CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a national stage entry from International Application No. PCT/EP2018/073594, filed on Sep. 3, 2018, and claims priority under 35 U.S.C. § 119 from German Patent Application No. 102017120522.5, filed on Sep. 6, 2017, the entire contents of all of which are incorporated herein by reference.

A light-emitting semiconductor device is specified.

This patent application claims the priority of the German patent application 10 2017 120 522.5, the disclosure content of which is hereby included by reference.

Epitaxially grown semiconductor structures are nowadays used for a variety of applications. In order to generate visible light in the green to red spectral range, mainly epitaxial structures with active zones based on InAlGaP and InAlGaAs semiconductor materials are used. However, it has been shown that, despite measures to increase the light extraction, such as roughening, the efficiency of such components can be low, which may be due, among other things, to the chemical stability of surfaces located near the active zone.

At least one object of particular embodiments is to provide a light-emitting semiconductor device.

This object is achieved by a subject-matter according to the independent claim. Advantageous embodiments and developments of the subject-matter are characterized in the dependent claims, and are also disclosed by the following description and the drawings.

According to at least one embodiment, a light-emitting semiconductor device has a semiconductor layer sequence. The semiconductor layer sequence can be manufactured in particular by an epitaxy method, i.e., by epitaxial growth of semiconductor layers on a growth substrate. Suitable epitaxy methods can be, for example, metal organic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE).

The semiconductor layer sequence comprises at least a light-emitting semiconductor layer which is intended and embodied to emit light during operation of the semiconductor device. The semiconductor layer sequence can be based on a phosphide and/or arsenide compound semiconductor material system, i.e., InxAlyGa1-x-yP and/or InxAlyGa1-x-yAs, each with 0≤x≤1, 0≤y≤1 and x+y≤1, and can comprise or consist of at least one semiconductor layer or a plurality of semiconductor layers based on such material. The phosphide compound semiconductor material system and the arsenide compound semiconductor material system can be briefly referred to as InAlGaP and InAlGaAs. A semiconductor layer sequence comprising at least a light-emitting semiconductor layer based on InGaAlP can, for example, emit light with one or more spectral components in a green to red wavelength range during operation of the semiconductor device. A semiconductor layer sequence comprising at least a light-emitting semiconductor layer based on InAlGaAs can, for example, emit light with one or more spectral components in a red to infrared wavelength range during operation of the semiconductor device.

The semiconductor layer sequence can be embodied according to the desired functionality of the light-emitting semiconductor device and can, for example, have several light-emitting semiconductor layers instead of the one light-emitting semiconductor layer described here and in the following. Furthermore, the semiconductor layer sequence can comprise at least a first and a second cladding layer, between which the light-emitting semiconductor layer is arranged. Here and in the following, as cladding layers are denoted in particular those semiconductor layers which are usually arranged in a semiconductor layer sequence in the direction of growth on both sides of the light-emitting semiconductor layer and which form a confinement area for charge carriers. Accordingly, the cladding layers have a larger band gap than the light-emitting semiconductor layer in between. The variation of the band gaps of the layers of the semiconductor layer sequence can be achieved by a variation of the phosphide and/or arsenide compound semiconductor material. In particular, the ratio of Ga atoms to Al atoms can lead to a variation of the band gap along with minor variations of the lattice parameters. Particularly preferentially, the first and second cladding layers in the semiconductor layer sequence, which is based on a phosphide and/or arsenide compound semiconductor material system, have a higher aluminum content than the light-emitting semiconductor layer. For example, in light-emitting semiconductor devices having a semiconductor layer sequence based on a phosphide compound semiconductor material system, first and second cladding layers with or made of Al0.25In0.25P or with higher aluminum contents can be advantageous.

The generation of light in the light-emitting semiconductor layer can be based on electroluminescence or photoluminescence. Accordingly, the light-emitting semiconductor device can be an electroluminescent semiconductor device or a photoluminescent semiconductor device. In both cases photons are generated by excitation and recombination of charge carriers, especially electron-hole pairs. In the case of an electroluminescent semiconductor device, the excitation, i.e., the generation of charge carriers in the semiconductor layer sequence, takes place by injecting an electric current in the semiconductor layer sequence. In this case, the light-emitting semiconductor component can be embodied, for example, as a light-emitting diode chip. The current injection is usually carried out through the cladding layers with a larger band gap than the light-emitting semiconductor layer into the light-emitting semiconductor layer, in which the charge carriers can recombine as described, generating photons. In the case of a photoluminescent semiconductor device, the excitation takes place by irradiation of excitation light, for example from an external pump light source, which excitation light can be absorbed in the semiconductor layer sequence and especially in the light-emitting semiconductor layer. Since photons are usually absorbed which have a higher energy than the photons generated by recombination in the light-emitting semiconductor layer, in the case of a photoluminescent semiconductor device it can in particular form a conversion element, also known as an epitaxial converter or epi-converter. As in the case of a semiconductor electroluminescent device, the light-emitting semiconductor layer in a semiconductor photoluminescent device is located between the cladding layers, which have a larger band gap than the light-emitting semiconductor layer, in order to achieve efficient confinement of charge carriers in the light-emitting semiconductor layer. In contrast to electroluminescent semiconductor devices, however, photoluminescent semiconductor devices do not require current spreading layers, which can typically be 1 to 2 μm thick, since no current injection is required and thus no current spreading is necessary. Furthermore, in the case of a photoluminescent semiconductor device, it is usually necessary to remove the growing substrate, especially if it is not or only slightly transparent to the light generated in the light-emitting semiconductor layer or to the excitation light. Epi-converters can therefore be more cost-effective and compact than light-emitting diode chips.

Furthermore, the semiconductor layer sequence can have further semiconductor layers, in particular between the first and second cladding layer of which one can be p-doped and the other n-doped, for example p- and/or n-doped charge carrier transport layers, further undoped and/or p- and/or n-doped confinement, cladding and/or waveguide layers, barrier layers, planarization layers, buffer layers and/or protection layers. In addition, the semiconductor device—can have one or more contact metallizations by means of which the semiconductor layer sequence can be electrically contacted in the case of an electroluminescent semiconductor device.

Furthermore, the semiconductor device can have a substrate, which can be a growth substrate, for example, on which the semiconductor layer sequence has been grown epitaxially. Alternatively, after the growth the semiconductor layer sequence can be transferred to a substrate embodied as a carrier substrate and the growth substrate can be removed. As substrate materials semiconductor materials such as GaAs, GaP, Ge or Si can be suitable. Moreover, it can also be possible that the semiconductor layer sequence is detached from the growing substrate after growing without transferring the semiconductor layer sequence to a carrier substrate, so that the semiconductor device can also be substrateless. As described above, this can be particularly advantageous in the case of a photoluminescent semiconductor device.

According to a further embodiment, the semiconductor layer sequence comprises at least a first semiconductor protection layer. The first semiconductor protection layer can, particularly preferably, be arranged directly on the first cladding layer on a side facing away from the light-emitting semiconductor layer and form an outer layer of the semiconductor layer sequence. In the following, an outer layer is defined here as a semiconductor layer of the semiconductor layer sequence, with which the semiconductor layer sequence ends along the growing direction of the semiconductor layers, i.e., which has a surface facing away from the light-emitting semiconductor layer, the surface forming an outer surface of the semiconductor layer sequence. Alternatively, the first semiconductor protection layer can be arranged inside the first cladding layer, which in this case is formed as the outer layer of the semiconductor layer sequence. For this purpose, the first cladding layer can in particular comprise a first and a second sublayer, between which the first semiconductor protection layer is arranged in direct contact. In particular, the first sublayer can be located between the semiconductor protection layer and the light-emitting semiconductor layer, while the second sublayer is applied to the side of the first semiconductor protection layer facing away from the light-emitting semiconductor layer and thus forms the outside of the semiconductor layer sequence.

In particular, the first cladding layer and the first semiconductor protection layer can comprise and, particularly preferred, be made of semiconductor materials from the same compound semiconductor material system. In other words, the first cladding layer and the first semiconductor protection layer each comprise or are be made of a semiconductor material based on InAlGaP or based on InAlGaAs. Furthermore, the first semiconductor protection layer has a lower aluminum content than the first cladding layer. Semiconductor layers with a high aluminum content can degrade during the procedure of wet chemical process steps and also, for example, during operation in atmospheres containing moisture and/or oxygen, as the high aluminum content can promote oxidation of the semiconductor material. The first semiconductor protection layer having a lower aluminum content than the first cladding layer means that the first cladding layer, or at least a first part of it, can be protected from such degradation by the first semiconductor protection layer applied thereon from the point of view of the light-emitting semiconductor layer. Accordingly, the light-emitting semiconductor layer can also be protected from degradation by the first semiconductor protection layer. In particular, the aluminum content of the first semiconductor protection layer can be selected such that the first semiconductor protection layer is transparent to the light generated by the light-emitting semiconductor layer during operation and is at the same time stable in an environment containing moisture and oxygen. It has proven to be particularly advantageous if the first semiconductor layer has an aluminum content of more than 0% and less than 12%. Furthermore, it can be advantageous if the first semiconductor protection layer has a thickness of greater than or equal to 10 nm and less than or equal to 100 nm. If the semiconductor component has a substrate, the semiconductor layer sequence is arranged on the substrate in particular with a side facing away from the first semiconductor protection layer.

According to a further embodiment, the first semiconductor protection layer is arranged inside the first cladding layer, as described above, wherein the first cladding layer has a roughened surface on an outer side facing away from the light-emitting semiconductor layer. In other words, as described above, the first semiconductor protection layer can be arranged directly between a first and a second sublayer of the first cladding layer, the second sublayer, which forms an outer surface of the first cladding layer and thus an outer surface of the semiconductor layer sequence, having the roughening. The roughening can, for example, be produced by an etching process such as wet chemical etching and thus be an etching structure with regularly or irregularly arranged elevations and depressions. Preferably, the roughening does not extend through the first semiconductor protection layer. Particularly preferably, the roughening extends only up to the first semiconductor protection layer. In other words, the roughening has structures, in particular depressions, with a maximum depth less than or equal to the thickness of the second sublayer of the first cladding layer, so that no channels formed by the roughening reach through the first semiconductor protection layer. In this case, the first semiconductor protection layer can protect the layers beneath the first semiconductor protection layer, as seen from the light-emitting semiconductor layer, from oxidation during the production of the roughening in the first cladding layer. It can also be achieved that the formation of channels or pores through the first cladding layer to the light-emitting semiconductor layer is avoided, thus increasing the stability of the semiconductor device even in an atmosphere containing moisture and/or oxygen.

According to a further embodiment, the roughening has a maximum structure depth of greater than or equal to 200 nm and less than or equal to 1 μm, and particularly preferred of greater than or equal to 500 nm and less than or equal to 700 nm. Accordingly, the second sublayer of the first cladding layer also preferably has a thickness that is greater than or equal to the specified values.

The first semiconductor protection layer can be undoped or have p-doping or n-doping, depending on the embodiment of the light-emitting semiconductor device. Furthermore, the first semiconductor protection layer can have the same doping as the first cladding layer.

According to a further embodiment, the semiconductor layer sequence has a second semiconductor protection layer on a side of the light-emitting semiconductor layer opposite the first semiconductor protection layer. This can be particularly advantageous if the semiconductor component is substrate-free. In particular, the second semiconductor protection layer can be arranged, as a further outer layer, directly on the second cladding layer on a side facing away from the light-emitting semiconductor layer. The second semiconductor protection layer can have one or more of the features described in connection with the first semiconductor protection layer. In particular, the first and second semiconductor protection layer can be based on the same semiconductor material. Depending on the embodiment of the semiconductor device, the first and second semiconductor protection layers can be the same or different with regard to doping.

In the semiconductor device described here, by additionally incorporating at least the first semiconductor protection layer on one side of the light-emitting semiconductor layer or also the first and second semiconductor protection layers on different sides of the light-emitting semiconductor layer near or on the outer sides of the semiconductor layer sequence, it is possible to achieve an advantageous result that the stability of the semiconductor layer sequence and thus of the semiconductor component in environments containing moisture and/or oxygen can be increased with respect to oxidative aging processes, since the composition of the semiconductor protection layer(s), which is different from that of the cladding layers, is more resistant to damaging environmental conditions. As a result, it can be possible to achieve improved luminescence properties in semiconductor devices embodied as light-emitting diode chips and, in particular, also in semiconductor devices embodied as epi-converters.

