Author: Jan Devenson
Dissertation title: InAs/AlSb short wavelenght quantum cascade lasers
Fields of science: Physical sciences, Physics (02P), Semiconductor physics (P265)
Scientific consultants: Habil. Dr. Alexei Baranov, Prof. Dr. Gintaras Valušis
Defence of the dissertation: 2010-10-26
Quantum cascade lasers (QCLs) are considered now as standard light sources for many chemical sensing applications in the mid-infrared above 4 µm. Some spectroscopic applications require injection semiconductor lasers emitting at shorter wavelengths in the vicinity of 3 µm. This spectral region is, in principle, accessible both for interband diode lasers and quantum cascade lasers (QCLs) operating at room temperature (RT). It deserves to note that performances of diode lasers rapidly degrade above 3 µm due to fundamental limitations such as increasing influence of nonradiative Auger recombination. High quality QCLs based on the InP technology are suited for λ > 3.8 µm but the extension their operation range towards shorter wavelengths is still a challenge due mainly to material limitations. Using adequate materials high performance QCLs operating at wavelengths as short as 3 µm or even below can be developed.
The InAs/AlSb material system seems to be at present the most promising for the development of short wavelength QCLs thanks to the high conduction band offset of 2.1 eV and the large Γ-L distance of 0.73 eV in InAs. Another advantage of this system is the small electron mass in InAs, which is favorable to obtain QCLs with high gain and low threshold. However, InAs/AlSb material system was not used for development of short wavelength QCLs mainly due to the difficulties associated with the epitaxial growth as there are no common atoms at the well/barrier interfaces. The first short wavelength antimonide-based QCL emitting near 4.5 µm at room temperature has been developed by NANOMIR group of the IES (Institut d’Electronique du Sud) in University Montpellier II in France and it was a starting point of my work at the same laboratory. The advantage of this new material system for development of short wavelength QCLs was obvious, however to fully exploit it variety of investigations on this material properties and
Importance for application
The mid-infrared range, sometimes called the fingerprint region of the electromagnetic spectrum, is of enormous scientific and technological interest since many molecules have their fundamental rotational-vibrational absorption bands in this range. The MIR absorption spectrum is very specific to the structure of a particular molecule, allowing highly selective detection. In addition, since these absorption lines are very strong (several orders of magnitude stronger than the overtone and combination bands in the NIR), concentrations in the parts-per-billion (ppb) to parts-per-trillion (ppt) ranges can be detected using relatively compact laser-based sensors. Fast, sensitive, and selective chemical sensors are needed in numerous applications. In industrial process control they are used for detection of contamination in semiconductor fabrication lines and for plasma monitoring, in law enforcement for drug and explosive detection, in automotive industry for engine exhaust analysis, in environmental science for pollution monitoring, in medical diagnostics for exhaled breath analysis, and in homeland security for detection of chemical airfare agents.
Another interesting feature of the mid-infrared are the atmospheric transmission windows between 3-5 µm and 8-12 µm which enable free-space optical communications, remote sensing, and thermal imaging. High power lasers in the 3-5 µm range will also enable the development of infrared counter-measures for homeland security.
Especially, application of intersubband transition based lasers is indispensable in a hot test environment such as the oil boring or other applications where temperature may reach 400 K.