Ion Channeling Analysis of Gallium Nitride Implanted with Deuterium
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channeling and TEM to examine lattice defects produced by the implantation of deuterium. EXPERIMENTAL PROCEDURES Wurtzite GaN films with (0001) orientation and thickness in the range of 1.4 - 2.3 prm were grown epitaxially by MOCVD on 420 mim thick c-oriented sapphire substrates as described elsewhere [7]. The GaN was n-type with a carrier density of - 1017/cm3 as determined by conductivity and Hall-effect measurements. The samples were implanted at room temperature with deuterium (D) at 50 keV to fluences of 10' 5 /cm 2 and 1017/cm 2 . This gives D concentration profiles peaking 0.4 pim beneath the surface at concentrations of about 0.05 and 5 atomic % for these two fluences [8]. Ion channeling measurements were done with the samples mounted on a 3 axis goniometer. D was analyzed by counting protons from the D( 3He,p)ox nuclear reaction with an incident beam of 0.85 MeV 3He' ions. With this energy D at depths up to about I pm will be detected and the peak in the nuclear reaction cross section [81 at 0.6 MeV occurs at the depth of the D. Analysis beams of 2 MeV 4 He were used to examine lattice damage caused by the D implantation. Energy spectra of 4He backscattered at 155 degrees were recorded for angles of incidence near the c-axis. The analysis beam size was typically 1 mm square and the angular divergence was 0.05 degree.
G 3.73 Mat. Res. Soc. Symp. Proc. Vol. 537 0 1999 Materials Research Society
EXPERIMENTAL RESULTS AND INTERPRETATION Lattice defects due to D implantation Transmission electron microscopy, both plan view and cross section, shows that GaN implanted with 50 keV H to fluences of 2xl0' 6/cm' and 10'7 /cm 2 and then vacuum annealed at 886°C for one hour, contains cavities with a typical size of 10 nm at the H implant depth [8]. These cavities are believed to result from precipitation of H2 gas. Such samples also contain planar defects typically -50 nm in diameter, which are shown by high resolution imaging [8] to be (0001) basal plane stacking faults containing one extra Ga-N bilayer bounded by a partial edge dislocation loop with a Burgers vector c/2[0001]. The atomic configuration of such faults has been discussed elsewhere [9]. TEM showed these cavities and stacking faults were not present in GaN implanted with H to a lower fluence of 10' 5/cm' and annealed at 886°C. The cavities and stacking faults can be seen in the micrographs shown in figure 1. 3600
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lb Fig. 1. Cross-section TEM of a bubble (a) and a stacking fault (b) in GaN implanted with 2x1016 HIcm2 and then vacuum annealed at 8860C for one hour. The bars indicate 5 nm.
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2. Energy spectra for channeled 2 MeV He backscattered from GaN. Yield from the implanted region appears at channels in the range from 90-120, while the surface corresponds approximately to channel 140.
Figure 2 shows channeled backscattering spectra for 2 MeV 4He incident along the [0001] axis for GaN implanted at room temperature with 1017 D/cm2. Also shown for comparison
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