Electron Spin Resonance onGaAs−AlxGa1−xAsHeterostructures

Photoconductivity measurements on $\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}-{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ heterostructures with photon energies $0.05 \mathrm{meV}<h\nu <0.14\mathrm{} \mathrm{meV}$ show resonance structures with a half-width of less than 0.002 meV in the magnetic field range $3 \mathrm{T}<B<\mathrm{}8\mathrm{} \mathrm{T}$. The resonances are only observed at magnetic field values where the Fermi level is located between spin-split levels and are attributed to electron spin resonance. The $g$ factor depends on the carrier density. The linear extrapolation of the resonance energy to $B=0\mathrm{} \mathrm{T}$ leads to a finite excitation energy.