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In this work we have studied the role of excitons in two different low barrier metal–semiconductor–metal (MSM) GaN-based UV photodetectors at high temperature. The active material of the two MSM devices consists of bulk GaN grown by metal organic chemical vapour deposition (MOCVD), and of an AlGaN/GaN heterostructure forming a two-dimensional electron gas (2DEG) grown by molecular beam epitaxy/magnetron sputtering epitaxy (MBE/MSE) system. The response of the devices has been characterized at the wavelength of 325 nm (He–Cd laser) as a function of the temperature in the range between room temperature and 700 K. The Arrhenius plot obtained by the decay times of the photocurrent allowed us to calculate the activation energies of some trapping mechanisms responsible of the persistent photocurrent (PPC). This shows that in both device the GaN excitonic resonances provide the most important contribution to the PPC on the millisecond time scale at low temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work we report on the high temperature characterization of two different interdigitated metal–semiconductor–metal (MSM) GaN-based photodetectors. The active material of the two MSM devices consists of bulk GaN grown by metal organic chemical vapor deposition (MOCVD), and of an AlGaN/GaN heterostructure grown by molecular beam epitaxy/magnetron sputtering epitaxy (MBE/MSE) system. Some of the trapping mechanisms which are at the origin of the persistent photocurrent (PPC) effects in GaN-based devices have been studied. The analysis of the decay time as a function of the temperature shows that in both devices the GaN excitonic resonances provide the most important contribution to the PPC on the millisecond time scale at low temperature. The densities of the trap centers involved in the PPC were obtained in both samples by measuring the photocurrent as a function of optical power sweeped in the upward and downward direction.