[Precision measurements of the Doppler broadening of positron annihilation radiations using a simultaneous and...

The precision measurement system of the Doppler broadening profiles of positron annihilation radiations using a simultaneous and comparative detection technique has been developed and was applied to the study of grown-in defects in indium phosphide (InP). Annihilation energy spectra in the specimen to be examined and in a standard one were simultaneously measured by a single pure Ge detector. Each specimen incorporated a 22Na positron source in a sandwiched form between two identical samples. The colinear directional correlation of two photon annihilation allows us to route the output of ADC (analogue to digital converter) to different memory sections. For the purpose of discrimination which source emitted the analysed gamma ray, two auxiliary NaI(Tl) detectors were used. Such a simultaneous and comparative measurement was found to be free of drift in electronics during the course of experiments over 10 weeks. Furthermore, the coincidence measurement reduced the background due to 1.28 MeV prompt gamma rays. This technique was applied to the detection of a positional distribution of grown-in defects in an InP wafer, which was slivered along a plane involving growth axis from the single crystal ingot grown by a liquid encapsulated Czochralski technique. The narrowing of Doppler broadening profiles was observed at the center and at the periphery of the wafer. This result well resembles the positional distribution of dislocations observed by the etch pit counting.