Pui-To Lai

Improving efficiency of organic photovoltaic cells with pentacene-doped CuPc layer

We have fabricated efficient heterojunction organic photovoltaic (OPV) cells based on pentacene-doped copper(II) phthalocyanine (CuPc) layer as donor and fullerene (C60) layer as acceptor. The power conversion efficiency of 4% pentacene-doped CuPc∕C60 OPV cell (3.06%) is increased by 77% compared with that of the standard CuPc∕C60 OPV cell (1.73%). The efficiency improvement can be attributed to the higher carrier mobility instead of the stronger photon absorption of the pentacene-doped CuPc layer.

Electrical Properties of HfTiON Gate-Dielectric GaAs Metal-Oxide-Semiconductor Capacitor With AlON as Interlayer

High- k HfTiON gate-dielectric GaAs MOS capacitors with and without AlON as interfacial passivation layer (IPL) are fabricated and their interfacial and electrical properties are compared. It is found that low interface-state density ( 1.5×1012 cm-2eV-1 at midgap), small gate leakage current ( 1.3×10-4 A/cm2 at Vg=Vfb+1 V), small capacitance equivalent thickness (1.72 nm), large equivalent dielectric constant (25.6), and high device reliability can be achieved for the Al/HfTiON/AlON/GaAs MOS device. All of these should be due to the fact that the AlON IPL on sulfur-passivated GaAs can effectively reduce the density of defective states and unpin the Femi level at the AlON/GaAs interface, thus greatly improving the interfacial and electrical properties of the device.

Performance Improvements of Metal–Oxide–Nitride–Oxide–Silicon Nonvolatile Memory with ZrO2 Charge-Trapping Layer by Using Nitrogen Incorporation

The properties of ZrO2 and ZrON as the charge-trapping layer (CTL) of metal–oxide–nitride–oxide–silicon memory are investigated. The microstructure and chemical bonding are examined by X-ray diffraction and X-ray photoelectron spectroscopy. It is found that nitrogen incorporation in ZrO2 can induce more charge-trapping sites, effectively suppress the formation of zirconium silicate (leading to better interface quality between the CTL and the SiO2 tunneling layer), and increase the dielectric constant of ZrO2, thus improving the memory performances (large memory window, high program/erase speed, good endurance characteristics, and small charge loss).

Improved memory characteristics by NH3-nitrided GdO as charge storage layer for nonvolatile memory applications

Charge-trapping memory capacitor with nitrided gadolinium oxide (GdO) as charge storage layer (CSL) is fabricated, and the influence of post-deposition annealing in NH3 on its memory characteristics is investigated. Transmission electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction are used to analyze the cross-section and interface quality, composition, and crystallinity of the stack gate dielectric, respectively. It is found that nitrogen incorporation can improve the memory window and achieve a good trade-off among the memory properties due to NH3-annealing-induced reasonable distribution profile of a large quantity of deep-level bulk traps created in the nitrided GdO film and reduction of shallow traps near the CSL/SiO2 interface.

Charge-trapping characteristics of fluorinated thin ZrO2 film for nonvolatile memory applications

The effects of fluorine treatment on the charge-trapping characteristics of thin ZrO2 film are investigated by physical and electrical characterization techniques. The formation of silicate interlayer at the ZrO2/SiO2 interface is effectively suppressed by fluorine passivation. However, excessive fluorine diffusion into the Si substrate deteriorates the quality of the SiO2/Si interface. Compared with the ZrO2-based memory devices with no or excessive fluorine treatment, the one with suitable fluorine-treatment time shows higher operating speed and better retention due to less resistance of built-in electric field (formed by trapped electrons) against electron injection from the substrate and smaller trap-assisted tunneling leakage, resulting from improved ZrO2/SiO2 and SiO2/Si interfaces.

Improved Charge-Trapping Characteristics of

The charge-trapping characteristics of BaTiO₃ film with and without Zr incorporation were investigated based on Al/ Al₂O₃/BaTiO₃/SiO₂/Si capacitors. Compared with the device without Zr incorporation, the one with Zr incorporation showed a similar memory window (8.3 V at ±12 V for 1 s), but higher program speed at low gate voltage (3.2 V at 100 μs + 6 V) and better endurance and data retention (charge loss of 6.4% at 150°C for 10⁴), due to the Zr-doped BaTiO₃ exhibiting higher charge-trapping efficiency and higher density of traps with deeper energy levels.

\hbox{BaTiO}_{3}

A TiON/HfON dual charge storage layer (CSL) with tapered bandgap structure is proposed for metal-oxide–nitride-oxide–silicon-type memory by using the inter-diffusion of Ti and Hf atoms near the TiON/HfON interface to form an intermixing layer of HfxTiyON with varying Hf/Ti ratio in the dual CSL during post-deposition annealing, as confirmed by transmission electron microscopy. The memory capacitor with TiON/HfON as dual-CSL shows a large memory window of 5.0u2009V at ±12u2009V for 100u2009μs, improved cycling endurance with little degradation after 105 cycles and good data retention with an extrapolated 10-yr window of 4.6u2009V at room temperature. These are highly associated with the tapered bandgap structure and appropriate trap distribution in the dual CSL. Therefore, the TiON/HfON dual-CSL structure provides a very promising solution for future charge-trapping memory applications.

by Zr Doping for Nonvolatile Memory Applications

Charge-trapping characteristics of SrTiO3 with and without nitrogen incorporation were investigated based on Al/Al2O3/SrTiO3/SiO2/Si (MONOS) capacitors. A Ti-silicate interlayer at the SrTiO3/SiO2 interface was confirmed by x-ray photoelectron spectroscopy and transmission electron microscopy. Compared with the MONOS capacitor with SrTiO3 as charge-trapping layer (CTL), the one with nitrided SrTiO3 showed a larger memory window (8.4 V at ±10 V sweeping voltage), higher P/E speeds (1.8 V at 1 ms +8u2002V) and better retention properties (charge loss of 38% after 104u2002s), due to the nitrided SrTiO3 film exhibiting higher dielectric constant, higher deep-level traps induced by nitrogen incorporation, and suppressed formation of Ti silicate between the CTL and SiO2 by nitrogen passivation.

Improved charge-trapping properties of TiON/HfON dual charge storage layer by tapered band structure

GaAs metal–oxide–semiconductor (MOS) capacitors with HfTiON as a gate dielectric and Ga2O3(Gd2O3) (GGO) as an interlayer annealed in NH3 or N2 are fabricated, and their electrical properties are characterized. Experimental results show that the HfTiON/GGO/GaAs MOS device annealed in NH3 exhibits a low interface-state density (1.1 × 1012 cm−2 eV−1), a small gate leakage current (1.66 × 10−4 A cm−2 at Vg = Vfb + 1 V), a large equivalent dielectric constant (25.7), and a good capacitance–voltage behavior. All these should be attributed to the fact that the GGO interlayer and postdeposition annealing in NH3 can effectively suppress the formation of interfacial Ga/As oxides and remove the excess As atoms at the GaAs surface, thus reducing the relevant defects at/near the GGO/GaAs interface.

Nitrided SrTiO3 as charge-trapping layer for nonvolatile memory applications

The charge-trapping properties of HfYON film are investigated by using the Al/HfYON/SiO2/Si structure. The physical features of this film were explored by transmission electron microscopy and x-ray photoelectron spectroscopy. The proposed device shows better charge-trapping characteristics than samples with HfON or Y2O3 as the charge-trapping layer due to its higher trapping efficiency, as confirmed by extracting their charge-trap centroid and charge-trap density. Moreover, the Al/Al2O3/HfYON/SiO2/Si structure shows high program speed (4.5 V at +14 V, 1 ms), large memory window (6.0 V at ±14 V, 1 s), and good retention property, further demonstrating that HfYON is a promising candidate as the charge-trapping layer for nonvolatile memory applications.