Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2002-09-30
2004-11-23
Wong, Don (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013, C257S096000
Reexamination Certificate
active
06822991
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention relates to semiconductor light emitting devices and, in particular, to semiconductor light emitting devices incorporating tunnel junctions.
2. Description of Related Art
Semiconductor light-emitting devices including light emitting diodes (LEDs), vertical resonant cavity light emitting diodes (VRCLEDs), vertical cavity laser diodes (VCSELs), and edge emitting lasers are among the most efficient light sources currently available. Materials systems currently of interest in the manufacture of high-brightness light emitting devices capable of operation across the visible spectrum include Group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials. Typically, III-nitride light emitting devices are fabricated by epitaxially growing a stack of semiconductor layers of different compositions and dopant concentrations on a sapphire, silicon carbide, III-nitride, or other suitable substrate by metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. The stack often includes one or more n-type layers doped with, for example, Si, formed over the substrate, a light emitting or active region formed over the n-type layer or layers, and one or more p-type layers doped with, for example, Mg, formed over the active region.
Mg-doped III-nitride layers tend to be highly resistive, requiring high voltage drop in order to provide enough positive charge carriers (holes) in the active region. In addition, current tends to concentrate in the most direct paths from the p-contact to the active region. Accordingly, device designs which increase current spreading, particularly in the p-type layers, are advantageous.
Semiconductor light emitting devices are often incorporated into systems, such as projectors and optical scanning devices, that include optics such as lenses. The cost of such optics tends to increase with increasing size, thus device designs that increase brightness without increasing size are desirable.
SUMMARY
In accordance with an embodiment of the invention, a light emitting device includes a first active region, a second active region, and a tunnel junction. The tunnel junction includes a layer of first conductivity type and a layer of second conductivity type, both thinner than a layer of first conductivity type and a layer of second conductivity type surrounding the first active region. The tunnel junction permits vertical stacking of the active regions, which may increase the light generated by a device without increasing the size of the source.
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Collins III William D.
Gardner Nathan F.
Nurmikko Arto V.
Leiterman Rachel V.
Lumileds Lighting U.S. LLC
Patent Law Group LLP
Vy Hung T
Wong Don
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