W. K. Chen

Oxygen-Dependent Instability and Annealing/Passivation Effects in Amorphous In–Ga–Zn–O Thin-Film Transistors

This letter discusses the reason for the instability of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) under both positive and negative bias stresses. This instability is significantly influenced by the oxygen content in the bulk IGZO and the surrounding environment. The as-fabricated low-temperature devices can only endure a single polarized bias stress. An a-IGZO TFT that is stable toward both positive and negative bias stresses with large relaxation times of 95 × 104 and 371 × 104 s, respectively, is achieved by annealing and passivation.

Electrical characterization of isoelectronic In-doping effects in GaN films grown by metalorganic vapor phase epitaxy

Indium isoelectronic doping was found to have profound effects on electrical properties of GaN films grown by metalorganic chemical vapor deposition. When a small amount of In atoms was introduced into the epilayer, the ideality factor of n-GaN Schottky diode was improved from 1.20 to 1.06, and its calculated saturation current could be reduced by 2 orders of magnitude as compared to that of the undoped sample. Moreover, it is interesting to note that In isodoping can effectively suppress the formation of deep levels at 0.149 and 0.601 eV below the conduction band, with the 0.149 eV trap concentration even reduced to an undetected level. Our result indicates that the isoelectronic In-doping technique is a viable way to improve the GaN film quality.

Isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition

The isoelectronic In-doping effect in GaN films grown by metalorganic chemical vapor deposition was investigated by using Raman scattering, scanning electron microscopy (SEM), and x-ray and photoluminescence (PL) measurements. In our study, the phonon spectra of films remain sharp without alloy formation after incorporation of small amounts of In atoms. The SEM pictures of the sample surface reveal greatly reduced nanopits indicating better surface flatness that is also supported by the multiple interference effect in the PL signals. More importantly, isoelectronic doping has caused the linewidth at 15 K of the near-band-edge emission of GaN to decrease sharply to 10 meV or less, reflecting improved optical property.

Dual gate indium-gallium-zinc-oxide thin film transistor with an unisolated floating metal gate for threshold voltage modulation and mobility enhancement

In this study, we propose a floating dual gate (FDG) indium-gallium-zinc-oxide (IGZO) thin film transistor (TFT) with a floating metal back gate that is directly contact with IGZO without a dielectric layer. The floating back gate effect is investigated by changing the work function (ϕ) of the back gate. The FDG IGZO TFT exhibits an improved field-effect mobility (μ), unchanged subthreshold swing (SS), high on/off current ratio, and a tunable threshold voltage ranged (Vth) from −5.0 to +7.9 V without an additional back gate power supply.

Amorphous indium-gallium-zinc-oxide visible-light phototransistor with a polymeric light absorption layer

This work demonstrates a real-time visible-light phototransistor comprised of a wide-band-gap amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistor (TFT) and a narrow-band-gap polymeric capping layer. The capping layer and the IGZO layer form a p-n junction diode. The p-n junction absorbs visible light and consequently injects electrons into the IGZO layer, which in turn affects the body voltage as well as the threshold voltage of a-IGZO TFT. The hysteresis behavior due to the charges at IGZO back interface is also discussed.

High-Performance Light-Erasable Memory and Real-Time Ultraviolet Detector Based on Unannealed Indium–Gallium–Zinc–Oxide Thin-Film Transistor

A light-erasable memory and a real-time ultraviolet (UV) detector were developed from an amorphous indium-gallium-zinc-oxide (IGZO) thin-film transistor fabricated at room temperature without post-annealing. The natural defects within the IGZO or at the dielectric interface serve as electron traps to support a writing operation (switching down the channel conductance). A negative gate bias accompanied by UV illumination performs an erasing operation (switching up the channel conductance). After the writing/erasing of the proposed memory, an on/off ratio greater than 104 was maintained for a testing duration of 10 000 s. A real-time UV detector was also developed, and a light/dark ratio of roughly 104 was demonstrated.

Thermal stability study of Ni/Ta n-GaN Schottky contacts

The Schottky behavior of Ni/Ta and Ni contacts on n-GaN was investigated under various annealing conditions by current–voltage measurements. It is found that with the addition of Ta between the Ni layer and the GaN substrate the thermal stability properties of devices can be significantly improved. Experimental results indicate that a high quality Ni/Ta n-GaN Schottky diode with an ideality factor and barrier height of 1.16 and 1.24 eV, respectively, can be obtained under 1 h annealing, at 700 °C.

Light-Enhanced Bias Stress Effect on Amorphous In-Ga-Zn-O Thin-film Transistor with Lights of Varying Colors

This study investigates the light-color-dependent bias stress effect on an amorphous indium-gallium-zinc-oxide (a-IGZO) thinfilm transistor (TFT). The color of incident photons with energies lower than the optical band gap of IGZO (3.2 eV) was varied from blue to infrared. Regardless of the bias polarity, light is regarded as a promoter for bias-stress-induced instability. The light response of the a-IGZO TFT is both colorand bias-polarity-dependent. VC 2011 The Electrochemical Society. [DOI: 10.1149/1.3584088] All rights reserved.

Carrier dynamics in isoelectronic ZnSe1−xOx semiconductors

This study explores the effects of both Oxygen and temperature on the carrier dynamics of isoelectronic ZnSe1−xOx (x=0.027 and 0.053) semiconductors using photoluminescence (PL) and time-resolved PL spectroscopy. We find that the Kohlrausch law is highly consistent with the complex decay traces induced by isoelectronic O traps, and the mechanism of carrier recombination undergoes a complicated change from trapped to free excitons with the increase in temperature. Complex recombination processes are clarified using the relaxation model based on various decay channels. These findings are consistent with the initial fall in the stretching exponent β followed by its monotonic increase with increasing temperature.

Time-resolved photoluminescence of isoelectronic traps in ZnSe1−xTex semiconductor alloys

Kohlrausch’s stretched exponential law correlates well with the photoluminescence (PL) decay profiles of ZnSe1−xTex. As the Te concentration increases, the stretching exponent β initially declines and then monotonically increases. This result can be understood using the hopping-transport and energy transfer model. The increase in the number of isoelectronic Te localized traps can reduce the PL decay rate and increase the linewidth, whereas the hybridization of the Te localized states with the valence-band edge states causes a reduction in both the lifetime and linewidth.