Deep levels in as-grown and Si-implanted In0.2Ga0.8As-GaAs strained-layer superlattice optical guiding structures

Trap levels in ∼2-μm In0.2Ga0.8As (94 Å)/GaAs(25 Å) strained-layer superlattices, suitable for optical waveguides, have been identified and characterized by deep-level transient spectroscopy and optical deep-level transient spectroscopy measurements. Several dominant electron and hole traps with concentrations ∼1014 cm−3, and thermal ionization energies ΔET varying from 0.20 to 0.75 eV have been detected. Except a 0.20-eV electron trap, which might be present in the In0.2Ga0.8As well regions, all the other traps have characteristics similar to those identified in molecular-beam epitaxial GaAs. Of these, a 0.42-eV hole trap is believed to originate from Cu impurities and the others are probably related to native defects. Upon Si implantation and halogen lamp annealing, new deep centers are created. These are electron traps with ΔET=0.81 eV and hole traps with ΔET=0.46 eV. Traps occurring at room temperature may present limitations for optical devices.