Mark N. Ruberto

The Laser‐Controlled Micrometer‐Scale Photoelectrochemical Etching of III–V Semiconductors

Laser-controlled photoelectrochemical etching of III-V semiconductors using micrometer-sized illumination regions has been investigated for varying laser parameters (power, spot size, wavelength) and etching solutions. The etching has been applied to a wide variety of semiconductor doping types. The micrometer spot size of the laser can induce higher etch rates for a given intensity when compared to broad illumination. In addition, the process has micrometer-scale resolution and highly directional etch anisotropy. In this electroless process the laser etching rate is influenced by light-induced voltage shifts in the surface potential. Finally, the dependence of the process resolution on carrier diffusion and etch depth is discussed

Laser fabricated GaAs waveguiding structures

We have applied the technique of laser‐induced etching to fabricate rib waveguides on a GaAs/AlGaAs heterostructure system. Light confinement of these guides was controlled by varying the depth of the etched trenches. Additionally, we have demonstrated directional couplers and two‐level waveguides using the in situ depth control of this single‐step process.

Laser-fabricated low-loss single-mode waveguiding devices in GaAs

A maskless laser etching technique was used to fabricate novel waveguides and waveguiding structures directly into the surface of GaAs/AlGaAs heterostructures. The modal and loss properties of these groove-defined structures have been measured as a function of waveguide geometry, and low-loss single-mode waveguides have been produced. The technique was used to fabricate various passive optical devices in a single processing step. Waveguide bend and branch losses were measured and are comparable to those in conventionally fabricated devices. Experimental results are described by simple theoretical models. The technique is attractive as a prototyping tool for developing and testing new integrated optic circuits. >

Graded-effective-index waveguiding structures fabricated with laser processing

The technique of laser direct-writing was used to fabricate low-loss, rib-like waveguides on GaAs/A1GaAs material. Since this is a inaskless fabrication process, laser-etched structures such as bends, tapers, and Y-branches are readily demonstrated. The ability to smoothly control the etch depth, and thus the effective index of refraction across the wafer, was used to make a compact directional coupler. Finally, the reduction of losses in waveguide tapers and bends by grading the effective index will be discussed.

Effect of carrier confinement on the laser-induced etching of GaAs/AlGaAs heterostructures

Laser‐induced photochemical etching was used to etch GaAs/AlGaAs multilayered material. In this carrier‐driven process, the confinement of photogenerated holes to the alternating GaAs layers resulted in the controlled lateral etching of buried GaAs layers. An application of this etching technique to forming microcleaved laser facets is described.

Rapid direct fabrication of active electro-optic modulators in GaAs

We have developed several direct-write laser processing techniques to masklessly fabricate prototypes of waveguiding devices in GaAs/AlGaAs substrates. This flexible technology allows the rapid, successive fabrication and testing of devices such as modulators. Previously, we had reported use of this technology to fabricate low-loss single-mode passive waveguiding structures and devices. In this paper, we report the fabrication of active electro-optic modulators. These devices include an electro-optic polarization modulator, an integrated amplitude modulator consisting of a polarization modulator and an on-chip polarizer, and an integrated Mach-Zehnder interferometer. >

Factors controlling resolution in the laser‐induced aqueous etching of semiconductors using a focused cw beam

We present a study of selected factors which can control or improve the resolution of light‐induced wet etching of semiconductors; specifically we examine the case of a focused Gaussian cw laser beam. The results have important implications for the recent application of the technique to the maskless fabrication of integrated optic device structures. Factors considered include semiconductor doping, solution composition, laser intensity, and the effect of applied bias. Results are discussed in the context of hole diffusion and drift in the semiconductor and transport through the solution/semiconductor interface.

Laser Processing of Integrated Optical Components

The current optoelectronics industry is hleaded toward increasing integration of a large number of passive and active components onto a single substrate. We discuss in this paper our technique for the maskless, laser-based fabrication of integrated optical components.“2 The process uses a focused laser beam to photoelectrochemically etch micrometer-scale grooves in GaAs/AlGaAs heterostructures, thereby patterning rib-like optical waveguide structures. The technique can be used as a prototyping tool for developing and testing new integrated optic circuits, and unique characteristics of the process offer the potential for fabricating novel integrated optic device structures.