Impurity Redistribution of Implanted and Annealed GaN

This Datareview discusses the redistribution of typical dopant atoms in GaN during the implant activation anneal. Secondary ion mass spectroscopy (SIMS) spectra of the impurity profiles (impurity concentration versus depth into the sample) before (as-implanted) and after annealing are presented. SIMS analysis is the primary method of characterising impurity distributions in semiconductors [2], This information can be used to roughly estimate a diffusivity, D , of the dopant at the temperatures studied by invoking the relationship 

Before discussing the redistribution of implanted dopants in GaN, it is necessary to briefly review the temperatures required to achieve electrical activity. Pearton et al reported that a temperature of 1100°C is required to achieve electrical activation of Si and Mg + P in GaN [3], However, this temperature is not sufficient to completely remove the implantation induced damage [4], To completely restore the crystal lattice, an annealing temperature of between 1250°C and 1600°C will be required [5], Most of the results on donor redistribution have been for anneals near 1100°C, as discussed in the following sections however, more experimental work must be done at the higher temperatures to characterise the effect of these higher temperatures. The following discussion is separated into common donor impurities (Si and O) and acceptor impurities (Be, Mg, Zn and Ca) in GaN. 

Si is the dopant most commonly used to create n-type GaN. FIGURE 1 shows the SIMS profile for 2 Si in GaN as-implanted and annealed (1050°C). Despite the interference in the mass 28 SIMS signal from 2 N2, the annealed Si profile demonstrates no measurable redistribution. Using a conservative estimate 

FIGURE 1 SIMS profile of28 Si-implanted (100 keV, 5 x 1014 cm 2) GaN as-implanted and annealed at 1050°C for 15 s. No measurable redistribution is seen at the peak of the annealed sample. 

Oxygen incorporation on an N-lattice site also acts as a donor in GaN. Furthermore, oxygen is thought to play a role in the background n-type conductivity in unintentionally doped material [6], The redistribution of O has also been studied with annealing up to 1125°C. Here again, no measurable redistribution is seen and an upper limit of 2.7 x 1013 cm2/s can be set on the diffusivity of O in GaN at 1125°C. 

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B3.2 Impurity redistribution of implanted and annealed GaN B3.3 Electrical properties of ion implanted and annealed GaN B3.4 Optical properties of implanted GaN... 

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