JPH0722343A - Vapor growth device - Google Patents

Abstract

PURPOSE:To contrive to form a II-VI compound semiconductor crystal thin film, which is doped with nitrogen and consists of ZnSe or the like, by a vapor growth device. CONSTITUTION:A vapor growth device is provided with a mechanism for turning nitrogen into a radical to introduce the radical in a thin film. This is a mechanism of a structure, wherein the nitrogen is led to a plasma generating chamber 8 and this nitrogen is excited by a high frequency or a microwave and is turned into plasma. The radical is introduced in the thin film and is used as an effective dopant. A metallic mesh 10 and a bellows 9 are made to interpose between the chamber 8 and a substrate. When a bias voltage is applied to the mesh, nitrogen ions can be prevented from colliding with the substrate 5 at high speed. A thin film crystal of a good crystallinity can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chemical vapor deposition apparatus capable of doping nitrogen into an epitaxial growth film of ZnSe. Red light emitting elements and green light emitting elements already exist and are widely used. Although there has been a long-standing demand for an element that emits blue color, an element having sufficient performance has not yet been obtained. The blue light emitting element should be able to be formed by forming a pn junction using a semiconductor crystal with a wide band gap.

[0002]

2. Description of the Related Art As a material for a light emitting element, in addition to having a wide band gap, it is a direct transition type, pn junction can be easily performed, a large substrate can be easily obtained, and a device process is easy. Is required. At present, there is no material that satisfies all such conditions. GaN, SiC, ZnS that satisfy any of the conditions
e, ZnS, GaAlN, ZnSSe and the like.

The subject matter of the present invention is a II-VI group compound semiconductor. For example, ZnSe, which has a bandgap of 2.7 eV, is a direct transition type semiconductor. However, this has a difficulty in that a large single crystal substrate cannot be formed and a p-type substrate cannot be formed. The ZnSe single crystal substrate is prepared by
Many methods such as high-pressure Bridgman method, sublimation method, iodine transportation method, solution growth method, piper method and the like have been tried. Z
Since nSe sublimes at high temperature unless high pressure is applied, it is difficult to form a melt, and the formation of a single crystal substrate has not yet been successful.

Therefore, using GaAs as the substrate, ZnS
Attempts are made to heteroepitaxially grow an e-film on this. To make a light emitting device, it is necessary to make a pn junction. For this purpose, n-type crystals and p-type crystals must be produced. However, it is difficult to control the conduction type.

It is difficult to make a p-type or n-type conduction type crystal. In the case of non-dope, it becomes n type. However, the carrier density is extremely low. Conventionally, Al, Ga, In and the like have been known as n-type impurities of ZnSe. However, when the amount of ^doping was increased, the n-type carrier density was rather decreased, and 10 ¹⁷ cm ^-3 was the maximum n-type carrier density. Such a low concentration is insufficient for a pn junction of a light emitting device.

However, more difficult is to make a p-type ZnSe crystal. First of all, I wondered what would become a p-type dopant. There is also a theory that Na, Li, etc. become p-type dopants, and there are attempts to do so. There is also an attempt to grow ZnSe by MBE (Molecular Beam Epitaxy). Various p-type dopants have been tried, but no p-type dopant has been obtained.

Nishizawa et al., Li-doped p-type ZnSe
It was announced that the crystal was manufactured by the vapor pressure controlled temperature difference method. This is not a thin film, but a bulk crystal. J.Nishizawa, K.Itoh, Y.Okuno and F.Sakurai: J.App
L. Phys. 57, 2210 (1985) However, the production of Li-doped ZnSe is difficult and poor in reproducibility. Further, the carrier density of p-type impurities is low. 8 x 10
^It does not exceed ¹⁶ cm ^-3 . In addition, Li easily diffuses in ZnSe, and the characteristics of the pn junction are not constant.

[0008] MIGITA et al. Say that a p-type ZnSe thin film was grown on a GaAs substrate using nitrogen as a dopant by a molecular beam epitaxy method. M.MIGITA, A.TAIKE, M.SHIIKI &H.YAMAMOTO;"p-type
conduction of ZnSe Highly Doped With Nitrogen by M
etalorganic Molecular Beam Epitaxy ", J. Crystal Gro
wth 101 (1990) 835-840

This is a molecular beam epitaxial growth method. Dimethyl Zn (DMZ) is used as a Zn raw material, and hydrogenated selenium H ₂ Se is used as a selenium raw material. These are not put into an ordinary molecular beam cell, but are introduced from the gas source cell into the molecular beam epitaxial device.
Nitrogen is also introduced from the gas source cell in the form of NH ₃ gas. The substrate is GaAs. This is heated in a susceptor to 250 ° C. to 450 ° C., and 1 to 4 × 10 ⁻⁵ To
It is said that vapor phase growth was performed with rr. This is p-type ZnSe and has a carrier density of 10 ¹⁸ c at a temperature of about 450 ° C.
m ^-3 . However, it is 10 ¹³ cm ⁻³ at 300 ° C. As a result, p-type ZnSe is obtained. However, this method does not have good reproducibility and does not have such characteristics by additional tests. Further, even though it is a p-type, there is a problem that the carrier density is too low. Even if nitrogen functions as a p-type dopant,
It may not fully penetrate into the ZnSe thin film.
For this reason, the density of the p-type carrier may be too low.

Subsequently, it was found that chlorine is effective as an n-type impurity. After this discovery, chlorine was used as an n-type impurity. This is zinc chloride (Z
nCl ₂ ) is used as a raw material. Chlorine doped ZnSe can also be made by molecular beam epitaxy. On GaAs substrate,
The molecular beam cells of Zn, Se and ZnCl ₂ are simultaneously irradiated. K. Ohkawa, T. Mitsuyu and O. Yamazaki: Ext. Abstr. 18th
Conf. Solid State Devices and Materials, Tokyo, 198
6, p635 When chlorine is used as an n-type impurity, a carrier density of about 10 ¹⁹ cm ^-3 can be realized. The carrier density is improved by an order of magnitude as compared with the case of Ga-dope.

As described above, nitrogen has been studied as a p-type impurity. However, it is difficult for nitrogen to enter the ZnSe crystal. Liquid phase epitaxy, MOCVD method, MB
Various attempts have been made to dope nitrogen into ZnSe by the E method or the like, but none of them could introduce nitrogen into ZnSe. Nitrogen did not enter ZnSe and did not become a p-type impurity.

However, Okawa et al. Proposed a radical doping method in which nitrogen is used as a radical to dope ZnSe. This is a method in which nitrogen gas is turned into active nitrogen by electric discharge and is applied as a molecular beam to a substrate together with a molecular beam of Zn and a molecular beam of Se. K. Ohkawa, T. Karasawa and T. Mitsuyu: 6th Int.Conf.M
olecular Beam Epitaxy, San Diego, 1990, PIII-21, J.Cr
yst.Growth 117,375 (1991) K. Ohkawa, A. Tsujimura, S. Hayashi, S. Yoshii and TM
itsuyu: Ext.Abstr.1992Int.Conf. Solid State Devic
es and Materials, Tsukuba, 1992 p.330 In this way, ZnSe pn junction can be formed by molecular beam epitaxy using chlorine as n-type and nitrogen as p-type.

[0013]

However, these successes use the molecular beam epitaxy method, and nitrogen is doped as a p-type impurity in the vapor phase growth method for growing a thin film at a lower vacuum degree. I haven't succeeded in that. The present invention proposes a method in which a raw material can be introduced in a gas state and nitrogen doping can be performed on a II-VI group compound semiconductor crystal in a vapor phase growth method capable of growing a thin film at a lower degree of vacuum.

[0014]

Means for Solving the Problems The present invention is directed to a reactor equipped with an inlet for introducing a group II element raw material and a group VI raw material.
A mechanism for introducing nitrogen as a radical is provided. This mechanism includes a plasma generation chamber, and the gaseous nitrogen introduced there is
Excited by microwave or high frequency to form radicals. Nitrogen radicals are introduced into the reactor. Since the group II element, the group VI source gas, and the nitrogen radical are introduced into the reaction furnace, a chemical reaction causes a nitrogen doped group II-VI compound semiconductor thin film to grow on the substrate.

Furthermore, by providing a metal mesh at the exit of the plasma generation chamber, the energy of ions can be controlled. Further, a bellows may be provided in the middle of the radical introduction tube to make the distance between the metal mesh and the substrate variable.

[0016]

Since the mechanism for introducing the nitrogen radicals including the plasma generation chamber is provided in the reaction furnace, the nitrogen radicals can be supplied to the inside of the vapor phase growth apparatus. Since both the group VI raw material and the group II raw material are introduced into the reaction furnace, the II-VI group compound semiconductor thin film containing nitrogen can be grown on the substrate kept at an appropriate temperature.

When a metal mesh is provided, it can be biased appropriately to change the kinetic energy of nitrogen ions. For example, when a positive voltage is applied, the positive ion energy that tries to exceed this is lost. Some may be pushed back. The fast nitrogen ions will not hit the substrate directly. When high-speed ions hit the thin film during crystal growth, the crystal structure may be disturbed, but this can be prevented by the action of the electric field of the metal mesh.
It is possible to grow a nitrogen doped ZnSe crystal having good crystallinity.

Further, the bellows makes it possible to make the distance between the metal mesh and the portion where the plasma generating chamber is present and the substrate variable. Neutral active species and ions have an average lifespan,
The type of neutral active species that the substrate can reach can be selected by changing the distance. This makes it possible to set optimal conditions.

[0019]

Embodiment An embodiment of the present invention will be described with reference to FIG. The reaction furnace 1 is a space that can be evacuated, and the source gas flows from top to bottom. There is an inlet 2 for Group VI raw materials at the top. This introduces a gaseous raw material containing Se, S, etc. into the reaction furnace. H ₂ Se, H ₂ S and the like. At the upper side of the reactor 1, there is an inlet 3 for Group II elements.
This introduces a raw material containing a Group II element in a gaseous state. Organometallic compounds can be used, for example.
In addition to this, a radical introduction port 4 is provided above the reaction furnace 1 for introducing nitrogen as an impurity. The feature of the present invention lies in that a tube portion for introducing radicals is provided in the vapor phase growth apparatus. In this example, pipes for introducing the three raw materials are separately provided above the reaction furnace 1. Either may be provided directly above. The Group VI raw material and the Group II element may be combined before entering the reactor.

A susceptor 6 for holding the substrate 5 is provided below the center of the reaction furnace. There is a heater inside or outside the susceptor 6. In this example, the built-in heater is used to heat the susceptor. In the case of an external heater, heating by a lamp or induction heating by a high frequency coil can be used. An exhaust port 7 is provided at the lower end of the reaction furnace 1. It is connected to a vacuum pump.

The nitrogen gas is introduced into the plasma generation chamber 8,
It becomes a radical of nitrogen here. To excite nitrogen,
A high-frequency coil 30 is provided here, and a high-frequency electric field is generated in the plasma generating chamber 8 by passing a high-frequency current through the high-frequency coil 30. Alternatively, a microwave oscillator may be provided and the microwave may be guided to the plasma generation chamber 8 by a waveguide. Radicals of nitrogen molecules are generated. In addition to neutral molecules and neutral atoms in the excited state, positive ion nitrogen is also present in this. There are various types of energy. It is also unclear which of the active species is effective as a nitrogen dopant. However, in the case of ions, due to the difference in electric field, they are accelerated by the time they reach the substrate,
It may have excessive energy.

A metal mesh 10 is provided in front of the plasma generation chamber 8 so that high-speed ions do not directly collide with the substrate.
To provide. A bellows 9 is provided further in front of the metal mesh 10. This is a member that can expand and contract while maintaining a vacuum state. The front end of the bellows 9 is connected to the radical introduction port 4 described above. An insulating collar 11 is sandwiched between the metal mesh 10 and the plasma generation chamber 8. This is to electrically insulate the plasma generation chamber 8 from the reaction furnace 1.

An external bias power source 20 is connected to the metal mesh 10 so that an arbitrary positive or negative voltage can be applied to the metal mesh 10. Ions are included in the nitrogen radicals, and the bias of the metal mesh 10 is adjusted in order to appropriately control the energy of the ions. Furthermore, the bellows can be expanded and contracted to arbitrarily set the distance between the plasma generation chamber and the substrate. The lifetimes of ions and neutral active species depend on their electronic states. It is desirable that only the active species preferable as the nitrogen dopant reach the substrate, and those that do not become the dopant do not strike the substrate. Since the vapor phase growth method has a low degree of vacuum, the mean free path of gas molecules and radicals is short. In order to
It is possible to control the distribution of the active species and the types of ions that reach the substrate by displacing the defects. The present invention appropriately displaces the bellows to change the distance between the substrate and the plasma generation chamber,
Empirically allows you to search for optimal conditions.

The bias given to the metal mesh and the fast ions which adversely affect the crystal structure due to the displacement of the bellows are eliminated, and only the neutral active species which become the dopant can reach the substrate. Thus high quality p-type ZnSe
Etc., a II-VI group compound semiconductor thin film crystal can be obtained.

The source gas supply system of the reactor shown in FIG. 1 will be described with reference to FIG. The group VI raw material gas cylinder 12 is, for example, Se.
Or S hydride, or Se or S organometallic gas. The Group VI raw material gas is passed through a valve 13 and a flow rate controller 14, and is fed from the Group VI inlet 2 to the reactor 1.
Enter inside.

The raw material of the group II element is contained in the bubbler 15 and kept at a constant temperature. Bubbling of the group II element is performed using high-purity hydrogen gas. Hydrogen gas can be used as a carrier to transport Group II elements in a gaseous state. After passing through the hydrogen gas, the valve 17 and the flow rate controller 18, the bubbler 15 is introduced into the bubbler 15 through the valve 19 and bubbled.
Hydrogen gas containing a Group II element passes through the valves 21 and 23 and is introduced into the reaction furnace 1 through the Group II inlet 3.
The proportion of hydrogen as a carrier gas can be arbitrarily determined by adjusting the opening of the valve 22, the valves 19 and 21, and the like. Nitrogen, which is a dopant, is supplied from a high-purity nitrogen gas cylinder through a valve 24 and a flow controller 2.
It is led to the plasma generation chamber 8 through 5. Such a raw material supply system is well known. Depending on the nature of the raw material, a bubbler may or may not be needed. The structure of the supply system is appropriately changed depending on the raw material.

[0027]

According to the present invention, a nitrogen-doped ZnSe thin film can be grown by a vertical vapor phase growth apparatus. N-type using MOCVD method instead of MBE method
A ZnSe thin film can be formed. Since the vapor phase growth apparatus is used, the group VI raw material is not a simple element, but a gas compound raw material that is easier to handle can be used. Similarly II
For the group element, a gas compound can be used as a raw material. A thin film can be formed at a higher pressure than the molecular beam epitaxy method.

Conventionally, there has been no means other than using a radical cell in molecular beam epitaxy for doping nitrogen into ZnSe. According to the present invention, a vertical vapor phase growth apparatus is provided with an introduction pipe for generating nitrogen radicals, and nitrogen is introduced into the reaction furnace as radicals.
A ZnSe thin film can be grown. Conventional p-type Z
Although nSe is said to be impossible in the vapor phase growth apparatus, the present invention makes this possible.

Further, if the distance between the radical generation space and the substrate is made variable, nitrogen radicals having optimum beam spread and optimum kinetic energy can be applied to the substrate. Further, when a metal mesh is provided in the radical introducing tube, the energy of ions in the radical can be adjusted. High-speed ions do not collide with the substrate and disturb the crystal structure of the thin film. It is possible to prevent damage to the thin film and grow a high quality p-type ZnSe thin film. If combined with chlorine dope, Z
A pn junction of nSe crystal can be produced. ZnS
e It is extremely effective in manufacturing a blue light emitting device.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a vapor phase growth apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a source gas supply system around the vapor phase growth apparatus of FIG.

[Explanation of symbols]

 1 Reactor 2 Group VI Inlet 3 Group II Inlet 4 Radical Inlet 5 Substrate 6 Susceptor 7 Exhaust 8 Plasma Generation Chamber 9 Bellows 10 Metal Mesh 11 Insulation Color 12 Group VI Gas Cylinder 13 Valve 14 Flow Rate Control -La 15 Bubbler 16 Pump 20 Bias power supply

Claims (3)

[Claims] 1. A reaction furnace capable of being evacuated, a susceptor provided inside the reaction furnace for supporting a substrate, a heater for heating the susceptor, and a gas state containing a group II element.
A group II raw material introducing pipe for introducing a group II raw material gas into the reaction furnace;
A group VI raw material introducing pipe for introducing a group VI raw material gas in a gaseous state containing a group element and a nitrogen radical introducing device for introducing nitrogen as a dopant, and the nitrogen radical introducing device is nitrogen. A plasma generation chamber that holds gas and turns it into plasma, a nitrogen gas excitation device provided in the plasma generation chamber, a radical introduction port provided at the tip of the plasma generation chamber, and a metal provided between the plasma introduction ports. A vapor phase growth apparatus comprising a mesh. 2. A reaction furnace capable of being evacuated, a susceptor provided inside the reaction furnace for supporting a substrate, a heater for heating the susceptor, and a gas state containing a group II element.
A group II raw material introducing pipe for introducing a group II raw material gas into the reaction furnace;
A group VI raw material introducing pipe for introducing a group VI raw material gas in a gaseous state containing a group element and a nitrogen radical introducing device for introducing nitrogen as a dopant, and the nitrogen radical introducing device is nitrogen. A plasma generating chamber that holds gas and turns it into plasma, a nitrogen gas excitation device provided in the plasma generating chamber, a plasma generating chamber and a bevel connected to the plasma generating chamber, and a radical provided at the tip of the bevel. A vapor phase growth apparatus comprising an introduction port and a metal mesh provided between the plasma introduction ports, wherein a distance between the plasma generation chamber and the plasma introduction port is variable. 3. A reaction furnace capable of being evacuated to a vacuum, a susceptor provided inside the reaction furnace for supporting a substrate, a heater for heating the susceptor, and a gas state containing a group II element.
A group II raw material introducing pipe for introducing a group II raw material gas into the reaction furnace;
A group VI raw material introducing pipe for introducing a group VI raw material gas containing a group element into a reaction furnace, and a nitrogen radical introducing device for introducing nitrogen as a dopant, and the nitrogen radical introducing device is nitrogen. A plasma generation chamber that holds gas and turns it into plasma, a nitrogen gas excitation device provided in the plasma generation chamber, a bevel connected to the plasma generation chamber, and a radical introduction port provided at the tip of the bezel, The plasma generating chamber, a metal mesh provided between the plasma inlet, and a power supply for applying a voltage to the metal mesh,
A vapor phase growth apparatus characterized in that an arbitrary voltage can be applied to the mesh.