EP3542392A1 - Semiconductor heterostructures with wurtzite-type structure on zno substrate - Google Patents
Semiconductor heterostructures with wurtzite-type structure on zno substrateInfo
- Publication number
- EP3542392A1 EP3542392A1 EP17797365.8A EP17797365A EP3542392A1 EP 3542392 A1 EP3542392 A1 EP 3542392A1 EP 17797365 A EP17797365 A EP 17797365A EP 3542392 A1 EP3542392 A1 EP 3542392A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- substrate
- heterostructure
- layer
- crystal structure
- semiconductor material
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
- 239000000758 substrate Substances 0.000 title claims abstract description 65
- 239000004065 semiconductor Substances 0.000 title claims abstract description 30
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 claims abstract description 92
- 239000011787 zinc oxide Substances 0.000 claims abstract description 45
- 239000000463 material Substances 0.000 claims abstract description 44
- 229910052984 zinc sulfide Inorganic materials 0.000 claims abstract description 33
- 238000000034 method Methods 0.000 claims abstract description 31
- 238000000151 deposition Methods 0.000 claims abstract description 16
- 230000005693 optoelectronics Effects 0.000 claims abstract description 14
- 238000004519 manufacturing process Methods 0.000 claims description 22
- 239000013078 crystal Substances 0.000 claims description 21
- 150000004767 nitrides Chemical class 0.000 claims description 12
- 230000008021 deposition Effects 0.000 claims description 11
- 239000011701 zinc Substances 0.000 claims description 7
- 238000001451 molecular beam epitaxy Methods 0.000 claims description 6
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 5
- 238000010438 heat treatment Methods 0.000 claims description 5
- 239000001301 oxygen Substances 0.000 claims description 5
- 229910052760 oxygen Inorganic materials 0.000 claims description 5
- 229910052725 zinc Inorganic materials 0.000 claims description 5
- 229910001199 N alloy Inorganic materials 0.000 claims description 4
- 229910052793 cadmium Inorganic materials 0.000 claims description 4
- 238000000137 annealing Methods 0.000 claims description 3
- 238000003486 chemical etching Methods 0.000 claims description 2
- 239000013256 coordination polymer Substances 0.000 claims description 2
- 239000010410 layer Substances 0.000 claims 7
- 229910001297 Zn alloy Inorganic materials 0.000 claims 2
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims 1
- 239000011241 protective layer Substances 0.000 claims 1
- 230000008569 process Effects 0.000 abstract description 9
- 238000000407 epitaxy Methods 0.000 abstract description 6
- 229910002601 GaN Inorganic materials 0.000 description 19
- 230000012010 growth Effects 0.000 description 19
- 230000007547 defect Effects 0.000 description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 6
- 230000008901 benefit Effects 0.000 description 6
- 229910052594 sapphire Inorganic materials 0.000 description 6
- 239000010980 sapphire Substances 0.000 description 6
- 229910052733 gallium Inorganic materials 0.000 description 5
- 229910052738 indium Inorganic materials 0.000 description 5
- 230000007246 mechanism Effects 0.000 description 4
- 229910052751 metal Inorganic materials 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 4
- 101001129902 Homo sapiens Peptidyl-prolyl cis-trans isomerase NIMA-interacting 4 Proteins 0.000 description 3
- 102100031653 Peptidyl-prolyl cis-trans isomerase NIMA-interacting 4 Human genes 0.000 description 3
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- 239000003929 acidic solution Substances 0.000 description 3
- 229910021529 ammonia Inorganic materials 0.000 description 3
- 230000015556 catabolic process Effects 0.000 description 3
- 238000005336 cracking Methods 0.000 description 3
- 238000006731 degradation reaction Methods 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 238000005530 etching Methods 0.000 description 3
- 230000010287 polarization Effects 0.000 description 3
- 229910052710 silicon Inorganic materials 0.000 description 3
- 239000010703 silicon Substances 0.000 description 3
- 239000000243 solution Substances 0.000 description 3
- 238000001039 wet etching Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- JMASRVWKEDWRBT-UHFFFAOYSA-N Gallium nitride Chemical compound [Ga]#N JMASRVWKEDWRBT-UHFFFAOYSA-N 0.000 description 2
- 229910000979 O alloy Inorganic materials 0.000 description 2
- YRKCREAYFQTBPV-UHFFFAOYSA-N acetylacetone Chemical compound CC(=O)CC(C)=O YRKCREAYFQTBPV-UHFFFAOYSA-N 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- PMHQVHHXPFUNSP-UHFFFAOYSA-M copper(1+);methylsulfanylmethane;bromide Chemical compound Br[Cu].CSC PMHQVHHXPFUNSP-UHFFFAOYSA-M 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 230000018109 developmental process Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000005684 electric field Effects 0.000 description 2
- 238000000635 electron micrograph Methods 0.000 description 2
- 238000002347 injection Methods 0.000 description 2
- 239000007924 injection Substances 0.000 description 2
- 230000003287 optical effect Effects 0.000 description 2
- 238000000879 optical micrograph Methods 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 230000006798 recombination Effects 0.000 description 2
- 238000005215 recombination Methods 0.000 description 2
- 229910010271 silicon carbide Inorganic materials 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 230000003698 anagen phase Effects 0.000 description 1
- 238000004630 atomic force microscopy Methods 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- 238000005229 chemical vapour deposition Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000013500 data storage Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 229910003460 diamond Inorganic materials 0.000 description 1
- 239000010432 diamond Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000001194 electroluminescence spectrum Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000001657 homoepitaxy Methods 0.000 description 1
- 238000002248 hydride vapour-phase epitaxy Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 239000012528 membrane Substances 0.000 description 1
- 238000002488 metal-organic chemical vapour deposition Methods 0.000 description 1
- 238000004377 microelectronic Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 125000002524 organometallic group Chemical group 0.000 description 1
- 239000012071 phase Substances 0.000 description 1
- 239000004038 photonic crystal Substances 0.000 description 1
- 229920002120 photoresistant polymer Polymers 0.000 description 1
- 210000004180 plasmocyte Anatomy 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 230000001681 protective effect Effects 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 230000002269 spontaneous effect Effects 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 238000005979 thermal decomposition reaction Methods 0.000 description 1
- 238000007669 thermal treatment Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 230000005641 tunneling Effects 0.000 description 1
- 238000000927 vapour-phase epitaxy Methods 0.000 description 1
- 238000003631 wet chemical etching Methods 0.000 description 1
- -1 ΑΙΝ Inorganic materials 0.000 description 1
Classifications
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- H—ELECTRICITY
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- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
- H01L29/04—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their crystalline structure, e.g. polycrystalline, cubic or particular orientation of crystalline planes
- H01L29/045—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their crystalline structure, e.g. polycrystalline, cubic or particular orientation of crystalline planes by their particular orientation of crystalline planes
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- H01L21/0254—Nitrides
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- H01L21/02565—Oxide semiconducting materials not being Group 12/16 materials, e.g. ternary compounds
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- H01L21/02598—Microstructure monocrystalline
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- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
- H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
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- H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having potential barriers, e.g. a PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic Table or AIIIBV compounds with or without impurities, e.g. doping materials
- H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
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- H01L29/2203—Cd X compounds being one element of the 6th group of the Periodic Table
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- H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
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- H01L29/267—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by the materials of which they are formed including, apart from doping materials or other impurities, elements provided for in two or more of the groups H01L29/16, H01L29/18, H01L29/20, H01L29/22, H01L29/24, e.g. alloys in different semiconductor regions, e.g. heterojunctions
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- H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L33/005—Processes
- H01L33/0062—Processes for devices with an active region comprising only III-V compounds
- H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
- H01L33/007—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound comprising nitride compounds
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- H01L33/16—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a particular crystal structure or orientation, e.g. polycrystalline, amorphous or porous
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- H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
- H01L33/26—Materials of the light emitting region
- H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
- H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
Definitions
- the invention relates to a method for producing a semiconductor material heterostructure having a wurtzite crystal structure, such a heterostructure and the manufacture of electronic or optoelectronic devices from such a heterostructure.
- the electronic and optoelectronic devices based on these materials generally comprise a heterostructure formed by so-called "active" layers deposited by epitaxy techniques on a monocrystalline substrate.
- Sapphire is currently the most commonly used material for the production of substrates on which layers of materials III-N will be deposited, in particular because of its high availability, its window of transparency in the visible and its stability at high temperature. (> 1500 ° C).
- the sapphire makes it possible to obtain active layers without deformation or in compressive stress, which can thus reach significant thicknesses (several tens of micrometers) without cracking.
- this material also has very harmful disadvantages: it is insulating, which prevents the manufacture of devices with a vertical structure, and its low thermal conductivity limits the permissible power density of the devices obtained.
- the sapphire has a crystalline structure (rhombohedral) different from that of materials III-N (wurtzite) and a high mesh size mismatch.
- This generates crystalline defects in the structures (stacking faults, dislocations, inversions of domains of different polarity %), which makes it impossible to obtain active layers of good structural quality according to certain orientations (non and semi polar) without resorting to complex technological processes, ie with several steps in the process (masking, surface preparation, resumption of growth, ).
- Silicon carbide has, itself, a mesh parameter close to that of many materials III-N, can be intentionally doped to allow the realization of vertical structures and its thermal conductivity is high.
- SiC Silicon carbide
- its industrial development is constrained by its very high cost compared to sapphire.
- Si Silicon
- Si is favored by its compatibility with the production lines of the microelectronics industry.
- its crystalline structure is of the "diamond” type, and not “wurtzite", which prevents obtaining active layers of good structural quality with certain orientations.
- the thermal expansion coefficient disagreement with the active layers is very important and can cause extensive stress in the latter and lead to the appearance of cracks. Growth on Si then requires the use of complex and expensive manufacturing processes to compensate for the extensive constraint by compressive stress.
- ZnO zinc oxide
- Wurtzite the wideband forbidden semiconductor materials that we want to deposit, close mesh parameters
- a small difference in the coefficients of thermal expansion with these materials a relatively high thermal conductivity and can be intentionally doped.
- a crystal structure of wurtzite type comprises two types of atoms; each of these two types of atoms forms a sub-network of the type hep (of the English “hexagonal close-packed", for “compact hexagonal stacking").
- the wurtzite structure is non-centrosymmetric, and therefore often associated with piezoelectric and / or pyroelectric properties.
- Figures 1A, 1B and 1C schematically illustrate Wurtzite structure and some of its growth plans.
- Planars "c”, (0001) and (000-1) are called polar; planes “a” (1 1 -20) and “m” (1 -100) are called non-polar; other planes having an angle with the plane c different from 0 ° and 90 ° are called semi-polar (for example the planes (1 1 -22) and (10-12)).
- F in t can reach several hundred or even thousands of kV / cm.
- the optoelectronic properties of the heterostructures are strongly dependent on this field which has harmful consequences on the functioning of the components: for example, in the case of LEDs and laser diodes (LDs), it leads to a reduction of the electron-hole pair recombinations and thus of the radiative efficiency in the quantum wells as well as an offset of the radiative transitions towards the long wavelengths.
- this field strongly modifies the band structure and the position of the energy levels in the heterostructures and therefore requires complex band engineering during device realization.
- LEDs and LDs emitting in the visible at long wavelengths (> 500 nm) and in the ultraviolet at short wavelengths ( ⁇ 350 nm) as well as for inter-subband devices (tunneling diodes, electro-optical modulators, photodetectors, quantum cascade components, etc.), it is desirable to suppress this polarization.
- orientations different from the orientation (0001) for example the non-polar or semi-polar orientations described above with reference to FIGS.
- active layers of polar or semi-polar orientation deposited on a sapphire, SiC or Si substrate generally have very high defect densities, unless complex and therefore expensive manufacturing processes are used. .
- the document WO 2015/177220 proposes to reduce the crystalline defects appearing during the epitaxy of the nitride of element III, by producing this epitaxy on the inclined flanks of the grooves which structure the surface of the zinc oxide substrate. However, this does not allow to maintain the same plane of orientation between the substrate and the element III nitride.
- FR 3031834 propose to reduce these crystalline defects by using a buffer layer comprising aluminum nitride between the substrate and gallium nitride. Nevertheless, the mesh parameters of aluminum nitride and zinc oxide are different, which degrades the crystalline quality of the whole. It is therefore necessary to deposit a sufficiently thick layer of gallium nitride to compensate for this degradation.
- US 2010/01 17070 discloses a light emitting device comprising semiconductor materials. This device is produced on a zinc oxide substrate on which a structured reflective layer is deposited. This structured layer is intended to improve the extraction of light inside the device. The characteristic dimensions of the structuring are therefore dependent on the desired refractive indices and the emission wavelengths of the device.
- the aim of the invention is to improve the structural, electronic and optoelectronic properties of heterostructures in semiconductor materials, in particular with a wide band gap, having a structure crystalline wurtzite type made on ZnO substrate, with a polar orientation, non-polar or semi-polar.
- the inventors have realized that this constraint induces a mechanism of plastic relaxation of the stressed epitaxial layer, which can occur according to various processes such as cracking, the generation of interface dislocations, .... This results in defects that degrade the electrical and / or optoelectronic properties of the heterostructure.
- the invention makes it possible to avoid this degradation.
- this object is achieved by a three-dimensional structuration in "mesas" of the surface of the ZnO substrate, having a flat surface, which allows the elastic relaxation of the stress in the active layers, thanks to the presence of edges free.
- the mesas have lateral dimensions - or at least one lateral dimension - that can reach a few hundred micrometers, or even a millimeter, and each mesa can correspond to an electronic or optoelectronic device made from the heterostructure. They also have a flat upper surface parallel to the surface of the substrate, and vertical side surfaces or inclined relative thereto.
- An object of the invention is therefore a method of manufacturing a heterostructure of semiconductor materials having a wurtzite crystal structure, comprising the following steps:
- Said mesas may have a smaller lateral dimension of between 10 and 1000 ⁇ and a height greater than or equal to 100 nm.
- Said structuring step can be implemented by chemical etching.
- the method may also comprise a step of thermal treatment of the structured surface of said substrate by annealing under an oxygen stream at a temperature greater than or equal to 600 ° C., implemented before said epitaxial deposition step of at least one layer semiconductor material having a crystal structure wurtzite type.
- Said epitaxial deposition step of at least one layer of semiconductor material having a wurtzite crystal structure can be implemented by molecular beam epitaxy.
- the method may also comprise a step of depositing a protective thin layer on at least one surface of said substrate other than the structured surface, implemented before said step of epitaxially deposition of at least one layer of semiconductor material having a crystal structure of wurtzite type.
- the structured surface may have a non-polar or semi-polar orientation.
- Said or each said semiconductor material layer having a wurtzite crystal structure may comprise at least one material chosen from a binary nitride, a binary oxide, a Zn (Mg, Cd) O alloy and an Al (Ga, In) N alloy. .
- Another object of the invention is a method of manufacturing at least one electronic or optoelectronic device comprising:
- Yet another object of the invention is a heterostructure comprising at least one layer of semiconductor material having a wurtzite crystal structure deposited over a surface of a zinc oxide monocrystalline substrate, characterized in that that said surface is structured in mesas.
- Said mesas may have a smaller lateral dimension of between 10 and 1000 ⁇ and a height greater than or equal to 100 nm.
- the structured surface of said substrate may have a non-polar or semi-polar orientation.
- Said or each said semiconductor material layer having a wurtzite crystal structure may comprise at least one material chosen from a binary nitride, a binary oxide, a Zn (Mg, Cd) O alloy and an Al (Ga, In) N alloy. .
- Figures 1A, 1B and 1C already described, represent the wurtzite type structure and some of its crystalline planes;
- FIGS. 2A and 2B illustrate the formation of cracks during the epitaxial growth of GaN layers on a ZnO substrate
- FIGS. 3A-3E represent different steps of a method according to one embodiment of the invention.
- Figure 4 shows electron microscopy images of a surface of a ZnO substrate structured in accordance with one embodiment of the invention
- FIGS. 5A and 5B show the effect of a heat treatment step of a method according to one embodiment of the invention
- FIGS. 6A and 6B show electron microscopy images of a GaN layer epitaxially grown on a surface of a structured ZnO substrate according to one embodiment of the invention.
- FIG. 2A is an image of a layer 1, 1 ⁇ thick of GaN epitaxially grown on a plane ZnO substrate c (orientation (0001), polar). Cracks oriented mainly along ⁇ 1 1 -20> directions can be observed. As explained above, these cracks are caused by the voltage stresses induced by the positive parametric mismatch between the ZnO substrate and the epitaxial layer. in GaN. More generally, this effect is observed in alloys (AI, Ga) N and (Zn, Mg) 0.
- FIG. 2B is a graph of crack density versus layer thickness. It can be seen that the critical thickness is of the order of 300 nm for the GaN / ZnO system, and that the crack density increases with the thickness of GaN, beyond this value. The consequence of these mechanisms of relaxation of the stress is that, in the case of LED structures for example, whose thickness is typically between 2 and 5 ⁇ , very high crack densities are observed.
- FIGS. 3A-3E illustrate the various steps of a method according to one embodiment of the invention, making it possible to prevent the appearance of these cracks.
- FIG. 3A shows a planar S substrate made of ZnO having an SD surface on which layers of wurtzite-type semiconductor materials must be epitaxially grown.
- the orientation of this SD surface may be polar, semi-polar or non-polar.
- the first step of the process consists of a structuring of the surface SD by three-dimensional patterns M in the form of mesas. These patterns will generate an elastic relaxation of the epitaxial layers which avoids the plastic relaxation of the stress in the active layers. This elastic relaxation is made possible thanks to the possibility of relaxation of the layers on the edge of the mesas M.
- the structuring of the ZnO can be carried out by wet etching or by dry process or by a combination of the two methods.
- An advantage of ZnO is the possibility of being able to use simple wet etching processes, usually with a strongly diluted acidic solution.
- ZnO can be efficiently etched in solutions such as highly diluted HNO 3 / HCl, HF / HNO 3 and also in non-acidic solutions such as acetyl acetone. See for example the article by J. Pearton, JJ Chen, WT Lim, F. Ren and DP Norton, "Wet Chemical Etching of Wide-Bandgap Semiconductors-GaN, ZnO and SiC", ECS Transactions, 6 (2) 501-512. (2007).
- Patterns are defined by a mask, typically a photoresist or metal, which is removed after the etching step. They can be square, circular, rectangular or diamond-shaped or elongated strips in one of the plane directions. Their lateral dimensions can vary from 100 nanometers to a few centimeters in the case of elongated strips; however, for stress relaxation to be effective it is necessary that the smallest lateral dimension does not exceed a few hundred micrometers, even a few millimeters. The use of patterns smaller than a few micrometers is possible, but hardly compatible with the manufacture of electronic or optoelectronic components. Thus, preferably, the patterns will have a smaller lateral dimension of between 10 and 1000 ⁇ .
- the engraving depth (and therefore the height of the mesas) must be greater than the thickness of the active layers. Typically, it can vary from 100 nm to several tens of micrometers.
- FIG. 4 shows optical microscope images of the surface of a ZnO substrate (plane c) structured by square mesas of a few hundred ⁇ of side (460 ⁇ for the left image and 315 ⁇ for the left image). right image) and a few micrometers high, obtained by wet etching using a solution of H 3 PO 4 strongly diluted in water, with a ratio 2 (H 3 PO 4 ) / 100 (H 2 O), in order to limit lateral etching.
- the surface of the substrate is subjected to a preparation operation by heat treatment at a temperature at least equal to 600 ° C. (or even 800 ° C.) and under an oxygen flow FO (FIG. 3C).
- This heat treatment can be preceded by a cleaning of the surface by the use of an oxygen-based plasma.
- atomic steps are obtained on the surface of the patterns.
- FIGS. 5A and 5B are images obtained by atomic force microscopy of the surface of a ZnO substrate (plane c) before (5A) and after (5B) a heat treatment by annealing at a temperature of 1000 ° C. for 2 minutes under a flow of oxygen.
- the surface Before the treatment, the surface is not smooth at the atomic scale, is scratched and retains polishing residues (silica particles, one of which has been highlighted by surrounding it with a circle). After the treatment, these scratches and contaminations disappear and we can clearly observe atomic steps.
- a deposition of a thin layer CP (FIG. 3D). These surfaces comprise the rear face and the lateral faces of the ZnO substrate.
- This thin layer may be an oxide (for example SiO 2 ) or a refractory nitride (for example Si 3 N 4 ).
- This deposition is carried out, for example by sputtering, before the growth of the active layers. It allows the use of epitaxial growth techniques such as organometallic vapor phase epitaxy (EPVOM, also known by the acronym MOCVD, for "Metalorganic Chemical Vapor Deposition") and hydride vapor phase epitaxy ( EPVH).
- EPVOM organometallic vapor phase epitaxy
- MOCVD Metalorganic Chemical Vapor Deposition
- EPVH hydride vapor phase epitaxy
- FIG. 3E illustrates, very schematically, the structure obtained after epitaxial deposition, directly on the structured surface of the substrate, of one or more active layers CA. More precisely, these layers are deposited directly - without the interposition of a buffer layer of a different material - on the flat upper surfaces of the mesas (unlike the document FR3031834 where it is necessary to insert a buffer layer of AlN before the epitaxy of active layers CA); they therefore have the same crystalline orientation as the ZnO substrate.
- discontinuous layers have free edges, in correspondence of the edges of the mesas M of the substrate, which allows the relaxation of the stresses.
- the active layers are also deposited in the grooves separating the mesas; these portions of the active layers are however not used.
- the deposition of the active layers can be carried out by techniques such as EPVOM or EPVH. According to a preferred embodiment of the invention, however, it is rather used molecular beam epitaxy (MBE, or MBE of the English "Molecular Beam Epitaxy").
- MBE molecular beam epitaxy
- This growth technique is advantageous because it allows the growth of nitride materials at much lower temperatures (300 to 400 ° C lower) than those used by EPVOM, which reduces the risk of thermal decomposition of ZnO.
- N 2 instead of ammonia (NH 3 ) as a nitrogen source using an RF plasma cell, which is not possible with the use of EPVOM as a technique. growth.
- ZnO is very reactive with respect to ammonia.
- this growth technique also allows the growth of ZnO / (Zn, Mg) O structures with the lowest residual dopings.
- FIGS. 6A and 6B show optical microscopy images of the structures obtained for two different crystallographic orientations: plane c (0001) - 6A - and plane m (1 -100) - 6B.
- the thickness of the active layer is 0.7 ⁇ and 0.6 ⁇ , respectively. In both cases, the absence of cracks is confirmed, although the deposited thickness is much greater than the critical cracking thickness (see Figure 2B).
- FIG. 7A shows an electroluminescence spectrum obtained at ambient temperature for such a polar LED with active layers - oriented (0001) or (000-1) - based on GaN - more precisely, it is a question of a quantum well LED (In, Ga) N / GaN - 400 ⁇ side and an injection current of 20 mA.
- the spectrum of Figure 7A is dominated by a peak emitting in the blue around 455 nm. This blue emission originates from the recombination of the carriers in the quantum wells (In, Ga) N / GaN, confirming that the fabrication of monolithic structures of GaN-based LEDs on structured ZnO substrates has been successfully carried out.
- Fig. 7B is a graph of LED output optical power as a function of injection current; the gray curve corresponds to the devices according to the invention, the black curve to those made on unstructured substrate.
- the invention makes it possible to obtain a strong improvement in the optical power, by at least a factor of 2 at 20 mA (from 40 to 80 ⁇ ⁇ ⁇ ) and 80 mA (from 105 to 220 ⁇ ⁇ ⁇ ) .
- the applications of the invention mainly concern the manufacture of micro- and optoelectronic components, and more particularly LEDs, lasers, high electron mobility or power transistors, quantum well photodetectors in the near and far infrared. (called QWIP), but also quantum cascading components (lasers and detectors) that require very large active layer thicknesses.
- QWIP quantum well photodetectors in the near and far infrared.
- the invention makes it possible to take advantage of the very high etching selectivity of ZnO with respect to the active layers to enable the production of microstructures (membranes, micro-disks, etc.) suitable for the manufacture of microcomponents for electronics. and photonics.
- microstructures membranes, micro-disks, etc.
- photonics For example, it is possible to manufacture a suspended structure formed by a GaN layer previously epitaxially grown on a ZnO substrate, and then chemically etched with an acidic solution (for example H 3 PO 4 ) strongly diluted in water.
- an acidic solution for example H 3 PO 4
- photonic crystals or metal / metal guides by selectively removing the substrate followed by a transfer to another substrate.
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Abstract
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FR1661191A FR3059147B1 (en) | 2016-11-18 | 2016-11-18 | SEMICONDUCTOR HETEROSTRUCTURES WITH WURTZITE TYPE STRUCTURE ON ZNO SUBSTRATE |
PCT/EP2017/079275 WO2018091502A1 (en) | 2016-11-18 | 2017-11-15 | Semiconductor heterostructures with wurtzite-type structure on zno substrate |
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