Lattice Location of Deuterium in Plasma and Gas Charged Mg Doped GaN
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charged samples the D concentration is higher than the Mg concentration, which indicates that the chemical potential for D from the plasma charging is much higher than from the gas charging. Transmission infrared absorption spectra were also measured in gas and plasma charged samples. In both cases similar absorption peaks were seen at 2320 cm-1 (shown in figures 1 and 2) which were not present prior to deuterium exposure. The increase in energy to 3120 cm-1 seen for this absorption peak in similar samples exposed to hydrogen shows that the absorption peak is due to stretch vibrations of H or D bound to nitrogen. This is also consistent with our observation that the 2320 cm-1 absorption peak disappears when D is removed from the samples by vacuum annealing. The fact that the peak area is similar for the gas and plasma charged samples while the D content is much larger in the plasma charged sample shows that at least in the plasma charged sample much of the D is in an IR inactive state. Similar IR absorption peaks were reported previously for GaN:Mg deuterated with a remote plasma system [13] and were ascribed to D at an antibonding position bound to nitrogen neighboring the Mg acceptor. Ion channeling studies of D were done by counting protons from the D(3He,p)α nuclear reaction using an incident analysis beam of 850 keV 3He+ ions. This gives counts from D to depths of about 1 µm. The analysis beam size was 1x1 mm. Channeling measurements were done with the samples at room temperature. The proton yield was measured as a function of angle between the analyzing ion beam and the crystallographic c-axis of the samples. When the analysis beam is aligned along the c-axis, channeling reduces the ion flux near the rows of host atoms and increases the flux near the center of the open channels, which causes a dip in the NRA yield if the D is near the host atom rows, or conversely, to a peak in yield if the D is near the center of the channel. Figure 1 shows the measured NRA yield normalized to the off-axis or random yield versus the angle between the analysis beam direction and the c-axis for the gas charged sample. The solid circles show measurements taken beginning on axis and stepping progressively farther from the axis, using an analysis ion beam dose of 1 microcoulomb at each angular position. The open circles show a repeat angular scan at the same location on the sample. The first scan shows a dip with halfwidth almost 1 degree and a small narrow central peak. In the second scan the dip is gone but a peak remains. The result that the on-axis yield is higher for the second scan than for the first scan shows that the analysis beam used for the first angular scan has caused a change in lattice location of some of the deuterium. Figure 2 shows the NRA channeling yield for the two plasma
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