JPH0697651B2 - Method for producing low resistance n-type zinc sulfide thin film - Google Patents

Description

The present invention relates to a method for producing a low resistance n-type zinc sulfide thin film used for an active layer or a confinement layer of a light emitting diode (LED) or a laser diode (LD).

<Outline of the Invention> A zinc sulfide thin film obtained by the method for producing a low-resistance n-type zinc sulfide thin film of the present invention is characterized in that a zinc sulfide single crystal thin film contains a group III element as a donor impurity. It is possible to fabricate a light emitting device using.

Furthermore, in the production method, an adduct obtained by equimolar mixing of dialkylzinc and dialkylsulfur or dialkylselenium as a zinc source is used, and when a zinc sulfide single crystal thin film is formed by the MOCVD method using hydrogen sulfide as a sulfur source, a group III By simultaneously supplying the organometallic compound of the element, it is possible to control the donor impurity and to manufacture a low-resistance n-type ZnS single crystal thin film.

<Prior Art> Zinc sulfide (ZnS), which is a direct-transition wide-gap compound semiconductor, has a bandgap of about 3.6 eV at room temperature, and is attracting attention as a short-wavelength light emitting device material. Up to now, attempts have been made to produce high-quality ZnS single crystal thin films by various crystal growth methods, but single crystal thin films at a level at which devices can be produced have not yet been obtained. This is because the vapor pressures of the constituent elements Zn and S are both high, so that lattice defects are likely to be included in the crystal growth process. In order to suppress lattice defects, it is said that reducing the growth temperature is one of the methods. In recent years, metal-organic vapor phase pyrolysis (MOCVD), molecular beam, which enables ZnS crystal growth at low temperature, has been proposed. The epitaxy method (MBE method) and the like are drawing attention.

The MOCVD method and MBE method enable crystal growth at a lower temperature than liquid phase epitaxial growth or vapor phase chemical growth method (CVD method), and the crystal growth process is largely deviated from the thermodynamic equilibrium state ( Since it proceeds in a non-equilibrium state, it is possible to suppress the generation of lattice defects and the incorporation of impurities. Good quality single crystal thin films by MOCVD and MBE have been reported. (See, for example, Japanese J.Appl.Phys., 22 (1983) L583 J. Crystal Growth, 53 (1981) 423) In order to apply ZnS to LEDs and LDs, conductivity and resistivity can be determined by doping impurities. Need to control. As described above, it is extremely difficult to control the conduction type and reduce the resistance of the thin film with ZnS, which easily contains lattice defects. Especially, the P-type ZnS can still be obtained by using the MOCVD method and the MBE method. I'm not in sight.

Since ZnS is n-type natively, it is considered that an n-type ZnS single crystal thin film is relatively easy to prepare, and some experimental examples have been reported. The outline will be described below.

1. Reduced pressure MO using dimethyl zinc (DMZ) and hydrogen sulfide (H ₂ S)
ZnS grown on GaAs by the CVD method showed low resistivity in the undoped state with no added impurities and in the as-grown state. For example, at a growth temperature of 300 ° C., the specific resistance ρ≈1 Ω · cm. (Proceedings of the 45th Autumn Meeting of the Japan Society of Applied Physics 1984 Autumn Meeting 12a-S-5 Page 630) 2. Zn grown on GaAs by MBE method with ZnS source
S was undoped and as-grown, and exhibited ρ ≈ 10 ³ Ω · cm. The growth temperature at which ρ was minimum was around 240 ° C.
(J. Crystal Growth 67 ((1984) 125.) 3. When growing ZnS on GaP by the low pressure MOCVD method using DMZ and H ₂ S, triethylaluminum (TEAl) was introduced as an n-type dopant, and Al ZnS: Al with the addition of was prepared.
Has the minimum value at. But even at 400 ° C ρ
It was as large as ≈ 10 ⁴ Ω · cm, which was not a level that could be applied to devices.

(Extended Abstracts of the 15th Conference on Sol
id State Devices and Materials, Tokyo, 1983, pp.349-3
52) <Problems and Objectives to be Solved by the Invention> Since ZnS has a band gap of 3.6 eV at room temperature,
High-quality ZnS should exhibit high resistance. Therefore, it is considered that the undoped low-resistance ZnS shown in the prior arts 1 and 2 has low resistance because of its low crystal quality. That is, there is a strong possibility that the lattice defects included or the impurities taken in during the growth process are the source of free electrons. Therefore, the reproducibility of the specific resistance is poor, and the specific resistance cannot be changed intentionally, which makes it difficult to apply to device fabrication.

The prior art 3 is one in which impurities are doped for the purpose of intentionally changing the specific resistance.
Has a high resistance of ρ = 10 ⁴ Ω · cm, so it cannot be applied to devices.

The object of the present invention is to produce a low resistance ZnS single crystal thin film which has been technically controlled by doping with an impurity element, which has not been realized so far.

<Means for Solving the Problems> The method for producing a low-resistance n-type zinc sulfide thin film of the present invention comprises an adduct obtained by mixing dialkylzinc and dialkylsulfur or a mixture of dialkylzinc and dialkylselenium. The obtained adduct is a zinc source, hydrogen sulfide is a sulfur source, and when supplying the zinc source and the sulfur source to a zinc sulfide thin film forming atmosphere by a metalorganic vapor phase thermal decomposition method, an organometallic compound containing a Group III element is a donor. It is characterized in that it is supplied as an impurity.

Furthermore, in the method for producing a low-resistance n-type zinc sulfide thin film of the present invention, the organometallic compound containing the Group III element is any one or more of the organometallic compounds containing Al, Ga or In. It is characterized by consisting of.

<Examples> FIG. 1 is a schematic view of a MOCVD apparatus used for producing a low resistance n-type ZnS single crystal thin film in the present invention.

A graphite susceptor coated with SiC is placed inside a horizontal quartz glass reaction tube, and a substrate is placed on top of it. The substrate is heated from the side of the reaction tube using a high-frequency heating furnace, an infrared furnace, a resistance heating furnace, or the like. The substrate temperature is monitored by a thermocouple embedded in the graphite susceptor. The reaction tube is connected to the exhaust system and the waste gas treatment system via a valve. The adduct obtained by equimolar mixing of dialkylzinc, which is a Zn source, and dialkylsulfur or dialkylselenium is enclosed in a bubbler.
Further, an organometallic compound serving as a source of the group III element, such as triethylaluminum (TEAl), trimethylgallium (TMGa), or triethylindium (TEIn), is enclosed in a bubbler.

A carrier gas and hydrogen sulfide are filled in a cylinder, respectively. The flow rates of the carrier gas and hydrogen sulfide purified by the purifier are controlled by a mass flow controller. The adduct and the group III organometallic compound enclosed in the bubbler are maintained at a predetermined temperature by a thermostatic bath.

By introducing an appropriate amount of carrier gas into this bubbler and performing bubbling, a desired amount of adduct and II
The Group I organometallic compound is vaporized and supplied. Bubbler,
The adduct, the group III organometallic compound, and hydrogen sulfide supplied from the cylinder are diluted with a carrier gas, merged, and then introduced into a reaction tube through a three-way valve. The three-way valve switches between introduction of raw material gas into the reaction tube and disposal to the waste gas treatment system. Although a horizontal reactor is shown in FIG. 1, the basic structure is the same in a vertical reactor. However, it is necessary to ensure the uniformity of the obtained film by providing a substrate rotating mechanism.

A specific manufacturing process of a low resistance n-type ZnS single crystal thin film containing a group III element will be described below.

Mirror-polished gallium arsenide (GaAs) and gallium phosphide (GaP) sliced on the (100) plane and the plane having a 5 ° or 2 ° shift from the (100) plane to the (110) plane
And silicon (Si) with trichloroethylene, acetone,
Etching is performed after ultrasonic cleaning with methanol. The etching conditions are as follows.

GaAs substrate H ₂ SO ₄ : H ₂ O ₂ : H ₂ O = 3: 1: 1 (volume ratio) 2 at room temperature
min GaP substrate HCl: HNO ₃ = 3: 1 (volume ratio) at room temperature for 30 seconds Si substrate HF: H ₂ O = 1: 1 (volume ratio) at room temperature for 2 min Etching is stopped using pure water, pure water, methanol After washing in, it was stored in Daiflon. Immediately before setting the substrate in the reaction tube, the substrate is taken out of the diflon, and the diflon is dried and removed by blowing dry nitrogen. After setting the substrate, the inside of the reaction tube is evacuated to about 10 ^-5 Torr to remove the gas remaining in the system. After introducing the carrier gas and returning the system to normal pressure, the temperature rise is started while flowing the carrier gas at about 1 to 2 l / min. An infrared heating furnace was used for heating. As the carrier gas, He with a purity of 99.9999% or H ₂ passed through a purifier was used. After the substrate temperature reaches a predetermined temperature and becomes stable, the supply of the raw material gas is started and the low resistance ZnS film is grown. However, in the case of a Si substrate, it is necessary to clean the substrate surface by heat treatment in a hydrogen stream at 900 ° C for about 10 minutes. The adduct used has a purity of 99.9999%
Is an adduct obtained by mixing equimolar amounts of dimethyl zinc and diethyl sulfur. This adduct has a vapor pressure of about 280 mmHg at 30 ° C. Triethylaluminum (TEAl) was used as an organometallic compound containing a Group III element.

The growth conditions are as follows.

Substrate temperature 350 ° C, distance from raw material inlet to substrate 20 cm, bubbling amount of adduct 30 ml / min at -15 ° C, TEAl bubbling amount 20 ml / min at -10 ° C, 2% H ₂ S diluted with He
Supply rate of 200 ml / min, total gas flow rate including carrier gas 4.
5 l / min, growth time 90 min After performing growth for a predetermined time, supply of raw materials is stopped and cooling is performed. During cooling, He or H ₂ is flowed at 1 to ₂ l / min. 2% He diluted H ₂ S to prevent thermal etching of the substrate surface
May be cooled while flowing about 50 to 60 ml / min. When the substrate returns to room temperature, the reaction tube is evacuated to remove hydrogen sulfide remaining in the system. After returning the system to atmospheric pressure, the substrate is taken out. The thickness of the ZnS: Al film obtained at this time is about 1 μm.
And the growth rate was about 0.7 μm / hr.

The ZnS: Al single crystal thin film prepared by the above process showed a reproducibility of about 0.1 to 100 Ωcm at room temperature with good reproducibility. When the growth temperature was changed from 300 ℃ to 400 ℃, the resistivity showed the minimum value around 330 to 370 ℃. The reproducibility of the dependency of the resistivity on the growth temperature was also good. Growth temperature 35
When the bubbling amount of TEAl at −10 ° C. was changed at 0 ° C., a decrease in the specific resistance was observed with an increase in the bubbling amount in the range of 15 ml / min to 25 ml / min.
When it was less than ml / min or more than 25 ml / min, the resistivity increased rapidly.

He-Cd laser (oscillation wavelength 3250A
When it was excited at (°), it showed strong blue emission at room temperature (emission wavelength 460-470 mm).

An example of the photoluminescence spectrum at room temperature of the low resistance ZnS film is shown in FIG.

Even when the excitation wavelength was changed from 250 mm to 400 mm using a xenon lamp, only the emission around 460 to 470 mm was observed. The above facts show that the ZnS: Al thin film produced by the present invention has an extremely high quality.

The ZnS thin film grown without introducing TEAl showed a high resistivity of at least 10 ⁵ Ω · cm, and no photoluminescence near 470 mm was observed. It can be seen that the decrease in resistivity and photoluminescence are due to Al doping.

In the above description, an adduct obtained by mixing equimolar amounts of dimethyl zinc and diethyl sulfur was described.
In addition, dimethylzinc and dimethylsulfur (vapor pressure of about 120mmHg at 20 ℃), diethylzinc and dimethylsulfur (30 ℃
The vapor adduct of about 88 mmHg) and the combination of diethylzinc and diethylsulfur (vapor pressure of about 15 mmHg at 20 ° C) are also obtained by equimolar mixing of dialkylzinc and dialkylsulfur, and are similar to the adduct of dimethylzinc and diethylsulfur. It can be used as the above and falls within the scope of the present invention. Also, four types of adducts obtained by combining dimethylselenium and diethylselenium with dimethylzinc and diethylzinc, which hardly decompose at a growth temperature of 400 ° C or lower, can be used in the same manner as the alkylsulfur adduct. It is included in the invention.

As can be easily inferred from the above description, similarly to the addition of Al to ZnS, the addition of Ga and In also corresponds to the corresponding organometallic compounds such as triethylgallium (boiling point = 143 ° C.) and triethylindium (boiling point = 184 ° C). C.) is possible. The ZnS: Ga, ZnS: In obtained when the supply amount calculated from the vapor pressure at the bubbling temperature and the flow rate of the bubbling gas was equal to that of triethylaluminum.
Showed similar electrical characteristics to ZnS: Al. According to the present invention, a low resistance ZnS single crystal thin film controlled by doping can be manufactured by the MOCVD method using an adduct as a Zn source.

Hereinafter, as a device application example of the low resistance ZnS manufactured by the present invention, manufacturing of a blue light emitting element will be described.

1. On an n-type GaAs substrate sliced on the (100) plane, about 3 Al-doped low resistance ZnS layers were formed according to the MOCVD process described above.
Grow μm.

2. After depositing Au-Ge (Ge = 12wt-%) on the back surface of the substrate at about 2000A °, heat-treat at 350 ° C for 5-10min in an inert atmosphere to form ohmic contact with the GaAs substrate.

3. Lay about 1000 A ° of SiO ₂ on ZnS by sputtering.

4. A semi-transparent Au electrode with a thickness of 300 to 500 A ° is laminated on SiO ₂ .

Surface A of the device having the MIS structure manufactured as described above
When a forward bias voltage was applied between the u electrode and the ohmic contact provided on the GaAs substrate, light emission was observed from around 1 to 2V. The emission spectrum had a peak at around 460-470 mm at room temperature, and the emission intensity increased in proportion to the current flowing through the device. The quantum efficiency was about 10 ^-5 . By confirming blue light emission in the MIS type device having ZnS: Al as the light emitting layer formed by the present invention, it was proved that the low resistance ZnS produced by the present invention was of a quality suitable for device fabrication.

The low-resistance n-type semiconductor thin film according to the present invention is not limited to the MIS type blue light-emitting element, but may be a heterojunction element formed with another compound semiconductor, such as a homojunction element formed by stacking with p-type ZnS. It is easy to apply it to LEDs, LDs, etc. using junctions.

<Effects of the Invention> As described above, according to the present invention, by the MOCVD method using H ₂ S as a sulfur source using an adduct obtained by equimolar mixing of dialkylzinc and dialkylsulfur or dialkylselenium as a zinc source. When a ZnS single crystal thin film was formed, by simultaneously supplying an organometallic compound of a group III element, a low resistance n-type ZnS single crystal thin film applicable to devices was realized. Moreover, it has become possible to manufacture the thin film while controlling donor impurities. It is convinced that the present invention, which uses the MOCVD method which is excellent in reproducibility and mass productivity, contributes significantly to the production of LEDs, LD active layers, and binding layers, which are extremely important for display, mainly in the blue region. To do.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a MOCVD apparatus used in the present invention. 1 ... Quartz glass reaction tube, 2 ... SiC-coated graphite susceptor, 3 ... Substrate, 4 ...
High frequency heating furnace or infrared furnace or resistance heating furnace, 5 ... Thermocouple, 6 ... Exhaust system, 7 ... Waste gas treatment system, 8, 9 ... Valve, 10 ... Bubbler with additional body, 11 ... … Bubblers containing organometallic compounds of Group III elements, 12… Cylinders containing carrier gas, 13… Cylinders containing hydrogen sulfide,
14 …… Gas purifier, 15 …… mass flow controller, 16
…… Constant temperature chamber, 17 …… Three-way valve, 18 …… Valve Fig. 2 shows the photoluminescence spectrum of low resistance ZnS: Al manufactured by the present invention.

Claims (2)

[Claims] 1. An adduct obtained by mixing dialkylzinc and dialkylsulfur or an adduct obtained by mixing dialkylzinc and dialkylselenium as a zinc source, hydrogen sulfide as a sulfur source, and organometallic vapor phase heat. A method for producing a low-resistance n-type zinc sulfide thin film, which comprises supplying an organometallic compound containing a group III element as a donor impurity when supplying the zinc source and the sulfur source to a zinc sulfide thin film forming atmosphere by a decomposition method. 2. The organometallic compound containing a Group III element is A
The method for producing a low-resistivity n-type zinc sulfide thin film according to claim 1, characterized in that it comprises any one or any two or more of organometallic compounds containing l, Ga or In.