THz quantum semiconductor devices

Terahertz (1 - 10 THz) quantum-well photodetectors and quantum-cascade lasers have been investigated. The design and projected detector performance are presented together with experimental results on several test devices, all working at photon energies below the optical phonons. Background limited infrared performance (BLEP) operations were observed for all samples (three in total) designed for different wavelengths. For lasers, a set of THz quantum-cascade lasers with identical device parameters except for the doping concentration has been studied. The delta-doping density for each period was varied from 3.2 x 10(10) to 4.8 x 10(10) cm(-2). We observed that the lasing threshold current increased monotonically with doping. Moreover, the measured results on devices with different cavity lengths provided evidence that the free carrier absorption caused waveguide loss also increased monotonically. Interestingly however, the observed maximum lasing temperature displayed an optimum at a doping density of 3.6 x 10(10) cm(-2).