Helmut Föll - Academia.edu (original) (raw)

Papers by Helmut Föll

ECS Meeting Abstracts, 2011

not Available.

Solar cells with an inhomogeneous distribution of high Rser are not well described by the standar... more Solar cells with an inhomogeneous distribution of high Rser are not well described by the standard I-V curve model. On such solar cells process optimization for improving the front surface passivation can not be monitored by I-V curve analysis. Therefore in this paper local CELLO maps are used instead of integral I-V curve data to benchmark different cleaning procedures. The CELLO technique allows the determination of solar cell parameters (τlife, Rser, Rshunt) locally and non-destructively by analyzing the current (dI) or voltage (dU) response of a globally illuminated solar cell (0.3 suns) to a local perturbation induced with a LASER beam. CELLO Rser maps are used to identify loss areas due to a high Rser and to dismiss cells where losses are dominated by Rser. CELLO maps taken at the maximum power point (mpp) are used for a qualitative (and quantitative) analysis of (local and global) efficiency losses. Further defects like surface damages, scratches or inhomogeneous SiN areas ar...

Physica Status Solidi C Current Topics in Solid State Physics, 2009

Physica Status Solidi C Current Topics in Solid State Physics, 2009

physica status solidi (a), 2000

Porous silicon layers etched through openings in an inert masking layer have been employed to pro... more Porous silicon layers etched through openings in an inert masking layer have been employed to produce microstructures in silicon. In order to overcome the isotropic nature of the porous silicon formation process around the mask edges, optimized organic electrolytes for etching macropores on p-type silicon were employed. New kinds of pores (dubbed ªtrenchesº) were found, which are sensitive to mechanical stress and may prove useful for microstructuring silicon. Systematic experiments are presented which investigate the stability, the crystal orientation dependence, and limitations of trench formation. A possible mechanism for the trench formation is discussed in terms of the ªcurrent burstº model.

physica status solidi (a), 2000

Silicon electrochemistry has many applications, but still a number of unanswered questions. This ... more Silicon electrochemistry has many applications, but still a number of unanswered questions. This paper reports on experimental results of current transient measurements and impedance spectroscopy along the I±U curve in the Si±HF system. The points of inflection of the I±U characteristics are found to be interesting, signaling the onset of new mechanisms supporting or suppressing current flow which are mostly coupled to oxide formation and/or dissolution. The results are interpreted in terms of interactions of current bursts in time and in space. Following this interpretation, in-situ monitoring of pore nucleation and growth with FFT impedance spectroscopy, allowed to identify several phases of macropore formation and optimal growth conditions. In-situ monitoring of macropore growth may therefore be used to control nucleation and growth of macropores.

Applied Physics B, 2004

We report on a generalized approach for the calculation of optical properties of various porous s... more We report on a generalized approach for the calculation of optical properties of various porous semiconductors. The presented methodology provides a simple method for predicting the type and value of optical anisotropy in different materials. Specifically, the cases of electrochemically etched mesoporous Si on (110)-oriented substrate and electrochemicallyetched porous InP and GaAs materials on (100) substrates are considered. The optical anisotropy of mesoporous Si is explained and the dependence of the optical birefringence of this material on various material parameters is obtained. The optical anisotropy of porous InP and GaAs with crystallographic pores is predicted based on the presented model.

Journal of Electrochemical Society, 2014

ABSTRACT Electrochemical deposition of Cu on structured silicon including groves and pores is cri... more ABSTRACT Electrochemical deposition of Cu on structured silicon including groves and pores is critical for several applications such as microelectronics, sensors, and energy applications. In the case of Cu filling of porous Si, the silicon skeleton can be either etched to produce free nano-or micro-structured Cu or can be left to form a nano-or micro-composite of Si/Cu. Deposition of metals into n-type porous Si is a relatively straight-forward process, due to the availability of electrons at the conduction band to reduce Cu cations. Cu deposition into p-type porous Si requires illumination, unfortunately, it enhances the growth on pore walls and results in either non-conformal growth or plug-in which lead to voids. In this work, it is shown that illuminating the back side of the wafer combined with insulating the pore walls and pore top leads to conformal growth of Cu from the pore-tip to the pore-top. Two approaches have been tested: wall thinning by chemical etching and SiO2 coating on the pore top. Massive wires have been obtained by completely and conformally filling porous Si without leaving gaps in the case of SiO2-coated samples. The conformal filling of p-type Si was obtained without using additives and without seed layer. (c) 2014 The Electrochemical Society. All rights reserved.

Philosophical Magazine A, 1979

The intrinsic and extrinsic stacking fault energies of silicon have been determined from images o... more The intrinsic and extrinsic stacking fault energies of silicon have been determined from images of double ribbons obtained using the weak–beam method of electron microscopy. The ribbons occurred in distorted regions of small–angle twist boundaries on {111} planes prepared by welding. The results are compared with values obtained from isolated dislocations in the screw and edge orientation in the same sample, which were found to be consistently lower than the values obtained from double ribbons. It is found that, contrary to other recent work, the ratio γMin γMex is actually only ∼ 14% greater than unity.

Philosophical Magazine A, 1982

... 1976, Pretorius, Ramiller, Lau and Nicolet 1977, Canali, Catellani, Ottaviani and Prudenziati... more ... 1976, Pretorius, Ramiller, Lau and Nicolet 1977, Canali, Catellani, Ottaviani and Prudenziati 1978, Ishiwara, Nagatomo and Furukawa 1978, Pretorius, Ramiller and ... of this pseudo-hexagonal system is quite similar to that of epitaxial PtSi on (111) Xi (sinha, Marcus, Sheng and ...

Physica Status Solidi, 2011

ECS Meeting Abstracts, 2011

not Available.

Solar cells with an inhomogeneous distribution of high Rser are not well described by the standar... more Solar cells with an inhomogeneous distribution of high Rser are not well described by the standard I-V curve model. On such solar cells process optimization for improving the front surface passivation can not be monitored by I-V curve analysis. Therefore in this paper local CELLO maps are used instead of integral I-V curve data to benchmark different cleaning procedures. The CELLO technique allows the determination of solar cell parameters (τlife, Rser, Rshunt) locally and non-destructively by analyzing the current (dI) or voltage (dU) response of a globally illuminated solar cell (0.3 suns) to a local perturbation induced with a LASER beam. CELLO Rser maps are used to identify loss areas due to a high Rser and to dismiss cells where losses are dominated by Rser. CELLO maps taken at the maximum power point (mpp) are used for a qualitative (and quantitative) analysis of (local and global) efficiency losses. Further defects like surface damages, scratches or inhomogeneous SiN areas ar...

Physica Status Solidi C Current Topics in Solid State Physics, 2009

Physica Status Solidi C Current Topics in Solid State Physics, 2009

physica status solidi (a), 2000

Porous silicon layers etched through openings in an inert masking layer have been employed to pro... more Porous silicon layers etched through openings in an inert masking layer have been employed to produce microstructures in silicon. In order to overcome the isotropic nature of the porous silicon formation process around the mask edges, optimized organic electrolytes for etching macropores on p-type silicon were employed. New kinds of pores (dubbed ªtrenchesº) were found, which are sensitive to mechanical stress and may prove useful for microstructuring silicon. Systematic experiments are presented which investigate the stability, the crystal orientation dependence, and limitations of trench formation. A possible mechanism for the trench formation is discussed in terms of the ªcurrent burstº model.

physica status solidi (a), 2000

Silicon electrochemistry has many applications, but still a number of unanswered questions. This ... more Silicon electrochemistry has many applications, but still a number of unanswered questions. This paper reports on experimental results of current transient measurements and impedance spectroscopy along the I±U curve in the Si±HF system. The points of inflection of the I±U characteristics are found to be interesting, signaling the onset of new mechanisms supporting or suppressing current flow which are mostly coupled to oxide formation and/or dissolution. The results are interpreted in terms of interactions of current bursts in time and in space. Following this interpretation, in-situ monitoring of pore nucleation and growth with FFT impedance spectroscopy, allowed to identify several phases of macropore formation and optimal growth conditions. In-situ monitoring of macropore growth may therefore be used to control nucleation and growth of macropores.

Applied Physics B, 2004

We report on a generalized approach for the calculation of optical properties of various porous s... more We report on a generalized approach for the calculation of optical properties of various porous semiconductors. The presented methodology provides a simple method for predicting the type and value of optical anisotropy in different materials. Specifically, the cases of electrochemically etched mesoporous Si on (110)-oriented substrate and electrochemicallyetched porous InP and GaAs materials on (100) substrates are considered. The optical anisotropy of mesoporous Si is explained and the dependence of the optical birefringence of this material on various material parameters is obtained. The optical anisotropy of porous InP and GaAs with crystallographic pores is predicted based on the presented model.

Journal of Electrochemical Society, 2014

ABSTRACT Electrochemical deposition of Cu on structured silicon including groves and pores is cri... more ABSTRACT Electrochemical deposition of Cu on structured silicon including groves and pores is critical for several applications such as microelectronics, sensors, and energy applications. In the case of Cu filling of porous Si, the silicon skeleton can be either etched to produce free nano-or micro-structured Cu or can be left to form a nano-or micro-composite of Si/Cu. Deposition of metals into n-type porous Si is a relatively straight-forward process, due to the availability of electrons at the conduction band to reduce Cu cations. Cu deposition into p-type porous Si requires illumination, unfortunately, it enhances the growth on pore walls and results in either non-conformal growth or plug-in which lead to voids. In this work, it is shown that illuminating the back side of the wafer combined with insulating the pore walls and pore top leads to conformal growth of Cu from the pore-tip to the pore-top. Two approaches have been tested: wall thinning by chemical etching and SiO2 coating on the pore top. Massive wires have been obtained by completely and conformally filling porous Si without leaving gaps in the case of SiO2-coated samples. The conformal filling of p-type Si was obtained without using additives and without seed layer. (c) 2014 The Electrochemical Society. All rights reserved.

Philosophical Magazine A, 1979

The intrinsic and extrinsic stacking fault energies of silicon have been determined from images o... more The intrinsic and extrinsic stacking fault energies of silicon have been determined from images of double ribbons obtained using the weak–beam method of electron microscopy. The ribbons occurred in distorted regions of small–angle twist boundaries on {111} planes prepared by welding. The results are compared with values obtained from isolated dislocations in the screw and edge orientation in the same sample, which were found to be consistently lower than the values obtained from double ribbons. It is found that, contrary to other recent work, the ratio γMin γMex is actually only ∼ 14% greater than unity.

Philosophical Magazine A, 1982

... 1976, Pretorius, Ramiller, Lau and Nicolet 1977, Canali, Catellani, Ottaviani and Prudenziati... more ... 1976, Pretorius, Ramiller, Lau and Nicolet 1977, Canali, Catellani, Ottaviani and Prudenziati 1978, Ishiwara, Nagatomo and Furukawa 1978, Pretorius, Ramiller and ... of this pseudo-hexagonal system is quite similar to that of epitaxial PtSi on (111) Xi (sinha, Marcus, Sheng and ...

Physica Status Solidi, 2011