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Nanocrystalline-silicon superlattices are produced by controlled recrystallization of amorphous-Si/SiO2 multilayers. The recrystallization is performed by a two-step procedure: rapid thermal annealing at 600–1000 °C, and furnace annealing at 1050 °C. Transmission electron microscopy, Raman scattering, x-ray and electron diffraction, and photoluminescence spectroscopy show an ordered structure with Si nanocrystals confined between SiO2 layers. The size of the Si nanocrystals is limited by the thickness of the a-Si layer, the shape is nearly spherical, and the orientation is random. The luminescence from the nc-Si superlattices is demonstrated and studied.

Photoluminescence properties and crystallization of silicon quantum dots in hydrogenated amorphous Si-rich silicon carbide filmsAnnealing of amorphous Si/SiO 2 superlattices produces Si nanocrystals. The crystallization has been studied by transmission electron microscopy and x-ray analysis. For a Si layer thinner than 7 nm, nearly perfect nanocrystals are found. For thicker layers, growth faults and dislocations exist. Decreasing the a-Si layer thickness increases the inhomogeneous strain by one order of magnitude. The origin of the strain in the crystallized structure is discussed. The crystallization temperature increases rapidly with decreasing a-Si layer thickness. An empirical model that takes into account the Si layer thickness, the Si/SiO 2 interface range, and a material specific constant has been developed.

Modern society is experiencing an ever-increasing demand for energy to power a vast array of electrical and mechanical devices. As hydrocarbon resources dwindle, utilization of ample nuclear energy and abundant solar energy becomes more and more attractive. For 50 years, since the invention of the transistor, semiconductor devices that convert the energy of nuclear particles [1±5] or solar photons [6,7] to electric current have been investigated. However, conventional two-dimensional (2D) planar diode structures exhibit a number of inherent deficiencies that result in relatively low energy-conversion efficiencies. A unique three-dimensional (3D) porous silicon p±n diode has been developed to form the basis of a novel betavoltaic battery. Using tritium to demonstrate the proof-ofconcept, the 3D diode geometry demonstrated a tenfold enhancement of efficiency compared to that of the usual 2D betavoltaic device geometry. Given the similarity of the energyconversion physics for betavoltaic and photovoltaic devices, significant efficiency gains due to this 3D geometry might be expected for many types of photo detectors and solar cells. The 3D diode was constructed on porous silicon (PS), which consists of a network of pores formed by electrochemical anodization of silicon substrates. According to the pore size, PS is classified as microporous (£ 2 nm), mesoporous (2±50 nm), or macroporous (> 50 nm). Such porous morphologies define a very large internal surface area, [8,9] which retains most of the characteristics associated with planar surface geometries, particularly for macropores. [10,11] Numerous investigations have been done on the physical and chemical properties of this complex material. [8,9,12] Moreover, it has been demonstrated that PS components can be integrated into microelectronic circuits in order to construct practical devices. [13] To date, however, PS has only been used as an antireflection and surface-passivation layer [14,15] in photovoltaic devices. It is believed that this work reports the first construction of conformal p±n junctions in PS. PS diodes with a 3D p±n junction structure were created as illustrated schematically in Figure 1 (see Experimental for details). The continuous p±n junction can be visualized as a 2D ªsheetº that is deformed to produce a uniform p±n junction layer on every accessible surface of the pore space. The builtin voltage [16] of the diodes was estimated to be~0.8 V, assuming an n-dopant concentration of~5 10 18 cm ±3 and an abrupt p±n junction doping profile. The metallurgical junction was about 200 nm below the surface, and the estimated depletion width on the p-side of the junction was~1.4 lm. The efficacy of the pore anodization procedure was investigated by means of scanning electron microscopy (SEM

A complete process compatible with conventional Si technology has been developed in order to produce a bipolar light-emitting device. This device consists of a layer of light-emitting porous silicon annealed at high temperature (800–900 °C) sandwiched between a p-type Si wafer and a highly doped (n+) polycrystalline Si film. The properties of the electroluminescence (EL) strongly depend on the annealing conditions. Under direct bias, EL is detected at voltages of ∼2 V and current densities J∼1 mA/cm2. The maximum EL intensity is 1 mW/cm2 and the EL can be modulated by a square wave current pulse with frequencies ν≥1 MHz. No degradation has been observed during 1 month of pulsed operation.

This work presents a comprehensive investigation of carrier transport properties in light-emitting porous silicon (LEPSi) devices. Models that explain the electrical characteristics and the electroluminescence properties of the LEPSi devices are developed. In metal/LEPSi devices, the forward current density–voltage (J–V) behavior follows a power law relationship (J∼Vm), which indicates a space charge current attributed to the carriers drifting through the high resistivity LEPSi layer. In LEPSi pn junction devices, the forward J–V behavior follows an exponential relationship (J∼eeV/nkT), which indicates that the diffusion of carriers makes a major contribution to the total current. The temperature dependence of the J–V characteristics, the frequency dependence of the capacitance–voltage characteristics, and the frequency dependence of the electroluminescence intensity support the models. Analysis of devices fabricated with a LEPSi layer of 80% porosity results in a relative permittivity of ∼3.3, a carrier mobility of ∼10−4 cm2/V s, and a free carrier concentration of ∼1013 cm−3.

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Correlation between the microstructure and electroluminescence properties of Er-doped metal-oxide semiconductor structures Appl. Phys. Lett. 94, 101916 (2009); 10.1063/1.3098474 Room-temperature 1.54 μm photoluminescence from Er-doped Si-rich silica layers obtained by reactive magnetron sputtering J. Appl. Phys. 94, 3869 (2003); 10.1063/1.1604479 Room-temperature 1.54 μm electroluminescence from Er-doped silicon-rich silicon oxide films deposited on n + -Si substrates by magnetron sputtering J. Appl. Phys. 90, 5835 (2001); 10.1063/1.1413231Effect of hydrogenation on room-temperature 1.54 μm Er 3+ photoluminescent properties of erbium-doped silicon-rich silicon oxide