Electron-beam-induced migration of hydrogen in Mg-doped GaN using Eu as a probe

We demonstrate the use of hydrogen-induced changes in the emission of isoelectric Eu ions, in Mg-doped $p$-type GaN, as a powerful probe to study the dynamics of hydrogen movement under electron-beam irradiation. We identify, experimentally, a two-step process in the dissociation of Mg-H complexes and propose, based on density functional theory, that the presence of minority carriers and the resulting charge states of hydrogen drive this process.

Figure 1

Left: UV light (UVL) CL spectra taken at room temperature before irradiation (red) and after (black). An increase in a band centered 3.20 eV is observed. Right: UVL CL spectra taken at 30 K. Two steps are observed, one occurring after 5 s (blue) and the other after 55 s (black).

Figure 2

Eu emission spectra taken before and after electron-beam irradiation at three different temperatures.

Figure 3

CEES taken (a) before and (b) after irradiation with a beam current of 6 nA. At this current the increase in Mg/Eu3 is accompanied by the appearance of a new site Mg/Eu2. (c) A partial recovery of Mg/Eu1 and 2 is observed after heating the sample to room temperature and returning to 105 K.

Figure 4

(a) The partial recovery of Mg/Eu1 and 2 is observed after irradiation is performed at 30 K and the sample is heated to room temperature and brought back down to 30 K. (b) No recovery is seen when the sample is irradiated at 295 K and cycled to 30 K. (c) The original spectra only returned after annealing in NH${}_3$, which gives support to the H nature of the complex. (d) No change is observed for either electron-beam irradiation or annealing for undoped Eu:GaN.

Figure 5

DFT models for four different configurations of the defect complex in Eu/Mg-codoped GaN: (a) A Eu-$V_{\mathrm{N}}$ center which does not contain Mg or H (Eu1 center). (b) The as-grown configuration (Mg/Eu1). (c) The configuration in which the hydrogen is captured by the nearest neighbor $V_{\mathrm{N}}$ after LEEBI (Mg/Eu2). (d) Metastable configuration of the hydrogen which induces a minimal perturbation on the Eu ion (Mg/Eu3).