U. G. Akano

Quasi-phase matched second-harmonic generation in an AlxGa1−xAs asymmetric quantum-well waveguide using ion-implantation-enhanced intermixing

Quasi-phase matched second-harmonic generation in the copropagating geometry is demonstrated in an asymmetric quantum-well waveguide. Modulation of the nonlinear susceptibility along the waveguide was achieved using a patterned quantum-well intermixing process. Photoluminescence measurements of the quantum-well bandedges indicate that a grating of alternating regions of intermixed and as-grown asymmetric quantum wells was produced for periods between 2 and 12 μm. The variation of the second-harmonic light intensity generated by guided incident light between λ=1480 and 1600 nm was measured. The resulting second-harmonic spectra show sharp quasi-phase matching resonances for grating periods near 3 μm, demonstrating that a periodic modulation of the quantum-well nonlinear susceptibility was produced.

Nonlinear optical response of As+‐ion implanted GaAs studied using time resolved reflectivity

The transient reflectivity response of GaAs with a 2% excess As concentration (GaAs:As), prepared by As+ ion implantation, has been measured at photon energies near the band gap. Results are compared with similar measurements on implanted GaAs with a 0.01% excess As concentration, and unimplanted GaAs. For GaAs:As, the transient refractive index change Δn, is larger than, but of the opposite sign to that of unimplanted GaAs. The measured carrier lifetime of 1±0.1 ps is identical to that of low‐temperature GaAs. The wavelength dependence of Δn indicates the presence of an induced absorption peak at photon energies near the band gap, which is attributed to band‐gap renormalization.

Ion implantation damage of InP and InGaAs

Abstract The damage accumulation and annealing processes in ion bombarded InP and InGaAs have been studied. Epitaxial InGaAs layers on (100) oriented InP and InP crystals were implanted with 16 O ions to produce a R p of 0.5 μm in each material for ion doses from 10 13 to 2 × 10 16 cm −2 , implant temperature from 80 to 373 K, and beam flux from 0.01 to 1.8 μA cm −2 . The retained damage following implantation was analyzed by the Rutherford backscattering/channeling technique. The results show that the response of each material to O ion bombardment is widely different for all implantation temperatures. Within the flux range studied, amorphous layers can be formed in InP at all temperatures up to 373 K for 16 O fluences ≥ 5 × 10 14 cm −2 . Strong dynamic defect annealing precludes amorphization of InGaAs at 290 K for O doses up to 5 × 10 15 cm −2 and beam flux up to 1.8 μA cm −2 .

Threshold dose for ion‐induced intermixing in InGaAs/GaAs quantum wells

We have determined the threshold dose for 8 MeV Bi+ ions to induce intermixing of GaAs quantum wells in AlGaAs and InGaAs quantum wells in GaAs after rapid thermal annealing at 850 °C. Our measured threshold for the GaAs/AlGaAs system agrees well with previous work. The threshold for the InGaAs/GaAs system is much lower and explains, at least in part, earlier difficulties in the lateral patterning of nanostructures by focused‐ion‐beam lithography.

Room‐temperature annealing of Si implantation damage in InP

Spontaneous recovery at 295 K of Si implant damage in InP is reported. InP(Zn) and InP(S) wafers of (100) orientation have been implanted at room temperature with 600 keV Si+ ions to doses ranging from 3.6×1011 to 2×1014 cm−2. Room‐temperature annealing of the resultant damage has been monitored by the Rutherford backscattering/channeling technique. For Si doses ≤4×1013 cm−2, up to 70% of the initial damage (displaced atoms) annealed out over a period of ≊85 days. The degree of recovery was found to depend on the initial level of damage. Recovery is characterized by at least two time constants t1<5 days and a longer t2≊100 days. Anneal rates observed between 295 and 375 K are consistent with an activation energy of 1.2 eV, suggesting that the migration of implant‐induced vacancies is associated with the reordering of the InP lattice.

Influence of dose rate and temperature on the accumulation of Si-implantation damage in indium phosphide

The influence of dose rate and temperature on the implantation damage accumulation in InP has been investigated. InP crystals were implanted at 80–323 K with 600 keV Si+ ions at a beam flux of 0.005–1.0 μA cm−2, and to total fluences of between 5×1012 and 2×1014 Si cm−2. The residual damage following implantation was analysed by the Rutherford backscattering/channeling technique. The results show that at 80 K, the influence of the beam flux on the accumulated displacement damage is small. However, at T≥295 K the displaced atom density, Nd, exhibits a power law dependence on J:Nd=αJn, with the value of n dependent on both the total ion dose and implant temperature. At 295 K and Si doses of 1–4×1013 cm−2, the value of n varies from 0.23 to 0.15.

Patterning the second-order optical nonlinearity of asymmetric quantum wells by ion implantation enhanced intermixing

The change in the second-order nonlinear susceptibility of an asymmetric quantum well (AQW) superlattice induced by ion beam-enhanced intermixing has been measured. The surface-emitted second-harmonic intensities radiated from implanted and masked areas of an AQW waveguide were measured and compared for incident wavelengths between λ=1480 and 1600 nm. Intermixing resulted in a 60 meV blueshift of the AQW band edge and a uniform suppression of the AQW second-order susceptibility, while the masked AQWs were unchanged.

Modification of the second‐order optical susceptibility in AlxGa1−xAs by ion‐beam induced amorphization

The optical second‐harmonic (SH) response of GaAs and Al0.6Ga0.4As bombarded with 1.2‐MeV energy As+ ions has been measured for doses ranging from 5×1012 to 2×1014 ions cm−2. The measured SH response vanishes at an ion dose of 2×1014 ions cm−2 as a result of ion induced amorphization. Thermal annealing at 600 °C greatly reduced the damage induced optical absorption, for λ=1.06 μm light, but had no effect on the SH susceptibility.

Photoluminescence spectra of trivalent praseodymium implanted in semi‐insulating GaAs

The photoluminescence spectrum of trivalent praseodymium, obtained by implantation and annealing of semi‐insulating GaAs, is reported. The photoluminescence spectrum, observed at 2, 10, 20, and 40 K, extends from 9716 to 4000 cm−1. Sharp lines are observed in groups centered at 9500, 7400, 6200, 5200, and 4500 cm−1. Nineteen 3HJ energy levels are identified from these data. Only one Pr3+ site is observed. These energy levels were fitted by a D4 crystal‐field model with a rms deviation of 64 cm−1. The zero phonon line at 4687.7 cm−1 is strongly coupled to the 62 and 79 cm−1 lattice phonons. All other groups show either a very weak coupling (6200 cm−1) or none to the lattice phonons.

Photoluminescence spectra of trivalent praseodymium implanted in semi-insulating GaAs

We have measured the photoluminescence (PL) spectrum of the Pr3+ ion implanted in semi-insulating GaAs. The sharp PL lines, attributed to transitions between 4f2 rare earth energy levels, extend from 9716 to 4000 cm-1. A fit of a crystal field Hamiltonian to energy levels derived from the data for D2d symmetry was obtained.