Xerox Corporation

Palo Alto Research Center Inc.

David W Treat

David P Bour

Robert L Thornton

Christopher L Chua

Thomas L Paoli

Michael A Kneissl

Noble Marshall Johnson

Ross D Bringans

G A Connell

John E Epler

Kevin J Beernink

Fernando A Ponce

Highly compact vertical cavity surface emitting laser structures formed by a lateral oxidation process are provided. Specifically, well-controlled oxidized regions bound and define the aperture of a laser structure in a current controlling oxidation layer, wherein the aperture comprises a conductive region in the oxidation layer. These oxidized regions are formed by the use of a pre-defined bounding pattern of cavities etched in the laser structure, which allow the embedded oxidation layer to be oxidized, and which results in a highly reproducible and manufacturable process.

Laterally oxidized vertical cavity surface emitting lasers

The polarization instability inherent in laterally-oxidized VCSELs may be mitigated by employing an appropriately-shaped device aperture, a misoriented substrate, one or more cavities or employing the shaped device aperture together with a misoriented substrate and/or cavities. The laterally-oxidized VCSELs are able to operate in a single polarization mode throughout the entire light output power versus intensity curve. Combining the use of misoriented substrates with a device design that has an asymmetric aperture that reinforces the polarization mode favored by the substrate further improves polarization selectivity. Other device designs, however, can also be combined with substrate misorientation to strengthen polarization selectivity.

Method and structure for eliminating polarization instability in laterally&#x2014;oxidized VCSELs

A pair of undoped spacer layers are provided adjacent to, or near to, a single quantum well aluminum gallium nitride active region. In various exemplary embodiments, the undoped spacer layers are provided between the single quantum well aluminum gallium nitride active region and carrier confinement layers. The undoped spacer layers reduce the threshold current for the laser device and improve the output characteristics.

Ultraviolet group III-nitride-based quantum well laser diodes

A method of using ammonia to form a GaAs alloy with nitrogen atoms is described. The method includes the operation of introducing ammonia with an agent to assist in the breakdown of the ammonia into a reaction chamber with the GaAs film. Agents that are described include radiation as well as compounds that include aluminum.

Method and apparatus for MOCVD growth of compounds including GaAsN alloys using an ammonia precursor with a catalyst

A photonic device includes a plurality of semi-conductor layers formed on a substrate. The semi-conductor layers include an active layer and a current controlling region in close proximity to the active layer. The current controlling region includes a relatively small electrically conductive section or aperture, and a relatively large non-conductive section. A plurality of channels in the device are arranged to bound the electrically conductive section within their perimeter. The channels are spaced close enough together, and close enough to the desired aperture region to permit a relatively brief oxidation process to precisely isolate the aperture. The remainder of the current controlling region, i.e. beyond the aperture is also altered to present a high resistance. The photonic device also includes a relatively large surface area electrical contact used to drive the device. The large size desirably lowers overall resistance.

Buried oxide photonic device with large contact and precise aperture

Method and structure for eliminating polarization instability in laterally-oxidized VCSELs

An index-guided semiconductor laser diode made by impurity-induced layer disordering (IILD) of GaInP and AlGaInP heterostructures. In some embodiments, prior to the IILD, wing regions flanking an active mesa region are etched down close to the active layer so that the selective IILD involves a shallow diffusion only. High-performance, index-guided (AlGa).sub.0.5 In.sub.0.5 P lasers may be fabricated with this technique, analogous to those made in the AlGaAs material system. Also described are several techniques for reducing parasitic leakage current via the IILD regions, which include methods for providing p-n junctions or high band gap materials to reduce the parasitic leakage. In other embodiments, a planar structure is produced but with an ultra-thin upper cladding layer. Only a shallow IILD step is necessary to penetrate below the active region. Excessive out coupling and absorption losses are avoided by choosing materials that will minimize such losses, especially a pure gold metal coating as the p-contact metal.

Index guided semiconductor laser biode with shallow selective IILD

Methods for defect-free impurity-induced laser disordering (IILD) of AlGaInP and AlGaAs heterostructures. Phosphorus-doped or As-doped films are used in which silicon serves as a diffusion source and silicon nitride acts as a barrier for selective IILD. High-performance, index-guided (AlGa).sub.0.5 In.sub.0.5 P lasers may be fabricated with this technique, analogous to those made in the AlGaAs material system. The deposition of the diffusion source films preferably is carried out in a low pressure reactor. Also disclosed is a scheme for reducing or eliminating phosphorus overpressure during silicon diffusion into III-V semiconducting material by adding a pre-diffusion anneal step. Defects produced during intermixing are also reduced using a GaInP or GaInP/GaAs cap.

Thermally processed, phosphorus- or arsenic-containing semiconductor

A QW diode laser generating orthogonally polarized multiple beams. The device incorporates quantum well active regions capable of, transitions to heavy hole and light hole band edges. The heavy hole transition provides TE-mode gain, while the light hole band provides mostly TM-mode gain. By controlling the compositions and thicknesses of the active regions, both modes can be obtained in a monolithic structure. In addition, the resulting laser polarization will be very sensitive to the threshold carrier density. With an intracavity loss modulator in such a structure, the polarization can also be controlled. Other ways of causing side-by-side lasers to operate, respectively, in their TE or TM modes are also described.

Multi-beam, orthogonally-polarized emitting monolithic quantum well

A QW diode laser whose polarization can be switched. In one embodiment, the device incorporates a tensile strained quantum well active region, whose thickness is adjusted so that the heavy hole and light hole band edges are of the same energy. Since the heavy hole transition provides TE-mode gain, while the light hole band provides mostly TM-mode gain, the resulting laser polarization will be very sensitive to the threshold carrier density. With an intracavity loss modulator in such a structure, the polarization could be switched. Other switching techniques are also described.

Polarization switchable quantum well laser

Ridged waveguide and selectively-buried ridged waveguide, index-guided, visible semiconductor lasers incorporating a lattice-mismatched, preferably tensile-strained, etch-stop layer in the design and fabrication of the laser. Compared with other structures with etch-stop layers that are lattice matched, the etch-stop layer of the invention would have greater etch-rate selectivity, and the resulting structure would be more optically transparent with less transverse mode distortion and would present fewer difficulties with layer regrowth. These advantages would translate into greater design flexibility, more reliable fabrication, and better device performance. A preferred material for the etch-stop layer is Ga.sub.x In.sub.1-x P (x&gt;0.5).

Semiconductor laser with tensile-strained etch-stop layer

In situ evaporation of selected surface regions or layers of compound semiconductors is accomplished without breaking the growth system environment employing photo induced evaporation enhancement in chemical vapor deposition epitaxy. Intense radiation from an energy source desorbs or causes evaporation of consecutive monolayers of atoms or combined atoms from the surface crystal by thermal evaporation. The desorbed atoms from the growth surface are removed atomic layer by atomic layer in a fairly uniform and systematic manner and may be characterized as 'monolayer peeling' resulting in a morphology that is sculpturally smooth and molecularly continuous. In this sense, the method of this invention is analogous to erasing or the etching of crystal material and is the antithesis to laser deposition patterning wherein erasure after growth or reduced rate of growth during growth provide 'negative growth patterning'. In principal, then, this patternable negative growth process is coupled with a positive growth process for providing selective thinning regions of semiconductor layers in three dimensional crystal structures limited only by the functional capabilities of the growth reactor. Selective monotonic increasing and decreasing film thickness in situ can be accomplished while beam illumination remains stationary for a predetermined period of time with exposure of the growth surface accomplished through a patterned mask or, alternatively, while the beam spot or multiple beam spots are modulated and scanned across the growth surface of the film.

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San Jose, CA, United States of America

David W Treat