The authors present a technique to reduce the facet reflectivity in quantum cascade lasers (QCLs) by tilted facets. In
order to minimize the Fabry-Pérot resonances, the feedback from the laser facets into the cavity must be minimized.
Due to intersubband selection rules, the light generated inside QCLs is TM polarized. This polarization purity in
QCLs enables the reduction of the facet reflectivity through the angle of light incidence at the laser facet. We
observed a maximum threshold current density when the facet is tilted 17° towards the surface normal. This is in
agreement with the calculated Brewster's angle for the QCL heterostructure.
The performance of quantum well infrared photodetectors (QWIP) can be significantly enhanced combining it
with a photonic crystal slab (PCS) resonator. In such a system the chosen PCS mode is designed to coincide
with the absorption maximum of the photodetector by adjusting the lattice parameters. However there is a
multitude of parameter sets that exhibit the same resonance frequency of the chosen PCS mode.
We have investigated how the choice of the PC design can be exploited for a further enhancement of QWIPs.
Several sets of lattice parameters that exhibit the chosen PCS mode at the same resonance frequency have
been obtained and the finite difference time domain method was used to simulate the absorption spectra of the
different PCS. A photonic crystal slab quantum well infrared photodetector with three different photonic crystal
lattice designs that exhibit the same resonance frequency of the chosen PCS mode were designed, fabricated and
This work shows that the quality factor of a PCS-QWIP and therefore the absorption enhancement can be
increased by an optimized PCS design. The improvement is a combined effect of a changed lattice constant, PC
normalized radius and normalized slab thickness. An enhancement of the measured photocurrent of more than
a factor of two was measured.