Modelling and experimental characterization of a quantum well photodetector at 9 µm

Quantum well based devices has been widely investigated in the recent years to be exploted as detectors in the infrared spectrum of light. Many advantages with respect to standard IR detection devices could be achieved, as examples the easy tunability of the detection wavelength related to the geometry of the device and the possibility to work at high frequency. The thesis work is mainly focused on detection of light, through 1D confined quantum systems, semiconductors quantum wells. The device characterized is a quantum well infrared photodetector, made of Ga0.47In0.53As/(Ga0.47In0.53As)0.5 − (Al0.48In0.52As)0.5 lattice matched to InP : Fe substrate, working in the mid-Infrared spectrum (9µm). The presence of a quaternary material employed as barrier allows to reach the detection wavelength at 9 µm.The optoelectronic properties of the device has been analyzed through I/V curves ,FTIR spectroscopy and laser based experiment at the detection wavalength. The limits of the device analyzed are related to the heteroepitaxy process, the second bound state is not optimized to be quasi resonant to the barrier, this leads to an harder extraction of carriers and to the presence of a strong dark current inside the device. The outcome of the characterization show that the device analyzed is working at cryogenic temperature,78K, where parasitic currents and temperature related phenomena are reduced, the responsivity reached at the operating voltage of 2V is 50 mA/W. The results presented are however below the expectations in terms of responsivity, for this reason they will be compared to another QWIP device of the same batch.