Ryan Munden

Electrical characterization of single GaN nanowires

In this paper a statistically significant study of 1096 individual GaN nanowire (NW) devices is presented. We have correlated the effects of changing growth parameters for hot-wall chemically-vapour-deposited (HW-CVD) NW sf abricated via the vapour–liquid–solid mechanism. We first describe an optical lithographic method for creating Ohmic contacts to NW field effect transistors with both top and bottom electrostatic gates to characterize carrier density and mobility. Multiprobe measurements show that carrier modulation occurs in the channel and is not a contact effect. We then show that NW fabrication runs with nominally identical growth parameters yield similar electrical results across sample populations of >50 devices. By systematically altering th eg rowth parameters we were able to decrease the average carrier concentration for these as-grown GaN NWs ∼10-fold, from 2.29 × 10 20 to 2.45 × 10 19 cm −3 ,a nd successfully elucidate the parameters that exert the strongest influence on wire quality. Furthermore, this study shows that nitrogen vacancies, and not oxygen impurities, are the dominant intrinsic dopant in HW-CVD GaN NWs.

Current rectification in a single GaN nanowire with a well-defined p-n junction

This letter discusses Mg incorporation in GaN nanowires with diameters ∼35 nm, fabricated by vapor–liquid–solid synthesis in p-type nanowires. Turning on the Mg doping halfway through the synthesis produced nanowires with p–n junctions that showed excellent rectification properties down to 2.6 K. The nanowires are shown to possess good-quality, crystalline, hexagonal GaN inner cores surrounded by an amorphous GaN outer layer. Most wires grow such that the crystalline c axis is normal to the long axis of the nanowire. The temperature dependence of the current–voltage characteristics is consistent with electron tunneling through a voltage-dependent barrier.

The effect of Mg doping on GaN nanowires

We present a comparison between the structural, chemical, and electrical properties of Mg-doped GaN nanowires grown by hot-wall chemical vapour deposition using two different Mg sources, namely, metallo-organic bis(methylcyclopentadienyl) magnesium and magnesium nitride powder. We find that Mg from the solid nitride source is more effectively incorporated into the nanowires while better maintaining the nanowire integrity. After Mg activation, the nanowires are partially or fully compensated. In comparison, vapour phase doping results in an obvious degradation of the nanowire morphology in spite of lower Mg incorporation levels.

Electron mobility study of hot-wall CVD GaN and InN nanowires

The group III-nitrides and their alloys represent a promising system for semiconducting device applications, especially for photonic devices, because they are direct band gap semiconductors with potential light emission from ultraviolet to infrared. Growth of GaN and InN nanowires was reported by a number of groups employing mainly catalyzed vaporliquid-solid (VLS) or catalyst-free vapor-solid (VS) growths ([1], [2] and References therein). One simple, economical and very successful method to grow both types of nanowires is using hot-wall chemical vapor deposition. Understanding the electronic properties of the as-grown nanowires is a crucial step towards their implementation in useful devices. Here we summarize the electric properties of a large number of devices (field-effect transistors) that we built with nanowires grown using this simple process. Both indium nitride and gallium nitride nanowires exhibit high carrier concentrations, with mobilities limited by impurity scattering. In particular, the gallium nitride nanowires appear to grow heavily compensated, as inferred from our theoretical estimates and annealing experiments.

Catalyst-free synthesis routine to indium nitride nanowires

A vapor-solid growth strategy (catalyst free) of one-dimensional materials was employed to synthesize hexagonal wurtzite InN nanowires with large yield as much as gram quantities on a hot-wall CVD system. Morphology characterization by FE-SEM revealed uniform nanowires with 700/spl deg/C growth temperature have /spl sim/70 nm average diameter and /spl sim/5-30 micron length. EDS, XRD and micro-Raman spectroscopy characterization showed the formation of high-purity hexagonal wurtzite InN nanowires. Further structural characterizations by high-resolution TEM and low-temperature electrical characterizations (mobility and carrier density) are being undertaken.

Electrical characterization of individual GaN nanowires

The authors performed a thorough electrical characterization of hot-wall-CVD fabricated GaN nanowires (NWs) by studying over 500 single NW devices, and have extracted the growth parameters responsible for wire quality. Wires were grown by the vapor-liquid-solid mechanism

Authentic Science Research and the Utilization of Nanoscience in the Non-Traditional Classroom Setting

Applications of nanoscience in the non-traditional classroom have successfully exposed students to various methods of research with applications to micro- and nano-electronics. Activities obtained from the NanoSense website associated with current global energy and water concerns are solid examples. In this regard, all 36 students in the 2008-2009 Science Research Program (SRP) prepared and delivered individual and group lesson plans in addition to their authentic, year-long research projects. Two out of 36 students selected nanoscience based projects in preparation for science fair competition in 2009. Additionally, preliminary research was conducted while participating in the Center for Research on Interface Structures and Phenomena (CRISP) Research Experience for Teachers (RET) Program in summer 2008 which supported the idea of developing a photolithography kit. This kit is intended to introduce high school students to the fundamentals of photolithography. In this paper, the design, implementation and feasibility of this kit in the high school classroom is described as well as details involving individual and group nanoscience based projects. Supporting educational models include self-regulated learning (SRL) concepts; situated cognition; social constructivism; Renzullis (1977) enrichment triad and Types I – III inquiry enrichment activities.

Microstructure and nanoelectronics of single GaN nanowire with well-defined p-n junction

We demonstrate the first example of a well-defined p-n junction fabricated in a GaN nanowire and the systematic investigation of its transport properties down to 2.6 K. XRD, Raman spectrum, HRTEM revealed the /spl sim/30 nm diameter wires, produced by vapor-liquid-solid synthesis in indium nanoparticle catalyst droplets, are shown to consist of a good-quality, crystalline, hexagonal GaN inner core surrounded by an amorphous GaN outer layer. Most wires grow such that the crystalline c-axis is normal to the long axis of the nanowire. The p-n junction is produced by turning on a source of Mg (a known p-dopant) halfway through the growth. The wires show excellent rectification properties with diode ideality factors as low as 5 for most nanowires. The temperature dependence of the current-voltage characteristics is consistent with electron tunneling through a voltage-dependent barrier. P-doped and n-doped GaN nanowires fabricated under similar conditions invariably produced linear current-voltage curves, indicating that the observed rectification arises as a result of the p-n junction and not from a metal-semiconductor Schottky contact junction. Surface potential imaging was employed to determine the exact position of the p-n junction along a single nanowire.

Publisher’s Note: “Current rectification in a single GaN nanowire with a well-defined p-n junction” [Appl. Phys. Lett. 83, 1578 (2003)]

Publisher’s Note: ‘‘Current rectification in a single GaN nanowire with a well-defined p-n junction’’ †Appl. Phys. Lett. 83, 1578 „2003...‡ Guosheng Cheng, Andrei Kolmakov, Youxiang Zhang, and Martin Moskovits Department of Chemistry & Biochemistry, University of California, Santa Barbara, California 93106 Ryan Munden and Mark A. Reed Departments of Electrical Engineering and Applied Physics, Yale University, New Haven, Connecticut 06520 Guangming Wang and Daniel Moses Institute for Polymers & Organic Solids, University of California, Santa Barbara, California 93106 Jinping Zhang Department of Materials, University of California, Santa Barbara, California 93106 @DOI: 10.1063/1.1618263#