Laser-induced magneto-optical transitions from deep levels in n-InSb

Abstract

We present a novel means for detecting and studying deep levels in high purity n-InSb with extremely sensitive magneto-optical techniques, combining sampling oscilloscope and lock-in amplifier methods. Oscillatory photoconductivity behavior in InSb has been investigated previously under a variety of conditions and in both n- and p-type samples. However, to our knowledge, no evidence has ever been presented for oscillatory magnetophotoconductivity (MPC) in n-InSb (or in any other semiconductor) caused by electron transitions from deep levels to the conduction band Landau levels. These studies allow a more precise determination and sensitive detection of deep levels through a more direct means than has been previously possible. We observe a resonant structure in the CO2 laser-induced MPC at liquid helium temperatures in n-InSb which is periodic in the inverse magnetic field and whose amplitude increases with the magnetic field. This behavior is typical for resonances involving Landau levels. The effect of lattice temperature, laser intensity, photon energy, and light polarization on the MPC is studied. The amplitude of this resonant structure saturates at moderate intensities (∼30 W/cm2) and shows no polarization dependence (for e⊥B and e∥B). These and other results indicate the presence of a deep level ≂74 meV below the conduction band edge (Eg ≂235 meV). Using a CO laser, a resonant structure is also observed from another deep level, ≂170 meV below the band edge. These deep levels could be caused by either lattice defects or residual impurities. Other structures observed with the CO2 laser are identified with LO phonon-assisted cyclotron resonance harmonic transitions within the conduction band, and two-photon magnetoabsorption interband transitions. ufoff