Application of pulsed UV laser processing to heteroepitaxial growth in the silicon/silicon-germanium system.

摘要

A pulsed XeCl excimer laser is used to grow ideally strained heteroepitaxial Si{dollar}sb{lcub}{lcub}it 1{rcub}-x{rcub}{dollar}Ge{dollar}sb x{dollar}/Si layers with Ge fractions up to 21% by intermixing a structure of electron beam evaporated a-Ge on Si (100). The rapid regrowth process induces an interfacial grading of the Ge fraction, which results in unusual stability of the layer strain upon heat treatment, as confirmed by MeV-ion channeling along {dollar}langle100rangle{dollar} and {dollar}langle110rangle.{dollar}; Amorphous Si, deposited and arsenic-implanted on top of previously formed Si{dollar}sb{lcub}{lcub}it 1{rcub}-x{rcub}{dollar}Ge{dollar}sb x{dollar}/Si layers, can be recrystallized using a single laser pulse. Very good epitaxial regrowth is achieved; the As dopant is immediately active; some outdiffusion of Ge and B into the top Si layer is observed.; For the Si{dollar}sb{lcub}{lcub}it 1{rcub}-x{rcub}{dollar}Ge{dollar}sb x{dollar} layers, Boron dopant is incorporated during the melt process by using a BF{dollar}sb3{dollar} gas ambient. Hall/van der Pauw and SIMS analysis reveal that the incorporated dopant dose scales with the number of laser pulses. The junction depth is controlled by the incident laser fluence. The melt time is monitored in-situ utilizing the transient reflectance of the sample during the phase transformations. A patterned reflective aluminum mask is used to obtain spatially selective melting. In-plane Hall mobilities are found to be lower for the heteroepitaxial junctions than for Si homojunctions. We believe this is due to different transport behavior for holes in the observed doping regime of 10{dollar}sp{lcub}18{rcub}{dollar}-10{dollar}sp{lcub}20{rcub}{dollar} cm{dollar}sp{lcub}-3{rcub}.{dollar} Quasiplanar p{dollar}sp+{dollar}/N heterojunction diodes are fabricated and exhibit near-ideal forward I-V characteristics. Heterojunction diodes exhibit lower turn-on voltages than equivalent Si homojunction diodes, indicative of a lowered bandgap. The turn-on voltages also depend on the B junction depth with respect to the Si{dollar}sb{lcub}{lcub}it 1{rcub}-x{rcub}{dollar}Ge{dollar}sb x{dollar}/Si interface. Both quantities are controlled independently by separating the epitaxy from the doping step.