Improved retention of phosphorus donors in germanium using a non-amorphizing fluorine co-implantation technique

Abstract

Co-doping with fluorine is a potentially promising method for defect passivation to increase the donor electrical activation in highly doped n-type germanium. However, regular high dose donor-fluorine co-implants, followed by conventional thermal treatment of the germanium typically results in a dramatic loss of the fluorine, as a result of the extremely large diffusivity at elevated temperatures, partly mediated by the solid phase epitaxial regrowth (SPE). To circumvent this problem, we propose and experimentally demonstrate two non-amorphizing coimplantation methods; one involving consecutive, low dose fluorine implants, intertwined with rapid thermal annealing (RTA) and the second, involving heating of the target wafer during implantation. Our study confirms that the fluorine solubility in germanium is defect-mediated and we reveal the extent to which both of these strategies can be effective in retaining large fractions of both the implanted fluorine and, critically, phosphorus donors.2

Diffusion and Dopant Activation in Germanium: Insights from Recent Experimental and Theoretical Results

“…The determined arsenic concentration profiles with respect to depth for arsenic-doped (blue line 3 × 10 13 As/cm 2 with 50 keV implantation energy) and fluorine + arsenic-co-doped (red line As: 3 × 10 13 As/cm 2 with 50 keV implantation energy; F: 1 × 10 15 F/cm 2 with 35 keV implantation energy) To address both these issues concurrently, double-donor doping and doping with aliovalent dopants was considered [2,89]. Double-donor doping is the process where a second n-type dopant is introduced in the lattice aiming to impact the electronic properties and defect-dopant processes [89][90][91][92][93][94]. Tsouroutas et al [90] investigated the diffusion and activation of P and as co-doped Ge using conventional thermal annealing (600-750 • C).…”

High level active n+ doping of strained germanium through co-implantation and nanosecond pulsed laser melting

“…123, 165101-1 than arsenic-vacancy (As-V) and antimony-vacancy (Sb-V) pairs. 23 Previous P þ F co-doping studies were carried out by co-implantation on Ge crystal wafers and Ge-on-Si substrates followed by rapid thermal annealing (RTA), 24,25 but the diffusion of P and F out of the sample during RTA keeps carrier concentrations below n þ levels. Non-equilibrium, rapid resolidification during pulsed laser melting (PLM) of P-implanted Ge crystal wafers can increase carrier activation to 1 Â 10 20 cm À3 levels; however, 20% of donors are still lost due to diffusion in some reports.…”

Phosphorus diffusion and activation in fluorine co-implanted germanium after excimer laser annealing

“…Many elements, such as carbon (C), nitrogen (N), and fluorine (F), have proved to be alternative co-doping ions to suppress dopant diffusion in the post-annealing process. [15][16][17] Among those elements, theoretical and experimental studies [13,[18][19][20][21][22] show that F owns a large electro-negativity and has been confirmed to be one of the best options because of its higher bonding energy with vacancy to form F n V m clusters than n-type dopants.…”