Evidence of a second acceptor state of theEcenter inSi1−xGex

Abstract

We have found evidence of a second acceptor state of the E center in Si 1−x Ge x by using positron annihilation spectroscopy. To achieve this, we studied proton irradiated n-type Si 1−x Ge x with a Ge content of 10%-30% and a P dopant concentration of 10 18 cm −3 , in which the number of Ge atoms around irradiation induced E centers was increased by annealing. When measuring the Doppler broadening of the annihilation line, the shape parameter S starts to decreases at 150 K with decreasing measurement temperature. This indicates that a charge transition in the upper half of the Si 1−x Ge x band gap, above the well known ͑0/Ϫ͒ level, takes place. Hence, we suggest that the increased concentration of germanium around the E center pulls down the localized second acceptor state into the Si 1−x Ge x band gap, making the Ge decorated E center a more effective trap for conduction electrons.

Increased p-type conductivity in GaNxSb1−x, experimental and theoretical aspects

“…However, a change in the charge state of the defect can lead to a somewhat different S parameter since the atoms neighboring negative vacancies can relax inwards. 54 For the layers with N, the measured large increase in the p-type conductivity indicates an increase in negatively charged defects in the material. In addition to the increase in charged defects, the calculations indicate that the added nitrogen can also affect the shape of the annihilation line in the case of positrons localizing at or near to nitrogen atoms.…”

Nonlinear stability ofEcenters inSi1−xGex: Electronic structure calculations

“…63 and references therein͒. In Si 1−x Ge x , the PAS results of Kuitunen et al 33 indicate that even a doubly negatively charged state is possible for a sufficiently high Ge content.…”

“…23-25͒ and Ge, [26][27][28][29][30] the systematic experimental or theoretical treatment of their stability over the composition range of Si 1−x Ge x is still a relatively uncharted research area. In recent studies, [31][32][33] both positronannihilation spectroscopy ͑PAS͒ and density-functional theory ͑DFT͒ were used to study phosphorus-vacancy ͑PV͒ pairs in Si-rich Si 1−x Ge x . Previous theoretical studies of Si 1−x Ge x have been devoted to the effect of composition on the formation of V, V-mediated diffusion, 2,21,22 and the interaction of V with extended defects.…”

Defect identification in semiconductors with positron annihilation: Experiment and theory

“…The situation is completely different for the Si-Ge alloys which have been studied to a large extent. Vacancy-donor complexes introduced by irradiation of n-type material (Sihto et al, 2003;Rummukainen et al, 2006;Kuitunen, Tuomisto, and Slotte, 2007), vacancy-fluorine complexes produced by F implantation (Edwardson et al, 2012), and the particularities related to the random alloy nature of Si-Ge alloys (Shoukri et al, 2005;Ferragut et al, 2010;Kilpeläinen et al, 2010Kilpeläinen et al, , 2011 have been studied in more detail.…”

“…There is significant room for improvement, but here it might not be sufficient to apply existing, even if state-of-the-art, theoretical methods to account for the randomness. The importance of the effects of the local environment of the vacancy defects being identified compared to the long-range disorder need to be elucidated (Kuitunen, Tuomisto, and Slotte, 2007;Kilpeläinen et al, 2010Kilpeläinen et al, , 2011. Systematic studies in all these materials are required in order to fully elucidate the vacancy defect identities and roles.…”