Proceedings Article | 3 February 2009
Proc. SPIE. 7230, Novel In-Plane Semiconductor Lasers VIII
KEYWORDS: Quantum cascade lasers, Quantum wells, Metalorganic chemical vapor deposition, Laser damage threshold, Continuous wave operation, Superlattices, Temperature metrology, Electro optics, Reliability, Fabrication
In this work we present the characteristics of a novel type of quantum-cascade (QC) laser: the deep-well (DW) QC
device, which, unlike conventional QC lasers, contains a superlattice of quantum wells and barriers of different
composition, respectively. The fabrication of DW-QC devices is made possible by the use of metal-organic chemical
vapor deposition (MOCVD), a crystal growth technique which allows one to easily vary the composition of wells and
barriers within QC structures, thus providing significantly increased flexibility in optimizing the device design. We have
designed such varying-composition QC structures to have deep quantum wells in and tall barriers in and around the
active region. DW- QC laser structures have fabricated into 19 μm-wide ridges and 3 mm-long chips. Threshold-current
densities as low as 1.5 kA/cm2 are obtained at room temperature in the 4.6-4.8 μm wavelength region. In conventional
QC lasers emitting in the 4.5-5.5μm range there is substantial thermionic carrier leakage from the upper laser level to the
continuum, as evidenced by a significant decrease in the slope efficiency above 250 K, which is understandable given
the relatively small (i.e., ~ 200 meV) energy differential, δE, between the upper lasing level and the top of the exit
barrier. For the DW design carrier leakage is suppressed due to deep active wells and tall barriers, such that δE reaches
values in excess of 400 meV. Preliminary results include a threshold-current characteristic temperature, T0, value of 218
K over the temperature range: 250- 340 K.
