The Metastability of Deep Donor Defects in Semiconductor Compounds

There is a whole class of deep donor defects which exhibit a metastable character, i.e. transform into a metastable state after a specific photo-excitation. Typical examples are the EL2 defect in GaAs and the DX center in several ternary III-V compounds. We shall present other defects which behave similarly, demonstrating that this metastable character is not specific of a defect but is a common behaviour of a class of defects. We shall also demonstrate that for all these defects the thermal excitation of electrons takes place in the L conduction band and that the metastable character is a direct consequence of this. This leads to a new concept of a metastable state, a result of an electronic metastability due to a band structure effect and not to a strong electron-phonon interaction.