Impurity band in the interfacial region of GaN films grown by hydride vapor phase epitaxy

Abstract

Using several derivatives of scanning force microscopy with conducting tips, we find direct evidence for the existence of a highly compensated donor impurity band in GaN films near the sapphire substrate interface. Scanning currentvoltage and capacitance microscopy measurements both show that the free electron density is much higher in the interfacial region of these films. However, surface contact potential images reveal that the Fermi level in the interfacial region is 50 meV to 100 meV deeper into the bandgap than it is in the less conducting bulk film. These results are inconsistent with a high density of electrons in the intrinsic conduction band. Rather, they point to the existence of a partially filled donor impurity band with the Fermi level in the impurity band. We show that this anomalous conduction behavior most likely originates from a high concentration of oxygen and the defective microstructure at the GaN/ sapphire interface.

Electronic transport properties of Ti-impurity band in Si

“…for the temperatures where the anomalous behaviour of both the sheet resistance and the Hall mobility occurs. The low mobility value and the independence with the temperature are typical of charge carriers within a very narrow band [10]. The low mobility value is close to the 0.4 cm 2 V −1 s −1 simulated value, temperature independent.…”

“…Electrical transport properties of semiconductors with an IB could be, in principle, quite different from those of 'standard' semiconductors and, as a consequence, a careful analysis of such properties seems to be mandatory. In fact, in III-V and II-VI semiconductors such as GaN and ZnO, an unintentionally introduced impurity band seems to be always present [10,11]. In the first semiconductor, a highly conductive layer that appears in the first stages of GaN growth [12] has been observed at the GaN/substrate interface.…”