High quality boron-doped epitaxial layers grown at 200°C from SiF4/H2/Ar gas mixtures for emitter formation in crystalline silicon solar cells

Abstract

Controlling the doping profile in solar cells emitter and front/back surface field is mandatory to reach high efficiencies. In the current state of the art, these doped layers are made by dopant diffusion at around 900°C, which implies potential temperature induced damages in the c-Si absorber and for which a precise control of doping is difficult. An alternative solution based on boron-doped epitaxial silicon layers grown by plasma-enhanced chemical vapor deposition (PECVD) from 200°C using SiF4/H2/Ar/B2H6 chemistry is reported. The structural properties of the doped and undoped epitaxial layers were assessed by spectroscopic ellipsometry (SE), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The incorporation of boron has been studied via plasma profiling time of flight mass spectrometry (PP-TOFMS) and secondary ion mass spectrometry (SIMS) measurements. The boron-doped epitaxial layers revealed excellent structural and electrical properties even for high carrier concentrations (>1019cm-3). Sheet resistances between 100 and 130 Ω/sq can been obtained depending on the thickness and the doping concentration, which is within the range of targeted values for emitters in c-Si solar cells. Electrochemical capacitance voltage (ECV) revealed a uniform doping profile around 3.1019 cm-3 and by comparing with SIMS measurement a doping efficiency around 50% has been found.

Si Electrochemical Liquid Phase Epitaxy: Low-Temperature Growth of Hyperdoped Epitaxial Si Films

“…Although such contacts are desirable, they are challenging to realize in practice because conventional deposition methods (e.g., chemical vapor deposition) for degenerately doped crystalline Si damages the properties of the absorber layer and/ or passivation layer because of the (high) process temperatures. 84,85 An ideal process for producing carrier-selective contacts would eliminate high temperatures. 86 In this regard, Si ec-LPE seems well suited.…”

Formation of inverse cones in crystalline silicon by selective etching of amorphous regions resulting from epitaxial breakdown

“…It can be achieved by multiple vacuum deposition methods, including molecular beam epitaxy (MBE) [1], hot-wire chemical vapour deposition (HWCVD) [2] and plasma-enhanced CVD (PECVD) [3][4][5]. In particular, the use of PECVD allows one to perform epitaxy at temperatures as low as 175°C, and produce films with a variety of doping properties and sharp doping profiles [6][7][8][9].…”

Transmission electron microscopy characterization of low temperature boron doped silicon epitaxial films

“…TEM enables to appreciate the microstructure of the layer particularly at the interface that is known to be critical for the performance of the device. It has already been used for low temperature silicon epitaxy to characterize mostly the crystalline quality [11][12] [13] or defects analysis such as H-platelets [14]. In this article, several TEM techniques were applied both to complete Chrostowski characterization [8] [9] and to provide new keys to understand better the epitaxy morphology and the annealing effect.…”