Speaker
Mr
Frank Wagner
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
Description
Understanding and control of diffusion profiles of intrinsic and extrinsic defects in semiconductors is of central importance for developing electronic and optoelectronic devices. In previous studies [1] it was shown that diffusion of Ag in CdTe can lead to uncommon diffusion profiles. The diffusion of Ag and Cu in CdTe crystals after implantation of 111Ag or 67Cu with 60 keV and annealing at 800 K for 60 min under Cd pressure showed symmetrically and peak-shaped depth profiles with respect to the center of the crystal. Thus the Ag or Cu atoms must have diffused from regions of low concentration to regions of higher concentration (up-hill diffusion) contrary to what is usually expected in diffusion experiments.
Simulations of the diffusion profiles taking into account the charge state and drift of the different defects are able to quantitatively explain the observed profiles [2]. Thereby, the shape of the profiles is reproduced if the dopant atoms Ag or Cu are dominantly present as positively charged interstitials. The penetration of interstitial Cd atoms, originating from the external Cd pressure, changes the initially Cd vacancies rich, p-type material, into n-type. The dopant profile then maps the position of the Fermi level, which reflects the profile of the intrinsic defects and the steep gradients of the dopant profile indicate the positions of pn junctions.
Here, new diffusion experiments using short lived radiotracers of other elements (Mn, Fe, K, Au, Co and Ni) implanted into II-VI semiconductors at ISOLDE are summarized.
The diffusion of Mn, Fe, and K did not show uncommon profiles upon diffusion annealing.
In contrast, the diffusion profiles of Au and Na showed almost the same features like Ag and Cu upon diffusion under Cd pressure. Furthermore, the penetration depth of Au indicates a diffusion coefficient being much larger than values published in the literature. The fast diffusion of Au observed here may be related to the ability to detect much lower concentrations due to the use of radiotracers (> 108 cm-3) as compared to "classical" techniques, like SIMS or RBS.
Also Co and Ni exhibit uncommon diffusion profiles which, however, are distinctively different from those observed for Ag, Cu, or Au. The profiles observed in CdZnTe under Cd pressure show box shaped profiles, ranging from the implanted surface up to the first pn junction. These profiles can be explained assuming that Ni and Co are highly mobile only in Cd rich material and that at diffusion temperature they are present as negatively charged interstitials.
The financial support of the BMBF under contract 05 KK1TSB/5 is gratefully acknowledged.
[1] H. Wolf, F. Wagner, Th. Wichert, and ISOLDE Collaboration, Phys. Rev. Lett. 94 (2005) 125901.
[2] H. Wolf, F. Wagner, Th. Wichert, R. Grill, and E. Belas, J. Electr. Mat. 35 (2006) 1350.
Author
Mr
Frank Wagner
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
Co-authors
Dr
Herbert Wolf
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
Mr
Jörg Kronenberg
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
Dr
Karl Johnston
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
Dr
Manfred Deicher
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
Prof.
Thomas Wichert
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
Mr
Thomas Wichert
(Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken, Germany)
