Laser Annealing of Defects in VPE and Cz Grown Gallium Arsenide with a Pulsed Nd:YAG Laser
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LASER ANNEALING OF DEFECTS IN VPE AND CZ GROWN GALLIUM ARSENIDE WITH A PULSED Nd:YAG LASER
P. M. MOONEY* and J. C. BOURGOIN Groupe de Physique des Solides de l'lNS,** Universitd de Paris VII, Tour 23 2, place Jussieu, 75221 Paris Cedex 05, FRANCE and J. ICOLE Laboratoire Centrale de Recherche, Thompson CSF, Corbeville, B.P. 10, Orsay, FRANCE
ABSTRACT Gallium arsenide crystals, both VPE and Cz grown, were annealed with a pulsed Nd:YAG laser. Gold Schottky diodes were fabricated and defects were studied using the DLTS technique. The native defect E(O.83eV) was found to anneal while other electron traps, E(0.39eV) in both materials and E(0.30eV) in Cz material, remained after irradiation. A new trap, E(0.7OeV), was observed after laser irradiation in both materials. Cz GaAs samples implanted with both Ga and As were also laser annealed. The E(0.83eV) level was not observed after implantation. The E(0.3OeV) trap and new levels, E(0.44eV) and E(0.6leV) were observed. C-V measurements and defect profiles indicate that the recrystallized layer is far from defect free.
INTRODUCTION During the last few years much work has been done showing that laser processing has some advantages over thermal annealing to recrystallize amorphous layers produced by ion implantation in silicon. [1] There have also been studies of point defects in silicon which either remain after or are introduced during this type of processing. 12-4] Gallium arsenide, however, has proved a more difficult material to anneal, often requiring a cap to prevent the loss of arsenic from the surface. [1] We have studied defects in single crystal GaAs irradiated with a Nd:YAG laser and report both the annealing of a native defect and the introduction of a new defect during laser processing. We also report results in ion implanted GaAs which suggest that the recrystallized layer is far from defect free. SAMPLE PREPARATION AND EXPERIMENTAL TECHNIQUES Three groups of samples were prepared for our experiments as follows. The first group were 15 15 16 3 VPE films doped with silicon to concentrations of 2x10 , 5x10 and 1x10 cm- , grown on oriented, pulled GaAs substrates. Each sample was irradiated with a 15 nsec pulse from a Nd:YAG 2 2 laser using simultaneously 1.06 um, 0.46 J/cm and 0.53 p•m, 0.56 J/cm . The second group were 16 3 made from undoped Cz grown GaAs with free carrier concentration 5x10 cm- . Each sample was irradiated with a laser pulse using either 1.06 p•m or 0.53 urm light at various energy densities ranging 2 2 from 0.2 J/cm up to 0.95 J/cm . This range of energy densities was chosen to be high enough to a
present address: IBM Thomas J. Watson Research Center, P.O. Box 218, Yorktown Heights, NY
**
10598 USA Laboratory associated with the CNRS
256 14 third recrystallize the amorphous layer but low enough to avoid changes in surface morphology. The group was prepared from the same GaAs material as the secnnd group, implanted with 2x10 atoms 2 /cm of both Ga and As at 300kev, creating an amorphous layer 2000A thick
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