Optoelectronic properties of p-n and p-i-n heterojunction devices prepared by electrodeposition of n-ZnO on p-Si

The importance of silicon based optoelectronic devices is due to the well developed silicon technology and its potential for device integration. ZnO/Si light emitting diodes reported in the literature are based mainly on ZnO films grown by the vapor-phase techniques. Electrodeposition, a cost-effective and simple method, has not been explored adequately for the fabrication of such devices. In this study, ZnO films were electrodeposited on the (100) plane of highly B-doped p-Si substrates. Heterojunction devices (p-n and p-i-n) were constructed and characterized by means of current-voltage, capacitance-voltage, photocurrent spectroscopy, photoluminescence, and electroluminescence measurements. Electrodeposition yields compact films with a native donor density similar to 10(17) cm(-3). Diffusion of boron from Si into ZnO, during an annealing process, yields graded p-n junctions with enhanced electroluminescence. Devices exhibit a reasonably good photoresponse in the ultraviolet-blue range. The absorption of subband gap photons in ZnO shows an Urbach tail with a characteristic energy of 115 meV. The absorption and emission of light involves two prominent defect levels in ZnO, namely, L-1 and E-1. (C) 2010 American Institute of Physics. [doi:10.1063/1.3490622]