DE102007055177A1 - Super luminescence diode for use in projection application, has semiconductor layer sequence with active area on semiconductor body, and mesa flanks attached to longitudinal ends of body and designed as diagonal, total reflecting mirrors - Google Patents

Abstract

The diode has a semiconductor layer sequence (5) with an active area (18) on a semiconductor body (10), where the active area is suitably embedded in a wave guide (20, 22) for delivery of light. The active area is surrounded by an upper covering layer (24) and a lower covering layer (16) facing a substrate. The upper covering layer is attached on the semiconductor body in a bar shaped manner. Mesa flanks are attached to longitudinal ends of the bar shaped semiconductor body and are designed as diagonal, total reflecting mirrors. The mesa flanks are passivated with silicon-nitride or oxide. An independent claim is also included for a method for manufacturing a luminescence diode.

Description

The The invention relates to a light-emitting diode, in particular a super-luminescent diode, which emits polarized light. The invention also relates a method for producing a light-emitting diode.

In Many applications use light sources with linearly polarized light sources Light needed. This applies, for example, to projection applications in which the Image information is generated by means of an LCD unit. As pictorial Elements in projection applications usually a numeric Aperture significantly smaller than 1, is a directed radiation desirable.

Linear Polarized light can be generated in a variety of ways. Usually becomes polarized light by processing unpolarized light generated. Therefore can for example, absorbent or reflective polarizing filters However, it is also possible to use a beam splitter to use.

These However, the procedure only uses part of the original radiation Light. For example, that part of the unpolarized light, which has a polarization that is not due to the polarizing filter can pass through for the further use not used.

Around to reduce the associated loss of efficiency, is in the state the technique known as polarization recycling, in which at least part of the false polarized light of the originally unpolarized Light continues to be used. However, this process is laborious and expensive.

Of Furthermore, the emission characteristic is often due to imaging Elements adapted to the respective application. However, it can the Étendue (radiating surface x radiation angle) can not be improved. As light sources and lasers could be used However, although the assembly and adjustment of optics consuming and so that is expensive.

consequently There is a need in the art for light sources that are polarized Produce light with high efficiency, without the aforementioned To show disadvantages.

It It is therefore an object of the invention to provide a light-emitting diode for polarized To create light or a method of production indicate the light-emitting diode, the linearly polarized light provides a simple way.

• – eine Halbleiterschichtenfolge mit einem in Wellenleiter eingebetteten zur Lichtabgabe geeigneten aktiven Gebiet auf einem Halbleiterkörper, das von einer oberen Mantelschicht und einer unteren dem Substrat zugewandten Mantelschicht umgebenen ist, wobei die obere Mantelschicht stegförmig auf einem Halbleiterkörper angebracht ist, und
• – jeweils eine Mesaflanke, die an den jeweiligen longitudinalen Enden des stegförmigen Halbleiterkörpers angebracht sind und die als schräge, total reflektierende Spiegel ausgebildet sind.

This object is achieved in a first aspect according to the invention by a light-emitting diode comprising:

• A semiconductor layer sequence with a waveguide-embedded light-emitting active region on a semiconductor body which is surrounded by an upper cladding layer and a lower cladding layer facing the substrate, wherein the upper cladding layer is web-mounted on a semiconductor body, and
• - Each one Mesaflanke, which are attached to the respective longitudinal ends of the web-shaped semiconductor body and which are formed as oblique, totally reflecting mirror.

• – Bilden einer Halbleiterschichtenfolge mit einem von einer oberen Mantelschicht und einer unteren Mantelschicht umgebenen und in Wellenleiter eingebetteten zur Lichtabgabe geeigneten aktiven Gebiet,
• – Bilden von Stegen aus der Halbleiterschichtenfolge, wobei die obere Mantelschicht stegförmig auf einem Halbleiterkörper angebracht ist, und
• – Bilden jeweils einer Mesaflanke, die an den jeweiligen longitudinalen Enden des stegförmigen Halbleiterkörpers angebracht werden und die als schräge, total reflektierende Spiegel ausgebildet werden.

This object is achieved in a second aspect according to the invention by a method for producing a light-emitting diode, comprising the following steps:

• Forming a semiconductor layer sequence with an active region, which is surrounded by an upper cladding layer and a lower cladding layer and embedded in waveguides, for the purpose of emitting light,
• - Forming webs from the semiconductor layer sequence, wherein the upper cladding layer is web-mounted on a semiconductor body, and
• - Forming a respective Mesaflanke, which are attached to the respective longitudinal ends of the web-shaped semiconductor body and which are formed as oblique, totally reflecting mirror.

According to the invention becomes a ridge-shaped light-emitting diode in thin-film technology created. To redirect the light vertically, totally reflective mesaflanken used. The oblique Mesaflanken preferably have an angle of about 45 ° a surface of the substrate. However, it is also possible the angle relative to the surface of Substrate to choose differently since only the decoupling reaches through the substrate must become. With a total reflection limit of about 18 ° can consequently the angle ranges from about 35 ° to 55 ° can be selected.

There in the active medium of a superluminescent diode charge carrier inversion prevails, intensifies the polarization difference between differently polarized Waves still while the propagation of light along the active medium.

consequently leads the Superluminescence operation due to the charge carrier inversion to a constriction of the emission spectrum a light emitting diode.

To a propagation of light along the To achieve quantum film, an epitaxial layer structure is used as in a laser diode. The active medium is embedded in a waveguide surrounded by cladding layers. Advantageously, the intensity profile of the wave within the waveguide can be adjusted via the layer structure. This determines the emission characteristic along one dimension.

In the other dimension, the waveguide by the expression of a Web waveguide formed. This ensures that the light is vertical meets the deflecting mirror. Thus, by a suitable dimensioning also the intensity course in the lateral direction below the web and thus the radiation characteristic be set in a different direction.

Next a higher one The degree of polarization can thus also have a narrow emission characteristic be achieved, which better to subsequent imaging elements can be adjusted. Because the light coupling surface no has active medium, even at the highest intensity no Destruction of the optical mirror take place.

advantageous Further developments of the invention are specified in the subclaims.

The The invention will now be explained in more detail with reference to the accompanying drawings. In show the drawing:

1 schematically a semiconductor layer sequence according to an embodiment of the invention and

2 a semiconductor body according to another embodiment of the invention.

In 1 is a semiconductor layer sequence 5 according to an embodiment of the invention. As will be explained below, the semiconductor layer sequence is 5 to form a superluminescent diode which emits polarized light.

The semiconductor layer sequence 5 includes a substrate 10 , on the epitaxially an etch stop layer 12 is applied. The etch stop layer 12 is later used to form mesa structures. Above the etch stop layer 12 closes a Stromaufweitungsschicht 14 on, which is intended for the operation of the superluminescent diode.

The area required for the light output is through an active area 18 educated. The active area 18 is in waveguide 20 . 22 embedded. The waveguides 20 . 22 are of a first cladding layer 16 and a second cladding layer 24 surround. Over the second cladding layer 24 is a contact layer 26 arranged.

In the 1 shown semiconductor layer sequence 5 FIG. 10 illustrates a super-luminescent mode light emitting diode that can be fabricated by epitaxial growth in thin film technology.

In strained quantum wells, the radiant intensity differs for transversal electric TE waves and for transverse magnetic TM waves. Transversal refers here to the quantum film plane in the active region 18 , This difference can be used especially for emission along the quantum well planes to emit polarized light.

When in the active medium of the superluminescent mode diode there is charge carrier inversion due to the greater than band gap predominant splitting of the quasifermin levels, the polarization difference between differently polarized waves still increases during the propagation of the light along the active medium 18 , Advantageously, the superluminescence operation due to the charge carrier inversion leads to a narrowing of the emission spectrum.

To propagate the light along the quantum well of the active medium 18 to reach is in the semiconductor layer sequence 5 according to 1 the active medium 18 is in the waveguide 20 . 22 embedded by the first and second cladding layers 16 . 24 is surrounded. Thus, over the layer structure of the semiconductor layer sequence 5 the intensity profile of the wave within the waveguide 20 . 22 and the radiation characteristic along the quantum film of the active medium 18 be determined.

2 shows a variety of semiconductor layer sequences 5 according to an embodiment of the invention on the substrate 10 are arranged. By suitable structuring, it is achieved that the semiconductor layers follow 5 web-shaped on the substrate forming a semiconductor body 10 are attached. In this dimension, the waveguide is formed by the expression of a ridge waveguide. This ensures that the light is within the active area 18 propagates perpendicular to a cutting line of the web.

In order to decouple the light from the ridge-shaped diodes, vertically deflecting, for example, 45 ° oblique, totally reflecting mesaflowers are provided for the deflection of light. However, it is also possible to choose the angle relative to the surface of the substrate differently, since only the coupling through the substrate must be achieved. At egg ner total reflection limit of about 18 °, therefore, the angle can be selected in the range of about 35 ° to 55 °.

There is one Mesaflanke each 30 . 32 designed as an oblique, totally reflective mirror. The mesaflars are at the respective longitudinal ends of the web-shaped semiconductor layer sequence 5 appropriate.

Due to the layer structure of the semiconductor layer sequence 5 and the choice of sizing consequently hits the light perpendicular to that from the mesaflars 30 . 32 formed deflecting mirror. By suitable dimensioning also the intensity profile in the lateral direction below the web and thus the radiation characteristic in another direction 40 . 42 be set.

Next a higher one The degree of polarization can thus also have a narrow emission characteristic be achieved, which better to subsequent imaging elements can be adjusted. Because the light coupling surface no has active medium, even at the highest intensity no Destruction of the optical mirror take place, such as by the Laser diodes known COMD effect (COMD = catastrophic optical mirror damage).

Farther the area of the deflection mirrors can be treated in such a way that Semiconductor damage, the one destruction cause the mirror, as with laser diodes, for example occur, be avoided. It can rely on existing processes resorted become. These treatments can for example by quantum well mixing, removal of oxides and in-situ passivation can be achieved. Unlike laser diodes Here, only a single treatment is needed while at Laser diodes two treatments for both mirrors are necessary. According to the invention, the treatment also performed in wafer bonding become.

Furthermore, it is provided in the decoupling area below the mesaflanken 30 . 32 to apply an anti-reflective coating.

Further Process steps include, for example, passivation with silicon nitride or silica. Other Passivierungsmaterialien known in the art are not excluded. About that In addition, a contact and / or solder metallization carried out becomes.

According to the invention can the the radiation characteristic of subsequent optical elements be adjusted.

As in 2 is shown, first the webs are formed, then the flanks necessary for the deflection and their mirrors are produced and optionally passivated. This is followed by passivation with a silicon nitride layer. Above the webs the passivation is opened.

Subsequently, will a contact and Lotmetallisierung applied and the semiconductor wafer on a carrier soldered. Further processing can be carried out with the process steps established for thin-film diodes respectively. Possible is also, the component decoupling with an anti-reflective To provide coating.

Next a higher one The degree of polarization can thus also have a narrow emission characteristic be achieved, which better to subsequent imaging elements can be adjusted. Because the light coupling surface no has active medium, even at the highest intensity no Destruction of the optical mirror take place.

Claims (19)

Luminescence diode, comprising: - a semiconductor layer sequence ( 5 ) with a waveguide ( 20 . 22 ) embedded active light emitting area ( 18 ) on a semiconductor body ( 10 ) obtained from an upper cladding layer ( 24 ) and a lower shell layer facing the substrate ( 16 ), wherein the upper cladding layer ( 24 ) web-shaped on a semiconductor body ( 10 ), and - in each case a Mesaflanke ( 30 . 32 ), which at the respective longitudinal ends of the web-shaped semiconductor body ( 5 ) are mounted and which are designed as oblique, totally reflecting mirror. Light-emitting diode according to Claim 1, in which the semiconductor layer sequence in the active region ( 18 ) Has carrier inversion, so that emitted light has a polarization state. A light-emitting diode according to claim 2, wherein the polarization state corresponds to linearly polarized light. Luminescence diode according to one of the preceding claims, in which the light propagation over a width of the web-shaped semiconductor body ( 5 ) is controllable. Light-emitting diode according to one of the preceding claims, which further comprises a substrate ( 10 ), so that their lateral light propagation over a thickness of the waveguide ( 20 . 22 ) is controllable. Luminescence diode according to one of the preceding claims, in which the mesaflanken ( 30 . 32 ) do not include an active area. Luminescence diode according to one of the preceding claims, in which a decoupling region below the mesaflanken ( 30 . 32 ) is provided with an anti-reflective layer. Luminescence diode according to one of the preceding claims, in which the mesaflanken ( 30 . 32 ) relative to a substrate ( 10 ) are formed as inclined flanks, wherein the inclined flanks form an angle between 35 ° and 55 °, preferably 45 °, with the surface of the substrate. Luminescence diode according to one of the preceding claims, in the radiation characteristic to subsequent optical elements is customizable. Method for producing a light-emitting diode, comprising the steps: - forming a semiconductor layer sequence ( 5 ) with one of an upper cladding layer ( 24 ) and a lower cladding layer ( 16 ) and in waveguides ( 20 . 22 ) embedded active light emitting area ( 18 ), - forming webs from the semiconductor layer sequence ( 5 ), wherein the upper cladding layer ( 24 ) web-shaped on a semiconductor body ( 10 ), and - each forming a mesaflanke ( 30 . 32 ), which at the respective longitudinal ends of the web-shaped semiconductor body ( 5 ) and which are formed as an oblique, totally reflecting mirror. Process according to Claim 10, in which the mesaflanken ( 30 . 32 ) are passivated. Method according to claim 11, in which the area of the mesaflanken ( 30 . 32 ) is treated by means of quantum film mixing, oxide removal and / or in situ passivation, so that the mesaflanken ( 30 . 32 ) do not include an active area. Method according to one of the preceding claims, in the above In addition, a passivation with silicon nitride or silicon dioxide is performed. Method according to one of the preceding claims, in the above In addition, a contact and / or Lotmetallisierung is performed. Method according to one of the preceding claims, in which the light propagation over a width of the web-shaped semiconductor body ( 5 ) is controllable. Method according to one of the preceding claims, further comprising a substrate ( 10 ) such that lateral light propagation across a thickness of the waveguide ( 20 . 22 ) can be controlled. Method according to one of the preceding claims, in which a decoupling region below the mesaflanken ( 30 . 32 ) is provided with an anti-reflective layer. Method according to one of the preceding claims, in which the mesaflanken ( 30 . 32 ) relative to a substrate ( 10 ) are formed as inclined flanks, wherein the oblique flanks form an angle between 35 ° and 55 °, preferably 45 °, with the surface of the substrate. Method according to one of the preceding claims, in the radiation characteristic of subsequent optical elements is adjusted.