DE102011102376A1 - Optoelectronic semiconductor chip i.e. thin-film LED, has n-type contact layer comprising transparent conductive oxide layer, where p-type and n-type contact layers are in electrical contact with p-side and n-side of body, respectively - Google Patents

Abstract

The chip (10) has an active layer (1a) arranged between a p-side (1c) and an n-side (1b) of a semiconductor body (1) for radiation generation. A p-type contact layer (21a) and an n-type contact layer (2) are in electrical contact with the p-side and the n-side of the body, respectively. The n-type contact layer comprises a transparent conductive oxide (TCO) layer. An electrically insulating layer (3) is arranged between the p-type and n-type contact layers. A silver layer of the n-type contact layer is guided through a perforation (22).

Description

The application relates to an optoelectronic semiconductor chip comprising a semiconductor body, a p-contact layer and an n-contact layer.

As the n-type contact layer for, for example, a GaN-based semiconductor body, there has conventionally been used a titanium layer and a silver layer deposited thereon. With such n-contact layers good electrical and optical properties can be realized. However, in such n-contact layers for good optical properties very thin titanium layers with thicknesses of less than 0.5 nm are necessary, which are difficult to produce and subject to various process variations.

In addition, although titanium has good electrical contact with n-GaN. However, titanium has a comparatively poor reflectivity, so that light emitted from the semiconductor body is adversely absorbed by the titanium layer of the n-contact layer. In contrast, silver is a good reflector for radiation in the visible spectral range. However, silver disadvantageously has an unfavorably high contact resistance to n-doped GaN. In addition, titanium and the combination of titanium and silver have various physical properties that may be detrimental to semiconductor chips. For example, titanium is very reactive and can easily oxidize, which can lead to a poorly conductive electrical barrier due to the increase in contact resistance.

It is an object of the present application to provide an optoelectronic semiconductor chip which avoids the above-mentioned disadvantages, which advantageously results in a semiconductor chip having an n-contact layer which has improved electrical and at the same time optical properties.

This object is achieved by an optoelectronic semiconductor chip with the features of claim 1. Advantageous developments of the semiconductor chip are the subject of the dependent claims.

In one embodiment, the optoelectronic semiconductor chip has a semiconductor body made of semiconductor material, a p-contact layer and an n-contact layer. The semiconductor body has an active layer provided for generating radiation. The semiconductor body further has a p-side and an n-side, between which the active layer is arranged. The p-contact layer is provided for electrically contacting the p-side of the semiconductor body. The n-contact layer is provided for electrical contacting of the n-side of the semiconductor body. The n-contact layer comprises a TCO (transparent conductive oxide) layer.

Transparent conductive oxides are transparent, conductive materials, usually metal oxides, such as zinc oxide, tin oxide, cadmium oxide, titanium oxide, indium oxide, indium tin oxide (ITO), aluminum zinc oxide (AZO), aluminum indium zinc oxide (ATO), indium zinc oxide (IZO), gallium zinc oxide (GZO) or gallium tin oxide (GTO). In addition to binary metal oxygen compounds such as ZnO, SnO ₂ or In ₂ O _{3 also} include ternary metal oxygen compounds such as Zn ₂ SnO ₄ , CdSnO ₃ , ZnSnO ₃ , MgIn ₂ O ₄ , GaInO ₃ , Zn ₂ In ₂ O ₅ or In ₄ Sn ₃ O ₁₂ or mixtures of different transparent conductive oxides to the group of TCOs. Furthermore, the TCOs do not necessarily correspond to a stoichiometric composition and may also be p- or n-doped.

The term "n-contact layer" and "n-side" should be understood as meaning, in particular, an n-doped contact layer and an n-doped side of the layers of the semiconductor body. Likewise, a p-contact layer and a p-side should be understood to mean a p-doped contact layer and a p-doped side of the layers of the semiconductor body.

In the present semiconductor chip, the conventionally used titanium layer is replaced by a layer of a transparent conductive oxide. The TCO layer may have a substantially greater thickness than the previously used titanium layer. Such TCO layers can be much better controlled compared to conventionally used titanium layers, adhere well and provide a good electrical contact to the semiconductor body of semiconductor material. In addition, such TCO layers are significantly less reactive and thus less susceptible to oxidation.

By means of an n-contact layer comprising a TCO layer, a highly reflective ohmic contact of the n-contact layer to the semiconductor body can be realized, in particular in conjunction with a highly reflective layer of the contact layer, such as a silver layer, disposed on the side of the TCO layer facing away from the semiconductor body. Such n-contact layers are well reproducible, easy to control in manufacture, have less contact resistance, are less reactive, and enable high yield due to stable contact resistance. Due to the transparency of the TCO layer for radiation in the visible spectral range, radiation emitted by the semiconductor chip is advantageously not absorbed by the n-contact layer, so that an improved radiation efficiency is made possible.

The semiconductor chip is preferably an optoelectronic semiconductor chip which enables the conversion of electrical power into, for example, constant or pulsed light emission, for example for data transmission, or vice versa. By way of example, the optoelectronic semiconductor chip is a radiation-emitting semiconductor chip. The semiconductor chip is preferably an LED, particularly preferably a thin-film LED. Within the scope of the application, a thin-film LED is considered to be an LED, during the manufacture of which the growth substrate on which the semiconductor body has been epitaxially grown is preferably completely detached.

The active layer of the semiconductor body preferably contains a pn junction, a double heterostructure, a single quantum well structure (SQW, single quantum well) or a multiple quantum well structure (MQW, multi quantum well) for generating radiation. The term quantum well structure unfolds no significance with regard to the dimensionality of the quantization. It includes, among other things, quantum wells, quantum wires and quantum dots and any combination of these structures.

The semiconductor body, in particular the active layer, preferably contains a III / V semiconductor material. III / V semiconductor materials are particularly suitable for generating radiation in the ultraviolet, over the visible to the infrared spectral range. The semiconductor body has a plurality of semiconductor layers epitaxially deposited on one another, in which the active layer is arranged. For example, the layers of the semiconductor body are grown on a growth substrate. The active layer separates the p-doped side of the semiconductor body from the n-doped side of the semiconductor body.

In a development, the p-contact layer and the n-contact layer are arranged on the same side of the semiconductor body. For example, the p-contact layer and the n-contact layer are arranged on the p-side of the semiconductor body. The side of the semiconductor chip opposite the contact layers preferably serves as the radiation exit side for the radiation generated in the semiconductor chip. From the radiation exit side, a large proportion of the radiation generated by the active layer is preferably coupled out of the semiconductor chip.

The semiconductor chip thus preferably has a one-sided contacting, so that the radiation exit side is free of contact structures and contact layers. As a result, absorption processes at the radiation exit side of the semiconductor chip are advantageously avoided, so that, with advantage, shadowing effects and efficiency losses can be minimized.

In a development, the p-contact layer directly adjoins the p-side of the semiconductor body, wherein the n-contact layer is arranged on the side of the p-contact layer facing away from the semiconductor body. Between the p-contact layer and the n-contact layer, an electrically insulating layer is arranged. The n-contact layer and the p-contact layer are thus electrically insulated from each other, so that a short circuit between the contact layers is prevented.

In the present case, the arrangement is thus as follows: n-contact layer, electrically insulating layer, p-contact layer and semiconductor body. The layers are arranged vertically one above the other.

The electrically insulating layer is, for example, a passivation layer which spatially and electrically completely separates the p-contact layer and the n-contact layer from one another. The p-contact layer and the n-contact layer are thus not in direct contact at any point.

In a development, the n-contact layer is led to the n-side by means of a breakdown through the p-contact layer and through the p-side of the semiconductor body. The p-contact layer and the p-side therefore have an opening into which the n-contact layer extends. The breakthrough pierces the active layer, so that the n-contact layer is led to the n-side of the semiconductor body. The breakthrough leads through the p-side and the active layer to the n-side, wherein the breakthrough additionally protrudes into the n-side and ends there.

The breakthrough has on the side regions the electrically insulating layer which electrically insulates the n-contact layer from the p-contact layer and the p-side of the semiconductor body.

The p-contact layer is therefore arranged directly on the p-side of the semiconductor body and provided for the direct electrical contacting of the p-side. The n-contact layer is arranged at a distance from the semiconductor body. The gap is formed by the p-contact layer and the electrically insulating layer. Due to the breakdown, the n-side of the semiconductor body can be electrically contacted by means of the n-contact layer.

The semiconductor chip can also have a plurality of openings, through which the n-contact layer is guided in each case. The openings are arranged at a distance from each other. The arrangement of the apertures is designed so that a possible homogeneous energization of the n-side of the semiconductor body is realized, so that a homogeneous radiation generation is ensured in the active layer.

In one development, the n-contact layer contains a silver layer, the TCO layer of the n-contact layer being arranged between the n-side of the semiconductor body and the silver layer of the n-contact layer. The n-contact layer is thus composed of two layers, the silver layer and the TCO layer. The silver layer forms a mirror layer, which is a good reflector for radiation in the visible spectral range. The high contact resistance of the silver layer to the semiconductor material of the semiconductor body can be improved by means of the TCO layer, so that a highly reflective ohmic contact of the n-contact layer is realized.

By way of example, the mirror layer is arranged on the side of the electrically insulating layer facing away from the semiconductor body and in the apertures. The TCO layer separates the silver layer from the semiconductor body, that is, it is arranged between the silver layer and the semiconductor body. In particular, the TCO layer directly adjoins the semiconductor material and the silver layer.

In a further development, the silver layer is guided through the opening and the TCO layer is arranged on the opening. Accordingly, no direct contact is formed between the silver layer and the semiconductor material, since the TCO layer is arranged therebetween. The TCO layer completes the breakthrough.

In one development, the TCO layer contains ZnO (zinc oxide) or SnO (tin oxide). The TCO layer may additionally be mixed with another metal or a mixture with other metals, such as aluminum, gallium and / or indium. For example, aluminum zinc oxide, aluminum tin oxide, gallium tin oxide, gallium zinc oxide, indium tin oxide or indium zinc oxide can be used. These materials are characterized by a low absorption in the visible spectral range and thus by a high transparency for radiation in the visible spectral range. In addition, these materials have a low contact resistance to the semiconductor material, so that a good ohmic contact is realized.

In a development, the TCO layer has a thickness of greater than 0.5 nm. Preferably, the TCO layer has a thickness in a range between 15 nm inclusive and 25 nm inclusive. Contact layers in such a thickness range are advantageously subject to low process variations during production. In addition, layers with such thicknesses are well reproducible due to the controllable production.

In one development, the semiconductor body has oblique side surfaces. For example, the semiconductor body is arranged on a carrier, wherein the lateral extent of the semiconductor body tapers at a distance from the carrier. The angle between the lateral extent of the carrier and inclined side surfaces is for example 45 ° C.

Due to the oblique side surfaces, total reflection effects of the radiation emitted by the active layer on the side surfaces can advantageously be reduced, so that advantageously the coupling-out efficiency of the semiconductor chip increases.

In a development, the semiconductor body is based on GaN. N-doped GaN has a good electrical contact with TCO, with the n-contact layer of the combination of TCO and silver to the semiconductor body of GaN, a highly reflective ohmic contact can be realized.

Further advantages and advantageous developments will become apparent from the following in connection with the 1 to 3 described embodiments. Show it:

1 a schematic cross section of an embodiment of a semiconductor chip,

2 a schematic section of the semiconductor chip according to the embodiment of the 1 , and

3 a schematic section of the n-contact layer according to the prior art.

In the figures, the same or equivalent components may each be provided with the same reference numerals. The illustrated components and their proportions with each other are not to be regarded as true to scale. Rather, individual components, such as layers, structures, components and areas for exaggerated representability and / or better understanding can be shown exaggerated thick or large dimensions.

In 3 is a cross section of a section of a semiconductor chip according to the prior art shown. The section shows in particular the n-contacting of the semiconductor chip. The semiconductor chip has an n-side 1b on, which is formed of semiconductor layers. In order to contact the n-side of the semiconductor chip, there is an n-contact layer 2 B . 2c Use. The n-contact layer is composed of a silver layer 2 B and a titanium layer 2c . the titanium layer 2c between n-side 1b of the semiconductor chip and silver layer 2 B is arranged.

The silver layer 2 B is therefore not in direct contact with the n-side of the semiconductor chip. The titanium layer 2c creates a good electrical contact to the n-side 1b of the semiconductor chip. Such titanium layers 2c However, they have a poor reflectivity of the radiation in the visible spectral range, so that the radiation is at least partially absorbed by the titanium layer, which leads adversely to a loss of radiation efficiency. In addition, the titanium layer 2c disadvantageously very reactive and easily oxidizable.

The silver layer 2 B is a good reflector for radiation in the visible spectral range, but has an unfavorably high contact resistance to the n-side 1b of the semiconductor chip.

The titanium layer 2c is conventionally made very thin due to the absorbent properties. For example, such a titanium layer 2c a thickness of at most 0.5 nm.

Such conventionally used N-contact layers comprising a titanium layer 2c and a silver layer 2 B Accordingly, have a plurality of disadvantages, such as absorption effects, adverse oxidation and adverse contact resistance.

In order to realize an n-contact layer which avoids these disadvantages, the conventionally used titanium layer is replaced by a TCO layer. The TCO layer with a silver layer arranged behind it has a low absorption with simultaneously good reflectivity for radiation in the visible spectral range. Such TCO layers can also be much better control than conventional titanium layers, adhere well, give good electrical contact and are much less reactive.

In 1 is a schematic cross section of a semiconductor chip 10 shown a semiconductor body 1 having. The semiconductor body 1 has an n-side 1b , a p-side 1c and an active layer 1a on that between n-side 1b and p-side 1c is arranged. The semiconductor body is preferably based on GaN. For example, the semiconductor body 1 a radiation-emitting semiconductor chip, preferably an LED, particularly preferably a thin-film LED.

The semiconductor body 1 has sloping side surfaces 11 on. Sloping side surfaces should be understood in particular to mean that the side surfaces are formed at an angle between 0 and 90 ° to the lateral extent of the layers of the semiconductor body. Preferably, the angle is between 45 ° and 90 °. Through the sloping side surfaces 11 Advantageously, the coupling-out efficiency of the radiation emitted by the active layer can be improved, since total reflection effects are reduced.

The semiconductor body 1 has a p-contact layer for p-contacting 21a and for n-contacting an n-contact layer 2 on. The p-contact layer 21a is for electrical contacting of the p-side 1c of the semiconductor body 1 intended. The n-contact layer 2 is for electrical contacting of the n-side 1b of the semiconductor body 1 intended.

In the present embodiment, the p-contact layer 21a and the n-contact layer 2 on the same side of the semiconductor body 1 arranged. In particular, the contact layers 21a . 2 on the p side 1c of the semiconductor body 1 arranged. The p-contact layer 21a borders directly on the p-side 1c of the semiconductor body 1 at. On the of the semiconductor body 1 opposite side of the p-contact layer 21a can be a current spreading layer 21b be arranged, providing a homogeneous current flow and current expansion on the p-side 1c of the semiconductor body 1 allows.

On the of the semiconductor body 1 opposite side of the p-contact layer 21a and the current spreading layer 21b is an electrically insulating layer 3 arranged. The electrically insulating layer is, for example, a passivation layer. On the from the p-contact layer 21a opposite side of the electrically insulating layer 3 is the n-contact layer 2 arranged. The electrically insulating layer 3 separates the p-contact layer 21a completely from the n-contact layer 2 , The electrically insulating layer 3 is thus between p-contact layer 21a and n-contact layer 2 arranged.

The n-contact layer 2 is by means of a breakthrough 22 through the p-contact layer 21a and through the p-side 1c of the semiconductor body 1 to the n-side 1b led the semiconductor chip. The breakthrough 22 extends through the p-contact layer 21a , the p-side 1c and the active layer 1a and ends in the n-side 1b of the semiconductor body 1 , The n-contact layer 21a , the p-side 1c and the active layer 1a be completely clear of the breakthrough 22 breached.

The semiconductor chip 10 can also have a number of breakthroughs 22 have, corresponding to the desired current injection in the n-side 1b of the semiconductor body 1 are arranged.

The n-contact layer 2 contains a silver layer and a TCO layer with the silver layer on that of the p-contact layer 21a opposite side of the electrically insulating layer 3 and in the breakthrough 22 or the breakthroughs is arranged. The TCO layer of the n-contact layer 2 is between the silver layer and the n-side semiconductor material 1b of the semiconductor body 1 arranged. In particular, the TCO layer is on the breakthrough 22 arranged.

The TCO layer is in 1 not shown for the sake of clarity. The n-contact of the n-contact layer 2 to the n-side 1b of the semiconductor body 1 is however in 2 shown in detail and explained.

For electrical insulation is the breakthrough 22 or are the breakthroughs with the electrically insulating layer 3 lined so that the n-contact layer 2 and the p-contact layer 21a as well as the p-side 1c Do not touch each other directly or form an electrical contact with each other.

The electrical contacting of the semiconductor chip 1 thus takes place on one side on the p-side of the semiconductor body 1 , On the p side 1c opposite side of the semiconductor body 1 a radiation exit side is formed, through which the radiation emitted by the active layer for the most part from the semiconductor chip 10 is decoupled. On the of the semiconductor body 1 opposite side of the n-contact layer 2 is a barrier layer 4 arranged, which is an ion diffusion between individual layers of the semiconductor chip 10 prevented.

On the of the n-contact layer 2 opposite side of the barrier layer 4 is a layer of solder 5 arranged, by means of which the semiconductor chip 10 on a carrier 6 applied and attached. The carrier 6 points to that of the semiconductor body 1 side facing away from an electrical connection layer 7 through which the electrical connection to the n-contact layer 2 can be produced.

In the embodiment of the 1 shown section A is in 2 shown enlarged. 2 shows in particular the electrical connection between the n-side 1b of the semiconductor body 1 and n-contact layer 2 , The cutout is in the area of a breakthrough 22 ,

The n-contact between the n-side 1b of the semiconductor body 1 and the n-contact layer 2 is about the TCO layer 2a educated. The n-contact layer 2 thus consists of the silver layer 2 B and the TCO layer 2a together, with the silver layer 2 B is not in direct contact with the semiconductor material. Between silver layer 2 B and semiconductor material of the n-side 1b is the TCO layer 2a arranged.

The TCO layer 2a has ZnO or ITO, for example. Alternatively or additionally, for example, tin oxide, aluminum zinc oxide, aluminum tin oxide, gallium tin oxide, gallium zinc oxide or indium zinc oxide find application. The thickness D of the TCO layer 2a is greater than 0.5 nm. Preferably, the thickness D of the TCO layer 2a in a range between 15 nm inclusive and 25 nm inclusive, for example at 20 nm.

The conventionally used thin titanium layer with a thickness of at most 0.5 nm is thus replaced by a substantially thicker layer of a transparent conductive oxide which, together with the silver layer arranged behind it, enables improved reflectivity and improved ohmic contact. Such thick TCO layers can be controlled much better than the conventionally used thin titanium layers. In addition, the TCO layers adhere well to good, give a good electrical contact and are much less reactive than the conventional titanium layer.

By means of the n-contact layer formed as described consisting of a silver layer and a TCO layer, a highly reflective ohmic contact can be ensured with advantage on the n-side of the semiconductor chip.

The invention is not limited by the description based on the embodiments of this, but includes each new feature and any combination of features, which in particular includes any combination of features in the claims, even if these features or combinations themselves are not explicitly in the claims or Embodiments are given.

Claims (11)

Optoelectronic semiconductor chip ( 10 ) comprising a semiconductor body ( 1 ) of semiconductor material, a p-contact layer ( 21a ) and an n-contact layer ( 2 ), wherein - the semiconductor body ( 1 ) an active layer provided for generating radiation ( 1a ), - the semiconductor body ( 1 ) a p-side ( 1c ) and an n-side ( 1b ), between which the active layer ( 1a ), - the p-contact layer ( 21a ) for electrical contacting of the p-side ( 1c ) of the semiconductor body ( 1 ) is provided, The n contact layer ( 2 ) for electrical contacting of the n-side ( 1b ) of the semiconductor body ( 1 ), and - the n-contact layer ( 2 ) a TCO layer ( 2a ) contains. Optoelectronic semiconductor chip according to claim 1, wherein the p-contact layer ( 21a ) and the n-contact layer ( 2 ) on the same side of the semiconductor body ( 1 ) are arranged. Optoelectronic semiconductor chip according to claim 2, wherein - the p-contact layer ( 21a ) directly to the p-side ( 1c ) of the semiconductor body ( 1 ), - the n-contact layer ( 2 ) at the of the semiconductor body ( 1 ) facing away from the p-contact layer ( 21a ), and - between the p-contact layer ( 21a ) and the n-contact layer ( 2 ) an electrically insulating layer ( 3 ) is arranged. Optoelectronic semiconductor chip according to claim 3, wherein the n-contact layer ( 2 ) by means of a breakthrough ( 22 ) through the p-contact layer ( 21a ) and through the p-side ( 1c ) of the semiconductor body ( 1 ) to the n-side ( 1b ) is guided. An optoelectronic semiconductor chip according to claim 4, wherein - the n-contact layer ( 2 ) a silver layer ( 2 B ), and - the TCO layer ( 2a ) of the n-contact layer ( 2 ) between the n-side ( 1b ) of the semiconductor body ( 1 ) and the silver layer ( 2 B ) of the n-contact layer ( 2 ) is arranged. Optoelectronic semiconductor chip according to claim 5, wherein - the silver layer ( 2 B ) through the breakthrough ( 22 ), and - the TCO layer ( 2a ) on the breakthrough ( 22 ) is arranged. Optoelectronic semiconductor chip according to one of the preceding claims, wherein the TCO layer ( 2a ) ZnO or ITO contains. Optoelectronic semiconductor chip according to one of the preceding claims, wherein the TCO layer ( 2a ) has a thickness greater than 0.5 nm. An optoelectronic semiconductor chip according to claim 8, wherein the TCO layer ( 2a ) has a thickness in a range between 15 nm inclusive and 25 nm inclusive. Optoelectronic semiconductor chip according to one of the preceding claims, wherein the semiconductor body ( 1 ) oblique side surfaces ( 11 ) having. Optoelectronic semiconductor chip according to one of the preceding claims, wherein the semiconductor body ( 1 ) based on GaN.

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