematically investigated. Analytical results revealed that the inferior polycrystallinity and the larger leakage current of the anatase structure of unirradiated TiO2 thin film could be effectively improved by raising the irradiation dose at low γ-ray doses [≦10u2009kGy(TiO2)]. However, any higher dose [>10u2009kGy(TiO2)] causes undesirable deterioration of the film crystallinity, yielding an increased leakage current. The optimal dose of γ-rays [10u2009kGy(TiO2) in this work] not only provides a proper energy transfer to the TiO2 film, but also reduces the oxygen deficiency and/or Si-diffusion contamination, resulting in a superior crystallinity, and thus causing the reduced leakage current. The excellent agreement between the E model (thermochemical-breakdown model) and the time-dependent-dielectric-breakdown data suggested strongly that the best long-term reliability of metal–oxide–semi...

The study of aging mechanism in ZnS:Mn thin-film electroluminescent devices grown by MOCVD

Evidence from DLTS and FTIR measurements strongly supports the assertion that the degradation mechanism of ZnS:Mn ACTFEL devices is mainly due to the deep electron trap, E 1 , which comes from the Mn activators reacting with surface water molecules. The photoluminescence measurements reveal that the Mn-related E t trap behaves like a nonradiative center. As a result, poor brightness characteristics including lower brightness and a higher threshold voltage were obtained when samples become aged.

Effect of rapid thermal annealing on radio-frequency magnetron-sputtered GaN thin films and Au/GaN Schottky diodes

The structural and optical properties of rf magnetron-sputtered GaN thin films on p+-Si substrates have been accessed as a function of rapid thermal annealing (RTA) temperatures from 800 to 1000u200a°C. The evidence has revealed that higher RTA temperatures not only assist the GaN films in recrystallizing into stable hexagonal form but also enhance the near-band-edge emission of GaN films in the photoluminescence spectrum. Moreover, a deep electron trap (Et) with activation energy Ec−Et≅0.39u200aeV detected at the surface of higher-RTA-temperature-treated GaN films was asserted to be a nitrogen-vacancy-related defect that takes a defect-assisted-tunneling role in the forward conduction process of Au/GaN Schottky diode. The greater reverse leakage current and lower breakdown voltage are suggested to be due to the effects of a lower barrier height and higher ideality factor that occurred in the higher-RTA-temperature-treated samples.

Deep Traps and Mechanism of Brightness Degradation in Mn-doped ZnS Thin-Film Electroluminescent Devices Grown by Metal-Organic Chemical Vapor Deposition

Evidence from deep level transient spectroscopy (DLTS) and Fourier transform infrared spectroscopy (FTIR) measurements strongly supported the assertion that the degradation mechanism of ZnS:Mn AC thin-film electroluminescent (ACTFEL) devices is mainly due to the deep electron trap, E t, which comes from the Mn activators reacting with water molecules. The photoluminescence measurements revealed that the Mn-related E t trap behaves like a nonradiative center. Furthermore, the X-ray diffraction experiments indicate that the crystallinity of ZnS:Mn phosphor films were destroyed in some degree by the E t trap. As a result, poor brightness characteristics including lower brightness and higher threshold voltage were obtained when samples become aged.

Luminescence improvement of SrS:Ce thin films by rapid thermal annealing: Evidence of energy-transfer model for SrS:Ce electroluminescent devices

SrS:Ce thin films and electroluminescent (EL) devices have been deposited on Si substrate using the rf magnetron reactive sputtering method and subsequently submitted to various thermal treatments. The effects of rapid thermal annealing (RTA) on the properties of SrS:Ce thin films and EL devices have been investigated and compared with results obtained using a conventional furnace. Subsequently, the higher temperature of RTA treatment not only remarkably improves the crystallization of SrS phosphor film in the (200) plane but also reduces oxygen interdiffusion problems and enhances both the interface states (Eit) as well as bulk trap (Ebt) densities. These effects all are important factors in yielding brighter electroluminescence. Furthermore, a physical band model based on energy-transfer concept is proposed to elucidate the electroluminescent mechanism of SrS:Ce EL devices. All evidence reveals that the efficient luminous center formed by the Ce atom associated with the Ebt bulk trap is the basis of thi...

The relation between luminous properties and oxygen content in ZnS:TbOF thin-film electroluminescent devices fabricated by radio-frequency magnetron sputtering method

The purpose of this paper is to study the relationship between the oxygen concentration and brightness degradation in ZnS:TbOF green thin-film electroluminescent (EL) devices. The characteristics including crystallinity, optical, and electrical properties were discussed. The brightness-voltage (B-V) measurement results shelved that with higher oxygen-content in ZnS:TbOF phosphor layer, lower brightness was measured. It was consistent with the poor crystallinity, worse photoluminescent intensity, and easier to get moisture in the oxygen-rich (O/Tb>1) phosphor film. Furthermore, deep level transient spectroscopy (DLTS) measurements identified that when the O/Tb ratio was greater than 1, the oxygen-related deep hole traps E/sub H1/ and/or E/sub H2/ could be detected in the ZnS:TbOF phosphor layer. These E/sub H1/ and/or E/sub H2/ traps were believed to be the main killers for the brightness of the device since they capture most of the holes from the generated electron-hole pairs. This evidence strongly supports that the modified energy transfer model is more dominant than direct impact excitation during the luminescent process.

Effects of gamma-ray irradiation on the microstructural and luminescent properties of radio-frequency magnetron-sputtered GaN thin films

The microstructural and luminescent properties of sputtered GaN thin films pre-irradiated and the (gamma) -ray irradiated were systematically investigated. Analytical results revealed that the increasing dose of (gamma) -rays could enhance the more occurrence of nitrogen vacancies which not only created a prominent deep level luminescence but also destroyed the crystallinity of GaN thin films. For lose dose of (gamma) -ray irradiation (4 Mrad (GaN)), evidence showed that by raising the irradiation dose, more associated Ga-H complexes will be effectively promoted, yielding an enhanced yellow bad emission. However for high dose of (gamma) -ray irradiation (4 Mrad (GaN)), further higher dose of (gamma) - rays could lead the dissociation of Ga-H complexes in GaN samples, resulting in a repressed yellow band emission.

Rapid thermal annealing effects on radio-frequency magnetron-sputtered P-type GaN thin films and Al/P-type GaN Schottky diodes

In this article, we report the effects of RTA on Mg-diffused GaN thin films and Al/Mg-diffused GaN Schottky diodes. After Mg-diffusion process, the samples were exposed to RTA treatment the temperature from 800 to 900 degree(s)C. The samples were studied by variable temperature Hall effect measurements, and PL spectroscopy. The reduced resistivity by higher RTA temperature is due to the increased activated acceptor. Evidence, showed that both near-band-edge emission and deep level luminescent in PL spectrum could be all enhanced by raising the RTA temperature. Considering the Al/Mg-diffused Schottky diodes, the higher RTA temperature resulting in the superior forward conduction characteristics are suggested to be due to the more concentrations of hole and lower resisivity of GaN thin film. However, the greater reverse leakage current and lower breakdown voltage were deduced to be the creation formation of Ga-Al compounds at the metal-semiconductor interface.

Deep traps and brightness degradation for oxygen-rich concentration in ZnS:TbOF thin film electroluminescent devices

The purpose of this work is to study the relationship between the oxygen-rich concentration and brightness degradation in ZnS:TbOF green A.C. thin-film electroluminescent devices. The results showed that higher oxygen-content (O/Tb>1) in the phosphor layer not only created the deep hole traps (E/sub t1/ and/or E/sub t2/) but also yielded the EL devices with moisture. As a result, lower brightness was obtained.

An investigation of deep electron trap at the different insulator-phosphor interfaces in ZnS:TbOF ACTFEL devices

Energy-resolved DLTS was utilized to measure the interface electron energy distribution at the insulator-semiconductor interface. The results showed that Ta/sub 2/O/sub 5//ZnS:TbOF has shallower interface state energy distribution and higher averaged interface state density than SiO/sub 2//ZnS:TbOF.