Photoluminescence and Sims Studies of Hydrogen Passivation of Mg-Doped P-Type Gallium Nitride
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attributed to the hydrogen passivation of nonradiative recombination centers. In GaP, Weber and Singh[7] reported the observation of hydrogen passivation of nonradiative center as well as the deactivation of donors and acceptors. In addition, there are several reports on the hydrogen passivation of Mg doped GaN[3,9-1 1]. S. Nakamura et al.[3] observed that the resistivity of Mg doped MOCVD grown GaN film decreases while the room temperature PL intensity increases when the film is thermally annealed in N 2 atmosphere at temperatures above 6000 C. In MBE grown GaN samples, M. Brandt et al.[9] studied the effects of hydrogen incorporation on Si donors and Mg acceptors. They observed that the remote-plasma deuteration of Mg doped ptype GaN at 600 0 C reduces the room temperature hole concentration by a factor often, while the deuteration of Si doped n-type GaN under the same conditions will not change the electron concentration. They also studied the heavily Mg doped MBE grown GaN by Raman spectroscopy and IR absorption[l0]. Local vibrational modes (LVM) at 2168 and 2219 cmq were found in these films and assigned to the Mg-H complexes. Very recently, W. Gotz et al[ I ] studied the effects of deliberate hydrogenation of GaN grown by MOCVD. The Mg-H complex formation in Mg doped p-type GaN was confirmed by the temperature dependence of the Hall measurements. In this work, we use photoluminescence (PL) correlated with secondary ion mass spectroscopy (SIMS) to study the effects of hydrogen passivation on the spectral positions and relative strengths of radiative transitions in both lightly and heavily Mg-doped GaN grown by MOCVD. EXPERIMENTAL The GaN samples used in this work were grown on A120 3 substrates oriented in the [0001] direction by metalorganic chemical vapor deposition (MOCVD) in the EMCORE multiwafer rotating disk reactor. An initial low-temperature GaN buffer layer of about 200A thickness was deposited at 530 0 C before the growth of GaN epilayer at 1040 0 C. Details of the growth process were reported elsewhere[12]. The resulting GaN epitaxial layer has the wurtzite crystal structure. Three GaN samples, identified as A, B, C were used in this study. Sample A is unintentionally doped GaN, however shows n-type, while B and C are Mg doped with B being lightly doped and C more heavily doped. The epitaxial layer thickness of all samples was about 2 pt m. The PL was excited at 5K with a N2 laser, and was detected with photomultiplier (PMT) and lock-in amplifier electronics. The Mg and H depth profiles were performed on a Physical Electronics 6300 secondary ion mass spectrometer. RESULTS AND DISCUSSIONS The typical distribution of H and Mg in the heavily Mg-doped sample C is shown in Fig. 1. Magnesium was found to be uniformly distributed through the film at approximately 6x1 09 /cm 3 while the hydrogen concentration decreased slowly through the film thickness. After annealing for 20 minutes at 7000 C in N 2 ambient, the hydrogen concentration dropped from a maximum concentration of 2x 10 18/cm3 to a uniform 2.5x
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