Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/83—Electrodes
  • H10H20/832—Electrodes characterised by their material
  • H10H20/835—Reflective materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/81—Bodies
  • H10H20/819—Bodies characterised by their shape, e.g. curved or truncated substrates
  • H10H20/82—Roughened surfaces, e.g. at the interface between epitaxial layers
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/81—Bodies
  • H10H20/814—Bodies having reflecting means, e.g. semiconductor Bragg reflectors
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/83—Electrodes
  • H10H20/832—Electrodes characterised by their material
  • H10H20/833—Transparent materials
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10H—INORGANIC LIGHT-EMITTING SEMICONDUCTOR DEVICES HAVING POTENTIAL BARRIERS
  • H10H20/00—Individual inorganic light-emitting semiconductor devices having potential barriers, e.g. light-emitting diodes [LED]
  • H10H20/80—Constructional details
  • H10H20/84—Coatings, e.g. passivation layers or antireflective coatings
  • H10H20/841—Reflective coatings, e.g. dielectric Bragg reflectors

Definitions

• the invention relates to a semiconductor light-emitting diode and to a method for producing a semiconductor light-emitting diode.
• Semiconductor light-emitting diodes have a layer stack of semiconductor layers whose materials (with respect to base material and dopant) are specifically selected and matched to one another in order to set the optoelectronic properties and the electronic band structure within the individual layers and at the layer boundaries to a predetermined extent.
• an optically active zone is produced which emits electromagnetic radiation during the current flow through the semiconductor layer stack. The generated radiation is first emitted in all directions, ie only partially in the emission direction of the semiconductor light emitting diode.
• an oxide layer of a transparent conductive oxide and one or more mirror layers are provided behind the semiconductor layer stack.
• the electromagnetic radiation impinging on the mirror layers is reflected to a proportion which depends on the difference of the optical refractive indices of the layers, on the conductivity of the mirror layer, on the transparency of the oxide layer and on the thickness of the oxide layer and the layers preceding it to the optically active zone.
• the material properties and material compositions of the respective layers are conventionally changed and optimized in addition to the layer thicknesses.
• the proportion of the electromagnetic radiation impinging on the mirror layer, which is reflected back by the mirror layer, could be increased, the light output of semiconductor light-emitting diodes could be increased.
• a semiconductor light-emitting diode with at least one p-doped light-emitting diode layer, an n-doped light-emitting diode layer and an optically active zone between the p-doped light-emitting diode layer and the n-doped light-emitting diode layer, with an oxide layer of a transparent conductive oxide and with at least one mirror layer is produced. wherein the oxide layer is disposed between the light-emitting diode layers and the at least one mirror layer and has a first interface facing the light-emitting diode layers and a second interface facing the at least one mirror layer, and wherein the second interface of the oxide layer has less roughness has as the first interface the oxide layer.
• a semiconductor light emitting diode in which the second interface of the oxide layer has a roughness smaller than 1.0 nm.
• the reflectance at the interface between the oxide layer and the mirror layer increases, and in particular the radiation components incident at large angles of incidence are reflected to a greater extent.
• the oxide layer is provided with a layer thickness of more than 5 nm, it is ensured that unevennesses of the first boundary layer of the oxide layer, which are caused by the roughness of the underlying uppermost semiconductor layer, are leveled and therefore do not adversely affect the roughness of the second boundary surface of the oxide layer ,
• the oxide layer and the mirror layer are located on the p side of the semiconductor light-emitting diode.
• the connection of the oxide layer initially involves an increase in the operating voltage of the semiconductor light-emitting diode, it can be compensated as described below.
• a p-doped semiconductor layer is arranged between the p-doped light-emitting diode layer and the oxide layer, which has a dopant concentration which is at least as large as the dopant concentration of the p-doped light-emitting diode layer.
• the p-doped semiconductor layer protects the p-doped light-emitting diode _
• the first boundary surface of the oxide layer adjoins the p-doped semiconductor layer.
• an n-doped semiconductor layer is arranged between the p-doped semiconductor layer and the oxide layer and that the oxide layer adjoins the n-doped semiconductor layer.
• an undoped semiconductor layer is provided between the p-doped semiconductor layer and the n-doped semiconductor layer. This forms a tunnel contact together with the two doped semiconductor layers, whereby the contact resistance of the tunnel contact is more than compensated by the low-resistance connection of the oxide layer via the n-doped semiconductor layer and the required operating voltage is therefore reduced overall.
• the oxide layer is electrically conductive.
• Suitable materials for the oxide layer are, for example, zinc oxide, indium tin oxide or indium zinc oxide.
• the second boundary surface of the oxide layer simultaneously forms a mirror surface of particularly low roughness.
• the mirror layer according to one embodiment comprises at least one metallic mirror layer.
• Suitable materials for the metallic mirror layer are, in particular, gold, silver or aluminum, where gold is suitable for reflection in the infrared range, silver for reflection in the visible wavelength range and aluminum for reflection in the UV range.
• At least one dielectric mirror layer is provided.
• the dielectric mirror layer increases the reflectance of the mirror on the back surface of the semiconductor light emitting diode.
• Suitable materials for the dielectric mirror layer are, for example, glass, silicon oxide, silicon nitride or silicon oxynitride.
• the dielectric mirror layer is arranged between the oxide layer and the metallic mirror layer and has local recesses in which the metallic mirror layer reaches as far as the second boundary surface of the oxide layer.
• the metallic mirror layer forms contacts with the transparent conductive oxide layer, starting from which, in the oxide layer, a lateral current spreading takes place over the entire base area of the semiconductor layer stack.
• Suitable base materials for the light-emitting diode layers are, for example, binary, ternary or quaternary III-V semiconductor materials, in particular those which are at least one of the elements - D -
• Aluminum, gallium and indium and at least one of nitrogen, phosphorus and arsenic examples include aluminum nitride, aluminum indium nitride, gallium nitride, aluminum gallium nitride, indium gallium nitride and indium gallium arsenide phosphide.
• the method for manufacturing the semiconductor light-emitting diode comprises
• its second interface has a roughness less than the roughness of its first interface and, in particular, less than 1.0 nm finished semiconductor light emitting diode for a stronger reflection or mirror effect at the interface between the oxide layer and the mirror layer.
• the oxide layer is deposited with a layer thickness of at least 5 nm, as a result of unevenness of the first interface of the oxide layer, which is characterized by the roughness of the da - -
• topmost semiconductor layer leveled and can not adversely affect the roughness of the second interface of the oxide layer.
• a p-doped semiconductor layer is deposited on the p-doped light-emitting diode layer whose dopant concentration is at least as great as the dopant concentration of the p-doped light-emitting diode layer.
• the p-doped semiconductor layer protects the p-doped light-emitting diode layer against crystal lattice damage during sputtering of the oxide layer.
• an undoped semiconductor layer and an n-doped semiconductor layer are deposited over the p-doped semiconductor layer and if the oxide layer is sputtered onto the n-doped semiconductor layer, a low-resistance connection of the oxide layer over the n-doped semiconductor layer results;
• the p-doped, the undoped and the n-doped semiconductor layer form a tunnel contact whose contact resistance is more than compensated by the low-resistance connection of the oxide layer to the n-doped semiconductor layer.
• forming the mirror layer comprises depositing at least one dielectric mirror layer, etching recesses in the dielectric mirror layer and depositing at least one metallic mirror layer on the dielectric mirror layer;
• the metallic mirror layer in the recesses of the dielectric mirror layer forms contacts with the oxide layer, from which, in the oxide layer, the lateral current spreading takes place over the entire base area of the semiconductor layer stack.
• FIG. 1 shows a first exemplary embodiment of a semiconductor light-emitting diode
• FIG. 2 shows a second exemplary embodiment of a semiconductor light-emitting diode
• FIG. 3 shows a third exemplary embodiment of a semiconductor light-emitting diode with a plurality of mirror layers
• FIG. 4 shows a fourth exemplary embodiment of a semiconductor light-emitting diode with a plurality of mirror layers
• FIG. 5 shows an enlarged schematic detail view of a preliminary semiconductor product during the production of a semiconductor light-emitting diode according to one of FIGS. 1 to 4.
• FIG. 1 shows a cross-sectional view of a first exemplary embodiment of a semiconductor light-emitting diode 10 which has a semiconductor layer stack 20.
• the generated electromagnetic radiation which is in the visible range, in the infrared range or in the UV range, is first emitted in all directions, it is intended to radiate as completely as possible through a radiation exit surface 25 of a radiation exit layer 1 (bottom in FIG. 1) is disposed on the side of the semiconductor layer stack which faces away from the oxide layer and the mirror layer.
• the radiation exit layer 1 is either a substrate layer remaining after all layers are grown on the substrate and the substrate is nearly g _
• the further layers are grown on the radiation exit layer 1 as follows: First, an n-doped light-emitting diode layer 2 and a p-doped light-emitting diode layer 4 are deposited.
• the light-emitting diode layers 2, 4 doped opposite to one another form a light-emitting diode layer sequence, as highlighted in FIG. 1 by dashed lines.
• an optically active zone 3 is formed, which causes an emission of electromagnetic radiation with sufficient bias of suitable polarity at the light emitting diode layers 2, 4.
• the n-doped light-emitting diode layer 2 is here doped with silicon and the p-doped light-emitting diode layer 4 is doped with magnesium, wherein the base material of the light-emitting diode layers 2, 4 is in each case a III-V semiconductor material.
• the radiation exit layer 1 serves for the protection and electrical insulation of the lower, n-doped light-emitting diode layer 2.
• an oxide layer 8 of a transparent conductive oxide is deposited on the side of the light-emitting diode layer sequence on which the p-doped light-emitting diode layer 4 is arranged (that is, in Figure 1 above).
• the oxide layer 8 contains a transparent electrically conductive oxide.
• the oxide layer serves to expand the current in the lateral direction parallel to the layer boundaries and to avoid undesired migration between the mirror layer and the semiconductor layer stack.
• FIG. 1 shows an exemplary embodiment in which the oxide layer 8 does not lie directly on the p - -
• doped light emitting diode layer 4 is deposited, but (to protect the p-doped light-emitting diode layer 4) first a p-doped semiconductor layer 5 is deposited, the dopant concentration is at least as large as that of the p-doped light-emitting diode 4.
• the oxide layer 8 of a transparent conductive oxide (TCO) is then deposited on the p-doped semiconductor layer 5.
• TCO transparent conductive oxide
• the roughness of the upper side of the p-doped semiconductor layer 5 predetermines the roughness R 1 of the first boundary surface 8 a of the oxide layer 8.
• the first interface of the oxide layer is here referred to that interface which faces the semiconductor layer stack (and in particular directly adjoins the uppermost, last deposited semiconductor layer of the layer stack).
• a transparent conductive oxide is about indium tin oxide, indium zinc oxide or zinc oxide.
• the conductivity can be increased by doping with aluminum or gallium.
• the deposition of the oxide layer is carried out by HF-assisted DC sputtering; This gives it an upper, second interface 8b, which has a particularly low roughness R2. After sputtering on the oxide layer 8, its second interface 8b is initially free; Finally, according to FIG. 1, the mirror layer 9 (in particular a metallic mirror layer 19) is deposited thereon. - -
• the interfaces between the respective layers of the semiconductor layer stack and between the semiconductor layer stack, the oxide layer and the mirror layer always have a certain roughness.
• the roughness is usually given as a numerical indication (approximately in nm) with the addition 'Rms' ('root means squared', root of the mean square deviation from the idealized interface plane, i.e. standard deviation of the height variation of the interface or surface).
• the averaging is done over a surface area of the respective surface or interface.
• the roughness of interfaces within the layer sequence for the semiconductor light-emitting diode 10 is conventionally preferably between 1.5 and 5 nm, but may also be substantially greater and more than 20 nm.
• deviations from the ideal crystal lattice contribute to the roughness, for example locally varying growth conditions or lattice distortions, also as a consequence of dopants.
• the materials and material combinations of the respective layers are conventionally optimized and matched to one another. Furthermore, layer thicknesses and refractive indices of the layers are optimized in order to achieve a constructive interference of the electromagnetic radiation reflected at the interfaces and thus a high brightness of the light-emitting diode.
• the second interface of the oxide layer which faces away from the semiconductor layer stack, that is the Mirror layer faces, an even greater roughness than the first interface of the oxide layer, since the transparent conductive oxide usually does not grow monocrystalline, but polycrystalline or amorphous.
• the RF-assisted DC sputtering process will be discussed with reference to FIG.
• the mirror layer 9 is deposited on the second interface 8b of the oxide layer 8 (exposed after the sputtering process has been carried out).
• the deposition of the mirror layer 9 is effected by a PVD (physical vapor deposition) or a CVD (chemical vapor deposition) method, in particular a PECVD method (plasma-enhanced chemical vapor deposition), by an MBE method (molecular beam epitaxy ) , one
• the mirror layer 9 in this embodiment is a metallic mirror layer 19 made of gold, silver or aluminum or an alloy containing at least one of these metals.
• the metallic mirror layer 19 may also comprise a plurality of layers each of a metal or a metal alloy.
• the materials and layer thicknesses of the oxide layer 8 and the mirror layer 9 are matched to one another such that the portion of the electromagnetic radiation emitted by the optically active zone 3, which is emitted in the direction of the oxide layer and the mirror layer, at the second - -
• Boundary surface 8b of the oxide layer 8 is reflected as completely as possible.
• the angle of incidence of the radiation to be reflected is subject to a statistical distribution and can basically assume any value between 0 degrees and 90 degrees relative to the surface normal of the reflecting interface of the mirror layer.
• the consequence of the low roughness of the second boundary surface 8b of the oxide layer 8 is that even at high angles of incidence relative to the surface normal of the second boundary surface 8b a larger proportion of the incident electromagnetic radiation is reflected altogether. As a result, the intensity of the electromagnetic radiation radiated by the semiconductor light-emitting diode is increased.
• FIG. 2 shows a second exemplary embodiment of a semiconductor light-emitting diode in which, in addition to the layers illustrated in FIG. 1, an undoped semiconductor layer 6 and an n-doped semiconductor layer 7 are provided between the p-doped semiconductor layer 5 and the oxide layer 8 are arranged.
• the n-type semiconductor layer 7 facilitates the connection of the oxide layer 8 of the transparent conductive oxide to the semiconductor layer stack 20.
• the undoped semiconductor layer 6 is arranged between the p-type semiconductor layer 5 and the n-type semiconductor layer 7. The sequence of the semiconductor layers 5, 6 and 7 forms a tunnel contact to the actual
• the same base materials as for the light-emitting diode layers 2, 4 are suitable. - -
• the thickness of the doped semiconductor layers 5, 7 is smaller than 30 nm in this embodiment; it lies, for example, between 3 and 20 nm. Furthermore, the layer thickness of the undoped semiconductor layer 6 in this embodiment is less than 20 nm; it is for example between 1 and 10 nm. Otherwise, the same statements apply to Figure 2 as for Figure 1.
• the layers of the semiconductor layer stack 20 shown in FIGS. 1 and 2 are deposited, for example, by a chemical vapor deposition (CVD) method, before the oxide layer 8 and then the mirror layer 9 are deposited on the semiconductor layer stack 20.
• CVD chemical vapor deposition
• the substrate is subsequently thinned or completely removed so that the radiation exit layer 1 is exposed.
• FIGS. 1 and 2 show exemplary embodiments in which the oxide layer 8 directly adjoins the underside of a metallic mirror layer 19
• FIGS. 3 and 4 show exemplary embodiments with an additional dielectric mirror layer 18 between the oxide layer 8 and the metallic mirror layer 19.
• the semiconductor layer stack 20 has the same construction as in FIG. 1; in Figure 4, it has the same structure as in Figure 2.
• the explanations to Figure 1 and 2 therefore also apply to Figure 3 and 4, respectively.
• the oxide layer 8 is deposited on the respectively uppermost semiconductor layer 5 or 7 by HF-assisted DC sputtering.
• a dielectric mirror layer 18 (at For example, of silicon oxide) deposited. Recesses 11 are then etched into the dielectric mirror layer 18 and a metallic mirror layer 19 is deposited on the dielectric mirror layer 18.
• the material of the metallic mirror layer 19 reaches up to the second boundary surface 8b of the oxide layer 8 and thus forms Knüpfeltitlee to the oxide layer 8. Starting from the Knüpfeltitleen then takes place in the transparent conductive oxide layer 8, the lateral current widening over the entire base area of the semiconductor layer stack 20.
• the mirror layer 9 comprises in this embodiment both a dielectric mirror layer 18 and a metallic mirror layer 19. Since the mirror layers 9; 18, 19 are deposited after the oxide layer 8, the roughness of the interface between the mirror layers 18 and 19 is reduced by the low roughness R2 of the second boundary surface 8b of the oxide layer 8 Low roughness of the second interface of the oxide layer also reduces, to some extent, the roughness of the interfaces of subsequent mirror layers. Otherwise, the same statements apply to FIGS. 3 and 4 as for FIGS. 1 and 2.
• the n-doped light-emitting diode layer 2 has a dopant concentration of less than 1 ⁇ 10 20 / cm 3 , in particular less than 1 ⁇
• the p-doped light-emitting diode layer 4 has a dopant concentration of less than 2 ⁇ 10 20 / cm 3 .
• the dopant concentration of the p-type semiconductor layer 5 is at least as large as that of the p-doped light-emitting diode layer 4 and is above 2 x 10 20 / cm 3 .
• the dopant concentration of the n-doped semiconductor layer 7 is greater than that of the n-doped light-emitting diode layer 2 and is above 2 ⁇ 10 20 / cm 3 .
• each of the two semiconductor layers 5, 7 is doped more heavily than the respective light-emitting diode layer 4, 2 of the same dopant type.
• the p-doped layers are doped with magnesium and the n-doped layers with silicon.
• the dopant concentration of the n-doped semiconductor layer 7 may also be smaller than the dopant concentration of the n-doped light-emitting diode layer 2.
• FIG. 5 shows an enlarged schematic detail view of a preliminary semiconductor product for producing the semiconductor light-emitting diode according to one of FIGS. 1 to 4, after sputtering on the oxide layer 8. Shown is an upper subregion of the uppermost layer of the semiconductor layer stack 20 and of the oxide layer sputtered thereon the transparent conductive oxide.
• the uppermost semiconductor layer is either the p-doped semiconductor layer 5 of FIG. 1 or 3 or the n-doped semiconductor layer 7 of FIG. 2 or 4.
• the roughness of the uppermost semiconductor layer predetermines the roughness R1 of the lower, first boundary surface 8a of the oxide layer 8, it is typically above 1.5 nm Rms , but can also assume much larger values - depending on the deposition method for the topmost semiconductor layer, its base material and their dopant concentration.
• Semiconductor layer 5 ( Figure 1 or 3) made of gallium nitride, the roughness of their top is between 1.2 to 1.8 nm.
• the HF-assisted DC sputtering method for depositing the oxide layer 8 from the transparent conductive oxide ensures that the roughness R2 of its second boundary surface 8b, as shown in FIG. 5, is smaller than the roughness R1 of the first boundary surface 8a, in particular smaller than 1.0 nm or even 0.5 nm.
• the oxide layer 8 is sputtered in the embodiments described herein with a layer thickness of between 1 and 50 nm, wherein the layer thickness can also be selected to be larger. If the oxide layer is deposited with a minimum layer thickness of, for example, 5 nm, unevenness which results from the underlying semiconductor layer 5 or 7 is leveled during the sputtering of the oxide layer. This ensures that the roughness R2 of the second boundary surface 8b of the oxide layer 8 is influenced only by the HF-assisted DC sputtering method, but not by height fluctuations of lower-lying semiconductor layers.
• the mirror layers which are arranged on the (deposited by the HF-assisted DC sputtering) oxide layer, have extremely smooth reflection surfaces.
• the uppermost semiconductor layer of the semiconductor layer stack exposed before the sputtering of the oxide layer 8 is hardly damaged by the HF-assisted DC sputtering method.
• the RF assisted DC sputtering process is used herein for depositing the oxide layer 8 from the transparent conductive oxide onto the uppermost layer of the - 1 -
• Semiconductor layer stack 20 used for the light emitting diode used for the light emitting diode.
• a high-frequency AC voltage is superimposed on an electrical DC voltage.
• the electrical power supplied for sputtering thus comprises a DC component (direct current) and a high-frequency component (HF; high frequency).
• the frequency of the high-frequency power component is, for example, 13.56 MHz.
• the combined DC / HF power is supplied, for example, to an electrode arranged in a sputtering chamber.
• the second boundary surface 8b of the oxide layer 8 deposited by the HF-assisted DC sputtering method and the boundary surfaces of the further mirror layers 18, 19 deposited on the second boundary surface 8b reflect a higher proportion of the electromagnetic radiation impinging on them due to the reduced roughness , This applies in particular to those radiation components which impinge on these boundary surfaces at relatively large angles of incidence relative to the surface normal.
• the semiconductor light-emitting diode 10 emits a greater intensity of electromagnetic radiation overall at its radiation exit surface 25.

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