Ion-implanted Emitter Research Articles

Perimeter and Area Components in the ${I}$ – ${V}$ Curves of 4H-SiC Vertical p+-i-n Diode With Al+ Ion-Implanted Emitters

This paper describes the separation between the area and the perimeter current density components of 4H-SiC vertical p+-i-n diode with a circular Al+ implanted emitter of different diameters in the range 150– $1000~\mu \text{m}$ and for temperatures of measurement in the range 30–290 °C. It is shown that before the diode series resistances become dominant, the forward current is given by the sum of an area plus a perimeter component, both of exponential trend with ideality factor 2; while toward high voltages, an area component with exponential trend and ideality factor 1 adds to the previous components. Moreover, this paper shows that forward area and perimeter current density components can be used for a straightforward identification of the parameters controlling the current transport, provided that they can be fit by the p-n junction equations in the frame of the abrupt junction approximation. Finally, this paper shows that the area reverse current density can be used for the identification of the electrically active defects in the drift layer.

Electrical and Structural Analysis of Crystal Defects After High-Temperature Rapid Thermal Annealing of Highly Boron Ion-Implanted Emitters

Ion implantation of boron is a promising technique for the preparation of p-type emitters in n-type cells. We use rapid thermal annealing with temperatures up to 1250 °C and annealing durations between 6 s and 20 min to anneal the implant-induced crystal defects. Experimental <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>$J_{0e}$</tex-math> </inline-formula> is compared with simulated and measured defect densities. Perfect dislocation loops are identified to be the dominating defect species after rapid thermal annealing (RTA) above 1000 °C. Even for emitters with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>$J_{0e}$</tex-math></inline-formula> values around 40 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , defects are present within the valleys of the textured surfaces after annealing. On textured Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -passivated boron emitters, we measure <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math>$J_{0e}$</tex-math></inline-formula> of 38 fA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> for a sheet resistance around 80 Ω/□ after very short annealing processes (1 min at 1200 °C).

A numerical simulation study of gallium-phosphide/silicon heterojunction passivated emitter and rear solar cells

The performance of passivated emitter and rear (PERC) solar cells made of p-type Si wafers is often limited by recombination in the phosphorus-doped emitter. To overcome this limitation, a realistic PERC solar cell is simulated, whereby the conventional phosphorus-doped emitter is replaced by a thin, crystalline gallium phosphide (GaP) layer. The resulting GaP/Si PERC cell is compared to Si PERC cells, which have (i) a standard POCl3 diffused emitter, (ii) a solid-state diffused emitter, or (iii) a high efficiency ion-implanted emitter. The maximum efficiencies for these realistic PERC cells are between 20.5% and 21.2% for the phosphorus-doped emitters (i)–(iii), and up to 21.6% for the GaP emitter. The major advantage of this GaP hetero-emitter is a significantly reduced recombination loss, resulting in a higher Voc. This is so because the high valence band offset between GaP and Si acts as a nearly ideal minority carrier blocker. This effect is comparable to amorphous Si. However, the GaP layer can be contacted with metal fingers like crystalline Si, so no conductive oxide is necessary. Compared to the conventional PERC structure, the GaP/Si PERC cell requires a lower Si base doping density, which reduces the impact of the boron-oxygen complexes. Despite the lower base doping, fewer rear local contacts are necessary. This is so because the GaP emitter shows reduced recombination, leading to a higher minority electron density in the base and, in turn, to a higher base conductivity.

Ion-implanted PERC Solar Cells with Al2O3/SiNx Rear Passivation

Ion implantation is an attractive candidate for PERC solar cells due to the single-sided emitter phosphorus doping. The oxide, which is formed during the implant anneal, can be used as rear passivation of PERC cells. However, the SiO2/SiNx rear passivation is very sensitive to the rear surface roughness and surface preparation. Hence, in this paper we evaluate Al2O3/SiNx rear passivation layers in combination with an oxide passivated ion-implanted emitter. We obtain emitter saturation current densities of 93 fA/cm2, which is significantly lower compared to a typical POCl3 diffused emitter with 140 fA/cm2. Ion-implanted PERC cells with Al2O3/SiNx rear passivation show conversion efficiencies up to 20.0% which is comparable to POCl3-diffused PERC cells. The emitter dopant profile can be adjusted by the thermal budget of the anneal in order to optimize the process window between Jsc and FF losses. The IQE and reflectance of implanted and POCl3-diffused PERC cells in the long wavelength regime are almost identical which demonstrates the successful implementation of the Al2O3/SiNx rear passivation to PERC cells with ion-implanted emitters. Future work will focus on simplifying the process flow in order to obtain a lean industrially manufacturable PERC process, leveraging the single side doping via ion implantation.