Characterization of chromium compensated GaAs as an X-ray sensor material for charge-integrating pixel array detectors

Abstract

A: We studied the properties of chromium compensated GaAs when coupled to charge integrating ASICs as a function of detector temperature, applied bias and x-ray tube energy. The material is a photoresistor and can be biased to collect either electrons or holes by the pixel circuitry. Both are studied here. Previous studies have shown substantial hole trapping. This trapping and other sensor properties give rise to several non-ideal effects which include an extended point spread function, variations in the effective pixel size, and rate dependent offset shifts. The magnitude of these effects varies with temperature and bias, mandating good temperature uniformity in the sensor and very good temperature stabilization, as well as a carefully selected bias voltage.

Characterization of Chromium Compensated GaAs Sensors with the Charge-Integrating JUNGFRAU Readout Chip by Means of a Highly Collimated Pencil Beam

“…This variation of the effective pixel size in chromium compensated GaAs was also observed by other groups like J. Becker et al [ 13 ]. The cause of this effect is unknown at this moment; however, it could explain the non-symmetric shape of the charge collection behavior in Figure 14 , but this is speculative.…”

“…The magnitude of this pedestal shift can reach up to −2 keV and is present in frames without photon interaction, i.e., it is a (partially) persistent effect. The origin of the effect is unclear; however, a similar effect has been observed previously also by other authors [13]. ).…”

“…Further details on the compensation process are explained in Reference [ 9 ]. Chromium compensated GaAs has been successfully evaluated as sensor material by several groups as it exhibits good spectral performance and stable detector operation, even under high photon fluxes which makes it a promising sensor material for X-ray detectors at synchrotrons or FELs [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”

Overview of GaAs und CdTe Pixel Detectors Using Medipix Electronics

“…GaAs sensors are also used in applications for Ultrafast Imaging. The latest publications by Becker et al [12] show that the combination of charge-integrating electronics requires significantly higher stability and homogeneity requirements for each individual pixel. Dislocations and intrinsic defects such as those present in Cr-compensated GaAs have an even greater influence on the reduction of efficiency and spatial resolution.…”

Space charge formation in chromium compensated GaAs radiation detectors

“…Semiinsulating (SI) GaAs compensated by in-diffused chromium (GaAs:Cr) appears nowadays a promising X-ray detector material overcoming known drawbacks of Liquid Encapsulated Czochralski (LEC) SI-GaAs significantly debased by EL2 defect [1][2][3]. GaAs:Cr exhibits extended electron lifetime and long-term stability at applied bias, conserving simultaneously profitable properties of GaAsbased room-temperature radiation detectors, especially the relatively high average atomic number (Z=32), moderate energy band-gap (Eg=1.42 eV) and high electron drift mobility (μde=2500 cm 2 /Vs) [4][5].…”