EP2612373A1

EP2612373A1 - Light emitting diode chip

Info

Publication number: EP2612373A1
Application number: EP11748397.4A
Authority: EP
Inventors: Karl Engl; Markus Maute; Stefanie Rammelsberger
Original assignee: Osram Opto Semiconductors GmbH
Current assignee: Ams Osram International GmbH
Priority date: 2010-09-03
Filing date: 2011-08-24
Publication date: 2013-07-10
Also published as: DE102010036269A1; CN103069590A; US20130221390A1; WO2012028513A1; KR20130054404A

Abstract

A light‑emitting diode chip (1) is specified comprising a semiconductor layer sequence (2) having an active layer (4) suitable for generating electromagnetic radiation (10), wherein the light‑emitting diode chip (1) has a radiation exit surface (11) at a front side, the light‑emitting diode chip (1) has a mirror layer (6) at least in regions at a rear side lying opposite the radiation exit surface (11), said mirror layer containing silver, wherein a protective layer (7) containing Pt is arranged on the mirror layer (6), and the protective layer (7) has a structure such that it covers the mirror layer (6) only in partial regions (8).

Description

description

LED chip The invention relates to a light-emitting diode chip.

This patent application claims the priority of German Patent Application 10 2010 036 269.7, the disclosure of which is hereby incorporated by reference.

So-called thin-film LED chips are known in which the original growth substrate of the

Dissolved semiconductor layer sequence and instead the

Semiconductor layer sequence at one of the original

Growth substrate opposite side by means of a

Lotschicht is connected to a carrier substrate. The

Radiation exit surface of the LED chip is in this case opposite to a carrier substrate

Surface of the semiconductor layer sequence arranged, ie on the side of the original growth substrate. In such a light-emitting diode chip, it is advantageous if the side of the semiconductor layer sequence facing the carrier substrate is provided with a mirror layer in order to radiate radiation emitted in the direction of the carrier in the direction of the light source

Redirecting the radiation exit surface and thereby the

Increase radiation yield.

For the visible spectral range, silver is particularly suitable as material for the mirror layer. Silver is characterized by a high reflection in the visible spectral range and is suitable for producing a good electrical contact with the semiconductor material. On the other hand Silver is susceptible to corrosion and migration of silver into adjacent layers may occur.

In order to protect a mirror layer of silver from corrosion, a protective layer is usually applied to the silver layer. As a protective layer is in particular a

Platinum layer suitable. However, it has been found that the reflection of the interface between the mirror layer and the semiconductor layer sequence by the application of a

Protective layer of platinum on the semiconductor layer sequence opposite interface of the mirror layer

can be affected. As a result, the light extraction and thus the efficiency of the LED chip is reduced. This effect may be due to the fact that the platinum is the usual for the application of the layers

Process temperatures penetrate into the silver layer and even to the opposite interface between the

Mirror layer and the semiconductor layer can get. The invention is based on the object, a

Specify LED chip with a back mirror layer, which is protected by a protective layer against corrosion, but at the same time the reflection of the interface between the silver layer and the

Semiconductor layer sequence is only slightly affected.

This object is achieved by a light-emitting diode chip according to independent claim 1. Advantageous embodiments and further developments of the invention are the subject of

dependent claims.

According to one embodiment, the light-emitting diode chip contains a semiconductor layer sequence, which has one for generating Having electromagnetic radiation suitable active layer. The light-emitting diode chip has on a front side a radiation exit surface through which the electromagnetic radiation emitted by the active layer emerges from the semiconductor layer sequence. The front side of the light-emitting diode chip is understood here and below to mean the side of the light-emitting diode chip at which the

Radiation exit surface is arranged. At one of the radiation exit surface opposite

Rear side, the LED chip at least partially on a mirror layer containing silver.

On the mirror layer is a protective layer for

Reduction of corrosion of the mirror layer arranged. The protective layer advantageously contains Pt or consists thereof.

The protective layer advantageously has such a structure that it covers the mirror layer only in partial areas

covered. The protective layer is thus structured in such a way that it does not cover the entire surface of the mirror layer in particular

covered. The mirror layer thus has subregions that are uncovered by the protective layer. Due to the fact that the mirror layer is not completely covered by the

Protective layer is covered, the diffusion of constituents of the protective layer is reduced in the mirror layer.

In particular, the fact that the protective layer the

Mirror layer only partially covered, a diffusion of Pt in the mirror layer and / or reduced to the interface between the mirror layer and the semiconductor layer sequence compared to a full-surface applied protective layer. In this way, the advantage increases Reflection of the interface between the

Semiconductor layer sequence and the mirror layer, whereby the light extraction of the LED chip improves and thus increases the efficiency.

The invention makes use of the finding that, surprisingly, a protective layer of Pt can function as a protective layer for a silver-containing mirror layer even if it does not have the mirror layer

completely, but only partially covered.

There are several possible explanations for this effect. On the one hand, it is conceivable that the material of the protective layer from the partial areas which cover the mirror layer penetrates into the mirror layer and there preferably along the

Silver grain boundaries diffused. This could become one

Stabilization of the material of the mirror layer contribute, since corrosion effects usually on the metallic

Apply grain boundaries. Furthermore, it is conceivable that the material of the protective layer according to its position in the electrochemical series of voltages occurring

electrical potentials modified so that

Corrosive effects are suppressed. Furthermore, it is also possible that another property of the material of

Protective layer, which at least partially penetrates into the mirror layer, such as an effect as a catalyst or the storage of hydrogen, a positive

Has an influence on the stability of the mirror layer. Due to the aforementioned possible effects results in a

Protective effect for the mirror layer even if the applied protective layer does not completely cover the surface of the mirror layer. In an advantageous embodiment, the area fraction of the mirror layer covered by the protective layer is between 10% and 70% inclusive. Particularly preferably, the protective layer covers an area fraction of between 30% and 50% inclusive of the mirror layer. This way will be a good one

Compromise between the protective effect of the protective layer to protect the mirror layer from corrosion and by the at least partial penetration of the material

Protective layer in the mirror layer related reduction of reflection at the interface between the

Achieved semiconductor material and the mirror layer.

In particular, it has been found that with a surface portion of the protective layer on the mirror layer of 10% to 70% and preferably from 30% to 50%, a largely stable against corrosion mirror layer with only a slight reduction in the reflection of the mirror layer compared to a mirror layer without Protective layer of Pt can be achieved.

The protective layer preferably has a thickness between 1 nm and 200 nm, particularly preferably between 10 nm and 40 nm.

The protective layer may be configured to include a plurality of spaced apart portions. The sections can be regular or

irregular on the of the semiconductor layer sequence

be distributed away from the boundary surface of the mirror layer. It is advantageous if the distances between the adjacent subregions of the protective layer on the one hand are not too large, so that the protective layer has sufficient

Protective effect for the mirror layer has. On the other hand, the distances should not be too small, otherwise, as in the case of complete coverage of the

Mirror layer, a significant reduction of the reflection by the penetration of the material of

Protective layer would occur in the mirror layer.

It is particularly advantageous if a distance between adjacent subregions is on average between 2 μπι and 20 μπι inclusive. Below the distance, the shortest distance between the edges becomes adjacent

Subareas understood.

In an alternative advantageous embodiment, the protective layer has a plurality of openings, wherein the protective layer provided with the openings of one or more contiguous structures on the surface of

Mirror layer forms. For example, it is possible that the protective layer is first applied over the entire surface of the mirror layer and subsequently a plurality of openings in the protective layer is produced. The structuring of the protective layer can be carried out in particular by means of photolithography. The openings preferably have on average a lateral extent between 2 μπι and 20 μπι.

In an advantageous embodiment, the protective layer has a grid structure with a plurality of rows and columns.

In particular, the grid structure may be a rectangular grid structure. In this case, the protective layer forms a stripe pattern on the interface of the mirror layer, the strips preferably extending in two mutually perpendicular directions across the interface of the mirror layer.

The widths of the rows and columns of the grid structure

are preferably in each case between 2 μπι and 20 μπι. Furthermore, it is advantageous if the distances of the rows and columns are in each case between 2 μπι and 20 μπι. In this case, openings are formed in the protective layer through the grid structure, whose lateral extent is in each case between 2 μπι and 20 μπι.

In a further advantageous embodiment, the protective layer has a around the edge of the mirror layer

circumferential edge web on. In this edge region, the protective layer is therefore preferably not of openings

interrupted. This is advantageous because the mirror layer is endangered by corrosion, in particular at its side edges. One of the protective layer opposite interface of the mirror layer is preferably adjacent to the

Semiconductor layer sequence on. Between the

Semiconductor layer sequence and the mirror layer is thus arranged in particular no intermediate layer such as a primer layer, which to a

Reduction of the reflection at the interface between the mirror layer and the semiconductor layer sequence could result. Rather, it has been found that the properties desired for the mirror layer can be achieved by good adhesion to the semiconductor material, good electrical connection to the semiconductor material and protection against corrosion and silver migration with a protective layer structured on one of the

Semiconductor layer sequence opposite side of

Mirror layer is applied. The mirror layer may in particular be connected to a p-type semiconductor region of

Semiconductor layer sequence adjacent. The LED chip is preferably at one of the

Mirror layer as seen from the semiconductor layer sequence opposite side connected to a carrier substrate. The carrier substrate is, in particular, a substrate which is different from a growth substrate of the semiconductor layer sequence and which is connected to the semiconductor layer sequence, for example, by means of a solder layer.

A growth substrate used for the epitaxial growth of the semiconductor layer sequence is preferably of the

LED chip detached. The LED chip thus preferably has no growth substrate. By virtue of the fact that the growth substrate is detached from the light-emitting diode chip and the radiation emitted in the direction of the carrier substrate is reflected toward the radiation coupling-out surface by means of the mirror layer, a light-emitting diode chip with a high efficiency is achieved.

The invention will be described below with reference to

Embodiments in connection with the figures 1 to 4 explained in more detail.

1A shows a schematic representation of a cross section through a light-emitting diode chip according to a first exemplary embodiment along the line AB of the plan view shown in FIG. 1B, FIG. 1B shows a plan view of the one with a structured view

Protective layer provided mirror layer of the embodiment of a shown in Figure 1A

LED chips, Figure 2 is a schematic representation of a plan view of the provided with a protective layer

Mirror layer in a light-emitting diode chip according to a further embodiment,

Figure 3 is a schematic representation of a plan view of the provided with a protective layer

Mirror layer in a light-emitting diode chip according to another embodiment, and

Figure 4 is a schematic representation of a cross section through a LED chip according to another embodiment.

Identical or equivalent components are each provided with the same reference numerals in the figures. The

Components shown and the proportions of the components with each other are not to be regarded as true to scale.

The light-emitting diode chip 1 illustrated in FIG. 1B in a view from below and in FIG. 1A in a cross-section along the line AB drawn in FIG. 1B contains one

Semiconductor layer sequence 2, the first

Semiconductor region 3 of a first conductivity type and a second semiconductor region 5 of a second conductivity type. Preferably, the first semiconductor region 3 is a p-type semiconductor region and the second semiconductor region 5 is an n-type semiconductor region. Between the first

Semiconductor region 3 and the second semiconductor region 5, an active region 4 is arranged. The active zone 4 of the LED chip 1 can, for example, be in the form of a pn junction, a double heterostructure, a single quantum well structure or a multiple quantum well structure

be educated. The term quantum well structure encompasses any structure, in the case of the charge carriers

Confinement a quantization of their

Experience energy states. In particular, the

Name Quantum well structure no information about the

Dimensionality of quantization. It thus includes quantum wells, quantum wires and quantum dots and any combination of these structures.

The semiconductor layer sequence 2 may in particular be based on a nitride compound semiconductor. "On one

Nitride compound semiconductor based "means in

present context, that the semiconductor layer sequence 2 or at least one layer thereof comprises a III-nitride compound semiconductor material, preferably In _x Al _y Gai- _x - _y N, where 0 <x <1, 0 <y <1 and x + y <1 This material does not necessarily have to be mathematically exact

Having composition according to the above formula. Rather, it may contain one or more dopants as well as additional

Have components that are the characteristic

essentially do not change the physical properties of the In _x Al _y Ga _x - _y N material. For the sake of simplicity, however, the above formula contains only the essential constituents of the crystal lattice (In, Al, Ga, N), even if these may be partially replaced by small amounts of other substances. The LED chip 1 emits electromagnetic radiation 10 through a radiation exit surface 11, which at the

Front of the LED chip 1 is arranged. to

Improvement of the radiation decoupling can the Radiation exit surface 11 may be provided with a roughening or a coupling-out structure (not shown).

In order to improve the efficiency of the light-emitting diode chip 1, the light-emitting diode chip 1 has a region at one side opposite the radiation exit surface 11

Mirror layer 6 on. Through the mirror layer 6 is

Advantageously, radiation which is emitted from the active layer 4 to the rear side of the light-emitting diode chip 1 is deflected towards the radiation exit surface 11.

The mirror layer 6 advantageously contains silver or consists thereof. A mirror layer of silver advantageously has a high reflection in the visible spectral range. Furthermore, silver is characterized by a high electrical

Conductivity off. The mirror layer 6 can, in particular, adjoin the first semiconductor region 3, in particular a p-type semiconductor region, and in this way form one of the electrical connections of the semiconductor layer sequence 2 of the light-emitting diode chip 1.

In the case of a mirror layer 6 made of silver, the problem may arise that it is comparatively susceptible to corrosion, which in particular after a long time

Operating time of the LED chip 1 could lead to a reduction of the radiation yield. To protect the mirror layer 6 from corrosion, is on the of the

Semiconductor layer sequence 2 remote interface 16 of the mirror layer 6, a protective layer 7 is arranged. The

Protective layer 7 preferably contains Pt or consists thereof. The platinum-containing protective layer 7 is characterized in that it is chemically inert and thus protects the mirror layer 6 from corrosion. The protective layer 7 is structured in such a way that it covers the mirror layer 6 only in partial regions 8. The

Mirror layer 6 is thus in particular not completely covered by the protective layer 7. As in the supervision of the

Mirror layer 6 to see in Figure 1B, the protective layer is, for example, structured such that it has a plurality of spaced-apart portions 8. In the illustrated embodiment, the protective layer 7 is formed by a plurality of circular sections 8. However, the subregions 8 of the protective layer 7 may alternatively assume other regular or irregular shapes. Likewise, the arrangement of the

Subregions 8 on the surface of the mirror layer 6 be regular or irregular.

It has been found advantageous that the

Protective layer 7, the mirror layer 6 before then

Corrosion protects when the mirror layer 6 only

partially covered. This effect can in particular be based on the fact that the material of the protective layer 7 partially diffuses into the mirror layer 6, wherein it

especially along the silver grain boundaries of

Mirror layer 6 diffuses and in this way a

typically prevents corrosion beginning at the grain boundaries.

The partial diffusion of the material of the protective layer 7 in the mirror layer 6 may be disadvantageous to the

Reflectivity of the mirror layer 6 at the interface 16 to the semiconductor layer sequence 2 effect, especially when the material of the protective layer 7 reaches the interface 16. It turned out that one Reduction of the reflection at the interface 16 between the semiconductor layer sequence 2 and the mirror layer 6 can thereby reduce that the protective layer 7 only on

Subregions of the mirror layer 6 is applied. Because the protective layer 7 only on portions of the

Mirror layer 6 is applied, it is possible to achieve a good compromise between a sufficient protection of the mirror layer 6 against corrosion on the one hand and a high reflectivity of the interface 16 between the

Semiconductor layer sequence 2 and the mirror layer 6

on the other hand.

In particular, it has been found that at the same time a comparatively high reflection and a good protection of the mirror layer 6 against corrosion can be achieved if the protective layer 7 has an area fraction between

including 10% and including 70% of

Mirror layer 6 covered. It is particularly advantageous if the protective layer 7 has an area fraction between

including 30% and including 50% of

Mirror layer 6 covered.

The thickness of the protective layer is advantageously between 1 nm and 200 nm inclusive, more preferably between 10 nm and 40 nm inclusive.

The distance between the spaced apart portions 8 of the protective layer 7 is preferably in the middle between

including 2 μπι and including 20 μπι.

FIG. 2 shows a plan view of the mirror layer 6 provided with the protective layer 7 in another Embodiment of the LED chip 1 shown. The embodiment differs from the embodiment shown in Figure 1 in that the

Protective layer 7 has a circumferential around the edge of the mirror layer 6 edge web 9. In addition, on the surface of the mirror layer 6 as in the first

Embodiment a variety of each other

spaced portions 8 arranged. The edge web 9 which surrounds the edge of the mirror layer 6 has the advantage that in this way the mirror layer 6 is well protected by the covering with the protective layer 7 in its edge region, in which the risk of corrosion is particularly great. in the

Edge region of the mirror layer 6 is the risk of

Increases corrosion, for example, moisture from the edges of the LED chip 1 into these areas

could penetrate.

FIG. 3 shows a further exemplary embodiment of the mirror layer 6 provided with the protective layer 7 in a plan view. In this embodiment, the

Protective layer 7 a lattice structure 12 of a plurality of rows 13 and columns 14, which are each formed of rigid-shaped regions of the protective layer. In particular, the grid structure 12 may be a rectangular grid structure with regularly arranged rows 13 and columns 14.

The rows 13 and columns 14 preferably each have widths between 2 μπι and 20 μπι on. Furthermore, the distances of the adjacent rows and / or columns are also between 2 μπι and 20 μπι. The spacing of the rows or columns is understood to mean the distance between the edges of the strips of the protective layer 7 forming the rows or columns. The grid structure 12 generates on the surface the mirror layer 6 a plurality of preferably equal openings 15. The openings 15 preferably have on average a lateral extent between 2 μπι and 20 μπι on. Preferably, the lattice structure 12, as in the embodiment described above, also forms an edge web 9 that surrounds the edge of the mirror layer 6, so that the

Mirror layer 6 is particularly protected in its edge region from corrosion. The previously described embodiments with a

structured protective layer 7 provided mirror layer 6 can in various embodiments of LED chips

I integrated in one of the

Radiation exit surface 11 opposite rear side have a mirror layer 6.

FIG. 4 shows a cross section through an exemplary embodiment of a so-called thin-film LED chip 1, which has a mirror layer 6 provided with a structured protective layer 7. Like the embodiment shown in FIG. 1A, the thin-film light-emitting diode chip 1 has a p-type semiconductor layer sequence 2

Semiconductor region 3, an n-type semiconductor region 5 and an active zone 4 arranged therebetween. Of the

LED chip 1 is at one of the radiation exit surface

II opposite the back, for example, connected to a solder layer 18 with a carrier substrate 19. The LED chip 1 has no growth substrate.

In particular, one for epitaxial growth of

Semiconductor layer sequence 2 used growth substrate from the now serving as the radiation exit surface 11

Interface of the semiconductor layer sequence 2 has been detached. Between the with the structured protective layer. 7

provided mirror layer 6 and the solder layer 18, a barrier layer 17 may be arranged, in particular, a diffusion of constituents of the solder layer 18 in the

Mirror layer 6 and vice versa reduced. The

Barrier layer 17 may be, for example, a Ti layer or a TiW (N) layer. The barrier layer may also comprise a plurality of sub-layers (not shown),

for example, a Ti / Pt / TiWN layer sequence. The

Barrier layer 17 can simultaneously as

Planarisierungsschicht for the structured protective layer 7 act.

The carrier substrate 19 may be, for example, a silicon or germanium substrate. The electrical contacting of the LED chip 1 takes place for example by means of a first contact layer 20 on the back of the carrier substrate and a second contact layer 21 on portions of the surface of the LED chip 1. Alternatively

Of course, any other arrangements of the contact layers of the LED chip 1 conceivable.

The invention is not limited by the description with reference to the embodiments. Rather, the includes

Invention every new feature as well as every combination of

Features, which includes in particular any combination of features in the claims, even if this feature or this combination itself is not explicitly in the

Claims or embodiments is given.

Claims

A light-emitting diode chip (1) having a semiconductor layer sequence (2) which has an active layer (4) suitable for generating electromagnetic radiation (10), wherein

the light-emitting diode chip (1) has a radiation exit surface (11) on a front side,

- The LED chip (1) on one of

Radiation exit surface (11) opposite

Rear has at least partially a mirror layer (6) containing silver,

- On the mirror layer (6) a protective layer (7) is arranged, which contains Pt, and

- The protective layer (7) has such a structure

has, that the mirror layer (7) only in

Partial areas (8) covered.

LED chip according to claim 1,

wherein the protective layer (7) has an area fraction of between 10% and 70% inclusive

Mirror layer (6) covered.

LED chip according to claim 2,

wherein the protective layer (7) has an area fraction of between 30% and 50% inclusive

Mirror layer (6) covered.

LED chip according to one of the preceding

Claims,

wherein the protective layer (7) has a thickness between 1 nm and 200 nm. LED chip according to claim 4,

wherein the protective layer (7) has a thickness between 10 nm and 40 nm.

LED chip according to one of the preceding

Claims,

wherein the protective layer (7) comprises a plurality of

Having spaced apart portions (8), wherein a distance of adjacent portions (8) in

Means between including 2 μπι and including 20 μπι amounts.

LED chip according to one of the preceding

Claims,

wherein the protective layer (7) has a plurality of openings (15), wherein the openings (15) have on average a lateral extent between 2 μπι and 20 μπι.

LED chip according to one of the preceding

Claims,

wherein the protective layer (7) has a grid structure (12) with a plurality of rows (13) and columns (14).

LED chip according to claim 8,

wherein the widths of the rows (13) and columns (14) are in each case between 2 μπι and 20 μπι.

LED chip according to claim 8 or 9,

wherein the distances of the rows (13) and columns (14) in each case between 2 μπι and 20 μπι amount.

11. LED chip according to one of the preceding

Claims,

wherein the protective layer (7) has an edge web (9) running around an edge of the mirror layer (6).

12. LED chip according to one of the preceding

Claims,

wherein the protective layer (7) opposite

Interface (16) of the mirror layer (6) to the

Semiconductor layer sequence (2) adjacent.

13. LED chip according to claim 12,

wherein a region of the semiconductor layer sequence (2) adjoining the mirror layer (6) is a p-type

Semiconductor region (3) is.

14. LED chip according to one of the preceding

Claims,

wherein the LED chip (1) at one of the

Mirror layer (6) seen from the

Semiconductor layer sequence (2) opposite side with a carrier substrate (19) is connected.

15. LED chip according to one of the preceding

Claims,

wherein the LED chip (1) has no growth substrate.