Indexed on: 24 Dec '18Published on: 19 Dec '18Published in: Applied physics letters
Applied Physics Letters, Volume 113, Issue 25, December 2018. This paper reports on the demonstration of quantum cascade detectors (QCDs) based on ZnO/ZnMgO quantum wells (QWs) grown by molecular beam epitaxy on an m-plane ZnO substrate. The TM-polarized intersubband absorption is peaked at a 3 μm wavelength. The sample has been processed in the form of square mesas with sizes ranging from 10 × 10 μm2 up to 100 × 100 μm2. The I-V characteristics reveal that 86% of the 260 devices are operational and that the surface leakage current is negligible at room temperature, which is not the case at 77 K. The photocurrent spectroscopy of 100 × 100 μm2 QCDs reveals a photocurrent resonance at a 2.8 μm wavelength, i.e., slightly blue-shifted with respect to the intersubband absorption peak. The photocurrent persists up to room temperature. The calibrated peak responsivity amounts to 0.15 mA/W under irradiation at Brewster's angle of incidence. This value allows us to estimate the transfer efficiency (1.15%) of the photoexcited electrons into the active QW of the next period.