Semiconductor Growth and Devices

The goal of this project is to advance the state-of-the-art in semiconductor crystal growth for optoelectronic device applications, with an emphasis on nanostructures of compound semiconductors. Nanowire and quantum dot devices have unique properties including high luminescent output and broad wavelength tunability, but their application is limited by the inadequacy of conventional methods to quantify basic properties such as carrier concentration and composition. We collaborate with teams inside and outside of NIST to develop new nanoscale metrologies. We also provide data, materials and devices to support the efficient manufacture of compound semiconductor optoelectronic devices and to support research in NIST, other government laboratories, and industry.

Compound semiconductor materials form the basis for the diode lasers, LEDs, photodetectors, and high-efficiency solar cells critical to optical communication, display, data storage, and energy conservation and generation. Many of these semiconductor devices now incorporate structures with a high degree of strain and nanostructures so small that the properties of the devices depend on their physical dimensions as well as the bulk materials properties.

A major focus in this project is the growth and processing of GaN nanowires for nanometrology and device applications. We have demonstrated that the GaN nanowires grown in our laboratory with catalyst-free molecular beam epitaxy (MBE) are strain-free, very low in chemical impurities and usually entirely free of structural defects.

These properties lead to high optical emission intensity, consistent doping behavior, and high mechanical resonance quality factors, all of which are needed for future technical applications that will surpass GaN thin films in performance. The nanowire architecture is also a framework for inventing new characterization tools and devices. A simple example is that the optical emission can be used to measure externally applied strain. Future devices will extend our work on nanowires-as-transistors and light emitters to include nanowire lasers, biosensor applications, near-field optical probes, oscillators for communications equipment, single-photon emitters and detectors, and integration of photonics with silicon circuitry.

The scientific understanding needed to engineer these devices will make use of our basic research in quantum dot and nanowire nucleation and growth mechanisms, including the role of strain in nanostructures. This project supports manufacturing of compound semiconductor devices with the world’s only composition standards for these materials. We also lead a cavity ringdown spectroscopy program that focuses on direct measurement of impurities in the source gases used in compound semiconductor manufacturing. We have achieved sensitivity below 50 nmol mol-1 for water in arsine and below 10 nmol mol-1 for water in phosphine.

• Defect-free GaN nanowires grown and characterized, leading to an R&D Micro Nano 25 Award for NIST in 2006
• Comprehensive model developed for estimating carrier concentration and mobility based on nanowire resistance
• Role of growth parameters in the uniformity of InGaAs quantum dot size and spacing explained
• First application of cavity ring down spectroscopy to measure water vapor as a contaminant in arsine and phosphine 
• AlGaAs composition Standard Reference Materials released in 2006