Contents I. Introduction
Silicon solar cell surface nanostructures - also called black silicon, or bSi - provide a definite advantage in terms of reflectance reduction [1]. The efficiency of bSi front-side emitter solar cells remains however poor due to three main issues: 1) the high recombination due to large surface area [2], 2) the high Auger recombination caused by heavy diffusion of dopants [3], and 3) the lack of conformality of metal contacts due to the high aspect ratio of the structures [4]. While the surface recombination issue can be solved by ALD Al2O3 passivation [5], [6], the two others still remain recurrent issues with the standard emitter formation techniques. However, alternative methods exist and could allow the fabrication of performant bSi emitters without modification of the nanostructures. For instance, ion implantation is a promising doping technique for bSi, as it uses a fixed dopant dose and thus allows better doping control than diffusion in bSi structures, causing less recombination [7]. Electron beam evaporation could constitute a solution for contact formation, as it allows low deposition rates to produce conformal layers [8] and ensures limited surface damage [9]. Here we study whether ion implantation and electron beam evaporation can be combined to fabricate metallized bSi emitters with limited recombination activity and low contact resistance. In addition, doping is an important parameter to consider when optimizing emitter passivation and metallization, but it is typically difficult to measure in bSi structures. Successful silicon nanowire doping measurements have been performed by CV measurements [10], although they remain complex due to the need for maintaining a contact with the nanowires. In this work, we utilize Raman spectroscopy, which has the advantage of being a contactless method. The first part of this paper focuses on doping mechanisms in bSi structures and the second one on contact performance.
