Native Point Defects in GaN and Related Compounds

Native defects have sometimes been invoked not just as sources of compensation, but as sources of doping. The nitrogen vacancy in GaN is a prime example for a long time the nitrogen vacancy was thought to be the source of n-type conductivity in GaN. As early as 1983 it was pointed out that unintentional incorporation of oxygen was a more likely explanation [1], Still, it is only recently that unintentional impurities have become widely accepted as the source of n-type conductivity, thanks in part to contributions from first-principles theory (see Datareview A8.1). In this Datareview we will describe some of those theoretical results, for vacancies as well as other native defects (self-interstitials and antisites). Experimental information about native defects in the nitrides is very scarce at this time we will include references where available. 

FIGURE 1 shows that self-interstitial and antisite defects are high-energy defects in GaN, and are thus unlikely to occur during growth. These defects can still be created by electron irradiation or ion implantation, of course. One such defect, created by electron irradiation, has been identified as a complex involving interstitial Ga [6], 

FIGURE 1 Formation energy as a function of Fermi level for native point defects in GaN under Ga-rich conditions. EF = 0 corresponds to the top of the valence band. 

In n-type GaN the lowest-energy native defect is the gallium vacancy (Vg ), a triple acceptor. This defect plays a role in donor compensation (see Datareview A8.1), as well as in the frequently observed yellow luminescence (see Datareview A8.7). 

First-principles calculations have also been performed for formation energies of native defects in AIN [8,9], The main conclusions are similar to those for GaN self-interstitials and antisites are high in energy - with the exception of the A1 interstitial in cubic AIN, which is a triple donor and could act as a compensating centre in p-type material. 

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A8.2 Native point defects in GaN and related compounds A8.3 O, C and other unintentional impurities in GaN and related compounds... 

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