Submonolayer Quantum Dot Quantum Cascade Long-Wave Infrared Photodetector Grown On Ge Substrate

A germanium (Ge) or germanium-on-silicon (Ge-on-Si) substrate is an attractive yet not well-studied platform for developing long-wave infrared photonics devices such as lasers and photodetectors. In this paper, we report a long-wave infrared quantum cascade photodetector grown on the Ge substrate with a submonolayer InAs/GaAs quantum dot as the infrared absorber. At 77K under zero bias, the detector shows a differential-resistance area (R0A) product of 298.7 Omega.cm(2). The normal-incident peak responsivity is 0.56mA/W observed at 8.3 mu m, corresponding to a Johnson noise limited detectivity of 1.5x10(8)cm.Hz(1/2)/W. In addition, the effect of the periodic stage number of active regions on device's performance is discussed in detail. The device characteristics presented in this work demonstrate the potential for monolithic integration of this quantum cascade detector with the Ge or Ge-on-Si substrate for large-scale, cost-effective sensing and imaging applications.