Buried heterostructure for lasers and light emitting diodes

Details Buried heterostructure for lasers and light emitting diodes Buried heterostructure for lasers and light emitting diodes

1999-03-05

2001-12-04

Leung, Quyen (Department: 2881)

Coherent light generators

Particular active media

Semiconductor

C372S045013

Reexamination Certificate

active

06327288

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to semiconductor laser diodes and more particularly relates to edge-emitting semiconductor lasers.
BACKGROUND OF THE INVENTION
Blue laser diodes (LDs) have the potential for increasing the storage capacity of optical disks over the densities currently available in compact disk systems based on red laser diodes. Increased storage capacity will open new markets for compact disks in motion picture distribution.
One class of blue emitting elements is based on group III-V nitride films such as GaN epilayers grown on sapphire substrates. To fabricate a laser, a ridge structure is constructed to provide an appropriate optical cavity having parallel mirrors at each end of the cavity. The laser cavity is typically formed by sandwiching an active gain layer between two layers of GaN doped to form n-type and p-type semiconductors. The GaN layers are constructed so as to form a waveguide by depositing the various layers and then etching the stack to form a ridge structure whose vertical walls provide the waveguide. The ends of the waveguide are mirrors that reflect the light generated in the active region back and forth. In GaN based LDs the mirrors are typically formed by cleaving or etching the ends of the waveguide to provide the reflecting surface of the mirror.
The ridge structure discussed above has two problems. First, the structure has poor heat dissipation. The heat generated in the active region must either be dissipated through the substrate or the walls of the ridge structure. The path to the substrate is restricted by the width of the ridge structure; hence, removing heat by transferring the heat to the substrate, which is typically in thermal contact with a heat sink, is difficult.
The second problem with ridge structured devices is the high voltages needed to operate the devices. The p-contact is typically an ohomic contact on the top of the ridge. The resistance of this contact must be overcome to drive the device. To reduce this resistance, the contact needs to have as-large an area as possible. However, the available area is limited by the area on the top of the ridge.
Broadly, it is the object of the present invention to provide an improved edge emitting laser diode.
It is a further object of the present invention to provide an edge emitting diode that does not utilize a ridge structure, and hence, avoids the above-described problems.
These and other objects of the present invention will become apparent to those skilled in the art from the following detailed description of the invention and the accompanying drawings.
SUMMARY OF THE INVENTION
The present invention is a laser diode that is constructed in a trench in a manner such that the material in the trench acts as a waveguide. The laser diode includes a first contact layer constructed from a first semiconducting material of a first carrier type, the first semiconducting material having a first index of refraction. The first contact layer has a trench therein, the trench having a bottom surface and side walls. The trench has a layer of a second semiconducting material of the first carrier type on the bottom surface. The second semiconducting material has a second index of refraction, the second index of refraction being at least one percent greater than the first index of refraction. The laser also includes a first dielectric layer covering the first layer in those regions outside of the trench and a first cladding layer constructed from a third semiconducting material of the first carrier type. The first cladding layer overlies the dielectric layer. An active layer for generating light by a recombination of holes and electrons, overlies the first cladding layer. A second cladding layer constructed from a fourth semiconducting material of the opposite carrier type from the first carrier type overlies the active layer. A second contact layer of a fifth semiconducting material of the opposite carrier type from the first carrier type overlies the second cladding layer. First and second electrodes provide electrical connections to the first and second contact layers. In the preferred embodiment of the present invention, the bottom surface of the trench and one of the walls of the trench are covered with an electrically conducting coating material on which the second semiconducting material will not nucleate. This embodiment of the present invention is particularly well suited for constructing laser diodes based on group m-v material systems such as GaN.


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Zheleva, Tsvetanka, et al. “Pendeo-Epitaxy—A New Approach for Lateral Growth of Gallium Nitride Structures”, Proceedings of the Symposium GaN and related Alloys, Boston, Nov. 30-Dec. 4, 1998.
Nakamura, Shuji, “InGaN Multiquantum=Weel-Structure Laser Diodes with GaN-AlGaN Modulation-Doped Strained-Layer Superlattices”, IEEE Journal of Selected Topics in Quantum Electronics, vol. 4, No. 1, May\June 1998, pp. 483-489.
Nakamura, Shuji, “Violet InGaN/GaN/AIGaN-Based Laser Diodes Operable at 50Degrees C with a FUndimental Tansverse Mode”, Japan Journal Applied Physics, vol. 38, 1999, pp. L226-229. Mar., 1999.

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