Fast, multi-wavelength, efficiency-enhanced pixelated devices based on InGaAs/InAlAs quantum-well

Several applications utilizing either synchrotron or conventional light sources require fast and efficient pixelated detectors. In order to cover a wide range of experiments, this work investigates the possibility to use InGaAs/InAlAs quantum well devices as photon detectors for a broad range of energies. Owing to their direct, low-energy band gap and high electron mobility, such devices may be used also at room temperature as multi-wavelength sensors from visible light to hard X-rays. Furthermore, internal charge-amplification mechanism can be applied for very low signal levels, while the high carrier mobility allows the design of very fast photon detectors with sub-nanosecond response times.Samples were grown by solid source molecular beam epitaxy on GaAs substrates. Metamorphic In0.75Ga0.25As/ In0.75Al0.25As heterostructures were obtained by relaxing the strain due to the lattice mismatch in the substrate by means of a composition-graded buffer layer. A two-dimensional electron gas forming in an In0.75Ga0.25As quantum well is sandwiched between In0.75Al0.25As barriers and is modulation-doped by a Si δ on its top. The samples have been pixelated by using standard photolithographic techniques. In order to fit commercially available readout chips, a pixelated sensor with pixel size of 172 × 172 μ m2 is currently under development. A small-scale version of the pixelated quantum well sensor has been preliminary tested with 100-fs-wide laser pulses and X-ray synchrotron radiation. The reported results indicate that these sensors respond with 100-ps rise-times to ultra-fast laser pulses. Synchrotron X-ray tests show how these devices exhibit high charge collection efficiencies, which can be imputed to the charge-multiplication effect of the 2D electron gas inside the well.