JPH0666279B2 - Method and apparatus for growing compound semiconductor thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and an apparatus for growing a p-type conductive thin film of a compound semiconductor composed of an element of Group IIb and an element of Group VIb of the Periodic Table of Elements. .

[Conventional technology and its problems]

In recent years, a method called metal organic vapor phase epitaxy (MOVPE) has been widely adopted as a method for growing a IIb-VIb group compound semiconductor thin film such as ZnS and ZnSe, which has been attracting attention as a blue light emitting material. In this MOVPE method, for example, an organic metal compound containing an element of Group IIb of the periodic table such as diethyl zinc [(CH ₃ ) ₂ Zn] and a VI such as hydrogen selenide (H ₂ Se).
A IIb-VIb group compound semiconductor thin film such as ZnSe has been grown on the substrate by vapor-decomposing a compound containing a group b element on the substrate. In the conventional method for obtaining a compound semiconductor thin film having p-type conductivity, Pb or As which is a Vb group element is doped, but in this method, P or As forms a deep impurity level. However, it has a drawback that it does not emit blue light. On the other hand, in order to solve the above-mentioned drawback, a method using ammonia (NH ₃ ) which is a compound containing N which is the same Vb group element has been attempted. It has been found that N easily forms a shallow acceptor level, but when the above-mentioned ammonia gas is used, the thermal decomposition temperature of ammonia (about 900
C.) is much higher than the growth temperature of the compound semiconductor thin film (about 300 to 500.degree. C.), ammonia is hardly decomposed and high concentration doping of N into the compound semiconductor thin film is extremely difficult. It was The present invention solves the above drawbacks of the prior art, provides a method for growing a p-type conductive IIb-VIb group compound semiconductor thin film in which the doping amount of nitrogen is controlled, and easily grows the thin film. It provides a growth device that can

[Means for solving problems]

In order to eliminate the conventional drawbacks, the present invention uses p-type conductivity IIb-.
In the epitaxial growth of a VIb group compound semiconductor thin film by a metal organic chemical vapor deposition method, plasma-excited nitrogen ions are supplied to a vacuum chamber to obtain a thin film containing nitrogen as a dopant.

More specifically, the present invention relates to Zn which is a group IIb element of the periodic table of elements.
And a group consisting of Cd, and a group VIb element of the periodic table of elements.
An element selected from the group consisting of S, Se and Te,
Introduced into the reaction vessel as an organometallic compound gas, hot gas phase decomposition on a substrate placed in the reaction vessel and heated to a predetermined temperature, at the same time, plasma-excited nitrogen ions are irradiated on the substrate, A compound semiconductor thin film containing nitrogen as a dopant is obtained on a substrate.

Particularly in plasma excitation, a better effect can be obtained by converting the plasma into highly active nitrogen ion plasma by electron cyclotron resonance (ECR) excitation.

Next, a growth apparatus for carrying out the growth method of the present invention will be described. In the growth apparatus of the present invention, the reaction container is composed of a vacuum chamber and a plasma generation chamber for supplying highly active nitrogen ions to the vacuum chamber, and the vacuum chamber has a nozzle for introducing an organometallic compound gas, A substrate holder having a heating mechanism; and an exhaust port, wherein the plasma generation chamber has a plasma excitation gas introduction nozzle, a microwave introduction waveguide, and a magnetic field generation coil for applying a static magnetic field to the plasma generation chamber. It is a configuration provided with.

The growth method and growth apparatus of the present invention are intended for IIb-VIb group compound semiconductors, and the types thereof are specifically ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe and solid solutions thereof, such as ZnS _x. Se _{1-x and the} like can be mentioned.

[Action]

Since the present invention uses highly excited nitrogen ions excited by plasma, the doping efficiency of the thin film is improved, and high-concentration nitrogen doping of 10 ¹⁶ cm ⁻³ or more, which was impossible by the conventional method, is easy. Becomes Further, since the gas pressure is low and the growth is at a low temperature, a high quality epitaxial film can be grown.

Embodiments of the present invention will be described below with reference to the drawings.

〔Example〕

(Example 1) FIG. 1 is a configuration diagram showing an example of an apparatus for growing a ZnSe compound semiconductor single crystal thin film used in the present invention, and FIG. 2 is a view showing a reaction vessel of the growth apparatus in FIG. It is a figure which shows one Example. 1 is a reaction container, 2 is an organometallic compound gas inlet, 3 is a hydrogen selenide gas cylinder, 4, 6 and 8 are gas flow controllers, 5 is a hydrogen gas cylinder, 7 is a bubbler container, 9 is an ammonia gas cylinder, and 10 is GaAs. Substrate, 11 substrate holder, 12 substrate heating mechanism, 13 nitrogen-doped ZnSe thin film, 14 plasma generation chamber, 15 microwave introduction waveguide,
16 is a magnetic field generation coil, 17 is a gas inlet for plasma excitation,
18 is a vacuum exhaust port, 19 is a plasma flow, 22 is a vacuum chamber, and 23 is a microwave introduction window. In this embodiment, electron cyclotron resonance is used for plasma excitation as shown in FIG.

The procedure for growing a thin film using the apparatus of the present invention will be described below, taking the case of growing a single crystal thin film of a ZnSe compound semiconductor as an example.

First, the inside of the vacuum chamber 22 is made into a high vacuum of 10 ⁻⁷ Torr or less by a vacuum exhaust device such as a diffusion pump connected to the vacuum exhaust port 18. Next, the substrate 10 is turned on by energizing the substrate holder 11.
Heat to 250-400 ° C. In order to generate nitrogen plasma, ammonia gas or nitrogen gas or a mixed gas of nitrogen gas and hydrogen gas is introduced from the plasma excitation gas inlet 17 to a gas pressure of 10 ⁻⁵ to 10 ⁻³ Torr. 2.45 GHz microwave from the microwave introduction waveguide 15 to the plasma generation chamber 1
4, and at the same time, a static magnetic field is applied to the plasma generation chamber 14 by the magnetic field generation coil 16. The electrons in the plasma generation chamber 14 exposed to the static magnetic field perform circular motion due to the Lorentz force, but when the frequency of the electrons is matched with the frequency of the introduced microwave, electron cyclotron resonance absorption occurs, and the microwaves are absorbed, and Generates active nitrogen plasma. The plasma generated by the electron cyclotron resonance is generated at a gas pressure lower than that of a normal glow discharge by two digits or more, and has an ionization rate and an electron temperature of about two digits and is extremely highly active plasma. The generated nitrogen plasma is drawn as a plasma flow 19 into the vacuum chamber 22 by the divergent magnetic field.

On the other hand, in the raw material diethylzinc liquid which is a constant temperature _{[(C 2 H 5) 2} Zn] it is sealed bubbler vessel 7 containing Zn constituting the ZnSe, flow regulating hydrogen by gas flow controller 6 The gas is bubbled to form hydrogen gas containing the required amount of diethylzinc. In this case, a required amount may be supplied from a gas cylinder filled with diethylzinc through a flow rate controller. In addition, a required amount is supplied from a gas cylinder 3 filled with hydrogen selenide, which is a raw material containing Se, which constitutes ZnSe, via a flow rate controller 4, and together with the raw material gas containing diethylzinc described above, an organic phase is formed in a gas phase. It is introduced into the vacuum chamber 22 through the metal compound gas inlet 2.

In the vacuum chamber 22, a GaAs substrate 10 is placed on a substrate holder 11, heated to a predetermined temperature by a substrate heating mechanism 12, and a ZnSe single crystal thin film containing nitrogen as a dopant is formed of GaAs.
It is grown on the substrate 10.

Here, the doping amount is controlled by the supply amount of the ammonia gas or the nitrogen gas or the mixed gas of the nitrogen gas and the hydrogen gas introduced from the plasma excitation gas introduction port 17.

(Example 2) A case where a ZnSe single crystal thin film is grown using the apparatus shown in Example 1 is shown.

After the vacuum chamber 22 is evacuated to a high vacuum of 10 ^-7 Torr or less, NH ₃ gas is supplied into the plasma generation chamber 14 at a rate of 1 to 100 cc / min to reduce the pressure to 10 ^-5 to 2 × 10 ^-4 Torr. A gas pressure is applied, and a microwave (2.45 GHz) and a magnetic field (875 Gauss) are applied to generate nitrogen plasma. Set the microwave input to 100-300W. Next, diethyl zinc was set at a temperature of 5 ° C., hydrogen gas bubbling was supplied at a rate of 10 cc / min, and hydrogen selenide gas was supplied at a rate of 2.5 cc / min to form a raw material gas into the reaction vessel 1. Introduce. At this time, the supply molar ratio of NH ₃ to the raw material gas is set to be in the range of 5 to 200. The distance between the organometallic compound gas inlet 2 and the substrate 10 is set within the range of 5 to 12 cm. In this way, G heated to 250 ° C
By spraying on the aAs substrate 10, a ZnSe single crystal film containing nitrogen as a dopant was grown at a rate of 0.5 μm per hour. On the surface of the obtained ZnSe single crystal film, a good mirror surface was formed and there was no problem in crystallinity. Also, ZnSe
The resistance of the single crystal film is several Ω. The resistance value was as low as cm or less. p-type carrier concentration is 5 × 10 ¹⁶ atoms / cm ^3, was a conventional ammonia can increase the doping amount more than about one order of magnitude as compared with the case of using as a nitrogen source. Furthermore, FIG. 3 shows the photoluminescence characteristics at a temperature of 77K. The broken line 20 indicates the case where P or As is doped as in the conventional case, and light emission other than blue is dominant. On the other hand, the solid line 21 represents the case where N was doped according to the present example, and the emission spectrum of the thin film was extremely good only in blue emission (around 462 nm), and very good results were obtained.

(Example 3) A hydrogen sulfide introduction system was added to the apparatus shown in Example 1 to obtain ZnSS.
An example of growing an e single crystal thin film will be described.

After the vacuum chamber 22 is evacuated to a high vacuum of 10 ^-7 Torr or less, NH ₃ gas is supplied into the plasma generation chamber 14 at a rate of 1 to 100 cc / min to reduce the pressure to 10 ^-5 to 2 × 10 ^-4 Torr. A gas pressure is applied, and a microwave (2.45 GHz) and a magnetic field (875 Gauss) are applied to generate nitrogen plasma. Set the microwave input to 100-300W. Next, the hydrogen gas passing through the flow rate controller is bubbled into a diethylzinc solution at a temperature of 5 ° C., and a gas containing a saturated vapor of diethylzinc is supplied at a rate of 10 cc / min.
Also, hydrogen selenide gas is 2.5 cc / min and hydrogen sulfide is 0.25 cc / min.
The raw material gas is supplied at a rate of min and introduced into the reaction vessel 1. At this time, the supply molar ratio of NH ₃ to the source gas is 5 to 20.
It should be in the range of 0. The distance between the organometallic compound gas inlet 2 and the substrate 10 is set within the range of 5 to 12 cm. In this way, Zn containing nitrogen as a dopant is sprayed onto the GaAs substrate 10 heated to 300 ° C.
A S _0.06 Se _0.94 single crystal film was grown at a rate of 0.5 μm per hour. On the surface of the obtained ZnSSe single crystal film, a good mirror surface was formed and there was no problem in crystallinity. The resistance of the ZnSSe single crystal film showed a low resistance value of 1 Ω · cm or less.
A p-type carrier concentration of up to 10 ¹⁷ pieces / cm ³ was obtained, and the doping amount could be increased by one digit or more as compared with the conventional case where ammonia was used as a nitrogen raw material. Furthermore, as for the photoluminescence characteristics, extremely good results were obtained in which only blue light emission (around 460 nm) was strong.

As an example of the IIb-VIb group compound semiconductor, ZnSe, ZnSSe are used.
However, it is needless to say that the method of the present invention can be applied to the growth of a thin film of ZnTe, CdS, CdSe, CdTe or the like or a solid solution thereof as a compound semiconductor other than the above. For example, when dimethyl tellurium [(CH ₃ ) ₂ Te] was supplied instead of hydrogen selenide in Example 2 for the purpose of growing ZnTe containing nitrogen as a dopant, the obtained film showed p-type conduction. , Green emission (550nm
Good photoluminescence properties were obtained only in the vicinity. Furthermore, in Example 3, when diethylcadmium [(C ₂ H ₅ ) ₂ Cd] was supplied instead of diethylzinc, a CdS _0.06 Zn _0.94 single crystal film containing nitrogen as a dopant was obtained, and the photoluminescence property was green emission ( Only around 530 nm), good quality results were obtained.

〔The invention's effect〕

As described in detail above, according to the present invention, a low-resistance p-type conductive thin film can be obtained by high-concentration nitrogen doping, so that a pn junction can be formed. Therefore, conventionally,
The realization of visible light lasers such as blue and green, which have been most strongly desired in the development of devices and devices in the information processing field such as optical disks, optical printers, and display elements, is promising. Further, according to the present invention, it is possible to grow a high-quality epitaxial thin film by a low-gas, low-temperature process, the consumption of the raw material gas is small, and it is easy to save energy, which is advantageous for industrialization.

[Brief description of drawings]

FIG. 1 is a system diagram showing the structure of a ZnSe single crystal thin film growth apparatus used in an embodiment of the present invention, FIG. 2 is an embodiment of a reaction vessel of the growth apparatus of the present invention, and FIG. It is a figure which shows the photo-luminescence characteristic in the temperature of 77 K of a crystal thin film. DESCRIPTION OF SYMBOLS 1 ... Reaction container, 2 ... Organometallic compound gas inlet port, 3 ... Hydrogen selenide gas cylinder, 4, 6, 8 ... Gas flow rate controller, 5 ... Hydrogen gas cylinder, 7 ... Bubbler container, 9 ...
Ammonia gas cylinder, 10 ... GaAs substrate, 11 ... Substrate holder, 12 ... Substrate heating mechanism, 13 ... Nitrogen-doped ZnSe thin film, 14
... Plasma generation chamber, 15 ... Microwave introduction waveguide, 16 ... Magnetic field generation coil, 17 ... Plasma excitation gas introduction port, 18 ... Vacuum exhaust port, 19 ... Plasma flow, 20 ... P concentration 10 ¹⁵ pieces / cm ³ Z
Emission spectrum of nSe thin film, 21 ... N concentration 5 × 10 ¹⁶ pieces / cm ³
Emission spectrum of ZnSe thin film, 22 ... Vacuum chamber, 23 ... Microwave introduction window.

Claims (3)

[Claims] 1. A group IIb element of the periodic table, Zn and Cd.
And a group selected from the group consisting of S, Se and Te which are elements of Group VIb of the Periodic Table of Elements are introduced into the reaction vessel as an organometallic compound gas and installed in the reaction vessel. Containing nitrogen as a dopant by irradiating plasma-excited nitrogen ions onto the substrate at the same time by thermal vapor phase decomposition on the substrate heated to the temperature II.
A method for growing a compound semiconductor thin film, comprising obtaining a thin film of a b-VIb group compound semiconductor. 2. The method for growing a compound semiconductor thin film according to claim 1, wherein the plasma excitation is electron cyclotron resonance excitation. 3. An apparatus for growing a compound semiconductor thin film, comprising a reaction chamber composed of a vacuum chamber and a plasma generation chamber for supplying nitrogen ions to the vacuum chamber, wherein the vacuum chamber introduces an organometallic compound gas. A nozzle, a substrate holder, and an exhaust port, the plasma generation chamber includes a plasma excitation gas introduction nozzle, a microwave introduction waveguide, and a magnetic field generation coil that generates a static magnetic field in the plasma generation chamber. An apparatus for growing a compound semiconductor thin film, comprising: