Thin Solid Films 517 (2009) 2469-2472 Intrinsic defects and metastability effects in Cu 2 O A. Mittiga, F. Biccari, C. Malerba ENEA Casaccia Research Center, via Anguillarese 301, 00123 Rome, Italy alberto.mittiga@enea.it Abstract Cu 2 O based junctions (both Schottky and ZnO/Cu 2 O heterojunctions) exhibit a metastable capacitance increase after illumination or reverse bias application. We show that this effect is related to the persistent photoconductivity in Cu 2 O substrates. To obtain a quantitative evaluation of defect properties we have measured conductivity vs T, Capacitance-Voltage, Persistent photoconductivity decay and capacitance transients at different temperatures. We show that it is impossible to explain these data using an electronic mechanism only. A new model which includes the formation-dissociation of intrinsic defect complexes (V Cu -V O ) can give instead a better agreement with the experimental data. 1 Introduction Cuprous oxide (Cu 2 O) is a semiconductor interesting for many applications: photovoltaics [1], spintronics [2] , non-volatile memories [3]. Thanks to the rather high value of the gap (about 1.95 eV at room temperature) it could be used in multijunction solar cells or IPV solar cells [4]. However, the highest energy conversion efficiency reached by a Cu 2 O solar cell [1] is one order of magnitude lower than its theoretical limit due to a lack of clear understanding of the properties of its intrinsic point defects and to the difficulties in the doping processes. Cu 2 O is spontaneously a p-type semiconductor: both experiments [5] and ab-initio calculations[6] suggest that this is due to negatively charged copper vacancies which introduce an acceptor level at about 0.3 eV above E V [6]. The experiments also show that Cu 2 O is a compensated material with a compensation ratio N A /N D ( N A and N D are the acceptor and donor density respectively) slightly larger than 1 and anyway less than 10 [7][8][9]. The acceptor density estimated from the CV measurements is in the range 10 14 - 10 15 cm -3 [10][9]. Cu 2 O shows p-type Persistent PhotoConductivity (PPC) and this fact was explained using a simple electronic model[11][12] where deep donors are able to capture and re-emit electrons but possess a very small capture cross section for holes (σ p ). The metastable conductivity increase was therefore attributed to the donor filling by light generated electrons and its decay to the electron emission. In this paper we investigate metastability effects in Cu 2 O using conductivity and PPC measurements on samples with two ohmic contacts and Capacitance-Voltage and Capacitance transients measurements on Cu 2 O based junctions (both Schottky and heterojunctions).