Cathodoluminescence investigation of silicon nanowires fabricated by thermal evaporation of SiO

Silicon nanowire samples fabricated by thermal evaporation of SiO powder were investigated by Cathodoluminescence. Three main bands were found at low temperatures, namely, peak 1 at about 620–650 nm (2.0–1.91 eV), peak 2 at 920 nm (1.35 eV), and peak 3 at 1280 nm (0.97 eV). An additional broad band (peak 4) in the infrared region with its maximum at ∼1570 nm (0.79 eV) appears at room temperature. The origins of the emission bands are discussed. The text was submitted by the authors in English.     

Combined CL/EBIC/DLTS investigation of a regular dislocation network formed by Si wafer direct bonding

Electrical levels of the dislocation network in Si and recombination processes via these levels were studied by means of the combination of grain-boundary deep level transient spectroscopy, grain-boundary electron beam induced current (GB-EBIC) and cathodoluminescence (CL). It was found two deep level traps and one shallow trap existed at the interface of the bonded interface; these supply the recombination centers for carriers. The total recombination probability based on GB-EBIC data increased with the excitation level monotonically; however, the radiative recombination based on D1-D2 CL data exhibited a maximum at a certain excitation level. By applying an external bias across the bonded interface, the CL signal of D-lines was enhanced dramatically. These results are consistent with our models about two channels of recombination via the trap levels. The text was submitted by the authors in English.     

Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD

Epitaxial Ge layer growth of low threading dislocation density (TDD) and low surface roughness on Si (1 0 0) surface is investigated using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Thin seed Ge layer is deposited at 300 °C at first to form two-dimensional Ge surface followed by thick Ge growth at 550 °C. Root mean square of roughness (RMS) of ∼0.45 nm is achieved. As-deposited Ge layers show high TDD of e.g. ∼4 × 10⁸ cm⁻² for a 4.7 μm thick Ge layer thickness. The TDD is decreasing with increasing Ge thickness. By applying a postannealing process at 800 °C, the TDD is decreased by one order of magnitude. By introducing several cycle of annealing during the Ge growth interrupting the Ge deposition, TDD as low as ∼7 × 10⁵ cm⁻² is achieved for 4.7 μm Ge thick layer. Surface roughness of the Ge sample with the cyclic annealing process is in the same level as without annealing process (RMS of ∼0.44 nm). The Ge layers are tensile strained as a result of a higher thermal expansion coefficient of Ge compared to Si in the cooling process down to room temperature. Enhanced Si diffusion was observed for annealed Ge samples. Direct band-to-band luminescence of the Ge layer grown on Si is demonstrated.     

Photoluminescence study on defects in multicrystalline silicon

We report on spatially resolved luminescence measurements on ribbon-grown silicon samples. It is found that the band-edge luminescence shows anomalous temperature behavior, namely an increase in the radiation intensity with temperature. Phosphorous diffusion gettering is found to enhance this effect. The anomalous temperature behavior is attributed to nonradiative recombination governed by shallow traps. A shift in the phonon replica of the band edge luminescence peak has been observed and associated with tensile stress. The text was submitted by the authors in English.     

EBIC and luminescence studies of defects in solar cells

Electron beam-induced current (EBIC) can be used to detect electronic irregularities in solar cells, such as shunts and precipitates, and to perform physical characterization of defects by, e.g. measuring the temperature dependence of their recombination activity. Recently also luminescence methods such as electroluminescence (EL) and photoluminescence (PL) have been shown to provide useful information on crystal defects in solar cells. In this contribution it will be shown that the combined application of EBIC, EL and PL may deliver useful information on the presence and on the physical properties of crystal defects in silicon solar cells. Also pre-breakdown sites in multicrystalline cells can be investigated by reverse-bias EL and by microplasma-type EBIC, in comparison with lock-in thermography investigations.     

Infrared light emission from porous silicon

Very intense broad sub-bandgap infrared (IR) light emission around 1,550 nm was observed on porous silicon by photoluminescence (PL) measurements. The integrated intensity of the IR signal is two orders of magnitude higher than that of the band–band emission in Cz silicon. PL measurements with the sample immersed in different media, e.g., in HF and H₂O₂, confirmed that the broad IR band originates from the Si/SiO _x interface. Electroluminescence spectroscopy was carried out on a porous silicon p–n junction sample contacted with indium-tin oxide. The IR band was detected at room temperature at both forward and reverse bias. The results indicate that radiative recombination through interface states is very efficient at room temperature.     

Influence of Dislocation Loops on the Near-Infrared Light Emission From Silicon Diodes

The infrared light emission of forward-biased silicon diodes is studied. Through ion implantation and anneal, dislocation loops were created near the diode junction. These loops suppress the light emission at the band-to-band peak around 1.1 mum. The so-called D1 line at 1.5 mum is strongly enhanced by these dislocation loops. We report a full study of photoluminescence and electroluminescence of these diodes. The results lead to new insights for the manufacturing approach of practical infrared light sources in integrated circuits.     

Regular dislocation networks in silicon as a tool for nanostructure devices used in optics, biology, and electronics

Well-controlled fabrication of dislocation networks in Si using direct wafer bonding opens broad possibilities for nanotechnology applications. Concepts of dislocation-network-based light emitters, manipulators of biomolecules, gettering and insulating layers, and three-dimensional buried conductive channels are presented and discussed. A prototype of a Si-based light emitter working at a wavelength of about 1.5 microm with an efficiency potential estimated at 1% is demonstrated.