EP2577719A1

EP2577719A1 - Method for removing residual extrinsic impurities in an n type zno or znmgo substrate, and for accomplishing p type doping of said substrate

Info

Publication number: EP2577719A1
Application number: EP11722473.3A
Authority: EP
Inventors: Isabelle Bisotto; Guy Feuillet
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2010-06-03
Filing date: 2011-06-01
Publication date: 2013-04-10
Also published as: FR2961013B1; US8852997B2; WO2011151409A1; US20130137214A1; FR2961013A1

Abstract

The invention relates to a method for purifying an n-type substrate made of ZnO and/or ZnMgO for reducing or removing the residual extrinsic impurities of the substrate with a view to p type doping at least a portion of the substrate, wherein a reactive species having a strong chemical affinity with at least one of the residual extrinsic impurities and/or capable of creating crystalline defects is introduced into at least one area of the substrate, said reactive species consisting of P, thus creating at least one so-called "getter" zone in the substrate, said zone being capable of trapping said residual extrinsic impurities and/or in which zone the residual extrinsic impurities are trapped; the substrate then annealed to diffuse the residual extrinsic impurities toward the "getter" zone, and/or out of the "getter" zone, preferably toward at least one surface of the substrate. The invention further relates to a method for preparing a substrate made of p-doped ZnO and/or ZnMgO including at least one step of purifying an n-type substrate made of ZnO and/or ZnMgO by the above purification method, wherein one or more reactive specie(s) not limited to phosphorus alone is/are employed.

Description

METHOD FOR REMOVING RESIDUAL EXTRINSIC IMPURITIES INTO ZNO OR ZNMgO TYPE N SUBSTRATE, AND FOR PERFORMING P TYPE DOPING OF THIS SUBSTRATE.

DESCRIPTION

TECHNICAL AREA

The invention relates to a method for at least partly removing residual extrinsic impurities in a n - type ZnO or ZnMgO substrate, and for performing a p - type doping of this substrate.

More specifically, the invention relates to a method for purifying a n-type ZnO and / or ZnMgO substrate to reduce or eliminate extrinsic impurities from the substrate for p-type doping of at least a portion of the substrate. substrate, this purification process using phosphorus as a reactive species.

The invention furthermore relates to a process for preparing a p-type at least partially doped ZnO and / or ZnMgO substrate comprising at least one step of purifying a ZnO and / or ZnMgO substrate. type n by said purification process, but in which one or more reactive species are used which are not limited to phosphorus alone.

The technical field of the invention can be broadly defined as that of the preparation, manufacture of p-doped ZnO or ZnMgO substrates, from n-type substrates. Note that the terms "substrate ZnO or ZnMgO n 'imply no limitation including the nature and shape of this substrate.

Thus, the substrate that could possibly be described as "structure" may be a "massive" ZnO or ZnMgO substrate with a thin or thick epitaxial layer of ZnO or ZnMgO, or even a "massive" ZnO substrate. or ZnMgO on which a thin or thick layer of ZnO or ZnMgO was epitaxially grown.

In other words, by substrate, is meant any ZnO or ZnMgO type material, whether it is derived from solid material or that it consists of layer (s) epitaxied (s) ZnO or ZnMgO, with or without quantum well structure and deposited on any type of material other than ZnO or ZnMgO.

The substrate may comprise, for example, an alternation of ZnO and ZnMgO layers with or without a quantum well structure.

STATE OF THE PRIOR ART

The development of the ZnO material is motivated by the fact that it has interesting electrical and optical properties for applications in the field of electro-optics.

The two advantages of ZnO are its large "gap" with ultraviolet emission and its high excitonic band energy of 60 meV.

ZnO is an intrinsic n-type semiconductor and its concentration of impurities of the type The donor varies according to the synthesis method used: hydrothermal synthesis, organometallic vapor phase epitaxy ("MOVPE"), molecular beam epitaxy ("MBE").

To produce an electronic and / or optical component, it is necessary to be able to obtain a junction, that is to say a homo-junction or a pn hetero-junction, namely to grow the large gap material ZnO and / or ZnMgO p-type on ZnO and / or n-type ZnMgO.

By homo-junction is meant that the two materials constituting the junction are identical, for example the two materials are both ZnO or ZnMgO; and by hetero-junction, it is meant that the two materials constituting the junction are different.

It is therefore necessary to convert an intrinsically n-type material to obtain a p-type material.

This doping step is crucial for the production of optoelectronic components but it remains very difficult to obtain quality p-n junctions.

The p-type doping process goes through a step of compensation of the activated residual donors of the material by the introduction of acceptors.

In addition, to really talk about doping and p-type conduction, it is necessary to have a concentration of activated acceptors well above the concentration of activated residual donors.

P-type doping can be obtained by in-situ doping. In this respect, mention may be made among others of the work of A. Tsukazaki et al. [1] which realized a ZnO pin structure, that is to say a ZnO structure of type p on insulating ZnO, itself on ZnO of type n, on a substrate of SCAM (ScAlMgO ₄ ) covered by a thin ZnO layer, by growth "MBE". The electroluminescence signal resulting from this structure is however very weak and spread over a wide spectral range from violet to green.

Other ways to obtain p-type doping of ZnO and / or ZnMgO are ex situ doping by ion implantation or by diffusion.

WO-A1-2007 / 117158 discloses ion implantation of a p-type layer to a maximum depth of 100 nm in an n-type ZnO substrate.

This low energy implantation (from 1 keV to 100 keV) is followed by a rapid thermal annealing by electron beam under vacuum.

With such implanting conditions, the potential acceptors are introduced to a small thickness, namely to a thickness of less than 100 nm, in the near surface, which is an area of the material known to be highly reactive.

In particular, the formation of a strongly doped n-type surface layer by adsorption of species present in the ambient atmosphere is often mentioned in the literature [2].

The estimated thickness of this n-type conductivity layer can be up to about ten nanometers and increases gradually with the time, which introduces a p doping instability obtained by this method and makes it difficult to control.

In addition, since the thickness of the area p is small, the injected carriers can recombine at the surface of the material and not at the junction and thus significantly reduce the effectiveness of the component.

In the literature, there are other demonstrations of p-doping in ZnO by ion implantation, especially for nitrogen implantations.

The article by B.T. Adekore et al. [3] in which donor / acceptor pairs are observed in photoluminescence at around 3.067 eV for a well-defined annealing temperature range between 850 ° C. and 1000 ° C., meaning the introduction of acceptors by implantation of nitrogen. . These authors also show by vertical current-voltage measurements the presence of a homo-junction p-n. Electroluminescence spectra are also presented but the signal is mediocre and results from the emission of the deep defect band. There is no, contrary to what the authors claim, emission corresponding to the "gap" of ZnO.

Other work conducted by Gu et al. [4] also highlight by current-voltage measurements the presence of a pn homo-junction by ion implantation of nitrogen and a weak electroluminescence signal centered in the range of green and not in the ultraviolet . Even if the presence of acceptors, by implantation in particular of nitrogen, or by other doping techniques is demonstrated optically and electrically in the literature, there is no electroluminescence (EL) in the associated UV at the junction. On the other hand, a low emission in the green, predominant in the EL spectrum, is observed. In addition, the breakdown voltages of the diodes obtained are relatively low (5 to 6 V), which suggests that the junction is of very poor quality.

Moreover, the technique of "gettering" (or trapping in French), consists of reducing or eliminating metallic impurities in the active regions of the electronic devices by trapping them in the secondary zones. It is widely used in microelectronics in the active area of silicon-based devices to reduce the concentration of metals such as iron. Indeed, the metal impurities are identified as being at the origin of the formation of deep levels degrading the electronic and / or opto ^¬ electronic silicon components. The creation of a "getter" zone outside the active zone of the devices makes it possible to obtain electrical characteristics of much better quality: in particular, it is observed that the leakage current of the diodes is greatly reduced and the breakdown voltages increased.

The "gettering" can be done by various processes, among which may be mentioned for example the diffusion of boron or phosphorus opposite back of the silicon, the damage of the substrate by laser irradiation and finally the ion implantation [5].

There are two main mechanisms for "gettingtering" impurities by ion implantation:

1) "Gettering" by crystalline defects: In this case, the "getter" zone is a heavily damaged area that contains many crystalline defects.

This technique is illustrated, for example, by US Pat. No. 4,975,126 in which the "getter" zone is created by a succession of oxygen or nitrogen implantation in a silicon substrate to create an insulating zone. electrically and full of defects. Trapping is carried out by the formation of weak bonds between the pendant bonds of the crystalline defects and the impurities of the material which makes it possible to fix the highly mobile impurities therein.

2) "Gettering" by the formation of a chemical phase between the metal impurities of the material and a reactive element.

This technique is illustrated, for example, by US Pat. No. 5,436,498 in which the formation of a stable chemical phase between a so-called reactive element derived from column VI of the periodic table of elements such as 0, is exposed. S, Se, Te ..., and the metallic impurity to trap. The trapping is achieved by the formation of strong bonds, which guarantees a stability of the "gettering" zone vis-à-vis the various thermal cycles then experienced by the material. Hydrothermal ZnO synthesis leads to the presence of a large lithium concentration in the bulk commercial substrate which migrates from the surface volume very easily during annealing. Lithium diffuses even at room temperature in ZnO to preferentially place itself in interstitial site where it is donor.

In ZnO substrate growth and in-situ (during growth) and ex-situ (after growth) doping processes, ZnO is heated. As a result, the migration of surface and layer species and their possible trapping is inevitable. This phenomenon is all the more marked that the surface area is rich in defects and / or that the dopant is likely to have a chemical reactivity with diffusing impurities.

The diffusion and trapping of lithium in the potentially p-type zone has been poorly described in the literature.

The study of the effect of the post-implantation annealing temperature on ZnO implanted with nitrogen was conducted by TM B0rseth et al. [6]. These authors demonstrated by SIMS analysis the "gettering" lithium in the area implanted with nitrogen (which is a theoretically acceptor element in ZnO) for annealing temperatures ^¬ post implantation of 600 ° C and 800 ° vs. They have observed that the lithium accumulated in the implanted zone is exo- diffused during annealing at 1000 ° C. Similar effects have been observed for an aluminum implantation at the surface (aluminum is placed in site donor in ZnO) by these same authors [7]. SIMS profiles indicate that for post implantation annealing ^¬ 900 ° C and 1000 ° C, lithium strongly migrated and was trapped in the implanted zone.

With regard to documents [6] and [7], the inventors came to the conclusion, which was not mentioned or suggested in these documents, that the absence of lithium exodiffusion in the case of implantation of aluminum can be explained by the "gettering" of lithium by the formation of a chemical phase with aluminum. On the other hand, the exo-diffusion of lithium at 1000 ° C. in the case of nitrogen implantation shows that lithium is weakly bound to the other atoms of the crystal lattice.

The inventors have thus demonstrated that lithium can be identified as one of the main problems for the control of ZnO and / or ZnMgO and especially of its p-type doping. Indeed, the "gettering" of lithium by the acceptors implanted or introduced by in-situ doping, or by the defects, for example implantation defects will totally or partially prevent the activation of acceptors and probably create centers of non-radiative recombinations.

In the literature, there are some studies describing the "gettering" of lithium by aluminum. For example, the lithium "gettering" of a LGO substrate (lithium gallate) for the growth of GaN [8] can be mentioned. The "getter" zone is either an AlGaN layer or a super AlGaN / GaN network. The "gettering" is possible thanks the high chemical affinity of lithium for aluminum. We can mention the known phases involving lithium and aluminum most relevant: L1 ₃ AI ₂ , Li ₂ Al, Al ₃ L1.

Similar studies [9] have been able to highlight, still for silicon substrates, the "gettering" of lithium by phosphorus. The "getter" zone is a phosphorized glass deposited on the surface of the sample to be treated (source POCI ₃ ).

Another impurity present in very large quantities in the ZnO is hydrogen, which is also an element that diffuses very easily. Hydrogen is known to passivate acceptors. In addition, just like lithium, hydrogen, in the interstitial position, is a donor in ZnO. On the other hand, few studies are reported in the literature on this subject. This is because hydrogen is a very light atom, which makes it technically very difficult to analyze.

There is therefore, in the light of the foregoing, a need for a method which allows efficient and high quality doping of n-type ZnO and / or ZnMgO. High quality p doping generally means that the substrate thus doped has a high carrier density and mobility.

STATEMENT OF THE INVENTION

This and other objects are achieved, according to the invention, by implementing in a process for preparing a p-doped ZnO and / or ZnMgO substrate at least one step of purifying a n-type ZnO and / or ZnMgO substrate to reduce or eliminate the residual extrinsic impurities of the substrate for the p-type doping of at least a portion of the substrate, this purification step being carried out by a method purification process in which at least one reactive species having a high chemical affinity with at least one of the residual extrinsic impurities and / or being capable of creating crystalline defects in said area of the substrate is introduced into at least one zone of the substrate, and thus creating in the substrate at least one so-called "getter" zone capable of trapping said residual extrinsic impurities and / or in which residual extrinsic impurities are trapped; then the substrate is annealed to diffuse residual extrinsic impurities to the "getter" zone, and / or out of the "getter" zone, preferably to at least one surface of the substrate. Note that "residual extrinsic impurities" generally means all impurities other than oxygen and zinc gaps and interstitials, which are already present in ZnO or ZnMgO (see below).

It should further be noted that "reactive species having a high chemical reactivity with at least one residual extrinsic impurity" is generally understood to mean that this species is capable of creating strong bonds with at least one of the residual extrinsic impurities. Generally, the strong bonds are not affected by the annealing and residual extraneous impurities thus trapped are not released during annealing.

The purification process also uses the phenomenon of exo-diffusion.

In the case of exo-diffusion, at least one reactive species is implanted in ZnO: this implantation will create crystalline defects; trapping is achieved by the formation of weak bonds between the pendant bonds of the crystalline defects and residual extrinsic impurities. With annealing, the weak bond will be broken and the residual extrinsic impurities will be released and will migrate out of the "getter" zone, generally to at least one surface of the substrate.

In fact, it can be said that during implantation to create crystalline defects, the amount of crystal defects created is high and in excess of residual extrinsic impurities.

As a result, not all defects are occupied, ie all defects do not form weak bonds with the impurities. During annealing, there is thus migration of impurities out of the "getter" zone and also migration of residual extrinsic impurities from the volume of the substrate to the "getter" zone where they will be trapped by the "free" crystalline defects appended.

By "volume" of the substrate, one generally understands the rest of the substrate that is to say the part that is not the "getter" zone, for example it may be the part of the substrate, such as one or more layers, underlying the "getter" zone.

During annealing, it also occurs in the "getter" area, a cure or removal of crystalline defects or holes.

Advantageously, the residual extrinsic impurities belong to the group consisting of metals and hydrogen.

Advantageously, the residual extrinsic impurities belong to the group consisting of lithium and hydrogen.

Advantageously, the reactive species is (are) chosen from the reactive species and / or acceptor of ZnO and / or ZnMgO, and the "getter" zone is n-type conductive or p, or semi-insulating or insulating.

According to the invention, it is generally desired to produce with the purified substrate a pn-homo or pn-hetero-junction diode (in fact, one may have, for example, a ZnO substrate and make epitaxial growth of ZnO or ZnMgO (heterojunction) or one may have, for example, a ZnO substrate and make a ZnO (homo-junction) growth having a "gettering" zone and preferably giving a light emitting signal in the range. ultraviolet light. An example of a p-n junction diode is shown in FIG. 4.

Therefore, for this purpose, according to the invention, an acceptor and / or donor reactive species in ZnO and / or ZnMgO will preferably be used for this purpose. generally know elements of columns I, III or V of the periodic table of elements.

This preference in the choice of reactive species is justified by the fact that it is generally desired to carry out, as specified above, a pn junction, a homo- or heterojunction, and that the current applied to the device. will preferentially pass through the "getter" zone. In this case (where the current applied preferentially passes through the "getter" zone), the conductivity of this "getter" zone must be known, not zero (ie the "getter" zone must not be not electrically insulating), and controlled by its n-type doping or p.

In the case where the current applied to the structure does not pass through the substrate, the "getter" zone may be insulating, and any other "getter" species for ZnO and / or ZnMgO may be used.

In addition, this "getter" zone must preferably be of crystalline quality at least equivalent to the crystalline quality of the material before the formation of the getter zone.

However, the material of the "getter" zone is not limited to materials that exhibit such crystalline quality.

Advantageously, the reactive species is (are) chosen from the elements of columns I, III or V of the periodic table of the elements. Advantageously, the reactive species is (are) chosen from phosphorus and aluminum.

Advantageously, the reactive species (s) is (are) introduced into at least one zone of the substrate by ion implantation, preferably by ionic multi-implantation.

This implantation or ionic multi-implantation can be, for example, implantation or multi-implantation hot or implantation or multi-implantation cold.

By "implantation or multi-implantation hot ionic" is meant that this implantation or multi-implantation is generally performed at a temperature between room temperature and 1000 ° C, preferably at a temperature above room temperature and up to at 1000 ° C, for example at a temperature of 500 ° C.

Indeed, implantation or multi-implantation hot can cure some of the defects at the same time they are created.

By performing implantation or multi-ion implantation hot, thus possibly decreases the temperature and duration of a subsequent annealing step.

By "implantation or multi-implantation cold ion", it is understood that this implantation is generally carried out at the temperature of liquid nitrogen, for example - 200 ° C. In all cases, however, it is necessary to anneal after implantation to cure crystalline defects.

The annealing temperature is then generally from 300 ° C. to 1100 ° C., for example of the order of 900 ° C.

Thus, in the case of multi-ion implantation at room temperature, it is necessary after annealing, for example at a temperature of the order of 700 ° C, to cure crystalline defects or dislocations.

Advantageously, the "getter" zone is in the form of a layer.

Advantageously, the "getter" zone is created on a surface of the substrate.

By "a surface of the substrate", it is generally meant that one of the surfaces of the "getter" zone, for example its upper surface, constitutes a surface of the substrate.

It has been demonstrated by the inventors that the poor quality of the p-type doping and the junctions obtained in the prior art represented by the documents cited above was certainly due to the high concentration of mobile or fixed impurities. (because the impurities can quite well be fixed in the network, and give rise to a poor p-type doping quality, such as lithium and hydrogen, present in ZnO and / or ZnMgO in very large quantities in the p-doped zone of the material, these mobile or fixed impurities being likely to compensate and / or passively acceptors introduced.

It can be said that the purification process implemented according to the invention makes it possible to carry out the p-type doping of ZnO and / or ZnMgO of the n type by trapping the residual extrinsic impurities by the crystalline defects and the formation of a chemical phase between the impurities and the reactive species introduced in order to allow the decrease and / or the elimination of the diffusion of residual extrinsic impurities

This reduction and / or elimination of the diffusion of the residual extrinsic impurities are carried out by a technique allowing their exo diffusions and / or their trapping.

The technique used according to the invention to thus purify the substrate is the so-called "gettering" technique, preferably by ion implantation.

In other words, the purification process implemented according to the invention makes it possible to ensure the trapping and / or to increase the exo-diffusion of impurities such as lithium and hydrogen from substrates or layers, in particular epitaxial layers (thin and thick) of ZnO and / or ZnMgO for performing the p-type doping of ZnO and / or ZnMgO, to obtain a high quality pn junction.

The invention is based on observations made in SIMS of samples implanted by phosphorus (which is a potentially accepting species in ZnO) and annealed at high temperatures for which has been observed a very important trapping lithium in the implanted area as shown in Figure 1.

It is clearly seen in FIG. 1 that the profile of lithium (curve B) is superimposed on the profile of the implanted phosphorus (curve A), and that the concentrations are similar, ie approximately 4x10 ¹⁸ at / cm of Li trapped for a profile. implantation at approximately 4x10 ¹⁸ at / cm ³ of phosphorus.

It may also be noted that the concentration of lithium by volume has decreased, since it is approximately 1 × 10 ¹⁷ at / cm ³ after implantation and annealing (curve B) against about 4x10 ¹⁷ at / cm ³ for a non-implanted raw substrate and not annealed (curve C).

The important "gettering" of lithium by phosphorus can be explained by the high chemical affinity of these two species. The known phases involving lithium and phosphorus are multiple, we can quote the most relevant: L1 ₃ P, LiP [10].

Phosphorus, like nitrogen, are elements of column V of the periodic table of potential elements and acceptors in ZnO. If the lithium migrates and becomes trapped in the implantation zone by forming a chemical phase with the doping species, or then binds to pendant bonds of crystalline defects (it should be noted that the dislocations are included in the definition crystalline defects), then it is understood that p doping of ZnO and / or ZnMgO is currently difficult whatever the doping technique used, that is to say that it is by ion implantation by diffusion or during the growth of thin and / or thick layers by vapor phase epitaxy of organometallic ("MOVPE") ), by molecular beam epitaxy ("MBE" or "MBE") etc., n-type or p-type doped.

It was also possible to demonstrate the trapping of hydrogen in the implanted nitrogen zone and annealed as shown in FIG. 2. 2x10 at / cm of hydrogen were observed for 6.2x10 at / cm of implanted nitrogens.

The diffusion of lithium and hydrogen and / or the trapping by the potentially accepting dopants in the implanted zone can explain on the one hand the difficulty of doping ZnO and / or ZnMgO of the p type and on the other hand, the absence of p-type control when it is obtained, which is very often observed in the literature.

In other words, the invention is based on the properties of certain ZnO extrinsic impurities used to decrease the density of residual extrinsic impurities.

It should be noted that in the present application, a distinction is made between, on the one hand, the residual extrinsic impurities which are already present in ZnO or ZnMgO, which come for example from the ZnO production process and which are other than gaps or interstitials of Zn or 0 and, on the other hand, extrinsic impurities that are voluntarily introduced into ZnO and / or ZnMgO. The reduction in the density of residual extrinsic impurities in the ZnO and / or ZnMgO obtained according to the invention then allows efficient p-doping in these materials which, until now, was limited by the presence of residual extrinsic impurities present in large amount in the substrates as in the epitaxial layers of ZnO and / or ZnMgO.

Commercial substrates and / or ZnO layers contain, for example, a large amount of lithium (around 4xl0 ¹⁷ at / cm ³ and hydrogen lxlO ¹⁸ at / cm ³ ).

The purification process implemented according to the invention makes it possible to purify ZnO and / or ZnMgO of type n with a view to doping it with a p-type.

This process relies in particular on the following mechanisms:

trapping impurities and in particular lithium and / or hydrogen by the crystal defects (induced by ion implantation or pre ^¬ existing in the material);

increased exo-diffusion of residual extrinsic impurities and in particular lithium and / or hydrogen trapped by crystalline defects (induced or pre-existing in the material). This is a phenomenon that consists of releasing impurities trapped by the crystalline defects by the surface. Thus, it is part of the continuity of the phenomenon described above. The concentration of trapped elements is greatly reduced, especially in the subsurface zone, which is often the active part of optoelectronic or electronic devices.

the trapping (or "gettering") of residual donor-type extrinsic impurities in ZnO and / or ZnMgO, such as lithium, by the possible formation of a chemical phase between the mobile impurity and the implanted element.

ZnO and / or ZnMgO purified by the purification process described above can be used for manufacturing electronic devices, electro-optical, electronic or opto ^¬ electronic and serve, for example, in the manufacture of light emitting diodes for the lighting substrates for the growth of epitaxial layers of ZnO and / or ZnMgO or any other material, for example GaN, or seed for the synthesis of material ZnO and / or massive ZnMgO. The purified material can also be used for the growth of ZnO and / or ZnMgO nanowires or any other material, for example GaN.

The purification process described above in the case where a reactive species which is specifically phosphorus is introduced into at least one zone of the substrate has never been described in the prior art, represented in particular by the documents cited above. .

The invention thus relates to a method for purifying a n-type ZnO and / or ZnMgO substrate to reduce or eliminate residual extrinsic impurities in the substrate for p-type doping of at least a portion of the substrate, which is introduced into at least one zone of the substrate a reactive species having a high chemical affinity with at least one residual extrinsic impurity, and / or being capable of creating crystalline defects, said reactive species being P, and thus creating in the substrate at least one so-called zone "Getter" capable of trapping said residual extrinsic impurities and / or in which residual extrinsic impurities are trapped; then the substrate is annealed to diffuse residual extrinsic impurities to the "getter" zone, and / or out of the "getter" zone, preferably to at least one surface of the substrate.

Advantageous embodiments of this purification process according to the invention have already been described above and are also described in the appended claims 2 to 7.

The invention furthermore relates to a method for preparing a p-type doped ZnO and / or ZnMgO substrate comprising at least one step of purifying a ZnO and / or ZnMgO n-type substrate by purification process as described above in the most general case, that is to say in the case where is introduced into at least one area of the substrate at least one reactive species, this reactive species not being limited to phosphorus alone.

The invention therefore also relates to a process for the preparation of a p-type doped ZnO and / or ZnMgO substrate comprising at least one step for purifying a ZnO and / or ZnMgO n-type substrate for reduce or eliminate residual extrinsic impurities from the substrate for doping purposes p-type of at least a portion of the substrate, said purification step being carried out by a purification process, in which at least one reactive species having a high chemical affinity with at least one of the substrate is introduced into at least one zone of the substrate; residual extrinsic impurities, and / or being capable of creating crystalline defects, and thus creating in the substrate at least one so-called "getter" zone capable of trapping said residual extrinsic impurities and / or in which the residual extrinsic impurities are trapped; then the substrate is annealed to diffuse residual extrinsic impurities to the "getter" zone, and / or out of the "getter" zone, preferably to at least one surface of the substrate.

Advantageous forms of the purification step of this method of preparation have already been described above and are also described in claims 9 to 15 attached.

This method of preparation has never been described in the prior art and has a number of advantages inherent to the purified substrate prepared by the purification process implemented according to the invention and which are mentioned in the present description.

In particular, the preparation method according to the invention makes it possible to stimulate ZnO and / or ZnMgO of the p type in a controlled and reproducible manner. In addition, the preparation method according to the invention ensures and controls efficient doping, that is to say a doping in particular to obtain an electroluminescence signal in the UV range.

The method according to the invention for preparing a ZnO and / or p-type doped ZnMgO substrate comprises, according to a first embodiment, the following successive steps:

a) a "getter" layer is created in a n-type ZnO and / or ZnMgO substrate from the upper surface of the substrate, for example by ion implantation;

b) the substrate is annealed to diffuse residual extrinsic impurities in the substrate beneath the getter layer to the getter layer;

c) the layer is eventually removed

"Getter";

d) the "getter" zone of ZnO and / or ZnMgO of type n or of type p is deposited, for example by epitaxy, on the "getter" layer or on the substrate from which has been removed.

e) optionally, in the case where in step d) ZnO and / or ZnMgO of the n type have been deposited, the p-type doping is carried out, for example by ion implantation or by diffusion, of the ZnO and / or n-type ZnMgO deposited;

f) a healing annealing of implantation defects, and activation of p-type dopants of ZnO and / or ZnMgO is optionally carried out. The process for preparing a substrate

ZnO and / or p-type doped ZnMgO according to the invention, in this first embodiment therefore generally consists in a purification of a ZnO and / or ZnMgO material by the purification method defined above (without any limitation on the reactive species), in the production on this purified material of layers epitaxially or deposited very high purity, and a p-type doping of these epitaxial layers or deposited.

More specifically, the purification by the process implemented according to the invention makes it possible to trap residual extrinsic impurities, such as for example lithium, present in large amounts in the ZnO and / or ZnMgO material in order to reduce or even eliminate their diffusion in the layers. epitaxially or deposited on a material of ZnO and / or ZnMgO. It also makes it possible to preserve an "epi-ready" surface, that is to say a surface ready to grow by epitaxy.

For this, we introduce a species in the near surface or more in volume, capable of creating numerous crystalline defects and / or having a high chemical affinity with the residual extrinsic impurities such as lithium, such as for example phosphorus, by exogenous route. situ (for example by ion implantation) or in-situ (during the growth of the layers) in the material of ZnO and / or ZnMgO.

In the case where the "gettering" is done by ion implantation, the material must be annealed at an optimal temperature to allow exo-diffusing and / or trapping the residual extrinsic impurities of the material, such as for example lithium and hydrogen , and to create a possible chemical phase between residual extrinsic impurities such as for example lithium and / or hydrogen and the implanted species. This "getter" zone can be optionally removed before growth by polishing, etching, etc.

The generally conductive "getter" zone, preferably of type n, has the following objectives:

purify ZnO and / or ZnMgO by volume of its residual extrinsic impurities, such as for example lithium by "gettering". The advantage of implantation and multi-implantation (several energies and associated doses) is to introduce a high concentration of reactive species and defects for:

o create a zone in which residual extrinsic impurity concentrations such as lithium and hydrogen trapped and / or removed from the substrate are greatly reduced: phenomenon of trapping by defects and / or exodiffusion,

o by the possible formation of a chemical phase between residual extrinsic impurities and a reactive donor and / or acceptor species in ZnO and / or ZnMgO introduced into ZnO and / or ZnMgO by ion implantation or during the growth of thin layers or thick (that is, in-situ).

achieve the first two objectives mentioned above while maintaining a conductivity of type n or of type p in the non-zero "getter" zone,

having a substrate of ZnO and / or ZnMgO whose residual extrinsic impurities are trapped, which will prevent the diffusion of the latter during the growth of thin or thick layers made on this substrate and / or heterostructures, and / or the production of nanowires. In summary, the purification process implemented according to the invention makes it possible to reduce or even eliminate the migration of residual extrinsic impurities, such as, for example, the migration of lithium and hydrogen in the layers subsequently produced on the ZnO material and / or or ZnMgO thus treated by the formation of a relatively thin barrier layer. Residual extrinsic impurities, such as for example lithium, will be absent from these layers, which can therefore be effectively doped with p-type or n-type high purity.

FIG. 3 represents the principle of trapping residual extrinsic impurities, for example lithium and hydrogen, of a ZnO and / or ZnMgO material in a substrate prepared by the preparation process of the invention according to the first embodiment of it.

Zone 1 (31) consists of ZnO and / or n-type ZnMgO with a thickness generally of 100 to 1000 μm, for example of a thickness of 500 μm. Zone 2 (32) consists of a ZnO and / or ZnMgO "getter" zone for trapping impurities such as lithium and hydrogen with a thickness generally of 100 to 500 nm, for example 500 nm.

Zone 3 (33) consists of ZnO and / or high purity n-type ZnMgO, without impurities, due to the presence of the "getter" layer underlying zone 2.

The n-type ZnO and / or ZnMgO of this zone may be in the form of a layer generally of a thickness of 10 to 1000 nm, for example 500 nm, and / or ZnO multiple quantum wells. / ZnMgO, for example 10 x ZnO: 5 nm / ZnMgO: 20 nm.

Zone 4 (34) consists of ZnO and / or p-type ZnMgO with a thickness generally of 100 to 1000 nm, for example 500 nm.

Figure 4A shows a p-n homogenization diode comprising the substrate of Figure 3 with front (35) and rear (36) contacts. The diode of Figure 4A is in a so-called "vertical configuration" configuration.

It should be noted that analog diodes can be made with the substrates of Figures 5 and 6 by providing them with adequate contacts.

Figure 4B shows a pn homo-junction diode having a substrate according to Figure 3 with contacts (37). The diode of FIG. 4B is in a so-called "horizontal configuration" configuration and therefore zones 3 and 4 as well as the position of the contacts have been modified with respect to the vertical configuration of FIG. 4A. In the case of this configuration or horizontal technology, the current flows mainly at the zones 3 (33) and 4 (34).

In a second embodiment of the process for preparing a p-doped ZnO and / or ZnMgO substrate according to the invention, the ZnO and / or ZnMgO material is purified of its impurities such as lithium and hydrogen and the p-type doping of this material.

This second embodiment of the method according to the invention for preparing a ZnO and / or p-type ZnMgO substrate can comprise two variants that make it possible both to purify the material of its residual extrinsic impurities such as lithium and hydrogen and the p-type doper.

The first variant of this second embodiment called Embodiment 2A comprises the following successive steps:

a) a deep "getter" layer having a thickness greater than or equal to 500 nm is created in a n-type ZnO and / or ZnMgO substrate from the upper surface of the substrate;

b) the substrate is annealed so as to spread the residual extrinsic impurities in the substrate beneath the getter layer to the getter layer (and trap the residual extrinsic impurities in the getter layer); ), and on the other hand, decrease the concentration of residual extrinsic impurities in the upper part of the getter layer, near its upper surface; c) at least one p-type dopant is introduced into the upper part of the "getter"layer;

d) a healing annealing of implantation defects and activation of the p-type dopants of the substrate is optionally carried out.

The second variant of this second embodiment called embodiment 2B comprises the following successive steps:

a) in a n-type ZnO and / or n-type ZnMgO substrate, from the upper surface of the substrate, a deep p-type layer having a thickness greater than or equal to 500 nm is created;

b) optionally performing a healing annealing of implantation and activation defects of the p-type dopants of the substrate;

c) creating in the p-type layer, from the upper surface of the p-type layer, a "getter" layer;

d) the substrate is annealed to diffuse the residual extrinsic impurities present in the substrate and in the p-type layer to the getter layer and trap residual extrinsic impurities in the getter layer;

e) eventually, the layer is removed

"Getter".

Embodiment 2A, consists in creating a deep getter layer and to be doped in p type above. Embodiment 2B is to do the reverse, i.e. to p-type deeply and to make a surface "getter" layer, which will then be removed by polishing, etching or other processes.

Embodiment 2A therefore uses a "deep gettering" technique while Embodiment 2B uses a "surface gettering" technique.

More specifically, what is meant by

"Deep gettering" in embodiment 2A, is the creation of a surface zone but deep enough which allows the trapping (see Figure 5), within this zone, residual extrinsic impurities, for example lithium to purify ZnO and / or ZnMgO by volume but especially to greatly reduce the concentration of residual extrinsic impurities, for example lithium and hydrogen in the near surface.

In the case of so-called technology

"Vertical" (which is represented in FIG. 4A), a good conductivity is retained in the "getter" zone, that is to say a conductivity greater than or equal to that of ZnO and / or ZnMgO of type n before purification.

In the case of a so-called "horizontal" technology (which is represented in FIG. 4B), the "getter" layer can be semi-insulating or insulating, indeed the conduction of the "getter" layer does not matter. The near surface area, for example of a thickness of 500 nm in which the concentration of impurities, for example lithium, will be greatly reduced, will then be p-type doped.

In this approach, the larger the area of

"Gettering" is deep plus the concentration of "getter" elements and the amount of defects induced by the introduction of these elements are high and the amount of impurities, for example lithium, trapped will itself be high.

Figure 5 shows the principle of "deep gettering" for trapping residual extrinsic impurities such as lithium and hydrogen from a ZnO and / or ZnMgO material and allowing p-type doping. Zone 1 (51) consists of ZnO and / or ZnMgO of type n

ZnO and / or n-type ZnMgO in this zone may be in the form of a layer generally of a thickness of 100 nm to 1 μm, for example 500 nm, and / or ZnO / ZnMgO multiple quantum wells, for example multiple quantum well 10 x ZnO: 5 nm / ZnMgO: 20 nm.

Zone 2 (52) is a zone of ZnO and / or ZnMgO, which is a "getter" zone for trapping residual extrinsic impurities such as lithium and hydrogen, generally of a thickness of 100 to 500 nm, for example 500 nm, whose n-type conductivity is generally necessary in the case of a vertical diode pn as described in Figure 4A. Zone 3 (53) is a zone of p-type doped ZnO and / or ZnMgO with a thickness generally of 100 to 1000 nm, for example 500 nm.

The formation of this structure generally requires the following three inseparable steps:

a) Formation of a "deep getter" layer, preferably conductive, on a ZnO material and / or ZnMgO, for example by ion implantation of donor or acceptor impurities for ZnO and / or ZnMgO as respectively the aluminum or phosphorus. The advantage of implantation and multi-implantation (several energies and associated doses) is to introduce a large concentration of reactive species and defects to trap and / or exo-diffuse a large concentration of impurities such as lithium, and possibly form a chemical phase.

b) Possible removal of the near surface to remove the impurities not completely exo-diffused during the annealing,

c) Formation of a p-type layer, for example over a thickness of about 500 nm, for example by ionic implantation of an acceptor element in ZnO and / or ZnMgO, it is preferably an element of column V or I of the periodic table of elements.

The first step is to form a conductive n-type "deep getter" layer that aims to: create a zone in which impurity concentrations such as lithium and hydrogen are greatly reduced, ie generally at concentrations below 10 ¹³ atoms / cm ³ due to a phenomenon of trapping by defects and exo-diffusion,

purify ZnO and / or ZnMgO by volume of its impurities such as lithium by "gettering" by the formation of a chemical phase between impurities such as lithium and a donor reactive species and / or acceptor in ZnO and / or or ZnMgO introduced into ZnO and / or ZnMgO by ion implantation or during the growth of thin or thick layers,

- To achieve the first two objectives mentioned above while retaining preferentially a non-zero conductivity in the "getter" zone, ideally at least equal to the conductivity of the ZnO material and / or ZnMgO before purification.

The second step has the sole objective of doping p-type ZnO and / or ZnMgO to a thickness for example of about 500 nm. In the present invention, whatever the embodiment, the reactive species is preferably chosen from extraneous residual impurities of ZnO and / or ZnMgO, preferentially donor of ZnO and / or ZnMgO (column III of FIG. periodic classification of the elements) so that the deep layer remains conductive n-type with a conductivity ideally at least equal to the conductivity of the ZnO material and / or ZnMgO before purification and avoid the formation of an electrically insulating layer.

However, it is not excluded to implant an acceptor species (columns I and V of the periodic table of the elements) and to keep a conductivity of type n ideally at least equal to that of the ZnO material and / or ZnMgO before purification. .

In Embodiment 2B, a "surface gettering" or surface trapping is performed.

Surface trapping has the same objectives as deep trapping but its realization is different.

The formation of this structure requires the following three inseparable steps:

a) Formation of a deep p-type layer for example by ion implantation of an acceptor element in ZnO and / or ZnMgO. This acceptor element is preferably an element of column V or column I of the periodic table of elements.

b) Formation of a layer on the surface, for example by ion implantation of donor or acceptor impurities for ZnO and / or ZnMgO, for example and respectively aluminum and phosphorus. The advantage of implantation and multi-implantation (several energies and associated doses) is to introduce a large concentration of species reactants and defects to trap and / or exo-diffuse a large concentration of impurities, for example lithium, and possibly form a chemical phase.

c) Removal of the surface "getter" area.

The first step of this embodiment 2B consists in forming a deep p-type ZnO / ZnMgO conductor layer over a thickness d generally greater than or equal to 500 nm.

The second step consists in creating a "getter" zone or trapping zone at the extreme surface of said deep layer.

"Extreme surface" means that the "getter" zone is created over a depth d less than the thickness of the deep layer, preferably over a depth of less than half the thickness of the deep ZnO layer. / P-type conductive ZnMgO for:

to create a zone in which the residual extrinsic impurity concentrations, for example lithium and hydrogen, are greatly reduced, namely generally less than 10 ¹³ atoms / cm ³ by a phenomenon of exo-diffusion of the impurities previously trapped by the defects ,

purify the ZnO and / or ZnMgO of its residual extrinsic impurities, for example its lithium by volume but especially in the p-type doped region, by the possible formation of a chemical phase between impurities such as lithium and a donor and / or acceptor reactive species introduced by ion implantation or during the growth of thin or thick layers.

The third step makes it possible to remove the "getter" zone which contains residual extraneous trapped impurities.

FIG. 6 represents the principle of surface "gettering" for trapping impurities such as lithium and hydrogen from a ZnO and / or ZnMgO material and allowing p-type doping.

Zone 1 (61) consists of ZnO and / or n-type ZnMgO.

The n-type ZnO and / or ZnMgO of this zone may be in the form of a layer, generally of a thickness of 1 to 500 μm, for example 1 μm, and / or of multiple quantum wells ZnO / ZnMgO of a thickness generally of 10 to 100 nm, for example 25 nm, or the ZnO and / or ZnMgO of this zone may be in a form similar to that of the layers (33) or (51) of FIG. 3, 4A, 4B and 5.

Zone 2 (62) is a p-doped ZnO and / or ZnMgO zone of a thickness generally of 100 to 1000 nm, for example 500 nm.

Zone 3 (63) is a "getter" area of

ZnO and / or ZnMgO trapping residual extrinsic impurities such as lithium, the conductivity of which does not matter. This zone generally has a thickness of 100 to 500 nm, for example 500 nm. The invention will be better understood on reading the detailed description which follows of the preferred embodiments of the method of the invention, given by way of illustration and not limitation.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is made with reference to the accompanying drawings, in which:

Figure 1 is a graph that gives the SIMS profile of a phosphor implanted ZnO substrate at Rp = 0.3 μm. Curve A gives the concentration of implanted phosphorus. Curve B gives the concentration of lithium trapped in the sample implanted with phosphorus after a post-implantation annealing. Curve C gives the concentration of lithium in a sample, ZnO substrate, crude, that is to say not implanted and not annealed.

On the ordinate is the concentration (in at / cm ³ ), and the abscissa is the analysis depth d (by SIMS) of the sample in ym.

Figure 2 is a graph that gives the SIMS profile of a nitrogen implanted ZnO sample and annealed at 600 ° C for 15 minutes under oxygen.

Curve A gives the implanted nitrogen concentration. Curve B gives the hydrogen concentration in the implanted zone by nitrogen after post-implantation annealing. Curve C gives the concentration of lithium in a sample, ZnO substrate, crude, that is to say not implanted and not annealed. On the ordinate is the concentration (in at / cm ³ ), and the abscissa is the depth of analysis of the sample d in ym.

FIG. 3 is a sectional side view of a p-type doped substrate obtained by the process according to the invention for preparing a p-type ZnO and / or ZnMgO substrate according to the first embodiment of this invention; this.

FIG. 4A is a sectional side view of a junction (homo-junction or hetero-junction) pn having a "getter" zone, this structure having been prepared by the method according to the invention for preparing a substrate in ZnO and / or p-type ZnMgO according to the first embodiment thereof. Figure 4A illustrates a so-called "vertical" technology.

FIG. 4B is a vertical sectional view of a junction (homo-junction or hetero-junction) pn having a "getter" zone, this structure having been prepared by the method according to the invention for preparing a substrate in ZnO and / or p-type ZnMgO according to the first embodiment thereof. Figure 4B illustrates a so-called "horizontal" technology.

FIG. 5 is a sectional side view of a p-type doped substrate obtained by the method according to the invention for preparing a p-type ZnO and / or ZnMgO substrate according to the embodiment 2A thereof. this.

FIG. 6 is a sectional side view of a p-type doped substrate obtained by the process according to the invention for the preparation of a substrate in ZnO and / or p-type ZnMgO according to Embodiment 2B thereof.

FIGS. 7A to 7F represent the successive steps of the method according to the invention for preparing a p-type ZnO and / or ZnMgO substrate according to the first embodiment thereof.

Figures 8A-8D show the successive steps of the method according to the invention for preparing a p-type ZnO and / or ZnMgO substrate according to Embodiment 2A thereof.

FIGS. 9A to 9D show the successive steps of the method according to the invention for preparing a ZnO and / or p-type ZnMgO substrate, according to embodiment 2B thereof.

It should be noted that in all the figures, the thicknesses and the sizes, and other values mentioned are only as examples, as an indication; and in no way constitute any limitation.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

According to a first embodiment of the preparation process according to the invention, the "gettering" purification of a ZnO or n-type ZnMgO substrate is carried out. The epitaxy or the deposition of very high purity layers on this purified substrate is then carried out, and the p-type doping of these layers.

Figure 7 describes the different possible steps for this first embodiment of the preparation process: Step 1 (Figure 7A):

Introduction, for example, by ionic implantation in a ZnO substrate or n-type ZnMgO, of a species having a high chemical affinity with residual extrinsic impurities, such as for example lithium, to form an area called "getter zone".

The n-type ZnO or ZnMgO substrate may be, for example, in the form of a n-type ZnO or ZnMgO layer with a thickness generally of 100 nm to 100 μm, preferably 50 μm (71). . The substrate may also be in the form of a so-called "solid" substrate generally having a thickness greater than or equal to 100 μm, or even 500 μm, for example 500 μm.

This species having a high chemical affinity for residual impurities, such as for example lithium, called "getter species" may be chosen, either from the impurities theoretically donor, preferably from column III of the periodic table of elements, or from impurities theoretically acceptor of ZnO or ZnMgO, preferentially of column I or V of the periodic table of elements.

For example, an ion multiplication of phosphorus can be performed at energies of 700 keV, 300 keV and 80 keV with a dose of 1 ^e at 15 / cm ² for each energy. Preferably, the "getter" zone will be n-conducting with a conductivity at least equal to that of the substrate before the purification step.

The "getter zone" generally constitutes a layer of ZnO and / or ZnMgO, generally of a thickness of 10 to 500 nm, for example 500 nm (72) on the surface of the substrate, or of the thin or thick epitaxial layer. .

Step 2 (Figure 7B):

Diffusion annealing of impurities such as lithium at high temperature to form the possible chemical phase between impurities such as lithium and the "getter" species and exo-diffuse impurities (73) such as lithium and / or hydrogen to the getter zone (72) and the near surface of the material. The annealing that can be envisaged is, for example, annealing at 1100 ° C. under O2 flushing for 1 hour. Step 3A (Figure 7C):

Growth of thin or thick layers respectively and preferably by MOCVD, MBE or CVT and / or realization of hetero-structures and / or nanowires on the "getter" layer (72).

For example, it is possible to carry out the growth of an n-type ZnO layer with a thickness generally of 10 nm to 100 μm, preferably of a thickness of 1 to 2 μm or of multiple quantum wells, for example 10 × ZnO of 5 μm. nm or ZnMgO of 20 nm (74).

Thanks to the "getter" layer (72), there is no or very little (that is to say a concentration less than 10 at / cm) of lithium diffusion in the epitaxial or deposited layers (74).

Step 4 (Figure 7E):

Doping of the layer (74) (in other words, introduction of a p-type dopant species into the layer) obtained in step 3, for example by ion implantation (76) after growth (exogenous doping). situ) nitrogen to energy 200keV, 120keV and 50 keV with the respective doses of ^e ^~ 15cm ^2, ^8, 14 cm ^"2 and 4 ^e 14 ^{cm" 2.}

It is also possible to perform p-type in-situ doping of the layers prepared, for example epitaxially or deposited, during the growth step 3.

This p-type doping, for example by implantation of nitrogen, is generally carried out over a thickness (75) of 100 nm to 1 μm, for example 500 nm of the ZnO or ZnMgO layer (74) deposited during the reaction. step 3.

Step 5 (Figure 7F):

Healing post-implantation annealing of implantation and activation defects of the dopants, acceptors, for example at 900 ° C. for 15 minutes under a scan of 0 ₂ .

In the case of an in-situ doping, it is also conceivable to produce an annealing post ^¬ growth or in-situ to activate the dopants.

In a variant of this embodiment, it is possible to add a step 2 bis (no shown) of removing, removing the "getter" layer in which impurities such as lithium and hydrogen are trapped.

This step 2a can be carried out for example by gentle chemical mechanical polishing.

At the end of this step 2bis, a growth step described in step 3B (FIG. 7D) is carried out on the n-type ZnO or ZnMgO substrate, purified by virtue of the action of the "getter" layer. .

According to a second embodiment of the preparation process according to the invention in a first variant, the p-type purification and doping of a ZnO or ZnMgO substrate is carried out, using a deep "gettering" technique. .

FIG. 8 describes the different steps of this second embodiment of the method:

Step 1 (Figure 8A):

Ionic implantation (83) in a ZnO substrate or in n-type ZnMgO (81), of a species having a high chemical affinity with residual extrinsic impurities, such as lithium, to form an area called "getter zone" (82), generally in the form of a layer (82).

This step is generally carried out analogously to step 1 of the first embodiment, with the difference that the zone, generally a "getter" layer, is not a thin, surface layer, but a "deep" layer. By "deep" layer, it is generally understood that this layer has a thickness greater than or equal to 500 nm, preferably 100 to 1000 nm, for example 500 nm or 1000 nm, with respect to a main surface of the substrate, generally relative to the upper surface of the substrate.

The n-type ZnO or ZnMgO substrate (81) may be, for example, in the form of a n-type ZnO or ZnMgO layer with a thickness of 100 nm to 100 μm, preferably 50 μm.

The substrate may also be in the form of a so-called "solid" substrate generally having a thickness greater than or equal to 100 μm, or even 500 μm, for example 500 μm.

This species having a high chemical affinity for residual extrinsic impurities such as lithium, called "getter species" can be chosen, either from the impurities theoretically donor, preferentially from column III of the periodic table of the elements, or from the impurities theoretically acceptor of ZnO or ZnMgO, preferentially from column I or V of the periodic table of elements.

For example, ionic multi-implantation (83) of the "getter" species such as phosphorus at energies of 700 keV, 300 keV and 80 keV can be carried out with a dose of l ^e 15 at / cm ² for each energy. . Preferably, the "getter" zone will be n-type conductive with a conductivity at least equal to that of the substrate before the purification step.

The "getter zone" (82) thus generally constitutes a layer, generally a thickness of 500 to 1000 nm, for example 500 nm or 1000 nm in depth, in the n-type ZnO or ZnMgO substrate, for example in the n-type ZnO or ZnMgO layer.

Step 2 (Figure 8B):

Diffusion annealing impurities at high temperature to form the possible chemical phase between impurities such as lithium and the species "getter" and / or exo-diffuse (84) impurities such as lithium and / or hydrogen to the surface of the "getter" area. The annealing that can be envisaged is, for example, annealing at 1100 ° C. under O2 flushing for 1 hour.

We thus obtain under the getter layer

(82) a purified n-type ZnO or ZnMgO substrate (81) over its entire thickness in which the impurities have been removed or reduced by the "getter" layer (82). At the level of the upper part of the "getter" layer (82), a surface layer (85), generally of a thickness of 10 to 100 nm, for example 100 nm, in ZnO or in ZnMgO of type n in which the impurities, generally lithium and hydrogen, are trapped and / or their concentrations are typically less than or equal to about 10 ¹³ to ¹⁴ cm.

Step 3 (Figure 8C):

P-type doping of the surface layer (85) of the zone (82) obtained in step 2 (in other words, introduction of a dopant species into the layer), for example by ion implantation (86) (ex-situ doping) of nitrogen at energies of 200 keV, 120 keV and 50 keV with the respective doses of 1 ^e 15 cm ^"2 , 8 ^e 14 cm ^{" 2} and 4 ^e 14 cm ^"2 .

Step 4 (Figure 8D):

In another variant of this embodiment, it is possible to add a step 2a consisting of removing, eliminating the "getter" layer of impurities such as lithium and hydrogen before step 3.

According to a second embodiment of the method according to the invention in a second variant, the p-type purification and doping of a ZnO or ZnMgO substrate is carried out, using a surface "gettering" technique.

FIG. 9 describes the different steps of this second embodiment of the method according to this second variant with a surface "gettering".

Step 1 (Figure 9A):

Formation of a p-type deep layer (92) in a substrate or layer (91) made of ZnO and / or ZnMgO as defined above. By "deep" layer is meant that this layer is made over a large thickness, for example greater than or equal to 500 nm, for example from 500 nm to 1000 nm, with respect to a main surface of the substrate, generally with respect to the upper surface of the substrate.

This layer may be made either by ion implantation (93) (ex-situ doping) of an acceptor element in the ZnO substrate and / or ZnMgO n-type. Preferably, it is an element of column V or I of the periodic table of elements. Or this layer can be made by in-situ doping, that is to say that is grown for example by "MOCVD" a layer of ZnO and / or ZnMgO by introducing potentially accepting dopants during growth .

A concrete example would be to perform a multi-implantation of nitrogen at energies of 200 keV, 120 keV and 50 keV with the respective doses of 1 ^e 15 cm ^"2 , 8 ^e 14 cm ^{" 2} and 4 ^e 14 cm ^"2 .

Step 2 (Figure 9B):

Healing annealing of defects in implantation and activation of the acceptors, for example at 900 ° C., for 15 minutes under a purge of oxygen, especially in the case where the acceptor is nitrogen.

Step 3 (Figure 9C):

A "getter" layer is formed in the deep p-type layer. The formation of this layer may be carried out for example by ion implantation (94) of a species that preferably has a high chemical affinity for residual extrinsic impurities such as lithium, called "getter species".

This species can be chosen either from the theoretically donor impurities for ZnO and / or ZnMgO, preferentially from column III of the periodic table of the elements, or from the theoretically accepting impurities of ZnO and / or ZnMgO, preferentially from column I or V of the periodic table of elements.

For example, it is possible to carry out a multi-ion implantation of phosphorus at energies of 700 keV, 300 keV and 80 keV with a dose of 1.10 ¹⁵ at / cm ² for each energy, or an aluminum implantation of energy equal to 80 keV with a dose of 1.10 ¹⁵ at / cm ² .

Preferably, and in the case of a "vertical" technology, the "getter" zone (95) will be n-type conductive with a conductivity at least equal to that of the initially non-implanted and non-annealed ZnO substrate.

The "getter zone" (95) generally constitutes a layer, generally of a thickness of 10 to 500 nm, preferably 100 to 500 nm, for example 100 nm or 500 nm, from the surface of the doped type layer. p.

Step 4 (Figure 9D): Diffusion annealing of the impurities is carried out for example at 1100 ° C. under O2 flushing for 1 hour in order to exo-diffuse residual extrinsic impurities such as lithium and / or hydrogen trapped on the flaws and possibly form a chemical phase. During this step, the impurities such as lithium and hydrogen present in the volume of ZnO and / or ZnMgO and in the ZnO and / or ZnMgO p-type zone migrate and are trapped in the "getter" zone. and / or exo-diffused towards the surface. The p-type doped zone is thus purified by elimination of its impurities such as lithium and hydrogen. Step 5 (not shown):

The "getter" zone may be removed, for example by gentle chemical mechanical polishing. In conclusion, the purification method implemented according to the present invention makes it possible to effectively purify a ZnO and / or ZnMgO material by decreasing the concentration of highly mobile extrinsic impurities such as lithium and hydrogen.

The main advantage of the process for preparing a ZnO and / or p-type doped ZnMgO substrate comprising at least one step of purifying a ZnO and / or ZnMgO n-type substrate implemented according to the invention , is the obtaining of ZnO and / or ZnMgO junctions by virtue of a p-type doping of ZnO material and / or ZnMgO. The method according to the invention ensures the control of this doping, that is to say its reproducibility and the obtaining of an intense electroluminescence signal in the UV.

The quality of p-type doping, demonstrated by high carrier densities and mobilities, is ensured by the significant reduction in the concentration of impurities such as lithium and hydrogen (preferentially donors in ZnO and / or ZnMgO). in the p-type region of commercial ZnO substrates and / or epitaxial or deposited layers of ZnO and / or ZnMgO on ZnO and / or ZnMgO substrates.

A device comprising a substrate and / or a thin or thick epitaxial layer at least partly doped p-type obtained by the method according to the invention both in its first embodiment (Figures 4A or 4B) that in its second embodiment, may be used in optoelectronics for the realization of pn junctions including the manufacture of light emitting diodes ("LED" or "LED" in English). These light-emitting diodes can be used, for example, for lighting with low energy consumption. REFERENCES

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[5] V.A. Perevoschikov and V.D. Skoupov, "Getterlng Defects In Semiconductors", Springer Berlin Heidelberg, p. 127 (2005).

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Claims

A method for purifying a n-type ZnO and / or ZnMgO substrate to reduce or eliminate residual extrinsic impurities from the substrate for pd doping at least a portion of the substrate, into which at least one zone of the substrate a reactive species having a high chemical affinity with at least one residual extrinsic impurity, and / or being capable of creating crystalline defects, said reactive species being P, and thus creating in the substrate at at least one so-called "getter zone" capable of trapping said residual extrinsic impurities and / or in which residual extrinsic impurities are trapped; then the substrate is annealed to diffuse residual extrinsic impurities to the "getter" zone, and / or out of the "getter" zone, preferably to at least one surface of the substrate.

2. The process according to claim 1, wherein the residual extrinsic impurities belong to the group consisting of metals and hydrogen.

3. The process according to claim 2, wherein said residual extrinsic impurities belong to the group consisting of lithium and hydrogen.

4. Method according to any one of the preceding claims, wherein the "getter" zone is n-type or p-conductive, or semi-insulating or insulating.

5. Method according to any one of the preceding claims, wherein the reactive species is (are) introduced into at least one area of the substrate by ion implantation, preferably by multi-implantation. ionic, hot or cold.

The method of any one of the preceding claims, wherein the area

"Getter" is in the form of a layer.

The method of any of the preceding claims, wherein the "getter" zone is created at a surface of the substrate.

A process for preparing a p-type doped ZnO and / or ZnMgO substrate comprising at least one step of purifying a ZnO and / or ZnMgO n-type substrate to reduce or eliminate the residual extrinsic impurities of the substrate for the p-type doping of at least a portion of the substrate, said purification step being carried out by a purification process, in which at least one reactive species having a high chemical affinity is introduced into at least one zone of the substrate with at least one residual extrinsic impurity, and / or being capable of to create crystalline defects, and thus creates in the substrate at least one so-called "getter" zone capable of trapping said residual extrinsic impurities and / or in which residual extrinsic impurities are trapped; then the substrate is annealed to diffuse residual extrinsic impurities to the "getter" zone, and / or out of the "getter" zone, preferably to at least one surface of the substrate.

9. The process according to claim 8, wherein the residual extrinsic impurities belong to the group consisting of metals and hydrogen.

The method of claim 9, wherein said residual extrinsic impurities belong to the group consisting of lithium and hydrogen.

11. Process according to any one of claims 8 to 10, in which the reactive species is (are) chosen from the reactive species donor and / or acceptor and the zone "getter" is conductive of the n or p type, or semi-insulating or insulating.

12. The method of claim 11, wherein the reactive species is (s) selected from the elements of columns I, III, or V of the periodic table of elements.

13. The method of claim 12, wherein the reactive species (s) is (are) selected from phosphorus and aluminum.

14. Process according to any one of claims 8 to 13, in which the reactive species or species is (are) introduced into at least one zone of the substrate by ion implantation, preferably by multi -Ithic implantation, hot or cold.

15. A method according to any one of claims 8 to 14, wherein the "getter" zone is in the form of a layer.

The method of any one of claims 8 to 15, wherein the "getter" zone is created at a surface of the substrate.

17. The method according to any one of claims 8 to 16, wherein the following successive steps are carried out:

b) the substrate is annealed to diffuse residual extrinsic impurities in the substrate beneath the getter layer to the getter layer; c) the layer is eventually removed

"Getter";

d) depositing, for example by epitaxy, on the "getter" layer or on the substrate from which has been removed the "getter" zone of ZnO and / or ZnMgO of n-type or p-type;

e) optionally, in the case where in step d) n-type ZnO and / or ZnMgO has been deposited, the p-type doping is carried out, for example by ion implantation or by diffusion, of ZnO and / or or n-type ZnMgO deposited;

f) a healing annealing of implantation defects, and activation of p-type dopants of ZnO and / or ZnMgO is optionally carried out.

18. A method according to any one of claims 8 to 16, wherein the following successive steps are carried out:

a) in a n-type ZnO and / or n-type ZnMgO substrate, from the upper surface of a substrate, a "deep getter" layer with a thickness greater than or equal to 500 nm is created;

b) the substrate is annealed so as to diffuse residual extrinsic impurities in the substrate under the "getter" layer to the "getter" layer, and on the other hand, to reduce the concentration of extrinsic impurities; residuals in the upper part of the getter layer, near its upper surface; c) at least one p-type dopant is introduced into the upper part of the "getter"layer;

19. A method according to any one of claims 8 to 16, wherein the following successive steps are carried out:

e) eventually, the layer is removed

"Getter".