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Abstract. An in-depth study of the physical and electrical properties of Sinanocrystals embedded in silicon dioxide is presented. These layers were fabricated with different Si concentrations by both ion implantation and plasma-enhanced chemical vapour deposition. Subsequently, LEDs devices based on a metal-oxide-silicon configuration with a ∼350 nm polycrystalline Si top electrode and an active layer of about 45-50 nm, were fabricated in conventional lithography process. In order to optimize the device performances, prior to the top electrode deposition, the structural and photoluminescent properties of the active layers were exhaustively studied.Devices fabricated by ion implantation exhibit a combination of direct current and field-effect luminescence under a bipolar pulsed voltages excitation. The onset of the emission decreases with the Si excess from 6 to 3 V. The direct current emission is attributed to impact ionization, and is associated with the reasonably high current levels observed in current-voltage measurements. This behaviour is in good agreement with transmission electron microscopy images that revealed a continuous and uniform Si-nanocrystals distribution. The emission power efficiency is relatively low, ∼10 −3 %, and the emission intensity exhibits fast degradation rates, as revealed from accelerated aging experiments.Devices fabricated by chemical deposition only exhibit field-effect luminescence which onset decreases with the Si excess from 20 to 6 V. The absence of the continuous emission is explained by the observation of a 5-nm region free of nanocrystals, which strongly reduces the direct current through the gate. The main benefit of having this nanocrystal-free region is that tunnelling current flow assisted by nanocrystals is blocked by the SiO 2 stack so that power consumption is strongly reduced, which in return increases the device power efficiency up to 0.1 % . In addition, the accelerated aging studies reveal a 50% degradation rate reduction as compared to implanted structures.PACS numbers: 73.63. Bd, 78.67.Bf, 85.60.Jb Submitted to: Nanotechnology Si nanocrystal-based LEDs fabricated by ion implantation and PECVD 2

We report on a field-effect light emitting device based on silicon nanocrystals in silicon oxide deposited by plasma-enhanced chemical vapor deposition. The device shows high power efficiency and long lifetime. The power efficiency is enhanced up to ϳ0.1% by the presence of a silicon nitride control layer. The leakage current reduction induced by this nitride buffer effectively increases the power efficiency two orders of magnitude with regard to similarly processed devices with solely oxide. In addition, the nitride cools down the electrons that reach the polycrystalline silicon gate lowering the formation of defects, which significantly reduces the device degradation. © 2008 American Institute of Physics. ͓DOI: 10.1063/1.2939562͔The materials based on silicon nanocrystals ͑Si-ncs͒ are attractive for a wide variety of electronic and optoelectronic applications thanks to their tunable emission in the visible range and their compatibility with mainstream complementary metal oxide semiconductor ͑MOS͒ technology. [1][2][3][4][5][6] In the last years, an increasing number of articles dealing with electroluminescence ͑EL͒ from Si-nc embedded in silicon oxide ͑Si-nc/ SiO 2 ͒ devices has been published. Many of them report emission under direct current ͑dc͒ polarization, 7-9 which usually leads to low emission efficiency and fast degradation. Other authors report emission under alternate current ͑ac͒ polarization, 3,10,11 applying the concept of field-effect luminescence, where the recombination takes place after the sequential injection from the substrate of electrons and holes. The alternate injection can be adjusted to a suitable duty cycle which optimizes not only the current flow but also the polarization stress and the device lifetime. In spite of this, the leakage current is still very high and, also in this case, leads to low power efficiencies. 10 Therefore, the reduction of the leakage current appears to be a key issue for the achievement of an efficient device. In this challenge, the addition of a thin silicon nitride ͑Si 3 N 4 ͒ layer in a typical metal nitrideoxide semiconductor ͑MNOS͒ configuration is presented as a promising solution. [12][13][14] The MNOS stack reduces the effective field in the oxide layer, lowering the current flow that, in MOS configurations, is strongly field dependent ͓Fowler-Nordheim ͑FN͔͒. 15 The additional nitride barrier hinders the gate injection without significantly affecting the injection from the substrate, thus enhancing the power efficiency, as will be demonstrated later on. Thanks to the thinness of the Si 3 N 4 buffer and to its relatively high dielectric constant, the overall thickness increase does not have a remarkable impact on the gate voltage. The device lifetime improves as the nitride matrix cools down the carriers from the oxide, reducing the damage generated at the polycrystalline silicon ͑top contact͒ interface.In the present work, we demonstrate a twofold improvement through the addition of a thin Si 3 N 4 control layer within the MOS stack. First, we show ...

CdS thin films deposited from chemical bath containing citratocadmium(II) and thiourea are intrinsic and highly photosensitive. In the present letter, we discuss the conversion of such films to n type by thermal diffusion of indium from an evaporated 50 nm indium film deposited on the CdS thin film. The process which takes place in the temperature range of 250 °C–350 °C involves the formation of an In2O3 surface layer which acts as a barrier preventing the outdiffusion of indium. This allows indium to diffuse into the CdS film and results in an indium-doped CdS thin film. The electrical conductivity of such films is about 300 Ω−1 cm−1. All beneficial optical properties of chemically deposited CdS thin films for application as a window material in heterojunction optoelectronic devices are retained.

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