JPH11157997A - Substrate for growing thin layer and emitter using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive and excellent substrate for growing thin layer that can stably produce magnesia spinel of high quality by not increasing, but rather lowering the crystal growth temperature for magnesia spinel, in addition, suitably permits the crystal growth from vapor phase such as epitaxial growth of gallium nitride and provide an emitter using the same. SOLUTION: This substrate for growing thin layer comprises magnesia spinel single crystal including a transition metal element and is used for growing semiconductor thin layer (single crystal) mainly containing gallium nitride. In an embodiment, this magnesia spinel single crystal contains 0.1-5.0 wt.% of TiO2 or MnO. The objective light-emitting device (LD) is prepared by arranging a laser element 3 having the semiconductor thin layers 31-35 at least containing gallium nitride on the substrate for growing thin layers thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to a blue laser diode device, a light emitting diode device, and the like, and is suitable for a thin-film growth substrate suitable for vapor-phase growth (particularly, epitaxial growth) of a high-quality gallium nitride-based semiconductor thin film. The present invention relates to a light emitting device such as various diode elements using the same.

[0002]

2. Description of the Related Art At present, a gallium nitride single crystal has a thickness of about 3.4.
It is expected that it has a band gap of eV and can be suitably used for a device emitting blue light. However, since the melting point of this crystal is high and the vapor pressure of nitrogen gas at the time of melting is very high at 10 ⁴ atm, it is extremely difficult to produce the crystal by a normal melting method. For this reason, MOV
It is synthesized by a vapor phase growth method such as PE (Metalorganic Vapor Phase Epitaxy). Substrates used for such a vapor phase growth are made of sapphire, gallium arsenide, silicon,
Single crystals such as magnesium oxide and silicon nitride have been used. Among them, high temperature (1200 ° C.)
A sapphire substrate that is stable even in a highly reducing hydrogen atmosphere has been put to practical use as a light emitting diode element substrate made of gallium nitride.

[0003] In order to use gallium nitride for a light emitting element of a laser diode (hereinafter also referred to as a light emitting device), it is necessary to form an end face required for laser oscillation. Since the substrate is formed by utilizing the cleavage of the substrate on which gallium nitride is epitaxially grown, the selection of the substrate is very important.

However, sapphire used as a substrate for the above-mentioned thin film growth has a weak cleavage property, and further has a cleavage of gallium nitride (1-100) (Note: Miller index "-1" is an inverted symbol of "1") Shall mean
Hereinafter, it will be described according to this).
-100) It is shifted about 30 degrees from the cleavage. For this reason, in the case of a sapphire substrate, it is not possible to make a cleavage surface of gallium nitride by using cleavage, which requires processes such as end face polishing and reflection film coating, which increases the cost and improves the quality of the cleavage. No mirror surface is obtained.

In view of the above problems, in recent years, (111)
In addition, magnesium spinel, which has the property of cleaving on the (100) plane, has been attracting attention as a substrate for epitaxial growth of gallium nitride, and in fact, examples of successful growth of gallium nitride have been reported (eg, Kuramata et al., Applied).
Physics Letters, Vol67 (1995), P2521-2523).

The cleavage surface of magnesia spinel (1)
The (11) or (100) plane coincides with the (1-100) cleavage direction of gallium nitride epitaxially grown on the (111) plane of magnesia spinel, so that an optical mirror surface can be obtained without special polishing. Thus, it can be said that applications of gallium nitride to laser diode elements are opening up.

In general, spinel (a crystal group having a spinel structure) has a lower hardness than that of sapphire (spinel is 7.5 to 8 with respect to Mohs hardness of 9 of sapphire). This has the advantage that back grinding (thinning of the growth substrate to facilitate element cutting) can be easily performed later, and the total processing cost can be reduced.

[0008]

However, since the melting point of magnesia spinel is much higher than the melting point of sapphire, that is, 2045 ° C., which is about 2150 ° C., crystal growth by the Czochralski method can produce good quality crystals at low cost. Will be quite difficult. Because magnesia spinel is colorless and transparent, it transmits radiant heat, making it difficult to achieve the heat balance necessary for crystal growth by the Czochralski method. Therefore, crystals grow rapidly immediately after seeding,
Crystal defects such as cell growth and air bubbles are generated, which causes the quality to remarkably deteriorate. As a countermeasure against this, it is conceivable to increase the temperature gradient. However, increasing the temperature gradient increases the temperature of the crucible, and the temperature of the crucible during growth is reduced to the melting point of Ir (iridium) of the crucible material (245).
0 ° C.), and there is a problem in durability when used at high temperatures.
In addition, the furnace material around the crucible also requires a special material, which increases the cost.

In the present invention, therefore, it is possible to stably produce a high-quality magnesia spinel with good reproducibility without raising the crystal growth temperature of magnesia spinel, but to increase the growth temperature. It is an object of the present invention to provide an inexpensive and excellent thin film growth substrate capable of favorably growing, and a light emitting device using the same.

[0010]

According to the present invention, a semiconductor thin film (single crystal) made of a magnesia spinel single crystal containing a transition metal element and containing gallium nitride as a main component is provided by the present invention. A thin film growth substrate (crystal growth substrate) for growth is provided.

Further, the substrate for thin film growth is characterized by comprising a magnesia spinel single crystal containing TiO ₂ or MnO in an amount of 0.1 to 5.0% by weight.

In particular, the magnesia spinel single crystal is 550
It has a light absorption spectrum characteristic (light transmittance) of 80% / mm or less in a wavelength band of １1400 nm.

Further, the light emitting device of the present invention is characterized in that a laser element made of a semiconductor thin film containing at least gallium nitride as a main component is provided on the thin film growth substrate.

An amorphous or crystalline buffer layer having a material similar in crystal structure to the thin film growth substrate and the semiconductor thin film is interposed between the thin film growth substrate and the semiconductor thin film containing gallium nitride as a main component. And may include such cases.

The laser element may include not only the semiconductor thin film but also other layers such as the buffer layer. Further, the buffer layer may be included in a substrate for crystal growth.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail.

First, a predetermined amount of an oxide of a transition metal such as Ti, Co, Cr, Mn, or Ni is added to an oxide mixture having a composition of MgAl ₂ O ₄ , and calcined at a temperature of 1200 to 1600 ° C. Is used as a raw material.

These raw materials are filled in a crucible made of, for example, Ir or Mo, and then placed in a high-frequency or resistance heating type single crystal growing furnace, and heated to a temperature higher than the melting point of the raw material. The internal material is melted. Then, after that, at a lifting speed of 1 to 5 mm / hour, the diameter is about 20 to 30 mm and the length is 30 to 60 mm by the Czochralski method.
Grow a single crystal.

Further, a wafer is processed from the grown single crystal to produce a wafer having a (111) plane as a main surface, and this wafer is used as a substrate for epitaxial growth (substrate for thin film growth).
And a double hetero structure in which an amorphous buffer layer and a single crystal mainly composed of gallium nitride are grown by vapor phase, and the active layer is sandwiched between layers having a band gap larger than the band gap. A semiconductor laser diode (light emitting device) made of a GaN (gallium nitride) compound semiconductor is manufactured.
The buffer layer is provided so as to reduce the difference between the lattice constant of the gallium nitride single crystal and the lattice constant of the crystal growth substrate as much as possible. There may be no layers.

Here, the substrate for thin film growth is preferably made of TiO ₂
Or a MnO 0.1 to 5.0 wt% (TiO ₂ is is particularly preferred 0.1 to 2.0 wt.%), Characterized in that it consists of a magnesia spinel single crystal for the additional inclusion. Further, the magnesia spinel single crystal has a thickness of 550 to 1400 nm.
It has a light absorption spectrum characteristic (light transmittance) of 80% / mm or less within a wide wavelength band. When the amount is less than the lower limit of the above weight%, there is almost no difference in light absorption spectrum characteristics from the magnesia spinel single crystal to which the transition metal element is not added, and when the amount exceeds the upper limit, the oxide of the transition metal element is hardly taken into the crystal. In addition, segregation causes crystal defects and cracks, so that a long crystal cannot be grown.

FIG. 1 is a perspective view of the semiconductor laser diode LD, and FIG. 2 is a cross-sectional view taken along the line XX of FIG. 2. As shown in FIG. A buffer layer 2 made of a gallium nitride or AlN (aluminum nitride) layer is provided, and a semiconductor multi-layer 3 forming a laser device is provided on the buffer layer 2.
As described above, the semiconductor laser diode LD is configured by disposing a laser element composed of a single crystal layer containing gallium nitride as a main component on the substrate 1.

The multi-layer 3 includes an n + layer 31 made of an n-type GaN layer doped with Si (silicon) provided on the front surface of the buffer layer 2 and an electrode 41 provided on the n + layer 31.
And Si doped A provided in a portion other than the electrode 41
An n layer 32 composed of an l _0.1 Ga _0.9 N layer, an active layer 33 composed of a GaN layer doped with Si, and a p layer 3 composed of an Al _0.1 Ga _0.9 N layer doped with Mg (magnesium).
4, a SiO ₂ (silicon oxide) layer 35 covering the
It is composed of an electrode 42 provided in the window of the O ₂ layer 35.

As shown in FIG. 1, the facing end faces 1b and 1b of the substrate 1 are cleaved along the (1-100) plane, and the facing end faces (resonant surfaces) of the multi-layer 3 are formed.
The surfaces on which 3a and 3a are formed are respectively end faces 1
b, 1b.

Hereinafter, a method of manufacturing the semiconductor laser diode LD shown in FIGS. 1 and 2 will be described. First, a spinel-type single crystal substrate having a (111) plane as a main surface is prepared, and after the substrate 1 is organically washed, it is set in a crystal growth section of a crystal growth apparatus. After evacuating the inside of the apparatus, hydrogen is supplied, and the temperature is raised to about 1200 ° C. in a hydrogen atmosphere to remove the hydrocarbon-based gas attached to the substrate surface.

Next, the temperature of the substrate 1 is lowered to about 500 ° C., TMG (trimethylgallium) and NH ₃ (ammonia) are supplied, and gallium nitride is grown on the substrate 1 to a thickness of about 300 μm. The buffer layer 2 is used. Next, the temperature of the substrate 1 is raised to 1030 ° C., and SiH ₄ (silane) is supplied in addition to the above-mentioned gas to form a Si-doped G
An n layer 31 composed of an aN layer is grown.

Once the substrate 1 is taken out of the growth furnace, n +
After masking a part of the surface of the layer 31 with SiO _2, it is returned to the growth furnace again, evacuated and supplied with hydrogen and NH ₃ ,
Raise the temperature to 1030 ° C. Next, TMA (trimethylaluminum), TMG and SiH ₄ are supplied to form SiO ₂
An Si-doped Al _0.1 Ga _0.9 N layer having a thickness of 0.5 μm is formed in a portion where 2 is not masked to form an n layer 32.

Next, TMG and SiH ₄ are supplied to form a Si-doped GaN layer having a thickness of 0.2 μm to form an active layer 33.
And Next, TMA, TMG and Cp ₂ Mg (biscyclopentadienyl magnesium) are supplied to form a 0.5 μm-thick magnesium-doped Al _0.1 Ga _0.9 N p-layer 34.

Next, the SiO ₂ used as a mask is removed with a hydrofluoric acid-based etchant, and the SiO ₂
After depositing the _two layers 35, a window is opened in a rectangular shape having a predetermined size, and is moved to a vacuum chamber to irradiate the p layer 34 with an electron beam. By this electron beam irradiation, the p-layer 34 showed p-conduction.
Then, the portion corresponding to the window of the p layer 34 and the n + layer 31
Metal electrodes 41 and 42 were formed, respectively. Here, the anode (electrode 42) is, for example, an upper layer: Au (gold) / a lower layer: Cr
A two-layer structure of (chromium) or a three-layer structure of upper layer: Au / intermediate layer: Pt (platinum) / lower layer: Ti (titanium), and the cathode (electrode 41) is, for example, upper layer: Au / intermediate layer: Ni ( Nickel) / Lower layer: Au-Ge (germanium) alloy 3
It has a layer structure or the like.

A large number of multiple layers 3 constituting the above-mentioned laser element are formed on one substrate 1. And this oxide substrate 1
1 and 2 can be obtained by simultaneously dividing the semiconductor laser diode and the multi-layer 3.

At the time of this division, the opposing end faces 3a and 3a of the multilayer 3 and the end faces 1b and 1b of the substrate 1 are divided by cleavage of the (1-100) plane of the gallium nitride single crystal.
The other end face is cut by a diamond cutter or the like and divided. Thus, an excellent semiconductor laser diode having high oscillation efficiency can be obtained. In addition, the thin film growth substrate of the present invention can significantly reduce crystal defects such as bubbles, crystal grain boundaries, and strains, and can produce a high-quality crystal substrate with a high yield compared to a conventional MgAl ₂ O ₄ spinel substrate. is there.

The (111) plane of the spinel-structured thin film growth substrate of the present invention has good matching with the gallium nitride (0001) plane, and the structural period of the bonding plane is shown in Table 1. The difference from gallium nitride (mismatch rate:
(| D1-D2 | / D1) x100, where D1: distance between nitrogen atoms on the (0001) plane of gallium nitride single crystal, D
2: The interatomic distance between oxygen atoms on the main surface on which a single crystal containing gallium nitride as a main component is vapor-phase grown is within 6.7%, and has the same consistency as that of a conventional magnesium spinel. As a result, a high-quality gallium nitride thin film can be produced.

Incidentally, the magnesia spinel single crystal of the present invention can be used within a wide light wavelength band of 550 to 1400 nm.
As long as it has a light transmittance of not more than% / mm, it may contain an element other than the above-mentioned transition metal element, and can be appropriately changed and implemented without departing from the gist of the present invention.

[0033]

EXAMPLES [Example 1] 4N MgO powder and 4N Al ₂ O
₃ powder, a TiO ₂ powder 4N 28.047: 70.
The mixture was weighed at a mixing ratio of 953: 1.0% by weight. After dry-mixing this raw material for 10 hours with an alumina ball, 1 t / c
What was press-molded at m ² and fired at 1600 ° C. was used as a raw material for crystal growth.

Iridium diameter 50 mm, height 50 m
A crucible having a thickness of 2 mm and a thickness of 2 mm was filled with 180 g of the above-mentioned raw material, and heated and melted to a melting point or higher, and then a magnesia spinel seed crystal having a <111> orientation was seeded on the melt surface. ~ 20rpm, pulling speed 3
It grew on conditions of 〜5 mm / h.

The grown crystal was a transparent blue crystal having an outer diameter of 25 mm and a length of 50 mm. As shown in FIG. 3, the crystal was highly controllable after seeding, and was a high-quality crystal free of cracks, grain boundaries and crystal distortion. In the drawing, K is a crystal growing rod, which indicates the shoulder of the grown crystal of J.

From this crystal, a diameter of 25 mm and a thickness of 0.5 m
A mirror surface wafer of the (111) plane of the m wafer was collected, and GaN, which is a blue light emitting semiconductor, was grown on the wafer. G
The aN growth process is performed at 1000 to 1200 ° C. in a reducing gas such as H ₂ or He. In this substrate, the film was formed normally without any damage to the substrate in the process. In addition, there was no problem in back polishing or braking in the device process, and the light emitting device could be manufactured with a high yield.

The amount of TiO ₂ added is 0.1 to 2.0% by weight.
However, when the addition amount exceeds 5.0% by weight, the effect of the addition of TiO ₂ is remarkably deteriorated due to a change in composition or a decrease in crystal quality due to cell growth in the lower portion of the crystal.

[0038] 500-
Although there is no absorption at a wavelength of 1500 nm, by adding TiO ₂ , the transmittance is 60% / mm or less over a wide range of 500 to 1050 nm as shown in FIG. The temperature difference with the liquid is reduced,
It is considered that the controllability of the crystal was improved.

[Example 2] 4N MgO powder and 4N Al ₂
28.047: 70.9 4N MnO powder in O ₃ powder
It was weighed at a mixing ratio of 53: 1.0% by weight. This material was dry-mixed with alumina balls for 10 hours and then 1 t / cm
^What was press-molded in ² and fired at 1600 ° C. was used as a raw material for crystal growth.

The same crucible as in Example 1 made of iridium was charged with 180 g of the above-mentioned raw material, and heated and melted at a temperature not lower than the melting point.
A magnesia spinel seed crystal having an orientation of 111> is seeded on the surface of the melt, and the temperature is gradually lowered while the rotation speed is 10 to 2
They were grown under the conditions of 0 rpm and a pulling speed of 3 to 5 mm / h.

The grown crystal was a transparent red crystal having an outer diameter of 25 mm and a length of 50 mm, which was a high quality crystal having high crystallographic controllability after seeding as in Example 1 and free from cracks, crystal grain boundaries and crystal distortion.

From this crystal, a diameter of 25 mm and a thickness of 0.5 mm
A mirror-finished wafer of the (111) plane of the wafer was collected, and GaN as a blue light emitting semiconductor was grown on the wafer. Ga
In the growth process of N, H ₂ or H
The process was performed in a reducing gas of e. In this substrate, the film could be formed normally without damaging the substrate in the process.
In addition, a light emitting element could be manufactured with a high yield without any problem due to back polishing or breaking in a device process.

The effect was observed when the amount of MnO added was in the range of 0.1 to 5.0% by weight. However, when the amount of addition exceeded 5.0% by weight, the crystal quality deteriorated due to composition fluctuation and cell growth in the lower part of the crystal. As a result, the effect of the addition of MnO was significantly deteriorated.

With no added magnesia spinel, 500 to
Although there is no absorption at a wavelength of 1500 nm, the addition of MnO results in a light transmittance of 60% / mm or less over a wide range of 500 to 1100 nm as shown in FIG. The temperature difference with the liquid is reduced,
It is considered that the controllability of the crystal was improved.

[Comparative Example] 4N MgO powder and 4N Al
_{The 2} O ₃ powder was weighed at a mixing ratio of 28.33: 71.67% by weight. This raw material was dry-mixed with alumina balls for 10 hours, and then press-molded at 1 t / cm ² and 1600 ° C.
The material fired in the above was used as a raw material for crystal growth.

180 g of the above-mentioned raw material was filled in the same iridium crucible as in Example 1, and after heating and melting to above the melting point,
A magnesia spinel seed crystal having a 111> orientation was seeded on the melt surface. After seeding, the crystals rapidly spread in the radial direction, but were grown under the conditions of a rotation speed of 10 to 20 rpm and a pulling speed of 3 to 5 mm / h while controlling the temperature. Because the crystal spreads rapidly in the radial direction, cell growth occurs and crystal defects such as crystal grain boundaries and bubbles are induced, and the expanded crystal as shown in FIG. 6 reaches the crucible wall, making crystal growth difficult. Also frequently occurred and reduced the crystal yield. In FIG. 6, K is a crystal growing rod, and J is a shoulder of the grown crystal.

On the other hand, seeding was attempted at a high temperature without rapid growth in the radial direction after seeding, but a problem of dissolving the seed crystal occurred, making it difficult to grow the crystal. This is because, as shown in FIG. 7, since the light absorption of magnesia spinel is a radiation wavelength and is almost 0% in a wide wavelength range of 500 to 1500 nm, which has a large influence on heating, there is no heat retention of the seed crystal. It is considered that the cause is that the temperature difference between the seed crystal and the melt increases.

The grown crystal is a transparent crystal having an outer diameter of 25 mm and a length of 50 mm. As shown in FIG. 6, the shoulder J after seeding grows at a right angle, and defects such as crystal grain boundaries, crystal distortion, cell growth, and bubbles are generated. Occurred.

From this crystal, a diameter of 25 mm and a thickness of 0.5 m
The mirror surface wafer of the m wafer surface (111) surface is sampled, and GaN
Although the light emitting device was manufactured, the manufacturing yield was remarkably reduced due to the step growth and polycrystallization of the semiconductor due to the crystal grain boundaries and strain.

[0050]

As described in detail above, according to the substrate for thin film growth of the present invention, the quality and yield of magnesia spinel single crystal, for which high-quality crystal growth was difficult due to difficulty in controlling the shoulder, was dramatically improved. Can be improved.

Further, a light emitting device using a gallium nitride based semiconductor thin film can be manufactured with good yield and high performance, thereby providing an excellent light emitting device.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a semiconductor laser diode according to the present invention.

FIG. 2 is a sectional view taken along line XX in FIG.

FIG. 3 is a front view showing the appearance of a grown crystal according to the present invention.

FIG. 4 is a graph illustrating the wavelength dependence of the transmittance of a magnesia spinel single crystal substrate containing TiO ₂ .

FIG. 5 is a graph illustrating the wavelength dependence of the transmittance of a magnesia spinel single crystal substrate containing MnO.

FIG. 6 is a front view showing the appearance of a grown crystal of a non-doped magnesia spinel single crystal.

FIG. 7 is a graph illustrating the wavelength dependence of the transmittance of a non-doped magnesia spinel single crystal substrate.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate 1a ... Main surface 1b ... End surface 2 ... Buffer layer 3 ... Multilayer (laser element) 3a ... Opposite end surface 31, 32, 33, 34 ... Gallium nitride Single crystal layer mainly composed of LD LD semiconductor laser diode (light emitting device)

Claims (4)

[Claims] 1. A substrate for growing a semiconductor thin film containing gallium nitride as a main component, wherein the substrate is made of a magnesia spinel single crystal containing a transition metal element. . 2. The magnesia spinel single crystal is made of TiO.
_2. The thin film growth substrate according to claim 1, wherein the substrate contains 0.1 to 5.0% by weight of ₂ or MnO. 3. The method according to claim 1, wherein the magnesia spinel single crystal is 550.
80% / m light transmittance in the wavelength band of ~ 1400 nm
2. The substrate for thin film growth according to claim 1, wherein m is not more than m. 4. The method according to claim 1, wherein:
A light-emitting device comprising a plurality of stacked semiconductor thin films containing at least gallium nitride as a main component.