Improved spectrometry of semi-insulating GaAs detectors by chemically thinning detector thickness

Abstract The spectrometric properties of a semiconductor detector depend on both, the base material quality and the electric collection field distribution. In the case of single pad semi-insulating (SI) bulk GaAs detectors with a circular electrode the electric field collecting the charge generated by the radiation is affected by electrode area, detector thickness and applied bias. Thinner and smaller detectors under higher bias obtain better spectrometric properties such as charge collection efficiency (CCE) and energy resolution (FWHM) due to a more intense electric collection field and fewer volume defects. However, the bulk SI GaAs substrate fabrication limits the lowest achievable wafer thickness to about 200 μm due to crystal fragility. We have developed the SI GaAs detectors of 60, 110, 155 and 200 μm thickness by wet chemical etching of 250 μm thick GaAs substrate. The samples were evaluated from point of view of electrical and spectrometric properties. The CCE and FWHM were evaluated with respect to detector thickness and applied bias. The highest achieved CCE increased with thinning detector material from 72% to 92%. The best energy resolution of about 80 keV for 5.5 MeV alpha particles was reached with the 60 μm thick detector.