1. Conclusions References 1. A. Galimberti et al., Nucl. Instrum. Meth. A 477, 317-322 (2002). 2. F. Capotondi et al., Thin Solid Films 484, 400-407 (2005). 3. M. Antonelli, et al., Journal of Instrumentation, 9, 05034 (2014). 4. J.W. Chen et.al., NIM in Physics Research A, 365, 273–284 (1995) The reported results indicate that our detectors 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 2DEG gas inside the QW. Moreover, by analysing the crosstalk between pixels, different pixelation strategies have been compared in order to plan an optimal one. Device Features and Experimental Setup QW sample Chamber Movable stage PHD school in Nanotechnology Fast, multi-wavelength, efficiency-enhanced pixelated device based on InGaAs/InAlAs quantum-wells T. Ganbold 1,2, M. Antonelli 3, G. Biasiol 1, R. Cucini 3, G. Cautero 3, R. H. Menk 3 1 CNR-IOM, TASC Laboratory, Area Science Park, Trieste, Italy 2 School in Nanotechnology, University of Trieste, Italy 3 Elettra – Sincrotrone Trieste S.C.p.A., Trieste, Italy Several applications utilizing either synchrotron or conventional light sources require fast and efficient pixelated detectors [1]. In order to cover a wide range of monitoring experiments, this work investigates the possibility to use InGaAs/InAlAs Quantum Well (QW) devices as photon detectors for a broad range of energies. Owing to their direct, low-energy band gap and high electron mobility, such QW devices may be used also at Room Temperature (RT) 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. InGaAs/InAlAs quantum well IntroductionIntroduction Metamorphic modulation doped In 0.75 Ga 0.25 As/ In 0.75 Al 0.25 As QW [2] 25-nm-thick wells were placed 55 nm beneath the surface and remotely Si-δ-doped with a 30-nm spacer 2D Electron Gas (2DEG) inside QW with Carrier device n = 7.7×10 11 cm -2 The carrier mobility µ = 1.1×10 4 cm 2 V –1 s –1 at room temperature Metamorphic modulation doped In 0.75 Ga 0.25 As/ In 0.75 Al 0.25 As QW [2] 25-nm-thick wells were placed 55 nm beneath the surface and remotely Si-δ-doped with a 30-nm spacer 2D Electron Gas (2DEG) inside QW with Carrier device n = 7.7×10 11 cm -2 The carrier mobility µ = 1.1×10 4 cm 2 V –1 s –1 at room temperature Working principle Results and Discussion Fig 1. Schematic view of the fabricated devices Light Sources Utilized for the Tests 1. Conventional crystallographic X-ray tube with silver target. Such a source provides a white beam with photon energies ranging from 6 keV to 50 keV with an intensity peak at 22 keV. The spot size has been reduced by a pinhole and a double-slit collimator down to 200 µm (FWHM) at the interaction point. 2. 400-nm titanium-sapphire laser. This UV source emits 100-fs-wide pulses at a 1-kHz repetition rate. For the reported measurements the laser beam has been focused within a 100-µm spot on the sample surface. 3. Synchrotron radiation (SR) SYRMEP beam line optics based on a double-crystal Si (111) monochromator which was set in 2 energies with 17 keV and 22 keV. The beamline provides at a distance of about 20 m from the source, a monochromatic, laminar-section X-ray beam with 522x522 mm 2 in our measurement. Beam exposure generates photo carriers, which can be collected at the surface contacts by applying a bias voltage to the die, giving then rise to measurable currents. QW detectors were mounted on an XY movable stage in order to perform the mesh scans. When the beam hits only one quadrant, there is no contribution from other channels. Then, as the beam crosses the clearance, a sharp switch between two currents takes place. While keeping the light spot in a fixed position on Device #3, the signal acquired through the high-frequency setup exhibited sub-ns response times, featuring rise/fall times of about 100 ps. Fig 2. Sub-ns response to the UV laser pulses Devices #1 and #2 were tested with conventional X-ray source. A decrease of total current in the etched channel was observed in case of 400mm clearance as the beam size is smaller than clearance [3]. However, Device #1 can keep the position sensitivity even the spot side is higher than the etched region (Fig. 3). Charge collection efficiency for photo-generated carriers was estimated in terms of bias voltage (Fig. 4). The efficiency is much higher than in GaAs solid state detectors [4], likely due to the faster carrier transfer in the 2 DEG. Device response in near UV laser light Cross-talk between pixels Enhanced efficiency and absorption linearity of the Device #3 Fig 3. Linear scan of QW devices with X-ray beam a)Device #2 b)Device #1 Fig 3. Linear scan of QW devices with X-ray beam a)Device #2 b)Device #1 a) b) Measure the currents Estimate position abeam Perform measurements on a sample rise time: 100 ps rise time: 100 ps Fig 4. Photo-generated charge collection efficiency of QW samples compared with bulk GaAs solid detectors [4] Fig 5. Absorption linearity in the current in Ion Chamber (I 0 ) and QW sample (I QW ) a) 17 keV b) 22 keV Fig 5. Absorption linearity in the current in Ion Chamber (I 0 ) and QW sample (I QW ) a) 17 keV b) 22 keV Beam position of SYRMEP is currently monitored by a ion chamber. We have compared our QW solid detector with the ion chamber in terms of absorption linearity with different thickness of Al absorbers. The linearity were recorded with both energies of 17 keV and 22 keV (Fig. 5). [4] a) b)