Speaker
Dr
Ulrich Wahl
(Instituto Tecnológico e Nuclear ITN)
Description
The group V impurities As and Sb are of interest as possible acceptor dopants in the
II-VI semiconductor ZnO and as isoelectronic impurities in the III-V semiconductor
GaN. Since the chemical valence of As and Sb is closer to O or N than to Zn or Ga, it
is in in both cases often assumed that As and Sb substitute for the anions of the
compound semiconductor, i.e. for O in ZnO and for N in GaN.
However, these simple arguments do not take into account the ionic size of these
impurities and there exist theoretical predictions that both foreign atoms are more
stable on cation (i.e. Zn or Ga) sites.
We report here on recent lattice location experiments of 73As (80.3 d) and 124Sb
(60.3 d)in ZnO and GaN by means of the emission channeling method. While it is found
that As is in its large majority incorporated in cation sites in ZnO (i.e. replacing
Zn), it turns out that it is amphoteric in GaN, occupying substitutional Ga and N
sites roughly in a ratio 1:1. The experiments with 124Sb are still ongoing but
preliminary results indicate the substitutional incorporation of Sb in Zn and Ga sites.
As and Sb are thus interesting cases of "anti-site" impurities, where the lattice
position is to a large extent dominated by atomic size rather than chemical valence.
Some consequences of this unusual behaviour will be discussed.
Author
Dr
Ulrich Wahl
(Instituto Tecnológico e Nuclear ITN)
Co-authors
Mrs
Ana Claudia Marques
(Centro de Física Nuclear da Universidade de Lisboa and CERN)
Mrs
Elisabete Rita
(Centro de Física Nuclear da Universidade de Lisboa)
Dr
Joao Guilherme Correia
(Instituto Tecnológico e Nuclear ITN and CERN)
Prof.
José C. Soares
(Centro de Física Nuclear da Universidade de Lisboa)
