Terahertz quantum cascade lasers based on quaternary AlInGaAs barriers

Terahertz quantum cascade lasers incorporating lattice-matched quaternary AlInGaAs barriers grown by molecular beam epitaxy on InP substrate are reported. Four quantum well active region devices exhibited lasing at 3.8 THz with threshold current densities as low as 74 A/cm2 at 10 K. From optical characterization and a doping study of the active region, an upper state lifetime of 8 ps, as well as a long transport time across the active region of 68 ps and a ratio of free carrier loss to gain cross sections of 4.6%, is reported. A maximum operating temperature of 130 K was achieved for a device with a conduction band discontinuity of 0.14 eV.