KR100958137B1 - ??type ZnO semiconductor by ?? and column ? impurity codoping - Google Patents

Abstract

The present invention relates to a method of realizing a p-type semiconductor by simultaneously doping Li and Group impurities in ZnO, wherein the impurity complex in which Li and Group impurities are combined by co-doping Li and Group impurities in ZnO The technical characteristic of acceptor energy level lowered by pure Li accept energy level is lower than that of pure Li, which forms an extremely shallow acceptor impurity level in ZnO, resulting in a high p-type semiconductor. In particular, when F is used together with Li among the Group V impurities, the impurity level becomes the shallowest, thereby enabling the implementation of a good p-type ZnO semiconductor.

p-type semiconductor, ZnO, Li, F, co-doped

Description

Ｐ-type ZnO semiconductor by doping Li and group impurities at the same time {ｐ-type ZnO semiconductor by Li and column Ⅶ impurity codoping}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ZnO semiconductor using impurity doping, and in particular, when the concentration of acceptor type Li and donor type VIII is large, an impurity complex of Li-VIII-Li is stably formed to form a crevice Li. The present invention relates to a p-type ZnO semiconductor co-doped with Li and Group VII impurities that block the formation of the structure and can produce holes of sufficient concentration through the shallow accepting level of the Li-VII-Li structure.

Currently, research on ZnO, the next generation semiconductor material, is being actively conducted, and research is being conducted to use not only a blue light emitting LED but also various optical materials and electrical materials using this material.

However, while ZnO is easy to implement n-type conductivity, it is known that it is very difficult to implement p-type conductivity, it is difficult to apply as a variety of optical semiconductors.

Therefore, efforts have been made to dope various impurities in ZnO so that ZnO can be realized with p-type conductivity, but have not been successful (Computational Materials Science 30 , 337-348, Su-Huai Wei (2004)).

The reason why it is difficult to implement the p-type conductivity can be largely presented in three ways.

First, the concentration of acceptor impurity is low, second, the reception energy level of acceptor impurity is deep within the bandgap, so the efficiency of charge generation is low at the temperature at which the device operates, and third, the Fermi level is the valence band. As it approaches the band, it is easier to create donor defects, so fermiform defects such as oxygen vacancies (V (O)) or Zn-slit (Zn _int ) are formed and Fermi It is understood that p-type ZnO is difficult to implement due to the compensating effect that disturbs the change of energy.

Therefore, according to a conventional theoretical study for the implementation of p-type electrical conductivity of ZnO, the method of substituting group 1 elements in the Zn site, which is a group 2 element, and the method of substituting group 5 elements in the O group, which is a Group 6 element, Although it is proposed, studies through the theoretical calculation and measurement of the electrical structure of these impurities are known to produce deep levels between these impurity bands (PRB, 66 , 073202, CH Park, SB Zhang and Su-Huai). Wei (2002))

The reason why the impurity level in the ZnO added impurity is so large is that in semiconductors such as Si and GaAs, the impurity trajectory is strongly coupled with the Bloch wave function of solid and spreads widely. In contrast, ZnO is an oxide having a high degree of divalent ionization, and since the radius of the impurity electron orbit in the form of hydrogen atom orbit formed around the doping impurities is small because the dielectric constant is large, the electron orbit of the impurity made in the material does not spread widely. This is because the electronic structure of the impurity is not greatly affected by the level of molecular orbits formed between the impurity and neighboring atoms.

In more detail, when a group 1 element impurity of various impurities is injected into ZnO, the group 1 element impurity combines with an oxygen atom located in a neighborhood to form an sp molecule orbit around a household band (VBM). The energy levels of the impurity orbits formed by the hybrid bond between the group-s orbits and the O-2p orbitals are such that the s level of group 1 atoms is higher than the s level of group 2 Zn. Because the VBM is located higher than the electron level of the VBM formed by the bond orbit, the acceptor level caused by the group 1 impurities is deeply formed in the band gap (between VBM and CBM). .

In addition, when injecting a Group 5 impurity among the impurities in ZnO, the level made by the Group 5 impurity is higher than the oxygen atom O-p orbital level, the impurity level deepens between band gaps for the same reason as above.

The results of the research so far indicate that Group 1 impurity Li forms the shallowest impurity level (0.1 eV above VBM), and N impurity has the shallowest level (VBM above). 0.4-0.5 eV position).

However, until now, it has been known to fail to generate p-type conductivity by using Li, because two structures in which Li atom replaces Zn site (Li _Zn ) and in the interstitial site (Li _int ) coexist. to be.

That is, since Li in the gap serves as a dopant-type impurity, the two structures compensate each other, so that it is difficult to realize good p-type electric conductivity when using Li impurity.

Therefore, in order to implement p-type ZnO, a method of using N impurity which mainly substitutes O-position stably is attempted. However, in this case, the receiving level generated by N is generated between 0.4 eV-0.5 eV above the VBM, so that the receiving level is deep, and there is also a problem that the solubility of N impurities is low. In order to solve this problem, studies on codoping or cluster-doping methods using at least two impurities using donor-type impurities such as Ga and In that replace Zn sites, rather than doping with only N impurities, have been recently conducted. Is going on.

This is because the codoping or cluster-doping method firstly, the coulomb interaction between impurity atoms in the main and the receiving impurity codoping not only improves the solubility of the dopant, but also reduces the formation energy of the dopant, thereby improving the formation of the main doping defect. Secondly, it is suggested that the transition level of defects can be lowered through the interaction between donor state-acceptor state. (PRL, 90 , 256401-1 LG Wang and Alex Zunger (2003), IEEE, 81 Changjie Zhou and Junyoung Kang (2004), JKPS, 39 , S23 Eun-Cheol Lee YS Kim, KJ Chang (2001))

However, the facts so far revealed that the 2p orbit of N is located between the bandgap of about 0.5eV, and despite the codoping, it is difficult to make the shallow level because the hybrid bond with the group III orbit is not strong enough. It is known.

In general, VBM is mainly composed of p-orbits of anions, and since Group 5 p-orbits directly intervene in the impurity levels, Group 5 creates a deeper level than Group 1, whereas Li is the shallowest impurity level in Group 1 impurities. 0.1 eV), and this impurity level of Li is formed to be much shallower than the level made by Group 5 impurity N, which is widely used now.

On the other hand, the problem of using Li impurity is that it is difficult to realize good p-type conductivity due to the formation of interstitial Li as described above, and that the receiving level of Li is formed near 0.1 eV above VBM, so that the shallow receiving level is lower than that of N. Although it is formed, it is still deeper than the receiving level that can be formed in other semiconductors, and there is a problem in that the discharge efficiency of the hole concentration is not large when the ZnO element is driven at room temperature.

It can be understood from the figure of FIG. 3- (b) that the level of Li is deep. The impurity level in the solid is determined by the interaction between the orbits of the impurity atoms and the neighboring atoms. According to the theory of quantum mechanics, the stronger the orbit hybrid, the lower the low energy orbital level and the higher the orbital level. And when the two orbital energies are closer, the effect of hybrid bonding is known to be greater. When the Li atom is substituted at the Zn site, the Li orbit forms a hybrid level with the O orbit, where the s-form orbit of Li is higher than the Zn-s orbit and is higher than the VBM level formed by the hybrid bond between Zn-O. Therefore, since the hybrid bond between Li impurity and O is smaller than the hybrid bond between Zn-O, the energy of the Li-O-bonded hybrid orbit located at a lower position is higher than the energy of the hybrid orbit between Zn-O. Because of this, the receiving level produced by Li impurity is known to be located at 0.1 eV above VBM (PRB, 66 , 073202, CH Park, SB Zhang and Su-Huai Wei (2002)).

In order to solve the above problems, the present invention is intended to implement a high quality p-type ZnO semiconductor by lowering the receiving level of Li and suppressing the formation of the interstitial Li, which is a major defect. In order to lower the reception level of Li, the 2p orbit and the Li-s orbit of oxygen adjacent to Li are to enhance the hybrid bond. In addition, it is intended to increase the stability of the receiving type Li that substitutes the Zn-site compared to the interstitial Li.

In order to achieve the above object, the present invention provides a technique for simultaneously implanting both Li and Group impurities in which ZnO, which is a group II-IV semiconductor, is co-doped with a dopant-type impurity Li and a donor group Group impurities. It features.

First, when Li and the Group VIII impurities coexist, when Li, the Group 1 element, replaces Zn, which is a Group III element, the Li becomes negative, and when the Group impurities replace O, the Group 6 element. A positive charge is generated. At this time, a strong Coulomb interaction between two impurities is applied, and the two impurities are bonded at neighboring atomic sites, resulting in a very stable Li-Ⅶ impurity complex. Secondly, when Li and the Group VIII impurities closely bond, a strong ionic bond is formed between the Group VII impurity element and the Group I impurity Li. Due to this, the Li periphery has a sp-shaped trajectory, and as shown schematically in Fig. 3- (b), the Li-s energy level around the conduction band minimum (CBM) is lowered, thereby allowing Li and The covalent bond between 2p orbits of neighboring O atoms is strengthened, and the electron orbital energy level of the Li-O orbit, which is mainly composed of O-2p orbits adjacent to Li, is lowered closer to VBM, and the extremely shallow receive level is achieved. Can be formed.

Accordingly, the present invention aims to realize a high quality p-type ZnO peninsula which is simultaneously doped with Li and Group III impurities by suppressing the formation of a shallow accept-type impurity level and at the same time suppressing the formation of Li- Li-Li and the interstitial Li _int . .

Herein, the concentration of the accept-type Li in the impurity is preferably higher than the concentration of the main donor group VIII impurity.

Here, it is preferable that the ratio between the receiving-type impurity Li and the concentration of the donor group VIII impurities is 2: 1.

Here, it is preferable that the said Group VIII impurity is element F.

In the present invention according to the above configuration, when Li is present alone, a shallow level is already formed at 0.1 eV above VBM. Li-O is influenced by co-doping through co-doping using Li impurities and group impurities. The level becomes shallower.

In addition, in the present invention, when the Li atom and the Group VIII impurities replace the Zn and O atoms, respectively, they become anions and cations, respectively, to form a Li- Li-Li impurity complex with the coulomb attraction interaction between the two impurities. For this reason, the bonding energy is increased for the formation of the composite, and at the same time, the formation of the interstitial impurity structure of Li can be blocked.

Therefore, simultaneous doping of Li and Group III impurities enables good p-type conductivity of ZnO.

In contrast to the combination of impurity electrons with delocalized solid orbitals in a common covalent semiconductor, ZnO is a high ionic material, so the addition of an impurity Molecular orbits are formed in which the orbitals of the contact ion atoms are confined only around the impurities.

In other words, the electron energy characteristics of the molecular orbital act ineffectively in the material, which makes it difficult to form shallow energy level when doping ZnO, and the electronic structure of ZnO is O-2p electron orbit and Zn-4s. Electrical properties are determined by hybridization of electron orbits.

Typically, a valence band and a conduction band are achieved by various hybridizations of the two orbits. The electron orbit of the Valace Band Maximum (hereinafter referred to as VBM) is mainly composed of 2p orbitals of oxygen atoms, and the energy of VBM is almost determined by the electron energy of O-2p, and the Conduction Band Minimim (hereinafter referred to as CBM). Since is mainly composed of Zn-4s orbits, CBM energy is determined by Zn-s electron energy.

In addition, shallow n-type doping has to be made for the n-type doping with high conductivity, and impurity levels must be higher than Zn-s electron energy, and high p-type conductivity is required to achieve high conductivity. It is also desired that the type impurity level be lower than the op electron energy.

If these conditions are met, the charges will flow at the end of the band made by the main material, while electron charges will flow freely in the CBM and electrons will flow freely in the VBM.

On the other hand, if CBM does not have free fluidity, and if VBM does not have free charge, the impurity level creates a deep level and acts as a trap center, hindering the flow of charge. Will interfere with the implementation of the p-type conductivity.

Accordingly, in order to realize p-type electrical conductivity of ZnO, Zn sites are substituted with Group 1 impurities, or O sites with Group 5 impurities, so that these impurities serve as acceptable impurities for electrical equilibrium. However, when the level of these impurities is doped in ZnO, deeply formed between the band gaps, it is difficult to implement a p-type semiconductor.

In particular, the atomic orbits of group 5 impurities are higher than the electron energy of the O-2p orbitals.In the case of N group 5 impurities, the 2p electron energy of N is close to the electron energy of the O-2p orbit, but the energy level is still deep within the band gap. Form the level in which it is located.

Recent studies have attempted to reduce the electron energy levels of N by combining group III impurities and N-type impurities, N, to reduce the level of p-type doping and prevent the formation of n-type defects. However, according to conventional calculations, the energy level of N's 2p orbit is known to be deeply located between the band gaps by 0.5 eV (PRB, 66, 073202, CH Park, SB Zhang and Su-Huai Wei (2002). ))

On the other hand, in the case of the group 1 impurities, the s orbital electrons of the impurities form an impurity level that hybridizes with the O-2p electron orbit, and in particular, in the case of Li, the impurity level is similar to the VBM of O-2p, which is about 0.09 eV. It is possible to make a low energy level of, but the problem of Li is that the substitutional structure and the niche structure have similar energy levels, so the two types of structures appear together, so that the electrical properties are mutually compensated, and thus they do not function properly as impurities. .

Therefore, in order to implement p-type ZnO, a method of using N impurity which mainly substitutes O-position stably is attempted. Also, a method of codoping which injects group III impurities simultaneously to change the deep state of N to a shallow state has been studied.

1 is a schematic diagram of an electron energy structure of an N-Ga-N impurity composite when Ga and N are co-doped with ZnO according to the related art (hereinafter, referred to as codoping). Here, codping means changing the energy level by adding one donor and two acceptors to a material to be made into a semiconductor in one reference unit, and may be referred to as co-doping.

As shown in (a) of FIG. 1, according to a codoping technique used for existing Ga and N impurities, a donor: Ga _Zn is formed by replacing Ga at _Zn , and an acceptor: N _O is substituted for N at _O. When the codoping is formed, the transition level of the energy level of acceptor: Ga + N, which is an N-Ga-N impurity complex, is shallower than the level formed when only one N is doped due to the interaction between Ga's main level and N's receiving level. It has been suggested that you can lose.

However, until now, as shown in (b) of FIG. 1, it has been known that hybrid cohesion with the Group III trajectory is not strong enough in codoping, causing difficulty in making shallow levels. In addition, according to the energy calculation using other pseudo-potentials, it is known that Ga-N due to codoping is actually located deeper in the bandgap than N-doped Zn-N level. In addition, the repulsive force due to the hybrid bonds received by the p-orbital level of O which does not bind to impurities is not great, and the Coulomb potential formed between the impurity complexes produced during codoping may increase the ionization energy of the charge. (PRB, 74, 081201-1 (R), Jinbo Li, Su-Huai Wei, Shu-shen Li Kian-Bai Xia (2006))

Figure 2 is a schematic diagram of the atomic structure of the added Li-F-Li composite formed when co-doping Li and F in group II-IV ZnO according to the present invention.

As shown in FIG. 2, the present invention is formed by a codoping method of Group 1 accepting impurities Li, and Zhuge Group 7 impurities F, which are known to form shallower receiving levels than N-, When codoping at a ratio of 2: 1, it is expected that the Li-F-Li impurity complex structure is easily formed at a high concentration by the strong electrostatic bonding of Li-2 and F.

In addition, these impurities have a covalent bond between Li-1 and F, which is adjacent to Li-1 and F, and Li-2 and F, thereby lowering the electron energy level of the hybrid bond of Li-O. It is expected that shallow receive levels will be formed at the point.

FIG. 3 is a schematic diagram of an electronic structure formed between Li-O of a Li-F-Li impurity composite formed by simultaneously injecting F of Li and Group VIII impurities into Group II-IV ZnO according to the present invention.

In FIG. 3 (a), blue is a schematic diagram explaining alternative type Li in place of Zn. Red is Zn, green represents oxygen and blue represents Li atom. In FIG. 3A, blue is a schematic diagram of the atomic structure of the interstitial Li, red is Zn, and green is oxygen. With this difference in structure, the interstitial Li does not bond with the surrounding atoms, and the electron energy of the Li-s orbit is positioned high as illustrated in (b) of FIG. 3 to emit electrons to the CBM. In addition, the Ta-type Li replaces the Group II atom Zn and bonds with the surrounding O-atoms, resulting in a lack of electrons, which is caused by the Li-O hybrid orbit near VBM as illustrated in FIG. Levels are formed.

It can be understood from the figure of FIG. 3- (b) that the level of Li is deep. The impurity level in the solid is determined by the interaction between the orbits of the impurity atoms and the neighboring atoms. According to the theory of quantum mechanics, the more orbital hybrid bonds, the lower the energy low orbital level, the higher the orbital level becomes higher. And when the two orbital energies are closer, the effect of hybrid bonding is known to be greater. When the Li atom is substituted at the Zn site, the Li orbit forms a hybrid level with the O orbit, where the s-form orbit of Li is higher than the Zn-s orbit and is higher than the VBM level formed by the hybrid bond between Zn-O. Therefore, since the hybrid bond between Li impurity and O is smaller than the hybrid bond between Zn-O, the energy of the Li-O-bonded hybrid orbit located at a lower position is higher than the energy of the hybrid orbit between Zn-O. Because of this, the receiving level produced by Li impurity is known to be located at 0.1 eV above VBM (PRB, 66 , 073202, CH Park, SB Zhang and Su-Huai Wei (2002)).

First, when Li and the Group VIII impurities coexist, when Li, the Group 1 element, replaces Zn, which is a Group II element, the Li becomes negative, and when the Group I impurities replace O, which is a Group 6 element. A positive charge is generated. At this time, a strong Coulomb interaction between two impurities is applied, and the two impurities are bonded at neighboring atomic sites, resulting in a very stable Li-Ⅶ impurity complex. Secondly, when Li and the Group III impurity are closely coupled, a strong ionic bond is formed between the Group I impurity element and the Group I impurity Li. Because of this, the Li trajectory is sp Formed orbits are formed, and as shown schematically in Figure 3- (b), the Li-s energy level around the conduction band minimum (CBM) is lowered, which results in a 2p orbital of Li and its neighboring O atoms. As the covalent bond between the two is enhanced, the electron orbital level of the receiving orbit of the Li-O orbit, which is mainly composed of O-2p orbits adjacent to Li, is lowered closer to VBM, thereby forming a very shallow receiving level.

(Calculation method)

The Vienna Ab-initio Simulation Package (VASP) was used to study the electronic structure of impurities in ZnO. Calculation of the binding structure of the impurity complex in the 36-atomic supercell was carried out. For the pseudo potential, the Perdew-Burke-Ernzerhof (PBE) exchange correlation function and the Projector Augmented Wave (PAW) method of the Generalized Gradient Approximation (GGA) method Was used.

Here, the Zn-3d orbit represents the semicore level, and when LDA calculation is performed, the Zn-3d orbit is located near -4.85eV below VBM, and the experimental value is located at -8.6eV and -7.5eV below VBM to calculate LDA. There is a significant difference between the values and the experimental values.

This is because the Zn-3d orbit is a confined orbit, so the Coulomb repulsive interaction is strongly active in the LDA calculation.

In the present invention, the LDA + U method was selected for more accurate calculation than the level of LDA calculation.

If U = 10eV in the 3d orbit of Zn, it is located at -8.1eV below VBM and is almost identical to the experimental value.

The electronic structure and density of electronic state of the wurtzite structure ZnO calculated by this method are shown in Figure 4.

The bandgap in this calculation was estimated to be low as 0.776 eV without considering the variable U, and about 1.876 eV when considering U = 10.

We considered a supercell with a 3c tetragonal wurtzite structure, and the calculated lattice constant of c = 4.62Å, bulk modulus of 148.588 Mbar, U = 0, the formation energy of ZnO is 3.56 eV, Matches. Structural parameters of all supercells used optimal values obtained by minimizing total energy and quantum mechanical forces.

In this calculation method, F among Li and Group VII elements in ZnO was selected to calculate the electron energy level of the Li-F-Li impurity composite.

Here, the hybrid bond between Li-O where Li replaced with O in the place of Zn is weakly bonded compared to the hybrid bond between Zn-O, and the position of the receiving level (Li-O) by Li is different from that of previous studies. Similarly, VBM was found to be about 0.1 eV.

In addition, a detailed calculation was performed on the F impurity in Group III impurities, and the electron orbits of F were combined to calculate the electron energy level of the electron orbit of the Li-F-Li impurity composite by Li and F. It was determined to be 0.006 eV below VBM below the level (0.1 eV above VBM), and it was found that the received level was formed. The reason for this is as described above, in which the ionic bond between Li and F has a sp2 characteristic of neighboring Li, and the energy is low compared to the sp3 orbit, and thus a low energy O-2p orbit and a stronger hybridity. A bond is formed, which lowers the energy level of the Li-O.

In addition, the formation energy of each impurity and impurity complex was studied to determine whether interstitial Li formation could be blocked when doping Li and group VII impurities simultaneously. For this purpose, F was selected from the impurities and detailed calculations were performed.

First, calculate the binding energy required for the bond between Li and F and convert the formation energy of the complex into Li _int. Compared with the formation energy.

The binding energy of the impurity composite is defined as follows.

E _b = {E _tot (Li _Zn + F _O ) + E _tot (ZnO)}-{E _tot (Li _Zn ) + E _tot (F _O )} --------------- (Equation 1)

E _tot is the total energy calculated from the exact same supercell and electrically neutral charge state, and when the binding energy E _b is negative, the impurity complexes of the same cell are more stable.

The binding energy between Li _Zn -F _O was calculated as -0.23eV as an exothermic reaction, which is a strong coulomb between Li _Zn ^-- F _O ⁺ when forming an electrically neutral Li _Zn ^-- F _O ⁺ impurity complex. It can be understood to be by manpower.

In addition, the impurity complex Li-F-Li shows that the total energy can be made very stable. In order to calculate the binding energy of the two, Li (-) + Li-F (0) + Considering the reaction ΔE → Li-F-Li (−), the binding energy is calculated to be −0.44 eV.

Formation enthalpy of defects or impurities in solids was calculated using the following equation.

ΔH (α, ｑ) = E (α, ｑ) + Σ _i n _i μ _i + _ｑ E _F , ------------------------- -(Equation 2)

For impurity A in ZnO

ΔE (α, ｑ)

= E (α, ｑ)-E (ZnO) + n _Zn E (Zn) + n _O E (O) + Σ _A n _A E (A) + qE _VBM ----- (Eq 3)

Here, E _F is the reference point of the VBM of ZnO, and μ _i means the chemical potential of the compound obtained from the gas or solid state. n represents the number of defects A, Zn, O, etc., and q represents the number of electrons that can be moved from the reservoir when the defect cell is formed.

In the present invention, when the Fermi level is located at the center of the bandgap, Li is less than Li in the crevice structure under the condition that F is sufficiently supplied under F-rich conditions through calculation of formation energy to be described later with reference to FIG. 4. It was calculated that the -F composite was more stable by -1.14613 eV.

Since the Li-F impurity complex is electrically neutral, its formation energy (formation Enthalphy) is not related to the change of Fermi level.

As mentioned above, it is known that ZnO is difficult to be doped into p-type due to the compensation effect of ZnO-type Li _int generation due to the substitution of Li-type _Zn in the Zn site (Li _Zn ). .

When F in ZnO substitutes for the O-position, Li is replaced by Zn, which is located next to F, to show that it can be more stable than that located in the niche Li (Li _int ). Was studied.

Li _int + F + ΔE → Li-F ---------------------------------------- (Equation 4)

E (Li-F) ^O + μ _Zn = {E (Li _int ⁺ ) + E (F ⁺ )} + 2E _fermi + ΔE --------------- (Equation 5)

At this time, if ΔE is large, it means that the energy of Li-F is higher than the energy of covalent impurity F and Li _int coexisting, which means that the formation of Li-F complex becomes difficult.

And as E _fermi gets closer to VBM, E _fermi becomes smaller, so that ΔE becomes larger and Li _int is easily formed.

In Equation 5, μ _Zn implies that Zn is released to Zn-reservoir when Li _int replaces the Zn site.

For this reason, as the crystal growth condition approaches Zn-poor (O-rich) to Zn-rich condition, μ _Z becomes high, and therefore ΔE increases, making Li-F difficult to produce.

E _fermi is located at VBM and Zn-poor (O-rich) is calculated as ΔE as ΔE = -0.16 eV, indicating that Li-F formation is more stable than Li _int + F formation.

On the other hand, under the Zn-rich condition, ΔE was calculated to be 4.25 eV in the above equation, which shows that the Li-F formation is relatively difficult compared to the Li _int formation, and thus the Zn-poor condition is advantageous to form the Li-F composite structure. Can be.

Therefore, Li-F shows that it can be formed well under Zn-poor (O-rich) conditions, and under these conditions, formation of donor defects such as O-vacancy or Zn-interstitial formation is suppressed. It can be seen that.

Earlier, we found that Li-F structure can be more stable than Li _int + F formation under Zn-poor (O-rich) condition when alternative F is present, and that O-vacancy or Zn _int formation is suppressed. I could see that.

Here, in the presence of Li-F (Li _int The stability of Li-F-Li formation to + Li-F) structure formation was compared by calculating the following energy values.

A = E ((Li-F-Li)) + E (ZnO: pure) + μ _Zn -E _fermi ------------------- (Equation 6)

B = E (Li _i ⁺ ) + E ((Li-F) ^O ) + E _fermi ------------------------------- (Equation 7)

D = A-B

D = {E ((Li-F-Li)) + E (ZnO: pure) + μ _Zn }-{E (Li _i ⁺ ) + E ((Li-F) ^O )}-2E _fermi

                                                                 -(Eq. 8)

If D <0, that is, the energy of formation of A <B, (Li-F-Li) is low, which means that Li-F-Li formation is more stable than Li _int formation, and if D> 0, Li _int It means that the formation is more stable.

As a result, when E _fermi = VBM, it was found that D = 0.373eV becomes negative under Zn-poor condition.

Therefore, ZnO with p-type conductivity with shallow accepting level can be made by crystal growth under Zn-poor conditions.

Figure 4 is a graph of the energy formation of the Li-F-Li impurity composite in the group II-IV ZnO according to the present invention calculated by the first principle electronic structure and total energy calculation method.

This form of energy was calculated using the equation (1), each of the case of using the Li ₂ O ₃ as ZnF _2, Li source as O _2, F source as an O source under the O-rich conditions in (a) of Fig. 4 The formation energy of impurities and complexes was calculated.

FIG. 3 (a) compares the formation energy of the Zn-substituted Li structure [FIG. 3 (a)] and the crevice Li [FIG. 3 (a '')] under O-rich conditions. The chemical potential of each atom was calculated using O ₂ gas and Li ₂ O ₃ as Li source under O-rich conditions.

In FIG. 4B, chemical potentials of F, O, and Li were calculated using Zn ₂ F as a source under F-rich conditions at the same time.

In the case of (a) of FIG. 4, Zn-rich conditions were used to compare the formation energy of the receiving type Li with that of the donor type gap Li. Under these conditions, the substitution of the Zn site becomes difficult, indicating that the interstitial Li is much more stable than the alternative, so that the Fermi level cannot be lowered below the center of the bandgap.

On the other hand, when calculated under O-rich conditions, when doping using only Li as a hole, when the Fermi level goes down to VBM, that is, when the hole concentration is very high, the formation energy of the alternative receiving type Li increases, resulting in the formation of the main type Li _int ^+. It still shows how easy it can be.

4B, however, when F coexists, the formation energy of the receiving Li-F-Li ⁻ is lower than that of Li _int ⁺ until the Fermi level is located at VBM. In other words, the formation of the receiving type Li shows that the formation energy near F is sufficiently low, indicating that the formation of the alternative type Li may be easier than the formation of the main type Li _int ⁺ . In other words, the formation of ZnO: Li, F under O-rich conditions due to the coexistence of F shows easy formation of alternative Li-F-Li, thus enabling the implementation of good quality p-type ZnO.

In order to consider various cases, the case of injecting F at a higher concentration by increasing the chemical potential of F was considered.

4 (c) shows that Li-F-Li becomes more energy stable than the crevice Li when co-ping Li-F-Li in ZnO under F-rich and O-rich conditions. In this case, it is possible to implement a p-type ZnO semiconductor simultaneously doped with Li and Group III impurities. In this case, it is assumed that ZnF ₂ is used as the Zn source and LiF is used as the Li source.

However, under the Zn-rich condition, even when using the F-rich condition, as shown in (d) of FIG. 4, when the Fermi level (E _fermi ) is lowered to 0.23 eV below the VBM, that is, when the hole concentration is high, the gap shape is formed. It shows that the formation of Li is not blocked. However, when F is absent, as compared with [case (a) of FIG. 4], it can be shown that the concentration of the hole charge can be increased to some degree. Shows this is possible.

In conclusion, when co-ping Li-F-Li in ZnO and growing under O-rich condition, Li _Zn formation becomes stable around F, and Li _int ⁺ (gap type Li) is suppressed, which simultaneously causes impurities of Li and F Doping indicates that a p-type ZnO semiconductor implementation is possible. 4 (c) shows that LF-Li impurities are much more stable than crevice Li under extreme conditions of O-rich and F-rich. Since the Coulomb's interaction between Li and F mainly affects the formation of the impurity complex, the Li- 을 -Li complex can be easily produced even with other Group III impurities.

FIG. 5 shows Li-F complexes when Li is in the II-IV group ZnO according to the present invention [FIG. 5- (2)] and when the Li-F complex is in the F neighborhood [FIG. 5- (3)] In the case of the F-Li impurity composite [Fig. 5- (4)], the electron energy state density showing the electronic structure was compared with that of pure ZnO [Fig. 5- (1)].

 As shown in FIG. 5, it was found that the receiving state is closer to VBM when Li is combined with F than when Li is alone. As shown in (3) of FIG. 5, the electronic structure of the Li-F impurity composite, in which Li and F are bonded, shows that the impurity level is very close to VBM so that the Li-F complex level is located at 0.008 eV directly above VBM. have.

The electronic structure was calculated for the Li-F-Li impurity composite structure in which two Li bonds around F in ZnO, and found that the impurity composite level is slightly higher than that of Li-F, but is still located at 0.006 eV directly above VBM. .

 FIG. 6 shows a comparison of the energy levels of O-p around impurities and the orbital energy of O located far from impurities.

As shown in Fig. 6- (2), when Li alone is present, a neighboring oxygen (Nearest) of oxygen adjacent to Li exists near VBM, which is created by the interaction between the Li-s orbit and the Op orbit. The orbital electron energy level is shown to be higher than the VBM level created by the interaction between the non-neighboring oxygen's Zn-s orbits.

6 (3) and (4) show that in the case of Li-F composite and Li-F-Li impurity composite, the electron orbital energy of Li proximity O is very large in VBM compared with Li _Zn (alternative Li). Shows you near. That is, when Li is placed in the F root, it can produce a shallow acceptor level close to VBM.

Summarizing the above results, in the case of doping using only Li-impurity in pure ZnO, the gap formation is sufficient to compensate for the electrical properties of Zn-site-substituted Li, so that ZnO becomes a p-type semiconductor. Making is known to interfere. However, in the present invention, as a result of studying a method of codoping F and Li among Group III impurities, when forming co-ping of Li and F, it becomes easy to form an impurity complex of Li-F-Li, and thus has a crevice type Li structure. It has been shown that the formation of can block to create holes of sufficient concentration.

In addition, not only the solubility of Li can be increased by codoping two Li and one F in ZnO, but also when Li is placed in the vicinity of F in the presence of F, that is, an impurity complex is formed, Relatively shallow formations just above the VBM have been shown to be possible.

These results show that Li-F-Li impurity complexes can be easily formed when co-ping Li and F in a ratio of 2: 1 to make ZnO a good p-type semiconductor.

The same applies to the other impurity, such as Cl and Br, as well as the F impurity used as the group impurity, so that Coulomb interaction can be expected to occur between the receiving impurity Li and the main impurity group impurity. have.

As a result, a Li-Ⅶ-Li impurity complex is formed, and since the complex is stabilized by Coulomb interaction, formation of a crevice Li (Li _int ) is suppressed, and also a receiving Li level and a donor type impurity level are suppressed. The interaction between the orbits acts to lower the energy level, where element F is preferred as an impurity. However, even when using other X-type impurities such as Cl or Br, they are placed in the neighborhood of this group impurity of Li. In fact, the first principle calculation shows that the receiving level of Li-Cl-Li impurity is 0.08 eV above VBM, and Li It was found that the receiving level of -Br-Li impurity was located at 0.12 eV.

That is, Li-Ⅶ-Li impurity complexes (where F is Cl, Br) generally form shallow accepting levels, but among them, Li-F-Li impurity complexes were found to form the ideally shallow accepting levels.

1-Schematic diagram of the electron energy structure of an N-Ga-N impurity composite when Ga and N are co-doped with ZnO according to the prior art.

2-Schematic diagram of the atomic structure of the added Li-F-Li composite formed when co-doping Li and F in Group II-IV ZnO according to the present invention.

3-Schematic diagram of the electronic structure of the Li-F-Li impurity composite formed when Li and F are simultaneously injected into Group II-IV ZnO according to the present invention.

Figure 4-Graph of the formation energy of Li-F-Li impurity composite in Group II-IV ZnO according to the present invention calculated by the first principle electronic structure and total energy calculation method.

5-Graph of electron energy state density showing electronic structure of Li-F-Li impurity composite formed upon co-doping of Li and F in Group II-IV ZnO according to the present invention.

FIG. 6 is a graph comparing the electron energy state density of Li-F-Li surrounding O atoms formed in ZnO: Li, F and the electron energy state density of O atoms away from impurities.

Claims (4)

ZnO, which is a group II-IV semiconductor, is co-doped with acceptor-type impurity Li having a lower energy than the O-2p orbit and the donor-type Group-III impurity forming a hole charge orbit, thereby injecting the acceptor-type impurities Li and VII. A p-type ZnO semiconductor simultaneously doped with Li and Group VIII impurities. The p-type ZnO semiconductor of claim 1, wherein the concentration of the impurity Li is relatively higher than that of the Group I impurity. The method according to claim 1 or 2, A p-type ZnO semiconductor co-doped with Li and Group VII impurities, wherein the concentration of the impurities Li and Group VIII impurities is 2: 1. The method of claim 3, wherein the Group VIII impurities are A p-type ZnO semiconductor co-doped with Li and Group VIII impurities, which is element F.

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