Zinc oxide (ZnO) is a promising candidate for application in ultraviolet (UV) photodetectors due to the large direct band gap and the high absorption coefficient in the UV spectrum range. UV detectors based on wide bandgap semiconductors like SiC, GaN and ZnO have received more and more attention due to their chemical and thermal stability in harsh environments. For applications in p-n diode detectors p-type doping of ZnO is necessary. It is known, however, that it is a difficult task due to the background n-type doping .

High quality dual acceptor doped ZnO:(As,Sb) films were grown on n-type GaN templates by plasma-assisted Molecular Beam Epitaxy (PA-MBE)and p-ZnO/n-GaN heterojunction structures have been fabricated [1]. The structure consists of a 3.5 um thick GaN layer on sapphire substrate covered by a  60 nm thick As and Sb-doped ZnO film. The quality of the heterojunction was examined by X-ray diffraction, atomic force microscopy (AFM) and scanning electron microscopy (SEM). The As and Sb concentration in ZnO, measured by secondary ion mass spectroscopy (SIMS), is 1x10²⁰ cm^-3. The maximum forward-to-reverse current ratio I_F/I_R in the obtained diode is of about 10⁵ at the applied voltage of  ±4 V, which is a very good result for this type of heterojunction. Electronic properties were examined by XPS study and the presence of As acceptors was also confirmed by low temperature PL study. Photodetector’s response to the pulse of light in the UV region is relatively fast <<1 ms. Photodetectors based on a presented diodes are highly selective (FWHM photocurrent peak ~12 nm), work both in atmospheric pressure and in vacuum.

Fig 1   Cuurent-voltage characteristics ZnO/GaN diodes dark and with UV  illumination.

The research was partially supported by the European Union within European Regional Development Fund, through grant Innovative Economy (POIG.01.01.02-00-008/08).

[1]E. Przeździecka, K. Gościński, M. Stachowicz, D. Dobosz, E. Zielony, J. M. Sajkowski, M. A. Pietrzyk, E. Płaczek-Popko, A. Kozanecki Sensors & Actuators: A. Physical  (2013), pp. 27-31

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