THz electroluminescence from non-polar ZnO quantum cascade structures

Semiconductor material systems based on GaAs or InP are excellent candidates for optoelectronics in the mid-IR to terahertz spectral range. Consequently, they have readily been used for devices like THz quantum cascade lasers (QCLs) in recent years. But besides significant progress in recent years, THz-QCLs are still limited to operate well below room temperature only [1] . One main driving mechanism for such (temperature-) limitations, is based on the relatively low LO-phonon energy in the primary used GaAs material system of E LO,GaAs ~ 36 meV. This yields, especially at high temperatures approaching room-temperature (E kT, room temp. ~ 26 meV), a very strong thermally activated non-radiative scattering process, that is competing with the wanted optical transition. To overcome these material limitations, we follow a disruptive approach: we changed and investigated another material system that has a much larger LO-phonon energy: ZnO (E LO, ZnO ~ 72 meV), which is promising above room temperature lasing operation [2] . In the following, we present our results for realizing, i.e. designing and fabricating [3] MESA structures with light outcoupling gratings into MBE-grown ZnO/ZnMgO THz QCL structures. In addition, we present the first observation of THz intersubband electroluminescence from the ZnO material system [4] .