Graded-gap AlxGa1-xAs detector for high-energy electron beam dosimetry

A new graded-gap p-Al0.2Ga0.8As-p-AlxGa1-xAs-n-GaAs detector structure with internal optical response was developed and investigated as a detector for high-energy electron beam dosimetry. An additional p-Al0.2Ga0.8As top layer was grown on the narrow-gap side of the structure. This thin (2 μm) top layer significantly reduces nonradiative surface recombination and increases detector sensitivity for high-energy electron beams by about 10-13%. The increase in doping level of the graded-gap AlxGa1-xAs layer from p=3x1017 to 1.9x1018 cm-3 increases detector sensitivity by about 2.3 times. The detector was encapsulated into a plastic body and fitted for dosimetric measurements in a water phantom. Linear response on absorbed dose and dose rate was obtained for beams with electron energies of 6, 12 and 20 MeV. A good agreement of relative depth dose distribution measured by the AlxGa1-xAs detector and ionization chamber is obtained for the 6 MeV energy electron beam, but a discernible discrepancy is observed for the higher electron energies.