This presentation is devoted to a comparative studies of a donor impurities contributing significantly to n-type conductivity in unintentionally doped GaN and InN binary nitrides.
One question crucial for understanding physicals properties of these compounds concerns the chemical nature of the donors present often in concentrations exceeding 1019 cm-3. The second one is related to their character and location of the related impurity levels in the band structure of both materials. In particular we discuss the conditions determining a role of these impurities as shallow or localized donors.
It has been found in GaN that oxygen forms an effective-mass-like donor state with the level situated » 30 meV below the conduction band (CB) minimum. Under sufficiently high pressures or alloying with Al, localized donor state can be formed by Oxygen and eventually it takes a role of a donor ground state. At ambient conditions this localized state of O is situated few hundreds of meV above the CB minimum.
In case of InN a situation is much less clear. It concerns an origin of high electron concentration which can exceed 1021 cm-3. Hydrostatic pressure studies show a strong transfer of electrons to the localized donor state in samples with electron concentration below about 5´1018 cm-3. Though the chemical nature of the donor state is unknown, its localized level (at ambient conditions) is located about few tens of meV above the CB minimum. The considered donor supplies about 5´1017 cm-3 electrons to the conduction band. It is suggestive to associate our findings with observations of an involvement of the localized donor state in radiative recombination of these materials. We discuss such a possibility in our presentation.