Sung-Yen Wei

TiO 2 -Based Metal–Semiconductor–Metal Ultraviolet Photodetectors Deposited by Ultrasonic Spray Pyrolysis Technique

This paper uses nonvacuum ultrasonic spray pyrolysis deposition method to grow TiO₂ for ultraviolet (UV) detection. The analyses of the materials like X-ray photoelectron spectroscopy, X-ray diffraction, and photoluminescence were investigated. The 600 °C annealing temperature is the optimum condition to obtain the anatase TiO₂. The metal-semiconductor- metal (MSM) photodetectors (PDs) with 3-, 5-, 7-, 10-μm finger spacing were fabricated and the performance was investigated. The PD with 10-μm finger spacing has the lowest dark current of 2.92 × 10^-11 A and the highest UV-to-visible rejection ratio (RUV/VIS) of 2.1 × 10⁵ at 5 V. The PD with 5-μm finger spacing has the lowest noise equivalent power of 2.57 × 10^-9 W and the highest detectivity (D*) of 5.46 × 108 cmHz^0.5W^-1. The rising time and the falling time of the PD are 5 and 12 s. In addition, the TiO₂-based MSM PD in this paper operated normally at 450 K; however, the performance is slightly degraded. The mechanisms causing degradation at high temperature were investigated.

Characterization of TiO 2 -Based MISIM Ultraviolet Photodetectors by Ultrasonic Spray Pyrolysis

In this letter, non-vacuum ultrasonic spray pyrolysis deposition was used to grow Al₂O₃/TiO₂ thin film as the metal-insulator-semiconductor-insulator-metal ultraviolet photodetector (MISIM UV PD). The anatase TiO₂ with 400 °C annealing was used as the active layer of the UV PD. X-ray diffraction and Raman spectra were used to characterize the crystal phase of the TiO₂. The Al₂O₃/TiO₂ MISIM UV PD has lower dark current (~57.2 pA), higher photoresponse (~24.48 A/W), and higher detectivity (~8.25 × 10¹³ Jones), all of which were better than the TiO₂ MSM UV PD. Similar device performance was obtained from the SiO₂/TiO₂ MISIM UV PD. The external quantum efficiency of the Al₂O₃/TiO₂ and SiO₂/TiO₂ MISIM UV PDs was 8204% and 6840%. Such high external quantum efficiency results from the internal photoconductive gain and the interfacial trap controlled charge injection.

Hetero-epitaxial growth of stoichiometry tunable Si1−xGex film via a low temperature aluminium-induced solid phase epitaxy (AI-SPE) process

A novel process of aluminum-induced solid-phase epitaxy (AI-SPE) is used to fabricate a hetero-epitaxial Si1−xGex (epi-SiGe) film on an sc-Si (100) substrate at relatively low temperatures (lower than 450 °C) using a 1/4 × 4′′ wafer. The stoichiometry of Ge in the epi-SiGe film can be easily tuned in the AI-SPE process by controlling the annealing temperature and the Ge fraction (x) of the initial a-Si1−xGex layer. The stoichiometry and epitaxial relationship of the epi-SiGe film were verified by grazing incidence X-ray diffraction (GI-XRD) and transmission electron microscopy (TEM). The AI-SPE mechanism is directly verified by in situ heating TEM. Based on the experimental results, it is concluded that the AI-SPE mechanism for the epi-SiGe film can be divided into four steps: (a) initial stage; (b) formation of a-Si1−xGex free atoms and diffusion along Al grain boundaries to the sc-(100) substrate surface; (c) nucleation of crystalline Si1−xGex at the surface of the sc-Si (100) substrate; and (d) crystal growth and layer exchange.

Enhanced electrocatalytic activities of pulse-mode potentiostatic electrodeposited single-crystal, fern-like Pt nanorods

Single-crystal and fern-like Pt nanorods (Pt-NR) were electrodeposited on carbon paper. The electrocatalytic activity of prepared Pt-NR electrodes, as determined by the catalyst mass activity (MA) and specific activity (SA) for the methanol oxidation reaction, are respectively 4.59 times and 10.54 times better than that of a commercial Pt-black catalyst.

Growth mechanism of an aluminium-induced solid phase epitaxial (AI-SPE) Si0.5Ge0.5 layer using in situ heating transmission electron microscopy

The mechanism of growth of an epitaxial Si0.5Ge0.5 layer on a single crystalline (sc) Si (100) substrate by aluminum-induced solid phase epitaxy (AI-SPE) at a relatively low temperature (450 °C) has been revealed using in situ heating transmission electron microscopy (TEM). The analysis of the thermodynamics exactly supports the finding from in situ TEM. It evidences that the Si0.5Ge0.5 prefers to nucleate at the interface of the Al layer and the sc-Si (100) substrate due to the lowest critical thickness for nucleation. Based on the results from in situ TEM and thermodynamic analysis, the germanium (Ge) virtual substrate of the compositional gradient can be successfully prepared via a multi-run AI-SPE process at low-temperature.

Investigation of TiO 2 -Based MISIM Ultraviolet Photodetectors With Different Insulator Layer Thickness by Ultrasonic Spray Pyrolysis Deposition

This work uses ultrasonic spray pyrolysis deposition to grow titanium dioxide and aluminum oxide (Al₂O₃) films, respectively, as an active layer and an insulator layer of the metal-insulator-semiconductor-insulator-metal (MISIM) photodetector (PD). 10-, 20-, and 30-nm-thick Al₂O₃ films were deposited and the I-V characteristics in the dark and under illumination were measured and investigated. The dark current was suppressed to 11.6 pA for the MISIM PD with the 30-nm Al₂O₃. In addition, the carrier transportation mechanisms of the dark current are analyzed. The photoresponsivity of the MISIM PD with the 10-nm Al₂O₃ was 8.22 A/W (at 10 V), which is much higher than 0.84 A/W of the metal-semiconductor-metal PD. The noise equivalent power and detectivity of the MISIM PD with the 10-nm Al₂O₃ were 2.28 × 10^-10 W and 2.4 × 10⁹ Jones. The PDs showed a slight degradation when the ambient temperature was up to 450 K.

Spray pyrolysis coating Al 2 O 3 :Cl/TiO 2 bilayer for PERC

In this study we use low-cost spray pyrolysis method to produce a Al₂O₃:Cl/TiO₂ bilayer as rear passivation layer to replace the common known Al₂O₃/SiNx laminate in PERC structure silicon solar cells. The TiO₂ and TiO₂/Al₂O₃ mixed thin film acts a competent barrier from molten aluminum paste during the co-firing process and high refractive index of those thin films demonstrated excellent internal back reflectance (IBR). Very high negative fixed charge concentration is up to 5 × 10¹² cm^-2 in TiO₂ thin film being observed and the interface trap density (D_it) can be controlled via Ti/Al ratio and ultra-thin Al₂O₃:Cl interfacial layer to maintain good passivation ability and the lowest result of D_it is 8 × 10¹⁰ cm^-2eV^-1 with a 6nm Al₂O₃:Cl interfacial layer. Through the use of Al₂O₃:Cl interfacial layer, the carrier lifetime of bulk wafer increase from 60μs to 120μs. All of the results show that this concept is very promising for high efficiency silicon solar cell application.