LIGHT-EMITTING SEMICONDUCTOR DEVICE, LIGHT-EMITTING SEMICONDUCTOR COMPONENT AND METHOD FOR PRODUCING A LIGHT-EMITTING SEMICONDUCTOR DEVICE

Abstract

The invention relates to, inter alia, a light-emitting semiconductor component comprising the following: a first mirror (102, 202, 302, 402, 502), a first conductive layer (103, 203, 303, 403, 503), a light-emitting layer sequence (104, 204, 304, 404, 504) on a first conductive layer face facing away from the first mirror, and a second conductive layer (105, 205, 305, 405, 505) on a light-emitting layer sequence face facing away from the first conductive layer, wherein the first mirror, the first conductive layer, the light-emitting layer sequence, and the second conductive layer are based on a III-nitride compound semiconductor material, the first mirror is electrically conductive, and the first mirror is a periodic sequence of homoepitaxial materials with varying refractive indices.

Claims

1. Light-emitting semiconductor device having a first mirror, a first conductive layer, a light-emitting layer sequence on a side of the first conductive layer remote from the first mirror, and a second conductive layer on a side of the light-emitting layer sequence remote from the first conductive layer, wherein the first mirror, the first conductive layer, the light-emitting layer sequence and the second conductive layer are based on a III-nitride compound semiconductor material, the first mirror is electrically conductive, and the first mirror is a periodic sequence of homoepitaxial materials with a differing refractive index.

2. Light-emitting semiconductor device according to claim 1, in which the first mirror comprises a periodic sequence of high-refractive-index mirror layers and low-refractive-index mirror layers, wherein the high-refractive-index mirror layers and the low-refractive-index mirror layers differ from one another by the concentration of a dopant.

3. Light-emitting semiconductor device according to claim 2, in which the high-refractive-index mirror layers and the low-refractive-index mirror layers have the same dopant.

4. Light-emitting semiconductor device according to claim 3, in which the dopant is tin or germanium.

5. Light-emitting semiconductor device according to claim 3, in which the low-refractive-index mirror layers have a dopant concentration of at least 210.sup.19 cm.sup.3 and the high-refractive-index mirror layers a dopant concentration of less than 110.sup.19 cm.sup.3.

6. Light-emitting semiconductor device according to claim 1, in which a further dopant which differs from the dopant is introduced at an interface between a low-refractive-index mirror layer and a high-refractive-index mirror layer.

7. Light-emitting semiconductor device according to claim 6, in which the further dopant is silicon and at most a monolayer of the further dopant is introduced.

8. Light-emitting semiconductor device according to claim 1, having a second mirror on a side of the second conductive layer remote from the light-emitting layer sequence, wherein the second mirror is formed with at least one of the following materials: semiconductor, insulator, metal.

9. Light-emitting semiconductor device according to claim 8, in which the second mirror is of similar construction to the first mirror, wherein the second mirror comprises a smaller number of mirror layers than the first mirror and the reflectivity of the second mirror is lower than the reflectivity of the first mirror.

10. Light-emitting device, characterized by a) a resonator with at least one mirror coating produced by epitaxy of a periodic sequence of homoepitaxial materials with a differing refractive index, b) a light-emitting group III-nitride layer or layer sequence, c) at least one substance which at least partially converts the luminescence of the group III-nitride layer and/or further group III-nitride layer, wherein the light-emitting device is based on a III-nitride compound semiconductor material.

11. Light-emitting device according to claim 10, in which the refractive index difference of the group III-nitride layers in the resonator is produced by modifying the doping.

12. Light-emitting device according to claim 11, wherein the resonator has doping of over 210.sup.19 cm.sup.3, preferably over 810.sup.19 cm.sup.3, and a lower doping of below 110.sup.19 cm.sup.3, preferably below 510.sup.18 cm.sup.3, for the respectively differently refractive layers.

13. Light-emitting device according to claim 10, characterized by an additional highly reflective mirror coating on the surface of the group III-nitride layers, which has a spectral bandwidth greater than the emission bandwidth of the light-emitting group III-nitride layer or group III nitride-layer sequence and the center wavelength of which corresponds to the wavelength to be emitted.

14. Light-emitting semiconductor device according to claim 10, in which the semiconductor device is one of the following semiconductor chips: light-emitting diode chip, laser diode chip, superluminescent diode chip.

15. Light-emitting component having at least one light-emitting semiconductor device according to claim 1, and a converter which is arranged downstream of the at least one light-emitting semiconductor device.

16. Light-emitting component according to claim 15, in which a distance is present between the at least one light-emitting semiconductor device and the converter.

17. Method for producing a light-emitting device according to said light-emittigen device comprising: a first mirror, a first conductive layer, a light-emitting layer sequence on a side of the first conductive layer remote from the first mirror, and a second conductive layer on a side of the light-emitting layer sequence remote from the first conductive layer, wherein the first mirror, the first conductive layer, the light-emitting layer sequence and the second conductive layer are based on a III-nitride compound semiconductor material, the first mirror is electrically conductive, and the first mirror is a periodic sequence of homoepitaxial materials with a differing refractive index, and wherein the low-refractive-index mirror layers and the high-refractive-index mirror layers of the first mirror and/or second mirror are produced by homoepitaxial growth.

18. Method according to claim 17, wherein the dopant is added only during growth of the low-refractive-index mirror layers.

Description

[0077] In the figures:

[0078] FIG. 1 is a schematic representation of a first exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely an LED structure with a lower, first mirror,

[0079] FIG. 2 is a schematic representation of a second exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely a modified LED according to FIG. 1, but with an upper tunnel contact,

[0080] FIG. 3 is a schematic representation of a third exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely an improved vertical LED or a vertical laser,

[0081] FIG. 4 is a schematic representation of a fourth exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely a structure as in FIG. 3, but with a converter layer at a distance from the LED or the vertical laser,

[0082] FIG. 5A is a schematic representation of a fifth exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely contacting of a structure as in FIG. 2 after processing and

[0083] FIG. 5B is a schematic representation of a sixth exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely a structure with an additional upper mirror and contacting through the mirror,

[0084] FIG. 6 is a graph plot for explaining one aspect of exemplary embodiments of a light-emitting semiconductor device described here.

[0085] Identical, similar or identically acting elements are provided with identical reference numerals in the figures. The figures and the size ratios of the elements illustrated in the figures relative to one another are not to be regarded as being to scale. Rather, individual elements may be illustrated on an exaggeratedly large scale for greater ease of depiction and/or better comprehension.

[0086] FIG. 1 shows a first exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely a simple LED structure with a lower, first mirror 102.

[0087] 100 is here the substrate, 101 an optional buffer layer, 102 the first mirror, in the form of a Bragg-mirror with x layer pairs (x: integer or integer 0.5) of low- and high-refractive-index material, and 103 a usually n-conductive first conductive layer around the light-emitting layer sequence 104, in this case having by way of example three layers, ideally located at a maximum of the electrical field strength of the optical wave. The layer pairs need not necessarily be integral, the value possibly also being half-integral depending on the start or end of the layer sequence. The layer pairs here in each case comprise a high-refractive-index mirror layer 102a and a low-refractive-index mirror layer 102b.

[0088] The substrate 100 may be a growth substrate for the following layers, onto which said layers are epitaxially deposited. It is furthermore possible for the substrate 100 to be a carrier which does not correspond to the original growth substrate. In this case, the growth substrate can be detached and the remaining, epitaxially deposited layers fastened to substrate 100. The substrate 100 may in this case in particular designed to be electrically conductive.

[0089] The light-emitting layer sequence 104 comprises group III-nitride semiconductors which ideally have a smaller band gap than the surrounding material, thus for example not only InGaN in a GaN matrix, but also InGaN in an InGaN matrix with a lower In content. The material's band gap should be located in the visible or ultraviolet region of the spectrum. The number here depends on the design of the LED, with one to ten such layers, usually between 2-5 nm thick and separated by a barrier layer which is typically of a thickness of between 5 nm and 15 nm, being considered advantageous.

[0090] The barriers may, however, also be thicker in order to place each light-emitting layer at the maximum of the electrical field amplitude of the optical wave. In order to ensure optimum current injection into the light-emitting layers, as many as possible such layers should be placed within an individual amplitude maximum.

[0091] An electron barrier, not shown here, may be introduced above the light-emitting layers. For example, in a GaN-based LED, an Mg-doped AlGaN layer with a thickness of 5-25 nm and an Al content of between 5-30% prevents electron injection into the following layer 105. 105 is typically a p-doped second conductive layer for hole injection into the layers 104. Above this layer or a partially or completely transparent contacting layer (not shown here), the luminescence converter 106, which converts the light arising in the light-emitting layer sequence 104 entirely or in part into for example longer-wave light, may then be applied. At high beam intensities, conversion to shorter wavelengths, for example using frequency multiplication material, is also possible. In this example, light is preferably emitted in the direction of the arrow indicated above the structure.

[0092] FIG. 2 shows a second exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely a modified LED like that in FIG. 1, but with an upper tunnel contact 208 through a highly n-doped layer 207. Simpler contacting and better current distribution of the upper contact is consequently possible. The other reference signs follow FIG. 1, but beginning with a 2 instead of with a 1. In this case, an MQW structure deposited on the layer 207 may serve as a converter 206 for converting some of the electrically generated light into longer-wave light.

[0093] FIG. 3 shows a third exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely an improved vertical LED or a vertical laser. Thanks to an upper, second mirror 309 with y mirror pairs, wherein y is <x and y is an integer or an integer 0.5, and the cavity 303-305 with an optical thickness which corresponds to an integral multiple of half the wavelength, and active layers, that is to say the light-emitting layer sequence 304, therein, a narrower emission spectrum is obtained and it is thus also possible, given appropriately high currents, to produce a VCSEL (vertical-cavity surface-emitting laser). The second mirror 309 is here ideally also made from the same material or a material from the same class of materials (AlInGaN) as the lower, first mirror 302.

[0094] With a highly n-doped layer 307 as the lower, low-refractive-index mirror layer 309a on the p-doped layer 305, it is then possible to produce a tunnel contact 308 similar to that shown in FIG. 2. The other reference signs again follow the preceding drawings. In principle, the upper, second mirror 309 may also be produced with other, even nonconductive materials, which, as a result of the larger jump in refractive index which is then usually available, only requires a few mirror pairs. In particular, a tunnel contact similar to that in FIG. 2 is then advantageous for the upper contact layer.

[0095] In the case of upward emission, thus in the direction of the arrow, the upper, second mirror 309 is generally less reflective than the lower, in order to maximize the stream of photons in the direction of the luminescence-converting layer, the converter 306, and not emit it unused in the other direction. In all the examples shown, the doping sequence, and thus also contacting, can in principle be reversed, that is to say the np junction may also be a pn-junction. All the examples may also be produced such that emission is towards the substrate. The latter may in principle also be removed or, after growth, be changed over to another carrier by rebonding. In this case, mirror reflectivity must be adapted to the other direction of emission.

[0096] FIG. 4 shows a fourth exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely a structure as in FIG. 3, but with a converter 406, in particular as a layer which is not directly on the structure or the upper contacting layer, but instead at a certain distance 410, which may be defined for example by a cavity or a further material such as a transparent silicone or a polymer. Heat can consequently be kept away from the converter and, depending on the embodiment, it is also possible to change or dispense with converter layers.

[0097] FIG. 5A shows a fifth exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely contacting of a structure as in FIG. 2 after processing. In this case, a circuit is produced by means of metalized coatings 511 and 513, which may be identical when an upper tunnel contact is used, with a wire 510 and 512 and a power supply (not shown), which circuit causes the device or the layers 504 in FIG. 2 to electroluminesce. The electroluminescence is then converted in the converter 506 entirely or in part into another wavelength.

[0098] FIG. 5B shows a sixth exemplary embodiment of a light-emitting semiconductor device described here or of a light-emitting semiconductor component described here, namely a structure with an additional upper, second mirror 509 and contacting through the mirror which ideally contains a p-n-tunnel contact, as shown in FIGS. 3 and 4 and designated 308 and 408. 523 is here the upper contact metal and 522 the upper connecting wire to a power source. In this example, the back contact is contacted, providing the substrate is conductive, via a metalized coating 521 on the back and a wire 520. It is in principle also possible to use a conductive oxide or a transparent conductive material, such as for example indium-tin oxide, instead of metal.

[0099] The graph plot of FIG. 6 shows the Borstein-Moss shift in bandgap energy E towards higher energies as a function of dopant concentration n. The dopant used here is germanium in GaN layers. The refractive index of the doped layers behaves reciprocally to the energy of the band gap, that is to say, the greater the energy of the band gap, the smaller is the refractive index. It is apparent from FIG. 6 that, counterintuitively, the band gap is not at its lowest in the undoped case, but instead has a minimum in the region of a dopant concentration of 10.sup.18 cm.sup.3. The refractive index is therefore at its maximum in the region of a dopant concentration of 10.sup.18 cm.sup.3, such that a maximum refractive index difference between the low-refractive-index and high-refractive-index mirror layers may be achieved with a dopant concentration of 10.sup.18 cm.sup.3 in the highly doped layer.

[0100] The examples shown here, or sub-aspects thereof, may be combined with one another as desired. In particular, the description made with reference to the exemplary embodiments does not restrict the invention to these embodiments. Rather, the invention encompasses any novel feature and any combination of features, including in particular any combination of features in the claims, even if this feature or this combination is not itself explicitly indicated in the claims or exemplary embodiments.

LIST OF REFERENCE SIGNS

[0101] 100, 200, 300, 400, 500 Substrate [0102] 101, 201, 301, 401, 501 Buffer layer [0103] 102, 202, 302, 402, 502 First mirror [0104] 102a, 202a, 302a, 402a, 502a High-refractive-index mirror layers [0105] 102b, 202b, 302b, 402b, 502b Low-refractive-index mirror layers [0106] 103, 203, 303, 403, 503 First conductive layer [0107] 104, 204, 304, 404, 504 Light-emitting layer sequence [0108] 105, 205, 305, 405, 505 Second conductive layer [0109] 106, 206, 306, 406, 506 Converter [0110] 207, 307, 407, 507 Highly n-doped layer [0111] 208, 308, 408, 508 Tunnel contact [0112] 309, 409 Second mirror [0113] 309a, 409a High-refractive-index mirror layers [0114] 309b, 409b Low-refractive-index mirror layers [0115] 410 Distance [0116] 510 Wire [0117] 511 Metalized coating [0118] 512 Wire [0119] 513 Metalized coating [0120] 520 Wire [0121] 521 Metalized coating [0122] 522 Contact metal [0123] 523 Contact metal