Dopant Distribution and Electrical Characteristics of Boron-Doped Si 1−x Ge x /Si p + /N Heterojunction Diodes Produced by Gas Immersion Laser Doping (GILD) / Pulsed Laser-Induced Epitaxy (PLIE)
Pulsed Laser-Induced Epitaxy / Gas Immersion Laser Doping is used to create borondoped heteroepitaxial p + /N Si 1−x Ge x /Si layers and diodes. Borontriflouride is used as the gaseous dopant source. The mechanisms of heteroepitaxial layer growth of Si 1−x Ge x using PLIE are described and impurity incorporation from the gas phase into the molten layer is investigated. Compared to other heteroepitaxial techniques, very different process parameters determine the growth. The energy fluence of the pulsed laser beam determines the melt depth and thus the layer thickness; Si and Ge intermix in the liquid phase, the diffusion of B dopant also depends on its diffusivity in the liquid phase. Boron incorporation is investigated as a function of laser energy fluence and number of laser pulses using SIMS and Hall-effect measurements. The dose of incorporated dopant is on the order of 10 13 cm −2 per pulse. The obtained boron profiles are flat except for a pile-up at the interface which is due to segregation. Boron and Germanium distribution are compared to turn-on voltage shifts obtained from p + /N Si 1-x Ge x /Si heterojunction diodes fabricated with the technique. A two-step Laser process to independently control metallurgical and electrical junction depth of the diodes has been implemented. The selective nature of the epitaxial process is emphasized.