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Researchers Submit Patent Application, "Semiconductor Chip That Emits Polarized Radiation", for Approval

June 4, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventor Lindberg, Hans (Regensburg, DE), filed on April 16, 2012, was made available online on May 22, 2014.

The patent's assignee is Osram Opto Semiconductors Gmbh.

News editors obtained the following quote from the background information supplied by the inventors: "Radiation-emitting semiconductor chips are advantageous light sources owing to their compact size and efficiency. However, on account of spontaneous emission the radiation generated is usually nondirectional and unpolarized. However, for applications such as LCD backlighting, for example, light sources that emit polarized radiation are advantageous.

"Both German Patent Publication No. DE 10 2007 062 041 and U.S. Patent Publication No. 2008/0035944 describe radiation-emitting semiconductor chips that emit polarized radiation. Furthermore, they describe that the radiation component which cannot couple out of the semiconductor chip on account of its polarization is at least partly recovered in the semiconductor chip by photon recycling."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventor's summary information for this patent application: "Embodiments of the invention specify a radiation-emitting semiconductor chip that generates polarized radiation in an efficient manner.

"In accordance with one embodiment, the radiation-emitting semiconductor chip comprises a semiconductor body comprising an active zone, which emits unpolarized radiation having a first radiation component of a first polarization and having a second radiation component of a second polarization. Furthermore, the radiation-emitting semiconductor chip comprises a grating structure, which acts as a wave plate or polarization filter and brings about an increase in one radiation component relative to the other radiation component in the radiation emitted by the semiconductor chip through a coupling-out side, such that the semiconductor chip emits polarized radiation having the polarization of the amplified radiation component, wherein the attenuated radiation component remains in the semiconductor chip. Furthermore, the radiation-emitting semiconductor chip comprises an optical structure, which converts the polarization of at least part of the attenuated radiation component remaining in the semiconductor chip into the polarization of the amplified radiation component. Furthermore, a reflective rear side is arranged opposite the coupling-out side.

"In addition to absorption and reemission processes in the active zone, therefore, the radiation component which remains in the semiconductor chip and which cannot couple out of the semiconductor chip on account of its polarization can be recovered by the change of the polarization by means of the optical structure.

"In one configuration of the radiation-emitting semiconductor chip, the grating structure, which is provided for increasing one radiation component relative to the other radiation component in the radiation emitted by the semiconductor chip through a coupling-out side, comprises a plurality of alternately arranged first grating regions of a first material and second grating regions of a second material. In particular, the grating regions of the same material are at a distance from one another which is smaller than a wavelength of the radiation generated by the active zone. Preferably, the distance is chosen such that the grating structure loses its diffraction properties. As a result, the grating structure behaves like a homogeneous medium having a uniform refractive index.

"In accordance with one preferred development, the first and second grating regions are embodied in strip-type fashion and are arranged parallel to one another. The width of the first and second grating regions should make up a fraction of the distance at which the grating regions of the same material succeed one another. Such small structures can be produced, for example, by lithographic techniques such as holographic lithography or a nanoimprint method.

"In accordance with a first variant, the grating structure acts as a waveplate. In particular, the grating structure in this case corresponds to a birefringent medium. In this case, the radiation component which is polarized parallel to the strip-type grating regions experiences a different effective refractive index than the radiation component which is polarized perpendicular to the strip-type grating regions. Preferably, the first radiation component experiences a different phase shift than the second radiation component upon transmission through the grating structure. By way of example, the thickness of the grating structure can be chosen such that the first radiation component, upon passing through the waveplate twice, experiences a phase shift of .pi. (pi), while the second radiation component experiences a phase shift different than .pi.

"Preferably, the grating structure acting as a waveplate is arranged between the active zone and the reflective rear side of the semiconductor chip. When setting a suitable distance between the active zone and the reflective rear side, account is taken of the total phase shift which the radiation emitted by the active zone and reflected at the rear side experiences between the active zone and the rear side. The distance between the active zone and the reflective rear side is set, in particular, in such a way that as a result of interference of radiation of the same polarization, one radiation component is amplified and the other radiation component is attenuated. By way of example, the distance is set in such a way that the first radiation component interferes constructively in the case of a phase shift of .pi., while the second radiation component interferes destructively.

"In accordance with one preferred variant, the first radiation component is polarized perpendicular to the strip-type grating regions. Furthermore, the second radiation component is polarized parallel to the strip-type grating regions.

"Advantageously, the perpendicularly polarized radiation component is emitted in a perpendicular direction, that is to say perpendicularly to the coupling-out side, while the parallel polarized radiation component is emitted in a horizontal direction, that is to say parallel to the coupling-out side.

"Consequently, the semiconductor chip in this variant emits perpendicularly polarized radiation.

"In accordance with one preferred embodiment, the first or second grating regions of the grating structure acting as a waveplate are formed from a material that is transmissive to the radiation generated in the active zone. For example, the first or second grating regions can be formed from SiO.sub.2, GaAs, AlGaAs, InGaAlP or GaN.

"Preferably, the first grating regions are produced by etching a surface of the semiconductor body, such that they are formed from the semiconductor material of the semiconductor body. The second grating regions are gas-filled, in particular air-filled, interspaces between the first grating regions. Some other transparent filling material, for example, a TCO (Transparent Conductive Oxide) is also conceivable for the second grating regions.

"In accordance with a second variant, the grating structure acts as a polarization filter. Preferably, one radiation component is transmitted at the grating structure acting as a polarization filter, and the other radiation component is reflected.

"In particular, the first grating regions of the grating structure contain or consist of a metal. The second grating regions can be for example gas-filled, in particular air-filled, interspaces between the first grating regions. By means of the strip-type grating regions that contain or consist of a metal, the radiation component which is parallel polarized is reflected, while the radiation component which is perpendicularly polarized is transmitted.

"The first radiation component can be, in particular, perpendicularly polarized, while the second radiation component is parallel polarized.

"In accordance with one preferred embodiment, the grating structure acting as a polarization filter is arranged on a surface of the semiconductor body that is on the coupling-out side. In this embodiment, the optical structure is advantageously arranged between that surface of the semiconductor body which is on the coupling-out side and the polarization filter. In particular, the optical structure is in this case embodied as a waveplate.

"Alternatively, the grating structure acting as a polarization filter can also be arranged between the active zone and the reflective rear side. In this case, in particular, the parallel polarized radiation component is reflected by the grating structure, while the perpendicularly polarized radiation component is transmitted and reflected by the reflective rear side. If the parallel polarized radiation component is intended to be amplified, in particular the distance between active zone and grating structure is set in such a way that the parallel polarized radiation component interferes constructively. If the perpendicularly polarized radiation component is intended to be amplified, in particular the distance between active zone and reflective rear side is set in such a way that the perpendicularly polarized radiation component interferes constructively.

"In one preferred configuration, the grating structure acting as a polarization filter is a contact structure serving for current spreading. In this case, the grating structure is preferably arranged at the coupling-out side of the semiconductor chip, such that the grating structure can be directly electrically contact-connected externally, for example, by means of a contact wire.

"The optical structure provided for changing the polarization of the radiation component remaining in the semiconductor chip can be a waveplate, like the grating structure. Furthermore, the optical structure can be a randomly roughened structure or else a predefined structure.

"The optical structure is arranged in particular within the semiconductor chip between the coupling-out side and the rear side.

"In accordance with one preferred embodiment, the optical structure comprises structured regions extending in a plane arranged parallel to a plane in which the grating structure extends, wherein the structured regions run transversely with respect to the grating regions of the grating structure. The structured regions are therefore not arranged parallel to the grating regions. The structured regions form with the grating regions an angle of greater than 0.degree. and less than 90.degree.. Preferably, the angle is 45.degree.. In this case, the radiation component which remains in the semiconductor chip and which is reflected by the structured regions experiences, in particular, a rotation of the polarization by 90.degree.. Preferably, the structured regions are arranged at least partly parallel to one another.

"By way of example, it is possible to embody the optical structure in the manner of the waveplate like a birefringent medium with alternately arranged structured regions having different refractive indexes. Furthermore, the structured regions can be depressions introduced into a semiconductor layer of the semiconductor body. The depressions can be gas-filled, in particular air-filled.

"In accordance with a further advantageous embodiment, the optical structure comprises structured regions having oblique side faces which run at an angle of greater than 0.degree. and less than 90.degree., obliquely with respect to a plane in which the grating structure extends. Preferably, the angle is 45.degree.. The radiation component which remains in the semiconductor chip experiences, in particular, a rotation of the polarization by 90.degree. upon reflection at two opposite side faces of two adjacent structured regions. Preferably, the structured regions are embodied as prisms or pyramids. These can be etched, for example, into a semiconductor layer of the semiconductor chip.

"In one preferred configuration, the reflective rear side is provided with the optical structure. By way of example, in this case, a rear-side surface of the semiconductor body can be provided with the optical structure and coated with a reflection layer, such that a reflective rear side having an optical structure is formed as a consequence.

BRIEF DESCRIPTION OF THE DRAWINGS

"The radiation-emitting semiconductor chip described here is explained in greater detail below on the basis of exemplary embodiments and the associated figures.

"FIG. 1A shows, in a schematic cross-sectional view, a first exemplary embodiment of the radiation-emitting semiconductor chip described herein;

"FIG. 1B shows a perspective enlarged view of the grating structure contained in FIG. 1A;

"FIGS. 2A and 2B show graphs with values for the effective refractive index and the thickness of a grating structure;

"FIG. 3A shows, in a schematic cross-sectional view, a second exemplary embodiment of the radiation-emitting semiconductor chip described herein;

"FIG. 3B shows a schematic plan view of the grating structure contained in FIG. 3A;

"FIG. 4 shows, in a schematic cross-sectional view, a third exemplary embodiment of the radiation-emitting semiconductor chip described herein; and

"FIGS. 5A, 5B, 6, 7, 8A and 8B show further exemplary embodiments of the optical structure described herein.

"Elements that are identical, of identical type or act identically are provided with the same reference signs in the figures."

For additional information on this patent application, see: Lindberg, Hans. Semiconductor Chip That Emits Polarized Radiation. Filed April 16, 2012 and posted May 22, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5550&p=111&f=G&l=50&d=PG01&S1=20140515.PD.&OS=PD/20140515&RS=PD/20140515

Keywords for this news article include: Electronics, Osram Opto Semiconductors Gmbh.

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Source: Electronics Newsweekly


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