Hydrogen and Acceptor Compensation in GaN

FIGURE 1 Formation energies as a function of Fermi level for IT, H° and H (solid lines), and for an H2 molecule (dashed line) in GaN [1], EF - 0 corresponds to the top of the valence band. 

In p-type GaN, H behaves as a donor (Ft) it thus compensates acceptors. The preferred location for FT is at the antibonding site behind a nitrogen atom. The diffusion barrier for FT is only 0.7 eV, which indicates a high diffUsivity at moderate to high temperatures. In n-type GaN, H behaves as an acceptor (H ) its most stable site is at the antibonding site behind a Ga atom. The migration barrier for FT is 

indicating a very low diffusivity. For Fermi-level positions below 2.1 eV FT is favoured higher Fermi-level positions favour H The neutral charge state is never stable [1]. This is characteristic of a so-called negative-U centre. 

FIGURE 1 also shows the formation energy of H2 molecules in GaN. It is clear that H2 is unstable with respect to dissociation into monatomic hydrogen. 

The behaviour of isolated interstitial hydrogen, as discussed in Section B, provides crucial information about interaction with impurities. Since both the solubility and the diffusivity of hydrogen in n-type GaN are low, hydrogen-donor complexes will rarely form, and we focus on complexes with acceptors. 

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A8.7 Yellow luminescence in GaN A8.8 Hydrogen and acceptor compensation in GaN A8.9 3d transition metals in GaN and related compounds A8.10 Er-doped GaN and AIN... 

Soon, Nakamura et al. (9) proposed a hydrogenation process whereby acceptor-H neutral complexes are formed in >-type GaN films as a compensation mechanism. Low-resistivity p-type GaN films, which were obtained by N2-ambient thermal annealing or LEEBI treatment, showed a resistivity as high as 1 X 10 Q cm after NHs-ambient thermal annealing at temperatures above 600°C. In the case of N2-ambient thermal annealing at temperatures between room temperature and 1000°C, the low-resistivity p-type GaN films showed no change in resistivity, which was almost constant between 2 and 8 Q cm, as shown in Fig. 11. 

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