R. G. Hunsperger

Channel optical waveguide directional couplers

We report the first demonstration of channel optical waveguide directional couplers. The closely spaced channel waveguides were fabricated in GaAs by proton implantation. Optical coupling was observed at 1.15 μ with complete light transfer out of the initial channel into adjacent channels in lengths of typically 2 mm.

Optical waveguiding in proton-implanted GaAs

We have produced optical waveguides in n‐type GaAs by implantation with 300‐keV protons. The guiding is shown to be due to the elimination of charge carriers from the implanted region. Annealing of the waveguide leads to very large reductions in the 1.15‐μ guided‐wave absorption.

Parallel end-butt coupling for optical integrated circuits

The method of parallel end-butt coupling has been used to couple GaAs laser diodes to Ta (2)O(5) thin film waveguides. Theoretical caluclations predict that a coupling efficiency into the lowest order waveguide mode of 90% is achievable if the thicknesses of the waveguide (t(g)) and the laser light emitting layer (t(L)) are equal. Experimentally, efficiencies as high as 45.1% have been measured for laser and waveguide combinations with t(g)/t(L) = 0.34. The tolerance to misalignment of the laser and waveguide has been theoretically and experimentally evaluated.

Channel Optical Waveguides and Directional Couplers in GaAs–Imbedded and Ridged

Two-channel imbedded directional couplers were fabricated with proton implantation, yielding complete light transfer in 2 mm. Ridged channel guides were fabricated by ion-micromachining epitaxial layers, and a method of directional coupling was demonstrated.

Proton‐implanted optical waveguide detectors in GaAs

Defect levels introduced by implanting GaAs with high-energy protons give rise to optical absorption at wavelengths greater than that of the normal absorption edge at 0.9 µ. Optical waveguide detectors may be fabricated by taking advantage of this absorption mechanism in the presence of a Schottky barrier depletion layer. Detector response times less than 200 ns and external quantum efficiencies of 16% have been observed.

The Presence of Deep Levels in Ion Implanted Junctions

It has been found that ion implantation doping results in the generation and diffusion of defect species, forming deep trapping levels. The effect of these levels on the electrical characteristics of zinc‐implanted GaAs diodes has been observed for the case of 70‐kV implantation at 400°C into substrates with n‐type concentrations ranging from 1 × 10^16 to 1.8 × 10^18 atoms/cm^3. Capacitance‐voltage measurements have indicated the presence of a semi‐insulating layer in the diodes, varying in thickness from 0.18 μ for the most heavily doped substrate to 2.7 μ for the lightest. Frequency dependence of the junction capacitance and power law variation of forward current vs voltage have also been observed and are attributed to deep levels.

MEASUREMENT OF ION IMPLANTATION LATTICE DAMAGE IN (111) GaAs USING THE SCANNING ELECTRON MICROSCOPE

We have measured the Coates‐Kikuchi pattern degradation of (111) GaAs in the 5‐ to 30‐keV incident electron energy range as a function of 60‐keV cadmium ion dose (1012 to 1015 Cd+/cm2) at room temperature. Pattern degradation is greater for a given dose at 5‐keV than it is at 30‐keV incident electron energy. Agreement is found between the pattern degradation and measurements of lattice disorder as determined by backscattering of 1‐MeV helium ions. Annealing of the ion‐bombarded samples at temperatures up to 450°C restores the Coates‐Kikuchi pattern quality as the lattice damage is reduced.

EFFECT OF ION‐IMPLANTATION DAMAGE ON THE OPTICAL REFLECTION SPECTRUM OF GALLIUM ARSENIDE

Optical (3–6 eV) reflectivity spectra of Cd+‐implanted layers of GaAs are examined as functions of dose in the range of 1012 to 8×1014 ions/cm2 and of annealing up to 600°C. Characteristic peaks in the crystalline spectrum decrease smoothly with dose, with some saturation observed at about 6×1013/cm2. Annealing tends to partially restore the spectra toward the crystalline form. Similarity with results for implanted silicon layers is noted. Reflectivity and observations of lattice damage by Rutherford scattering are correlated.

Ion‐implanted GaAs injection laser

Ion implantation has been used as a doping technique to fabricate an injection laser in GaAs. The dopant atom is Zn. At 77 °K the threshold current density is 2×103 A/cm2.

Ga1−xAlxAs Produced by Al+ Ion Implantation of GaAs

GaAs has been converted to Ga1−xAlxAs by implanting GaAs substrates with 30‐KeV Al+ ions and subsequently annealing at 900 °C. The maximum ion dose used was 2×1016/cm2, corresponding to a calculated peak concentration of approximately 1022 Al atoms/cm3. The emission spectra of electroluminescent diodes formed in the material were measured.