DE102007057708A1 - Optoelectronic component e.g. LED with emission wavelength below six hundred nanometers, has barrier layers and active layer with grating constants, which are smaller around specific percentages than grating constants of gallium arsenide - Google Patents

Abstract

The component has a radiation-emitting active layer (1) arranged between barrier layers (2), where the active layer and the barrier layers are made of respective indium-aluminum-gallium-phosphide combinations. The barrier layers include a wide electronic bandgap than the active layer. The barrier layers and the active layer include respective grating constants, which are smaller around 0.2 percentages or 1 percentage than the grating constants of gallium arsenide. Parameters of the active layer are selected such that the active layer includes a direct bandgap.

Description

The The invention relates to an optoelectronic component according to the General term of the patent claim 1.

at optoelectronic components such as LEDs or semiconductor lasers The basis of InAlGaP is the radiation-emitting active layer usually enclosed between shell layers, wherein the Coat layers a larger electronic band gap have as the active layer to the charge carriers in the active layer. For components, emit the comparatively short-wave radiation, for example at wavelengths less than 600 nm with LEDs or less than 650 nm in semiconductor lasers, the internal efficiency and the temperature behavior of the device often disadvantageous Leakage currents of charge carriers from the active Layer affected in the region of the cladding layers. The cause is that the achievable altitude the electronic barrier of the cladding layers opposite the active layer is insufficient to thermally excited charge carriers at the typical operating temperatures of optoelectronic components in the active layer.

A Reduction of the charge carrier concentration and one with it associated reduction of unwanted leakage currents could indeed by the production comparatively thicker active layers are achieved. However, this measure brings in semiconductor lasers due to those for laser operation required minimum density of charge carriers for the production of optical amplification are needed, no advantages. Furthermore, LEDs increase with an increase in the layer thickness the active layer also the proportion of non - radiative recombination processes and the re-absorption of the generated light in the active layer, so that limits the overall efficiency of an LED in this way only can be improved.

One Approach to increase the band gap of the barrier layers based on it, grid-spanned layers from the material system To use InAlGaP. It is exploited that the band gap strained Semiconductor materials in a tensile stress opposite the band gap of unstressed material is increased. The maximum layer thickness of the strained material is limited and usually not sufficient to charge the charge carriers in to include the active layer efficiently enough.

From the publication WO 2004/017433 A1 is an optoelectronic device based on InAlGaP known, which has an enclosed between two barrier layers active layer of a strained InAlGaP quantum well structure.

Of the Invention is based on the object, an optoelectronic component based on InAlGaP, where the internal efficiency is determined by a targeted utilization of the band structure properties of the material system InAlGaP is improved.

These The object is achieved by an optoelectronic component having the features of claim 1. Advantageous embodiments The invention is the subject of the dependent claims.

In one embodiment of the invention, an optoelectronic component has a radiation-emitting active layer of In _x1 (Al _{y1 Ga1 -y1} ) _1-x1 P with 0 ≦ x1 ≦ 1 and 0 ≦ y1 ≦ 1, which is formed between barrier layers of In _x2 (Al _{y2 Ga1 -y2} ) _1-x2 P where 0≤x2≤1 and 0≤y2≤1. The barrier layers have a larger electronic band gap than the active layer. Furthermore, the active layer and the barrier layers each have a lattice constant which deviates by at least 0.2% from the lattice constant of GaAs.

The Invention exploits the knowledge that the internal efficiency a radiation-emitting optoelectronic component on the Base of InAlGaP can be improved by having the active Layer and the barrier layers that surround the active layer, have such a material composition that their lattice constant in contrast to conventional lattice-matched growing up on GaAs differs by at least 0.2% from the lattice constant of GaAs.

Especially was found to be through one of the lattice constant non-GaAs lattice constant of the active layer and the barrier layers a bigger electronic barrier between the achieve active layer and the barrier layers. In this way, a reduction caused by leakage currents the internal efficiency of the device through transitions of Charge carriers from the active layer in the barrier layers conditional, counteracted.

Prefers are the lattice constants of the active layer and the barrier layers each at least 0.2% less than the lattice constant of GaAs. Particularly preferred are the lattice constants of the active Layer and the barrier layers each at least 1% lower as the lattice constant of GaAs. In this way are targeted the band structure properties of the material system InAlGaP to increase the electronic barrier between the active layer and the Barrier stories exploited.

The dependence of the electronic band gap on the lattice constant in the material system InAlGaP is known per se from band structure calculations which are described, for example, in US Pat 1 and 3 the publication WO 2004/017433 are shown. From such band structure calculations, it can be seen that, in particular with a lattice constant which is smaller than that of GaAs, an increased electronic band gap can be achieved in the material system InAlGaP.

at a preferred embodiment is the material composition the active layer, characterized by the parameters x1 and y1 is chosen such that the active layer has a direct bandgap having. This advantageously allows direct recombination of charge carriers under emission of radiation in the active layer. From band structure calculations it follows that a direct band gap in the material system InAlGaP in particular at values for the lattice constant greater than 5.57 Å. A preferred value of the lattice constant is therefore within a range between 5.57 Å and 5.64 Å, the latter Value is about 0.2% below the lattice constant of GaAs, the is about 5.65 Å. In this area is one hand the electronic band gap greater than at a lattice constant corresponding to the lattice constant of GaAs, and further, the semiconductor material has a region in this region direct band gap.

Under In the context of the application, the active layer is not just a single layer to understand, rather, the active layer can also by a for Radiation generation provided multilayer system may be formed. In the case of an active layer composed of several individual layers should the indicated advantageous embodiments, in particular with regard to the lattice constant, for the entirety of apply to radiation generation layers. In particular, can the active layer has a pn junction, a double heterostructure, a single quantum well structure or a multiple quantum well structure contain. The term quantum well structure includes in the frame the registration in particular any structure in the charge carriers by confinement a quantization of their energy states can learn. In particular, the name includes Quantum well structure no information about the dimensionality the quantization. It thus includes, among other things, quantum wells, Quantum wires and quantum dots and any combination of these Structures.

The Barrier layers preferably have a lower gallium content 1-y2 as the active layer. That way advantageous a particularly large band gap achieve in the barrier layers. Particularly preferred are the Barrier layers no gallium, for the gallium content In this case, the barrier layers therefore have 1-y2 = 0.

Since the active layer and the barrier layers have a lattice constant that differs by at least 0.2% from the lattice constant of GaAs, it is not readily possible to grow these layers in high crystalline quality on GaAs. The device therefore preferably includes a substrate having a lattice constant less than GaAs. In this case, a substrate made of GaAs _x P _1-x with 0 ≦ x <1 is particularly preferably used. Alternatively, it is also possible to use a substrate made of one of the quaternary materials AlGaAsP or InAlGaP.

In a further preferred embodiment, the component contains a substrate made of GaAs, wherein one or more buffer layers of GaAsP, AlGaAsP or InAlGaP are arranged on the GaAs substrate, the uppermost layer of the buffer layers having a lattice constant which is lower than GaAs. The uppermost buffer layer thus advantageously forms a quasi-substrate for the epitaxial growth of the further layers, which in particular contain the barrier layers and the active layer. The buffer layers are preferably a semiconductor layer sequence comprising a plurality of layers which contain GaAs _x P _1-x , for example the phosphorus content 1-x increasing stepwise from the lowest buffer layer applied to the GaAs substrate up to the uppermost buffer layer. The buffer layers are preferably semiconductor layer sequences which have a superlattice structure. Particularly suitable buffer layer sequences are per se from the document DE 10 2005 056 950 A1 The disclosure content of which is hereby incorporated by reference with respect to the possible configurations of the buffer layer sequence.

at the buffer layers are preferably metamorphic layers, that means layers that are almost unstressed on the surface Grown substrate or the respective underlying semiconductor layer are. A metamorphic growth can be especially at comparatively low Growth temperatures, of 700 ° C or less, for example in the range of 450 ° C to 700 ° C, can be achieved.

The Barrier layers and the active layer are preferably on Substrate or a quasi-substrate passing through the top of one or more buffer layers is formed, lattice-matched. The Barrier layers and the active layer are therefore preferred grown unstressed on the substrate or quasi substrate.

at an alternative embodiment facing the barrier layers the substrate or the uppermost buffer layer has a tensile strain. This embodiment is based on the knowledge that by a tensile Tensioning of the barrier layers in relation to the selected Substrate or quasi substrate a further increase in the electronic Band gap can be achieved.

The optoelectronic device need not necessarily have the growth substrate used to grow the barrier layers and the active layer. In particular, the optoelectronic component can be a thin-film component, wherein a thin-film component is understood to be a component in which a growth substrate used for epitaxially growing the layer sequence, which comprises the active layer and the barrier layers, has been subsequently removed. The basic principle of a thin-film component is, for example, in I. Schnitzer et al., Appl. Phys. Lett. 63 (16), 18 October 1993, 2174-2176 ,

at the optoelectronic component is preferably an LED or a semiconductor laser.

Especially can I use an LED with the optoelectronic component an emission wavelength of less than 600 nm or around a semiconductor laser having an emission wavelength of less than 650 nm or even less than 600 nm. Under the emission wavelength becomes the wavelength understood, in which the emitted radiation, the intensity maximum having.

The invention will be described below with reference to embodiments in connection with 1 to 5 explained in more detail.

It demonstrate:

1 a schematic representation of a cross section through a first embodiment of an optoelectronic device according to the invention,

2 a schematic representation of a simulation of the bandgap energy as a function of the lattice constant for InGaP and InAlP,

3 a schematic representation of a cross section through a second embodiment of an optoelectronic device according to the invention,

4 a schematic representation of a cross section through a third embodiment of an optoelectronic device according to the invention, and

5 a schematic representation of a cross section through a fifth embodiment of an optoelectronic device according to the invention.

Same or equivalent elements are in the figures with the same Provided with reference numerals. The figures are not to be considered as true to scale Rather, individual elements can be exaggerated for clarity be shown large.

At the in 1 shown first embodiment of an optoelectronic device according to the invention is an LED.

The LED contains a radiation-emitting active layer 1 from In _x1 (Al _{y1 Ga1 -y1} ) _1-x1 P with 0 ≤ x1 ≤ 1 and 0 ≤ y1 ≤ 1. The active layer 1 Not only may it be a single layer, but it may include one or more radiation generation layers, such as a pn junction, a double heterostructure, a single quantum well structure, or a multiple quantum well structure. In the context of the application, the term quantum well structure encompasses in particular any structure in which charge carriers can undergo quantization of their energy states by confinement. In particular, the term quantum well structure does not include information about the dimensionality of the quantization. It thus includes quantum wells, quantum wires and quantum dots and any combination of these structures.

The active layer 1 is between barrier layers 2 from In _x2 (Al _{y2 Ga1 -y2} ) _1-x2 P with 0 ≤ x2 ≤ 1 and 0 ≤ y2 ≤ 1. The barrier stories 2 that the active layer 1 surrounded, have the purpose of electronic charge carriers in the active layer 1 and thus reduce unwanted leakage currents that would otherwise be reduced by the internal efficiency of the optoelectronic device. For this purpose, the barrier layers exhibit 2 a larger electronic band gap than the active layer 1 on.

The active layer 1 and the barrier stories 2 each have a lattice constant that deviates by at least 0.2% from the lattice constant of GaAs. It is particularly advantageous if the barrier layers 2 have a lattice constant at least 0.2% lower than GaAs. In a particularly preferred embodiment, the lattice constants of the active layer 1 and the barrier stories 2 each at least 1% less than the lattice constant of GaAs. For example, the lattice constant of the active layer and the Barri can be smaller by about 1.2% than the lattice constant of GaAs.

By depositing the barrier layers 2 and the active layer 1 With a lattice constant deviating by at least 0.2% from GaAs, a larger electronic bandgap can be achieved compared to conventional LED layer sequences grown on lattice-matched GaAs. In particular, a larger electronic band gap of the barrier layers 2 can be achieved, whereby unwanted leakage currents from the active layer 1 into the barrier layers 2 be reduced.

For electrical contacting, the LED contains, for example, a first electrical contact 5 at one of the active layer 1 opposite side of the substrate 3 and another electrical contact 6 at one of the substrate 3 remote side of the semiconductor layer sequence. Between the one from the substrate 3 remote barrier layer 2 and the second electrical contact 6 For example, a current spreading layer 4 be arranged. The optoelectronic component can also be further, in 1 not shown layers.

The barrier stories 2 preferably have a material _composition In _x2 (Al _{y2 Ga1 -y2} ) _1-x2 P, in which the gallium portion 1-y2 is less than in the active layer 1 , The barrier layers particularly preferably have no gallium, so that for the gallium portion of the barrier layers 1-y2 = 0. In this way, a comparatively large electronic band gap of the barrier layers 2 in particular larger than the electronic band gap of the active layer 1 ,

The semiconductor layer sequence of the optoelectronic component, in particular the active layer 1 and the barrier stories 2 contains, for example, as in 1 shown on a semiconductor substrate 3 grew up.

The semiconductor layer sequence, in particular the active layer 1 and barrier layers 2 are advantageously lattice-matched to the substrate 3 grew up. Since the lattice constants of the active layer 1 and the barrier stories 2 By at least 0.2% of the lattice constant of GaAs differ, a substrate made of GaAs is not suitable for this because it is not possible to grow InAlGaP in sufficiently high crystalline quality with such a large lattice mismatch. In order to enable an unstressed growth, it is preferable instead to choose a substrate which has a lattice constant which is lower than that of GaAs. Preferably, the substrate is a GaAs _x P ₁ -x substrate with 0 ≦ x <1. Alternatively, however, a substrate made of a quaternary semiconductor material such as, in particular, AlGaAsP or InGaAlP, which has a suitable lattice constant, could also be used.

At the in 1 illustrated embodiment, for example, the active layer 1 and the barrier layer 2 have a lattice constant reduced by about 1.2% over the lattice constant of GaAs. The optoelectronic component in this case contains, for example, a substrate 3 GaAs _0.7 P _0.3 , a first barrier _layer of Al _0.65 In _0.35 P, which is for example n-doped, an active layer or layer sequence 1 Al _0.65x Ga _{0.65 (1-x)} In _0.35 P with 0 ≤ x <1, and a second of the active layer 1 in the growth _direction subsequent second barrier _layer of Al _0.65 In _0.35 P, which is for example p-doped. Between the second barrier layer 2 and the p-contact 6 can be a current spreading layer 4 which is preferably also lattice-matched to the substrate and contains, for example, AlGaAsP or InAlGaAsP.

The dependence of the electronic band gap on the lattice constant is given in 2 illustrating the electronic band structure for GaInP and AlInP materials. 2 shows the electronic band gap for the material system Ga _x In _1-x P at the Γ-point (curve 20 ), at the X-point (curve 21 ) and at the L point (curve 22 ). Further shows 2 the electronic band gap for the material system Al _x In _1-x P at the gamma point (curve 30 ), at the X-point (curve 31 ) and at the L point (curve 32 ). For the active layer 1 Preferably, a material composition is selected in which the semiconductor material has a direct bandgap. This is according to band structure calculations, in particular in the 2 hatched area of the case. The lattice constant is greater than 5.57 Å for a material composition with a direct band gap.

This in 3 illustrated second embodiment of an optoelectronic device according to the invention substantially corresponds to the in 1 In particular, it contains a first barrier _layer of Al _0.65 In _0.35 P, which is for example n-doped, an active layer or layer sequence 1 Al _{0.65 x} Ga _{0.65 (1-x)} In _0.35 P with 0 ≤ x <1, and a second of the active layer 1 in the growth _direction subsequent second barrier _layer of Al _0.65 In _0.35 P, which is for example p-doped.

In contrast to the first exemplary embodiment, however, the component contains a GaAs substrate instead of a growth substrate made of GaAs _0.7 P _0.3 3 with a buffer layer sequence grown thereon 7 , The GaAs substrate 3 with the buffer layers episode 7 acts as a quasi-substrate for epitaxially growing the subsequent layers, in particular the active layer 1 and the barrier stories 2 , The buffer layer sequence 7 contains, for example, a layer sequence of several layers 7a . 7b . 7c . 7d and 7e , whose lattice constants are stepwise from the lattice constant of the GaAs substrate 3 , which is about 5.65 Å, to a lattice constant which differs by at least 0.2% from the lattice constant of GaAs, at the surface of the uppermost layer 7e the semiconductor layer sequence 7 present, reduced. In particular, it may be in the layers of the semiconductor layer sequence 7 to act metamorphic layers that have grown relaxed and thus each lattice-matched to the underlying layer. In particular, it may be in the layers of the buffer layer sequence 7 to act layers of GaAs _1-x P _x , in which the phosphorus content x starting from the bottom layer 7a up to the top layer 7e gradually increases. Alternatively, the semiconductor layer sequence 7 also have a superlattice structure or a gradient layer. Suitable buffer layer sequences for forming a quasi-substrate are in particular from the document DE 10 2005 056 950 A1 known.

This in 4 illustrated third embodiment of an optoelectronic device according to the invention substantially corresponds to the second embodiment, but wherein the barrier layers 2 have the composition Al _0.7 In _0.3 P, so have a greater proportion of aluminum than the barrier layers of the second embodiment. Due to the increased aluminum content in this embodiment, the barrier layers 2 Tensile braced. The acceptance of such a tensile stress has the advantage that the electronic band gap is further increased due to the increased aluminum content compared to unstressed layers. Due to the increased band gap of the barrier layers 2 become unwanted leakage currents from the active layer 1 advantageously further reduced and thus improves the internal efficiency of the optoelectronic device.

At the in 5 illustrated fourth embodiment of an optoelectronic component according to the invention is in contrast to the embodiments previously shown not an LED, but an edge-emitting semiconductor laser.

Like the LEDs of the second and third embodiments, the semiconductor laser is on a quasi-substrate which is a GaAs substrate 3 and a semiconductor layer sequence deposited thereon 7 whose topmost layer 7e has a lattice constant reduced by at least 0.2% over GaAs.

The active layer 1 of the semiconductor laser contains a single or multiple quantum well structure containing, for example, Ga _0.65 In _0.35 P layers. The active layer of the edge emitting semiconductor laser is between waveguide layers 8th containing, for example, Al _0.26 Ga _0.39 In _0.35 P, included. The waveguide layers 8th are in turn of barrier layers 2 containing, for example, Al _0.7 In _0.3 P, enclosed. In this choice of materials of the layers, the lattice constant of the semiconductor layer structure, in particular the active layer 1 and the barrier stories 2 by about 1.2% from the lattice constant of GaAs. In this way, in particular, a semiconductor laser can be realized which has a shorter wavelength than conventional semiconductor lasers which are grown lattice-matched on a GaAs substrate. In particular, the semiconductor laser can laser radiation 9 emit at an emission wavelength of 650 nm or less.

The The invention is not by the description based on the embodiments limited. Rather, the invention includes every new feature as well any combination of features, especially any combination includes features in the claims, also if this feature or combination itself is not explicit specified in the patent claims or exemplary embodiments is.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 2004/017433 A1 [0005]
• WO 2004/017433 [0012]
• - DE 102005056950 A1 [0017, 0044]

Cited non-patent literature

• I. Schnitzer et al., Appl. Phys. Lett. 63 (16), 18 October 1993, 2174-2176. [0021]

Claims (15)

Optoelectronic component with a radiation-emitting active layer ( 1 ) of In _x1 (Al _{y1 Ga1 -y1} ) _1-x1 P with 0 ≦ x1 ≦ 1 and 0 ≦ y1 ≦ 1, which are formed between barrier layers ( 2 ) of In _x2 (Al _{y2 Ga1 -y2} ) _1-x2 P where 0≤x2≤1 and 0≤y2≤1, the barrier layers ( 2 ) have a larger electronic band gap than the active layer ( 1 ), characterized in that the active layer ( 1 ) and the barrier layers ( 2 ) each have a lattice constant which differs by at least 0.2% from the lattice constant of GaAs. Optoelectronic component according to claim 1, characterized in that the lattice constants of the active layer ( 1 ) and the barrier layers ( 2 ) are each at least 0.2% smaller than the lattice constant of GaAs. Optoelectronic component according to claim 2, characterized in that the lattice constants of the active layer ( 1 ) and the barrier layers ( 2 ) are each at least 1% smaller than the lattice constant of GaAs. Optoelectronic component according to one of the preceding claims, characterized in that the parameters x1 and y1 of the active layer ( 1 ) are selected such that the active layer ( 1 ) has a direct band gap. Optoelectronic component according to claim 4, characterized in that the lattice constant of the active layer ( 1 ) between 5.57 Å and 5.64 Å inclusive. Optoelectronic component according to one of the preceding claims, characterized in that the barrier layers ( 2 ) have a lower gallium content 1-y2 than the active layer ( 1 ). Optoelectronic component according to claim 6, characterized in that for the gallium content of the barrier layers ( 2 ) 1-y2 = 0 holds. Optoelectronic component according to one of the preceding claims, characterized in that the component is a substrate ( 3 ) containing a lattice constant lower than GaAs. Optoelectronic component according to claim 8, characterized in that the substrate ( 3 ) GaAs _x P _1-x with 0 ≤ x <1. Optoelectronic component according to one of Claims 1 to 7, characterized in that the component is a substrate ( 3 ) of GaAs, wherein on the substrate ( 3 ) one or more buffer layers ( 7 ) are arranged of GaAsP, AlGaAsP or InAlGaP, wherein the uppermost layer ( 7e ) of the buffer layers has a lattice constant lower than that of GaAs to form a quasi-substrate for epitaxially growing further layers comprising the barrier layers ( 2 ) and the active layer ( 1 ) train. Optoelectronic component according to one of claims 8 to 10, characterized in that the barrier layers ( 2 ) and the active layer ( 1 ) to the substrate ( 3 ) or the uppermost buffer layer ( 7e ) are lattice-matched. Optoelectronic component according to one of claims 8 to 10, characterized in that the barrier layers ( 2 ) relative to the substrate ( 3 ) or the uppermost buffer layer ( 7e ) have a tensile strain. Optoelectronic component according to one of the claims 1 to 7, characterized in that the component is a thin-film component is. Optoelectronic component according to one of the preceding Claims, characterized in that the optoelectronic Component an LED with an emission wavelength of is less than 600 nm. Optoelectronic component according to one of the preceding Claims, characterized in that the optoelectronic Component, a semiconductor laser with an emission wavelength of less than 650 nm.