R. D. Goldberg

Defect diffusion in ion implanted AlGaAs and InP: Consequences for quantum well intermixing

InGaAs/GaAs/AlGaAs and InGaAs/InGaAsP/InP laser structures, with InGaAs quantum wells approximately 1.85 μm beneath the surface, were implanted with ions having energies up to 8.6 MeV. Intermixing of the quantum wells, after rapid thermal annealing, was monitored through changes in the energy, linewidth, and intensity of the photoluminescence peak from the quantum wells. Where the defects had to diffuse primarily through Al0.71Ga0.29As, these quantities correlate strongly, for short anneal times, with calculated vacancy generation and ion deposition at the depth of the quantum well prior to annealing. This suggests that the defect diffusion length in the AlGaAs and/or GaAs is quite low. For diffusion primarily through InP, the photoluminescence data correlated well with the calculated total number of vacancies created in the sample, suggesting that defect diffusion is very efficient in InP.

Enhanced degradation resistance of quantum dot lasers to radiation damage

We compare the degradation of InAs/GaAs quantum well (QW) and quantum dot (QD) laser diodes following irradiation by high energy (8.56 MeV) phosphorous ions. Over a fluence range of 108–1011 ions/cm2, the degradation of the low temperature QD photoluminescence and electroluminescence emission is greatly suppressed relative to that of QW based devices (×100 and ×1000, respectively at the highest dose studied). Irradiated QD laser diodes demonstrated lasing action over the entire range of fluences, and 2 orders of magnitude beyond the maximum dose sustainable by QW devices. The improved damage response of QD based structures results from efficient collection and localization of electrons and holes by QDs in the active region, which limit carrier transfer to nonradiative centers. This work suggests the suitability of QD device architectures for use in radiation environments, and in high power applications, wherever nonradiative processes promote the degradation or failure of traditional QW devices.

Band‐gap tuning of InGaAs/InGaAsP/InP laser using high energy ion implantation

The technique of ion‐induced quantum well intermixing using broad area, high energy (1 MeV P+) ion implantation has been used to tune the emission wavelength of an InGaAs/InGaAsP/InP multiple quantum well (MQW) laser operating at 1.5 μm. The optical quality of the band‐gap shifted material is assessed using low‐temperature photoluminescence (PL). The band‐gap tuned lasers are characterized in terms of threshold current density and external quantum efficiency and exhibit blue shifts in the lasing spectra of up to 63 nm. This approach offers the prospect of a powerful and relatively simple fabrication technique for integrating active as well as passive optoelectronic devices.

ENHANCED GROUP-V INTERMIXING IN INGAAS/INP QUANTUM WELLS STUDIED BY CROSS-SECTIONAL SCANNING TUNNELING MICROSCOPY

Cross-sectional scanning tunneling microscopy is used to study InGaAs/InP quantum-well intermixing produced by phosphorus implantation. When phosphorus ions are implanted in a cap layer in front of the quantum wells (in contrast to earlier work involving implantation through the wells), clear strain development is observed at the interfaces between quantum well and barrier layers after annealing. This is interpreted in terms of enhanced group-V compared to group-III interdiffusion.

Polarization insensitive InGaAs/InGaAsP/InP amplifiers using quantum well intermixing

A polarization insensitive optical amplifier based on a lattice matched InGaAs/InGaAsP/InP multiple quantum well (MQW) laser structure operating at 1.5 μm has been fabricated through vacancy enhanced quantum well intermixing using broad area, high energy (1 MeV P+) ion implantation. A simple model shows that if the interdiffusion rate of the anions is larger than that of the cations, the blue shift in the ground state heavy hole transition energy after implantation and annealing is greater than the light hole state blue shift, bringing the two bands together. Current–voltage measurements indicate that junction characteristics are well maintained after implantation. This simple technique for fabricating polarization insensitive optical amplifiers is readily extended to the monolithical integration of such devices along with other passive and active optoelectronic devices and opens the door to practical photonic integrated circuits.

Chemical information in positron annihilation spectra

Positron annihilation spectra of arsenic‐ and gold‐implanted silicon are compared with spectra from bulk samples of arsenic and gold. Spectra with strongly reduced background intensities were recorded using a two detector coincidence system with a variable‐energy positron beam. It is shown that features in the high‐momentum region of the spectra (∼514–520 keV) can be identified with particular elements and that this identification is independent of structure, i.e., whether the element forms the bulk or is an implanted impurity. Proportionality between the intensity of characteristic spectral features and the fraction of annihilating positrons is also demonstrated, using the native oxide on a silicon wafer as a test case.

HIGH-RELIABILITY BLUE-SHIFTED INGAASP/INP LASERS

InGaAsP/InP quantum well (QW) ridge waveguide lasers emitting nominally at 1310 nm have been ‘‘blue‐shifted’’ selectively (as much as 70 nm) on a full 50‐mm‐diameter wafer after growth. P+ ion implantation at 1 MeV, 200 °C through a variable thickness SiO2 mask was used to induce various degrees of QW intermixing after postimplantation annealing at 700 °C. Irrespective of the amount of intermixing induced (blue shift), all fabricated devices exhibited 20–25 mA lasing threshold current and 0.25–0.30 W/A differential quantum efficiency. Device reliability was equivalent to standard (nonimplanted) lasers when the wavelength shift was 35 nm or less, corresponding to predicted lifetime in excess of 25 years while operating cw at 25 °C. The performance and reliability data clearly indicate that the concentration of residual defects introduced in the active region by the implantation/annealing process is negligibly small. The present results, which are a product of a straightforward fabrication process, suggest ...

Secondary defect formation in self-ion irradiated silicon

Abstract A detailed experimental study has been made of the evolution of extended secondary decondary defects which form during rapid thermal anneals of 0.5 MeV energy self-ion irradiated silicon. The implant fluence (2 × 10 15 ions/cm 2 ), flux and substrate temperature (91°C) were chosen so that primary damage levels were well below saturation. Cross-sectional transmission electron microscopy (X-TEM), Rutherford backscattering-channeling spectroscopy (RBS-C) and variable-energy positron annihilation techniques (VEP) have been used to allow partial discrimination between vacancy- and interstitial-type defects. The growth and development of the defect band and of specific types of extended defects within the band has been followed up to anneal temperatures of 1000°C, where the majority are shown to have dissipated. X-TEM has revealed the formation of a previously unreported tubular defect which is found in a narrow temperature range of 700–765°C. The occurrence of this defect correlates with the positron annihilation analysis which shows that a small concentration of defects with vacancy character is present after annealing in the same temperature range. In addition, positron annihilation analysis has allowed an assessment of the role played by defects lying in regions appearing defect-free by the other techniques (RBS-C and TEM). The implications of these findings to existing models involving secondary defect production are discussed.

Dynamic Annealing and Amorphous Phase Formation in Si, GaAs and AlGaAs Under Ion Irradiation

Ion damage processes and amorphous phase formation are compared in Si, GaAs and Al x Ga 1-x As materials in the critical regime where dynamic defect annealing is strongly competing with ion damage production. It is shown that the nature of residual damage is very strongly dependent on temperature, ion dose and dose rate in this critical regime for both Si and GaAs and that the amorphous phase can be “nucleated” by high levels of extended defects. In Al x Ga 1-x As, the amorphous phase is increasingly more difficult to nucleate with increasing Al concentration at LN 2 temperature but can be nucleated at sufficiently high implantation doses for all Al concentrations. No dose rate effect is observed for Al x Ga 1-x As. This behaviour is discussed in terms of the availability of mobile defects and bonding configurational changes during irradiation.

Bandgap tuning of semiconductor Quantum Well laser structures using high energy ion implantation

Abstract Ion implantation induced Quantum Well (QW) intermixing using high energies (2 to 8 MeV As+ and P+) has been shown to be an effective technique for achieving spatially selective tuning of QW laser structures ( InGaAs GaAs and InGaAs InP ). Work illustrating the effects of ion dose, energy, current density and implant temperature is presented for the InGaAs GaAs QW laser structure, using photoluminescence as a diagnostic tool to help optimise these parameters. This work is then extended to the InGaAs InP QW laser structure where significant differences are observed, in particular concerning the ion implantation depth relative to the depth of the QWs.