Inhomogeneous broadening of Zeeman absorption peak of shallow donor in semi-insulating GaAs

Magnetooptical absorption measurements of shallow donors in semi-insulating GaAs are carried out to investigate the roles of EL2 centers for the Zeeman absorption peak of shallow donors. The transition from a stable state to a metastable state of EL2 centers by infrared irradiation involves a photoquenching of EL2, which also induces a decrease of shallow donors. Photoquenching changes the role of EL2 as a compensator. The change of the compensation affects the linewidth of the absorption peak due to the Stark effect, In that effect, contributions from the transition and from ionization of EL2 are studied separately. Although the delay time variation of the absorption intensity of the peak after pulsed bandgap excitation is sensitive to photoquenching, the linewidth is almost independent of the transition. Ionization, however, causes broadening of the linewidth.