G.L. Christenson

Long-wavelength resonant vertical-cavity LED/photodetector with a 75-nm tuning range

A design for a highly tunable long-wavelength LED/photodetector has been investigated. The device consists of a GaAs-based distributed Bragg reflector (DBR) that is wafer-bonded to InP-based active layers, with a surface-micromachined tunable top DBR mirror to produce the wavelength shift. A 1.5-/spl mu/m device has been fabricated with a continuous tuning range of 75 nm. An extinction ratio of greater than 20 dB existed across the entire tuning range.

Overcoming the pseudomorphic critical thickness limit using compliant substrates

We demonstrated the high‐quality molecular beam epitaxy growth of exceedingly thick In0.14Ga0.86As pseudomorphic layers on thin, free‐standing, compliant GaAs substrates. We first fabricated 800‐A‐thick compliant platforms before growing a lattice‐mismatched layer on the platform. The layer we grew exceeds its usual critical thickness by about twenty times without strain relaxation. X‐ray analysis confirms a shift in the InGaAs peaks grown on the compliant substrate, indicating an unrelaxed strain of 0.9%. Moreover, atomic force microscope profiles verify that layers grown on compliant substrates are much smoother than layers grown on a plain substrate.

Wafer bonding technology and its optoelectronic applications

This paper describes the wafer bonding technology and its applications to optoelectronic devices and circuits. It shows that the wafer bonding technology can create new device structures with unique characteristics and can form integrated optoelectronic circuits containing optical, electronic and micro-mechanical devices.

Integrated micro-optical interferometer arrays

Surface micromachining is an emerging technology that has rapidly found its applications in optoelectronics and micro-optics. Micromachining technology will become even more attractive to optical applications if micromechanical devices can be treated as readily available add-on structures to photonic devices such as lasers, detectors, and modulators for new functionalities. Recently, we have developed a low temperature, low stress surface micromachining process that has such features. Using this technology, we fabricated micromachined Fabry-Perot tunable filters and integrated them with various optical devices operating at 1.3/1.55 micron wavelength regimes.

Optical reading and writing on GaAs using an atomic force microscope

Optically aided reading and writing of gold and tungsten mounds on proton‐implanted, multiple quantum well InGaAs/GaAs wafers has been demonstrated using an atomic force microscope (AFM). The system is relatively simple, requiring only a diode laser as the light source, providing a novel, compact, optoelectronic memory system.

Surface micromachined long wavelength LED/photodetector with a continuous tuning range of 75 nm

We have investigated a new design for a highly tunable, vertical cavity, long wavelength LED/photodetector. A device operating at 1.5 /spl mu/m has been built with a tuning range spanning 75 nm, with an extinction ratio of greater than 20 dB throughout the tuning range. The device is composed of a bottom GaAs/AlAs distributed Bragg reflector (DBR) that is grown on a GaAs substrate, an InP-based active gain region, and a surface micromachined tunable top DBR mirror. The top mirror is suspended in air above the active region by selectively removing a sacrificial polyimide layer while leaving side posts intact to support the structure. A laser driver supplies the current to the active region, which results in light output from the top side of the device. A voltage can then be applied between the suspended top mirror and the contact to the InP-based active region, resulting in an electrostatic attraction between the mirror and the base structure. This causes the top mirror to move towards the active region, thus decreasing the Fabry Perot cavity length, and altering the output wavelength of the device. The device has potential applications in optical interconnects and communications.

Wafer bonding technology and its applications in optoelectronic devices

The new optoelectronic integrated technology--wafer bonding is described. The results of wafer bonding and applications in several new types of optoelectronic devices are presented.

Surface-micromachined tunable resonant cavity LED using wafer bonding

Surface micromachining and wafer bonding techniques have been integrated to fabricate a dual-use resonant cavity tunable LED/photodetector operating at 1.5 micrometers . The device has a tuning range of 75 nm, and a spectral linewidth of 4 nm, with an extinction ratio of greater than 20 dB throughout the tuning range. The device has potential applications in WDM networks and optical interconnects due to the small physical size, beam profile, and wafer-scale fabrication and testing possibilities. A GaAs/AlAs distributed Bragg reflector (DBR) is integrated with an InGaAsP strain-compensated multiple quantum well gain medium using wafer bonding. The InGaAsP material with a central wavelength of 1.52 micrometers is grown lattice-matched on an InP substrate. After wafer bonding, the InP substrate is removed, leaving the active layers on the GaAs-based mirror and substrate. The top DBR mirror of the resonant cavity is formed using surface micromachining techniques. The mirror consists of a 4 5 pair S1/S1O2 DBR and a T1/W support and contact layer. These materials are deposited on a sacrificial polymide layer above the InP-based gain medium. The polymide is selectively etched to release the membrane, creating an air gap between the top mirror and the epitaxial layers. When a voltage is applied between these two layers, the membrane is deflected towards the substrates, changing the Fabry-Perot cavity length, and causing a corresponding change in the resonance wavelength of the device. The device functions as a resonant cavity photodetector by reverse biasing the multiple quantum well region. The absorption bandwidth and wavelength running are identical to the emission characteristics of the same device when used as an LED.

Tunable long wavelength LED using wafer bonding and micromachining technologies

We have combined the technologies of wafer bonding and micromachining to produce a tunable LED at 1.51 /spl mu/m. The bonding technique allows us to combine an InP-based multiple quantum well structure with a GaAs-based Bragg mirror for higher reflectivity than traditional InP-based mirrors. Micromachining techniques then allow us to suspend a mirror above the surface of the substrate to provide a tuning method for the LED.

New optical readout technique for ultra-high capacity information storage using microelectromechanical tips

Ultra-high capacity information storage is a goal pursued by many researchers in the fields of optical computation and optical signal processing. We present for the first time a new optical technique combining electro-optic probing and micromechanical tips to perform the readout and writing for an ultra-high capacity memory. Potentially, this technique could achieve a storage density of 1 Terabit/cm/sup 2/.