Positron probing of gamma-irradiated Ge doped with P, As, Sb, and Bi: Changes in atomic structures of defects due to n→p conversion
✍ Scribed by N.Yu. Arutyunov; V.V. Emtsev
- Publisher
- Elsevier Science
- Year
- 2009
- Tongue
- English
- Weight
- 203 KB
- Volume
- 404
- Category
- Article
- ISSN
- 0921-4526
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✦ Synopsis
The emission of the high-momentum annihilation radiation from the subvalent ion core shells and electron density around a positron localized at a vacancy-group-V-impurity atom complexes produced in oxygen-lean Ge doped with P, As, Sb, and Bi by irradiation with 60 Co gamma-rays at room temperature have been investigated with the help of the angular correlation of annihilation radiation (ACAR) before and after n-p conversion. The probability of positron annihilation in the subvalent shells of atoms incorporated in dominant radiation centers was found to be dependent on the ratio of the ion core radii r i (P 5+ , As 5+ )/r i (Ge 4+ )o1 and r i (Sb 5+ , Bi 5+ )/r i (Ge 4+ )41, respectively. In passing from P to As impurity atoms the activation energy DE e of electron emission to be detected by DLTS measurements is increased by $(+0.017 eV) vs. the increase of the electron density parameter to be reconstructed by ACAR data, Dr 0 s ¼ r 0 s (As)Àr 0 s (P)E0.029 a.u. On the contrary, in passing from Sb to Bi impurity atoms, DE e value is decreased by $(À0.028 eV) whereas the electron density parameter rises by Dr 0 s ¼ r 0 s (Bi)Àr 0 s (Sb)E0.04 a.u. After n-p conversion a marked decrease in both the electron density and the number of ion cores around the positron points to the fact that the radiation-produced complexes with group-V-impurity atoms (P, As, Sb, Bi) are of a multi-vacancy character. The deep acceptor states in the forbidden gap (E v +0.1), (E v +0.12), (E v +0.16) eV to be attributed to the P-, As-, Sb-, and Bi-containing multi-vacancy centers, respectively, were found to contribute to lessening the electron density around the trapped positron. It is argued that a close similarity of the As 5+ and Ge 4+ ion cores results in a small (but marked) augmentation in the electron density around the positron in As-containing multi-vacancy centers after n-p conversion. A trend for inward relaxation of the ion cores is observed in all radiation-produced centers studied.