N-type doping of SiC-passivated Ge by pulsed laser melting towards the development of interdigitated back contact thermophotovoltaic devices

In this article, a method for phosphorous (n-type) doping of germanium based on spin-on dopant sources and Pulsed Laser Melting (PLM) throughout an amorphous silicon carbide (a-SixC1-x:H) layer, which provides both surface passivation and electrical isolation, has been demonstrated, paving the way towards the development of Ge-based interdigitated back contact thermophotovoltaic devices. This method offers simultaneous opening of the a-SixC1-x:H layer and creation of a heavily doped region underneath without using photolithographic steps, eventually enabling a low-cost and scalable manufacturing process. This article focuses on the optimization of the n+/p junction formation by studying the effect of different laser energy fluences and number of pulses on the diffusion profiles measured by secondary ion mass spectrometry, and on the electrical performance characterized by Van der Pauw-Hall technique. Additionally, the crystalline quality after PLM has been analyzed by Rutherford backscattering measurements in channeling conditions, high-resolution X-Ray diffraction and transmission electron microscopy. High level of donor activation (up to 1·1019 cm−3), low sheet resistance (≈50 Ω/□), and high mobility (275–700 cm2/V·s) have been obtained, with a weaker dependency of these parameters on the explored laser energy fluence range. A prototype diode has been developed demonstrating a rectifying behavior but with high saturation current densities. Point-like contact formation will be implemented in future works to reduce the laser irradiated area, and thus, improve the surface passivation and device characteristics.