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
  • H10H20/81—Bodies
  • H10H20/811—Bodies having quantum effect structures or superlattices, e.g. tunnel junctions
  • H10H20/812—Bodies having quantum effect structures or superlattices, e.g. tunnel junctions within the light-emitting regions, e.g. having quantum confinement structures
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
  • H01L2924/0001—Technical content checked by a classifier
  • H01L2924/0002—Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/30—Structure or shape of the active region; Materials used for the active region
  • H01S5/305—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure
  • H01S5/3086—Structure or shape of the active region; Materials used for the active region characterised by the doping materials used in the laser structure doping of the active layer
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
  • H01S5/00—Semiconductor lasers
  • H01S5/30—Structure or shape of the active region; Materials used for the active region
  • H01S5/34—Structure or shape of the active region; Materials used for the active region comprising quantum well or superlattice structures, e.g. single quantum well [SQW] lasers, multiple quantum well [MQW] lasers or graded index separate confinement heterostructure [GRINSCH] lasers
• • 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
  • H10H20/811—Bodies having quantum effect structures or superlattices, e.g. tunnel junctions
• • 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
  • H10H20/822—Materials of the light-emitting regions
  • H10H20/824—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP
  • H10H20/825—Materials of the light-emitting regions comprising only Group III-V materials, e.g. GaP containing nitrogen, e.g. GaN

Definitions

• the present application relates to an optoelectronic semiconductor chip having a multiple quantum well structure.
• Optoelectronic semiconductor chips having a multiple quantum well structure are disclosed, for example, in the publications WO 01/39282 A2 and US Pat. No. 5,831,277.
• An optoelectronic semiconductor chip which has an active zone which contains a multiple quantum well structure provided for generating electromagnetic radiation.
• the active zone is in particular a subarea of an epitaxial semiconductor layer sequence.
• the semiconductor chip is, for example, a light-emitting diode chip or a laser diode chip.
• the active zone contains a plurality of successive quantum well layers.
• each quantum well layer is arranged between two barrier layers assigned to it.
• a barrier layer and a quantum well layer follow one another in the active zone.
• each quantum well layer is preceded by a barrier layer assigned to it and an additional barrier layer assigned to it follows it.
• the statements "preceding” and “below” are to be understood in the present context in each case in the direction from an n-side to a p-side of the semiconductor chip, between which the active zone is arranged.
• quantum well structure and “quantum well layer” in the present context have no significance with regard to the dimensionality of the quantization.
• the quantum well defined by one quantum well layer and the two barrier layers assigned to it may be a quantum well, at least one quantum wire or at least one quantum dot or a combination of at least two of these structures.
• the multiple quantum well structure has at least one first quantum well layer which is n-doped and which is arranged between two n-type doped barrier layers adjoining the first quantum well layer.
• first quantum well layer and the two barrier layers assigned to it are n-doped.
• an n-type doped layer is understood as meaning a layer doped with at least one n-type dopant, such as silicon. It is conceivable that two different layers, such as a quantum well layer and a barrier layer, are n-doped with different n-type dopants.
• all n-type doped quantum well and barrier layers are doped with the same n-type dopant or with the same n-type dopants.
• the multiple quantum well structure further comprises at least one, preferably exactly one second quantum well layer which is undoped and which is arranged between two barrier layers adjacent to the second quantum well layer, one of which is n-doped and the other is undoped.
• the second quantum well layer follows the first quantum well layer.
• the barrier layer preceding the second quantum well layer is n-doped and the barrier layer following the second quantum well layer is undoped.
• an undoped layer is understood as meaning a layer which is essentially free of an n-dopant or p-type dopant.
• an undoped layer can also have a low concentration, in particular a vanishingly low concentration, of the n- and / or p-dopant-for example due to diffusion of an n- and / or p-dopant.
• An n-type dopant is present in particular in a low concentration in the undoped layer if its concentration in the undoped layer is smaller by at least 40 percent, preferably by at least 70 percent, than the concentration of the n-type dopant in the first quantum well layer.
• the multiple quantum well structure has at least one third quantum well layer, which is undoped and arranged between two, likewise undoped, barrier layers adjoining the third quantum well layer.
• the third quantum well layer of the second quantum well layer is subsequently arranged in the active zone.
• the inventors have found that a particularly high efficiency of the semiconductor chip is achieved by means of such a sequence of the first, second and third quantum well layer (s). In particular, the efficiency is increased over conventional semiconductor chips at high operating currents.
• the optoelectronic semiconductor chip is provided, for example, for operation with an operating current of greater than or equal to 80 mA.
• the multiple quantum well structure has at least one fourth quantum well layer, which is undoped and which is arranged between two n-type doped barrier layers adjoining the fourth quantum well layer.
• the fourth quantum well layer follows the at least one first quantum well layer and precedes the second quantum well layer.
• the semiconductor chip with the fourth quantum well layer advantageously has a particularly low forward voltage. In other words, a predetermined operating current is achieved with a particularly low operating voltage.
• the semiconductor chip with at least one fourth quantum well layer is provided, for example, for operation with a low operating current, for example with an operating current of approximately 20 mA.
• the multiple quantum well structure contains at least as many first and third quantum well layers. In one development, it contains more first than third quantum well layers. The inventors have determined in extensive comparative experiments that the semiconductor chip is particularly efficient if the number of first quantum well layers is chosen to be greater than or equal to the number of third quantum well layers.
• the active zone has at most ten quantum well layers. Preferably, it has five or more quantum well layers.
• the semiconductor chip particularly preferably has between seven and nine quantum well layers, the boundaries being included. Experiments by the inventors have shown that such a semiconductor chip generates a particularly high luminous flux at a given operating current. In particular, a saturation behavior of the luminous flux is particularly low with increasing operating current.
• the active zone precedes a superlattice of pairs of alternating layers in the direction from the n-side to the p-side of the semiconductor chip.
• the superlattice extends for example over a layer thickness of less than or equal to 50 .mu.m, in particular of less than or equal to 30 .mu.m. For example, it has a layer thickness of about 25 nm.
• the alternating layers of the superlattice for example, have a layer thickness of less than or equal to 5 nm, in particular they have a layer thickness of about 0.5 to 2 nm, the boundaries being included. At least one Layer of each pair of alternating layers is n-type doped. In one embodiment, the entire superlattice is n-doped.
• the small layer thickness of the superlattice of 50 ⁇ m or less By means of the small layer thickness of the superlattice of 50 ⁇ m or less, a particularly low forward voltage of the semiconductor chip is achieved.
• the n-type doped first quantum well layer (s) By means of the n-type doped first quantum well layer (s), a good charge carrier injection into the at least one third quantum well layer is achieved even with the small layer thickness of the superlattice.
• the first quantum well layer, the two barrier layers adjoining the first quantum well layer and / or the n-doped barrier layer adjoining the second quantum well layer is doped with an n-type dopant, in particular at a concentration of greater than or equal to 1 ⁇ 10 18 atoms / cm 3 ,
• the first quantum well layer and the two barrier layers adjoining the first quantum well layer have the same n-type dopant in the same concentration.
• the n-type doped barrier layer adjoining the second quantum well layer comprises the n-type dopant in the same concentration as the first quantum well layer and / or like the barrier layers adjacent to the first quantum well layer.
• Two layers in this case have the n-type dopant "in the same concentration" if the concentration of the n-type dopant between the layers differs by 20 percent or less, preferably by 10 percent or less, for example by 5 percent or less.
• the barrier layers have, for example, a layer thickness of between 5 and 12 .mu.m, preferably between 6 and 11 nm. _ n
• the quantum well layers have a layer thickness between 1 and 5 nanometers, preferably between 2 and 3 nm, the boundaries being included in each case.
• the layer thickness of the barrier layers is about 10 nm and the layer thickness of the quantum well layers is about 2.5 nm. Comparative experiments of the inventors have shown that the semiconductor chip with such layer thicknesses of the barrier layers and / or the quantum well layers has a particularly low saturation of the luminous flux with increasing operating current ,
• the semiconductor chip is free of a growth substrate.
• the semiconductor chip is a thin-film semiconductor chip.
• a reflective layer is applied or formed which reflects back at least part of the electromagnetic radiation generated in the epitaxial semiconductor layer sequence;
• the thin-film semiconductor chip contains a carrier element which is not the growth substrate on which the semiconductor layer sequence has been grown epitaxially but a separate carrier element which was subsequently attached to the epitaxial semiconductor layer sequence,
• the growth substrate of the epitaxial semiconductor layer sequence is formed by the epitaxial semiconductor layer sequence removed or thinned such that it alone is not free-floating together with the epitaxial semiconductor layer sequence, or
• the epitaxial semiconductor layer sequence has a thickness in the range of 20 microns or less, in particular in the range of 10 microns.
• the support element is preferably permeable to radiation emitted by the semiconductor chip.
• the epitaxial semiconductor layer sequence preferably contains at least one semiconductor layer with at least one surface which has a mixing structure which, in the ideal case, leads to an approximately ergodic distribution of the light in the epitaxial semiconductor layer sequence, i. it has as ergodically stochastic scattering behavior as possible.
• a basic principle of a thin-film semiconductor chip is described, for example, in I. Schnitzer et al. , Appl. Phys. Lett. 63 (16), 18 October 1993, 2174 - 2176, the disclosure of which is hereby incorporated by reference.
• Examples of thin-film semiconductor chips are described in the publications EP 0905797 A2 and WO 02/13281 A1, the disclosure content of which is hereby incorporated by reference.
• a thin-film semiconductor chip is to a good approximation a Lambertian surface radiator and is therefore particularly suitable for use in a headlight.
• the active zone of the semiconductor chip, in particular the epitaxial semiconductor layer sequence of the semiconductor chip is based in one embodiment, on a III-V compound semiconductor material, such as a nitride compound semiconductor material such as InAlGaN.
• the semiconductor layer sequence is based on an II / VI compound semiconductor material.
• a III / V compound semiconductor material has at least one element of the third main group such as Al, Ga, In, and a fifth main group element such as B, N, P, As.
• the term "III / V compound semiconductor material” includes the group of binary, ternary or quaternary compounds containing at least one element from the third main group and at least one element from the fifth main group, for example nitride and phosphide compound semiconductors. Such a binary, ternary or quaternary compound may also have, for example, one or more dopants and additional constituents.
• an II / VI compound semiconductor material includes at least one element of the second main group such as Be, Mg, Ca, Sr, and a sixth main group element such as O, S, Se.
• an II / VI compound semiconductor material comprises a binary, ternary or quaternary compound comprising at least one element from the second main group and at least one element from the sixth main group.
• Such a binary, ternary or quaternary compound may additionally have, for example, one or more dopants and additional constituents.
• the II / VI compound semiconductor materials include: ZnO, ZnMgO, CdS, ZnCdS, MgBeO.
• On nitride compound semiconductor material based means in this context that the semiconductor layer sequence or at least part thereof, particularly preferably at least the active zone and / or the growth substrate, a nitride compound semiconductor material, preferably in n Al ⁇ Ga n - m N comprises or consists of this, where O ⁇ n ⁇ l, 0 ⁇ m ⁇ 1 and n + m ⁇ 1.
• this material does not necessarily have a mathematically exact composition according to the above formula. Rather, it may, for example, have one or more dopants and additional constituents.
• the above formula contains only the essential constituents of the crystal lattice (Al, Ga, In, N), even if these can be partially replaced and / or supplemented by small amounts of further substances.
• the semiconductor chip is provided for emitting electromagnetic radiation having an intensity maximum in the green spectral range.
• FIG. 1 shows a schematic cross section through an optoelectronic semiconductor chip according to a first exemplary embodiment
• Figure 2 a schematic cross section through the active zone of the optoelectronic semiconductor chip according to the first embodiment and a schematic Concentration profile of an n-dopant in the active zone, and
• Zone of an optoelectronic semiconductor chip according to a second embodiment and the concentration profile of an n-type dopant in the active zone are also possible.
• FIG. 1 shows a schematic cross section through an optoelectronic semiconductor chip according to a first exemplary embodiment.
• the optoelectronic semiconductor chip has an epitaxial semiconductor layer sequence 2 on a growth substrate 1.
• the growth substrate 1 is removed or at least heavily thinned.
• the semiconductor layer sequence 2 is based for example on an InAlGaN compound semiconductor material. It is made, for example, on a growth substrate 1 comprising or consisting of sapphire.
• the semiconductor layer sequence 2 contains at least one n-contact layer 21 and one p-contact layer 27 between which an active zone 20 containing a multiple quantum well structure for generating radiation is arranged.
• the semiconductor layer sequence 2 has a current spreading layer 22 and two further n-doped layers 23, 24 in the course of the n-contact layer 21 to the active zone 20.
• the semiconductor layer sequence 2 in the present case has two further p-doped layers 25, 26.
• the further n-doped and / or p-doped layers, or at least one or some of these layers, are, for example, charge-confinement layers.
• the n-contact layer 21 has a layer thickness of 3 ⁇ m.
• the n-contact layer 21 comprises GaN. It is preferably n-doped with silicon as the n-type dopant, for example at a concentration of 3 ⁇ 10 18 atoms / cm 3 .
• the current spreading layer 22 has, for example, a layer thickness of 1 ⁇ m. It is expediently highly n-doped, for example with silicon in a concentration of 1 ⁇ 10 19 atoms / cm 3 . So it has a high electrical transverse conductivity.
• the other two n-doped layers in the present case each have a layer thickness of 0.5 ⁇ m. They have, for example, both gallium nitride n-doped with silicon as the n-type dopant.
• the silicon concentration is, for example, in the active zone 20 facing another n-doped layer 24 8 x 10 17 atoms / cm 3 .
• the silicon is in a concentration of
• the p-contact layer 27 contains, for example, GaN.
• the further p-doped layers 25, 26 contain, for example, AlGaN. In the present case this is the case of the active zone
• the p-contact layer and the further p-doped layers 25, 26 are doped, for example, with magnesium as the p-dopant.
• the concentration of the p-dopant here is lower than in the other p-conducting layers 25, 26.
• the p-dopant is present, for example, in a concentration of greater than or equal to 6 ⁇ 10 19 atoms / cm 3 , for example in a concentration of approximately 1 ⁇ 10 20 atoms / cm 3 .
• the active zone 20 of the semiconductor string sequence 2 is shown enlarged.
• the active zone 20 is shown in a schematic cross section.
• the left-hand portion of FIG. 2 schematically shows the concentration 4 of the n-dopant of the layers imaged in the right-hand region.
• the arrow 3 designates the direction from an n-side to a p-side of the semiconductor layer sequence 2 between which the active zone 20 is arranged, that is to say in particular the direction from the n-contact layer 21 to the p-contact layer 27.
• the active zone 20 of the semiconductor chip according to the first exemplary embodiment has a quantum well structure with seven quantum well layers 210, 220, 230. In the direction 3 from the n to the p-side, three first quantum well layers 210, a second quantum well layer 220 and three third quantum well layers 230 follow one another.
• Each two adjacent quantum well layers 210, 220, 230 are separated from each other by a barrier layer 250, 260.
• Another of the barrier layers 260 follows the last of the third quantum well layer 230. In this way, each of the quantum well layers 210, 220, 230 is arranged between exactly two barrier layers 250, 260.
• the quantum well layers 210, 220, 230 and the barrier layers 250, 260 are preceded by a superlattice structure 270.
• the superlattice structure 270 consists of pairs of alternating InGaN and GaN layers, which for example each have a layer thickness of less than or equal to 1 nm. They are doped, for example, with a concentration of 1.5 ⁇ 10 18 atoms / cm 3 with silicon as n-type dopant.
• the three first quantum well layers 10 following the superlattice structure 270 and the barrier layers 250 assigned to them, between which the first quantum well layers 210 are arranged, are likewise doped with silicon as n dopant, for example in a concentration between 1 ⁇ 10 18 atoms / cm 3 and 8 x 10 18 atoms / cm 3 , in particular between 2 x 10 18 and 4 x 10 18 atoms / cm 3 , the boundaries each being included.
• the first quantum well layers 210 are followed by the second quantum well layer 220, which is preceded by a barrier layer 250, which is also assigned to a first quantum well layer 210.
• the barrier layer 250 preceding the second quantum well layer 220 is n-doped.
• the barrier layer 260 following the second quantum well layer 220 like the second quantum well layer 220 itself, is undoped.
• three third quantum well layers 230 are arranged between in each case two undoped barrier layers 260.
• the semiconductor chip is intended for operation with an operating current of, for example, 80 mA.
• a large part, in particular practically all of the electromagnetic radiation emitted by the semiconductor chip is generated in at least one, preferably several, in particular all, of the third quantum well layers 230 or in the third quantum well layers 230 and the second quantum well layer 220.
• the first quantum well layers 210 do not or hardly contribute to the generation of radiation.
• FIG. 3 shows the active zone 20 of a semiconductor chip according to a second exemplary embodiment in schematic cross section.
• the concentration profile of the n-type dopant of the layers shown in the right-hand region is schematically plotted.
• the semiconductor chip according to the second embodiment differs from that of the first embodiment in that the active region 20 includes only a single third quantum well layer 230. In addition, it contains two fourth quantum well layers 240, which are the first quantum well layers 210 and precede the second quantum well layer 220. Overall, therefore, the active zone 20 in the second exemplary embodiment also contains seven quantum well layers 210, 220, 230, 240.
• the fourth quantum well layers 240 are undoped. Each of the fourth quantum well layers 240 is disposed between two adjacent n-type doped barrier layers 250. In the present case, the n-type dopant has the same concentration in all the barrier layers 250 doped with the n-type dopant and in the first quantum well layers 210.
• the semiconductor chip according to the second embodiment is particularly intended for operation with an operating current of about 20 mA.
• the invention is not limited by the description based on the embodiments thereof. Rather, it includes every new feature and every combination of features, which in particular includes any combination of features in the embodiments and claims, even if this feature or this combination is not explicitly stated in the exemplary embodiments or claims.

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• 2007
  • 2007-09-26 DE DE102007046027A patent/DE102007046027A1/de not_active Withdrawn
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