Ali Javey (Advisor)

Research Advised by Professor Ali Javey

BPN461: Low Energy Electronics

Ha sul Kim
2011

We introduce a novel transistor based on the inter-band tunneling by III-V materials. The type II staggered heterojunction between two compound semiconductors can provide an electron tunneling by quantum mechanical effect from the valence band to the conduction band of semiconductors, and result in reduced sub-threshold swing compared to diffusion in MOSFETs. This allows for these devices to be operated at lower voltages, and thus function with less power consumption.

Project end date: 08/18/11

BPN581: Shape-Controlled Synthesis of Single-Crystalline Nanopillar Arrays by Template-Assisted Vapor-Liquid-Solid Process

Onur Ergen
Daniel J. Ruebusch
Hui Fang
2011

In this work highly regular, single-crystalline nanopillar arrays with tunable shapes and geometry are synthesized by the template-assisted vapor-liquid-solid growth mechanism. The grown nanopillars faithfully reproduce the shape of the pores because during the growth the liquid catalyst seeds fill the space available, thereby conforming to the pore geometry. The process is highly generic for various material systems, and as an example, CdS and Ge nanopillar arrays with square, rectangular, and circular cross- sections are demonstrated. This technique has great potential im many...

BPN577: Ultra-Thin Body, Mixed Anion Arsenide-Antimonide XOI FETs

Hui Fang
Steven Chuang
Kuniharu Takei
Ali Javey
2011

We demonstrate ultrathin body (UTB) high mobility InAsSb-on-insulator (XOI) n-FETs. The devices are obtained by the epitaxial layer transfer (ELT) of ultrathin InAsSb layers (thickness, 7-17 nm) onto Si/SiO2 substrates. InAsSb XOI FETs exhibit a peak effective mobility of ~5000 cm2/V-s and an ION/IOFF ratio of over 104. The top-gated devices exhibit an impressive ION of ~0.24 mA/μm (LG~500 nm) at VDD=0.5 V and a SS of ~109 mV/dec. These results demonstrate the utility of the XOI platform for obtaining high mobility n-FETs on Si by using mixed anion arsenide-antimonide as the active...

BPN579: Top-Down and Bottom-Up Approaches to Anti-Reflective Templates for Efficient Photoelectrochemical Solar-to-Fuel Conversion

Cary Pint
2011

Due to tightened regulations on environmental control and high demand on clean fuel, there is great interest in developing a method whose process and product are both eco-friendly. Hydrogen is a fuel of high quality and zero emission. Hydrogen can be directly produced by splitting water into H2 and O2. This project focuses on photochemical splitting of water using solar energy and InP as the photocatalyst. In an effort to enhance the efficiency, the InP is textured to have very low reflectivity.

Project end date: 08/19/11

BPN465: Conformal Ultra-shallow Junction Formation for 3-D Structured InP Nanopillar Solar Cell

Kee Cho
Onur Ergen
Rehan Kapadia
2011

Solar energy represents one of the most abundant and yet least harvested source of renewable energy. We report a PV structure that incorporates 3D, single crystalline n-CdS nanopillars, embedded in poly- crystalline thin films of p-CdTe, to enable high absorption of light and efficient collection of the carriers. Through experiments and modeling, we demonstrate the potency of this approach for enabling highly versatile solar modules on both rigid and flexible substrates with enhanced carrier collection efficiency arising from the geometric configuration of the NPLs. We performed...

BPN647: Ultra-Thin Body, Mixed Anion Arsenide-Antimonide XOI FETs

Hui Fang
Steven Chuang
Kuniharu Takei
2011

We demonstrate ultrathin body (UTB) high mobility InAsSb-on-insulator (XOI) n-FETs. The devices are obtained by the epitaxial layer transfer (ELT) of ultrathin InAsSb layers (thickness, 7-17 nm) onto Si/SiO2 substrates. InAsSb XOI FETs exhibit a peak effective mobility of ~5000 cm2/V-s and an ION/IOFF ratio of over 104. The top-gated devices exhibit an impressive ION of ~0.24 mA/micron (LG~500 nm) at VDD=0.5 V and a SS of ~109 mV/dec. These results demonstrate the utility of the XOI platform for obtaining high mobility n-FETs on Si by using mixed anion arsenide-antimonide as the...

BPN635: Structured Substrates for Enhancing the Water-Splitting Efficiency of Earth Abundant Materials

Maxwell Zheng
2011

Here we focus on nano- and micro-structuring earth abundant materials to improve their water splitting performance, primarily by increasing the optical path length. The focus is on isolating structural effects and so we fix the material system to be titanium dioxide. In one structure we use texturized carbon nanotubes as the back contact. In another, we are planning to use micro-scale triangular grooves.

Project end date: 02/06/12

BPN640: p-InP nanopillars for highly efficient water splitting

Min Hyung Lee
2011

The photoelectrochemical evolution of hydrogen using p-InP nanopillar arrays decorated with metallic co-catalyst is explored. The nanopillar devices exhibit an great enhancement in the conversion efficiency, as compared to planar substrates. This behavior is mainly attributed to the low surface reflectivity of nanopillar arrays along with the enhanced surface area for catalytic reactions. Of particular importance to this architecture is the use of InP as the absorber layer, which is known to have a low carrier surface recombination velocity, thereby minimizing the loss of...

BPN641: InAs XOI Gas Sensor

Junghyo Nah
2011

The objective of InAs XOI gas sensor project is twofold. First, the role of size effect on sensor performance will be systematically investigated. Our XOI device structure provides a unique platform to perform this study since we can precisely control material thicknesses and transfer them on a SiO2/Si substrate. Based on this study, we will determine physical role of size effect on sensor performance. This result will be also essential to determine an optimum NR thickness for gas sensors. Secondly, we will implement multiple gas detection sensor modules on a single chip by...

BPN567: Compound Semiconductor on Insulator (XOI) FETs

Rehan R. Kapadia
Kuniharu Takei
Hui Fang
Steven Chuang
2012

Due to their high mobility, the integration of compound semiconductors on Si has been actively studied over the past several years. This integration, however, presents significant challenges. The conventional method of addressing this problem consists of growth of multiple epilayers of materials to address the lattice mismatch between Si and the desired semiconductor, leading to highly complex fabrication techniques. Here we demonstrate high performance compound semiconductor on insulator (XOI) field effect transistors (FET) consisting of ultra-thin InAs nanoribbons (NR) on insulator...