Hyperdoping of Epitaxial Ge:P Layers by UV Nanosecond Laser Processing

This thesis investigates the potential of Pulsed Laser Melting (PLM) for achieving efficient n-type hyperdoping in epitaxial Ge:P layers and for overcoming the activation limits of conventional doping techniques. Epitaxial Ge:P wafers grown by Low Energy Plasma Enhanced Chemical Vapor Deposition (LEPECVD) were processed by nanosecond ultraviolet laser pulses at varying energy densities and, in selected cases, subjected to Rapid Thermal Processing (RTP) to assess the thermal stability of the metastable hyperdoped layers. The structural, electrical, and optical properties of the processed samples were analyzed through Secondary Ion Mass Spectrometry (SIMS), Van der Pauw–Hall measurements, Fourier-transform infrared spectroscopy, Atomic Force Microscopy (AFM), and Conductive Atomic Force Microscopy (C-AFM). The results demonstrate that PLM enables active dopant concentrations far exceeding the solid solubility limit, while preserving the crystalline quality and surface morphology of the epitaxial layers. Electrical characterization revealed activation fractions up to ~80% of the incorporated phosphorus, representing a substantial improvement over as-grown conditions. Thermal stability studies indicated a rapid deactivation of dopants above 175 °C, highlighting the necessity of low-thermal-budget integration strategies. Furthermore, a depth-resolved characterization methodology based on C-AFM was developed and validated, enabling nanoscale profiling of active dopant distributions in beveled cross-sections. The technique exhibited excellent agreement with SIMS data, establishing C-AFM as a powerful complement to conventional electrical characterization. Overall, this work confirms the effectiveness of PLM for controlled hyperdoping of germanium and introduces a novel methodology for high-resolution depth-resolved dopant activation analysis, paving the way for the integration of hyperdoped Ge:P layers into advanced photonic and electronic devices.