Articles de revista
http://hdl.handle.net/2117/2413
20190625T03:51:32Z

Transport mechanisms in silicon heterojunction solar cells with molybdenum oxide as a hole transport layer
http://hdl.handle.net/2117/133721
Transport mechanisms in silicon heterojunction solar cells with molybdenum oxide as a hole transport layer
García Hernansanz, Rodrigo; Garcia Hemme, E.; Montero, D.; Olea Ariza, Javier; Prado Millán, Álvaro del; Martil, Ignacio; Voz Sánchez, Cristóbal; Gerling Sarabia, Luis Guillermo; Puigdollers i González, Joaquim; Alcubilla González, Ramón
Heterojunction solar cells based on molybdenum suboxide (MoOx) deposited on ntype crystalline silicon have been fabricated. The hole selective character of MoOx is explained by its high workfunction, which causes a strong band bending in the Si substrate. This bending pushes the surface into inversion. In addition, the substoichiometry of the evaporated MoOx layers leads to a high density of states within the bandgap. This is crucial for charge transport. The JV electrical characteristics at several temperatures were analysed to elucidate the dominant charge transport mechanisms of this heterojunction structure. We have identified two different transport mechanisms. At low bias voltage, transport is dominated by hole tunnelling through the MoOx gap states. At higher voltage the behaviour is similar to a Schottky junction with a high barrier value, due to the high MoOx work function. These results provide a better understanding of the hole selective character of MoOx/ntype silicon heterocontacts, which is key to further improve this new kind of solar cells.
© <2018>. This manuscript version is made available under the CCBYNCND 4.0 license http://creativecommons.org/licenses/byncnd/4.0/
20190530T12:41:05Z
García Hernansanz, Rodrigo
Garcia Hemme, E.
Montero, D.
Olea Ariza, Javier
Prado Millán, Álvaro del
Martil, Ignacio
Voz Sánchez, Cristóbal
Gerling Sarabia, Luis Guillermo
Puigdollers i González, Joaquim
Alcubilla González, Ramón
Heterojunction solar cells based on molybdenum suboxide (MoOx) deposited on ntype crystalline silicon have been fabricated. The hole selective character of MoOx is explained by its high workfunction, which causes a strong band bending in the Si substrate. This bending pushes the surface into inversion. In addition, the substoichiometry of the evaporated MoOx layers leads to a high density of states within the bandgap. This is crucial for charge transport. The JV electrical characteristics at several temperatures were analysed to elucidate the dominant charge transport mechanisms of this heterojunction structure. We have identified two different transport mechanisms. At low bias voltage, transport is dominated by hole tunnelling through the MoOx gap states. At higher voltage the behaviour is similar to a Schottky junction with a high barrier value, due to the high MoOx work function. These results provide a better understanding of the hole selective character of MoOx/ntype silicon heterocontacts, which is key to further improve this new kind of solar cells.

3D simulations of interdigitated backcontacted crystalline silicon solar cells on thin substrates
http://hdl.handle.net/2117/132892
3D simulations of interdigitated backcontacted crystalline silicon solar cells on thin substrates
Jin, Chen; Martín García, Isidro; Ortega Villasclaras, Pablo Rafael; Calle Martín, Eric; Alcubilla González, Ramón
Interdigitated back contact technology is a promising candidate to be applied to thin crystalline silicon solar cells because of its simpler oneside interconnection while allowing a more flexible front surface treatment. This work explores the efficiency potential of IBC cSi solar cells applied to thin cSi substrates through 3D device simulations. In particular, we explore the impact of substrate thickness and front surface recombination velocity on cell performance with special attention to the different behavior in carrier collection of two different rearsurface doping structures. Firstly, the model is validated by comparing simulation results to a fabricated device on 280¿µmthick substrates with stripelike p+ and n+ diffusions. It is revealed that efficiencies of 16–17% are reachable for substrates on the 10–15¿µm range without changing the technology developed for thick ones. Next, the rear doping structure is modified leading to doped regions just under the metal contacts. This type of structure is expected in solar cells where hightemperature diffusions are replaced by pointlike laser doped contacts, which is a feasible alternative to be applied to thin substrates. Simulation results show that diffusion length requirements for those locallydoped structures are more demanding due to the reduction of emitter regions. As a result, very well passivated front and rear surfaces are required to maintain shortcircuit current densities to reasonable values. Finally, for both structures opencircuit voltage is kept almost constant with reduced thickness, despite the strong reduction in shortcircuit current. Simulations show a reduction of dark saturation current density with substrate thinning due to the redistribution of dark current densities that flow parallel to the device surface.
© <2018>. This manuscript version is made available under the CCBYNCND 4.0 license http://creativecommons.org/licenses/byncnd/4.0/
20190510T19:04:07Z
Jin, Chen
Martín García, Isidro
Ortega Villasclaras, Pablo Rafael
Calle Martín, Eric
Alcubilla González, Ramón
Interdigitated back contact technology is a promising candidate to be applied to thin crystalline silicon solar cells because of its simpler oneside interconnection while allowing a more flexible front surface treatment. This work explores the efficiency potential of IBC cSi solar cells applied to thin cSi substrates through 3D device simulations. In particular, we explore the impact of substrate thickness and front surface recombination velocity on cell performance with special attention to the different behavior in carrier collection of two different rearsurface doping structures. Firstly, the model is validated by comparing simulation results to a fabricated device on 280¿µmthick substrates with stripelike p+ and n+ diffusions. It is revealed that efficiencies of 16–17% are reachable for substrates on the 10–15¿µm range without changing the technology developed for thick ones. Next, the rear doping structure is modified leading to doped regions just under the metal contacts. This type of structure is expected in solar cells where hightemperature diffusions are replaced by pointlike laser doped contacts, which is a feasible alternative to be applied to thin substrates. Simulation results show that diffusion length requirements for those locallydoped structures are more demanding due to the reduction of emitter regions. As a result, very well passivated front and rear surfaces are required to maintain shortcircuit current densities to reasonable values. Finally, for both structures opencircuit voltage is kept almost constant with reduced thickness, despite the strong reduction in shortcircuit current. Simulations show a reduction of dark saturation current density with substrate thinning due to the redistribution of dark current densities that flow parallel to the device surface.

Bipolar transistor vertical vertical scaling framework
http://hdl.handle.net/2117/131231
Bipolar transistor vertical vertical scaling framework
Castañer Muñoz, Luis María; Alcubilla González, Ramón; Benavent, A
Scaling factors for current and transit time are derived for polysilicon emitter, silicon based heterojunction bipolar transistors. It is shown that a simple set of analytical equations in integral form can be used to analyse the above scaling properties and by introducing two “heterojunction factors” can be extended to the scaling analysis of heterojunction bipolar transistors.
20190403T16:44:26Z
Castañer Muñoz, Luis María
Alcubilla González, Ramón
Benavent, A
Scaling factors for current and transit time are derived for polysilicon emitter, silicon based heterojunction bipolar transistors. It is shown that a simple set of analytical equations in integral form can be used to analyse the above scaling properties and by introducing two “heterojunction factors” can be extended to the scaling analysis of heterojunction bipolar transistors.

Analysis of the conductance transient in thick film tin oxide gas sensors
http://hdl.handle.net/2117/131230
Analysis of the conductance transient in thick film tin oxide gas sensors
Vilanova, X; Llobet Valero, Eduard; Alcubilla González, Ramón; Sueiras, Jl; Correig, X
In this paper, we analyse the conductance transient of a Taguchi TGS822 sensor under a step change in the vapour concentration. A diffusionlimited range in the conductance transient is observed. Adjustments between the theoretical calculations based on a nonlinear diffusionreaction model and the experimental results alloy a constant, t', to be estimated, which is independent of the final conductance value and depends, among other parameters, on the effective diffusion coefficients of vapours in the porous tin oxide sensor. From transient measurements of organic solvents (benzene and oxylene) we have obtained t' values that are independent of concentration and characteristic for each vapour. This new parameter can give useful information for gas/vapour recognition.
20190403T16:27:48Z
Vilanova, X
Llobet Valero, Eduard
Alcubilla González, Ramón
Sueiras, Jl
Correig, X
In this paper, we analyse the conductance transient of a Taguchi TGS822 sensor under a step change in the vapour concentration. A diffusionlimited range in the conductance transient is observed. Adjustments between the theoretical calculations based on a nonlinear diffusionreaction model and the experimental results alloy a constant, t', to be estimated, which is independent of the final conductance value and depends, among other parameters, on the effective diffusion coefficients of vapours in the porous tin oxide sensor. From transient measurements of organic solvents (benzene and oxylene) we have obtained t' values that are independent of concentration and characteristic for each vapour. This new parameter can give useful information for gas/vapour recognition.

Space charge recombination in pn junctions with a discrete and continous trap distribution
http://hdl.handle.net/2117/130962
Space charge recombination in pn junctions with a discrete and continous trap distribution
Pallarès Marzal, Josep; Marsal Garví, Lluís Francesc; Correig, Xavier; Calderer Cardona, Josep; Alcubilla González, Ramón
Space charge ShockleyReadHall recombination currents in the presence of discrete or continuous distributions of recombination centres are analysed. For a single level trap, depending on its position inside the forbidden band, asymptotic values both for the ideality factor of the currentvoltage characteristic and for the activation energy of the saturation current are obtained. The analysis is extended to continuous trap distributions and the currentvoltage characteristics obtained are explained in terms of the simple theory developed for single level traps.
20190327T17:57:45Z
Pallarès Marzal, Josep
Marsal Garví, Lluís Francesc
Correig, Xavier
Calderer Cardona, Josep
Alcubilla González, Ramón
Space charge ShockleyReadHall recombination currents in the presence of discrete or continuous distributions of recombination centres are analysed. For a single level trap, depending on its position inside the forbidden band, asymptotic values both for the ideality factor of the currentvoltage characteristic and for the activation energy of the saturation current are obtained. The analysis is extended to continuous trap distributions and the currentvoltage characteristics obtained are explained in terms of the simple theory developed for single level traps.

Analytical modelling of bjt neurtral base region under variable injection conditions
http://hdl.handle.net/2117/130753
Analytical modelling of bjt neurtral base region under variable injection conditions
Bardés Llorensí, Daniel; Alcubilla González, Ramón
We present a set of closed form analytical solutions of the transport equation in the base of bipolar transistors. The presented 1D solutions hold for variable injection conditions, arbitrary doping profiles and arbitrary intrinsic carrier concentrations along the base, allowing to consider bandgap narrowing effects and a variable composition base (e.g. Si1xGex graded base). The above solutions lay on the commonly used assumption of zero majority carrier current in the neutral zone, and are valid up to the onset of the Kirk effect. Two solutions are analysed; the zeroorder solution, found as a correction of the low injection case, and the first order solution, derived as a correction of the zeroorder case. The perturbative procedure can naturally be iterated leading to an exact solution, which is used to assess the accuracy of the proposed analytical solutions. The firstorder solution shows the best tradeoff between accuracy and complexity.
20190321T19:05:33Z
Bardés Llorensí, Daniel
Alcubilla González, Ramón
We present a set of closed form analytical solutions of the transport equation in the base of bipolar transistors. The presented 1D solutions hold for variable injection conditions, arbitrary doping profiles and arbitrary intrinsic carrier concentrations along the base, allowing to consider bandgap narrowing effects and a variable composition base (e.g. Si1xGex graded base). The above solutions lay on the commonly used assumption of zero majority carrier current in the neutral zone, and are valid up to the onset of the Kirk effect. Two solutions are analysed; the zeroorder solution, found as a correction of the low injection case, and the first order solution, derived as a correction of the zeroorder case. The perturbative procedure can naturally be iterated leading to an exact solution, which is used to assess the accuracy of the proposed analytical solutions. The firstorder solution shows the best tradeoff between accuracy and complexity.

Electrical properties of PECVD amorphous siliconcarbon alloys from amorphouscrystalline heterojunctions
http://hdl.handle.net/2117/130752
Electrical properties of PECVD amorphous siliconcarbon alloys from amorphouscrystalline heterojunctions
Marsal Amenós, Félix; Pallarés Viña, Miguel Juan; Correig Blanchar, Francesc Xavier; Domínguez Pumar, Manuel; Bardés Llorensí, Daniel; Calderer Cardona, Josep; Alcubilla González, Ramón
Heterojunction diodes fabricated by plasma enhanced chemical vapour deposition of ntype amorphous silicon carbide on ptype crystalline silicon are analysed by measuring their currentvoltage characteristics. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage, the current is due to recombination in the amorphous side of the space charge region, while at higher voltages, the current becomes space charge limited. At reverse bias, the current can be explained by tunnelling models. The space charge limited currents in these heterojunctions have been used to determine the density of states in the ntype aSi1  xCx:H gap. The results show the increase in localized states when approaching the conduction band edge.
20190321T18:59:42Z
Marsal Amenós, Félix
Pallarés Viña, Miguel Juan
Correig Blanchar, Francesc Xavier
Domínguez Pumar, Manuel
Bardés Llorensí, Daniel
Calderer Cardona, Josep
Alcubilla González, Ramón
Heterojunction diodes fabricated by plasma enhanced chemical vapour deposition of ntype amorphous silicon carbide on ptype crystalline silicon are analysed by measuring their currentvoltage characteristics. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage, the current is due to recombination in the amorphous side of the space charge region, while at higher voltages, the current becomes space charge limited. At reverse bias, the current can be explained by tunnelling models. The space charge limited currents in these heterojunctions have been used to determine the density of states in the ntype aSi1  xCx:H gap. The results show the increase in localized states when approaching the conduction band edge.

Distribution of recombination currents in the space charge of heterostructure bipolar devices
http://hdl.handle.net/2117/130751
Distribution of recombination currents in the space charge of heterostructure bipolar devices
Pallares, J; Marsal, L F; Correig, X; Calderer Cardona, Josep; Alcubilla González, Ramón
This paper addresses the problem of the space charge region ShockleyReadHall (SRH) recombination currents in heterojunctions with one noncrystalline side. A formulation which generalizes previous works is discussed. The approach is based on the driftdiffusion model with a thermionicfield emission boundary condition. The main physical parameters which determine the relative contribution of each zone of the space charge region (SCR) to the total recombination current are identified. The general analysis is applied for the first time to amorphous/crystalline heterojunctions and design criteria are established to minimize the total recombination current.
20190321T18:54:34Z
Pallares, J
Marsal, L F
Correig, X
Calderer Cardona, Josep
Alcubilla González, Ramón
This paper addresses the problem of the space charge region ShockleyReadHall (SRH) recombination currents in heterojunctions with one noncrystalline side. A formulation which generalizes previous works is discussed. The approach is based on the driftdiffusion model with a thermionicfield emission boundary condition. The main physical parameters which determine the relative contribution of each zone of the space charge region (SCR) to the total recombination current are identified. The general analysis is applied for the first time to amorphous/crystalline heterojunctions and design criteria are established to minimize the total recombination current.

Analysis of conduction mechanisms in annealed nSi1xCx:H/pcrystalline Si heterojunction diodes for different doping concentrations
http://hdl.handle.net/2117/130750
Analysis of conduction mechanisms in annealed nSi1xCx:H/pcrystalline Si heterojunction diodes for different doping concentrations
Marsal, L F; Pallares, J; Correig, X; Orpella García, Alberto; Bardés Llorensí, Daniel; Alcubilla González, Ramón
We fabricated and characterized annealed ntype amorphous Si1xCx on ptype crystalline silicon heterojunction diodes with three different base doping concentrations: NA~1016,¿1018, and 1020¿cm3. The conduction mechanisms were determined by analyzing the temperature dependence of the current–voltage characteristics. The results show that the diodes with low doping concentrations (1016¿cm3) are ideal, because the phosphorous slightly diffuses into the crystalline silicon, whereas diodes with higher doping concentrations (1018–1020¿cm3) are dominated by multitunneling capture emission. The increase in the base acceptor doping concentration also causes excess current over the ideal diode current at low forward bias and an increase in the leakage reverse current.
20190321T18:42:17Z
Marsal, L F
Pallares, J
Correig, X
Orpella García, Alberto
Bardés Llorensí, Daniel
Alcubilla González, Ramón
We fabricated and characterized annealed ntype amorphous Si1xCx on ptype crystalline silicon heterojunction diodes with three different base doping concentrations: NA~1016,¿1018, and 1020¿cm3. The conduction mechanisms were determined by analyzing the temperature dependence of the current–voltage characteristics. The results show that the diodes with low doping concentrations (1016¿cm3) are ideal, because the phosphorous slightly diffuses into the crystalline silicon, whereas diodes with higher doping concentrations (1018–1020¿cm3) are dominated by multitunneling capture emission. The increase in the base acceptor doping concentration also causes excess current over the ideal diode current at low forward bias and an increase in the leakage reverse current.

Insitu doped amorphous Si0.8C0.2 emitter bipolar transistors
http://hdl.handle.net/2117/130749
Insitu doped amorphous Si0.8C0.2 emitter bipolar transistors
Orpella García, Alberto; Bardés Llorensí, Daniel; Alcubilla González, Ramón; Marsal, L F; Pallarès Marzal, Josep
The fabrication and characterization of in situdoped amorphous Si/sub 0.8/C/sub 0.2/ emitter transistors are presented. Emitter Gummel numbers exceeding 10/sup 14/ s/cm/sup 4/ are reported for the first time in this type of structure. The high values obtained for G/sub E/ are believed to be due to the valance band discontinuity between the Si/sub 0.8/C/sub 0.2/ layer and the crystalline part of the emitter, which effectively blocks the minority carrier injection from the base into the noncrystalline part of the emitter.
20190321T18:37:58Z
Orpella García, Alberto
Bardés Llorensí, Daniel
Alcubilla González, Ramón
Marsal, L F
Pallarès Marzal, Josep
The fabrication and characterization of in situdoped amorphous Si/sub 0.8/C/sub 0.2/ emitter transistors are presented. Emitter Gummel numbers exceeding 10/sup 14/ s/cm/sup 4/ are reported for the first time in this type of structure. The high values obtained for G/sub E/ are believed to be due to the valance band discontinuity between the Si/sub 0.8/C/sub 0.2/ layer and the crystalline part of the emitter, which effectively blocks the minority carrier injection from the base into the noncrystalline part of the emitter.