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Properties of metal-insulator transition and electron spin relaxation in GaN:Si

We investigate properties of doping-induced metal-insulator transition in GaN:Si by means of electron spin resonance and Hall effect. While increasing the doping concentration, Si-related bands are formed below the bottom of the GaN conduction band. The D0 band of single-occupied Si donor sites is centered 27 meV below the bottom of the GaN conduction band, the D- band of double-occupied Si states at 2.7 meV below the bottom of the GaN conduction band. Strong damping of the magnetic moment occurs due to filling of the D- states at Si concentrations approaching the metal-insulator transition. Simultaneously, shortening of electron spin relaxation time due to limited electron lifetime in the single-occupied D0 band is observed. The metal-insulator transition occurs at the critical concentration of uncompensated donors equal to about 1.6 * 10^18 cm^-3. Electronic states in metallic samples beyond the metal-insulator transition demonstrate non-magnetic character of double-occupied states.