Method to form and condition nanoscale units inside an all-silicon light-to-electricity converter especially a photovoltaic cell, characterized in the following succession of steps:
- A. step of impurity doping;
- the initial n-type doping profile (e.g., phosphorous) using an impurity diffusion or doping implantation during amorphization, shaped by the so-called low-temperature thermal P diffusion at T<1000° C. in the homogeneously lightly or moderately p-type doped wafer, e.g., pre-doped by boron, or by another method from a surface source or an implanted impurity doping source, combined with an impurity diffusion leading to heavily doped local zones finalizing previous doping, e.g. obtained by the diffusion;
- B. step of PN junction creation by diffusion or implantation to assume a unidirectional functioning of conditioned nanoscale units as an energy valve and a geometry space valve;
- C. step of surface treatment, i.e., of the pre conditioning of the wafer surface after the diffusion or after the doping implantation process to allow a good control of the implanted volume;
- D. step of buried amorphization by either a self Si implantation or by phosphorous, i.e., P implantation with 10-200 keV ion beam irradiation or other suitable irradiations as an electron beam;
- e.g. a single ion implantation using exclusively phosphorous doping ions (P) leads simultaneously to heavily doped material with buried amorphization, while the Si ion amorphization requires an impurity doping profile obtained during preceding or following n-type doping (P);
- E. step of creation of secondary generation centers by shifting out two Si atoms from an elementary cell of Si crystalline structure by using relatively low energies per displaced atom (about 2.5 eV/atom) by focalized energy beams as ion beam, electron beam or other suitable irradiations to form a system of two interacting vacancies called divacancy having prolonged electron bonds that can capture and localize electrons to build a conditioned nanoscale unit;
- said nanoscale unit becomes technically useful in that it contains permanently four captured electrons where one of them is weakly bonded in a heavily n-type doped material, e.g., provided with the high phosphorous doping (Si:P);
- F. step of bringing together a specific and useful set of electron energy levels that complete the fundamental Si energy bands for an efficient photoconversion by locally concentrate conditioned nanoscale units;
- G. step of thermal treatment of the buried Si amorphization using an annealing cycle that is performed preferentially at about 500-550° C. which dilutes small a-Si inclusions in c-Si and c-Si inlusions in a-Si;
- H. step of constitution of stabilized metamaterial nanolayers by the thermal annealing cycle by placing the above mentioned conditioned nanoscale units within the crystalline <c-Si> phase that are sufficiently numerous and well distributed in a well-defined nanospace by means of a solid state epitaxy that leads to clear separation of both silicon phases, crystalline and amorphized, as well as to sharp planar a-Si/c-Si heterointerfaces, the same annealing cycle leads to the creation of more or less planar-like nanolayers that are smoothly wrapping each amorphization in order that nanolayers are 3 to 10 nm thick and are uniform, without any faults and inequalities;
- I. step of conditioning the dense population of nanoscale units by superposing physical effects that are two built-in fields:
- electrical field and mechanical field and previously performed doping that allows:
- the quasi-permanent doubly negative charge-state of conditioned nanoscale units due to the heavily doping of zone occupied by conditioned nanoscale units and of the space surrounding this zone to render locally a suitable n-type behavior;
- J. step of activation of the elementary units, for example at 350-450° C.;
- K. step of conditioning electron transport by two different mechanisms, the conduction in and out of conditioned nanoscale units;
- out by the conduction band and in by the impurity band and an ultrafast recharging of conditioned nanoscale units due to an electron conduction through the impurity band;
- L. step of spatial localization of conditioned nanoscale units suited for incident photons to be converted, preferentially by placing conditioned nanoscale units within the upper wafer region;
- M. step of final conditioning of nanoscale units during all operations of the converter by conserving their population after any period of temperature rising during the technological processing of the converter;
- and
- N. step of device final processing:
- AR coating, electronic passivation, metallizations.