Electrical conduction and electroluminescence in MOS devices based on Si nanocrystal embedded in SiOx-Si-Nd films

International audienceSilicon heterojunctions have been extensively studied for the understanding the physics of the device as well as their applications to majority carrier rectifier, photodetectors, solar cells and indirect gap injection lasers. Because of its indirect bandgap, silicon is highly inefficient material for light emitter. However, to overcome this problem different approaches were developed in this last decade for the fabrication of Si-based light emitting sources made of silicon nanoclusters (Sinc) embedded in silica or silicon oxynitride (SiO2-Sinc or SiOxNy-Sinc) matrix. In addition, IR light emitting properties were also reported in matrix embedding Sinc and rare earth. In such system, the emitting rare earth ions benefit from the quantum confinement properties of the carriers generated within Sinc to be efficiently excited by an energy transfer mechanism. Electroluminescence of silicon rich oxide based IR light emitting devices is limited by the difficulty in carrier injection. The aim of this work is to study the electrical and the optical properties of MOS diodes made of silicon rich oxide SiOx-Si-Nd thin layers for future electroluminescent devices, which benefit from the efficient sensitizing effect of Si nanoclusters towards the neodynium ions. In this way, Al/SiOx-Si-Nd/p-Si devices are fabricated are elaborated on p-type (111) oriented silicon substrates with resistivity in the range 0.001-0.005 cm. First, a SiOx-Si-Nd active layer is deposited by reactive magnetron sputtering of a pure SiO2 target with Nd2O3 chips under a mixture of hydrogen/argon plasma, which was subsequently submitted to an optimized annealing treatment at 1050°C under N2 flux. Next, aluminum was thermally evaporated on the active layer. Both aluminum and active layers were patterned by wet etching to define the geometry of the device. A second thermal evaporation of aluminum on the back surface was carried out to ensure the ohmic contact with the p-type crystalline silicon. Finally, the devices were annealed into forming gas (H2:N2, 10%) at 390°C during an optimum duration to stabilize the electrical properties of the devices. The conduction mechanisms and the optical properties of the MOS structures are studied in relation with the silicon content (9, 11, 13, 14 or 16%) of the silicon rich oxide SiOx-Si-Nd laye