S. A. Pappert

Photoelastic waveguides and the controlled introduction of strain in III‐V semiconductors by means of thin film technology

We have investigated the use of thin film technology to introduce controllable and thermally stable stress into semiconductor heterostructures. Two simple schemes are used. The first scheme is to use interfacial reactions between a metal and the substrate, such as Ni, Co, Pd, and Pt on GaAs/AlGaAs. The induced stress in the structure is reproducible and controllable because the volumetric change for a given reaction is fixed, as long as the deposited film is fully reacted to form a compound. The stability of the stress depends on the stability of the compound. In the case of Ni and Co on GaAs/AlGaAs, the induced stress is thermally stable up to 600 °C. Evaporated films and reacted films are usually under tension. The second scheme is to use rf sputtered W or WNi alloy films where W or WNi is sputtered onto a negative dc biased substrate. This scheme effectively provides highly compressed films. The thermal stability depends on the concentration of Ni in the WNi alloy. Using the two schemes above, we have ...

Ion mixing of III‐V compound semiconductor layered structures

Compositional disordering of III‐V compound superlattice structures has received considerable attention recently due to its potential application for photonic devices. The conventional method to induce compositional disorder in a layered structure is to implant a moderate dose of impurity ions (∼1015/cm2) into the structure at room temperature, followed by a high‐temperature annealing step (this process is referred to as IA here). Ion irradiation at room temperature alone does not cause any significant intermixing of layers. The subsequent high‐temperature annealing step tends to restrict device processing flexibility. Ion mixing (IM) is capable of enhancing compositional disordering of layers at a rate which increases exponentially with the ion irradiation temperature. As a processing technique to planarize devices, ion mixing appears to be an attractive technology. In this work, we investigate compositional disordering in the AlGaAs/GaAs and the InGaAs/InP systems using ion mixing. We found that the ion...

Laser spectral linewidth dependence on waveguide loss measurements using the Fabry–Perot method

The critical role of the optical source spectral linewidth in semiconductor low loss waveguide measurements using the Fabry–Perot resonance method is analyzed. For 5‐mm‐long GaAs/AlGaAs waveguides with losses in the 1 dB/cm range, a frequency stabilized single mode laser with a linewidth of less than 0.01 A is required to obtain a loss value accurate to within 5%.

Photoelastic waveguides formed by interfacial reactions

The fabrication of low‐loss photoelastic waveguides in GaAs/AlGaAs layered structures by thin film reactions is investigated. The waveguides are formed by opening a narrow window stripe, a few microns wide, in an otherwise continuous Ni layer under tension deposited on a semiconductor structure. The local tensile stress induced by the Ni layer in the semiconductor causes the local refractive index to increase, thus providing the guiding mechanism. Annealing the sample at 250 °C for 1 h induced an interfacial reaction between the Ni film and the substrate to form Ni3GaAs. The formation of an interfacial compound stabilizes the stresses, making the stress state independent of the deposition system and technique. Single‐mode waveguide propagation losses as low as 1.4 dB/cm at 1.53 μm wavelength have been obtained on annealed waveguides. Further annealing up to 600 °C did not cause degradation in the optical confinement, thus indicating a thermally stable planar waveguide fabricated by this process. Other pho...

Simultaneous disordering and isolation induced by ion mixing in InGaAs/InP superlattice structures

The phenomenon of simultaneous compositional disordering and the formation of electrical resistive layers induced by oxygen implantation in InGaAs/InP superlattices has been investigated. The disordering characteristics have been studied as a function of implantation temperature and ion dose. It was found that implantation at elevated temperatures (referred to as the IM or ion mixing process) usually leads to much more efficient disordering compared to implantation at room temperature followed by annealing at the same elevated temperature (referred to as the implantation plus annealing process). Of particular interest is the observation that ion mixing at 550 °C with 1×1013 O+/cm2 leads to significantly more disordering than implantation with the same dose at room temperature followed by annealing at 550 °C for the same period of ion mixing time. In addition, the electrical resistance of the ion‐mixed layer at 550 °C increases 2600 times for the p‐type InGaAs/InP superlattice structure, whereas the sample...

Planar, low‐loss optical waveguides fabricated by solid‐phase regrowth

Planar, low‐loss AlGaAs/GaAs waveguides have been fabricated using the solid‐phase regrowth (SPR) process. Single‐mode waveguide with a propagation loss as low as 1.6 dB/cm have been obtained. This process requires only thin‐film deposition and low‐temperature short‐duration annealing (i.e., 650 °C for 30 s), thus making the SPR method a much simplified technique to induce compositional disordering. Simultaneous electrical isolation and compositional disordering are also demonstrated with the SPR process.

Compositional disordering by solid phase regrowth

The principle of solid phase regrowth (SPR)has been used to induce compositional disordering in AlGaAs/GaAs superlattice structures in the temperature range of 400 °C (30 min)–650 °C (30 s) as compared to the conventional diffusion method in the temperature range of 600–850 °C for hours. The SPR process is simple to implement, requiring only thin‐film deposition and annealing. The crystal quality as well as the photoluminescence signals emerging from the disordered region generally improve with increasing processing temperature. The simplicity, the low process temperature, and the short process duration of the SPR technique are distinct advantages for optoelectronic applications, especially for self‐aligned devices.

Planar 1.3 and 1.55 μm InGaAs(P)/InP electroabsorption waveguide modulators using oxygen ion mixing and the photoelastic effect

Efficient 1.3 and 1.55 μm InP‐based electroabsorption waveguide modulators with planar device structures have been demonstrated. Elevated temperature oxygen ion implantation and/or the photoelastic effect induced by W metal stressor stripes deposited on the semiconductor surface have been used to produce these self‐aligned planar guided‐wave devices. The oxygen ion mixing process has been used to simultaneously achieve compositional disordering and electrical isolation of superlattice material while the photoelastic effect has been used to improve the lateral mode confinement. A 1.3 μm Franz–Keldysh modulator with a ≳10 dB extinction ratio at 2 V and a 1.55 μm device with a ≳10 dB extinction ratio at 7 V are reported. These single growth step planar processing techniques have also been used to fabricate relatively low‐loss (<4 dB/cm) double heterostructure InGaAs(P)/InP single‐mode optical waveguides which demonstrate their usefulness in developing InP‐based photonic integrated circuits.

High speed and high saturation power electroabsorption modulator for analog transmission

A high speed electroabsorption modulator (EAM) with high saturation optical power is desirable for analog fiber link applications, as the link gain increases quadratically with the optical power. EAMs with multiple-quantum-well (MQW) active layers are popular photonic applications. In this paper we also discuss the design and fabrication of the traveling wave (TW) electrode for the InGaAs QW EAM for high speed (>40 GHz) operation.

Planar InGaAsP/InP photoelastic waveguides with low propagation loss

Abstract Planar, low-loss double heterostructure InGaAsP/InP waveguides have been fabricated employing the photoelastic effect induced by metal stressor stripes deposited on the surface of the semiconductor structure. Single-mode guiding is observed in regions beneath a window stripe in an otherwise continuous Ni film deposited on the waveguide structure (type A), or in regions beneath a narrow stripe of W film sputtered on the waveguide structure (type B). The lowest measured propagation loss is 2.0 dB/cm for the type A and 3.5 dB/cm for type B waveguides at the 1.52 μm optical wavelength. The lateral waveguiding depends on both the annealing temperature and the semiconductor layer structure beneath the metal. Both types of waveguides on InP/InGaAs/InP maintain low loss, single mode guiding for temperature ≤ 300°C. Preliminary planar photoelastic optical devices such as splitters and couplers have also been demonstrated.