Interband cascade laser
Mid-infrared laser diodes using interband transitions for low-power operation.
Interband cascade lasers (ICLs) are laser diodes that emit coherent light across much of the mid-infrared range. They are built from semiconductor heterostructures grown epitaxially, using layers of indium arsenide (InAs), gallium antimonide (GaSb), aluminum antimonide (AlSb), and their alloys. ICLs share several features with quantum cascade lasers (QCLs): both rely on bandstructure engineering for optimized designs, and both recycle injected electrons to generate multiple photons. The key difference is that ICLs produce photons through interband transitions, whereas QCLs use intersubband transitions. Because of this, the rate at which carriers in the upper laser subband thermally relax to the lower subband is governed by interband Auger, radiative, and Shockley-Read recombination—processes that are typically much slower than the longitudinal optical phonon interactions that drive intersubband relaxation in mid-infrared QCLs. This slower relaxation allows ICLs to achieve lasing at lower electrical input powers than QCLs.
The basic idea for an ICL was proposed by Rui Q. Yang in 1994. His key insight was that a type-II heterostructure, similar to those used in interband resonant tunneling diodes, could enable cascade lasers that generate photons via interband transitions. Yang and his collaborators at various institutions, along with groups at the Naval Research Laboratory and elsewhere, refined the design and developed the technology. Continuous-wave (cw) lasing at room temperature was first demonstrated in 2008, with an emission wavelength of 3.75 μm. Since then, room-temperature cw operation has been achieved across wavelengths from 2.9 μm to 6.2 μm. At cooler temperatures, ICLs have emitted light between 2.7 μm and 11.2 μm. When operating in cw mode at ambient temperature, ICLs require much lower input power than competing mid-infrared semiconductor laser technologies.
**Theory of operation**
In a standard multiple quantum well laser, the active quantum wells are connected in parallel, so a large current is needed to replenish each well with electrons as it emits light. In a cascade laser, the wells are connected in series, which raises the voltage but lowers the current. This trade-off is advantageous because the power dissipated by the device’s series resistance (Rs) equals I²Rs, where I is the current. The lower current in a cascade laser thus reduc
- field
- Semiconductor laser technology
- known_for
- Mid-infrared laser diodes using interband transitions in cascade structures
- inventor
- Rui Q. Yang (1994)
- first_cw_room_temperature_demonstration
- 2008
- emission_wavelength_range_cw_room_temp
- 2.9 μm to 6.2 μm
- emission_wavelength_range_cooler_temps
- 2.7 μm to 11.2 μm
Lore & Background
The basic concept of an interband cascade laser was proposed by Rui Q. Yang in 1994. His key insight was that incorporating a type-II heterostructure similar to those used in interband resonant tunneling diodes would facilitate cascade lasers using interband transitions for photon generation. Further improvement and development were carried out by Yang and his collaborators at several institutions, as well as by groups at the Naval Research Laboratory and other institutions. ICLs lasing in continuous wave mode at room temperature were first demonstrated in 2008, with an emission wavelength of 3.75 μm. Subsequently, continuous wave operation at room temperature has been demonstrated with emission wavelengths ranging from 2.9 μm to 6.2 μm, and at cooler temperatures from 2.7 μm to 11.2 μm.
Reader's Guide
Interband cascade lasers represent a significant advancement in mid-infrared semiconductor laser technology, particularly for applications requiring low electrical input power. Unlike quantum cascade lasers, which rely on intersubband transitions and fast longitudinal optical phonon relaxation, ICLs use interband transitions where carrier relaxation is governed by slower interband Auger, radiative, and Shockley-Read recombination processes. This allows ICLs to achieve laser action at lower electrical input powers than competing mid-IR semiconductor laser technologies. The cascade design connects quantum wells in series, reducing current and thus power loss from series resistance, though more stages can worsen thermal performance. ICLs are fabricated using molecular beam epitaxy on GaSb or InAs substrates, with materials closely lattice matched near 6.1 Å. A distinctive feature is the ability to operate without a p-n junction, using injectors as rectifying barriers. Carrier rebalancing via n-doping of the electron injector helps optimize performance by equalizing electron and hole concentrations at threshold. The 'W' quantum well configuration maximizes optical gain by increasing spatial overlap of electron and hole wavefunctions. ICLs have been demonstrated with emission wavelengths from 2.7 μm to 11.2 μm, covering a large part of the mid-infrared spectrum.
Did You Know?
- ICLs use interband transitions, unlike quantum cascade lasers which use intersubband transitions.
- The first continuous wave room temperature ICL was demonstrated in 2008 with an emission wavelength of 3.75 μm.
- ICLs can be electrically pumped without a p-n junction, using injectors as rectifying barriers.
- The 'W' quantum well configuration in ICLs sandwiches a GaInSb hole quantum well between two InAs electron quantum wells to maximize optical gain.
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