J. L. Merz

Beam divergence of the emission from double‐heterostructure injection lasers

Far‐field emission patterns of GaAs–AlxGa1‐xAs double‐heterostructure lasers have been measured to determine the dependence of the beam divergence as a function of active layer thickness d and composition x. The beam divergence in the plane of the junction θ∥ is ∼ 10°, while the beam divergence perpendicular to the junction plane θ⊥ is considerably larger and depends strongly on d and x. Curves are given for θ⊥ and the confinement factor Γ as a function of d between 0.05 and 2.0 μ for x = 0.1, 0.2, 0.3, and 0.4. These curves were calculated by considering the laser as a dielectric waveguide with a refractive index step between GaAs and AlxGa1−xAs.

GaAs double heterostructure lasers fabricated by wet chemical etching

GaAs double heterostructure lasers compatible with monolithic intergration of optical devices have been fabricated by wet chemical etching. Results for a variety of laser orientations are reported. External differential quantum efficiencies as high as 18% have been achieved, as well as threshold current densities as low as 4.2 kA/cm2. An analysis for the evaluation of etched‐mirror properties is presented. Using this analysis, it was found that etched mirrors had reflectivity R?0.22±0.05 and scattering losses S=0.3±0.1.

Study of intensity pulsations in proton‐bombarded stripe‐geometry double‐heterostructure AlxGa1−xAs lasers

The pulsations in the laser emission from several lasers have been studied as a function of temperature, cavity length, external mirror illumination, and effect of mirror etching. Selected DH lasers with 12‐μm‐wide stripes delineated by proton bombardment and 380‐μm‐long cavities were used. The modulation depth of the pulsations at 300 °K increases approximately linearly with current above a threshold value and becomes fully modulated at high output powers. At intermediate temperatures, the modulation exhibits a similar initial slope but is not complete at the highest measured output. At low temperatures, well‐developed pulsations are not observed; the modulation reaches a maximum at a low amplitude level and then decreases. The frequency dependence of the pulsations indicates that when the modulation level is increasing, the frequency f is relatively constant, and above the maximum moduation f 2 increases approximately linearly with output power. The dependence on cavity length was studied using a series...

Preparation and Optical Properties of AlxGa1−xP

Aluminum‐doped GaP has been grown from solution with concentrations up to 30% Al. The crystals are stable and do not corrode in air. Evidence that the system is forming an Al–Ga alloy is provided by an observed shift of the absorption edge and photoluminescence from those of GaP by 0.10 eV to higher energies. The green photoluminescence peaking at 2.306 eV (4.2°K) is studied and identified as pair emission. A weak band at 1.92 eV is also seen, analogous to the highly efficient Zn–O red band at 1.82 eV in Al‐free GaP. The implications of this shift in photoluminescence energy are discussed.

Loss measurements in GaAs and AlxGa1−xAs dielectric waveguides between 1.1 eV and the energy gap

Loss measurements in thick dielectric slab waveguides of GaAs cladded by AlGaAs liquid‐phase‐epitaxy layers have been made utilizing spontaneous Raman scattering. In these experiments, incident radiation at 1.06 μm is focused onto a cleaved edge of the waveguide layer and Raman‐scattered photons are detected at 90°. The attenuation of the resulting signal is measured as a function of the propagation distance along the guide. Spatial resolution of 0.2–0.5 mm has been achieved for samples 3–5 mm long. Results are reported for a variety of GaAs waveguide layers, including lightly doped p‐type layers, n‐type layers varying between 1016 and 1018 cm−3, and AlxGa1−xAs waveguide layers with x?0.1. For waveguides with impurity concentrations above the mid‐1017 cm−3 range, the loss is dominated by free‐carrier absorption, but for relatively pure layers of GaAs and AlGaAs a residual loss well below 1 cm−1 is observed. Transmission measurements as a function of photon energy between 1.1 eV and the energy gap of the m...

Photoluminescence of Ion‐Implanted Oxygen in ZnTe

Photoluminescence from the oxygen isoelectronic trap implanted into ZnTe is investigated for various ion doses and annealing conditions. The characteristic oxygen spectrum is observed after annealing either in zinc vapor or in vacuum. The anticipated isotope shift is observed in the spectrum for samples implanted with 18O without the usual 16O contamination found in conventionally doped samples. In isochronal anneal studies the intensity of the oxygen luminescence peaks at 300°–400°C. For samples annealed in Zn vapor the anneal curves show a slight dip at higher temperatures, whereas for vacuum anneals the curves fall off rapidly. The dose for maximum luminescence is found to be a function of the anneal temperature. Much of the gross lattice damage is annealed at 500°C; at this temperature the luminescence peaks at a dose of ∼1014 ions/cm2, corresponding to an implanted concentration of ∼2×1018/cm3. Although reasonable luminescence intensities have been achieved, compared with conventionally doped samples...

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...

GaAs double-heterostructure photodetectors

AlxGa1−xAs‐GaAs structures grown by LPE have been investigated for optical power conversion at 8500 A. Comparison is made between single‐ and double‐heterostructure configurations, both in theory and experiment; relative merits of each structure are discussed. Good I‐V characteristics have been realized for these devices, with series resistance as low as 0.16 Ω. For small‐area (5–6 mm2) devices operating at a few mW power, fill factors between 0.75 and 0.81 and internal quantum efficiencies exceeding 90% have been achieved for each structure investigated. Power conversion efficiencies as high as 46% were obtained at 8500 A, after correcting for reflection losses; this approaches the theoretical limit for space‐charge‐limited devices. The devices were also evaluated as solar batteries, with efficiencies of 13–14% reported, corresponding to internal efficiencies as high as 18%.

Loss measurement in p‐type GaAs dielectric waveguides using Raman scattering

Raman scattering measurements have been made to determine losses in p‐type GaAs slab waveguides cladded by Al0.3Ga0.7As epitaxial layers. For these measurements, 1.064‐μm laser light is focused onto a cleaved edge of the waveguide layer and the Raman‐scattered photons are detected at 90°. The attenuation of the resulting signal is measured as a function of the propagation distance along the waveguide. Five Ge‐doped waveguide layer samples, ranging in concentration from 3×1016 to 3×1018 cm−3, were measured. Results are reported for samples 3–5 mm long having layer thicknesses of ∼5–6 μm. Losses from 0.8 to 12.2 cm−1 have been measured. Comparison is made with earlier results in n‐type GaAs.

Raman Scattering Technique to Evaluate Losses in GaAs Dielectric Waveguides

Loss measurements in dielectric slab waveguides of GaAs cladded by AlGaAs epitaxial layers have been made utilizing spontaneous Raman scattering. In these experiments, incident radiation at 1.06 μm is focused onto a cleaved edge of the waveguide layer and Raman-scattered photons are detected at 90°. The attenuation of the resulting signal is measured as a function of the propagation distance along the guide. Spatial resolution of 0.2 to 0.5 mm has been achieved for samples 3 to 8 mm long. Losses from 0.25 to 8.8 cm−1 have been measured to ±0.1 cm−1. The experimental technique is described in detail, and its use illustrated by results obtained for a variety of GaAs waveguide layers.