Free carrier absorption in silicon

Schroder, D. K.; Thomas, R.N.; Swartz, J. C.

doi:10.1109/t-ed.1978.19066

Cited by 155 publications

(62 citation statements)

References 11 publications

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“…These structures represent solar cells in which the emitter and back-surface field (possible sources of free-carrier absorption) have been omitted, so that parasitic absorption at 1200 nm occurs only in the silver reflector (note that, with a doping density of 1.5310 15 cm 23 , the wafer itself has a free-carrier absorption coefficient of 2310 23 cm 21 at 1200 nm and absorbs only 0.01% of light per pass 24 ). The measured spectra are shown with symbols in Figure 6.…”

Section: Resultsmentioning

confidence: 99%

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

2013

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Imperfect internal reflectance of near-bandgap light reduces the performance of all solar cells, and becomes increasingly detrimental as absorbers become thinner. We consider light incident on the silicon/dielectric/metal structure at the back of rear-passivated crystalline silicon solar cells with surface textures that are large enough for geometric optics. By calculating the absorbance in the metal as a function of the angle of incidence, we discover three results that are important for understanding and improving rear reflectors in many types of solar cells. First, significant parasitic absorption occurs in the metal layer in two cases: s-and p-polarized propagating modes (near-normal angles of incidence) when the dielectric thickness is adjusted to cause destructive interference of the reflected beams, and p-polarized evanescent modes (angles of incidence above the semiconductor/dielectric critical angle) that excite surface plasmon polaritons at the metal surface. Second, the latter loss dominates; a well-designed rear dielectric passivation layer must suppress the penetration of evanescent waves to the metal. Third, when used as an input in a simple analytical model, the average rear internal reflectance calculated by assuming a Lambertian angular distribution of light accurately predicts the total reflectance and absorbance of a solar cell. INTRODUCTIONThe current trend towards higher silicon solar cell efficiencies has brought rear-passivated designs-including PERC (passivated emitter and rear cell), 1 interdigitated back contact 2 and heterojunction 3 structures-to the forefront of both research and production. While the impetus for rear passivation is a reduction in surface recombination and a corresponding gain in open-circuit voltage (V oc ), the dielectric passivation layer (or transparent conductive oxide layer in silicon heterojunction cells) can be made to simultaneously serve an optical role, thus increasing short-circuit current density (J sc ) too. Several authors have observed that even high-conductivity metals like silver are poor reflectors on textured silicon solar cells, and that a dielectric buffer layer increases the rear internal reflectance of infrared (IR) light. 1,[4][5][6] In thin-film silicon solar cells that employ nanoscale textures and metallic rear reflectors, transparent conductive oxide (TCO) rear buffer layers suppress localized surface plasmons that are excited in the metal by the rough surfaces. 7-10 For alkaline-textured monocrystalline wafers with micrometer-sized pyramids, however, a different loss mechanism must be responsible for parasitic absorption in the metal. In optical simulations of planar Si/SiO 2 /Al structures, Campbell observed diminished internal reflectance both above and below the Si/SiO 2 critical angle for thin SiO 2 layers, revealing that evanescent as well as propagating modes may be absorbed in the metal. 4,5 In a recent

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Section: Resultsmentioning

confidence: 99%

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

2013

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“…tion and effect of the doping on absorption profile. The optical transmissivity of doped silicon is a function of the sheet resistance and incident wavelengths [48]. Hence, the peak responsivity of the OPFET device can be controlled by adjustment of doping in the absorption layer.…”

Section: Resultsmentioning

confidence: 99%

Optically Controlled Silicon MESFET Fabrication and Characterizations for Optical Modulator/Demodulator

Chattopadhyay¹,

Overton²,

Vetter³

et al. 2010

JSTS:Journal of Semiconductor Technology and Science

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Abstract-An optically controlled silicon MESFET (OPFET) was fabricated by diffusion process to enhance the quantum efficiency, which is the most important optoelectronic device performance usually affected by ion implantation process due to large number of process induced defects. The desired impurity distribution profile and the junction depth were obtained solely with diffusion, and etching processes monitored by atomic force microscope, spreading resistance profiling and C-V measurements. With this approach fabrication induced defects are reduced, leading to significantly improved performance. The fabricated OPFET devices showed proper I-V characteristics with desired pinch-off voltage and threshold voltage for normally-on devices. The peak photoresponsivity was obtained at 620 nm wavelength and the extracted external quantum efficiency from the photoresponse plot was found to be approximately 87.9%. This result is evidence of enhancement of device quantum efficiency fabricated by the diffusion process. It also supports the fact that the diffusion process is an extremely suitable process for fabrication of high performance optoelectronic devices. The maximum gain of OPFET at optical modulated signal was obtained at the frequency of 1 MHz with rise time and fall time approximately of 480 nS. The extracted transconductance shows the possible potential of device speed performance improvements for shorter gate length. The results support the use of a diffusion process for fabrication of high performance optoelectronic devices.

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“…We used 1 Ω cm for the resistivity of the III-V and Si region, corresponding to doping concentration of around 10 16 cm −3 , and 1 × 10 −4 Ω cm 2 for the metal/semiconductor interfacial contact resistance, although their variation hardly affect the current density profile result as we tested. Note that for this doping concentration additive α i induced by free carrier absorption is on the order of 0.1 cm −1 at 1.55 μm [8,9], much smaller than α metal i calculated in Section 2.2, and therefore negligible. Fig.…”

Section: Lateral Current Confinementmentioning

confidence: 55%

Novel III-V/Si hybrid laser structures with current injection across conductive wafer-bonded heterointerfaces: A proposal and analysis

Tanabe

Iwamoto

Arakawa

2011

IEICE Electron. Express

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Abstract:We propose two novel III-V/Si hybrid laser structures with patterned window arrays in metal thin film wafer-bonding layers. The metal-mediated bonded III-V/Si heterointerface exhibits high electrical and thermal conductivity while allowing optical coupling between the III-V gain layer and the underneath Si waveguide through the openings in the metal bonding layer. We numerically examine the validity of the proposed hybrid laser structures through calculations of their modal propagation loss by metal's absorption and threshold current densities. We also propose another hybrid laser structure utilizing conductive direct semiconductor/semiconductor wafer bonding exploiting a spatial gain profile well overlapped with the waveguide mode and no metal-induced loss relative to those metal-mediated-bonded. All of these three structures have advantages such as spontaneous lateral current confinement and simpler fabrication over conventional oxidemediated-bonded hybrid lasers.

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Free carrier absorption in silicon

Cited by 155 publications

References 11 publications

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

Improving metal reflectors by suppressing surface plasmon polaritons: a priori calculation of the internal reflectance of a solar cell

Optically Controlled Silicon MESFET Fabrication and Characterizations for Optical Modulator/Demodulator

Novel III-V/Si hybrid laser structures with current injection across conductive wafer-bonded heterointerfaces: A proposal and analysis

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