Impurity distribution and electrical characteristics of boron-doped Si_1−x Ge _x /Si p ⁺/N heterojunction diodes produced using pulsed UV-laser-induced epitaxy and Gas-immersion laser doping

Abstract

A two-step pulsed UV-laser process which independently controls the metallurgical and electrical junction depth of a Si_1−x Ge _x /Si heterojunction diode has been implemented. Pulsed Laser-Induced Epitaxy (PLIE) combined with Gas-immersion Laser Doping (GILD) are used to fabricate boron-doped heteroepitaxial p ⁺/N Si_1−x Ge _x /Si layers and diodes. Borontrifluoride is used as the gaseous dopant source in the GILD process step. Boron incorporation and activation are investigated as a function of laser energy fluence and the number of laser pulses using SIMS and Halleffect measurements. The dose of incorporated dopant is on the order of 10¹³ cm⁻² per pulse. The B profiles obtained are flat except for a peak at the interface resulting from segregation effects. The B and Ge distributions are compared with shifts in the turn-on voltage of p ⁺/N Si_1−x /Si heterojunction diodes produced by the process. The GILD/PLIE process is spatially selective with the resulting diodes fabricated being quasiplanar. Hole mobilities in the heavily doped Si_1−x Ge _x films are found to be slightly lower than in comparable Si films.