A varied shaping time noise analysis of Al0.8Ga0.2As and GaAs soft X-ray photodiodes coupled to a low-noise charge sensitive preamplifier

The noise sources affecting Al0.8Ga0.2As and GaAs spectroscopic X-ray photon counting p+-i-n+ photodiodes connected to a custom low-noise charge sensitive preamplifier are quantified by analysing the system's response to pulses from a signal generator and varying the system's shaping amplifier's shaping time (from 0.5 μs to 10 μs). The system is investigated at three temperatures (−10 °C, +20 °C and +50 °C) in order to characterise the variation of the component noise sources and optimum shaping time with temperature for Al0.8Ga0.2As and GaAs diodes. The analysis shows that the system is primarily limited by dielectric noise, hypothesised to be mainly from the packaging surrounding the detector, for both types of diode and at each temperature.