Deep Diffusion Doping of Macroporous Silicon (original) (raw)
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Silicon Doping Performed by Different Diffusion Sources Aiming Co-Diffusion
In this work several diffusion sources are investigated, aiming at simultaneous phosphorus and boron doping of silicon from different diffusion sources. This challenging process step is called co-diffusion. In the context of this work boron-and phosphorus-doped silicate glass (BSG and PSG) as solid diffusion sources and phosphorus oxychloride (POCl 3) as gaseous precursor for phosphorus diffusion are investigated. The combination of solid and gaseous diffusion sources leads to a high flexibility in adjusting sheet resistances on the one hand and to a simplification of process flows on the other. In this work the sheet resistance of p +-doped areas is varied in the range of R sh = 50-300 Ω/sq by varying composition and thickness of the solid diffusion sources. The deposition of these solid diffusion sources is carried out by plasma-enhanced chemical vapor deposition (PECVD) using two different process equipments. The excellent passivation capability of the highly p +-doped silicon surfaces has lead to dark saturation current densities J 0 = 29.6 fA/cm 2. In the case of silicon n +-doping with gaseous diffusion sources, the variation of sheet resistance is possible by adjusting the gaseous composition in the ambience during diffusion. The sheet resistance has been varied in the range of R sh = 50-500 Ω/sq. In the case of n +-doping the measured dark saturation current densities have been J 0 = 58.6 fA/cm 2 and thus show the high potential of these diffusions for implementation in process sequences of high efficiency silicon solar cells.
Transport mechanisms in porous silicon
Journal of Applied Physics, 1998
The current transport mechanism through porous silicon ͑PS͒ films fabricated from 8 to 12 ⍀ cm p-type silicon (p-Si) substrates has been investigated using current-voltage I(V) measurements on metal/PS/p-Si/metal devices in the temperature range of 77-300 K. The characteristics for all devices show a rectifying behavior with ideality factor very close to unity. A value of 0.7 eV is obtained for the barrier height at the interface between PS and bulk p-Si at room temperature and the barrier height is found to increase with rising temperature. A band model is proposed in order to explain the observed characteristics.
In this work plasma-enhanced chemical-vapor deposition (PECVD) technology was used to deposit boron-doped silicate glasses (BSG) and phosphorus-doped silicate glasses (PSG) as solid diffusion sources with the goal of implementing locally doped p+- and n+-areas into monocrystalline silicon. For this purpose, several process sequences were carried out to pattern these layers before the diffusion step in a tube furnace using a wet chemical etch process in combination with an inkjet printed etch resist. The evaluated technology leads to a locally doped area on the wafer surface with a minimum feature size of approximately 100 μm. Boron-doped p+-areas in silicon with a sheet resistance of less than 25 Ω/sq (boron surface concentration NA>1019 cm-3) were achieved from BSG and phosphorus-doped n+-areas with a sheet resistance of less than 10 Ω/sq (phosphorus surface concentration ND>1020 cm-3) from PSG. An excellent electrical contacting behavior of physical vapor deposited aluminum ...
Applied Physics Research, 2015
In this work, we try to make a p-type monocristalline silicon pn junction using an easier doping method. We combined spin-coating thin film deposition method and solid doping technique. This technique can be considered as variety of the SOD method. In this study, phosphorous-based gel compounds was prepared and deposited by spin coating. Heat treatment would thus, after deposition of thin layer, diffuse phosphorus atoms into the substrate to obtain a pn diode. Study by Secondary Ions Mass Spectrometry (SIMS) showed a surface phosphorus concentration of 10 20 at/cm 3 incorporated within the silicon substrate to a depth of 300 nm. The microwave phase-shift (µW-PS) technique is used to determine the bulk lifetime (τ b) of minority carriers. In this technique, the phase-shift between a microwave beam (10 GHz) and a sine-modulated infrared excitation is related to τ b and to the surface recombination velocity (S) (Palais, Clerc, Arcari, Stemmer & Martinuzzi, 2003). The lifetime τ b mean values vary from 7 µs for a p-type Silicon to 97 µs for phosphorus-diffused silicon. The surface recombination velocity S varies from around 500 to 1000 cm.s-1 .
Gettering impurities from crystalline silicon by phosphorus diffusion using a porous silicon layer
The possible benefits of phosphorus-based gettering applied to crystalline silicon wafers have been evaluated. The gettering process is achieved by forming porous silicon (PS) layers on both sides of the Si wafers. The PS layers were formed by the stain-etching technique, and phosphorus diffusion using liquid POCl 3-based source was done on both sides of the Si wafer. The realized phosphorus/PS/Si/PS/phosphorus structure undergoes a heat treatment in an infrared furnace under an O 2 /N 2 controlled atmosphere. This heat treatment allows phosphorus to diffuse throughout the PS layer and to getter eventual metal impurities towards the phosphorus doped PS layer. The gettering effect was evaluated using four probe points, Hall effect measurements and the light beam induced current (LBIC) technique. These techniques enable to measure the density and the mobility of the majority carrier and the minority carrier diffusion length (L d) of the Si substrate. We noticed that the best gettering is achieved at 900 1C for 90 min of heat treatment. After gettering impurities, we found an apparent enhancement of the mobility and the minority carrier diffusion length as compared to the reference substrate.
An investigation on the effect of porosity on the transport properties of porous silicon
International Journal of Microstructure and Materials Properties, 2013
Microelectronics technology today is dominated exclusively by Silicon (Si). The inefficiency of Si to emit light even at cryogenic temperatures has been overcome with the discovery of porous silicon (PS) and its visible luminescence at room temperature. The present investigation aims at analysing the effect of increasing porosity on the transport properties of porous silicon with reference to field and temperature-dependent dark and photo conductivity and further substantiating the results with modulation techniques. Pure Silicon wafer of n-type was made porous by immersion in an appropriate etchant for a few minutes. The conductivity was found to increase as porosity increased and this effect could be attributed to the increase in the trap levels, with increasing porosity. Temperature-dependent studies reveal a decrease in activation energy with increase in porosity indicating an increase in conductivity. Reflectance and electroreflectance measurements were used to calculate the band gap of porous silicon. It was found to lie closer to the direct band gap of silicon. A reduction in the band gap of porous silicon has been observed.
Porous Silicon Science and Technology
1995
A. Naudon, H. Muender and C. Ortega). A good overview on theoretical models has been particularly appreciated during the 4 hour course given by M. Hybertsen, R. Tsu and M. Lannoo. More prospectively, the aspects related to optoelectronic devices based on porous silicon were presented by W. Lang, A. Bsiesy and N. Koshida. The optical properties of porous silicon were indeed not forgotten (P. Calcott, J.C. Vial and F. Koch) but they were presented along with what was well known and well established in other systems (R. Ferreira for II-VI and III-V nanostructures, E. Bustarret for the amorphous silicon). In addition we had reserved one hour a day for the evening seminars where hot topics were discussed (P. Fauchet, P.A. Badoz, H. Muender, etC. Levy-Clement). The school was introduced by a general review on porous silicon given by L.T. Canham.