Persistent photocurrent spectroscopy of GaN metal-semiconductor-metal photodetectors on long time scale

Some of the trapping mechanisms responsible for the persistent photocurrent effects in GaN metal-semiconductor-metal photodetectors have been studied on a time scale of several hours by analyzing the photocurrent decay kinetic as a function of temperature. The analysis of the Arrhenius plot of the decay kinetic on a long time scale shows two activation energies of about 140 meV and 1 eV. Such values are in good agreement with two slope changes observed in the room temperature photocurrent spectrum around 2.40 and 3.25 eV, in the GaN energy band gap. According to the Lucovsky theory the 140 meV activation energy was interpreted as due to the transition from a deep localized state to the conduction band edge, whereas the 1 eV activation energy was interpreted as due to the transition from the valence band edge to a deep localized state. Therefore, the persistent photocurrent on long time scale is primarily due to the presence of donor deep and acceptor deep states generated by gallium vacancies, gallium antisites, and carbon impurities.