JP2001226200A - LOW RESISTANCE p-TYPE SINGLE CRYSTAL ZnS AND ITS PRODUCING METHOD - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low resistance p-type single crystal of ZnS (zinc sulfide) for a light emitting element. SOLUTION: A p-type ZnS single crystal thin film contains a p-type dopant composed of at least one element selected from Li, Na and N, an n-type dopant composed of at least one element selected from b, Al, Ga, In and Cl and at least one element selected from Ag and Cu. When the ZnS single crystal is formed, at least one of Ag and Cu is doped and, at the same time, the n-type dopant and p-type dopant are doped in such a manner that the concentration of the p-type dopant is higher than that of the n-type dopant.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a low-resistance p-type single crystal ZnS (zinc sulfide) for a light emitting device and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, low resistance n-type ZnS (zinc sulfide) can be easily prepared by doping technology of B (boron), Al (aluminum), Ga (gallium), In (indium), or Cl (chlorine) element. And many reports have been made.

However, the Journal of the Japan Society of Applied Physics (Hiroyuki Okuyama, Akira Ishibashi, "Present and Future of ZnSe-Based Light-Emitting Devices", Applied Physics, Vol. 65, No. 7, 687-696, 1996,
P. 690, Table 1), for p-type ZnS (zinc sulfide), there is only a report on those having high resistance due to doping using Li (lithium).

The present inventors have previously reported a method for reducing the resistance of ZnS (S. Iida et al. Jpn. J. Appl. Phys., V
ol. 28, 1989, L535, S. Iida et al. J. Crys. Growth, vol. 1
According to this method, N is added to increase the amount of Zn and facilitate the escape of S, but this method is not practical because of its limited solubility.

On the other hand, in order to obtain luminescence characteristics in ZnS, conventionally, Cu (copper), Ag (silver),
Au (gold) has been added (“Optical Properties Handbook”, pp. 524 to 525, Asakura Shoten Co., Ltd.). These are called activators (emission centers). At this time,
A donor called a coactivator is added to change the emission color to blue, green, and red. Conventionally, as this donor, A
l (aluminum), Cl (chlorine), Br (bromine), I
(Iodine) has been widely used. However, these are all n-type conductivity types. As mentioned above,
As for ZnS (zinc sulfide) which also has light emission characteristics, there is no report on low-resistance p-type single crystal ZnS (zinc sulfide).

[0006]

As a single crystal thin film of ZnS (zinc sulfide), a p-type single crystal ZnS (zinc sulfide) having a low resistivity to which a luminous substance is added can be synthesized. (Aluminum), Ga (gallium), I
Low-resistance n-type Z already realized by impurity doping using n (indium) or Cl (chlorine)
By combining with nS (zinc sulfide), a pn junction can be realized in the same semiconductor compound.

[0007] This pn junction is called a homojunction, and enables high quality and low cost in the production of semiconductor devices such as light emitting diodes, semiconductor lasers, and thin film solar cells. As an example, an ultraviolet semiconductor laser diode required for high-density recording and transmission of
(Zinc sulfide).

Although p-type ZnS (zinc sulfide) can be made of high resistance, the growth of a low-resistance and p-type ZnS (zinc sulfide) single crystal thin film has a self-compensation effect and a p-type dopant. Was not possible due to the small solubility of further,
It has been difficult to grow a p-type ZnS (zinc sulfide) single crystal thin film having light emission characteristics due to impurity doping.

[0009]

Means for Solving the Problems Accordingly, the present inventors have:
In order to realize light emission characteristics, Ag, which is an Ib group element,
A new doping method for doping at least one element of Cu and stabilizing by incorporating a p-type dopant into ZnS (zinc sulfide) has been developed, and has successfully solved the above-mentioned problems.

That is, the present invention relates to a p-type dopant comprising at least one of Li, Na and N, and B, A
It contains an n-type dopant composed of at least one of l, Ga, and In and at least one of Ag and Cu, which are Group Ib elements, has a resistivity smaller than 0.08 Ω · cm, and has a hole concentration of less than 0.08 Ω · cm. Is 5.6 × 10 ¹⁸ / cm ³ or more, a low-resistance p-type single crystal ZnS (zinc sulfide).

Further, the present invention provides a p-type dopant comprising at least one of Li, Na and N, an n-type dopant comprising Cl and at least one element of Ag and Cu, and Low resistance p-type single crystal ZnS (zinc sulfide), characterized by having a hole density of less than 0.60 Ω · cm and a hole concentration of 1.4 × 10 ¹⁷ / cm ³ or more.
(Claim 2).

Further, according to the present invention, the concentration ratio between the contained p-type dopant and the n-type dopant is from 1.3: 1 to 1: 1.
The low-resistance p-type single crystal ZnS (zinc sulfide) according to claim 1 or 2, wherein the ratio is 0: 1 (claim 3). In order to be p-type, it is necessary that p-type concentration> n-type concentration.
₂ , Zn ₃ N _{2 and the} like are deposited. Preferably, the concentration ratio between the p-type dopant and the n-type dopant is from 1.3: 1 to 4: 1, more preferably 2: 1.

Further, according to the present invention, the content of at least one element of Ag and Cu is at least 1 × 10 ¹⁴ / cm ^{3 in} atomic concentration. It is a low-resistance p-type single crystal ZnS (zinc sulfide).

Further, according to the present invention, when forming a single crystal of ZnS (zinc sulfide), at least one of Ag and Cu is doped, and an n-type dopant and a p-type dopant are doped with a p-type dopant concentration. Is a method for producing a low-resistance p-type single crystal ZnS (zinc sulfide) according to any one of claims 1 to 4, wherein the doping is performed so as to be higher than an n-type dopant concentration. ).

The p-type single crystal ZnS (zinc sulfide) thin film of the present invention is produced by MOCVD (Metal Organic Chemical Vapor Deposition).
por Deposition) method, VPE (Vapor Phase Epitaxy)
Method and MBE (Molecular Bea
At least one of p-type and n-type dopants in the form of atoms and Ag and Cu, which are Group Ib elements, is doped using a method such as m epitaxy).

According to this method, the n-type dopant and the p-type dopant
By doping with a p-type dopant, an increase in electrostatic energy due to Coulomb repulsion between p-type dopants can be suppressed, and energy gain can be generated by Coulomb attraction between n-type and p-type dopants.

By incorporating the p-type dopant by the effect of the electrostatic interaction gain, the p-type dopant can be further stabilized, and the p-type dopant can be stably doped to a high concentration. When doping the n-type dopant and the p-type dopant, the doping may be performed with different doping times, but it is preferable to dope simultaneously.

Further, by doping an n-type dopant and a p-type dopant into a ZnS (zinc sulfide) single crystal, a pair of an n-type dopant and a p-type dopant is added to the ZnS (zinc sulfide) single crystal. As a result, the acceptor level in the forbidden band formed by the method of the present invention is shallower than the acceptor level in the forbidden band formed when only the p-type dopant is doped alone. As a result, the hole concentration of the activated carriers increases.

Further, the n-type dopant having the opposite charge shortens the scattering mechanism by the p-type dopant. As a result, the hole mobility of carriers can be greatly increased, so that the resistivity, which is inversely proportional to the product of the hole concentration and the hole mobility, is greatly reduced as compared with the case of single doping, and a low-resistance p-type ZnS A (zinc sulfide) single crystal is obtained.

Further, according to the present invention, the p-type dopant concentration is
The method for producing a low-resistance p-type single crystal ZnS (zinc sulfide) according to claim 5, wherein doping is performed so as to be higher than the concentration of Ag + Cu element (claim 6). In this case, Ag and Cu, which are Group Ib elements, do not affect the conductivity type and contribute to the emission characteristics. The p-type dopant concentration is made the same order of magnitude or one order of magnitude higher than the n-type dopant concentration so that the conductivity type becomes p-type.

Further, the present invention relates to a low-resistance p-type single crystal ZnS.
(Zinc sulfide), and then cooled,
7. The low-resistance p-type single crystal ZnS according to claim 5, wherein the heat treatment is performed at 900 ° C. while applying an electric field.
(Zinc sulfide). As a result, hydrogen mixed as impurities can be removed from the crystal. At less than 600 degrees, H does not become unstable,
If the temperature exceeds 900 ° C., ZnS becomes unstable and the elements evaporate.

Further, the present invention provides a p-type dopant and / or
The n-type dopant and / or at least one element of Ag and Cu is electronically excited by a radio wave, a laser, an X-ray, or an electron beam into an atomic state. A method for producing the low-resistance p-type single crystal ZnS (zinc sulfide) according to any one of claims 7 to 9 (claim 8).

[0023]

The operation of the present invention will be described below in detail.
Conventionally, a luminous body using Zn vacancies has been used. However, Zn vacancies cause thermal and mechanical instability of the lattice, and electrical and optical characteristics deteriorate over time. Will happen. The present invention does not utilize Zn vacancies as described above as a luminous body, but instead replaces the Zn position by doping with an Ib group element such as Ag or Cu, and solves the problem of deterioration based on lattice instability. There is an action to solve.

Conventional n-type dopants include B and A
Although a group of elements of 1, Ga, In, and Cl are used, B, Al, Ga, and In substitute for the position of Zn, but Cl substitutes for the position of S similarly to N. The replacement positions compete with each other, which affects the resistivity and the hole concentration.

As an n-type dopant, for example, In (indium) is used, and as a p-type dopant, for example, N (indium) is used.
By using (nitrogen) and further adding, for example, with In: N = 1: 2, a strong chemical bond is directly formed between In and N as the first proximity in the ZnS crystal thin film, and N-In
Form a complex consisting of -N.

When N (nitrogen) is doped alone, the acceptor level not only forms a deep level of 100 meV or more, but also has a smaller covalent radius and a larger electronegativity. ) Is replaced by S (sulfur), which results in an increase in the energy of the lattice system, which in turn induces S (sulfur) vacancies in the vicinity. This also acts as a donor and lowers crystallinity. N (nitrogen) moves between lattices, and the role is reversed from the acceptor to the donor. This prevents low resistance p-type formation.

On the other hand, by utilizing In having a covalent bond radius larger than that of Zn, in the (In, N) co-doped crystal, as a result of the formation of the above-described complex, the doped N (nitrogen) becomes The chemical bonding force and the mechanical stability are also stabilized, and as a result, the holes move as a carrier activated at room temperature because they move to a shallow level, and a low-resistance p-type single crystal ZnS (zinc sulfide) is formed. A thin film is obtained.

The effect of doping a p-type dopant and an n-type dopant simultaneously is that the donor
An acceptor pair is formed, (1) the increase in electrostatic energy due to Coulomb repulsion between the p-type dopants is increased, and the solubility of the p-type dopant is increased. The doping method extends over 100 angstroms, but shortens it to tens of angstroms, thereby increasing the mean free path of carriers.
(3) As a result of the strong bond between the p-type dopant and the n-type dopant, the acceptor level becomes shallower than in the case of solely doping only with the p-type dopant, and the concentration of holes that are carriers increases at lower temperatures. Furthermore, (4)
Some of the n-type dopants include Ag and Cu in the Ib group emission center.
And that the wavelength of light can also be controlled by the interaction with.

As described above, the group Ib elements Ag, Cu
The positive synergistic effect of the combination of the emission characteristic control by doping and the conductivity control by p and n simultaneous doping,
It becomes possible to stably dope a p-type dopant to a high concentration while having a light emitting characteristic, and as a result, a ZnS single crystal thin film can be manufactured as an optoelectronic material in a visible to ultraviolet region.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as an embodiment of the present invention, a vapor phase epitaxial growth (VPE: VaporPhaseEpita) will be described.
xy) method, GaAs (gallium arsenide) substrate
A method for forming a type single crystal ZnS (zinc sulfide) thin film will be described. FIG. 1 shows a schematic view of an apparatus of the ZnS single crystal thin film VPE method. A known device can be used as the device itself. The reaction tube 1 is connected to a flow controller (MFC) by a gas introduction tube 10. A gas introduction pipe for H ₂ or H ₂ + NH ₃ is cut in the center of the flange 2,
Movable raw material ports 7, 8, 9 are provided. The electric furnace has a substrate section 3, a maximum temperature section 4, a raw material section I5, a raw material section II.
There are six zones

The carrier gas was an open tube system using only hydrogen gas or a mixture of hydrogen gas and NH ₃ (ammonia), and ZnS powder was used as a raw material. The temperatures of the raw material part I and the raw material part II are from 80 ° C to 800 ° C, the temperature of the highest temperature part is 800 to 920 ° C, and the substrate temperature is about 540 ° C to 600 ° C. The operating conditions are summarized in Tables 1, 2, and 3.

In the raw material portions I and II, the raw material reacts with H ₂ to generate a gas containing the constituent elements. In the highest temperature section,
The temperature of the gas becomes the highest, the temperature of the gas decreases in the substrate portion, and the temperature is constant (540-6
(Control at 00 ° C.), and the material is deposited and grown on the substrate.

The ZnS single crystal thin films shown in Table 1 are all p-type, and the conduction type was determined by the sign of the Seebeck voltage by the hot probe method. The growth time is 2 hours to 5 hours, and the grown film thickness is 0.5 μm to 4 μm. The electrical characteristics were obtained by measuring the Hall effect. As shown in Table 2, the substrate 11 is made of n-type GaAs (1
00) is used. Table 3 summarizes the sources and the purity of the added impurity raw materials.

[0034]

[Table 1]

[0035]

[Table 2]

[0036]

[Table 3]

In Table 1, for comparison, when only N is doped, when N and Ag are simultaneously doped,
When co-doping with N and In, N, Ag and Cl
The electrical characteristics measured for the case of co-doping are described. As shown in Table 1, when N, Ag, and In were simultaneously doped, the one with the lowest resistivity and the highest carrier density was obtained. When N, Ag and Cl are co-doped, N and Cl are substituted at the S position.
, The resistivity is higher and the carrier density is lower than in the former case.

FIG. 2 shows the structural arrangement of two acceptors and one donor in a ZnS (zinc sulfide) crystal determined using the first principle band structure calculation method. The large black circle at the center is In, and the small black circles are all Zn. An open circle is S, and an oblique line is N in the white circle. As can be seen from this figure, the following structure is formed by the inclusion of In as a donor together with N as an acceptor in ZnS (zinc sulfide) crystal.

Embedded image It was confirmed that the crystallographic structure of N was stabilized, and that N could be stably doped to a higher concentration. In addition,
Ag of the group Ib element is located in the crystal almost independently of In and N.

[0039]

As described above, the low-resistance p-type single crystal ZnS (zinc sulfide) of the present invention can be combined with the already realized low-resistance n-type ZnS (zinc sulfide) to provide an energy gap. Since the size can be freely controlled, its application to light emitting diodes and semiconductor lasers, which are high-performance optoelectronic materials in the visible to ultraviolet range, is expanding.

Further, the application area can be expanded to a photoelectric conversion device, for example, a low resistance semiconductor such as a solar cell. Further, according to the manufacturing method of the present invention, low-resistance p-type single crystal ZnS (zinc sulfide) can be easily obtained.

[Brief description of the drawings]

FIG. 1 shows a low-resistance p-type single crystal Z on a substrate by a VPE method.
1 is a schematic side sectional view of an apparatus for forming an nS (zinc sulfide) thin film.

FIG. 2 shows Zn determined using the first principle band structure calculation method
FIG. 3 is a schematic diagram showing a structural arrangement of a p-type dopant and an n-type dopant in S (zinc sulfide) crystal.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 33/00 H01L 33/00 D

Claims (8)

[Claims] 1. A p-type dopant composed of at least one of Li, Na, and N, an n-type dopant composed of at least one of B, Al, Ga, and In;
g, containing at least one element of Cu, having a resistivity of less than 0.08 Ω · cm and a hole concentration of 5.6 ×
Low resistance p-type single crystal ZnS (zinc sulfide) having a resistivity of 10 ¹⁸ / cm ³ or more. 2. A p-type dopant comprising at least one of Li, Na and N, an n-type dopant comprising Cl and at least one element of Ag and Cu, and having a resistivity of 0.60Ω. A low-resistance p-type single crystal ZnS (zinc sulfide), which is smaller than cm and has a hole concentration of 1.4 × 10 ¹⁷ / cm ³ or more. 3. The low-resistance p-type according to claim 1, wherein the concentration ratio of the contained p-type dopant to the n-type dopant is from 1.3: 1 to 10: 1. Single crystal ZnS (zinc sulfide). 4. The low resistance p according to claim 1, wherein the content of at least one element of Ag and Cu is at least 1 × 10 ¹⁴ / cm ^{3 in} atomic concentration.
Type single crystal ZnS (zinc sulfide). 5. When forming a single crystal of ZnS (zinc sulfide), at least one of Ag and Cu is doped, and an n-type dopant and a p-type dopant are added at a p-type dopant concentration of n-type. The low-resistance p-type single crystal ZnS according to any one of claims 1 to 4, wherein the doping is performed so as to be higher than the dopant concentration.
(Zinc sulfide). 6. The method according to claim 5, wherein doping is performed so that the p-type dopant concentration is higher than the concentration of Ag + Cu element. 7. The method according to claim 5, wherein after forming the low-resistance p-type single crystal ZnS (zinc sulfide), the substrate is cooled and further heat-treated at 600 to 900 ° C. while applying an electric field. A method for producing low-resistance p-type single crystal ZnS (zinc sulfide). 8. A p-type dopant and / or an n-type dopant and / or at least one element of Ag and Cu which has been atomized by electronic excitation with a radio wave, a laser, an X-ray, or an electron beam. The method for producing a low-resistance p-type single crystal ZnS (zinc sulfide) according to any one of claims 5 to 7, wherein: