Long Wavelength Antimony-Based Devices

Interest in light sources emitting in the mid-infrared (MIR) wavelength region (2-5 micron) is growing due to their use in telecommunication and molecular spectroscopy applications. The former takes advantage of an atmospheric transparent window for MIR wavelengths and the latter due to the strong absorption lines of certain carbon-based and polluting gases. The goal of this project is to fabricate a room temperature, continuous wave, antimony-based laser and use this light source in photo-acoustic spectroscopy system for the detection of trace amounts of volatile impurities in petrochemicals.

For quantum well semiconductor lasers, the wavelength is a function of well width, valence and conduction band offsets, carrier effective mass, and the band gap of the quantum well material. Hence, simulations were performed to determine the quaternary alloy compositions and the relative thicknesses of the quantum wells and barriers in order to achieve the desired wavelength. Apart from the active region, adjusting the cladding layer thickness also allows the optical mode, the confinement factor and loss to be varied.

Currently, the molecular beam epitaxial growth conditions that are necessary to grow the aforementioned laser structure are being determined. The MBE growth conditions include the substrate temperature, V/III flux ratio, and growth rate. Each quaternary film will be characterized after growth using the high resolution x-ray diffractometer in the Center for Material Science and Engineering (CMSE) to determine the layer composition, the layer thickness, the surface roughness, and lattice relaxation. The surface roughness can also be determined by using an atomic force microscope (AFM) and/or a scanning electron microscope (SEM); the composition will also be confirmed by Auger Electron Spectroscopy (AES). The MBE growth conditions can be optimized by measuring the full-width at half-maximum of the photoluminescence and/or x-ray diffraction peaks. Optical and electrical properties will be measured by photoluminescence, ellipsometry and Hall measurements.