R. T. Young

Laser annealing of boron‐implanted silicon

The properties of boron‐implanted silicon annealed by high‐power Q‐switched ruby laser radiation are compared with results obtained by conventional thermal annealing. Laser annealing of the implanted layer results in significantly increased electrical activity, as compared to thermally annealed implanted silicon. This correlates well with transmission electron microscopy and ion‐channeling measurements which show a dramatic removal of displacement damage as a result of laser annealing. A substantial redistribution of the implanted boron concentration profile occurs after laser annealing which cannot be explained by thermal diffusion in the solid.

Laser Annealing of Ion-Implanted Semiconductors

The physical and electrical properties of ion-implanted silicon annealed with high-powered laser radiation are described. Particular emphasis is placed on the comparison of materials properties that can be achieved with laser annealing to those which can be achieved by conventional thermal annealing. Applications of these techniques to the fabrication of high-efficiency solar cells, and potential applications of this new technique to other materials areas are discussed.

p‐n junction formation in boron‐deposited silicon by laser‐induced diffusion

A technique for p‐n junction formation in silicon, based on deposition of boron on silicon at room temperature followed by laser irradiation is described. Transmission electron microscopy and electrical measurements indicate that as a result of the laser irradiation the boron is dissolved in the silicon and becomes electrically active. Diode characteristics of p‐n junctions produced by this technique are quite good. The dopant profile distribution has been obtained using secondary ion mass spectrometry and is in qualitative agreement with simplified theoretical calculations.

Effects of pulsed ruby‐laser annealing on As and Sb implanted silicon

The effects of pulsed (Q‐switched) ruby‐laser annealing of arsenic‐ and antimony‐implanted silicon (1×1015 to ∼2×1016 cm−2) has been studied by Rutherford ion backscattering, TEM, and ion channeling. The laser pulses were of ∼50‐nsec time width and of 1.5–1.7 J/cm2 energy density. Analysis of the dopant profiles before and after annealing leads to the conclusion that the dopants diffuse under normal kinetics in a melted silicon layer over an average time interval of about 0.27‐μsec after the laser power has been absorbed. Recrystallization of the melt layer is by liquid‐phase epitaxial regrowth from the substrate. The recrystallized zone is found to be free of significant structural defects for all specimens except the very highest antimony doses, in which case some near‐surface (∼400 A) precipitation at dislocations is observed. Atom‐location measurements reveal that 98–99% of the retained dopant is in substitutional lattice sites even when the dopant concentration greatly exceeds the limit of solid solu...

A comparative study of laser and thermal annealing of boron‐implanted silicon

Transmission electron microscopy has been used to study the effects of high‐power laser pulses on as‐grown and boron‐implanted silicon. No defects (dislocations, dislocation loops, and stacking faults) were observed in either as‐grown or boron‐implanted (doses 3×1015 and 2×1016 ions cm−2) silicon after pulsed laser treatment. In thermally annealed specimens, on the other hand, a significant amount of damage was retained even after annealing at 1100 °C for 30 min. After thermally annealing the implanted laser‐treated specimens at 600 and 900 °C for 30 min, no defects were observed for low‐dose specimens; however, in high‐dose specimens, precipitation of boron occurred after 600 °C annealing and it increased after annealing at 900 °C. These results and the electrical measurements on these samples suggest that the boron atoms in the precipitates are electrically inactive.

Laser processing for high-efficiency Si solar cells

High‐efficiency silicon solar cells can be fabricated by ion implantation followed by pulsed laser annealing. The proper choice of implantation parameters (energy and dose), laser energy density, substrate temperature, etc., and the improvement of the minority carrier diffusion length of the starting material are important factors in obtaining high efficiency cells. In this paper, we report on experiments which show that substrate heating during pulsed laser annealing can improve the electrical properties of the emitter regions of solar cells. We have also found that the open circuit voltage and the fill factor of ion‐implanted, laser‐annealed cells can be improved by increasing the emitter dopant concentration, whereas the short circuit current remains fairly constant; these results are in only qualitative agreement with theoretical predictions. By using ion implantation followed by laser annealing to form p‐n junctions, laser damage gettering to enhance the minority carrier diffusion length, and laser‐i...

Electrical and structural characteristics of laser‐induced epitaxial layers in silicon

We have used pulsed‐laser radiation to grow homoepitaxial p‐n junctions in silicon. Doped amorphous silicon was deposited on (100) and (111) silicon substrates and annealed with a Q‐switched ruby laser. By this technique, perfect epitaxial layers with good electrical characteristics and controlled dopant profiles can be achieved. The technique can potentially be competitive with or replace ion implantation for many semiconductor‐device applications.

High‐efficiency Si solar cells by beam processing

Utilizing two recently developed beam processing techniques, i.e., gas discharge implantation and XeCl excimer laser annealing, p‐n junction silicon solar cells with total area (∼2 cm2) AM1 efficiencies as high as 16.5% have been made. These cells are of a particularly simple structure, fabricated without any sophisticated processing steps, and subjected to no high‐temperature treatment.

Laser annealing of diffusion‐induced imperfections in silicon

High‐temperature diffusion of boron or phosphorus into silicon leads to the formation of spherical precipitates and/or dislocation loops in the diffused layer which influence electrical junction characteristics. These diffusion‐induced imperfections can be removed by high‐energy pulse laser treatment. The boron or phosphorus atoms previously contained in the precipitates become electrically active and the resulting dopant concentration can exceed the solid solubility limit.

Radiation damage in neutron transmutation doped silicon: Electrical property studies

Radiation damage in neutron‐transmutation‐doped (NTD) silicon, irradiated to introduce 5×1013 to 6×1016 phosphorus cm−3, has been studied by electrical property measurements. The experimental results indicate that thermal‐neutron‐induced (n,γ) recoil‐type damage can be annealed at 400 °C. The nature of any remaining lattice defects and their annealing behavior above 400 °C is a function of the fast‐neutron fluence. Small defect clusters are present in Si irradiated with a light‐to‐moderate fast‐neutron fluence (?5×1018 n cm−2), and temperature‐dependent Hall coefficient measurements indicate that at least two deep acceptor levels and one deep donor level are formed during annealing. One of these acceptor levels anneals at ∼450 °C, and the other two levels anneal at ∼550 °C. A shallow acceptor level near the valence band that anneals at 750 °C is also observed. Larger defect clusters which reduce the electron mobility tremendously and distort the band structure are formed in heavily irradiated Si (5×1018 t...