Dependence of optically oriented and detected electron spin resonance on donor concentration in n-GaAs

Electron spin resonance of donors in GaAs has been observed through optical orientation and detection of spins. GaAs samples doped below the metal–insulator transition were studied. The resonance linewidth increases as the concentration of donors is reduced, due to the dependence of the T2* spin lifetime on correlation effects between donor electrons. The linewidth of the lowest doped sample (3×1014 cm−3) corresponds to a T2* of 5 ns, which is the value predicted for electrons in the non-interacting, localized limit. The nuclei need to be simultaneously depolarized in order to make the electron resonance observable.