William J. Mosby

The relative Raman cross sections of vitreous SiO2, GeO2, B2O3, and P2O5

We report the relative HH Raman spectra obtained from high‐purity bulk samples of the primary glass formers SiO2, GeO2, B2O3, and P2O5. With 514.5‐nm excitation, the peak Raman cross sections of these glasses have relative strengths of 1, 9.2, 4.7, and 5.7, respectively. The superior scattering strength of the latter three glasses suggests that they be used for increasing the gain and tuning range of fiber Raman lasers. The Raman spectra of mixed glasses containing GeO2, P2O5, and Na2O (or K2O) indicate that lasers made of these or similar materials may be continuously tunable over a range of 1300 cm−1.

Monolithic waveguide coupled cavity lasers and modulators fabricated by impurity induced disordering

Describes results on AlGaAs integrated optoelectronic devices consisting of combinations of buried passive waveguide regions with active multiple quantum well gain regions. The authors have developed a technique for accomplishing this integration in which the waveguide regions have greatly reduced propagation loss at the gain wavelength of the active media. They have incorporated sections of waveguide into laser cavities, and the resulting low (7-11 mA) threshold currents and weak dependence of threshold current on waveguide length confirm the reduced loss and waveguiding nature of the waveguide regions. They have used these structures to monolithically couple laser amplifiers to electroabsorption modulators. Among their results on these devices are electroabsorption modulators with contrast ratios of 23:1 and monolithic Q-switch operation resulting in pulse widths of less than 200 ps. The relative simplicity with which these structures are fabricated via impurity induced disordering techniques promises to result in major impact on practical systems for monolithic integration. >

Unified planar process for fabricating heterojunction bipolar transistors and buried‐heterostructure lasers utilizing impurity‐induced disordering

We describe results on a novel geometry of heterojunction bipolar transistor that has been realized by impurity‐induced disordering. This structure is fabricated by a method that is compatible with techniques for the fabrication of low threshold current buried‐heterostructure lasers. We have demonstrated this compatibility by fabricating a hybrid laser/transistor structure that operates as a laser with a threshold current of 6 mA at room temperature, and as a transistor with a current gain of 5.

Properties of closely spaced independently addressable lasers fabricated by impurity‐induced disordering

We describe the fabrication and characteristics of closely spaced (10 μm) dual‐beam laser sources by the process of impurity‐induced disordering. We present data demonstrating that these devices are capable of high efficiency and reliable operation when operated in a p‐side up configuration. We also show that these devices can be placed in close proximity with a minimal amount of thermal and electrical interaction between devices. These features have significant implications for the realization of high‐density arrays of independently addressable lasers for optical interconnection of integrated circuits and optical imaging systems.

Demonstration and properties of a planar heterojunction bipolar transistor with lateral current flow

The authors present fabrication techniques and device performance for a novel transistor structure, the lateral heterojunction bipolar transistor. The lateral heterojunctions are formed by impurity-induced disordering of a GaAs base layer sandwiched between two AlGaAs layers. These transistor structures exhibit current gains of 14 for base widths of 0.74 mu m. Transistor action in this device occurs parallel to the surface of the device structure. The active base region of the structure is completely submerged, resulting in a reduction of surface recombination as a mechanism for gain reduction in the device. Impurity-induced disordering is used to widen the bandgap of the alloy in the emitter and collector, resulting in an improvement of the emitter injection efficiency. Since the device is based entirely on a surface diffusion process, the device is completely planar and has no steps involving etching of the III-V alloy material. These advantages lead this device to be considered as a candidate for optoelectronic integration applications. The transistor device functions as a buried heterostructure laser, with a threshold current as low as 6 mA for a 1.4- mu m stripe. >

Raman characterization of hydroxyl in fused silica and thermally grown SiO2

We developed Raman spectroscopy to characterize the hydroxyl (OH) solubility in fused silica and thermally grown steam SiO2 from 695 to 1000‡C and 1–10 atm steam pressure. The technique was extended to measure the OH diffusion profiles in bulk v-SiO2, and the derived diffusion coefficients supplement those published in the literature. Fused silicas processed with higner fictive temperatures display larger initial OH solubilities which decrease with time, but saturations at temperatures as low as 600‡C remove much of the prior thermal history as the glass structurally relaxes. The OH solubility appears to be proportional to the square root of external steam pressure; however, the quasiequilibrium temperature dependence is unresolved. The behavior of OH in fused silica and the thermally grown oxide is very similar when the two materials are identically processed.

Surface skimming buried heterostructure laser with applications to optoelectronic integration

We demonstrate the ability to fabricate low‐threshold current buried heterostructure lasers with the critical active layers in close proximity to the surface of the laser crystal. These structures readily lend themselves to applications involving optical field interactions on the surface of the crystal. We further demonstrate the compatibility of these structures with lateral heterojunction bipolar transistor fabrication.

Low threshold buried‐heterostructure quantum well lasers by excimer laser assisted disordering

Laser assisted disordering based upon a direct‐write Ar+ laser beam has been established as a fabrication technique for high quality optoelectronic devices. In this letter, we report a new form of laser assisted disordering in which an excimer laser beam, photolithographically patterned, is used to define the incorporation of Si impurity into GaAs‐AlGaAs heterostructure crystals. During a subsequent thermal anneal the diffusing Si induces layer disordering to a depth of ∼1 μm. The excimer laser assisted disordering process is characterized as a function of the energy density of the laser beam. Also, this technique is used to fabricate high quality buried‐heterostructure lasers. With a reflective rear facet, the typical cw threshold current is 4 mA and the maximum power output is 27 mW. The devices exhibit single fundamental mode operation with subsidiary longitudinal side modes suppressed by 34 dB.

Achievement of high gain in a multiple quantum channel lateral heterojunction bipolar transistor

We describe refinements in the geometry of a lateral heterojunction bipolar transistor that have allowed us to greatly improve the dc characteristics of these devices. By reducing the base dimensions to 0.35 μm and improving the abruptness of the grading at the base‐emitter p‐n junction, we have achieved maximum current gains in excess of 600.

High gain lateral heterojunction bipolar transistors and application to optoelectronic integration

Refinements in the geometry of a novel AlGaAs lateral heterojunction bipolar transistor structure that have made it possible to greatly improve the DC characteristics of these devices are described. By reducing the base dimensions to 0.35 mu m and improving the abruptness of the grading at the base-emitter p-n junction, maximum current gains in excess of 600 have been achieved. Demonstration of these values of gain establishes the viability of this device architecture for making a wide variety of electronically functional circuits. The improvements have been realized with only a relatively small penalty in increased difficulty of device fabrication. In addition, the complete planarity of the fabrication process for these devices makes them very attractive for optoelectronic integration applications.<<ETX>>