It was noted that the substitution of isotopes was well established, in photoluminescence spectroscopy, as a means of unambiguously determining the identity of defect impurities. The technique was limited to those cases where stable isotopes of probable defect constituents were available, and where the associated line-shifts were greater than the available resolution. By using radioactive isotopes, the appearance or disappearance of a spectrum at a rate which was consistent with the radioactive half-life of the isotope could provide information on the chemical identity of defect impurities. The minimum detectable defect populations in photoluminescence studies were frequently low, and this made it suitable when low concentrations or small volumes were involved. Various examples of the use of this technique were reported. Thus, Si was implanted with radioactive 111In (half-life = 2.8d), and was treated so as to produce the intense photoluminescence which was characteristic of In-doped material. The luminescence intensity was found to decay non-exponentially, and at a higher rate than was expected for the 111In half-life, whereas the neutral In acceptor bound exciton luminescence intensity decayed as expected. New spectral features were found to appear after several half-lives, and were attributed to Cd; the daughter atom of 111In. Preliminary results which were obtained for Hg-implanted Si were also reported, together with data on As-implanted GaAs, which were shown to be consistent with Hall and resistivity measurements. These results confirmed the feasibility of using radioactive isotopes in photoluminescence spectroscopy.

S.E.Daly, M.O.Henry, C.A.Frehill, K.Freitag, R.Vianden, G.Rohrlack, D.Forkel: Materials Science Forum, 1995, 196-201, 1497-502