JP2010073749A - Method for growing zinc-oxide-based semiconductor, and method for manufacturing semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for growing, on a substrate, a zinc-oxide-based semiconductor small in crystalline defects and excelling in single crystallinity and flatness; and a high-performance and high-reliability semiconductor element, particularly, a high-performance semiconductor light emitting element excelling in luminous efficiency, element life and mass productivity. <P>SOLUTION: The method for growing a zinc-oxide-based semiconductor includes steps of: (a) forming a first single-crystal layer by executing crystal growth at a first low growth temperature of 250-450°C and at a low growth pressure of 1-30 kPa by using an organic metal compound without containing oxygen and steam in an MOCVD method; (b) forming a second single-crystal layer on the first single-crystal layer by executing crystal growth at a second low growth temperature higher than the first low growth temperature and at a pressure higher than the low growth pressure; and (c) forming a third single-crystal layer on the second single-crystal layer by executing crystal growth at a high growth temperature and at a pressure higher than the low growth pressure. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for growing a zinc oxide based semiconductor and a method for manufacturing a semiconductor element, and more particularly to a method for growing a zinc oxide based semiconductor layer by MOCVD and a method for manufacturing a semiconductor light emitting element using the same.

  Zinc oxide (ZnO) is a direct transition type semiconductor having a band gap energy of 3.37 eV at room temperature, and is expected as a material for optical elements in the blue or ultraviolet region. In particular, the exciton binding energy is 60 meV and the refractive index n = 2.0, which is very suitable for a semiconductor light emitting device. Further, the present invention can be widely applied not only to light emitting elements and light receiving elements but also to surface acoustic wave (SAW) devices, piezoelectric elements, and the like. In addition, the raw material is inexpensive and harmless to the environment and the human body.

  In general, MOCVD (Metal Organic Chemical Vapor Deposition) method, MBE (Molecular Beam Epitaxy) method, and the like are used as crystal growth methods for zinc oxide compound semiconductors. The MBE method is a crystal growth method under an ultra-high vacuum, and has problems such as expensive equipment and low productivity. On the other hand, the MOCVD method has the advantages that the apparatus is relatively inexpensive, allows large area growth and simultaneous growth of a large number of sheets, has high throughput, and is excellent in mass productivity and cost. .

  As a crystal growth method of zinc oxide using the MBE method, for example, a low-temperature ZnO layer having a single crystal characteristic is grown on a sapphire substrate, and then flattened by heat treatment at a high temperature, and then a high-temperature ZnO layer is grown. A method for obtaining a ZnO layer with good crystallinity is disclosed (Patent Document 1). More specifically, a low-temperature grown ZnO single crystal layer formed by using a growth temperature lower than the crystal growth temperature for growing a ZnO single crystal is disclosed. However, the method disclosed in this document is a growth condition / method effective only for the MBE method, and such a method cannot be applied to the MOCVD method. That is, as is well known (for example, Patent Document 2), the growth conditions of the MBE method capable of crystal growth under non-stoichiometric (non-stoichiometric composition) conditions cannot be directly applied to the MOCVD method. Therefore, a method for growing a single crystal layer of a zinc oxide based semiconductor using MOCVD has been actively studied.

Various methods for crystal growth of zinc oxide (ZnO) or a zinc oxide based semiconductor on a different material substrate such as sapphire (Al ₂ O ₃ ) by MOCVD have been disclosed so far (for example, Patent Documents 2 and 3). . For example, in Patent Document 2, MgZnO microcrystals are formed on an A-plane sapphire substrate or C-plane silicon carbide substrate using O ₂ as an oxygen source as a reserve buffer layer, and the microcrystal serves as a seed crystal to serve as a buffer layer body. It is disclosed that an MgZnO crystal is formed on the entire surface of a substrate. Patent Document 3 discloses that a polycrystalline or amorphous laminate formed at a low temperature is annealed at a high temperature to form a buffer layer. However, in such a method, a defect remains between adjacent crystal grain boundaries when the polycrystal is converted into a single crystal by heat treatment. In addition, defects remain in the grain boundary coalescence at the stage where the buffer layer main body grows crystallites. Therefore, it is difficult to greatly reduce crystal defects. Thus, conventionally, attempts have been made to improve the crystallinity by forming a buffer layer made of polycrystal, microcrystal, or amorphous. However, the method for improving the crystallinity by MOCVD is complicated, and it is difficult to remove the crystal on the substrate. It was difficult to grow high quality ZnO-based crystals.

  As described above, although many methods for growing a ZnO-based single crystal on a sapphire substrate or the like by the MOCVD method have been proposed, there are many problems as a method for growing a simple and high-quality ZnO-based single crystal.

  In addition, in the case of MOCVD, when grown in an environment where crystallinity is improved (about 600 ° C. or higher), it tends to become (hexagonal) columnar crystals, network crystals, and (hexagonal) disk-like crystals oriented in the c-axis direction. There is. In such a polycrystal or imperfect single crystal that is strongly oriented in the crystal axis direction, the grain interface and transition cause leakage current and local current concentration of the semiconductor element, leading to deterioration of element characteristics and element life. In particular, in a semiconductor light emitting device, characteristics such as light emission efficiency and device life are deteriorated due to leakage current and current concentration. Furthermore, when the crystal surface is not flat, it leads to a decrease in process accuracy and a manufacturing yield in a semiconductor process such as lithography and etching. In addition, the production yield is reduced in cleavage and braking.

Thus, conventionally, it has been difficult to grow a flat ZnO-based semiconductor single crystal with few grain interfaces and transitions on a heterogeneous substrate such as a sapphire substrate by MOCVD. In order to achieve high performance and high reliability of a semiconductor device, particularly a semiconductor light emitting device having a large operating current density, it is extremely important to develop a crystal growth method with few crystal defects and close to a flat ideal crystal.
Japanese Patent No. 3424814 JP 2005-340370 A Japanese Patent No. 3859148

  The present invention has been made in view of the above-described points, and an object of the present invention is to provide a method for growing a zinc oxide based semiconductor crystal having few single crystal defects and excellent single crystallinity and flatness on a substrate. is there. Another object of the present invention is to provide a high-performance and high-reliability semiconductor device, particularly a high-performance semiconductor light-emitting device excellent in light emission efficiency and device lifetime. It is another object of the present invention to provide a semiconductor light emitting device with a high manufacturing yield and excellent mass productivity.

  The present invention is a method for crystal growth of a zinc oxide-based semiconductor layer on a substrate by MOCVD, using an organometallic compound not containing oxygen and water vapor, (a) a first in the range of 250 ° C. to 450 ° C. Forming a first single crystal layer by performing crystal growth at a low growth temperature and a low growth pressure in the range of 1 kPa to 30 kPa, and (b) a second low temperature higher than the first low growth temperature. Performing crystal growth at a growth temperature and a pressure higher than the low growth pressure to form a second single crystal layer on the first single crystal layer; and (c) from a high growth temperature and the low growth pressure. Forming a third single crystal layer on the second single crystal layer by performing crystal growth at a high pressure.

  Further, the present invention is a method for producing a semiconductor light emitting device by laminating a zinc oxide based semiconductor layer on a substrate by MOCVD method, using an organometallic compound not containing oxygen and water vapor, (a) 250 ° C. to Performing crystal growth at a first low growth temperature within a range of 450 ° C. and a low growth pressure within a range of 1 kPa to 30 kPa to form a first single crystal layer; and (b) the first low growth. Performing crystal growth at a second low growth temperature higher than the temperature and a pressure higher than the low growth pressure to form a second single crystal layer on the first single crystal layer; and (c) high Performing crystal growth at a growth temperature and a pressure higher than the low growth pressure to form a third single crystal layer on the second single crystal layer; and (d) from the high growth temperature and the low growth pressure. The third single crystal is grown at a high pressure. It is characterized by having a step of forming a light emitting layer above a.

  The high growth temperature can be a temperature in the range of 700 ° C to 850 ° C. The second low growth temperature can be a temperature in the range of 500 ° C to 650 ° C.

  Furthermore, the pressure higher than the low growth pressure can be a pressure in the range of 40 kPa to 120 kPa.

Further, the first single crystal layer is a zinc oxide (ZnO) layer, and the second single crystal layer and the third single crystal layer are Mg _x Zn _(1-x) O (0 ≦ x ≦ 0.43) layer.

  Hereinafter, a method for growing a zinc oxide-based semiconductor crystal layer having excellent single crystallinity and flatness on a substrate by MOCVD will be described in detail with reference to the drawings. Further, a semiconductor light emitting element (LED: Light Emitting Diode) will be described as an example of the semiconductor element formed by the growth method.

  The “low growth temperature” defined in the present specification is, for example, about 200 ° C. to 650 ° C., generally 50 ° C. to 500 ° C. than the temperature of crystal growth for growing a ZnO single crystal. This is a low temperature. The “high growth temperature” is generally a growth temperature suitable for growing a ZnO single crystal, and is a temperature higher than the above “low growth temperature” and about 850 ° C. or less.

FIG. 1 is a cross-sectional view showing a zinc oxide based semiconductor crystal layer (hereinafter referred to as a ZnO based semiconductor layer) grown on a substrate 10 according to the present invention. More specifically, the first ZnO layer 11A, the second ZnO layer 11B, and the ZnO-based semiconductor layer 12 are grown on the sapphire substrate using the MOCVD method. In the following, a case where Mg _x Zn _{(1-x) 2} O (0 ≦ x ≦ 0.68) is grown as the ZnO-based semiconductor layer 12 will be described as an example.

  In the following, the ZnO-based semiconductor may be another compound crystal based on ZnO. For example, a ZnO-based compound crystal in which a part of Zn (zinc) is replaced with calcium (Ca) may be used. Alternatively, a ZnO-based compound crystal in which part of O (oxygen) is replaced with selenium (Se), sulfur (S), tellurium (Te), or the like may be used.

  An MOCVD apparatus (not shown) used for crystal growth has a reaction vessel (chamber), and in the reaction vessel, a susceptor that holds the substrate 10, a heater that heats the susceptor, and a shower head that blows material gas onto the substrate. Is provided. Further, a pressure adjusting device for adjusting the exhaust pump and the pressure in the container is provided.

As the substrate 10, an α-sapphire single crystal sapphire (Al ₂ O ₃ ) substrate having a corundum structure is used. In the present embodiment, the first ZnO layer 11A is grown on the sapphire A plane using the sapphire A plane ({11-20} plane) as a crystal growth plane. Hereinafter, a substrate having a sapphire A plane ({11-20} plane) as a principal plane (crystal growth plane) is also referred to as an A-plane sapphire substrate. Here, the Miller index {} indicates a representative value of an equivalent surface.

  In this example, a material containing no oxygen was used as the organometallic compound material (or organometallic material). That is, a material that does not contain oxygen atoms in its constituent molecules and a material that does not contain oxygen molecules were used.

More specifically, DMZn (dimethylzinc) was used as the zinc (Zn) source, Cp2Mg (biscyclopentadienylmagnesium) was used as the magnesium (Mg) source, and TEGa (triethylgallium) was used as the gallium (Ga) source. In addition to the above materials, DEZn (diethyl zinc), TMGa (trimethyl gallium), or the like can be used. An organometallic material that does not contain oxygen is easily pyrolyzed at a low temperature, and reacts with O ₂ (oxygen) or H ₂ O (water vapor) even at room temperature, which is suitable for crystal growth at a low temperature.

H ₂ O (water vapor) was used as a liquid material as an oxygen source. H ₂ O is suitable for low-temperature growth of ZnO crystals because it has high reactivity with an organometallic material that does not contain oxygen in the molecule even at room temperature. Further, the H ₂ O molecule has a large polarization in the molecule, and has two lone electron pairs, and is excellent in the adsorption ability to the crystal surface and the like.

TMGa (trimethylgallium) was used as the n-type impurity source, and NH ₃ (ammonia) gas was used as the p-type impurity source. Note that these gases may be diluted with an inert gas such as nitrogen or Ar (argon).

  Further, nitrogen was used as a transport (carrier) gas. Liquid or solid material vapor and gaseous material (hereinafter referred to as material gas) are fed into the showerhead by the carrier gas and supplied to the substrate.

  FIG. 2 shows a crystal growth sequence used for crystal growth by the MOCVD method. First, the A-plane sapphire substrate 10 was set on the susceptor in the MOCVD apparatus, and the reaction vessel pressure was adjusted to 10 kPa (kilopascal) (time T = T1).

Next, supply of H ₂ O (water vapor) as an oxygen source from the shower head to the substrate 10 at a flow rate of 640 μmol / min was started (T = T2). The substrate 10 was heated from room temperature (RT) to 900 ° C. with a heater, and the substrate 10 was degassed for 10 minutes (T = T3 to T4). Thereafter, H ₂ O (water vapor) was kept flowing at the same flow rate until the growth was completed.

After the degassing treatment, the substrate temperature was lowered to 400 ° C. (first low growth temperature), and DMZn (dimethylzinc) as a zinc raw material was supplied to the substrate 10 at a flow rate of 1 μmol / min for about 15 minutes (T = T5−5). T6: Growth period of the first ZnO layer 11A, period G1A in FIG. At this time, the water vapor flow rate and the flow rate ratio of the organic metal (DMZn) (F _H2O / F _DMZn ratio), so-called VI / II ratio, is 640.

  Thus, a ZnO layer (first low temperature growth single crystal) having a growth temperature (Tg) of 400 ° C. under a reduced pressure growth condition (growth pressure Pg = 10 kPa), a growth rate of 1.7 nm / min, and a layer thickness of 25 nm. Layer, hereinafter also simply referred to as a first single crystal layer). 11A was grown.

  After the growth of the ZnO layer 11A, the substrate temperature was raised to 800 ° C. and heat treatment (annealing) was performed for 3 minutes (T = T7 to T8). As will be described later, this heat treatment further improved the crystallinity and flatness of the ZnO layer 11A.

After the heat treatment (annealing) of the first ZnO layer (first single crystal layer) 11A was completed, the second ZnO layer 11B was grown at a higher temperature and higher pressure than in the case of the first ZnO layer 11A. That is, the substrate temperature was lowered from the heat treatment temperature (800 ° C.) to 600 ° C. (second low growth temperature) higher than the first low growth temperature. The reaction vessel pressure was increased from 10 kPa (low growth pressure) to 80 kPa (high growth pressure). After the substrate temperature was stabilized, DMZn was supplied onto the ZnO layer 11A from the shower head at a flow rate of 10 μmol / min (T = T9 to T10: growth period of the second ZnO layer 11B, period G1B in FIG. 2). The flow rate ratio _(F H2O _/ F _MO ratio) of water vapor flow rate and organometallic this time (DMZn), so-called VI / II ratio is 64. DMZn was supplied for about 2.5 minutes, the growth rate was 16 nm / min, and the thickness of the second ZnO layer (the second low-temperature grown single crystal layer, hereinafter simply referred to as the second single crystal layer) was 40 nm. ) 11B was formed.

After the growth of the second ZnO layer 11B was completed, the ZnO-based semiconductor layer 12 was grown at a temperature (high growth temperature) higher than that of the second ZnO layer (second single crystal layer) 11B. That is, the substrate temperature was raised from 600 ° C. (second low growth temperature) to 800 ° C. (high growth temperature) while maintaining the reaction vessel pressure at 80 kPa. After the substrate temperature was stabilized, DMZn was supplied onto the ZnO layer 11B from the shower head at a flow rate of 10 μmol / min (T = T11 to T12: growth period of the ZnO-based semiconductor layer 12, period G2 in FIG. 2). The flow rate ratio _(F H2O _/ F _MO ratio) of water vapor flow rate and organometallic this time (DMZn), so-called VI / II ratio is 64. DMZn was supplied to the substrate 10 for about 60 minutes, and a ZnO-based semiconductor layer (ZnO layer) 12 having a growth rate of 17 nm / min and a layer thickness of about 1 μm was formed.

  Note that the waiting time until the substrate temperature is stabilized before the growth of the ZnO-based semiconductor layer 12 can also be used as the heat treatment of the second ZnO layer 11B.

Thus, at a growth temperature (800 ° C.) higher than the growth temperature of the second ZnO layer 11B, the growth rate is 17 nm / min and the layer thickness is about 1 μm. Hereinafter, also referred to as a third single crystal layer). In this embodiment, the case where ZnO is grown as the ZnO-based semiconductor layer 12 will be described as an example, but the present invention is not limited to this. In addition to DMZn, for example, Mg _x Zn _(1-x) O crystal that is a ternary crystal is grown by using Cp2Mg (biscyclopentadienylmagnesium) that is an organometallic compound that does not contain an oxygen atom. be able to.

  After the growth of the ZnO-based semiconductor layer 12 was completed, it was cooled while flowing water vapor. After the substrate temperature became 300 ° C. or lower, the supply of water vapor was stopped (T = T13).

As described above, the first ZnO layer (first single crystal layer) 11A, the second ZnO layer (second single crystal layer) 11B, and the ZnO-based semiconductor layer (third single crystal) are formed on the substrate. A substrate with a crystal growth layer (hereinafter simply referred to as a substrate with a growth layer) 15 on which the layer 12 was grown was manufactured.
[Crystallinity of first ZnO layer (first low-temperature grown single crystal layer) 11A]
The first ZnO layer (first single crystal layer) 11A obtained by the above-described growth process (T = T5 to T6) is a single crystal that is c-axis oriented on an A plane ({11-20} plane) sapphire substrate. Is a layer. That is, a {0001} plane of zinc oxide is laminated on a substrate having a {11-20} plane of α-sapphire single crystal as a main surface. The single crystallinity and flatness of the ZnO layer 11A were examined by RHEED (reflection high-energy electron diffraction) and AFM (atomic force microscope) measurements.

FIG. 3A is a diagram showing an RHEED diffraction image of the grown ZnO layer 11A when heat treatment (annealing) is not performed after the growth step (T = T5 to T6) is completed. As shown in FIG. 3A, streak-like RHEED diffraction images arranged at equal intervals were obtained. This shows that the surface crystal arrangement is single and smooth. Further, it was found by RFM (atomic force microscope) measurement that Rms (root mean square roughness) of 1 μm ² area was 0.62 nm (nanometer). Since the c-axis length (lattice constant) of the ZnO crystal was c = 5.207 Å, the surface roughness was equivalent to the c-axis length of the ZnO crystal, and it was found that the crystal layer surface was flat. From these results, it was confirmed that the ZnO layer 11A is a single crystal layer with good flatness.

FIG. 3B shows an RHEED diffraction image when a heat treatment is performed at a temperature of 800 ° C. for 3 minutes after the growth of the ZnO layer 11A. In this embodiment, the pressure Pa during the heat treatment is set to a low pressure (Pa = Pg = 10 kPa, which is the same as during crystal growth). Further, as described above, heat treatment is performed while supplying H ₂ O (water vapor) to the substrate 10, that is, in a water vapor atmosphere.

  As shown in FIG. 3 (b), it was confirmed that the RHEED diffraction image was more clearly streaked by the heat treatment than when the heat treatment was not performed (FIG. 3 (a)). . In addition, in AFM measurement, it was found that Rms (root mean square roughness) was 0.5 nm or less, which was less than the c-axis length of the ZnO crystal. Therefore, it was confirmed that the single crystallinity and flatness were improved by the heat treatment. That is, the first single crystal layer 11A is a low-temperature grown single crystal layer that is a thin film but flat at the sub-nano level.

  Thus, the ZnO layer 11A already has good flatness and a single crystal layer at the stage where the crystal growth is completed, and further improves the single crystallinity by heat treatment, and is not more than the c-axis length of the ZnO crystal. It was confirmed to have a flatness of

Although the case where a ZnO layer is grown as the first single crystal layer 11A and the second single crystal layer 11B has been described as an example, another compound crystal based on ZnO may be used.
[Growth conditions for first low-temperature grown single crystal layer 11A]
In this example, an A-plane sapphire substrate which is the {11-20} plane of α sapphire (α-Al ₂ O ₃ ) is used as the substrate 10, DMZ is used as the organometallic compound material not containing oxygen, and the growth temperature is set. The case where the first ZnO layer (first single crystal layer) 11A is grown at 400 ° C. and a growth pressure of 10 kPa has been described as an example. Further, the case where the growth rate is 1.7 nm / min and the growth layer thickness is 25 nm has been described as an example.

However, the conditions such as the substrate, the material gas, the growth temperature, the growth pressure, the growth rate, the growth layer thickness and the like shown in the above embodiments are merely examples, and are not limited thereto. The growth conditions including the heat treatment conditions were changed to grow the ZnO layer 11A, and the conditions for growing a single crystal layer with high flatness were examined. Hereinafter, the growth conditions of the first ZnO layer (first single crystal layer) 11A will be described in detail.
<Board>
An A-plane sapphire substrate is optimal. This is because the lattice mismatch between the A plane of the sapphire crystal and the C plane of the ZnO crystal is small. That is, the lattice mismatch between the sapphire <0001> direction (oxygen atom) and the ZnO <11-20> direction (zinc atom) is 0.07%, and the sapphire <10-10> direction (oxygen atom) and ZnO <10- The lattice mismatch in the 10> direction (zinc atom) is 2.46%. Here, since the ZnO <11-20> direction is locked to the sapphire <0001> direction, the ZnO crystal can grow a single crystal without forming a 30 ° rotation domain during growth.

In addition, as a usable substrate, in the case of a ZnO crystal with c-axis orientation on the substrate surface, the substrate surface has lattice matching points at rotationally symmetric positions of 60 °, 120 °, and 180 °. Any crystal substrate may be used. Further, in the case of an a-axis or m-axis oriented ZnO crystal, any crystal substrate in which a lattice matching point exists at a rotationally symmetric position of 180 ° may be used. For example, an R-plane sapphire substrate, an M-plane sapphire substrate, a SiC (silicon carbide) substrate, a GaN (gallium nitride) substrate, a Ga ₂ O ₃ (gallium oxide) substrate, a Si (silicon) substrate, or the like can be used.
<Growth temperature>
It is appropriate that the growth temperature is generally lower than a crystal growth temperature (referred to as “high growth temperature”) for growing a ZnO single crystal (referred to as “low growth temperature”). This is because at the high growth temperature, island-like growth is easy and layered single crystals are hardly formed.

More specifically, the growth temperature is preferably in the range of 250 ° C to 450 ° C. Furthermore, it is more preferable that it exists in the temperature range of 300 to 400 degreeC. At 250 ° C. or lower, the migration length becomes short, so that it becomes easy to be amorphous or polycrystallized. Further, as described above, when the temperature is higher than 450 ° C., island-shaped growth is likely to occur, and flatness is likely to be lowered (Rms value is increased).
<Growth pressure>
For single crystal growth, the migration length of reactive chemical species (DMZn, H ₂ O, intermediate products, Zn atoms before crystallization, O atoms before crystallization, etc.) on the substrate surface should be large. . Therefore, the reduced pressure growth is suitable, and specifically, the growth pressure is preferably 1 kPa to 30 kPa, more preferably 5 kPa to 20 kPa. When the growth pressure is 1 kPa or less, the growth rate is remarkably slowed.
<Material gas>
In order to form a ZnO single crystal layer under a low growth pressure and a low growth temperature, it is necessary to select a material having high mutual reactivity. This is because if the mutual reactivity is low, the crystal does not grow, or becomes amorphous or polycrystallized. As the Zn source, an organometallic compound that does not contain oxygen in the constituent molecules and has high reactivity with the oxygen source material is suitable. In addition to the DMZn described above, for example, there is DEZn (diethyl zinc). As the oxygen source, H ₂ O (water vapor) having a large intramolecular polarization and high reactivity with the organometallic compound material is suitable.
<Growth rate>
The growth rate is preferably in the range of 0.4 nm / min to 9 nm / min. Furthermore, it is more preferable to be within the range of 0.8 nm / min to 4 nm / min. When the growth rate is 9 nm / min or more, the surface irregularities become large, and sufficient flatness may not be obtained.
<Growth layer thickness>
The growth layer thickness is preferably in the range of 5 nm to 60 nm, and preferably in the range of 10 nm to 40 nm. Furthermore, it is more preferably 15 nm to 30 nm. That is, when the layer thickness is less than 5 nm, the crystal layer may not sufficiently cover the substrate surface. On the other hand, when the thickness is 60 nm or more, the unevenness of the surface becomes large and sufficient flatness may not be obtained.
<VI / II ratio (F _H2O / F _MO ratio)>
The water vapor flow rate and the organometallic (DMZn) flow rate ratio (F _H2O / F _DMZn ratio) may be about 2 or more. Specifically, about 2000 is sufficient. The water vapor flow rate is preferably about 70% of the saturated water vapor amount in which water vapor does not aggregate in the shower head.
<Heat treatment conditions>
As described above, the ZnO layer 11A already has good flatness and single crystal layer at the stage where crystal growth is completed. However, by performing heat treatment, the single crystallinity and flatness can be further improved. it can. Further, it is preferable to perform the heat treatment under a low pressure where the migration length becomes long. Note that the pressure range suitable for the heat treatment is the same as the growth pressure range of the ZnO layer 11A.

Specifically, the heat treatment temperature of the grown ZnO layer 11A is suitably 700 ° C. to 1100 ° C. The processing time is suitably in the range of 1 to 60 minutes. More preferably, the treatment temperature is 800 ° C. to 1000 ° C., and the treatment time is 3 minutes to 10 minutes. If the treatment temperature is less than 700 ° C., the effect is low, and if it is 1100 ° C. or more, the layer surface becomes rough. Further, when the treatment time is 60 minutes or more, film defects may occur due to film evaporation.
[Growth conditions for second low-temperature grown single crystal layer 11B]
<Growth temperature>
As a condition for forming a uniform layer on the ZnO layer 11A, 500 ° C. to 650 ° C. is preferable. If the growth temperature is lower than 500 ° C., the crystallinity is not sufficient and a heat treatment is required. Further, at 650 ° C. or higher, island growth occurs on the ZnO layer 11A.
<Growth pressure>
The growth pressure of the second ZnO layer (second single crystal layer) 11B is preferably 40 kPa to 120 kPa. This is because lateral growth (two-dimensional growth mode) is promoted and the growth layer is flattened. This upper limit value is an upper limit value of the airtightness of the MOCVD apparatus and is not a film forming condition.
<Growth layer thickness>
The layer thickness of the second ZnO layer (second single crystal layer) 11B is preferably 5 nm to 80 nm. If it is thinner than 5 nm, the covering (coverage) of the ZnO layer 11A is not sufficient. On the other hand, if it is thicker than 80 nm, hill rocks are generated on the surface. Furthermore, it is more preferable that it is 20 nm-60 nm.
<Growth rate>
The growth rate is preferably 60 nm / min or less and is preferably in the range of 5 nm / min to 60 nm / min. This is to prevent the occurrence of abnormal growth.
[Growth conditions of ZnO-based semiconductor layer (high-temperature grown single crystal layer) 12]
Conditions under which growth in the two-dimensional crystal growth mode (lateral growth mode) is performed on the second ZnO layer (second single crystal layer) 11B that is flat at the sub-nano level and has excellent single crystallinity. A ZnO-based semiconductor layer (high temperature grown single crystal layer, third single crystal layer) 12 is grown.

Here, in the present embodiment, the organic metal compound material (DMZn) not containing oxygen and water vapor are used on the ZnO layer 11B to achieve high temperature growth (800 ° C.), and the growth pressure is the same as in the case of the ZnO layer 11B. In addition, the case where the Mg _x Zn _(1-x) O crystal layer (second crystal layer) 12 is grown on the ZnO layer 11B at 80 kPa higher than the growth pressure of the ZnO layer 11A has been described as an example. Further, the case where the growth rate is 17 nm / min and the growth layer thickness is 1 μm has been described as an example.

However, the growth conditions of the ZnO-based semiconductor layer 12 on the ZnO layer 11B shown in the above embodiment are merely examples, and are not limited thereto. The growth conditions were changed to grow a ZnO-based semiconductor layer on the ZnO layer 11B, and the conditions for growing the ZnO-based semiconductor layer 12 excellent in flatness and single crystal were examined. Below, the growth conditions for growing the ZnO-based semiconductor layer (third single crystal layer) 12 on the second ZnO layer (second single crystal layer) 11B will be described in detail.
<Growth pressure>
It was found that the crystallinity is improved by increasing the growth pressure. That is, it was found that when the growth pressure is increased, lateral growth (two-dimensional growth mode) is promoted, and the plane (C plane) perpendicular to the c-axis is flattened. It has been found that a high growth pressure is desirable for obtaining a flat crystal growth surface with good crystallinity and no irregularities or pits on the surface of the ZnO-based semiconductor layer (high temperature growth single crystal layer). Specifically, the growth pressure is preferably 40 kPa or more. Moreover, 60 kPa or more is more preferable, and it is further more preferable that it is 80 kPa or more. As an upper limit, about 120 kPa is appropriate. This upper limit value is an upper limit value of the airtightness of the MOCVD apparatus and is not a film forming condition.
<Growth temperature>
It has been found that as the growth temperature increases, the transition density decreases, the crystallinity improves, and the flatness improves. Specifically, 700 ° C. or higher at which a flat surface is formed in the c-axis direction is preferable. The upper limit is about 850 ° C. where growth becomes difficult with H ₂ O (water vapor). A temperature range of 740 ° C. to 810 ° C. is preferable, and 780 ° C. to 810 ° C. is most preferable.
<Growth layer thickness>
Surface morphology, flatness and crystallinity were evaluated by SEM (scanning electron microscope) and TEM (transmission electron microscope). FIG. 4 shows a cross-sectional TEM bright field image (layer thickness: 1.05 μm) after growing the ZnO-based semiconductor layer (third single crystal layer) 12 and surface SEM images (SEM-1˜) of growth layers having different growth layer thicknesses. SEM-4). In addition, the surface structure seen in SEM images of SEM-3 and SEM-4 was taken by intentionally putting the part where microcrystals were attached within the field of view as proof that the focus was on the surface. It is a thing. In addition, as a whole, adhesion of microcrystals is rare.

When the layer thickness (t) is 0.06 μm (SEM-1) and 0.13 μm (SEM-2), the pit densities are 1.8 × 10 ⁹ cm ⁻² and 3.7 × 10 ⁸ cm ⁻² , respectively. The transition occurring from the substrate interface decreases with increasing layer thickness. When the layer thickness is 0.5 μm (SEM-3), the gap due to the pit disappears and the transition converges. That is, the disappearance of the gap due to the pit is related to the convergence of the transition. As described above, the ZnO-based semiconductor layer 12 formed on the second ZnO layer (second single crystal layer) 11B grows in a substantially film shape from the initial growth stage, and is generated from the substrate interface as the layer thickness increases. It has been found that the threading transitions that are present show a marked decrease. It was also found that the growth layer was completely flattened at the early stage of growth with a layer thickness of 0.5 μm, and the transition density was significantly reduced. Further, as can be seen from the SEM image (SEM-4) of the growth layer having a layer thickness (t) of 1.05 μm, it grows while maintaining flatness thereafter. Therefore, the growth layer thickness is preferably 0.5 μm or more.

On the other hand, when the ZnO-based semiconductor layer 12 is grown on the first ZnO layer 11A without forming the second ZnO layer 11B, the layer thickness may be 1.5 μm or more in order to obtain high flatness. Although it is preferable, the thickness of the ZnO-based semiconductor layer for obtaining high flatness can be reduced by providing the second ZnO layer 11B. In addition, it is possible to form a ZnO-based semiconductor layer 12 with few crystallinity and good crystallinity.
<Growth rate>
The growth rate is preferably in the range of 5 to 60 nm / min. When the growth rate is 60 nm / min or more, abnormal growth tends to occur.
<Crystal composition>
As the ZnO-based semiconductor layer 12, for example, Mg _x Zn _{(1-x) 2} O (0 ≦ x ≦ 0.43) crystal can be used. However, as the Mg composition x increases, the lattice constant difference in the a-axis direction increases and the defect density of the deposited semiconductor crystal layer increases, so it is more preferable that the range is 0 ≦ x ≦ 0.3.

Further, as described above, the ZnO-based semiconductor layer 12 may be another compound crystal based on ZnO. For example, a ZnO-based compound crystal in which a part of Zn (zinc) is replaced by Ca may be used, or a ZnO-based compound crystal in which a part of O (oxygen) is replaced by Se, S, Te, or the like. There may be.
<Material gas>
Growth at a high temperature makes it possible to obtain a high-quality ZnO crystal by sufficiently obtaining the migration length of the reactive chemical species on the crystal growth surface. On the other hand, it becomes difficult for the gaseous material to be an oxygen source to adhere to the substrate surface, and growth is hindered. As the oxygen source, H ₂ O (water vapor) that has a large polarization in the molecule and is adsorbed on the substrate surface even at a high temperature is suitable.

As the Zn source, an organometallic compound that does not contain oxygen and has high reactivity with the oxygen source material is suitable. In addition to the DMZn described above, for example, there is DEZn (diethyl zinc). As the Mg source, there is Cp2Mg (biscyclopentadienylmagnesium).
<Dopant>
To adjust the conductivity type (n-type) of the ZnO-based semiconductor layer 12, any one of TMGa (trimethylgallium), TEGa (triethylgallium), TMAl (trimethylaluminum), TMIn (trimethylindium), and TEIn (triethylindium) is used. What is necessary is just to add more than a kind.

In addition, it is preferable to dope in the latter half of the growth time during which the crystal plane is flattened. Specifically, it is more preferable to add it after the layer thickness of 0.25 μm. That is, the ZnO-based semiconductor layer 12 is preferably an undoped layer having a layer thickness of at least 0.25 μm.
<Growth sequence>
FIG. 5 shows a crystal growth sequence of a modified example of this embodiment. In this modification, the growth of the second ZnO layer (second single crystal layer) 11B is continued until the growth of the ZnO-based semiconductor layer (ZnO layer) 12 starts. The other growth conditions are the same as in the above example.

  More specifically, in the embodiment described above, the second ZnO layer (second single layer layer) is raised before the substrate temperature is raised from 600 ° C. (second low growth temperature) to 800 ° C. (high growth temperature). Crystal layer 11B has been grown (growth period T = T9 to T10, period G1B in FIG. 2). In this modification, the supply of DMZn is continued until the growth start of the ZnO-based semiconductor layer 12 (T = T11), and the growth period of the second single crystal layer 11B is set to T = T9 to T11 (period G1B ′ in FIG. 5). ). However, the temperature raising time is preferably within 10 minutes from the viewpoint of preventing the occurrence of hill rocks.

  6 shows that when a ZnO-based semiconductor layer (third single crystal layer) 12 is grown on the first ZnO layer 11A (LT1), the growth period is T = T9 to T10 (period G1B in FIG. 2). When the ZnO-based semiconductor layer 12 is grown on the second ZnO layer 11B (LT2A), the growth period is set to T = T9 to T11 (period G1B ′ in FIG. 5), and the ZnO-based semiconductor layer 12 is grown on the second ZnO layer 11B. When the semiconductor layer 12 is grown (LT2B), the half width (FWHM) of the X-ray diffraction (0002) ω and (10-10) ω rocking curves is shown.

  When the ZnO-based semiconductor layer 12 is grown on the second ZnO layer 11B (LT2A, LT2B), the crystallinity is superior, and the growth of the second ZnO layer 11B is continued until the growth of the ZnO-based semiconductor layer 12 starts. (LT2B) is further excellent in crystallinity.

  As described above in detail, when the above growth conditions are used, a high flatness is obtained on the second ZnO layer (second single crystal layer) 11B which is a thin film but has excellent flatness and single crystallinity. ZnO-based semiconductor layer 12 having the properties and crystallinity can be grown. That is, the ZnO-based semiconductor layer (third single crystal layer) 12 can be grown so as to have a layer thickness sufficient for application to element manufacturing while having higher flatness and crystallinity. It can be widely applied to device manufacturing. For example, a light emitting layer (active layer), an LED light emitting operation layer, a cladding layer in a semiconductor laser element, or an element operation layer such as an electronic device can be directly grown on the ZnO-based semiconductor layer 12. Alternatively, the ZnO-based semiconductor layer 12 grown under the above-described growth conditions may be grown as a part of the LED light emitting operation layer, the cladding layer, or the element operation layer.

Here, in this specification, an operation layer or an element operation layer refers to a layer composed of a semiconductor to be included in order for a semiconductor element to perform its function. For example, a simple transistor includes a structural layer formed by a pn junction of an n-type semiconductor, a p-type semiconductor, and an n-type semiconductor (or a p-type semiconductor, an n-type semiconductor, and a p-type semiconductor). Note that a semiconductor layer that includes a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer (or a p-type semiconductor layer and an n-type semiconductor layer) and emits light by recombination of injected carriers, particularly, emits light. This is called the operation layer.
[Growth layered substrate 15]
The substrate with a growth layer 15 obtained by the above process can be used for the manufacture of semiconductor elements in the MOCVD apparatus without cooling. Alternatively, after cooling, a semiconductor element can be manufactured using an MOCVD apparatus or another crystal growth apparatus.

  That is, if the substrate with growth layer 15 is used, a single crystal is grown directly on the single crystal layer (ZnO-based semiconductor layer 12) having excellent single crystallinity and flatness using an MOCVD apparatus or another crystal growth apparatus. Can be done. Therefore, a high-quality ZnO-based semiconductor layer having few crystal defects and excellent single crystallinity and flatness can be formed.

  Further, using the substrate 15 with a growth layer, optical semiconductor elements, various electronic devices, and the like are formed by various methods other than MOCVD, such as MBE, plasma CVD, PLD (Pulsed Laser Deposition), and hydride VPE. It is also possible.

  As described above, according to the present invention, a growth in which a high-quality single crystal layer with few crystal defects, excellent single crystal properties and flatness, which can be applied to manufacture of optical semiconductor elements and various electronic devices is formed. A layered substrate can be provided.

  FIG. 7 shows a cross-sectional view of a semiconductor light emitting device structure grown on a substrate 10 according to the present invention. More specifically, the growth layer in which the first ZnO layer (first single crystal layer) 11A, the second ZnO layer (second single crystal layer) 11B, and the ZnO-based semiconductor layer 12 are formed according to the above embodiment. A light emitting operation layer (hereinafter also referred to as an LED operation layer) 20 including an n-type ZnO-based semiconductor layer 21, a ZnO-based semiconductor active layer 22, and a p-type ZnO-based semiconductor layer 23 was formed on the attached substrate 15. Further, the crystal growth conditions of the LED operation layer 20 were the same as the growth conditions of the ZnO-based semiconductor layer 12 in the above-described examples unless otherwise specified below. That is, the crystal growth sequence is the same as that shown in FIG. 2, and the same growth temperature, growth pressure, material gas, etc. as the period (G2) of T = T11 to T12 are used. An n-type ZnO-based semiconductor layer 21, a ZnO-based semiconductor active layer 22, and a p-type ZnO-based semiconductor layer 23 were sequentially grown. The growth conditions such as the growth temperature and the growth pressure of the LED operation layer 20 do not necessarily have to be the same as the growth conditions of the ZnO-based semiconductor layer 12. That is, the crystal growth conditions of the LED operation layer 20 are preferably within the range of the crystal growth conditions of the ZnO-based semiconductor layer 12.

As described above, the LED operation layer is grown on the ZnO-based semiconductor layer 12 having good flatness and single crystallinity under the growth conditions similar to those of the ZnO-based semiconductor layer 12, thereby obtaining a flat and excellent crystallinity LED. It is possible to form an operating layer. In the following, a case where Mg _x Zn _{(1-x) 2} O is used as the ZnO-based semiconductor will be described as an example.

  After growing the undoped ZnO-based semiconductor layer 12, the n-type ZnO-based semiconductor layer 21 was grown while maintaining the growth temperature and pressure (growth temperature 800 ° C., pressure 80 kPa). As described above, the undoped ZnO-based semiconductor layer 12 preferably has a layer thickness of at least 0.25 μm.

H ₂ O (water vapor) was kept at 640 μmol / min, and the DMZn flow rate was increased from 10 μmol / min to 30 μmol / min to grow a Ga-doped Mg _x Zn _(1-x) O crystal having a layer thickness of 3 μm. The flow rate of the Mg material gas (Cp2Mg) may be adjusted according to the Mg crystal composition x.

Further, since the conductivity type (n-type) _{control, Mg x Zn (1-x} ) simultaneously TEGa crystal growth of _{O Mg x Zn (1-x} ) concentration of O in the crystal 5 × ¹⁰ 18 ^{(cm -3} ).

Next, the DMZn flow rate was reduced to 1 μmol / min to grow an active layer 22 (Mg _x Zn _(1-x) O crystal) having a layer thickness of 30 nm. Here, the H ₂ O (water vapor) flow rate ratio (VI / II ratio) with respect to the DMZn flow rate was increased from 21 to 640 by reducing the flow rate of DMZn. Thereby, oxygen vacancies and the like in the growth layer can be reduced, so that high luminous efficiency can be obtained.

Next, the p-type ZnO-based semiconductor layer 23 was grown. Specifically, N (nitrogen) -doped Mg _x Zn _(1-x) O crystal having a layer thickness of 100 nm was grown at a DMZn flow rate of 1 μmol / min. Here, simultaneously with the crystal growth of Mg _x Zn _(1-x) O, NH ₃ (ammonia) is supplied as a p-type impurity material (dopant) at a flow rate of 180 μmol / min, and the nitrogen impurity concentration Na (N) = 8. Crystal growth was performed so as to be × 10 ¹⁹ (cm ⁻³ ).

  After the above steps were completed, the pressure of 80 kPa was maintained while flowing water vapor until the substrate temperature reached 300 ° C. After the substrate temperature became 300 ° C. or lower, the water vapor was stopped and the substrate was waited until the substrate temperature reached room temperature, and then taken out from the reaction vessel.

Incidentally, it has been described a case of using the _{Mg x Zn (1-x)} O crystals as n-type ZnO based semiconductor layer 21, active layer 22 and p-type ZnO based semiconductor layer 23. in this case,
n-type ZnO-based semiconductor layer 21: Mg _x Zn _{(1-x) 2} O (0 ≦ x ≦ 0.43),
p-type ZnO-based semiconductor layer 23: Mg _x Zn _{(1-x) 2} O (0 ≦ x ≦ 0.43),
Active layer 22: Mg _x Zn _(1-x) O / Mg _y Zn _(1-y) O
(0 ≦ (x, y) ≦ 0.43: y <x)
Can be used.

  Here, the Mg crystal composition x may be 0.63 or less if the layer thickness is about 0.5 μm or less, and 0.43 or less if the layer thickness is 0.5 μm or more. This is because MgO in the MgZnO crystal causes phase separation when the Mg composition increases.

  In addition, each of the n-type ZnO-based semiconductor layer 21, the active layer 22, and the p-type ZnO-based semiconductor layer 23 may have a multilayer structure in accordance with the light emitting element characteristics. Further, an MQW (Multi quantum well) structure may be adopted as the active layer 22. In particular, in the case of an MQW active layer, fluctuations in the layer thickness of the crystal layer (well layer, barrier layer) change the quantum level energy, quantum level density, etc., greatly affecting the emission wavelength, internal quantum efficiency, etc. Further, the effect of using the ZnO-based semiconductor layer 12 having excellent flatness and single crystallinity is further remarkable.

The board | substrate 25 with an LED operation layer manufactured at the said process was evaluated with the differential interference microscope and the scanning electron microscope (SEM). Fig.8 (a) is a differential interference microscope image (FIG.8 (a)) of the surface of the board | substrate 25 with an LED operation layer manufactured by the said process. For comparison, FIG. 8B shows a differential interference microscope image when the LED operation layer is formed at a growth temperature (Tg) of 680 ° C. From these results, it was confirmed that the substrate with LED operation layer 25 manufactured by the above-mentioned process has an extremely flat mirror surface from the macroscopic region to the microscopic region without any irregularities or pits on the surface.
[Manufacture of semiconductor light emitting devices]
A semiconductor light emitting element (LED) is manufactured by the following steps using the substrate 25 with an LED operation layer manufactured in the above process. FIG. 9 is an element top view of the semiconductor light emitting element (LED) 30, and FIG. 10 is a cross-sectional view of the LED 30. FIG. 10 shows that two LEDs 30 and an element partitioning groove 32 for separating them by braking are formed.

  First, using a photolithography technique, a resist mask having a shape covering the region (element region) in the element section 31 was formed. Next, using wet etching, the p-type ZnO-based semiconductor layer 23, the active layer 22, and the n-type ZnO-based semiconductor layer 21 in the opening outside the element section 31 were partially removed to a predetermined depth. Finally, the resist was removed by washing, and element partition grooves 32 were formed.

  Since the surface of the substrate with LED operation layer 25 of the present invention is flat and mirror-like on the entire substrate (for example, a 2-inch substrate), the resist can be applied and formed with a uniform thickness. Further, since there is no unevenness on the surface, there is no exposure blur of the transfer pattern in the photolithography process, and transfer can be performed with high accuracy.

  Next, the p-side electrode 33 was formed using photolithography, EB (electron beam) deposition, or the like. The p-side electrode 33 is formed by depositing Ni (nickel) with a thickness of 0.3 to 10 nm and Au (gold) with a thickness of 5 to 20 nm, and using an RTA (rapid thermal annealer) in an oxygen 10% atmosphere. A translucent electrode was formed by treatment at 500 ° C. for 30 seconds.

  Next, a Ni / Pt / Au electrode pad material was laminated in this order with a thickness of 3 to 10 nm / 100 nm / 1000 nm on the p-side electrode 33 by EB vapor deposition to form a p-side connection electrode 34.

  Further, by using photolithography, Ti / Au was laminated on the exposed surface of the n-type ZnO-based semiconductor layer 21 in this order by EB deposition in a thickness of 10 to 100 nm / 1000 nm, respectively, to form the n-side connection electrode 35. .

  After the electrodes were formed in this way, the LED operation layer side was attached to a protective substrate, the back side was ground and polished, and formed into a 100 μm thick wafer. Next, after a protective sheet was pasted on the surface side on which the electrodes were formed, a scribe groove 36 perpendicular to each other was formed on the back surface corresponding to the central portion of the element partition groove 32 using a scribe device.

  In braking, the knife edge 37 was applied from the element partitioning groove 32 side of the opposing surface of the scribe groove 36, loaded with the knife edge 37, and cleaved in the scribe groove direction. Similarly, the substrate was rotated 90 ° and cleaved in the direction of the scribe groove 36 perpendicular to the substrate.

  Since the surface of the substrate with LED operation layer 25 of the present invention has no unevenness, the bottom of the element partition groove 32 can be formed extremely flat, and the bottom surface of the partition groove can be accurately pressed by the knife edge 37. Accordingly, since stress is applied evenly during the pressure cleavage, the occurrence of cleavage failure due to chipping of the element sections, displacement of the cleavage surface, etc. can be reduced, and the cleavage yield is improved. In addition, there were no potential crystal grain boundaries (domains) existing in the crystal plane, chipping of the crystal layer originating from the grain boundaries was reduced during cleavage, and the separation yield was improved.

  When the element was formed using the substrate 25 with LED operation layer of the present invention, the yield of resist pattern formation was about 98%. Also, the cleavage yield was very good, about 98%.

  As described above, the LED operation layer is grown on the ZnO-based semiconductor layer 12 on which a high-quality single crystal layer with few crystal defects and excellent single crystallinity and flatness is formed. It is possible to form a high-performance LED that can form an excellent LED operating layer, has high emission efficiency with suppressed leakage current and current concentration, and has excellent device life. In addition, high process accuracy can be obtained in lithography and etching semiconductor processes, and the manufacturing yield in cleavage and braking is also high.

  In the above-described embodiments, the case where the present invention is applied to a semiconductor light emitting element (LED) has been described as an example, but the present invention is not limited thereto. For example, the present invention can be applied to an optical semiconductor element or an electronic device that can be formed using a ZnO-based semiconductor layer, such as a semiconductor laser (LD), a surface acoustic wave device, or a MOSFET.

As described above in detail, according to the present invention, H ₂ having high reactivity between an organometallic compound material not containing oxygen and the organometallic compound material on a different material substrate such as an A-plane sapphire substrate. Using O (water vapor), crystal growth can be performed at a low growth temperature and a low growth pressure to grow a single crystal layer (first single crystal layer) of zinc oxide. Further, the single crystallinity and flatness of the growth layer can be further improved by performing the heat treatment under a low pressure (reduced pressure) and in a water vapor atmosphere. Furthermore, crystal growth is performed on the first single crystal layer at a low growth temperature to grow a single crystal layer (second single crystal layer) of a zinc oxide-based compound semiconductor, thereby improving single crystallinity and flatness. Can be improved. The single crystal layer is excellent in flatness and single crystallinity and has few crystal defects. Furthermore, since the MOCVD method is used, large area growth and large number growth are possible. Therefore, it is excellent in mass productivity and manufacturing cost.

  Further, a ZnO-based compound semiconductor layer having higher flatness and crystallinity can be grown on the second single crystal layer having excellent flatness and single crystallinity. The ZnO-based compound semiconductor layer (third single crystal layer) 12 can be grown so as to have not only high flatness and crystallinity but also a layer thickness sufficient for application to device manufacturing. Therefore, an LED light emitting operation layer, a cladding layer in a semiconductor laser element, an element layer of an electronic device, and the like can be directly grown on the ZnO-based semiconductor layer 12.

  By growing an LED operation layer on the ZnO-based semiconductor layer 12, an LED operation layer that is flat and excellent in crystallinity can be formed, and the light emission efficiency with high leakage current and current concentration is suppressed, and the output is high. High performance LED can be provided. Furthermore, it is possible to manufacture an LED having an excellent element lifetime. Furthermore, high accuracy can be obtained also in the semiconductor process, and the manufacturing yield in cleavage and braking is also high.

It is sectional drawing which shows the 1st and 2nd low growth temperature crystal | crystallization layer and ZnO type semiconductor layer which were grown on the board | substrate by this invention. It is a figure which shows the crystal growth sequence used for the crystal growth by MOCVD method. It is a figure which shows the RHEED diffraction image when (a) heat processing is not performed and (b) heat processing is performed after the growth of the 1st ZnO layer. It is the cross-sectional TEM image after growing a ZnO-type semiconductor layer (3rd single crystal layer), and the surface SEM image (SEM-1-SEM-4) of the growth layer of different growth layer thickness. FIG. 4 is a diagram showing a crystal growth sequence of a modified example of Example 1. When the high-temperature growth layer is grown on the first low-temperature growth layer (LT1), when the growth period is grown on the second ZnO layer 11B where the growth period is T = T9 to T10 (LT2A), the growth period is T = It is a figure which shows the half value width (FWHM) of the X-ray diffraction rocking curve when it grows on the 2nd ZnO layer 11B which is T9-T11 (LT2B). 1 is a cross-sectional view of a semiconductor light emitting device structure grown on a substrate according to the present invention. It is the differential interference microscope image (a) of the substrate surface with an LED operation layer manufactured by this invention, and the differential interference microscope image (b) of the substrate surface which formed the LED operation layer at the growth temperature of 680 degreeC. It is an element top view of a semiconductor light emitting element (LED). It is sectional drawing of a semiconductor light emitting element (LED).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Substrate 11A 1st low temperature growth single crystal layer 11B 2nd low temperature growth single crystal layer 12 ZnO type compound semiconductor layer (high temperature growth single crystal layer)
15 substrate with crystal growth layer 20 LED operation layer 21 n-type semiconductor layer 22 active layer 23 p-type semiconductor layer 25 substrate with LED operation layer

Claims (18)

A method for crystal growth of a zinc oxide based semiconductor layer on a substrate by MOCVD,
Using oxygen-free organometallic compound and water vapor,
(A) performing crystal growth at a first low growth temperature within a range of 250 ° C. to 450 ° C. and a low growth pressure within a range of 1 kPa to 30 kPa to form a first single crystal layer;
(B) Crystal growth is performed at a second low growth temperature higher than the first low growth temperature and a pressure higher than the low growth pressure to form a second single crystal layer on the first single crystal layer. Forming step;
(C) performing crystal growth at a high growth temperature and a pressure higher than the low growth pressure to form a third single crystal layer on the second single crystal layer;
A method characterized by comprising:   The method according to claim 1, wherein the high growth temperature is a temperature within a range of 700C to 850C.   The method according to claim 1 or 2, wherein the second low growth temperature is a temperature within a range of 500C to 650C.   The method according to any one of claims 1 to 3, wherein the pressure higher than the low growth pressure is a pressure within a range of 40 kPa to 120 kPa.   The method according to claim 1, wherein the substrate is an α-sapphire single crystal and a crystal growth surface is a {11-20} plane. The first single crystal layer and the second single crystal layer are zinc oxide (ZnO) layers, and the third single crystal layer is Mg _x Zn _{(1-x) 2} O (0 ≦ x ≦ 0.43). 6. The method according to claim 1, wherein the method is a layer.   The method according to any one of claims 1 to 6, wherein a thickness of the first single crystal layer is in a range of 5 nm to 60 nm.   The method according to any one of claims 1 to 7, wherein a thickness of the second single crystal layer is in a range of 5 nm to 80 nm.   The method according to any one of claims 1 to 8, wherein a layer thickness of the third single crystal layer is 0.5 µm or more.   The method according to any one of claims 1 to 9, wherein the growth rate of the second single crystal layer and the third single crystal layer is 60 nm / min or less.   The step of forming the second single crystal layer includes changing the growth temperature from the second low growth temperature to the high growth temperature when shifting to the step of forming the third single crystal layer. The method of claim 1 including the step of forming two single crystal layers. A method of manufacturing a semiconductor light emitting device by stacking a zinc oxide based semiconductor layer on a substrate by MOCVD,
Using oxygen-free organometallic compound and water vapor,
(A) performing crystal growth at a first low growth temperature within a range of 250 ° C. to 450 ° C. and a low growth pressure within a range of 1 kPa to 30 kPa to form a first single crystal layer;
(B) Crystal growth is performed at a second low growth temperature higher than the first low growth temperature and a pressure higher than the low growth pressure to form a second single crystal layer on the first single crystal layer. Forming step;
(C) performing crystal growth at a high growth temperature and a pressure higher than the low growth pressure to form a third single crystal layer on the second single crystal layer;
(D) performing crystal growth at a high growth temperature and a pressure higher than the low growth pressure to form a light emitting layer on the third single crystal layer;
A method characterized by comprising:   The method according to claim 12, wherein the high growth temperature is a temperature within a range of 700C to 850C.   The method according to claim 12 or 13, wherein the second low growth temperature is a temperature within a range of 500C to 650C.   The method according to any one of claims 12 to 14, wherein the pressure higher than the low growth pressure is a pressure within a range of 40 kPa to 120 kPa.   The method according to any one of claims 12 to 15, wherein the substrate is an α-sapphire single crystal and a crystal growth surface is a {11-20} plane. The first single crystal layer is a zinc oxide (ZnO) layer, and the second single crystal layer and the third single crystal layer are Mg _x Zn _{(1-x) 2} O (0 ≦ x ≦ 0. 43) A method according to any one of claims 12 to 16, characterized in that it is a layer.   18. The method according to claim 12, wherein the third single crystal layer includes an undoped layer having a thickness of at least 0.25 μm formed on the third single crystal layer. .