Інститут фізики напівпровідників ім. В.Є. Лашкарьова НАН України
Національна академія наук України


The method of doping and purification of crystals by electric drift

№3 The department of photoelectric phenomena
I.V. Markevich, N.O. Korsunska, L.V. Borkovska, L.Yu. Khomenkova

Importance and effectiveness of the development. The doping of II-VI compounds by different dopants including Cu and Ag is usually realized during crystal growth, by diffusion from the surface or by ion implantation. The common disadvantage of such techniques is high amount of unstable intrinsic defects generated due to high temperatures  of  doping procedure or bombardment with high-energy ions. This complicates the determination of the parameters of local centers related to incorporated interstitials as well as the clarification of their influence on electrical, photoelectrical and luminescent characteristics of the materials. Besides, the determination of the diffusion parameters of impurities becomes not reliable due to the changes of material characteristics in this case.
The alternative method for the doping based on the heating of the crystals under simultaneous applying of electric field is proposed. In this case, the electric field allows to increase the velocity of doping process and to decrease the temperature of doping. The drift of charged defects in the external field can be used for the purification of semiconductor materials from undesirable impurities too.

The main advantages of the development in comparison with existing analogues. Proposed by us technique allows to make the doping and the purification of crystals at low temperatures and low values of electric filed.

Electro-drift based method for the doping of CdS crystals by copper

  Institute of monocrystals, Kharkiv, Ukraine, 1979 (laboratory setup) V. Lashkaryov Institute of Semicon-dutor Physics, NAS Ukraine, Kyiv, Ukraine, 2002 (laboratory setup)
Temperature of CdS doping by copper, °C 400-500 300-350
Electric field for CdS doping by copper, V/cm 102-104 5·101-102

Short description of the development. Both doping and purification of the crystals occur under electric field applied to specific electrodes. By this method, doping of “pure” CdS crystals by copper and silver as well as extraction of these impurities from doped crystals under electric field have been performed. The optimal regimes for both processes have been found. The method mentioned can be used for detection and investigation of moving defects in the crystals. It was applied for study of the defects in CdS and CdSe crystals. In particular, the parameters of copper and silver diffusion in different crystallographic directions in CdS crystals were estimated and the effect of anisotropy of copper and silver diffusion were found, the effect of anomalous drift of defects in CdSe crystals was revealed and investigated.
The view of doped crystals is shown below.

  1. 022 022 2
    а)  b)
    022 3 022 4
    c) d)

Doping of CdS crystals by copper (a-d) in the direction perpendicular )a,b) and parallel (c,d) to c-axis. The view of doped crystal obtained under natural illumination (a,b) and under band-to-band excitation light (c,d).