Deep traps and persistent photocapacitance in p-SnO2/i-ZrxSn1-xO2/n-SnO2 p-i-n diodes

Current-voltage characteristics in the dark and under illumination, capacitance-voltage characteristics and admittance spectra in the dark and under illumination were measured for two sets of p-SnO2:Mg/i-ZrxSn1-xO2/n-SnO2/n+-SnO2:Nb structures. These data strongly point to the structures demonstrating clear-cut persistent photocapacitance behavior existing for temperatures above room temperature. The phenomenon is shown to be due to the centers in the i-ZrxSn1-xO2 layer. These centers are believed to be related to residual Nb donors coming from Nb doped SnO2 layers. The analogy is drawn between the above-mentioned effect and the persistent photocapacitance phenomena in n-type doped AlGaN films for varying Al compositions that have been convincingly explained in the literature as in fact due to some of the standard n-type dopants being DX-like centers with a high barrier for capture of electrons. For the two studied p-SnO2/i-ZrxSn1-xO2/n--SnO2/n+- SnO2:Nb samples the thermal ionization energy, the barrier for capture of electrons, the optical ionization energy of the centers responsible for persistent photo- capacitance have been estimated. The results suggest that the photoresponsivity of the samples increases when increasing the Zr mole fraction closer to the value of x = 0.3 and the concentration of centers responsible for persistent behavior decreasing from some 1017 cm- 3 to some 1016 cm- 3 .