Feb 12 – 14, 2007
CERN
Europe/Zurich timezone

Exotic diffusion phenomena in II-VI semiconductors

Feb 14, 2007, 2:15 PM
25m
Council Chamber, 503/1-001 (CERN)

Council Chamber, 503/1-001

CERN

Speaker

Dr Herbert Wolf (Technische Physik, Universitaet des Saarlandes, D-66041 Sasarbruecken, 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. Usually, diffusion profiles in all materials are characterized by a depth profile decreasing monotonously from the source of the diffusing species. In some compound semiconductors for certain dopant atoms, however, completely different diffusion profiles can be obtained. Depending on the external vapor pressure during Ag diffusion in CdTe, for identical conditions of temperature and time very different concentration profiles can be observed. E.g. after diffusion at 800 K for 60 min under Cd pressure a peak-shaped profile and under Te pressure a U-shaped profile was observed [1]. In compound semiconductors, like CdTe or ZnTe, large concentrations of intrinsic point defects can be obtained by inducing slight deviations from stoichiometry by exposing the respective material to external vapor pressures of one of its constituents. It turned out that variations of the deviation from stoichiometry during the diffusion process strongly influence the diffusion profile of fast diffusion elements like e.g. Ag or Cu in CdTe. The observed unusual diffusion profiles can be described quantitatively by a model based on defect reactions of the Ag dopant with intrinsic defects [2]. In a semiconductor, intrinsic as well as extrinsic defects can assume different charge states and, in addition, an inhomogeneous distribution of charged defects causes an internal electric field. The model, therefore, considers the presence of different charge states of the participating defects and a drift force acting on the charged defects due to the internal electric field. It turned out that, e.g. in case of Ag diffusion in CdTe, the flux of the Ag atoms essentially is determined by its positively charged interstitial fraction. In addition, the Ag profile essentially reflects the actual distribution of intrinsic defects. A principal question arising from the observation of the unusual diffusion profiles described above is the possible formation of such profiles for other combinations of compound semiconductor and dopant. The formation of diffusion profiles for different dopant atoms in different II VI semiconductors was investigated at ISOLDE using the short-lived isotopes 24-Na, 43-K, 65-Ni, and 56-Mn. In case of 24-Na in CdS and CdTe some features of unusual diffusion profiles similar to Ag in CdTe have been observed but for a quantitative description the model mentioned above might to be modified to some extent. In case of 65-Ni in CdZnTe a different type of an unusual diffusion profile has been observed, which most probably reflects some atypical inhomogeneities of the used host crystal. [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

Primary author

Dr Herbert Wolf (Technische Physik, Universitaet des Saarlandes, D-66041 Sasarbruecken, Germany)

Co-authors

Mr Frank Wagner (Technische Physik, Universitaet des Saarlandes, D-66041 Sasarbruecken, Germany) Mr Joerg Kronenberg (Technische Physik, Universitaet des Saarlandes, D-66041 Sasarbruecken, Germany) Dr Manfred Deicher (Technische Physik, Universitaet des Saarlandes, D-66041 Sasarbruecken, Germany) Prof. Thomas Wichert (Technische Physik, Universitaet des Saarlandes, D-66041 Sasarbruecken, Germany)

Presentation materials