GaSb-based Laser Diodes for Gas Sensing Applications in the 2-4um Range

Dr. James Gupta
Institute for Microstructural Sciences
National Research Council of Canada

Thusrday, June 10, 2010 at 3:00pm
Engr IV Faraday Room 67-124

Abstract
A growing awareness of the environmental implications of industrial activities has led to an urgent need for extensive process and emissions monitoring. In many industries this involves the detection of potentially lethal trace gases which are by-products of a standard process, or harbingers of an unforeseen catastrophe. Other gaseous species can contribute to the formation of smog, or to poor air quality in homes or commercial buildings.

Fortunately, many of these gases have strong absorption features at infrared wavelengths. This allows the gas concentrations to be monitored in-situ using the technique of tuneable diode laser absorption spectroscopy (TDLAS), in which the gas species of interest is detected by modulating the emission wavelength of a single-mode laser through a suitable absorption line.

At the NRC, we are developing semiconductor laser diodes for gas analysis at several key wavelengths between 2 and 4um. The structures are grown by molecular beam epitaxy (MBE) using GaSb and related alloys on GaSb substrates. Typical structures involve optical waveguides containing InGaAsSb quantum wells with AlGaAsSb separate confinement layers, surrounded by low-index AlGaAsSb cladding layers. The emission wavelength is critical for these applications, and requires very careful MBE compositional control of both the group-III and group-V elements.

Single-mode distributed feedback (DFB) lasers have been developed for the detection of HF gas at 2.4um, with applications in aluminum production facilities and petroleum alkylation plants. We have also developed single-mode lasers near 2.6um, for the detection of H2S, CH4 and H2O.

For organic compounds having strong spectral absorption beyond 3um, unambiguous identification of the broad C-H stretch features requires a laser with broadband, mode-hop-free continuous tuning. We have recently demonstrated a widely-tunable external cavity laser with continuous-wave operation at 3.24um based on long-wavelength laser diodes employing type-I InGaAsSb quantum wells and quinary AlInGaAsSb barriers. This provides a single-mode source at wavelengths corresponding to the main absorption features of methane gas, which is important for both environmental monitoring and space applications.

Biography
Dr. Gupta has been developing MBE techniques and devices based on novel III-V materials since 2001 and is the coordinator of the Institute's Mid-IR Antimonide Lasers program. Previously at IMS, he studied dilute nitride lasers on GaAs substrates and achieved the first 1550nm DFB lasers and 1550nm optically-pumped VCSELs with that materials system. He also studied rare-earth oxides and silicates as alternative gate dielectrics for silicon CMOS and is a co-inventor of a US patent for a novel high-K material suitable for the 100nm node and beyond. He received his doctorate from Simon Fraser University, Vancouver, Canada in 1999 based on studies of single- and sub-monolayer InAs films in GaAs produced by metalorganic chemical vapor deposition. He is the co-author of 100 publications in peer-reviewed journals and refereed conference proceedings.