Understanding phosphorus diffusion into silicon in a MOVPE environment for III–V on silicon solar cells (original) (raw)
Related papers
Journal of Physics D: Applied Physics, 2013
Dual-junction solar cells formed by a GaAsP or GalnP top cell and a silicon bottom cell seem to be attractive candidates to materialize the long sought-for integration of III-V materials on silicon for photovoltaic applications. One of the first issues to be considered in the development of this structure will be the strategy to create the silicon emitter of the bottom subcell. In this study, we explore the possibility of forming the silicon emitter by phosphorus diffusion (i.e. exposing the wafer to PH 3 in a MOVPE reactor) and still obtain good surface morphologies to achieve a successful III-V heteroepitaxy as occurs in conventional III-V on germanium solar cell technology. Consequently, we explore the parameter space (PH 3 partial pressure, time and temperature) that is needed to create optimized emitter designs and assess the impact of such treatments on surface morphology using atomic force microscopy. Although a strong degradation of surface morphology caused by prolonged exposure of silicon to PH 3 is corroborated, it is also shown that subsequent anneals under H 2 can recover silicon surface morphology and minimize its RMS roughness and the presence of pits and spikes.
Energy Procedia, 2013
In this paper, we present the development of accurate process simulations for the processes leading to the formation of the n-type (phosphorus doped) regions in high efficiency crystalline silicon solar cells. We consider the Phosphorus profile formation either using POCl 3 diffusion or by ion implantation; the t results are applicable for the formation of the Front Surface Field, emitter, as well as the Back Surface Field regions. The main focus in this paper was on the modeling of the oxidation process, both in terms of the oxide growth rate dependence on the substrate doping concentration and on the doping diffusion enhancement due to oxidation. The detailed description of these two phenomena allows for the accurate prediction of the doping distribution and the oxide thickness, enabling the engineering of the junction formation based on process simulations. For the model calibrations we have used both POCl 3 and Phosphorus ion implanted samples, annealed at various temperatures, durations and ambient conditions (oxidizing or inert), so as to quantify the effect of transient and oxidation enhanced diffusion and dopant enhanced oxidation.
Silicon, 2016
The main purpose of this work is to demonstrate the possibility of diffusion process perfection during silicon solar cells manufacturing by CFD simulation. Presently, the major community of PV industries uses a p-type silicon solar cell as the starting material. In this work too, boron doped silicon wafers are considered to form solar cells. Likewise, phosphorus oxy-chloride (POCl 3) is used as a precursor for phosphorus diffusion. To do this, we evaluate the throughput of an industrial low-pressure diffusion tube furnace in order to realize uniform emitters. The lowpressure tube furnace is designed to obtain emitter standard sheet resistances of about 60 /sq and wafer uniformity less than 3 %. An up-to-date control model using for the first time a CFD numerical code has been derived from some previous work, to achieve better wafer to wafer temperature distribution. Moreover, a numerical process was built using an Atlas-Silvaco® TCAD Simulation Package where we can demonstrate that the short circuit current density (I sc) increases from 4.97 to 6.53 mA/cm 2 compared to the conventional photovoltaic process. This (I sc) enhancement can be attributed to the strong temperature effect on furnace atmosphere. Our result proves that we can target electrical H.
Journal of Applied Physics, 2006
We have investigated the gettering of transition metals in multicrystalline silicon wafers during a phosphorus emitter diffusion for solar cell processing. The results show that mainly regions of high initial recombination lifetime exhibit a significant lifetime enhancement upon phosphorus diffusion gettering. Nevertheless, transition metal profiles extracted by secondary ion mass spectrometry in a region of low initial lifetime reveal significant gradients in Cr, Fe, and Cu concentrations towards the surface after the emitter diffusion, without exhibiting a significant enhancement in the lifetime. In a region of higher initial lifetime, however, diminutive concentration gradients of the transition metal impurities are revealed, indicating a significantly lower initial concentration in these regions. From spatial maps of the dislocation density in the wafers, we find that lifetime enhancements mainly occur in regions of low dislocation density. Thus, it is believed that a generally higher concentration of transition metals combined with an impurity decoration of dislocations in regions of high dislocation density limit the initial lifetime and the lifetime after the phosphorus diffusion, in spite of the notable gettering of transition metal impurities towards the surface in these regions. Furthermore, after a hydrogen release from overlying silicon nitride layers, we observe that only regions of low dislocation density experience a significant lifetime enhancement. This is attributed to impurity decoration of the dislocations in the regions of both high dislocation density and high transition metal impurity concentration, reducing the ability of hydrogen to passivate dislocations in these regions.
International Journal of Scientific & Technology Research, 2014
The emitter formation constitutes a crucial step in the manufacturing of the crystalline silicon solar cells. Several techniques are used in the photovoltaic industry and the most well-known one is based on the POCl3 diffusion in cylindrical quartz tube. Despite the efficiency of this technique to be reproducible, economic and simple, it presents the major inconvenient to have a heavily doped region near the surface which induces a high minority carrier recombination. To limit this effect, an optimisation of diffused phosphorous profiles is required. Our modelling of phosphorus profiles is summarized in the presence of an erfc distribution near to the surface and other Gaussian distribution in the bulk region of the emitter. However, this work is devoted to study the effects of the temperature, diffusion time, surface concentration and doping profile on the crystalline silicon solar cells performances by using the new parameters. The first results of our numerical modelling carried out by the Silvaco Atlas® simulation package show the possibility to improve the efficiency by 2.78%. This result is also confirmed by the IQE calculus which present an obvious enhancement in short wavelength region (380-450nm) about 23%.
IEEE Transactions on Electron Devices, 2000
ABSTRACT In this paper, we have presented the experimental results of phosphorus diffusion in silicon for the cases of rapid thermal processing (RTP) and rapid photothermal processing (RPP). In the case of the RPP, other than thermal energy, the vacuum ultraviolet photons are used as an additional source of energy. We have investigated the secondary-ion-mass-spectroscopy impurity profiles at different concentrations of P in Si. Based on our own experimental results and the data published in the open literature, we have provided an explanation of the enhanced diffusion both for the RTP and RPP cases. The thermal factor leads to the excitation (vibration) of atoms and quantum energy to the electron system excitation. As compared with the pure thermal process, the quantum-energy contribution provides a reduced activation energy and a higher diffusion coefficient.
Solar Cells, 1985
Diffusion of phosphorus into p-type silicon from spun-on phosphorosilica films has been induced by means of incoherent light from a xenon arclamp. A suitable process for solar cell preparation appears to be heating for 20 s to 1000 °C, followed by gradual cooling. Sheet resistivities of around 35 ~2/[] may be achieved under these conditions, with no appreciable degradation of the bulk-material properties. Doping profiles measured by the Hall effect exhibit a maximum concentration of 2 -3 X 1020 cm -3 at the silicon surface and a junction depth of about 1500 A. A number of test-cell batches have been prepared from single-as well as polycrystalline material, and very favourable and reproducible spectral-response characteristics have been found. In spite of the non-optimized cell design and a rather primitive antireflective coating, AM 1 efficiencies of up to 12.7% (single-crystal cell) and 8.2% (polycrystalline cell) have been recorded.
Applied Physics Letters, 2003
A vacancy-mediated diffusion mechanism has been assumed in traditional models of P diffusion in Si. However, recent experiments have suggested that for intrinsic P diffusion in Si, the interstitial-assisted diffusion mechanism dominates. Here, we describe first-principles calculations of P diffusion in Si performed to study interstitial- and vacancy-mediated diffusion mechanisms. Special care is taken with regard to structural minimization, charge state effects and corrections. We calculated the defect formation energies and migration barriers for the various competing P-interstitial diffusion mechanisms, as well as P-vacancy diffusion energetics in different charge states. For P-interstitial diffusion, we find overall diffusion activation energies of 3.1-3.5 eV for neutral and +1 charge states, in close agreement with experiments at intrinsic conditions. For P-vacancy diffusion, our calculation is in agreement with previous calculations in the neutral case, but suggests that only P+V= plays a role in the heavily doped n region while the interstitial mechanisms may dominate in near-intrinsic regions.
Integration of III-V materials on silicon substrates for multi-junction solar cell applications
2011 Proceedings of the 8th Spanish Conference on Electron Devices (CDE'2011), 2011
The work presented here aims to reduce the cost of multijunction solar cell technology by developing ways to manufacture them on cheap substrates such as silicon. In particular, our main objective is the growth of III-V semiconductors on silicon substrates for photovoltaic applications. The goal is to create a GaAsP/Si virtual substrates onto which other III-V cells could be integrated with an interesting efficiency potential. This technology involves several challenges due to the difficulty of growing III-V materials on silicon. In this paper, our first work done aimed at developing such structure is presented. It was focused on the development of phosphorus diffusion models on silicon and on the preparation of an optimal silicon surface to grow on it III-V materials.
Journal of Materials Science, 1990
The chemical vapour deposition technique for the fabrication of p-n junction silicon solar cells is reported. This technique involves the use of native oxide on silicon to limit the diffusion flux and yields lower surface concentrations of impurities and shallow p-n junctions. Photo-Jithography is used for cell fabrication. Data are given to demonstrate the effects of technological parameters on solar cell performance and the controllability of the diffusion parameters obtained by this technique.