Photostimulated gettering of deep band-gap impurities from semiconductors by resonance excitation: Fe from Cd0.98Fe0.02Se.

Abstract

Impurities that lie deep in the band gap of a semiconductor (deep impurities) behave as a strong recombination center as shown by the Schockley-Read mechanism for surface recombination [A. Rothwarf and K. W. Boer, Prog. Solid State Chem. 10, 71 (1975)]. Thus, removing such impurities from the semiconductor is imperative for the optimal operation of photonic devices and solar cells, in particular. In the following work a method is proposed to remove such impurities. In this process resonance excitation of electrons (holes) from the impurity level into the conduction (valence) band leads to ionization of the impurity, which in turn leads to fast outdiffusion of the impurity and its dissolution by a chemical (electrochemical) reaction at the semiconductor surface. As a demonstration of this principle Fe, which is a deep donor in CdSe, is selectively removed from a ${\mathrm{Cd}}_{0.98}$${\mathrm{Fe}}_{0.02}$Se crystal. A giant diffusion constant (D=${10}^{\mathrm{\ensuremath{-}}9}$ ${\mathrm{cm}}^{2}$/sec) is measured for Fe in this experiment. The application of this process for the control of impurity profiles in various semiconductor devices is briefly discussed.