Investigation of Germanium Hyperdoping by Pulsed Laser Melting

In recent years the interest of both scientific community and industry in germanium (Ge) has seen a spike, owing to its specific properties. Germanium exhibits interesting electrical properties, mainly a high carrier mobility and low resistivity, and optical properties that make it a prime candidate for the use in optical devices, such as material for infrared (IR) lenses and fibre optics. Its integration in advanced applications in nanoelectronics, plasmonics, photonics, laser production, as well as quantum computing, require high doping levels. However, most of the major dopants in germanium exhibit a low solid solubility limit and even lower active concentrations at thermal equilibrium, that is even more true for n-type dopants. The UV nanosecond Pulsed Laser Melting (PLM) annealing technique is a promising methodology to achieve high levels of doping while inhibiting dopants diffusion. The process is characterized by a fast melting and re-crystallization of the materials’ surface layer that allows for a strong out-of-equilibrium incorporation of dopants atoms inside the lattice matrix, with an active dopant concentration higher than the equilibrium concentration (hyperdoping). During the thesis, several in-situ P doped Ge and Si0.15Ge0.85 layers epitaxially LEPECVD grown on Si have been subjected to PLM processes. Their electrical and structural properties have been investigated to assess the modifications induced by the laser anneal. We explored a broad range of PLM process conditions, P chemical concentration and thickness of the grown layers, which were characterized by Secondary Ion Mass Spectrometry, Raman spectroscopy, Atomic Force Microscopy and VdP-Hall electrical measurements. Moreover, Rapid Thermal Processes were performed in order to assess the samples’ thermal induced deactivation. We show that, although hyperdoped concentrations well in excess 1x1020cm-3 can be reached over thicknesses of several hundreds of nm with excellent morphology and crystalline quality, the active dopants start to deactivate in the range 300-400°C, which must be carefully evaluated and taken into account for subsequent processing step.