The Behavior of Ion-Implanted Hydrogen in Gallium Nitride
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G 5.8 Mat. Res. Soc. Proc. Vol. 537 © 1999 Materials Research Society
Experiments involving nuclear-reaction analysis (NRA) of H employed the deuterium (2H), which was detected by counting protons from the 3He-induced reaction H( He,p) 4 He using a Si surface-barrier detector. As a result of the energy dependence of the reaction cross CROSS SECTION 60 6 section [7] and the continuous slowing 3 of the He particles within the target, the proton yield was affected by the 40 depth distribution of the 2H as well as 44 2H by its quantity, and 2H concentration < , versus depth could be obtained by z ,,C•) PROFILE: 20 02 measuring proton yield versus incident 3 1017 2H22 He energy and performing a deconvolution [8]. Ion-channeling Z 1016 analysis of 2H lattice location was M 1015 carried out using the same nuclear 0 0 0 1.0 0.8 0.6 0.4 0.2 0.0 reaction with the specimen manipulated DEPTH(pi) in a 3-axis goniometer. The thickness of the GaN films was monitored by Fig. 1. Calculated depth profiles of implanted 2H and Rutherford backscattering spectrometry the differential nuclear cross section for (RBS) with 1.7-MeV 'H to determine 0.85-MeV 3He with a scattering angle of 135'. when annealing produced significant loss of material. Ion-channeling analysis of defects was performed using RBS with 2-MeV 4 He. All of the channeling analyses were axial, with rotational averaging about the axis to avoid planar channeling. Infrared vibrational spectroscopy was carried out using the 1H and 2H isotopes with multiple implanted layers being introduced to increase signal strength. These measurements were made at room temperature with a resolution of 4 cm-1. Samples for TEM were prepared by ion-thinning and were observed at an electron energy of 300 keV. 2isotope 3
RESULTS AND INTERPRETATION Hydrogen Release During Isochronal Annealing The retention of implanted 2H within GaN was monitored by NRA during a sequence of ]-hour vacuum anneals at temperatures incremented by -100'C. These experiments were carried out on specimens that had been implanted with 1015, 1016 or 1017 21Hcm 2 at room temperature and 50 keV to produce the calculated [9] depth profiles shown in Fig. 1. The NRA was performed with an incident 3He energy of 0.85 MeV, which, using published results for the nuclear cross section [7] and He stopping powers [101, is calculated to result in the depthdependent differential cross section shown in Fig. 1. The nuclear-reaction yield under these conditions provides a quantitative measure of the amount of 2H remaining within the implanted region. Results from these experiments are presented in Fig. 2, where the retained fraction of 2H is plotted versus temperature. The anneal at the highest temperature, 980'C, produced significant loss of material from the GaN film as observed by RBS, so that the corresponding datum does not provide a quantitative measure of 2H release by diffusion. In the case of the lowest implantation dose, effects of the analysis beam on the release were observed, so each measurement was made at a new location o
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