DE102006063104B4 - LED semiconductor body and use of an LED semiconductor body - Google Patents

Abstract

LED semiconductor body (1) with at least one first radiation-generating active layer (2) and at least one second radiation-generating active layer (3), which is stacked in the vertical direction above the first active layer (2) and connected in series with the first active layer (2), wherein:- the first active layer (2) and the second active layer (3) are electrically conductively connected by means of a contact zone (4),- a semiconductor layer (5) of a first conductivity type is arranged downstream of the first active layer (2) in the vertical direction,- a semiconductor layer (6) of a second conductivity type is arranged between the semiconductor layer (5) of the first conductivity type and the second active layer (3), wherein the semiconductor layer (6) of the second conductivity type directly follows the semiconductor layer (5) of the first conductivity type in the vertical direction,- the semiconductor layer (5) of the first conductivity type has a first free region (9) uncovered by semiconductor material,- the semiconductor layer (6) of the second Conductivity type has a second free region (10) uncovered by semiconductor material,- the contact zone (4) extends from the first free region (9) to the second free region (10) and- the first (2) and the second (3) active layer are monolithically integrated in the semiconductor body (1), wherein the LED semiconductor body (1) has no tunnel junction between the first (2) and second (3) active layers.

Description

The invention relates to an LED semiconductor body and the use of an LED semiconductor body.

For optical applications such as projection applications or display backlighting, a high luminance is desirable. In conventional LED semiconductor bodies, the amount of radiation generated depends on the current intensity with which the LED semiconductor body is operated. However, the current density in the active layer should not exceed a maximum current density that depends on the material system used, as otherwise there is a risk that excessive aging effects will adversely shorten the service life of the LED semiconductor body.

For example, in the publications US 2004 / 0 129 944 A1 , EN 10 2004 004765 A1 , US 2004 / 0 183 088 A1 , JP H11 - 233 827 A and JP H07 - 183 576 A Semiconductor components are described, each of which has several radiation-emitting active zones arranged one above the other.

It is an object of the present invention to provide an LED semiconductor body with an increased luminance.

This object is achieved by an LED semiconductor body according to patent claim 1.

Furthermore, it is an object of the present invention to provide uses of an LED semiconductor body with an increased luminance.

This object is achieved by uses according to patent claims 11 to 14.

Advantageous developments and embodiments of the invention are the subject of the dependent claims.

An LED semiconductor body according to the invention has at least one first radiation-generating active layer and at least one second radiation-generating active layer, which is stacked in the vertical direction above the first active layer and is connected in series with the first active layer, wherein the first active layer and the second active layer are electrically conductively connected by means of a contact zone.

In the present case, the contact zone is to be understood as an area of comparatively good electrical conductivity, wherein the contact zone is preferably designed without tunnel contact and thus does not represent a tunnel junction. Moreover, in the LED semiconductor body according to the invention, no tunnel junction is required for charge carrier transfer between the first and second active layers. According to at least one embodiment, the LED semiconductor body has no tunnel junction between the first and second active layers. This has the advantage that the LED semiconductor body can also be made from materials with which a tunnel junction is relatively difficult to realize epitaxially. Although the active layers could be connected in parallel, so that a tunnel junction would be superfluous, a parallel connection would have the disadvantage that, with different series resistances, the same current could not be injected into the two active layers or could only be injected with considerable additional effort. Advantageously, according to the invention, it is possible to ensure sufficient charge carrier transfer between the first and second active layers by means of the contact zone and also to inject the same current into the two active layers by means of the series connection.

In the present series circuit, the pn junctions of the active layers are preferably arranged in the same direction so that they form a pn-pn or np-np structure. It goes without saying that with more than two active layers, a pn-...-pn or np-...-np structure is preferred.

In addition to a simple pn junction, the active layers can have a double heterostructure, a single quantum well or a multiple quantum well (MQW) structure. Examples of MQW structures are given in the publications WO 2001 / 039 282 A2 , WO 1998 / 031 055 A1 , US 5 831 277 A , EP 1 017 113 B1 and US 5 684 309 A described.

Within the scope of the invention, two arrangements of the contact zone are particularly preferred. According to a first arrangement, the contact zone is arranged on a side flank of the semiconductor body. According to a second, unclaimed arrangement, the contact zone is integrated between the first active layer and the second active layer in the LED semiconductor body.

Since the first active layer and the second active layer are connected in series, the contact zone expediently connects a semiconductor layer of a first conductivity type to a semiconductor layer of a second conductivity type when the active layers are arranged in the same direction. According to at least one embodiment, the semiconductor layer of the first conductivity type is arranged downstream of the first active layer in the vertical direction, while the semiconductor layer of the second conductivity type is arranged in the vertical direction between the semiconductor layer of the first conductivity type and the second active layer. wherein the semiconductor layer of the second conductivity type directly follows the semiconductor layer of the first conductivity type in the vertical direction.

For example, the semiconductor layer of the first conductivity type may be a p-doped semiconductor layer and the semiconductor layer of the second conductivity type may be an n-doped semiconductor layer. Alternatively, the semiconductor layer of the first conductivity type may be an n-doped semiconductor layer and the semiconductor layer of the second conductivity type may be a p-doped semiconductor layer. This depends on the arrangement of the pn junctions of the active layers.

According to a non-claimed embodiment, in order to improve the charge carrier transfer in a semiconductor body whose contact zone is arranged on the side flank, the semiconductor layer of the first conductivity type and the semiconductor layer of the second conductivity type can form a tunnel junction which supports the charge carrier transfer in addition to the contact zone. In particular, the semiconductor layer of the first conductivity type and the semiconductor layer of the second conductivity type can be highly doped for this purpose.

According to at least one embodiment, the semiconductor layer of the first conductivity type has a first free area uncovered by semiconductor material. Furthermore, the semiconductor layer of the second conductivity type has a second free area uncovered by semiconductor material. In particular, the semiconductor layer of the second conductivity type can protrude from the rest of the semiconductor body, while the semiconductor layer of the first conductivity type protrudes from the layer of the second conductivity type. Thus, the shape of the semiconductor body between the first active layer and the second active layer can correspond to a step shape in cross section at least on one side flank. It should be noted that the LED semiconductor body has a layer sequence of layers, at least a part of which contains a semiconductor material. In the present case, the free area uncovered by semiconductor material is to be understood as an area that is uncovered by a semiconductor material used for the layers of the layer sequence.

According to at least one embodiment, the contact zone extends from the first free area to the second free area. In particular, the contact zone can be a contact layer. For example, the contact layer can at least partially cover the first free area and the second free area.

The materials used for the contact zone or the dimensions of the contact zone are preferably selected depending on the transverse conductivity of the layers that electrically connect the contact zone. For example, a p-doped GaN layer has a relatively low transverse conductivity, which is why the contact zone should be formed over a relatively large area or should contain a material with high electrical conductivity.

According to a preferred embodiment of the LED semiconductor body, the contact zone contains a metallic material. Such a contact zone is characterized by comparatively good electrical conductivity. This advantageously facilitates the charge carrier transfer between the first active layer and the second active layer.

In an alternative or further embodiment of the LED semiconductor body, the contact zone can be formed from a TCO (transparent conductive oxide) such as indium oxide, tin oxide, indium tin oxide (ITO) or zinc oxide. A contact zone that contains a TCO is advantageously radiation-permeable, so that the radiation generated in an area below the contact zone can be coupled out of the semiconductor body through the contact zone.

According to at least one embodiment, the first and the second active layer are monolithically integrated in the semiconductor body. The first and the second active layer can be produced in a common production step.

Furthermore, the semiconductor body in the invention can be a thin-film semiconductor body. If the semiconductor body is composed of prefabricated layer stacks, the individual layer stacks can be thin-film semiconductor bodies.

• - an einer zu einem Trägerelement hin gewandten ersten Hauptfläche einer strahlungserzeugenden Epitaxieschichtenfolge ist eine reflektierende Schicht aufgebracht oder ausgebildet, die zumindest einen Teil der in der Epitaxieschichtenfolge erzeugten elektromagnetischen Strahlung in diese zurückreflektiert;
• - die Epitaxieschichtenfolge weist eine Dicke im Bereich von 20µm oder weniger, insbesondere im Bereich von 10µm auf; und
• - die Epitaxieschichtenfolge enthält mindestens eine Halbleiterschicht mit zumindest einer Fläche, die eine Durchmischungsstruktur aufweist, die im Idealfall zu einer annähernd ergodischen Verteilung des Lichtes in der epitaktischen Epitaxieschichtenfolge führt, d.h. sie weist ein möglichst ergodisch stochastisches Streuverhalten auf.

A thin-film semiconductor body is characterized in particular by at least one of the following characteristic features:

• - a reflective layer is applied or formed on a first main surface of a radiation-generating epitaxial layer sequence facing a carrier element, which reflects at least part of the electromagnetic radiation generated in the epitaxial layer sequence back into the latter;
• - the epitaxial layer sequence has a thickness in the range of 20µm or less, in particular in the range of 10µm; and
• - the epitaxial layer sequence contains at least one semiconductor layer with at least one surface that has a mixing structure that ideally leads to an approximately ergodic Distribution of light in the epitaxial epitaxial layer sequence, ie it exhibits as ergodic stochastic scattering behavior as possible.

A basic principle of a thin-film LED chip is, for example, I. Schnitzer et al., Appl. Phys. Lett. 63 (16), October 18, 1993, 2174 - 2176 described.

A thin-film semiconductor body is, to a good approximation, a Lambertian surface radiator and is therefore particularly suitable for projection applications.

As already mentioned, in the second arrangement the contact zone is integrated into the LED semiconductor body between the first active layer and the second active layer.

According to a non-claimed embodiment, the semiconductor body has a first layer stack which comprises the first active layer, and a second layer stack which comprises the second active layer. In this embodiment, the contact zone is particularly preferably embedded between the first layer stack and the second layer stack.

The first layer stack has, in particular, in addition to the first active layer, a semiconductor layer of a first conductivity type, and the second layer stack has, in addition to the second active layer, a semiconductor layer of a second conductivity type. The first and second layer stacks are preferably made from two individual wafers. To produce the semiconductor body, the wafers can be bonded to one another in such a way that the semiconductor layer of the first conductivity type and the semiconductor layer of the second conductivity type face one another.

According to a further non-claimed embodiment, the contact zone is arranged between the semiconductor layer of the first conductivity type and the semiconductor layer of the second conductivity type. The contact zone is thus arranged in the main beam path of the semiconductor body, while in the first arrangement the contact zone is arranged in particular outside the main beam path.

According to a preferred embodiment, the contact zone is a contact layer.

According to a further non-claimed embodiment, the contact zone has at least a first region and at least a second region. The second region is particularly preferably electrically conductive. The first region can be electrically conductive or insulating. For example, the contact zone can have a second region in the form of a contact pad or elongated contact web, wherein a material surrounding the second region forms the first region. The second region is advantageously arranged such that it creates an electrical connection between the first and the second layer stack. In particular, the second region can contain a metallic material. The second region is preferably applied to a surface of the first or second layer stack facing the opposite layer stack. Alternatively, each layer stack can have at least one second region which is arranged such that two second regions come to rest on top of one another when the two layer stacks are stacked on top of one another.

The contact zone expediently contains a material that is permeable to the radiation generated by the first and/or second active layer. Thus, no significant radiation losses are to be feared due to the contact zone arranged in the main beam path.

The contact zone can contain a TCO. The contact zone can also contain an adhesive.

Furthermore, according to a non-claimed embodiment, a first connecting layer can be applied to the semiconductor layer of the first conductivity type and a second connecting layer can be applied to the semiconductor layer of the second conductivity type. The connecting layers can be provided in particular to further improve the charge carrier transfer between the layer stacks. The connecting layers preferably contain a radiation-permeable and electrically conductive material such as TCO. The contact zone is particularly preferably arranged between the first connecting layer and the second connecting layer.

Furthermore, a mechanical connection is advantageously established by means of the contact zone between the first and second layer stacks.

Preferably, the first and second active layers generate radiation of the same wavelength. This advantageously increases the amount of radiation compared to conventional LED semiconductor bodies.

More preferably, the main radiation from the LED semiconductor body occurs in a vertical direction. In particular, the main radiation occurs within a comparatively narrow solid angle, so that the luminance is advantageously increased The luminance is the optical power per emission area of the semiconductor body and solid angle element.

Particularly preferably, the radiation generated by the first active layer passes through the second active layer. This is particularly advantageous in combination with a reflection layer, which can be provided to reflect the radiation generated by the active layers in a vertical direction. In contrast to active layers that generate radiation of different wavelengths, the absorption of reflected radiation by the other active layer has no adverse effect on the total radiation emitted.

According to a variant, the semiconductor body contains, preferably one of the two active layers or both active layers, Al _n Ga _m In _1-nm P, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n+m ≤ 1.

According to a further variant, the semiconductor body contains, preferably one of the two active layers or both active layers, Al _n Ga _m In _1-nm As, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n+m ≤ 1.

According to a further variant, the semiconductor body contains, preferably one of the two active layers or both active layers, Al _n Ga _m In _1-nm N, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n+m ≤ 1.

The LED semiconductor body according to the invention can advantageously be used for a radiation-emitting component, because by means of the LED semiconductor body, high luminances can be achieved with a comparatively small component size.

Furthermore, the LED semiconductor body according to the invention or the radiation-emitting component which has the LED semiconductor body according to the invention can be used in particular for general lighting, for backlighting, for example of displays, or for projection applications.

Further features, advantages and developments of the invention will become apparent from the following in connection with the 1 to 4 explanations given.

• 1 eine schematische Querschnittsansicht eines Ausführungsbeispiels eines erfindungsgemäßen LED-Halbleiterkörpers,
• 2 eine schematische Querschnittsansicht eines nicht-beanspruchten Ausführungsbeispiels eines LED-Halbleiterkörpers,
• 3 eine schematische Querschnittsansicht eines nicht-beanspruchten Ausführungsbeispiels eines LED-Halbleiterkörpers,
• 4 eine schematische Querschnittsansicht eines nicht-beanspruchten Ausführungsbeispiels eines LED-Halbleiterkörpers.

They show:

• 1 a schematic cross-sectional view of an embodiment of an LED semiconductor body according to the invention,
• 2 a schematic cross-sectional view of a non-claimed embodiment of an LED semiconductor body,
• 3 a schematic cross-sectional view of a non-claimed embodiment of an LED semiconductor body,
• 4 a schematic cross-sectional view of a non-claimed embodiment of an LED semiconductor body.

The 1 The LED semiconductor body 1 shown in accordance with an embodiment has a first radiation-generating active layer 2 and a second radiation-generating active layer 3, wherein the active layers are arranged one above the other in the vertical direction, i.e. parallel to a radiation direction and perpendicular to a main extension direction of the active layers. A first semiconductor layer 5 of a first conductivity type, for example a p-conductive semiconductor layer, and a second semiconductor layer 6 of a second conductivity type, for example an n-conductive semiconductor layer, are arranged between the active layers 2, 3.

The arrangement of the two active layers 2, 3 in the LED semiconductor body 1 advantageously increases the total amount of radiation generated. Since the dimensions of the LED semiconductor body 1 change only insignificantly compared to an LED semiconductor body with only a single active layer and in particular the cross section of the LED semiconductor body is independent of the number of active layers, the luminance is also advantageously increased.

The semiconductor body 1 has a contact zone 4 which electrically connects the semiconductor layer 5 to the semiconductor layer 6. The semiconductor body 1 is preferably processed on at least one side flank in such a way that part of the semiconductor layer 5 and the semiconductor layer 6 are exposed, whereby a first free area 9 uncovered by semiconductor material and a second free area 10 uncovered by semiconductor material are formed. The contact zone 4 extends from the first free area 9 to the second free area 10 and covers them at least partially. The contact zone 4 can contain a metal, a metal compound or a radiation-permeable oxide (TCO) such as ITO.

Furthermore, according to a non-claimed embodiment, the two semiconductor layers 5, 6 can be highly doped to improve the electrical connection, so that an efficient tunnel junction with a low electrical contact resistance is created during operation.

The LED semiconductor body 1 has a rear contact 7, which is arranged vertically in front of the active layers 2 and 3. Furthermore, the LED semiconductor body 1 has a front contact 8, which is arranged downstream of the active layers 2 and 3 in the vertical direction. This forms a vertically conductive component which is characterized by a comparatively homogeneous current distribution within the LED semiconductor body 1.

Furthermore, the semiconductor body 1 can be arranged on the side of the rear contact 7 on a carrier element (not shown). In this case, the carrier element preferably contains an electrically conductive material. For example, the semiconductor body 1 can be a thin-film semiconductor body. In this case, the LED semiconductor body 1 is grown in particular on a growth substrate that is different from the carrier element and subsequently mounted on the carrier element, which can be done for example by means of soldering, bonding or gluing, wherein the growth substrate is preferably detached from the LED semiconductor body. The rear contact 7 can simultaneously serve as a mirror, so that radiation components that impinge on the rear contact 7 are reflected in the vertical direction, that is to say in this case in the direction of a radiation coupling-out side of the LED semiconductor body 1.

In the 1 In the embodiment shown, the active layers 2 and 3 are preferably monolithically integrated in the semiconductor body 1. In contrast, in the 2 In the illustrated non-claimed embodiment, a single first layer stack I comprising the active layer 2 and a single second layer stack II comprising the active layer 3 are connected to one another to obtain the LED semiconductor body 1. The manufacturing step of connecting the two layer stacks I and II is symbolized by the arrows.

A contact layer is arranged on the layer stack I, which forms the contact zone 4 after the two layer stacks I and II are connected. Alternatively, the contact layer can be arranged on the layer stack II. The contact zone 4 is subsequently integrated into the LED semiconductor body 1 between the first active layer 2 and the second active layer 3. The contact layer contains an electrically conductive material. Furthermore, the contact layer is permeable to the radiation of the active layer 2 and/or the active layer 3. The contact layer preferably contains an adhesive, so that the two layer stacks I and II are mechanically connected by means of the contact layer.

A rear contact 7 can be applied to the layer stack I, while a front contact 8 can be formed on the layer stack II. The contacts can be applied before or after the two layer stacks I and II are connected.

In the 3 In the illustrated non-claimed embodiment of an LED semiconductor body 1, two layer stacks I and II are also arranged on top of one another, wherein the contact zone 4 between the layer stacks I and II is integrated into the LED semiconductor body 1. The contact zone 4 has a first region 4a and a plurality of second regions 4b. The second regions 4b are embedded in the first region 4a. Preferably, the second regions 4b are electrically conductive. The region 4a can be electrically conductive or insulating. As shown, the second regions 4b can be designed in the form of contact pads, wherein a second region 4b is arranged on the layer stack I and another second region 4b is arranged on the layer stack II. The two layer stacks I and II are connected to one another in such a way that the two regions 4b lie on one another. The layer stacks I and II are electrically conductively connected to one another by means of the second regions 4b. Furthermore, the active layers 2 and 3 and the contact zone 4 are arranged relative to one another such that the active layers 2 and 3 are connected in series.

The two layer stacks I and II can be bonded to one another by means of the second regions 4b. In addition, the first region 4a can contain an adhesive that mechanically connects the two layer stacks I and II. Preferably, the first region 4a is permeable to the radiation generated by the active layer 2 and/or the active layer 3.

The 4 The LED semiconductor body 1 shown in accordance with a non-claimed embodiment has a first layer stack I and a second layer stack II arranged downstream of the first layer stack I in the vertical direction, with the contact zone 4 being arranged between the layer stack I and the layer stack II. The contact zone 4 comprises a first region 4a and a second region 4b. The first region 4a and the second region 4b are arranged between a first connecting layer 4c and a second connecting layer 4d. The first connecting layer 4c and the second connecting layer 4d preferably serve to improve the charge carrier transfer between the layer stacks I and II. For example, the connecting layers 4c and 4d can contain a radiation-permeable electrically conductive oxide (TCO) such as ITO. The connecting layers 4c and 4d are particularly preferably applied to the respective layer stack before the two layer stacks I and II are connected. One of the two layer stacks I and II is further connected to the second region 4b, which in particular in particular designed as a contact pad or contact web. The second region 4b contains a material, in particular a metal, with a low electrical resistance, so that a comparatively good current flow can take place across the contact zone 4. The first region 4a preferably contains an adhesive, so that the layer stacks I and II are mechanically connected, in particular by means of the first region 4a.

Claims (14)

LED semiconductor body (1) with at least one first radiation-generating active layer (2) and at least one second radiation-generating active layer (3), which is stacked in the vertical direction above the first active layer (2) and connected in series with the first active layer (2), wherein: - the first active layer (2) and the second active layer (3) are electrically conductively connected by means of a contact zone (4), - a semiconductor layer (5) of a first conductivity type is arranged downstream of the first active layer (2) in the vertical direction, - a semiconductor layer (6) of a second conductivity type is arranged between the semiconductor layer (5) of the first conductivity type and the second active layer (3), wherein the semiconductor layer (6) of the second conductivity type directly follows the semiconductor layer (5) of the first conductivity type in the vertical direction, - the semiconductor layer (5) of the first conductivity type has a first free area (9) uncovered by semiconductor material, - the semiconductor layer (6) of the second conductivity type has a second free region (10) uncovered by semiconductor material, - the contact zone (4) extends from the first free region (9) to the second free region (10) and - the first (2) and the second (3) active layer are monolithically integrated in the semiconductor body (1), wherein the LED semiconductor body (1) has no tunnel junction between the first (2) and second (3) active layers. LED semiconductor body (1) according to Claim 1 , wherein the contact zone (4) is arranged on a side flank of the LED semiconductor body (1). LED semiconductor body (1) according to one of the preceding claims, wherein the contact zone (4) is a contact layer. LED semiconductor body (1) according to one of the preceding claims, wherein the contact zone (4) contains a metallic material. LED semiconductor body (1) according to one of the preceding claims, wherein the contact zone (4) contains a TCO. LED semiconductor body (1) according to one of the preceding claims, which is a thin-film semiconductor body. LED semiconductor body (1) according to one of the preceding claims, wherein the first (2) and the second (3) active layer generate radiation of the same wavelength. LED semiconductor body (1) according to one of the preceding claims, whose main radiation occurs in the vertical direction. LED semiconductor body (1) according to one of the preceding claims, wherein the radiation generated by the first active layer (2) radiates through the second active layer (3). LED semiconductor body (1) according to one of the preceding claims, wherein: - the semiconductor body (1), preferably one of the two active layers (2,3) or both active layers (2,3), contains Al _n Ga _m In _1-nm P, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n+m ≤ 1, or - the semiconductor body (1), preferably one of the two active layers (2,3) or both active layers (2,3), contains Al _n Ga _m In _1-nm As, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n+m ≤ 1, or - the semiconductor body (1), preferably one of the two active layers (2,3) or both active layers (2,3), contains Al _n Ga _m In _1-nm N, where 0 ≤ n ≤ 1, 0 ≤ m ≤ 1 and n+m ≤ 1. Use of an LED semiconductor body (1) according to one of the Claims 1 until 10 for a radiation-emitting component. Use of an LED semiconductor body (1) according to one of the Claims 1 until 10 for general lighting. Use of an LED semiconductor body (1) according to one of the Claims 1 until 10 for backlighting, for example of displays. Use of an LED semiconductor body (1) according to one of the Claims 1 until 10 for projection applications.

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