Abstract:
Quantum cascade laser (QCL) is a promising candidate for comparatively less
developed terahertz spectral range. Design-dependent emission frequency and sequential
pumping make QCL suitable for Hetero-active region operation, which
can emit multiple frequency at the same time. From this multiple frequency emitting
QCL, using various tuning techniques, we can achieve a broadband terahertz
emission from a single QCL cavity. GaAs based multiple frequency emitting
QCL has already been reported, but GaN based QCLs provide significant advantages
over traditional GaAs based QCLs due to their higher LO phonon energy.
We propose a hetero cavity terahertz GaN based QCL emitting around 1.5 THz, 4
THz, and 7 THz. Using bias tuning, we have achieved an ultra-broadband emission
covering a range of 1–10 THz. Current mismatch is an inherent problem in
the hetero-structure devices. We calculate the effect of current mismatching in
hetero-active structures. We find that both higher and lower current injection results
in lower population inversion and hence lower gain, and mismatch of more
than 10% results in gain less than typical loss in the cavity. Waveguide design
is of significant importance in terahertz range due to the confinement problem of
longer wavelength. We design and optimize the waveguide for the QCL using
double metal configuration to support the broadband emission of 1–10 THz.
