JPH07118453B2 - Manufacturing method of semiconductor superlattice - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to the production of a semiconductor superlattice, which is an important constituent element of a visible short-wavelength light emitting device, which is desired to be put into practical use as a light source for a color sensor, a full-color display or the like. Concerning the law.

<Prior Art> Since the optical and electrical properties of a compound semiconductor superlattice can be controlled by a laminated structure of thin films, it is possible to manufacture a bulk semiconductor crystal or a device having characteristics that cannot be obtained by an epitaxial thin film. If the thickness of the individual thin films that make up the superlattice is reduced to about 50Å or less, even when materials with different thin film lattice constants are stacked, they will be distorted so that the lattice constants in the plane direction match each other. As a result, crystal growth can be performed without causing misfit dislocations and the like. Such a superlattice is referred to as a strained superlattice, and since it is not necessary to consider the lattice matching condition as in the conventional epitaxial growth, it has an advantage of widening the range of material combinations and selections in device design. II of strained superlattice
An example of application to a group VI compound semiconductor is shown below.

Prior art 1. Zn on a GaAs substrate by hot wall epitaxy
Strained superlattices composed of S and ZnSe and strained superlattices composed of ZnSe and ZnTe were formed. (For example, J. Crystal Growth 72 (1985)
299.Appl.Phys.Lett., 48 (1986) 236. etc.) Prior art 2. ZnSe on InP substrate by molecular beam epitaxy method (MBE method)
Strained superconductors composed of ZnTe and ZnTe were formed.

(See, for example, Appl.Phys.Lett., 48 (1986) 296.) Prior art 3. GaAs substrate by metalorganic vapor phase pyrolysis (MOCVD) using dimethylzinc, hydrogen sulfide, and hydrogen selenide as raw materials ZnS on
A strained superlattice composed of e and ZnS _0.1 Se _0.9 was formed.

(See, for example, Appl. Phys. Lett., 47 (1985) 955.) <Problems to be Solved by the Invention> The above-described conventional technique has the following problems.

Prior Art 1. The hot wall epitaxy method is a crystal growth method that applies a vacuum evaporation method, and supplies a raw material to a growth substrate by evaporating a heated and melted raw material in a vacuum.
It is difficult to control the growth rate of the film because the amount of evaporation from the surface of the melted raw material depends on the surface area of the raw material and the heating method. Further, since the flux of the evaporated raw material depends on the shape of the reservoir containing the raw material, it is difficult to control, and the amount of the raw material reaching the substrate tends to be non-uniform.
Therefore, a film thickness distribution is likely to occur. Therefore, a large-diameter substrate cannot be processed and mass production capability is low.

Prior art 2. The molecular beam epitaxy method (MBE method) is a growth method with excellent film thickness controllability, but it is used from an exhaust system and a vacuum chamber to obtain an ultra-high vacuum of 10 ^-10 to 10 ^-11 Torr. Since it is established, the device itself is expensive and the maintenance cost is high.

Conventional technology 3. Metal-organic vapor phase pyrolysis (MOCVD) is a technology suitable for mass production because it supplies raw materials as a gas, has excellent film thickness controllability, and can process many large substrates. But ZnSe,
When dimethylzinc and hydrogen sulfide or hydrogen selenide are used as growth materials for ZnS _0.1 Se _0.9, the raw materials introduced into the reactor react with each other in the gas phase, producing fine particles such as ZnS and ZnSe. . The particles adhere to the thin film growth surface on the substrate,
Since the crystal growth process is hindered, the characteristics of the obtained film are deteriorated.

Therefore, the present invention solves such a problem, and an object thereof is to provide a manufacturing method for mass-producing a superlattice structure composed of a high-quality II-VI group compound semiconductor thin film.

<Operation> In the MOCVD method, thin film growth is governed by the amount of raw material supplied. Since the raw material supply amount is precisely controlled by the mass flow controller, the thin film growth rate, film thickness controllability, and composition controllability are extremely high. Further, by optimizing the shapes of the reaction furnace for growth and the susceptor for holding the substrate, it is possible to process a large number of large-diameter wafers.

Since dialkylzinc forms an adduct with dialkylsulfur or dialkylselenium, the reactivity as a Lewis acid is remarkably lowered, so that the reaction does not proceed at all even when it is stored with hydrogen sulfide or hydrogen selenide at around room temperature.
When the adduct introduced into the reaction furnace reaches the heating zone near the substrate, it dissociates to produce dialkylzinc, which reacts with hydrogen sulfide or hydrogen selenide to grow a thin film. The dialkylsulfur or dialkylselenium generated by the dissociation of the adduct does not thermally decompose and therefore does not participate in the thin film growth. By the mechanism described above, formation of ZnS and ZnSe fine particles, which is a problem when dialkylzinc is used as a zinc source, can be suppressed, and a high quality thin film can be grown.

<Example> Table 1 collectively shows dialkylzinc (R ₂ Zn) dialkylsulfur (R ₂ S) and dialkylselenium (R ₂ Se) used in synthesizing the adduct used in the present invention.

Of R ₂ Zn and R ₂ S or R ₂ Se, the amount of the low-boiling component of both is mixed in excess, and after reaction and aging by heating, the excess component is distilled off to remove the adduct. Synthesized. The general formula of the adduct is:

The R ₂ Zn-R ₂ SR ₂ Zn-R ₂ Se-synthesized adducts each show a unique vapor pressure, and the purity can be improved by repeating distillation. Table 2 shows specific examples of vapor pressure.

The synthesis of the adduct is not limited to the compounds shown in Table 1, but R ₂ Zn, R ₂ S, and R ₂ Se other than those shown in Table 1 can be synthesized, and all of them are included in the scope of the present invention.

FIG. 1 shows a schematic diagram of the structure of the MOCVD apparatus used in the present invention.

A graphite susceptor 2 is set and a substrate 3 is placed inside a horizontal reaction furnace 1 made of transparent quartz. The substrate 3 is heated by the high frequency induction heating coil 4. The substrate temperature is monitored by a thermocouple 5 whose tip is embedded inside the susceptor. The reaction furnace 1 is connected to a high vacuum exhaust system 7 via a valve 6. The reaction gas that has left the reaction furnace 1 is connected to a rotary pump 9 via a valve 8 and reaches a gas processing device 10. The valve 8 has a function of keeping the internal pressure of the reaction furnace 1 constant.

The valves 11 to 16 supply the gas introduced by the three-way valve to either one of the main lines 17 and 18 or the waste lines 19 and 20. The main lines 17 and 18 are introduced into the reaction furnace 1 after joining. The waste lines 19 and 20 reach the rotary pump 23 via the valves 21 and 22, respectively, and are introduced into the gas treatment device 10. The valves 22 and 21 have a function of adjusting the internal pressures of the waste lines 19 and 20, respectively, and adjust the internal pressures of the waste lines 19 and 20 to be equal to the main lines 17 and 18, respectively. 24 is a mass flow controller, which precisely controls the gas flow rate. The cylinder 25 is filled with hydrogen gas which is a carrier gas, and after being highly purified by the purifier 26,
Supplied. The bubbler 27 is filled with an adduct,
It is kept at a predetermined temperature by a constant temperature bath 28. The adduct is
Since it is liquid in the temperature range from -20 ℃ to around room temperature, it can be supplied as vapor by bubbling the carrier gas. The supply amount can be controlled by the flow rate of the bubbling gas and the temperature of the bubbler. The valve 30 has a pressure adjusting function,
The upstream side of the valve 30 including the liquid surface of the additional body inside the bubbler is kept at atmospheric pressure. The cylinders 31 and 32 are filled with hydrogen sulfide and hydrogen selenide diluted with hydrogen gas, and the supply amount is controlled by the mass flow controller 24.

The manufacturing procedure of the semiconductor superlattice is given below.

The valve 12 is supplied with the carrier gas containing the adduct vapor, and the valve 11 is supplied with the carrier gas at the same flow rate. Further, valves 13 and 15 are supplied with hydrogen selenide and hydrogen sulfide, respectively, and valves 14 and 16 are supplied with carrier gas at the same flow rates as valves 13 and 15, respectively. The carrier gas for diluting the raw material flows at the same flow rate in the main lines 17 and 18 and the waste lines 19 and 20, respectively. The internal pressure of the main lines 17 and 18 shows a value corresponding to the internal pressure of the reactor 1 determined by the gas flow rate and the valve 8, and the internal pressure of the waste lines 19 and 20 is set to 17 and 18 of the valves 22 and 21, respectively. It is set equal to the internal pressure. Valve 11
And 12, 13 and 14, and 15 and 16 operate in pairs. That is, when one is connected to the main line, the other is connected to the discard line. When switching the gas, both are switched simultaneously. By this operation, the reactor 1,
The raw material gas can be switched between the main line and the waste line while keeping the internal pressures of the main lines 17 and 18 and the waste lines 19 and 20 constant. Fluctuations in the internal pressure of the reactor 1 due to gas switching induce fluctuations in the growth rate, and cause unevenness in the film thickness of the thin film forming the superlattice structure and in-plane thickness distribution, which can be suppressed as much as possible. I want it.

When manufacturing a superlattice by switching between hydrogen sulfide and hydrogen selenide, the following is performed. When supplying hydrogen sulfide, connect valves 15 and 14 to main line 18 and
3, 16 are connected to the waste line 20. At this time, hydrogen sulfide is supplied to the reaction furnace 1 through the main line 18, and hydrogen selenide is discarded. Then, the valves 15 and 16 are simultaneously switched. At this time, only the carrier gas is supplied to the reaction furnace 1 and the growth is interrupted, resulting in the interval state. Thereafter, the valves 13 and 14 are simultaneously switched to supply hydrogen selenide to the reaction furnace 1. Similarly, hydrogen sulfide and hydrogen selenide can be alternately supplied to the reaction furnace 1 by continuing the switching of the valve through an interval of an appropriate length.

FIG. 2 shows an example of a sequence of supplying the raw material gas to the reaction furnace 1 in the present invention. The adduct is continuously supplied, and hydrogen sulfide and hydrogen selenide are alternately supplied to form a superlattice. In FIG. 2, the horizontal axis represents the time axis. Reference numerals 33, 36, and 39 respectively indicate the supply timings of the adduct, hydrogen selenide, and hydrogen sulfide. 34, 37 and 40 show the state where the raw material is supplied to the reaction furnace, and 35, 38 and 41 show the state where the raw material is not supplied. As you can see from the combination of raw material supply, growth started from zero time and 42
ZnSe and 44 indicate the time zone during which ZnS is growing, and 43 indicates the interval at which the growth is interrupted.

The thickness of ZnSe and ZnS can be arbitrarily changed by setting the time of 42 and 44. If the three-way valves 11 to 16 are driven by a sequencer, the above growth sequence can be easily carried out.

FIG. 3 shows an embodiment of the supply sequence of the source gas to the reaction furnace 1 in the present invention. The superlattice is formed by alternately repeating simultaneous supply of the adduct and hydrogen selenide and the adduct and hydrogen sulfide.

In FIG. 3, the horizontal axis represents the time axis. 45, 48, 51 show the supply timing of the adduct, hydrogen selenide, hydrogen sulfide, respectively, 46, 49, 52 are the state where the raw material is being fed to the reactor, and 47, 50, 53 are the raw material are being fed. Each of the states is not performed. Start growing from time zero, 54
ZnSe and 56 indicate the time zone during which ZnS is growing, and 55 indicates the interval at which the growth is interrupted.

Specifically, the superlattice structure was manufactured under the following growth conditions according to the sequence shown in FIG. 2 or FIG.

Growth substrate: (100) plane of gallium arsenide Growth temperature: 325 ℃ Reactor internal pressure: 70 Torr (CH ₃ ) ₂ Zn-Se (CH ₃ ) ₂ bubbling gas flow rate: Bubbler temperature -15 ℃ 10ml / min (- Vapor pressure at 15 ℃ is 21mmHg) Hydrogen-based 10% H ₂ Se supply: 50ml / min Hydrogen-based 2% H ₂ S supply: 250ml / min Hydrogen flow through 17,18,19,20: 2.5 per line The growth rate of ZnSe and ZnS is about 1Å / se under the condition of / min or more.
It was c. The superlattice structure was determined by setting the supply times of hydrogen sulfide and hydrogen selenide based on the growth rate. The interval was 1 to 2 seconds.

FIG. 4 shows a diffraction x-ray chart of a superlattice structure consisting of ZnSe5Å.ZnS50Å and 400 repeating layers. Diffraction peaks reflecting the long-period structure of the superlattice are observed, indicating that the superlattice is formed.

Figure 5 shows the photoluminescence spectrum at 77 ° K of a superlattice structure consisting of ZnSe10Å, ZnS45Å, and a repeating period of 360 layers. Due to the quantum effect in the superlattice structure, the emission peak energy shifts to a higher energy side than the band gap energy of ZnSe. Further, the emitted light is due to the quantized electron-hole pair, and no emission involving deep levels on the long wavelength side is observed at all, so the obtained superlattice has high purity and high quality. Is shown.

In the method for manufacturing a superlattice according to the present invention, the above (C
_{H 3) 2 Zn-Se (} CH 3) not only ₂ adduct, shown in Table 1
A superlattice structure can be produced even by using an adduct obtained by all combinations of R ₂ Zn, R ₂ S, and R ₂ Se,
When the supply amount determined by the vapor pressure of the adduct and the bubbling gas flow rate were the same, a superlattice structure having the same characteristics as those of the above-described examples could be manufactured.

In addition, in the schematic diagram of the MOCVD apparatus shown in FIG.
In a similar arrangement, making it possible a superlattice structure comprising a liquid crystal layer such ZnSe10Å-ZnS ₀₁ Se ₀₉ 50Å by increasing the number of number of three-way valves and gas lines. Further, by setting a dopant, it is possible to dope the ZnSe layer or the ZnS layer. As an example of application of superlattice structure device
A ZnSe25Å-ZnS25Å superlattice ZnSe layer was selectively doped to fabricate a light emitting device. After forming a superlattice composed of Al-doped ZnSe layers with a repetition period of 300 layers on the (100) plane of n-type gallium arsenide, a ZnSe layer was laminated with a superlattice composed of N-doped layers of 300 repetition periods. . Each superlattice layer is N-
Type and P-type conductivity was exhibited. When an ohmic contact was formed on the gallium arsenide substrate and the P-type superlattice layer and forward bias was applied, light emission was observed from around 2.5 V, and pure blue light emission with a peak wavelength of 460 nm was exhibited. The fact that light emission in the long wavelength region is not observed indicates that the superlattice according to the present invention has high purity and high quality and can be applied to a blue light emitting device.

The present invention is not limited to the ZnSe and ZnS superlattices shown in the above-mentioned examples, but superlattice systems containing zinc telluride (ZnTe), for example, ZnSe-ZnTe system, ZnS-ZnTe system, ZnS.
It can be applied to the xSe1-x (0 <x <1) -ZnTe system and is included in the present invention.

<Effects of the Invention> As described above, according to the present invention, in a method for producing a semiconductor superlattice in which a large number of II-VI group compound semiconductor thin films are alternately laminated, dialkylzinc and dialkylsulfur or dialkylselenium are used as zinc sources. By using an adduct synthesized from, the formation of zinc sulfide thin film and zinc selenide thin film by metalorganic vapor phase pyrolysis using hydrogen sulfide as a sulfur source and hydrogen selenide as a selenium source.
It has become possible to mass-produce high-quality superlattice structures composed of II-VI group compound semiconductor thin films. We are convinced that the present invention greatly contributes to the visible short wavelength light emitting device represented by the blue region.

[Brief description of drawings]

FIG. 1 is a schematic diagram of the structure of an MOCVD apparatus according to the present invention. 1 ... Reactor, 2 ... Graphite susceptor, 3 ...
… Substrate, 4 …… High frequency induction heating coil, 5 …… Thermocouple,
6 ... Valve, 7 ... High vacuum exhaust system, 8 ... Valve, 9
...... Rotary pump, 10 …… Gas processor, 11 to 16…
… Three-way valve, 17,18 …… Main line, 19,20 …… Disposal line, 21,22 …… Valve, 23 …… Rotary pump, 2
4 …… Mass flow controller, 25 …… Cylinder with carrier gas, 26 …… Refiner, 27 …… Bubbler with adduct, 28 …… Constant bath, 29 …… Valve, 30 …… Valve,
31 …… Cylinder containing hydrogen sulfide diluted with hydrogen, 32 ……
A cylinder containing hydrogen selenide diluted with hydrogen. FIG. 2 is a sequence diagram of the supply of the source gas to the reaction furnace in the present invention. 33 …… Adduct supply timing, 36 …… Hydrogen selenide supply timing, 39 …… Hydrogen sulfide supply timing, 3
4,37,40 …… The state that the raw material is supplied to the reactor, 35,3
8,41 …… In the state where the raw material is not supplied to the reactor, 42 ……
Time zone of growing ZnSe, 43 ... Interval, 44 ...
… The time when ZnS is growing. FIG. 3 is a supply sequence diagram of the raw material gas to the reaction furnace in the present invention. 45 …… Addition body supply timing, 48 …… Hydrogen selenide supply timing, 51 …… Hydrogen sulfide supply timing, 4
6,49,52 …… The state where the raw material is supplied to the reactor, 47,5
0,53 …… No raw material is supplied to the reactor, 54 ……
Time zone during growth of ZnSe, 55 …… interval, 56…
… The time when ZnS is growing. FIG. 4 is a diffraction X-ray chart of a superlattice produced by the present invention. FIG. 5 is a photoluminescence spectrum at 77 ° K of the superlattice produced by the present invention.

Claims (3)

[Claims] 1. A method for producing a semiconductor superlattice comprising a plurality of II-VI group compound semiconductor thin films laminated on a substrate, wherein the zinc source is an adduct synthesized from dialkylzinc and dialkylsulfur, or dialkylzinc. Using an adduct synthesized from dialkyl selenium, hydrogen sulfide as a sulfur source, and hydrogen selenide as a selenium source, a zinc sulfide thin film and a zinc selenide thin film can be formed by a metalorganic vapor phase pyrolysis method. A method of manufacturing a characteristic semiconductor superlattice. 2. The hydrogen sulfide and the above-mentioned hydrogen sulfide in the state where the adduct synthesized from dialkylzinc and dialkylsulfur as the zinc source or the adduct synthesized from dialkylzinc and dialkylselenium is continuously supplied. 2. The semiconductor superlattice according to claim 1, wherein the zinc sulfide thin film and the zinc selenide thin film are alternately laminated on the substrate by alternately supplying hydrogen selenide. Manufacturing method. 3. An adduct synthesized from dialkylzinc and dialkylsulfur as the zinc source, or a state in which the adduct synthesized from dialkylzinc and dialkylselenium and the hydrogen sulfide are supplied, and as the zinc source. By alternately repeating the adduct synthesized from dialkylzinc and dialkylsulfur or the adduct synthesized from dialkylzinc and dialkylselenium and the state of supplying the hydrogen selenide. The method for producing a semiconductor superlattice according to claim 1, wherein zinc thin films and the zinc selenide thin films are alternately laminated.