Identification of vacancy defects in compound semiconductors by core-electron annihilation: Application to InP

Abstract

We show that the Doppler broadening of positron annihilation radiation can be used in the identification of vacancy defects in compound semiconductors. Annihilation of trapped positrons with surrounding core electrons reveals chemical information that becomes visible when the experimental background is reduced by the coincidence technique. We also present a simple calculational scheme to predict the high-momentum part of the annihilation line. The utility of the method is demonstrated by providing results for vacancies in InP. In electron irradiated InP the isolated In and P vacancies are distinguished from each other by the magnitude of the core electron annihilation. In heavily Zn-doped InP we detect a native vacancy defect and identify it to a P vacancy decorated by Zn atoms.

Microscopic identification of native donor Ga-vacancy complexes in Te-doped GaAs

“…This allows the identification of vacancies and vacancy-impurity complexes, especially when measurements are correlated to calculations of the momentum distribution. 13 The coincident detection of both 511-keV ␥ quanta from single annihilation events allows the observation of the high momentum annihilation distribution due to a strong reduction of the disturbing background. [13][14][15][16] Ga vacancies in highly Si-doped GaAs were identified using that Doppler-broadening coincidence technique.…”

“…13 The coincident detection of both 511-keV ␥ quanta from single annihilation events allows the observation of the high momentum annihilation distribution due to a strong reduction of the disturbing background. [13][14][15][16] Ga vacancies in highly Si-doped GaAs were identified using that Doppler-broadening coincidence technique. 17 The experiment could, however, not decide whether the vacancies are isolated or a part of a complex because the Si Ga donor on the second nearest site is not expected to contribute much to the annihilation.…”

“…The high momentum part of this distribution can be used to identify the chemical surrounding of the annihilation site. [13][14][15][16] This is based on the fact that tightly bound core electrons with high momenta retain their element-specific properties even in a solid. This allows the identification of vacancies and vacancy-impurity complexes, especially when measurements are correlated to calculations of the momentum distribution.…”

Structure of the[ZnIn−VP]defect complex in Zn-doped InP

“…The resulting values of E d R (4) are converged to at least 0.02-0.04 eV and usually to an order of magnitude or so better. Hence we do most relaxations with a 2ϫ2ϫ2 k-point grid, only checking key ones at 4ϫ4ϫ4.…”

“…Both groups identify two separate positron lifetimes corresponding to two different forms of the same complex: a shorter lifetime of about 260-280 ps indicating an effective vacancy volume similar 1,4 to that of the free V P and a longer lifetime of around 330 ps corresponding to a larger effective vacancy volume. Both groups identify the two forms as different charge states of the complex, the most stable ͑in p-type material͒ being neutral, with a 0/Ϫ1 transfer level lying near the bottom of the band gap, 0.2Ϯ0.1 eV above the valenceband edge according to Slotte et al They believe 2 that the neutral form has a volume larger than the free vacancy and that the complex shrinks to a volume similar to the free vacancy when excited into its Ϫ1 charge state.…”