Our research involves a wide variety of equipment, instrumentation, and laboratories across the UW-Madison Engineering campus. These provide us with broad capabilities from epitaxial semiconductor growth through complex device testing. The tabs below give an overview of some of our facilities and activities.
We operate a multi-wafer close-coupled showerhead metalorganic chemical vapor deposition (MOCVD) reactor to grow III-V semiconductor materials. The reactor is configured for materials including Gallium, Indium, Aluminum, Arsenic, Phosphorous, Antimony and Bismuth. Silicon, Zinc and Carbon are used as dopants and Carbon Tetrabromide is available for in-situ etching. It produces very high quality semiconductor films and has been successfully used to grow a wide range of optoelectronic devices, including photovoltaic cells, quantum cascade detectors, quantum cascade lasers, and other custom heterostructures.
Optical, electrical, thermal, and other material/device properties are characterized with a variety of instrumentation in our laboratory and in shared facilities. Some examples include:
- Bruker V70 Fourier transform infrared (FTIR) spectrometer with step-scan capability, Hyperion 2000 microscope, and accessories for attenuated total reflectance, variable-angle reflectance, and hemispherical reflectance. Several detectors and sources enable measurements from the visible to far infrared. Spot sizes can range from tens of microns to centimeter scale. Custom modifications and temperature-controlled stages enable direct measurements of thermal emission from samples up to 1,500 °C.
- Custom thermal test facility allows calorimetric measurement of the thermal conductivity or thermal resistance of thin films and other solid samples.
- Three-omega system for measurement of thermal transport through-plane, in-plane, and across boundaries of thin films.
- Electrical probe station and Hall effect system are used to measure electrical characteristics such as carrier concentration, sheet resistance, and contact resistance.
- Surface morphology and three-dimensional feature sizes with nanometer resolution can be measured with a shared laser scanning microscope.
- We also utilize user facilities in the Soft Materials Characterization Laboratory and the Nanoscale Imaging and Analysis Center within the Wisconsin Centers for Nanoscale Technology. Some notable capabilities include atomic force microscopy (AFM), scanning electron microscopy (SEM) with electron channeling contrast imaging (ECCI), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravametric analysis (TGA), and ultraviolet through infrared ellipsometry.
We employ a variety of microfabrication processes and equipment to turn multilayer semiconductor materials into functional structures or devices. These include activities such as photolithography, wet and dry chemical etching, and deposition of metals and dielectrics. This work is performed both in our own laboratory and in the Nanoscale Fabrication Center of the Wisconsin Centers for Nanoscale Technology.
After fabricating devices, we test their performance in custom measurement facilities in our laboratory, like the photograph above where a quantum cascade photovoltaic cell is being illuminated by infrared radiation. Other facilities include a photovoltaic quantum efficiency measurement system with capabilities to 4.5 μm wavelengths, as well as a solar simulator for current-voltage measurements under illumination. We also utilize an experimental setup located in a vacuum chamber that tests the performance of thermal/electrical/optical energy conversion devices, such as thermophotovoltaic cells, through simultaneous electrical and calorimetric measurements. This facility can accommodate different thermal emitters and devices ranging in size from about 1 x 1 cm to 10 x 10 cm, emitter temperatures up to 1800 °C, and controlled device temperatures. It also provides a high view factor from the cell to the emitter to obtain realistic performance indicators.
