Chemisorbed Oxygen at Pt(111): a DFT Study of Structural and Electronic Surface Properties

Simulations based on density functional theory are used to study the electronic and electrostatic properties of a Pt(111) surface covered by a layer of chemisorbed atomic oxygen. The impact of the oxygen surface coverage and orientationally ordered interfacial water layers is explored. The oxygen adsorption energy decreases as a function of oxygen coverage due to the lateral adsorbate repulsion. The surficial dipole moment density induced by the layer of chemisorbed oxygen causes a positive shift of the work function. In simulations with interfacial water layers, ordering and orientation of water molecules strongly affect the work function. It is found that the surficial dipole moment density and charge density are roughly linearly dependent on the oxygen surface coverage. Moreover, we found that water layers exert only a small impact on the surface charging behavior of the surface

Polarization-matched GaInN/AlGaInN multi-quantum-well light-emitting diodes with reduced efficiency droop

Blue multi-quantum-well light-emitting diodes (LEDs) with GaInN quantum wells and polarization-matched AlGaInN barriers are grown by metal-organic chemical vapor deposition. The use of quaternary alloys enables an independent control over interface polarization charges and bandgap and has been suggested as a method to reduce electron leakage from the active region, a carrier loss mechanism that can reduce efficiency at high injection currents-an effect known as the efficiency droop. The GaInN/AlGaInN LEDs show reduced forward voltage, reduced efficiency droop, and improved light-output power at large currents compared to conventional GaInN/GaN LEDs. (c) 2008 American Institute of Physics.open11343414sciescopu

1/f Noise Characteristics of AlGaN/GaN FinFETs with and without TMAH surface treatment

In this paper, we have fabricated and investigated the AlGaN/GaN fin-shaped field-effect transistors (FinFETs) with and without TMAH surface treatment. DC and noise characteristics of the FinFETs were compared to evaluate the interface quality between Al2O3 layer and the side-wall GaN surface. The tetramethyl ammonium hydroxide (TMAH)-treated device with a fin width of 70 nm and gate length, L-g = 5 mu m exhibited excellent device performances, such as drain current of 0.16 mA and transconductance (g(m)) of 0.11 ms, both 30% improved, and extremely small gate leakage current of about 10(-9) at V-gs = -5 V which is approximately two orders lower in magnitude compared to that of the device without TMAH treatment. Improved low-frequency noise performances were obtained for TMAH treated device due to the enhanced side-wall quality after the TMAH surface treatment. The trap density was found to be reduced approximately one order after TMAH treatment. Thus, simple surface treatment not only smoothens the sidewall surface but also eliminates the plasma damage caused during the fin etching, which leads to the reduction of trap density in AlGaN/GaN FinFETs. (C) 2015 Elsevier B.V. All rights reserved.115sciescopu