  Terahertz quantum cascade lasers based on InGaAs wells and quaternary
AlInGaAs barriers were measured in magnetic field. This study was carried out
on a four quantum well active region design with photon energy of 14.3 meV
processed both with Au and Cu waveguides. The heterostructure operates up to
148 K at B=0 T and in a Cu waveguide. The complete magneto-spectroscopic study
allowed the comparison of emission and transport data. Increasing the magnetic
field, the low effective mass of the InGaAs wells allowed us to reach the very
strong confinement regime. At B=12 T, where the cyclotron transition is almost
resonant with the LO-phonon, we recorded a maximum operating temperature of 195
K for the devices with Cu waveguide. Additional lasing at 5.9 meV was detected
for magnetic fields between 7.3 and 7.7 T.
