Relaxation gan / ingan structures and methods of making same

Abstract

The present invention relates to a relaxed GaN / InGaN structure and a method for manufacturing the same, comprising the following steps: a) providing a device comprising: a GaN / InGaN structure comprising a conductively doped GaN layer (204) locally covered with InGaN terraces (100), the InGaN terraces comprising a doped InGaN layer (101) and an undoped or weakly doped InGaN layer (102), an electrically insulating layer (300) covering the conductively doped GaN layer (204) between the InGaN terraces (100); b) electrically connecting the conductively doped GaN layer (204) and a counter electrode (500) to a voltage or current generator; c) immersing the device and the counter electrode (500) in an electrolyte; d) applying a voltage or a current between the conductively doped GaN layer (204) and the second electrode (500) to porosify the doped InGaN layer (101); e) epitaxially forming an InGaN layer on the InGaN terraces (100) to obtain a relaxed epitaxially grown InGaN layer (400).

Description

Technical Field

[0001] This invention relates to the general field of color microdisplays.

[0002] This invention relates to a relaxation method for GaN / InGaN structures.

[0003] This invention also relates to a relaxor GaN / InGaN structure and its manufacturing method.

[0004] This invention has applications in many industrial fields, especially in the field of color microdisplays based on microLEDs with a pitch of less than 10 μm. Background Technology

[0005] Color microdisplays include red, green, and blue pixels (RGB pixels).

[0006] Blue and green pixels can be made of nitride materials, while red pixels can be made of phosphor materials. To combine these three types of pixels on the same substrate, a technique known as "pick-and-place" is typically used. However, for microdisplays with pixels smaller than 10μm, this technique is no longer suitable due to alignment issues and the time required to implement it at this scale.

[0007] Another solution is to use quantum dots (QDs) or nanophosphors to perform color conversion. However, controlling the deposition of these materials on small pixels is difficult, and their flow resistance is not strong enough.

[0008] Therefore, the key is to be able to naturally obtain three RGB pixels on the same substrate using materials from the same family. InGaN is the most promising material for this. In fact, based on its indium concentration, this material can theoretically cover the entire visible spectrum. Blue InGaN-based microLEDs have already shown high brightness, far exceeding their organic counterparts. To emit green wavelength light, the quantum well (QW) of the LED should contain at least 25% indium, while for red light emission, at least 35% indium is required. Unfortunately, the poor miscibility of InN in GaN and the inherent strong compressive stress from growing the InGaN active region on GaN lead to a quality degradation in InGaN materials with an indium content higher than 20%.

[0009] Therefore, it is crucial to reduce the overall stress of GaN / InGaN-based structures.

[0010] Several solutions have been considered to address this problem.

[0011] One solution is to form nanostructures, such as nanowires or nanocones, to enable stress relaxation through free edges. Axial nanowire growth can be achieved via molecular beam epitaxy (MBE). However, the low growth temperatures used in MBE growth lead to a decrease in internal quantum efficiency (IQE). Cones are used to bend dislocations; in particular, intact cones have a semi-polar plane that favors indium doping and reduces the electric field within the active region. For truncated cones, the truncated surface allows quantum well growth on the c-plane, resulting in more uniform emission compared to emission along the semi-polar plane of an intact cone. Alternatively, growth can also occur planarly on planes outside the c-plane of the wurtzite structure, such as on a semi-polar plane that is more favorable for indium doping.

[0012] Another solution is to reduce the stress in the active region of the LED structure by using a substrate or pseudo-substrate whose lattice parameter is closer to that of the InGaN alloy of the quantum well. Thus, the incorporation rate of In in InGaN can be increased even with a planar structure. It has been shown that as the substrate lattice parameter increases, the internal electric field decreases compared to a stress layer with the same indium concentration, and the quantum well emission shifts to red [1]. The resulting relaxed InGaN layer allows for the growth of III-N heterostructures via metal-organic vapor phase epitaxy (MOVPE). However, to date, the only substrate that can support this demonstration is through smart cut. TM Soitec pseudo-substrate InGaNOS obtained by the technique.

[0013] Another solution to reduce the overall stress in GaN / InGaN-based LED structures is to porosilicate the GaN layer. In reference [2], a stack was first prepared consisting of a sapphire substrate covered with an unintentionally doped GaN layer (uidGaN) and an n+ doped GaN layer. The doped GaN layer served as the anode and platinum wire served as the cathode. Electrochemical porosilicate treatment was performed by applying a voltage of 15 V in an oxalic acid solution (0.2 M) for 30 minutes and then in a KOH solution (0.06 M) under ultraviolet radiation at 9 V for 30 minutes. The porosilicated GaN layer obtained in this way allows the growth of a multi-quantum-well (MQW) LED structure consisting of an n+ GaN layer, five GaN / InGaN quantum wells (QWs), and a p GaN contact layer. Significant stress relaxation leads to better electrical and optical performance, especially in terms of photoluminescence (PL).

[0014] However, the crystal quality of the GaN layer in an LED depends on the pore size and porosity of the porous GaN layer, as well as the desired thickness. Therefore, suitable parameters must be found each time, which complicates the industrialization of this method. Summary of the Invention

[0015] The object of this invention is to provide a method that overcomes the shortcomings of the prior art and enables the acquisition of at least partially or even fully relaxed GaN / InGaN structures for manufacturing, for example, red, green, and blue pixels.

[0016] Therefore, the present invention provides a method for fabricating at least partially relaxed GaN / InGaN structures, the method comprising the following steps:

[0017] (a) Provides an apparatus comprising:

[0018] A GaN / InGaN structure comprising a conductive doped GaN layer partially covered with InGaN mesas, wherein the InGaN mesas consist of doped InGaN layers and undoped or weakly doped InGaN layers.

[0019] An electrically insulating layer is formed by covering the InGaN mesa with conductive doped GaN layers.

[0020] (b) Electrically connect the conductive doped GaN layer and the counter electrode of the device to a voltage generator or a current generator.

[0021] (c) Immerse the device and the counter electrode in the electrolyte.

[0022] (d) Applying a voltage or current between the conductive doped GaN layer and the second electrode to porosilicate the mesa-doped InGaN layer.

[0023] (e) An InGaN layer is formed on the InGaN mesa by epitaxy, thereby obtaining a relaxed epitaxially grown InGaN layer.

[0024] The fundamental difference between this invention and existing technologies lies in the step of selectively porosifectizing the mesa-doped InGaN layer using an electrochemical method. Porosimetry occurs within the volume of the doped InGaN layer.

[0025] The undoped or weakly doped InGaN layer is electrically insulating and is not porosized in step d). Therefore, it can be used as an epitaxial regeneration layer on the mesa.

[0026] The pore size can be easily adjusted based on mesa doping, applied voltage, and / or the selected electrolyte (properties and / or concentration) to achieve the desired relaxation rate, thereby obtaining the desired wavelength emitted by the active region (quantum well) through reepitaxy.

[0027] Porosity improves extraction efficiency, especially when the pore size is comparable to the target wavelength.

[0028] This step can be performed with low heat consumption, especially at room temperature (usually around 20-25°C), which avoids sublimation of the countertop material.

[0029] During epitaxial growth, the growth temperature used (typically 900°C to 1000°C) modifies the porosity layer, particularly by increasing the porosity of the layer, thereby providing additional degrees of freedom while maintaining lattice parameters suitable for the epitaxial regenerated layer.

[0030] At the end of the method, a GaN / InGaN structure that is at least partially relaxed or even fully relaxed is obtained.

[0031] Advantageously, the undoped or weakly doped InGaN layer has a thickness of 0.25 nm to 3 nm.

[0032] Advantageously, the electrical insulating layer is a SiO2 layer or a SiN layer.

[0033] Advantageously, the indium content in the InGaN mesa is greater than or equal to 8%. This ensures indium-rich, high-quality re-epitaxy.

[0034] Advantageously, the thickness of the mesa is less than 100 nm. Therefore, despite the high concentration of indium, the defect density of the mesa remains limited.

[0035] According to the first advantageous alternative, the device provided in step a) is manufactured by first forming an electrically insulating layer and then forming an InGaN mesa.

[0036] According to another advantageous alternative, the device provided in step a) is manufactured by first forming an InGaN mesa and then forming an electrically insulating layer.

[0037] Advantageously, a conductive doped GaN layer covers a sapphire or silicon support.

[0038] Advantageously, the method includes performing implantation doping or metal-organic vapor phase epitaxial doping on the InGaN mesa. Implantation on the InGaN mesa is selective.

[0039] Advantageously, the doped InGaN layers on the mesa have different doping types from one mesa to another. This results in pixels (e.g., three pixels) having different doping levels, thus producing different relaxation percentages and consequently different emission wavelengths. This alternative embodiment is advantageous for forming multispectral devices, such as LEDs of different colors or multicolor microdisplays in a simplified manner.

[0040] According to an advantageous implementation, the InGaN mesa of the structure provided in step a) is obtained by following the steps of:

[0041] Apply a full-board InGaN layer.

[0042] Local implantation doping or metal-organic vapor phase epitaxial doping steps are performed in the full-plate InGaN layer to form doped and undoped regions.

[0043] An unintentionally doped or weakly doped full-plate InGaN layer is deposited onto the full-plate InGaN layer.

[0044] The entire InGaN layer is etched by removing undoped or weakly doped regions to form InGaN mesa locally, which includes both doped and undoped or weakly doped InGaN layers.

[0045] Advantageously, the doped regions have different doping types, and therefore the doped InGaN layers on different mesas have different doping types.

[0046] This method has many advantages.

[0047] Easy to implement.

[0048] It can be used for mesa with a small thickness (typically less than 100nm).

[0049] The structured countertop provides a malleable effect.

[0050] Compared to a stress-bearing layer with the same indium concentration, it can lead to partial or complete stress relaxation and reduce piezoelectric polarization.

[0051] It allows for the use of a so-called "bottom-up" approach to fabricate microLEDs (μLEDs) and microdisplays: after the mesa is pixelated, the growth of optical structures (N, QW, P) can be achieved regardless of pixel size, and alignment issues during the "pick-and-place" process can be resolved.

[0052] The pixel etching process does not affect the efficiency of micro LEDs, which makes it possible to manufacture micron or submicron pixels.

[0053] This invention also relates to a GaN / InGaN structure, comprising:

[0054] Conductive doped GaN layer,

[0055] The InGaN mesa comprises a porosilicated InGaN layer and an undoped or weakly doped InGaN layer, preferably with a thickness of 0.25 nm to 3 nm.

[0056] Relaxed epitaxially grown InGaN layer.

[0057] Advantageously, the thickness of the undoped or weakly doped InGaN layer is 2 nm to 3 nm. This layer is non-porous.

[0058] A porous layer is a layer with a porosity greater than 1%. Preferably, it ranges from 5% to 70%. The upper limit is the maximum porosity before the mesa layering begins.

[0059] Other features and advantages of the invention will become apparent from the following additional description.

[0060] Obviously, this additional description is merely illustrative of the subject matter of the invention and should not be construed as limiting the subject matter. Attached Figure Description

[0061] The invention will be better understood after reading the description of exemplary embodiments given for illustrative purposes only and not for limitation, with reference to the accompanying drawings, in which:

[0062] Figure 1A and Figure 1B A device including a GaN / InGaN structure according to different specific embodiments of the present invention is schematically shown in cross-sectional view form.

[0063] Figure 2A , Figure 2B , Figure 2C and Figure 2D Different steps of a method for manufacturing an apparatus comprising a GaN / InGaN structure according to a specific embodiment of the present invention are illustrated schematically.

[0064] Figure 3A , Figure 3B and Figure 3C Different steps of a method for manufacturing an apparatus comprising a GaN / InGaN structure are illustrated schematically according to another specific embodiment of the present invention.

[0065] Figure 4 The steps of electrochemical anodizing an InGaN mesa are illustrated schematically in a specific embodiment of the present invention.

[0066] Figure 5 It is a graph showing the different phenomena (pre-breakdown, porosimetry and electropolishing) that occur during the anodizing step according to a specific embodiment of the invention, which vary with doping rate and applied potential.

[0067] Figure 6A and Figure 6B The epitaxial regrowth on an InGaN mesa is illustrated schematically according to different specific embodiments of the present invention.

[0068] Figure 7A , Figure 7B , Figure 7C and Figure 7DThese are atomic force microscopy (AFM) images of a 0.8% InGaN layer before porosification, after porosification, after porosification and annealing, and finally after epitaxial regrowth.

[0069] The different parts shown in the diagram are not necessarily drawn to a uniform scale in order to make the diagram clearer.

[0070] Different possibilities (alternatives and implementations) should be understood as not mutually exclusive and can be combined with each other.

[0071] Furthermore, in the following description, given that the structure is oriented in the manner shown in the diagram, terms that depend on the structure's orientation, such as "above", "above", "below", etc., are used. Detailed Implementation

[0072] This invention is particularly applicable to the field of color microdisplays, especially in the manufacture of red, green, and blue pixels, but it is not limited thereto. This invention can also be used in the photovoltaic field and even in the field of photocatalytic water splitting, because, on the one hand, InGaN absorbs throughout the visible spectrum, and on the other hand, its valence and conductivity band are within the range of water stability, which are the thermodynamic conditions necessary for water splitting reactions. This invention may also be significant for the manufacture of LEDs or long-wavelength emitting lasers.

[0073] A method for obtaining partially or fully relaxed GaN / InGaN structures includes porosiform treatment of InGaN by electrochemical anodic oxidation according to the following steps.

[0074] a) Provide an apparatus comprising:

[0075] The GaN / InGaN structure includes a conductive doped GaN layer 204 partially covered by an InGaN mesa 100, which includes a doped InGaN layer 101 and an undoped or weakly doped InGaN layer 102.

[0076] An electrically insulating layer 300 is formed by a conductive doped GaN layer 204 covering the InGaN mesa 100.

[0077] b) Electrically connect the conductive doped GaN layer 204 and counter electrode 500 of the device to a voltage or current generator.

[0078] c) Immerse the device and counter electrode 500 in the electrolyte.

[0079] d) Apply a voltage or current between the conductive doped GaN layer 204 and the second electrode 500 to porosilicate the doped InGaN layer 101 of the mesa 100.

[0080] e) Epitaxy is performed on the InGaN mesa 100 to obtain an epitaxially grown, at least partially relaxed, preferably fully relaxed, InGaN layer.

[0081] The degree of relaxation corresponds to:

[0082] Δa / a =(a c2 -a c1 ) / a c1

[0083] a c1 The lattice parameters of the initial layer, and

[0084] a c2 represents the lattice parameters of the relaxation layer.

[0085] If a c2 Corresponding to the lattice parameters of the solid material, the relaxation degree of this layer is 100%.

[0086] when a c1 =a c2 At that time, it was assumed that the layer would bear stress.

[0087] Partial relaxation refers to a relaxation level exceeding 50%.

[0088] The device provided in step a) includes a GaN / InGaN structure. More specifically, the device includes a stack 200, on which a conductive doped GaN layer 204 is on top, which is covered by and in contact with an InGaN mesa 100.

[0089] Advantageously, the stack 200 covered by the InGaN mesa 100 includes:

[0090] Support layer 201 or support, such as sapphire or silicon;

[0091] The first layer 202 is preferably unintentionally doped gallium nitride (GaN) (uid GaN), and / or the second layer 203 is preferably doped GaN (n GaN).

[0092] The third layer corresponding to the conductive doped GaN layer 204 is preferably a highly doped GaN (n++GaN).

[0093] Unintentionally doped GaN means a concentration below 5%. e 17 at / cm 3 .

[0094] Doped GaN means a concentration greater than 10 18 at / cm 3 .

[0095] Highly doped GaN means a concentration greater than 10. 19 at / cm 3 .

[0096] Preferably, the stack 200 consists of the aforementioned layers. In other words, it does not include any other layers.

[0097] For example, the thickness of the support layer 201 ranges from 350 μm to 2 mm. This thickness depends on the properties and dimensions of the support layer 201. For example, the thickness is 350 μm for a 2-inch diameter sapphire support and 1.3 mm for a 6-inch diameter sapphire support.

[0098] For example, the thickness of the first 202 layer is in the range of 500 nm to 5 μm. This uid layer should absorb the stress associated with lattice mismatch between GaN and the substrate. Typically, its thickness is between 1 μm and 4 μm.

[0099] For example, the thickness of the second layer 203 is in the range of 100nm to 1μm: its existence is to ensure the quality of the material of the upper layer 204.

[0100] For example, the thickness of the third 204 layer ranges from 100 nm to 500 nm. It should have sufficient conductivity, and its minimum thickness varies with the doping rate.

[0101] The third conductive layer 204 of the stack 200 is in direct contact with the mesa 100 to be porosized. During the electrochemical anodizing step, the conductive layer 204 of the stack 200 is used to re-contact the stack 200. This conductive layer 204 is electrically connected to a voltage or current generator.

[0102] Mesa 100, also known as a facade, is a raised element. These mesa are obtained, for example, by etching a continuous layer or several stacked continuous layers, leaving only a certain number of "protrusions" of that layer or these layers. Etching is typically plasma etching (or dry etching). These protrusions allow for the definition of pixels.

[0103] Preferably, the side of the platform 100 is perpendicular to the stack 200.

[0104] The dimensions (width and length) of mesa 100 are in the range of 500 nm to 500 μm. Width and length refer to the dimensions of the surface parallel to the underlying stack.

[0105] The spacing between the two consecutive mesa 100 ranges from 50 nm to 20 μm.

[0106] The InGaN mesa 100 consists of a doped InGaN layer 101 and an undoped or weakly doped InGaN layer 102.

[0107] Preferably, the countertop includes two layers, 101 and 102.

[0108] Doped InGaN refers to so-called highly doped layers, where the doping concentration is greater than 10⁻⁶. 18 at.cm 3 Even greater than 10 19 at.cm 3 The doping technique will be selected based on the porosimetry (with or without illumination). The doped InGaN layer 101 is conductive and is porosimetric in step d).

[0109] So-called weakly doped InGaN refers to InGaN with a doping concentration of less than 5.10. 17 at.cm 3 The doping level is low enough that the layer is electrically insulating. Therefore, layer 102 is not anolyzed and thus not porosized in step d).

[0110] Advantageously, the thickness of the doped layer 101 of the mesa 100 is in the range of 10 nm to 100 nm, preferably about 30 nm. A thin layer (less than 100 nm) can contain a high In concentration while maintaining good material quality (few defects). Thickness refers to the dimension of the mesa perpendicular to the stack below.

[0111] For example, the thickness of the undoped or weakly doped InGaN layer 102 is in the range of 1 nm to 5 nm, preferably 2 nm to 3 nm. This layer should provide a continuous interface to ensure long bonding during epitaxial regeneration. Advantageously, it is chosen to be thin, for example, between 0.25 nm and 3 nm, so that it is defect-free and can be relaxed by means of the subsequent porosification process of the underlying layer 101 and epitaxial regeneration on the mesa.

[0112] The conductive layer 204 is covered by an electrically insulating layer 300 between the mesa 100 so that it does not come into contact with the electrolyte solution during the porosimetry step and is therefore not porosimetry.

[0113] The electrical insulating layer 300 can be an oxide or a nitride. Silicon oxide or silicon nitride is preferred. For example, its thickness is in the range of 5 nm to 100 nm. For stoichiometric nitrides or oxides, a thickness of 30 nm or less will be chosen.

[0114] according to Figures 2A to 2D The first alternative embodiment shown can be manufactured according to the following steps.

[0115] A stack 200 is provided, which includes a support 201, such as sapphire or silicon, on which a first layer 202 of doped GaN and / or a second layer 203 of doped GaN and a third conductive layer 204 of highly n-doped GaN are sequentially covered.

[0116] A highly doped InGaN layer 101 is formed, followed by an undoped or weakly doped InGaN layer 102.

[0117] For example, photolithography is used to structure a highly doped InGaN layer 101 and an undoped InGaN layer 102 to form a mesa 100.

[0118] An electrically insulating layer 300, such as SiO2 or SiN, is formed between the mesa 100 to passivate the conductive layer 204.

[0119] Controlled etching of mesa 100 allows the etching to stop either above or within the n++ GaN layer. "Above the n++ GaN layer" refers to the interface between the n++ GaN layer 204 and the doped InGaN layer 101. In other words, the n++ GaN layer is not completely etched during electrochemical porosification to ensure its conductivity.

[0120] According to such Figures 3A to 3C The alternative embodiment shown can be manufactured according to the following steps.

[0121] A stack 200 is provided, which includes a support 201, such as sapphire or silicon, on which a first layer 202 of doped GaN and / or a second layer 203 of doped GaN and a third conductive layer 204 of highly n-doped GaN are sequentially covered.

[0122] An electrically insulating layer 300, such as SiO2 or SiN, is formed to partially cover the conductive layer 204.

[0123] By forming a doped InGaN layer 101 and an undoped or weakly doped InGaN layer 102, a mesa 100 is formed in the region of the conductive layer 204 that is not covered by the electrically insulating layer 300.

[0124] According to this embodiment, the electrically insulating layer 300 can be obtained by depositing a continuous layer and then etching it. Alternatively, the electrically insulating layer 300 can be deposited using a mask. Then, localized growth of the mesa 100 is performed.

[0125] According to these alternative embodiments, doping of the doped layer 101 of the mesa 100 can be performed, for example, by implanting silicon (Si(n)) or magnesium (Mg(p)).

[0126] The doped layers 101 of the mesa 100 can have the same or different doping types. For a given applied potential, using different doping types allows the porosity of the mesa to be varied according to their initial doping levels. Therefore, the mesa will relax more or less and be more or less able to incorporate indium into the doped layers. Thus, after epitaxial regeneration, pixels of different colors can be easily obtained.

[0127] According to a preferred embodiment, the InGaN mesa in the structure provided in step a) can be obtained by following the steps described below.

[0128] A so-called full-plate InGaN layer (i.e., a continuous layer) is deposited on a conductive, highly n-doped GaN layer 204.

[0129] Implantation steps are performed locally within the entire InGaN layer to obtain doped regions and less-doped or even undoped regions. For example, for three n-type doping levels, photolithography and hard masks can be performed, followed by silicon implantation.

[0130] Advantageously, so-called healing heat annealing is performed.

[0131] For example, unintentional or weakly doped elements (typically with a residual value of 5.10) can be removed via epitaxy. 16 / cm 3 and 1.10 17 / cm 3 A full-plate InGaN layer is deposited on the full-plate InGaN layer between (between).

[0132] The entire InGaN layer is etched by removing unimplanted regions through undoped or weakly doped InGaN layers, thereby forming an InGaN mesa 100 comprising a doped InGaN layer 101 and an undoped or weakly doped InGaN layer 102.

[0133] As an illustration, for example, hard masks such as SiN or SiO2 type masks can be used to perform implantation and alignment marking (e.g., Al, Ti, TiN) to align the mesa with the implantation region. Using two different masks, two regions with different implantation energies can be formed, thus allowing for two different doping types in addition to, for example, the initial doping of a doped plate via MOCVD. Alignment marking ensures that the mask used for implantation and the mask used for mesa etching are aligned.

[0134] The same mask will be used for both injection and mesa etching.

[0135] Advantageously, for an undoped or weakly doped InGaN layer with a low thickness, the implantation of the underlying InGaN layer can be performed through this layer.

[0136] For p-type doping, magnesium can be implanted.

[0137] Advantageously, the doped regions have different doping types, resulting in different doping types in the doped InGaN layers of the mesa. At a fixed potential, the higher the doping rate, the greater the porosity. The relaxation degree of the dense InGaN layer depends on the porosity of the mesa. Therefore, when re-epitaxically growing InGaN on a dense layer, different amounts of indium can be incorporated (due to reduced "composition pull effect" (i.e., pushing In atoms towards the surface, thus preventing them from being incorporated into the layer)). Thus, after epitaxy of the complete LED structure, if the deviation between the relaxation levels of the mesa is large enough, red, green, and blue (RGB) mesa can be obtained on the same substrate and in a single growth step.

[0138] Alternatively, in these different embodiments, metal-organic chemical vapor deposition (MOCVD) doping can be used instead of implantation doping, especially with Si or Ge as the dopant. For example, three consecutive epitaxial steps can be performed through sequential masking operations to obtain three different doping levels in order to form an RGB mesa at the end of the method.

[0139] The following text will describe n-type doping, but it can be p-type doping.

[0140] In step b), the device and counter electrode (CE) 500 are electrically connected to a voltage or current generator. Figure 4 This device acts as the working electrode (WE). It is referred to below as a voltage generator, but it can also be a current generator used to apply current between the device and the counter electrode.

[0141] The counter electrode 500 is an electrode made of a conductive material, such as a metal like platinum.

[0142] In step c), the electrodes are immersed in an electrolyte, also known as an electrolytic cell or electrolyte solution. The electrolyte can be acidic or alkaline. For example, the electrolyte can be oxalic acid, or it can be KOH, HF, HNO3, NaNO3, or H2SO4.

[0143] Step c) can be performed before step b).

[0144] In step d), a voltage is applied between the device and the counter electrode 500. This voltage can range from 1V to 100V. For example, the voltage can be applied for a period ranging from a few seconds to several hours. Porosification is complete when there is no longer any current at the applied potential. At this point, the entire doped structure is porosified and the electrochemical reaction stops.

[0145] The difference in doping rate allows for high selectivity between porosimetry and electropolishing. Figure 5This "graph" allows for the definition of individual doping rates for given conditions, thereby enabling selectivity between highly doped and weakly doped regions at a given potential.

[0146] The electrochemical anodizing step can be performed under ultraviolet (UV) light. The method can also include a first electrochemical anodizing without UV radiation and a second electrochemical anodizing by adding UV radiation. This embodiment is particularly meaningful because, for example, the upper n+ doped layer can first be porosified, and this porosification process abruptly stops on the undoped GaN; then, UV light can subsequently generate charges in the undoped GaN, thus porosifying the undoped GaN.

[0147] Advantageously, porosity occurs throughout the entire volume of the doped InGaN layer 101 of the mesa 100.

[0148] At the end of the porosification step, the porosity of the doped InGaN layer 101 is at least 10%, preferably in the range of 25% to 50%.

[0149] The maximum size (height) of the pore can vary from a few nanometers to a few micrometers. The minimum size (diameter) can vary from a few nanometers to one hundred nanometers, especially from 30 nm to 70 nm.

[0150] The resulting porosity (porosity and pore size) depends on the doping of the InGaN layer 101 on the mesa 100 and the process parameters (applied voltage, time period, electrolyte properties and concentration, chemical post-treatment or annealing). The penetration rate / segregation rate can be controlled by changing the porosity. During epitaxial growth, porosity (especially pore size) may vary depending on the applied temperature.

[0151] The porosiformation step provides a fully or partially relaxed doped InGaN layer 101.

[0152] After the porosimetry step, epitaxial regeneration is performed on the InGaN mesa 100 (step e), for example, to form an epitaxially regenerated LED.

[0153] Epitaxial re-growth was performed on the undoped InGaN layer 102 of mesa 100. Since layer 102 was not porosified during the electrochemical anodizing step, epitaxial re-growth was possible on a continuous, dense, pore-free 2D layer. This facilitated epitaxial re-growth and resulted in a more resistive epitaxial layer. Defects associated with porosity aggregation were avoided.

[0154] Different growth processes can be used to form the epitaxially grown layer 400.

[0155] according to Figure 6AIn the first alternative embodiment shown, the regrowth is lateral, and subsequent pixelation steps are advantageously performed by etching. Side passivation can also be achieved with a layer of relatively small thickness (e.g., 3 nm), preferably using atomic layer deposition (ALD).

[0156] According to such Figure 6B In the alternative embodiment shown, regrowth occurs vertically above the mesa. In this alternative, the pixel corresponds to the mesa below.

[0157] Advantageously, the epitaxially grown layer 400 is gallium nitride or indium gallium nitride.

[0158] Advantageously, a passivation layer will be deposited on the mesa 100 and the sides of the epitaxially regenerated LED, for example, by atomic layer deposition (ALD). The passivation layer can be aluminum oxide. The passivation layer can have a thickness of a few nanometers, for example, 2 nm to 5 nm.

[0159] For example, the epitaxial growth stack of an all-InGaN LED can sequentially include the following layers starting from the unintentionally doped InGaN layer 102.

[0160] The n-doped InGaN layer preferably has the same In concentration as the InGaN layer of the substrate.

[0161] An active region having one or more InGaN / (Ga,In)N quantum wells that emit red or green light.

[0162] p-doped AlGaN or GaN-based electronic barriers.

[0163] For p-doped InGaN layers, the In concentration is preferably less than or equal to the In concentration of n-InGaN layers.

[0164] The p++ doped InGaN layer preferably has the same In concentration as the p-InGaN layer.

[0165] More specifically, an all-InGaN LED structure can sequentially include the following layers.

[0166] InGaN substrate.

[0167] From 15×In 0.03 Ga 0.97 A 350nm n-doped InGaN layer formed by N / GaN (20nm / 1.8nm thickness).

[0168] From 5×In 0.40 Ga 0.60 N / In 0.03 Ga 0.097 Multiple quantum wells (MQWs) are formed by N (thickness 2.3nm / 5, 7, 11nm).

[0169] uid In 0.03 Ga 0.97 N layers (10nm).

[0170] Al 0.1 Ga 0.9 N:Mg layer (20nm).

[0171] Mg-doped In 0.03 Ga 0.97 N-layer (125nm).

[0172] p++ doped In 0.03 Ga 0.97 N-layer (25nm).

[0173] An illustrative and non-limiting example of an embodiment:

[0174] In this example, a stack 200 is used, which includes: a sapphire support 201, a (uid)GaN layer 202, a doped GaN (n GaN) layer 203, and a highly doped GaN (n++GaN) layer 204.

[0175] To fabricate the InGaN mesa 100, an In layer with a thickness of less than 100 nm is deposited on the stack 200. 0.0008 Ga 0.992 N(n-doped: 10) 19 at / cm 3 Layer 101. To facilitate subsequent epitaxial regrowth, a thinner (2 nm to 3 nm) undoped InGaN layer 102 with the same composition was deposited.

[0176] Mesa 100 was then fabricated using conventional photolithography techniques. The resulting mesa 100 had dimensions ranging from 500 nm to 10 μm. Controlled etching of the InGaN layer allowed the etching to stop on or within the n++ GaN layer.

[0177] Then, the n++GaN layer 204 is passivated with a layer 300, such as SiO2 or SiN.

[0178] AFM image of the InGaN layer before porosification, as shown Figure 7A As shown.

[0179] Then, the InGaN mesa was porosiformed by electrochemical anodic oxidation in an electrolyte solution containing 0.1 mol / L to 0.5 mol / L (e.g., 0.2 mol / L) oxalic acid. A voltage of 24 V was applied. The In concentration contained in the mesa was then close to that of the quantum well, and the mesa was fully or almost completely relaxed. AFM images of the porosiformed InGaN layer are shown below. Figure 7BAs shown.

[0180] Then annealing is performed, for example at 900°C. Figure 7C ).

[0181] Finally, epitaxial regeneration was performed on the InGaN mesa 100. Figure 7D ).

[0182] Photoluminescence (PL) characteristics have been described. Before porosification, the emission wavelength of the 0.8% InGaN sample was 356 nm. After epitaxial regeneration, the emission wavelength was 364 nm. Samples prepared with 2% InGaN also showed the same trend. This deviation in PL could be a sign of stress relaxation and / or increased In infiltration.

[0183] References

[0184] [1]Even et al, "Enhanced In incorporation in full InGaN heterostructure grown on relaxed InGaN pseudo-substrate", Appl. Phys. Lett. 110, 262103 (2017).

[0185] [2] Jang et al, "Electrical and structural properties of GaN films and GaN / InGaN light-emitting diodes grown on porous GaN templates fabricated by combined electrochemical and photoelectrochemical etching", Journal of Alloys and Compounds 589(2014)507-512.

Claims

1. A method for fabricating at least partially relaxed GaN / InGaN structures, comprising the following steps: a) Provides an apparatus comprising: The GaN / InGaN structure includes a conductive doped GaN layer (204) partially covered with an InGaN mesa (100), wherein the InGaN mesa (100) includes a doped InGaN layer (101) and an undoped or weakly doped InGaN layer (102) above the doped InGaN layer (101). An electrically insulating layer (300) covers the conductive doped GaN layer (204) between the InGaN mesa (100). b) Electrically connect the conductive doped GaN layer (204) and counter electrode (500) of the device to a voltage generator or a current generator; c) Immerse the device and the counter electrode (500) in the electrolyte; d) Apply a voltage or current between the conductive doped GaN layer (204) and the second electrode (500) to porosilicate the doped InGaN layer (101) of the InGaN mesa (100); e) An InGaN layer is formed on the InGaN mesa (100) by epitaxial growth, thereby obtaining a relaxed epitaxially grown InGaN layer (400).

2. The method according to claim 1, wherein, The thickness of the undoped or weakly doped InGaN layer (102) is in the range of 0.25 nm to 3 nm.

3. The method according to claim 1 or 2, wherein, The electrical insulating layer (300) is a SiO2 layer or a SiN layer.

4. The method according to claim 1 or 2, wherein, The device provided in step a) is manufactured by forming the electrically insulating layer (300) and then forming the InGaN mesa (100).

5. The method according to claim 1 or 2, wherein, The device provided in step a) is manufactured by forming the InGaN mesa (100) and then forming the electrical insulating layer (300).

6. The method according to claim 1 or 2, wherein, The conductive doped GaN layer (204) covers a sapphire or silicon support (201).

7. The method according to claim 1 or 2, wherein, The thickness of the InGaN mesa (100) is less than 100 nm.

8. The method according to claim 1 or 2, wherein, The method includes the steps of implantation doping or metal-organic vapor phase epitaxial doping on the InGaN mesa (100).

9. The method according to claim 8, wherein, The doped InGaN layer (101) of the InGaN mesa (100) has different doping types.

10. The method according to claim 1 or 2, wherein, The InGaN mesa (100) of the GaN / InGaN structure provided in step a) is obtained according to the following steps: Deposit a full-plate InGaN layer; Local implantation doping or metal-organic vapor phase epitaxial doping steps are performed in the full-plate InGaN layer to form doped and undoped regions; An undoped or weakly doped full-plate InGaN layer is deposited onto the full-plate InGaN layer; The undoped region is removed by etching the undoped or weakly doped InGaN layer across the entire InGaN plate, thereby locally forming an InGaN mesa (100) comprising a doped InGaN layer (101) and an undoped or weakly doped InGaN layer (102).

11. The method according to claim 10, wherein, The doped regions have different doping types.

12. A GaN / InGaN structure manufactured by the method according to any one of claims 1 to 11, comprising, in sequence: Conductive doped GaN layer (204). InGaN mesa (100), the InGaN mesa (100) includes a pore-doped InGaN layer (101) and an undoped or weakly doped non-pore InGaN layer (102) located above the pore-doped InGaN layer (101). A relaxed epitaxially grown InGaN layer (400) is in contact with the undoped or weakly doped non-porous InGaN layer (102).

13. The GaN / InGaN structure according to claim 12, wherein, The thickness of the undoped or weakly doped InGaN layer (102) is in the range of 0.25 nm to 3 nm.

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