On the possible identification of defects using the autocorrelation function approach in double Doppler broadening of annihilation radiation spectroscopy

The recent revived interest in the use of double-Doppler broadening of anni hilation radiation (D-DBAR) spectroscopy, which employs two Ga detectors in back-to-back geometry, has stemmed mainly from its potential in defect ide ntification as a result of its elemental sensitivity through core annihilat ions in atoms at the defect site. Emphasis has thus largely concentrated on the high momentum spectral range. In contrast the present work emphasizes the need to also focus attention on the low momentum region of the D-DBAR s pectra. It is argued that the root 2 improved resolving power of D-DBAR, in conjunction with spectral deconvolution, should give future 1D (one dimens ional) momentum data approaching in quality those obtainable using 1D-ACAR (angular correlation of annihilation radiation), thus forming an alternativ e technique for observing the structure containing diffraction patterns tha t originate from annihilations with localized electron states at positron t rapping defects. Rotation of the sample about a specified crystal axis, and the binning of events by angle, is suggested as a means of extending the t echnique to form a 2D- (two dimensional) DEAR counterpart to 2D-ACAR. The a dvantages of considering the real space positron electron wavefunction prod uct AF (autocorrelation function), obtained by simple manipulation of the D -DBAR data in Fourier space, are outlined. In particular the possible visua lization offered in real space of a defect's physical geometry, with the pr ospect of building up a library of contour patterns for future defect ident ification, is discussed, taking the silicon monovacancy in Si and the negat ive As vacancy in GaAs as examples.