Influence of doping on the performance of terahertz quantum-cascade lasers

Abstract

The authors present the effects of the doping concentration on the performance of a set of terahertz quantum-cascade lasers emitting around 2.75THz. The chosen design is based on the longitudinal-optical-phonon depopulation of the lower laser state. An identical structure is regrown varying the sheet density from 5.4×109to1.9×1010cm−2. A linear dependency of the threshold current density on the doping is observed. The applied field where lasing takes place is independent of the doping. The field is responsible for the alignment of the cascades and therefore the transport of the electrons through the structure.

THz and sub‐THz quantum cascade lasers

“…Since the threshold current densities do not follow the prediction (see Fig. 8) we may argue that the threshold condition in this case is affected by the injection efficiency leading to voltage-controlled device [53]. This may explain the quite different threshold current densities displayed by these two lasers (J N 891 thresh = 203 A/cm 2 , J N 899 thresh = 144 A/cm 2 ).…”

“…The unique feature of the QC laser is that it is a unipolar device: in principle the system does not have a transparency current. This quantity is represented for the QCL by the current flow necessary to align the levels and to inject electrons in the upper lasing state [53]. Laser threshold is then determined entirely by the cavity losses.…”

Simulating terahertz quantum cascade lasers: Trends from samples from different labs

“…Here, we study two subclasses of this design type. In the designs BurghoffAPL2011, 43 MartlOE2011, 44 and BenzAPL2007, 45 a two well injector is used, similar to the pioneering design of Ref. 36, whereas the other samples use RT injection directly from the ground state of the phonon well into the upper laser state as proposed in Ref.…”

Photonic bandstructure engineering of THz quantum-cascade lasers

“…15 The design is comparable to the structure published in Ref. 16. The active region is slightly modified to shift its gain maximum to 2.2 THz; the exact growth sequence is 9.7/3.2/16.3/4.3/7/3.1/8.4/5.7 nm, where the barriers are marked with bold letters.…”