J. C. North

Differential etching of ion‐implanted garnet

A new technique for generating precise surface structures in single‐crystal garnet materials is described. The crystals are ion implanted in localized areas using photoresist as an implantation mask. The photoresist is removed and the crystals are etched in phosphoric acid. The damaged volumes produced by the ion implantation etch at a substantially greater rate than the undamaged material, thereby producing surface structures. Groove depth can be precisely defined and reproduced by controlling the implantation parameters: ion species, energy, and dose. Undercutting is minimal and etching conditions are not stringent. The method is superior to both standard chemical etching and ion milling. The process has been characterized for H, He, and Ne implantations. It is shown that the temperature dependence of the etching rates for damaged and undamaged material is the same. The increase in etching rate is proportional to the damage concentration. The etching rate profiles are therefore synonymous with the damage profiles produced by the implantation. Etching rates more than three orders of magnitude greater than that of undamaged material have been observed. The etching rates for the three elements used correlate fairly well with the theoretical nuclear stopping power, and the groove depths obtained correlate with the theoretical ion ranges. This method has been used to produce serrated edge grooves which serve as rails for magnetic bubble propagation in conductor‐groove bubble propagation circuits.

Ion Implanted Patterns for Magnetic Bubble Propagation

Localized ion implantation through photoresist masks has been used to produce rails which guide bubbles in garnet epitaxial films. Implantation expands the lattice so that the implanted regions are in lateral compression. In garnets with negative magnetostriction, these shallow regions have stress‐induced easy axes parallel to the film surface. Bubbles adhere to the edges of the implanted regions due to magnetostatic and magnetostrictive effects. Using overlaying conductor patterns, bubbles in these tracks have been propagated at frequencies up to 600 kHz. No harmful effects on mobility or coercivity have been observed and “hard bubbles” are suppressed under the implanted regions. Ion implantation also provides a new method of producing field‐access bubble propagation patterns directly in garnet films. The in‐plane magnetization in the implanted regions can be rotated by an in‐plane applied field. Bubbles in the underlying garnet follow the moving poles at the edges of the implanted regions. The implanted...

Optical and channeling studies of ion‐bombarded GaP

Below‐gap optical absorption, above‐gap reflectivity, photoluminescence, and He ion channeling backscattering measurements are reported for ion‐bombarded GaP. Each of the four experiments provides a measure of disorder. A one‐to‐one correspondence exists between the absorption, reflectivity, and backscattering measurements, and all three exhibit comparable sensitivity to damage. Photoluminescence is ∼ 100 times more sensitive. The absorption results suggest that every implanted ion species produces amorphous regions associated with each projectile and that these regions have properties very much like those of cold‐deposited amorphous films. The results are interpreted in terms of a model which ascribes these amorphous regions to localized melting followed by rapid quenching to a glassy (amorphous) state in which short‐range tetrahedral order remains intact. The damaged volume per bombarding ion as determined from absorption data is ∼6 times larger than that determined from channeling measurements. Althoug...

Nitrogen concentration in GaP measured by optical absorption and by proton‐induced nuclear reactions

A method is described for the determination of the nitrogen concentration in GaP crystals from optical absorption measurements. The method has been calibrated by measuring the absolute nitrogen concentration by nuclear reaction quantitative analysis in the same samples for which the optical absorption was measured. The relationships between the nitrogen concentration, the integrated absorption of the A line (2.3172 eV), and the optical absorption at Ax (2.3275 eV) at 4.2°K are given by [N] cm−3=8.5×1014∫αA d E=3.4 ×1016αAx, where α is measured in cm−1 and d E in meV. Previous formulas which have commonly been used to determine the nitrogen concentration in terms of optical absorption overestimate the nitrogen concentration by about a factor of 5. Also the application of these formulas has varied between laboratories. Section I describes the determination of nitrogen concentrations by nuclear microanalysis. Measurements have been made in the range from [inverted lazy s]5×1016 to [inverted lazy s]1018 cm−3 ...

A semi-insulated gate gallium-arsenide field-effect transistor

Proton bombardment has been used to make a semi-insulated gate gallium-arsenide field-effect transistor. This technique combines the simplicity of the metal semiconductor FET technique, the advantage of operating the device using positive as well as negative bias on the gate, and the possible use of higher conductivity material for the channel, which may result in a higher transconductance and a higher saturated current density.

Nuclear microanalysis of oxygen concentration in liquid‐phase epitaxial gallium phosphide

The total bulk oxygen concentration has been determined in GaP layers grown by liquid‐phase epitaxy. Layers were grown doped with 18O enriched oxygen, and the 18O concentrations were measured by detecting α particles emitted during proton irradiation using the nuclear reaction 18O(p, a)15N. The relative concentrations of 18O and 16O were determined from exciton luminescence of the LiI–LiGa–OP complex at 4.2°K after Li diffusion, thus enabling the total bulk oxygen concentrations to be determined. The total solid solubility of oxygen in GaP containing the optimum zinc concentration for efficient luminescence from Zn‐O nearest‐neighbor pairs, 5 × 1017 cm−3, ranged from [sine wave] 5 × 1016 cm−3 at [sine wave] 1040°C to [sine wave] 9 × 1016 cm−3 at ≳1100°C. Measurements on a layer doped with tellurium and oxygen failed to detect any 18O, indicating that the total oxygen concentration was probably < 4 × 1016 cm−3. The experimental results confirmed the presence of Ga2O3 coprecipitates when the oxygen added to...

Optical absorption in ion‐bombarded magnetic garnet films

Optical absorption measurements are reported for the damaged surface layers produced by proton and neon bombardment of iron‐garnet liquid‐phase‐epitaxial films. The excess optical absorption is shown to be an absorption tail on O(2p)→Fe(3d) charge‐transfer bands centered near 4 eV with about 10% contributed by higher‐energy optical transitions. The distribution of states for Ne bombardment is different from that for H bombardment, and in the case of Ne the state distribution depends on the dose. Saturation at a photon energy of 2.2 eV occurs at an absorption coefficient of ∼2×104 cm−1. The average damage density over the damaged layer thickness is observed to increase with decreasing H energy, in agreement with hard‐bubble‐suppression data and nuclear stopping power considerations. Based on optical absorption and hard‐bubble‐suppression results it is estimated that the dose window for hard bubble suppression corresponds roughly to an average disorder range from ∼3–30% amorphous (amorphous defined opticall...

Multijunction AC or DC integrated GaP light emitting diode array

An ac or dc GaP LED array has been designed and fabricated which has potential as a direct replacement for several tungsten filament lamps and as an illuminator for new design considerations. In designing such an LED for high-voltage application, series light emitting junctions rather than series resistors are used as a voltage divider to maximize the light output/power input ratio. A figure of merit is modeled and calculated which provides a measure of total light output for a given applied current and voltage as a function of the number of series diodes. The optimum number of series diode for a given ac voltage is Vrms/1.94. Thermal calculations based upon chip size, power dissipation, and thermal contact resistance predict a peak temperature rise of 30°C for the bonded die approach. n- and p-type liquid phase epitaxial layers were grown on semi-insulating substrates, p-n junctions on the same chip were electrically isolated utilizing either proton bombardment or chemically etched trenches. An Au metallization scheme provides the series-parallel interconnection required for ac or dc operation while maintaining junction isolation. The light emitting junction areas are mesas, with edges shaped to redirect internally generated light out to the viewer. The near field radiation pattern demonstrates the optical effectiveness of the shaped-mesa emitters.

Tapered windows in phosphorus-doped SiO 2 by ion implantation

Phosphorus-doped SiO2is frequently used as a dielectric coating in silicon integrated circuits. It is important that windows in this dielectric have sufficiently tapered walls so that the subsequent metallization has good step coverage. It is shown here that tapered windows can be made in both Nitrox-deposited ∼ 1-percent phosphorus-doped SiO2and Silox-deposited ∼ 7-percent phosphorus-doped SiO2as well as undoped SiO2by an ion implantation which produces a thin damaged layer at the top of the oxide. The damaged layer etches at a faster rate than the undamaged oxide. This fast-etching layer undercuts the photoresist which serves as the etching mask and results in window walls having slopes in the range of 30-40° with respect to the wafer surface. Tapering windows by ion implantation is a dependable process that gives reproducible results without having to rely on the art of photoresist liftoff methods.

Laser vaporization of metal films &#8212; Effect of optical interference in underlying dielectric layers

The interference of incident laser light with light reflected from dielectric interfaces is important in the completeness with which a laser beam vaporizes thin metal films, even though the dielectric layers lie underneath the metal film being vaporized. A structure consisting of titanium-platinum links on a two level dielectric consisting of silicon nitride and silicon dioxide on a silicon substrate was used to demonstrate the effect. The resistance of laser vaporized titanium-platinum links varied by more than seven orders of magnitude as the thickness of the silicon dioxide, the lower dielectric, was varied. The thicknesses of underlying dielectric layers are, therefore, parameters which must be taken into account when using a laser beam to produce high resistance open circuits in metal films.