Ling-Xuan Qian

Improved Performance of Amorphous InGaZnO Thin-Film Transistor With

In this paper, a comparative study of amorphous InGaZnO thin-film transistors with Ta2O5 and TaLaO gate dielectrics has been conducted. It is found that the electrical characteristics of thin-film transistors, including saturation carrier mobility, subthreshold swing, hysteresis, and on-off current ratio, can be effectively improved by the incorporation of La in Ta2O5 gate dielectric, which is ascribed to the fact that La incorporation can enlarge the bandgap of Ta oxide and its conduction-band offset with InGaZnO and also reduce the trap densities in the gate dielectric and at the InGaZnO/gate-dielectric interface. As a result, the sample with higher La concentration in the gate dielectric presents superior electrical characteristics, e.g., a high carrier mobility of 30.9 cm2/V · s, a small subthreshold swing of 0.17 V/dec, and slight hysteresis. Moreover, low-frequency noise measurement and X-ray photoelectron spectrum further support that the improvements in electrical properties are due to reduced trap densities induced by the incorporation of La in the Ta2O5 gate dielectric.

\hbox{Ta}_{2}\hbox{O}_{5}

A four-terminal photodetector was fabricated on the (2¯01)-dominant β-Ga2O3 thin film which was deposited in a plasma-assisted molecular beam epitaxy system. The suitability of this film for solar-blind DUV detection was proved by its transmission spectra. Moreover, the device operating in a specific voltage-current mode can accurately detect the DUV radiation both qualitatively and quantitatively. Accordingly, a dark/photo voltage ratio of 15 was achieved, which is comparable to that of previously-reported β-Ga2O3 interdigital metal-semiconductor-metal photoconductor. More importantly, the aperture ratio of our proposed device exceeds 80%, nearly doubling that of the conventional interdigital metal-semiconductor-metal devices including photoconductor and Schottky-type photodiode, which can intensively benefit the detection efficiency. Furthermore, it was found the dark/photo voltage ratio was nearly trebled with the assistance of two Zener diodes, and further enhancement can be expected by increasing the...

Gate Dielectric by Using La Incorporation

Recently, amorphous InGaZnO ultraviolet photo thin-film transistors have exhibited great potential for application in future display technologies. Nevertheless, the transmittance of amorphous InGaZnO (~80%) is still not high enough, resulting in the relatively large sacrifice of aperture ratio for each sensor pixel. In this work, the ultraviolet photo thin-film transistor based on amorphous InGaMgO, which processes a larger bandgap and higher transmission compared to amorphous InGaZnO, was proposed and investigated. Furthermore, the effects of post-deposition annealing in oxygen on both the material and ultraviolet detection characteristics of amorphous InGaMgO were also comprehensively studied. It was found that oxygen post-deposition annealing can effectively reduce oxygen vacancies, leading to an optimized device performance, including lower dark current, higher sensitivity, and larger responsivity. We attributed it to the combined effect of the reduction in donor states and recombination centers, both of which are related to oxygen vacancies. As a result, the 240-min annealed device exhibited the lowest dark current of 1.7 × 10−10 A, the highest photosensitivity of 3.9 × 106, and the largest responsivity of 1.5 × 104 A/W. Therefore, our findings have revealed that amorphous InGaMgO photo thin-film transistors are a very promising alternative for UV detection, especially for application in touch-free interactive displays.

β-Ga2O3 solar-blind deep-ultraviolet photodetector based on a four-terminal structure with or without Zener diodes

Recently, monoclinic Ga2O3 (β-Ga2O3) photodetectors (PDs) have been extensively studied for various commercial and military applications due to the merits of intrinsic solar rejection, high gain, and great compactness. In this work, c-plane sapphire substrates were annealed under different temperatures in a vacuum furnace prior to the molecular beam epitaxy (MBE) of β-Ga2O3 thin film, which yielded a smoother surface and even a terrace-and-step-like morphology on the substrate, resulting in improved crystallinity of the epitaxial film. Accordingly, both the dark and photo currents of β-Ga2O3 metal-semiconductor-metal (MSM) PDs were increased by the enhanced carrier mobility (μ) of the more crystalline film. However, the substrate-annealing temperature must be sufficiently high to offset the rise of the dark current and thus achieve a remarkable improvement in the photodetection properties. As a result, the PD fabricated on the 1050 °C-annealed substrate exhibited extremely high sensitivity, for example, high responsivity (R) of 54.9 A/W and large specific detectivity (D*) of 3.71 × 1014 Jones. Both parameters were increased by one order of magnitude because of the combined effects of the dramatic increase in μ and the effective reduction in defect-related recombination centers. Nevertheless, the latter also prolonged the recovery time of the PD. These findings suggest another way to develop β-Ga2O3 PD with extremely high sensitivity.

Amorphous InGaMgO Ultraviolet Photo-TFT with Ultrahigh Photosensitivity and Extremely Large Responsivity

p-Ga₂O₃ thin films were epitaxially grown on the as-supplied and vacuum-annealed c-plane sapphire substrates, and the structural and deep-ultraviolet photosensitive properties were investigated. It was found that the vacuum-annealing pretreatment yielded a smoother substrate surface, and thus resulted in a significant improvement in the crystal quality of β-Ga₂O₃ epitaxial film. As a result, both dark and photo currents of P-Ga₂O₃ photodetector were increased. However, the increase extent of photocurrent was relatively small unless the substrate-annealing temperature was high enough. The result can be attributed to three factors compromising each other: carrier mobility, the transitions from valence-band tail to conduction band, and recombination centers. Accordingly, the p-Ga₂O₃ photodetector fabricated on the 1050 °C-annealed substrate exhibited excellent deep-ultraviolet photosensitive properties, for example, a large photocurrent of 3540 nA, a high responsivity of 143.3 A/W, and an outstanding photo-to-dark current ratio of 2.48×10⁴.

High-sensitivity β-Ga 2 O 3 solar-blind photodetector on high-temperature pretreated c-plane sapphire substrate

In this work, both the structural and ultraviolet photosensitive properties of amorphous InGaMgO thin film were in-depth investigated. It was found the transmittance of InGaMgO thin film was as high as nearly 90% in the visible spectra region, leading to a large bandgap over 3.5 eV. In addition, it was revealed the treatment of post deposition annealing in oxygen can effectively improve the ultraviolet photosensitive properties of InGaMgO thin film. Particularly, the photodetector based on the 240-min annealed InGaMgO thin film exhibited excellent device performance, for instance, a high responsivity of 2.8×103 A/W and a large photo-dark current ratio of 1.1×102. However, some degradations were observed when the annealing time was longer than 480 min.

Solar-blind deep-ultraviolet photodetector based on the β-Ga 2 O 3 thin film grown on annealed c-plane sapphire substrate

β-Ga 2 O 3 solar-blind deep-ultraviolet photodetectors were fabricated based on as-supplied and annealed c-plane sapphire substrates. It was found the β-Ga 2 O 3 epitaxial film exhibited better crystalline quality, and accordingly the fabricated device performed significantly improved characteristics, for example, higher responsibility (153 AAV), by adopting annealed sapphire substrate. However, the degradations in dark current and response time were also observed on the photodetector based on annealed sapphire substrate, possibly attributed to higher carrier mobility and longer carrier lifetime in β-Ga 2 O 3 epitaxial film respectively.

The effects of O 2 annealing on the characteristics of IGMO-based UV photodetector

A comparative study on the electrical characteristics of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) with HfLaO and HfLaON gate dielectrics is conducted. With the appropriate incorporation of nitrogen into the HfLaO gate dielectric, the saturation mobility of the TFTs can reach 31.3 cm2 V−1 s−1, which is more than twice that of the control sample with the HfLaO gate dielectric, as a result of the passivation of traps at/near the dielectric/a-IGZO interface by the nitrogen incorporation. However, the electrical characteristics (such as saturation mobility, on-current, and on-current/off-current ratio) of the devices tend to deteriorate with excessive nitrogen incorporation owing to nitrogen-related defects generated in the dielectric.