Isoelectronic defect

An isoelectronic impurity is a lattice defect in a crystal in which one atom has been replaced by another that has the same electronic structure as the valence shell. An example of this is a nitrogen atom on a phosphorus lattice site in Galliumphospid. Such an impurity is of importance in semiconductor physics . An isoelectronic defect is zero-dimensional, i.e. H. a point defect .

Meaning for light emitting diodes

Indirect semiconductors have a very low probability of emitting light , since quasi-impulses have to be transferred when the conduction band minimum is recombined into the valence band maximum . The generated photon cannot absorb it because it only has a very small pulse, so that a phonon must always be involved in the emission process . In most cases, this also absorbs the energy difference, so that no photon is emitted at all.

An isoelectronic defect provides localized states, so-called deep defects. These states are at the gamma point of the Brillouin zone , so they have a quasi-momentum of zero. Optical transitions from these states are also possible in indirect semiconductors, so that the light yield increases. The wavelength of the emitted light can also change, e.g. B. with gallium phosphide it is longer, d. H. redshifted.

literature

• SM Sze: Physics of Semiconductor Devices. 2nd Edition John Wiley and Sons 1981, ISBN 0-471-05661-8 .
• Peter Y. Yu, Manuel Cardona: Fundamentals of Semiconductors . Springer, Berlin / Heidelberg / New York 1996, ISBN 3-540-58307-6 .