Semiconductor Structure

Abstract

1. A semiconductor structure (1) comprising: a substrate (2); a base layer (10) comprising an AlGaN layer and disposed above the substrate (2); and at least one group (20) of layers disposed above the base layer (10), each of the at least one group (20) of layers comprising: a first layer (21) which is an InGaN layer and comprises quantum dots (24); and a second layer (22) which is an InGaN layer and disposed on and above the first layer (21), the second layer (22) laterally surrounding the quantum dots (24) of the first layer (21), the InGaN material composition of the second layer (22) being different from the InGaN material composition of the first layer (21).

Description

[Technical Field]

[0001] The present inventive concepts relate generally to semiconductor structures. [Background technology]

[0002] Nitride semiconductors, i.e., compounds of nitrogen with elements from the third group of the periodic table, offer numerous advantages over silicon. Devices based on them offer promising candidates to replace silicon-based electronic devices. For example, such devices may offer faster switching speeds, increased electron mobility, lower resistance, and higher breakdown voltages.

[0003] However, nitride semiconductors often contain dislocations, and although various methods have been developed to reduce such dislocations, further improvements are possible. Summary of the Invention [Problem to be solved by the invention]

[0004] It is an object of the inventive concept to provide a semiconductor structure that enables epitaxial growth of high quality nitride semiconductors. It is a further object of the inventive concept to enable high quality electronic devices, including fast, reliable, and inexpensive electronic devices. [Means for solving the problem]

[0005] These and other objects of the inventive concept are at least partly achieved by the invention as defined in the independent claims. Preferred embodiments are set out in the dependent claims.

[0006] In this text, abbreviations of natural elements are used according to the periodic table, e.g., Al means aluminum, Ga means gallium, As means arsenic, Mg means magnesium, O means oxygen, and Si means silicon.

[0007] Compounds comprising multiple elements may be referred to herein by combinations of element symbols. For example, gallium nitride may be referred to as GaN, and aluminum nitride may be referred to as AlN. Some compounds may have ratios of their relative elemental compositions. For example, aluminum gallium nitride may be referred to as Al x Ga 1-x N, where x is a variable that can take on values ​​between 0 and 1. Subscripts indicate the relative proportion of the preceding element, e.g., x=0.5 or Al 0.5 Ga 0.5 In the case of N, it can be understood that in terms of the atomic content of Group III, 50% is aluminum and 50% is gallium, while in terms of the atomic content of Group V, 100% is nitrogen. AlGaN alone, without a ratio, can alternatively refer to aluminum gallium nitride of a different composition. Group III and Group V in this specification refer to Group III and Group V of the periodic table, respectively.

[0008] According to a first aspect, A substrate; a base layer comprising an AlGaN layer and disposed above the substrate; at least one group of layers disposed above the base layer, each of the at least one group of layers comprising: a first layer, the first layer being an InGaN layer and comprising quantum dots; a second layer, the second layer being an InGaN layer, disposed on and above the first layer, the second layer laterally surrounding the quantum dots of the first layer, the InGaN material composition of the second layer being different from the InGaN material composition of the first layer; At least one group of layers comprising: A semiconductor structure is provided, comprising:

[0009] It has been found that quantum dots (QDs) can encapsulate dislocations during epitaxial growth of nitride semiconductors. This allows the quantum dots (QDs) to prevent or reduce the diffusion of dislocations above the second layer. The quantum dots can prevent or reduce the diffusion of dislocations above the second layer in a direction perpendicular to the substrate. Hereinafter, the direction perpendicular to the substrate, i.e., the growth direction, is referred to as the vertical direction. Furthermore, the direction parallel to the substrate is referred to as the lateral direction.

[0010] The substrate may be a non-nitride substrate, such as a silicon substrate, a sapphire substrate, or a silicon carbide substrate. Because substrates of nitride semiconductor materials are difficult and / or expensive to manufacture, or in some cases impossible to manufacture, it may be advantageous to grow nitride semiconductors on such non-nitride substrates. However, the use of non-nitride substrates may cause dislocations, for example, in the base layer. Such dislocations may be prevented from diffusing vertically and thereby from reaching device layers above the second layer.

[0011] Silicon substrates can be particularly advantageous because they are inexpensive and compatible with common semiconductor processing methods. In particular, the silicon substrate can have a top surface with Miller indices of {111}.

[0012] It should be understood that the present invention also provides advantages when the substrate is a nitride substrate, for example a GaN substrate. Dislocations can also form when using nitride substrates, in which case it is advantageous to contain the dislocations.

[0013] The base layer is disposed above the substrate, for example, directly above the substrate. The base layer can be an AlGaN layer of any composition from AlN to GaN. A base layer comprising an AlN layer, for example, an AlN layer directly above the substrate, for example, directly above a silicon substrate, is advantageous. For example, a sputtered AlN layer directly above a silicon substrate is advantageous because the defect density at the interface between the sputtered AlN and the silicon may be low.

[0014] At least one group of layers is disposed above the base layer, e.g., directly above the base layer. Thus, the first layer is disposed above the base layer, e.g., directly above the base layer. The at least one group of layers may include more layers than the first and second layers. For example, the first layer may be, for example, an intermediate layer between the zeroth layer and the second layer.

[0015] The quantum dots in the first layer may have a height, i.e., a vertical size, of 1 to 20 nm. The quantum dots in the first layer may have a width, i.e., a horizontal size, of 10 to 20 nm. The quantum dots in the first layer may be shaped like a pyramid, a truncated pyramid, or a dome. The side facets of the quantum dots may form inclined surfaces, such as planes at an angle to the horizontal direction.

[0016] The first layer may have a volume corresponding to 2 to 10 monolayers, e.g., 8 to 10 monolayers. For example, when 8 to 10 monolayers are grown lattice-mismatched to the underlayer, the monolayers may rearrange in a self-assembly process to form quantum dots.

[0017] In some embodiments of the present invention, the quantum dots form islands, which may be truncated pyramids, pyramids with apexes, spheres, circular disks, or elliptical disks. The quantum dots in the first layer may be quantum dots that form at a high density by self-assembly. The quantum dots in the first layer may be, for example, Stranski-Krastanov quantum dots. This allows the first layer to include a wetting layer in addition to the quantum dots. Alternatively, the quantum dots in the first layer may be Volmer-Weber quantum dots. Self-assembled quantum dots may provide high quantum dot density and / or small quantum dots, which may be beneficial for providing efficient encapsulation of dislocations.

[0018] The second layer is disposed above the first layer, for example, directly above the first layer, and the second layer laterally surrounds the quantum dots of the first layer, so that the quantum dots of the first layer can be partially or completely embedded in the second layer.

[0019] During epitaxial growth of the second layer, dislocations can be confined. For example, vertically propagating dislocations can be confined. One mechanism for confinement can be the development of side facets on the quantum dots. The development of these side facets can cause dislocations to bend laterally. This can occur under at least some growth conditions, as will be understood throughout this application.

[0020] The above is also applicable when the base layer comprises pillars or nanopillars. For example, during epitaxial growth of the second layer, dislocations propagating vertically on and above the tops of the pillars or nanopillars can be confined, while dislocation-free areas formed between the pillars continue to grow without dislocations. As mentioned above, one mechanism for confinement can be the development of side facets of the quantum dots, which cause dislocations to bend laterally.

[0021] In a first example, for example, dislocations propagating vertically from the base layer through the quantum dots in the first layer may bend laterally when the second layer is grown on the side facets of the quantum dots, thereby confining the dislocations in the second layer and preventing them from propagating further vertically.

[0022] In a second example, dislocations created when a first layer is overgrown with a second layer can also be forced to propagate laterally, for example by the development of side facets in quantum dots.

[0023] Additionally or alternatively, dislocation containment may be facilitated by dislocation coalescence. For example, a dislocation generated in a first quantum dot may coalesce with a dislocation generated in a second quantum dot. This may terminate the two dislocations and prevent them from propagating further.

[0024] As a result, there is high quality, e.g., high crystalline quality, semiconductor material above the quantum dots in the first layer, e.g., the portion of the second layer above the quantum dots in the first layer has high quality and / or the layer above the second layer has high quality.

[0025] This allows the second layer, or a layer above the second layer, to be used for a device, such as a transistor or a light-emitting diode. As a result, the second layer, or a layer above the second layer, may comprise a portion of a transistor, such as the source, body, or drain of a transistor. However, it should be understood that a semiconductor structure may have advantages even if it does not yet comprise a portion of a transistor or light-emitting diode. For example, a semiconductor structure may be sold as a template, e.g., an epi-ready template, on which further epitaxial growth may be performed. Such a template may enable the fabrication of high-quality devices, such as high-quality transistors or light-emitting diodes.

[0026] By way of example, the semiconductor structure may comprise or enable a GaN complementary metal-oxide semiconductor (CMOS) device or a more-than-Moore CMOS device, and thus be beneficial for using GaN in very large-scale integration (VLSI) device fabrication.

[0027] As another example, a semiconductor structure may include or allow for the growth of a heterojunction above the quantum dots in the first layer. The heterojunction may be an interface between two different semiconductor materials. The heterojunction may be configured to form a two-dimensional electron gas (2DEG). Such a heterojunction may be used to create a high electron mobility transistor (HEMT). Such a heterojunction may be highly sensitive to dislocations, and therefore, it may be particularly advantageous to have a first layer with quantum dots below the heterojunction.

[0028] In addition to containing dislocations, quantum dots may have additional benefits. For example, quantum dots have been found to aid in charge carrier recombination, thereby improving devices such as transistors above the quantum dots. For example, HEMTs can be improved by placing quantum dots at least 1 micrometer away from the 2DEG. Such quantum dots can be configured to have a bandgap of 1.6-1.8 eV, which can be in the middle of the bandgap of the surrounding material. Quantum dots can be configured as recombination centers, which can prevent light from emitting in a "non-radiative" form due to high p-doping. In other words, quantum dots can be resistive and / or non-conductive to electrons.

[0029] Therefore, it is an object of the present invention to provide quantum dots as recombination centers by using quantum dots as artificial atoms. Currently, recombination centers for high-frequency GaN HEMT power amplifiers (PAs) are provided by iron atoms, which act as electron trap states and acceptors for electrons near the conduction band edge. Iron dopants in the GaN crystal structure can create gallium vacancy states as deep donor states 0.70 eV above the valence band. By having a band gap in the middle of the GaN band gap, the quantum dots exhibit states that can act as both acceptors and donors.

[0030] Therefore, it is preferred that the quantum dots comprise InGaN, which has a band gap lower than that of GaN. Due to the miscibility gap of InN and GaN, an indium concentration in the range of 5-20%, or in the range of 5-10%, is therefore a preferred embodiment of the present invention.

[0031] Such a semiconductor structure can enable high switching frequencies for HEMTs. GaN HEMT devices have short on-times due to low on-resistance. However, at high frequencies, the devices still have significantly slower off-times, which can hinder high-frequency applications. By promoting the recombination of electron and hole charge carriers in quantum dots, which can be optimized through band engineering, the inventors have found that frequencies on the order of 24 to 56 GHz can be achieved, suitable for the fifth-generation technology standard for broadband cellular networks (5G). This would also be beneficial for providing energy-efficient sub-6 GHz GaN HEMT-on-silicon devices as an alternative to silicon LDMOS technology.

[0032] At least one group of layers may comprise multiple groups of layers, such that the semiconductor structure may comprise multiple layers comprising quantum dots. For example, the semiconductor structure may comprise: a first group of layers above the base layer, the first group of layers comprising a first layer and a second layer, the first layer of the first group of layers being a layer of InGaN and comprising quantum dots, and the second layer of the first group of layers being a layer of InGaN disposed above the first layer of the first group of layers, the second layer of the first group of layers laterally surrounding the quantum dots of the first layer of the first group of layers; a second group of layers above the first group of layers, the second group of layers comprising a first layer and a second layer, the first layer of the second group of layers being a layer of InGaN and comprising quantum dots, the second layer of the second group of layers being a layer of InGaN disposed above the first layer of the first group of layers, the second layer of the second group of layers laterally surrounding the quantum dots of the first layer of the first group of layers; It may comprise:

[0033] By using several groups of layers of self-assembled quantum dots, dislocations can be contained even more efficiently than with a single group of layers. For example, a dislocation that propagates through a first group of layers, e.g., by passing between quantum dots, can be contained by a second group of layers.

[0034] It should be understood that the groups of layers in the groups of layers may not necessarily be identical: they may differ, for example, in quantum dot size or composition.

[0035] The semiconductor structure comprises, for at least one of the at least one group of layers: The indium content of the InGaN of the first layer is higher than the indium content of the InGaN of the second layer. It can be configured as follows.

[0036] This may allow the first layer to comprise a material with a larger lattice constant than the second layer, which may allow the first layer to comprise a material with a smaller bandgap than the second layer, which may provide efficient containment of dislocations.

[0037] The semiconductor structure comprises, for at least one of the at least one group of layers: The material composition of the InGaN in the first layer is In x Ga 1-x N, and x is a number in the range 0 to 0.2 or 0.2 to 0.4 Such a composition has been found to provide particularly efficient containment of dislocations.

[0038] For example, a semiconductor structure can be (from bottom to top): It can be substrate / AlGaN / InGaN / InGaN-QD / AlGaN, where the InGaN-QD has an indium composition of up to 50%, in other words x≦0.5.

[0039] To give a further example, a semiconductor structure can be (from bottom to top): Silicon substrate / AlGaN / InGaN / In 0.30 Ga 0.70 It can be N-QD / AlGaN.

[0040] The semiconductor structure comprises, for at least one of the at least one group of layers: The density of quantum dots in the first layer is 10 9 cm -2 ~10 13 cm -2 Between It can be configured as follows.

[0041] The semiconductor structure comprises, for at least one of the at least one group of layers: The density of the quantum dots in the first layer is at least 10 10 cm -2 is It can be configured as follows.

[0042] It has been found that the above-mentioned densities of quantum dots provide particularly efficient confinement of dislocations. A high density of quantum dots can be advantageous in providing efficient confinement of already formed dislocations. At the same time, too high a density of quantum dots can lead to the formation of new dislocations. In this sense, 10 9 cm -2 ~10 13 cm -2 A density of quantum dots in the range of 10 13 cm-2 It should be understood that the cost may be higher than

[0043] It should be understood that the density of quantum dots refers to the number of quantum dots per unit area in the plane comprising the quantum dots.

[0044] The semiconductor structure may be configured such that the quantum dot layer (ie, the first layer) is lattice-mismatched to the underlying or overlying layer.

[0045] In a first example of lattice mismatch, consider the situation where a quantum dot layer (ie, a first layer) is lattice mismatched to an underlying layer.

[0046] The semiconductor structure comprises, for at least one of the at least one group of layers: The lattice constant of the material in the first layer is at least 0.5% greater than the lattice constant of the material in the layer immediately below said first layer at room temperature. It can be configured as follows.

[0047] Thus, the first layer may be lattice-mismatched to the layer immediately below the first layer. The lattice mismatch may be at least 0.5%. Such lattice mismatch may be a driving force for the formation of self-assembled quantum dots. Thus, the quantum dots in the first layer may be formed due to the lattice mismatch.

[0048] In a second example of lattice mismatch, consider the situation where the quantum dot layer (ie, the first layer) is lattice mismatched to the upper layer.

[0049] The semiconductor structure comprises, for at least one of the at least one group of layers: The lattice constant of the material in the first layer is at least 0.5% greater than the lattice constant of the material in the second layer at room temperature. It can be configured as follows.

[0050] Thus, the first layer may be lattice mismatched to the second layer, and the lattice mismatch may be at least 0.5%.

[0051] It should be understood that when two crystalline materials are combined, one or both materials may be strained to at least partially accommodate the lattice constant of the other material. Therefore, it should be understood that the lattice constants mentioned above are nominal lattice constants, in other words, the lattice constants of the materials when unstrained. In other words, the lattice constants are unstrained lattice constants.

[0052] The semiconductor structure includes a base layer: a primary layer, the primary layer being a layer of semiconductor material and comprising pillars extending in a direction perpendicular to the substrate; a secondary layer, the secondary layer being a layer of semiconductor material, the secondary layer being configured to laterally surround the pillars of the primary layer; The sensor may be configured to include:

[0053] The primary layer may comprise AlGaN, e.g., AlN. The primary layer may comprise sputtered AlN. The secondary layer may comprise Al x Ga 1-x N, where 0≦x≦0.95. The secondary layer may comprise Al x Ga 1-x N, where 0≦x≦0.40. The secondary layer may comprise Al x Ga 1-x N, where 0≦x≦0.20. In a preferred embodiment of the sublayer, the sublayer is GaN. The pillars may have a diameter in the range of 1 to 100 nm, preferably in the range of 5 to 50 nm, more preferably in the range of 10 to 30 nm. The pillars may be nanowires.

[0054] The secondary layer may grow as a shell on the pillars of the primary layer, thereby surrounding the pillars. A semiconductor layer structure comprising pillars surrounded by another layer may promote the containment and accumulation of dislocations along the shell of the pillars, thus reducing the amount of material defects and cracks that propagate to the surface of the semiconductor layer structure.

[0055] Dislocations may tend to propagate laterally between pillars, especially when they grow epitaxially along the length of the nanowire, for example, as shells from different nanowires coalesce to form a common thin film. Because the dislocations bend laterally, they can be prevented from propagating further. The quantum dots, or a third layer grown on the second layer, can be silicon-doped.

[0056] As an example of the benefits of the base layer with the primary and secondary layers described above, consider the following.

[0057] The primary layer can be deposited by sputtering AlN (or AlGaN) onto a silicon substrate, e.g., a silicon substrate with a top surface having Miller indices of {111}. Sputtered AlN is not necessarily single-crystalline, and grain boundaries can form under at least some growth conditions. Vertical pillars can then be etched from the AlN layer and therefore contain grain boundaries. When the pillars are laterally overgrown by depositing a secondary layer, Al(x)Ga(1-x)N growth can be seeded by these grain boundaries. Dislocations, at least under some growth conditions, have a particular tendency to propagate laterally between pillars in the M direction of the wurtzite crystal structure (the M direction is lateral as a result of the substrate being a Si{111} substrate). This allows dislocations to laterally coalesce with dislocations from other nanowire structures to form dislocation-free thin films. Defects can thereby be eliminated, at least to some extent, so that the amount of defects and cracks propagating to the surface of the semiconductor layer structure is reduced. When the pillar shells laterally integrate into the common thin film, which then begins to grow in the C direction, dislocations can be trapped and prevented from diffusing in the C direction (i.e., prevented from diffusing vertically). This allows strain caused by growth on the silicon substrate to be accommodated by initially forming dislocations, but at least some of the dislocations can be confined and prevented from further diffusing vertically. Dislocations that escape the base layer above the nanopillars can then be confined during the growth of the group of layers comprising the quantum dots. Additionally or alternatively, other types of dislocations, such as dislocations associated with the integration of the pillar shells between and above the nanopillars, can be confined during the growth of the group of layers comprising the quantum dots.

[0058] It has been found that the combination of pillars and quantum dots can be particularly useful for confining dislocations that have not been filtered up to the immediate height of the nanopillars. Many dislocations can already be confined in the base layer. Dislocations that escape the base layer and propagate to at least one group of layers can be confined there by the quantum dots. Pillars and quantum dots can complement each other and confine different types of dislocations.

[0059] According to a second aspect, there is provided a method for manufacturing the semiconductor structure of the first aspect, comprising: providing a substrate; forming a base layer over a substrate; forming at least one group of layers above the base layer by forming a first layer and forming a second layer, wherein forming the at least one group of layers comprises forming first layer quantum dots by self-assembly for at least one of the at least one group of layers; A method is provided, comprising:

[0060] Forming the layers of the semiconductor structure can be done by any kind of epitaxial growth, for example by metalorganic vapor phase epitaxy (MOVPE) or molecular beam epitaxy (MBE).

[0061] As previously mentioned, the quantum dots in the first layer can be self-assembled quantum dots. The quantum dots in the first layer can be, for example, Stranski-Krastanov quantum dots. This allows the first layer to include a wetting layer in addition to the quantum dots. Alternatively, the quantum dots in the first layer can be Volmer-Weber quantum dots. Self-assembled quantum dots can provide high quantum dot density and / or small quantum dots, which can be beneficial for providing efficient containment of dislocations. Furthermore, the self-assembly process can be advantageous in combination with a patterning process. For example, when quantum dots formed by self-assembly are combined with a base layer including pillars formed by patterning, e.g., lithographic patterning, the self-assembly process can compensate for non-uniformities in the patterning process.

[0062] According to the above, the self-organized formation of quantum dots can be driven by the lattice mismatch between the first layer and the second layer.

[0063] Forming the at least one group of layers may comprise forming a first layer of quantum dots by Stranski-Krastanow growth for at least one of the at least one group of layers.

[0064] Stransky-Krastanow growth can be a growth mode that provides suitable quantum dot size and / or quantum dot density.

[0065] Stransky-Krastanow growth may be a growth mode favorable for forming quantum dots, which can promote the containment of dislocations propagating from below without forming many new dislocations. Thus, the net effect of such quantum dots may be a reduction in dislocations propagating further up the first layer comprising the quantum dots.

[0066] Forming the at least one group of layers may include, for at least one of the at least one group of layers: shutting off the gas flow for at least 5 seconds between forming the first layer and forming the second layer, the gas flow comprising nitrogen. It may comprise:

[0067] For example, the gas flow can be interrupted for 10 to 20 seconds between forming the first layer and forming the second layer. The gas flow comprising nitrogen can be, for example, a gas flow comprising nitrogen gas and / or a gas flow comprising ammonia.

[0068] Such blocking can provide a suitable quantum dot size and / or density. For example, the first layer can be formed by planarly growing 2 to 10 monolayers, e.g., 8 to 10 monolayers. Blocking the flow of nitrogen gas can be considered as stopping the Group V supply. Alternatively, the Group III supply can be blocked by blocking the flow of Group III precursor gases, e.g., blocking trimethylgallium and / or triethylgallium in a nitrogen or ammonia gas atmosphere. Group III and Group V herein refer to Group III and Group V of the periodic table of elements.

[0069] The interruption may stop further growth. During the interruption, the planar monolayer may rearrange to form quantum dots, e.g., rearrange to form a wetting layer and quantum dots.

[0070] Forming the at least one group of layers may include, for at least one of the at least one group of layers: and terminating the formation of the first layer based on a photoluminescence signal from the quantum dots of the first layer. It may comprise:

[0071] The photoluminescence spectrum can depend on the quantum dot size and / or quantum dot density, so photoluminescence can be used to fine-tune the quantum dot size and / or quantum dot density.

[0072] As a first example, the formation of the first layer can be terminated when the photoluminescence spectrum indicates that the quantum dots have reached a threshold size, which can be a threshold value indicating quantum dots with a height of 1-20 nm and / or a width of 10-20 nm.

[0073] As a second example, the formation of the first layer can be terminated when the photoluminescence spectrum indicates that the quantum dots have reached a threshold density. 10 cm -2 Quantum dot densities exceeding 10 9 cm -2 ~10 13 cm -2 This can indicate a density of quantum dots that is between .

[0074] Forming the base layer comprises: forming a primary layer, the primary layer being a layer of semiconductor material, the primary layer comprising pillars extending in a direction perpendicular to the substrate; forming a secondary layer, the secondary layer being a layer of semiconductor material, the secondary layer configured to laterally surround the pillars of the primary layer; and The primary layer is formed in an atmosphere comprising hydrogen and nitrogen, and / or the secondary layer is formed in an atmosphere comprising nitrogen.

[0075] The base layer can be an intermediate layer of AlN or AlGaN. Using strain in InGaN growth on an intermediate layer of AlN or AlGaN as the driving force for quantum dot formation is a preferred embodiment of the present invention. Reducing dislocations at these interfaces can mitigate cracking of the GaN HEMT epitaxial wafer. The intermediate layer can have a thickness of 10 to 30 nm and is grown until a growth cutoff of 5 to 20 seconds occurs, at which time quantum dots are formed. The intermediate base layer, as used herein, can be interpreted as a layer between the quantum dot layer (first layer) and another layer.

[0076] The primary layer may be formed in an atmosphere comprising hydrogen and nitrogen, with the hydrogen to nitrogen molar ratio being between 2 to 1 (i.e., twice the amount of hydrogen) and 1 to 2 (i.e., twice the amount of nitrogen). In particular, the primary layer may be formed in an atmosphere comprising hydrogen and nitrogen with a hydrogen to nitrogen molar ratio of 1 to 1, i.e., equal amounts of hydrogen and nitrogen.

[0077] The above, as well as additional objects, features, and advantages of the inventive concept will be better understood through the following illustrative, non-limiting detailed description, taken in conjunction with the accompanying drawings, in which like reference numerals are used for like elements unless otherwise noted. [Brief explanation of the drawings]

[0078] [Figure 1] 1 is a cross-sectional view of a semiconductor structure. [Figure 2] 1 is a cross-sectional view of a semiconductor structure. [Figure 3] 1 is a cross-sectional view of a semiconductor structure. [Figure 4] 1 is a cross-sectional view of a semiconductor structure. [Figure 5] 1 is a cross-sectional view of a semiconductor structure. [Figure 6] 1 is a cross-sectional view of a semiconductor structure. [Figure 7] 1 is a top view of a semiconductor structure. [Figure 8] 1 is a flowchart of a method. [Figure 9] 1 is a flowchart of a method. [Figure 10] FIG. [Figure 11] FIG. DETAILED DESCRIPTION OF THE INVENTION

[0079] The technical contents and detailed description of the present invention, together with the accompanying drawings, are described according to preferred embodiments which are not used to limit the scope of the claims. The present invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and will fully convey the scope of the present invention to those skilled in the art.

[0080] 1 to 6 illustrate semiconductor structures 1 according to the present invention. The semiconductor structures 1 are shown in cross-sectional views. Each semiconductor structure 1 comprises: A substrate 2; a base layer 10 comprising an AlGaN layer and disposed above the substrate 2; At least one group of layers 20 disposed above the base layer 10, each of the at least one group of layers 20 comprising: a first layer 21, the first layer 21 being a layer of InGaN and comprising quantum dots 24; a second layer 22, which is an InGaN layer, disposed above the first layer 21, the second layer 22 laterally surrounding the quantum dots 24 of the first layer 21, and the InGaN material composition of the second layer 22 being different from the InGaN material composition of the first layer 21; at least one group 20 of layers comprising Equipped with.

[0081] The quantum dots 24 in the first layer 21 can be self-assembled quantum dots. The quantum dots 24 in the first layer 21 can be, for example, Stransky-Krastanov quantum dots. The first layer 21 can include a wetting layer 26 in addition to the quantum dots 24, as shown in FIG. 1 . Alternatively, the quantum dots 24 in the first layer 21 can be Volmer-Weber quantum dots 24. The Volmer-Weber quantum dots 24 can be formed directly on the base layer 10 without the wetting layer 26, as shown in FIG. 2 . Thus, there can be gaps between the quantum dots 24 where the layer below the first layer 21 (in FIG. 2 , the base layer 10) is in contact with the second layer 22.

[0082] 3 illustrates how quantum dots 24 can cause dislocations 4 to bend laterally. The figure illustrates two dislocations 4 propagating vertically from the interface between the substrate 2 and the base layer 10, through the base layer 10, and through a quantum dot 24 in the first layer 21. Each illustrated dislocation 4 then bends laterally in the second layer 22.

[0083] 4 illustrates a semiconductor structure 1 comprising multiple groups of layers 20, in this case three groups of layers 20. Each group of layers 20 herein comprises a first layer 21 and a second layer 22. The quantum dots in different groups of layers do not necessarily need to be aligned. This allows quantum dots in the first group of layers to be located at lateral positions where quantum dots in the second group of layers are not present.

[0084] By using several groups of layers, dislocations can be efficiently confined: for example, a dislocation that propagates through a first group of layers by passing between quantum dots can be confined by a second group of layers.

[0085] FIG. 5 illustrates a semiconductor structure 1 including a heterojunction 30 above the quantum dots 24 of the first layer 21. The heterojunction 30 is the interface between two different semiconductor materials. In FIG. 5, the heterojunction 30 is the interface between the second layer 22 and the barrier layer 32. The barrier layer 32 may have a larger bandgap than the underlying layer, in this case the barrier layer 32. The barrier layer 32 may be an AlGaN layer, and the underlying layer, in this case the second layer 22, may be a GaN layer.

[0086] The heterojunction 30 can be configured to form a 2DEG. Such a heterojunction 30 can be used to make a HEMT. Figure 5 can be seen as an example of such a HEMT, in which a source electrode 40, a gate electrode 42, and a drain electrode 44 are disposed on the surface of the semiconductor structure 1 above the heterojunction, in this case on top of a barrier material.

[0087] FIG. 6 is a cross-sectional side view of the semiconductor structure 1, in which the base layer 10 is a primary layer 11, which is a layer of semiconductor material and which comprises pillars 14 extending in a direction perpendicular to the substrate 2; a secondary layer 12, the secondary layer 12 being a layer of semiconductor material, the secondary layer 12 being configured to laterally surround the pillars 14 of the primary layer 11; FIG. 7 is a cross-sectional view from the top of the same semiconductor structure 1, the cross-section being taken along line A in FIG. 6. The pillars 14 can be arranged in an array, as shown in the cross-sectional view from the top of FIG. 7. Alternatively, the pillars 14 can be randomly distributed. It should be understood that during maskless overgrowth of the pillars 14 with GaN, dislocations can propagate vertically, while the dislocations are filtered to form a dislocation-free layer just above the height of the pillars. In some embodiments, quantum dots can be provided as dislocation filters for vertically propagating dislocations on top of the nanopillars. In other embodiments, one or more layers of quantum dots can be provided abutting an AlN or Al(x)Ga(l-x)N intermediate layer, which provides the driving force for the formation of the quantum dots.

[0088] FIG. 8 shows a flowchart of a method 100 for fabricating a semiconductor structure 1. According to the method 100, a substrate 2 is first provided (S102). Then, a base layer 10 is formed above the substrate 2 (S110). Thereafter, at least one group of layers 20 is formed above the base layer 10 by forming a first layer 21 and a second layer 22 (S120). Forming the at least one group of layers 20 includes forming quantum dots 24 in the first layer 21 by self-assembly for at least one of the at least one group of layers 20 (S124). This can be achieved by placing the substrate 2, e.g., a silicon substrate, in a reactor cell of a metalorganic vapor phase epitaxy (MOVPE) system and supplying precursor gases at suitable pressures and temperatures to grow layers of the semiconductor structure 1. Alternatively, the base layer 10, or portions of the base layer 10, can be formed before placing the substrate 2 in the MOVPE system. For example, the base layer 10, or portions of the base layer 10, may be formed by sputtering AlN or AlGaN onto the substrate 2.

[0089] Forming the quantum dots 24 in the first layer 21 can be performed by Stranski-Krastanow growth, whereby the material forming the quantum dots 24 can be grown lattice-mismatched to an underlying layer, for example, lattice-mismatched to a base layer or lattice-mismatched to a second layer 22 of a preceding group of layers.

[0090] The step of forming at least one group of layers (S120) may comprise one or more optional steps, in addition to forming quantum dots 24 (S124), as shown in FIG.

[0091] For example, the gas flow may be interrupted for at least 5 seconds between forming the first layer 21 and forming the second layer 22 (S125), and the gas flow may be a nitrogen gas flow. Thus, the nitrogen gas or ammonia gas flow may be interrupted for at least 5 seconds. The interrupted gas flow may be the entire Group V feed gas flow in the MOVPE reactor cell. Alternatively, the interrupted gas flow may be a portion of the entire Group V feed gas flow in the MOVPE reactor cell.

[0092] As another example, layer formation of the first layer 21 can be terminated based on a photoluminescence signal from the quantum dots 24 in the first layer 21 (S126). The photoluminescence signal, as used herein, can be obtained by illuminating the semiconductor structure 1 with light, e.g., laser light, and collecting photon emissions from the quantum dots 24. The photon emissions, as used herein, can be collected using, for example, a microscope objective, e.g., a microscope objective with a long working distance. The collected light can be sent to a spectrometer, thereby obtaining a spectrum. Each quantum dot can produce at least one spectral peak that can be characteristic of the quantum dot size. A spectral peak with high energy (shorter spectral wavelength) can indicate a smaller quantum dot. A spectral peak with lower energy (longer spectral wavelength) can indicate a larger quantum dot. Many quantum dots can contribute to the photoluminescence signal. However, the same principles as in the case of a single quantum dot can apply. If the photoluminescence signal is centered near a short spectral wavelength, most of the quantum dots can be considered to be high-energy quantum dots, i.e., small quantum dots. As the quantum dots grow larger, the spectrum of the photoluminescence signal can drift toward longer wavelengths. When the spectral peak of the photoluminescence signal is centered near a threshold, this can be considered an indicator that the quantum dots 24 have reached a threshold size and the formation of the first layer 21 can be terminated (S126). When the spectral peak of the photoluminescence signal has a specific width and / or position, this can be considered an indicator that the quantum dots 24 have reached a threshold density and the formation of the first layer 21 can be terminated (S126).

[0093] As previously described, the quantum dots 24 may be combined with a base layer 10 comprising pillars. Thus, forming the base layer 10 (S110) may comprise forming a primary layer 11, the primary layer 11 comprising pillars 14 extending in a direction perpendicular to the substrate 2. For example, a semiconductor material may be deposited on the substrate 2 and then lithographically patterned and etched to form the pillars 14. A secondary layer 12 may then be formed, the secondary layer 12 configured to laterally surround the pillars 14 of the primary layer 11. The material of the primary layer 11 may be grown, for example, by MOVPE. Alternatively, the material of the primary layer 11 may be a sputtered semiconductor material. The material of the secondary layer 12 may be, for example, an epitaxially grown semiconductor material, for example, grown by MOVPE.

[0094] The primary layer 11 may be formed in an atmosphere comprising hydrogen and nitrogen. The secondary layer 12 may be formed in an atmosphere comprising nitrogen. The primary layer 11 may be formed in an atmosphere comprising hydrogen and nitrogen with a hydrogen to nitrogen molar ratio between 2:1 and 1:2. In particular, the primary layer may be formed in an atmosphere comprising hydrogen and nitrogen with a hydrogen to nitrogen molar ratio of 1:1. The above may be applicable when the material of the primary layer 11 is grown by MOVPE as well as when the material of the primary layer 11 is sputtered.

[0095] As previously discussed, quantum dots 24 can form recombination centers. This allows quantum dots 24 to replace iron dopants as recombination centers. Figures 10-11 illustrate the difference between iron dopants and quantum dots 24.

[0096] 10 schematically illustrates a band diagram for an iron-doped semiconductor, e.g., GaN. The diagram illustrates a valence band 70 and a conduction band 72. The diagram further illustrates the energy level 74 of the iron dopant. The iron dopant in the crystalline structure of GaN can create a gallium vacancy state as a deep donor state 0.70 eV above the valence band 70.

[0097] 11 is a schematic diagram of a band diagram for a semiconductor, e.g., GaN, including the energy structure 76 of the quantum dots 24. The energy structures 76 of three quantum dots 24 can be seen in the diagram. As shown, the quantum dots 24 can form potential wells in both the valence band 70 and the conduction band 72. As shown, holes can exist in the potential well of the valence band 70. Similarly, electrons can exist in the potential well of the conduction band 72. Thus, because the quantum dots 24 have a band gap in the middle of the GaN band gap, the quantum dots 24 can function as both acceptors and donors.

[0098] The inventive concepts have been described above primarily with reference to a limited number of examples. However, as will be readily apparent to those skilled in the art, examples other than those disclosed above are equally possible within the scope of the inventive concepts as defined by the appended claims.

Claims

1. A substrate (2), a base layer (10) comprising an AlGaN layer and disposed above the substrate (2); At least one group of layers (20) disposed above the base layer (10), each of the at least one group of layers (20) comprising: a first layer (21) made of InGaN and comprising quantum dots (24); a second layer (22) made of InGaN, disposed on and above the first layer (21), the second layer (22) laterally surrounding the quantum dots (24) of the first layer (21), and a material composition of the InGaN of the second layer (22) different from a material composition of the InGaN of the first layer (21); At least one group of layers (20) comprising: a heterojunction (30) disposed above the quantum dots (24) of the first layer (21), the heterojunction (30) being configured to form a two-dimensional electron gas; A semiconductor structure (1) comprising:

2. The semiconductor structure (1) of claim 1, wherein the at least one group (20) of layers comprises a plurality of groups (20) of layers.

3. For at least one of said at least one group (20) of layers:

3. The semiconductor structure (1) according to claim 1 or 2, wherein the indium content in the InGaN of the first layer (21) is higher than the indium content of the InGaN of the second layer (22).

4. For at least one of said at least one group (20) of layers: The material composition of the InGaN of the first layer (21) is In ｘ Ga １－ｘ N and x is a number in the range 0.1 to 0.2 or 0.2 to 0.

4.

5. For at least one of said at least one group (20) of layers: The density of the quantum dots (24) in the first layer (21) is 10 ９ cm －２ ~10 １３ cm －２ The semiconductor structure (1) according to any one of claims 1 to 4, wherein

6. For at least one of said at least one group (20) of layers: The density of the quantum dots (24) in the first layer (21) is at least 10 １０ cm －２ 6. The semiconductor structure (1) according to any one of claims 1 to 5, wherein

7. For at least one of said at least one group (20) of layers:

7. The semiconductor structure (1) according to any one of claims 1 to 6, wherein the lattice constant of the material in the first layer (21) is at least 0.5% larger at room temperature than the lattice constant of the material in the layer immediately below the first layer (21).

8. For at least one of said at least one group (20) of layers:

8. The semiconductor structure (1) according to any one of claims 1 to 7, wherein the lattice constant of the material in the first layer (21) is at least 0.5% larger than the lattice constant of the material in the second layer (22) at room temperature.

9. The base layer (10) a primary layer (11) of semiconductor material and comprising pillars (14) extending in a direction perpendicular to the substrate (2); a secondary layer (12) of semiconductor material, the secondary layer (12) being configured to laterally surround the pillars (14) of the primary layer (11); Equipped with The semiconductor structure (1) according to any one of the preceding claims, wherein the primary layer (11) or the secondary layer (12) forms the AlGaN layer of the base layer (10).

10. A method (100) for manufacturing a semiconductor structure (1) according to any one of claims 1 to 9, comprising: Providing the substrate (2) (S102); forming the base layer (10) above the substrate (2) (S110); forming the at least one group (20) of layers above the base layer (10) by forming the first layer (21) and the second layer (22) (S120), wherein forming the at least one group (20) of layers comprises forming the quantum dots (24) of the first layer (21) by self-assembly for at least one of the at least one group (20) of layers (S124); forming a heterojunction (30) above the quantum dots (24) of the first layer (21), the heterojunction (30) being configured to form a two-dimensional electron gas; A method (100) comprising:

11. 11. The method of claim 10, wherein forming the at least one group of layers comprises forming the quantum dots of the first layer by Stransky-Krastanow growth for at least one of the at least one group of layers.

12. forming (S120) the at least one group of layers (20) includes, for at least one of the at least one group of layers (20): interrupting (S125) the gas flow for at least 5 seconds between forming the first layer (21) and forming the second layer (22), wherein the gas flow is a gas flow comprising nitrogen; 12. The method (100) of claim 10 or 11, comprising:

13. forming (S120) the at least one group of layers (20) includes, for at least one of the at least one group of layers (20): and terminating the formation of the first layer (21) based on a photoluminescence signal from the quantum dots (24) of the first layer (21) (S126).

13. The method (100) of any one of claims 10 to 12, comprising:

14. The step of forming the base layer (10) (S110) includes: forming a primary layer (11), said primary layer (11) being a layer of semiconductor material, said primary layer (11) comprising pillars (14) extending in a direction perpendicular to said substrate (2); forming a secondary layer (12), the secondary layer (12) being a layer of semiconductor material, the secondary layer (12) being configured to laterally surround the pillars (14) of the primary layer (11); Equipped with 14. The method (100) according to any one of claims 10 to 13, wherein the primary layer (11) is formed in an atmosphere comprising hydrogen and nitrogen and / or the secondary layer (12) is formed in an atmosphere comprising nitrogen.

15. 15. The method (100) of any one of claims 10 to 14, wherein at least a portion of the base layer is formed by reactive sputtering of AlN or AlGaN.

16. The method (100) of claim 15, wherein the intermediate layer (10) has a thickness of 10 to 30 nm.

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