JP4647286B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

The present invention relates to a semiconductor device used for a light emitting element such as a light emitting diode (LED) and a laser diode (LD) in which a GaN compound thin film is formed on a β-Ga ₂ O ₃ single crystal substrate, and a method for manufacturing the same, The present invention relates to a semiconductor device capable of forming a single crystal thin film made of a GaN-based compound with high crystal quality and a method for manufacturing the same.

FIG. 3 shows a conventional semiconductor device. The semiconductor device 30 includes an Al ₂ O ₃ substrate 31, a buffer layer 32 made of AlN formed on the surface of the Al ₂ O ₃ substrate 31 at a low temperature, and a MOCVD (Metal Organic Chemical Vapor Deposition) on the buffer layer 32. And a GaN growth layer 33 formed by epitaxial growth by the method (see, for example, Patent Document 1).

According to this semiconductor device 30, by forming the buffer layer 32 between the Al ₂ O ₃ substrate 31 and the GaN growth layer 33, the mismatch of lattice constants is alleviated and the deterioration of the crystal quality is suppressed.
Japanese Patent Publication No. 52-36117

  However, even if the conventional semiconductor device 30 is provided with the buffer layer 32, the lattice mismatch cannot be sufficiently relaxed, and it is difficult to obtain a high-quality GaN growth layer 33. Therefore, when applied to a light-emitting element, the crystallinity of the light-emitting layer is not sufficient, and there is a limit to improvement in light emission efficiency.

  Accordingly, an object of the present invention is to provide a semiconductor device capable of forming a single crystal thin film made of a GaN-based compound with high crystal quality and a method for manufacturing the same.

In order to achieve the above object, the present invention provides a substrate made of a β-Ga ₂ O ₃ single crystal having a main surface and a main surface of the substrate, and the c-axis is substantially perpendicular to the main surface. And a buffer layer made of a wurtzite structure GaN-based compound, and a wurtzite structure GaN-based compound formed on the buffer layer and having a c-axis substantially perpendicular to the main surface. A single crystal thin film, and the substrate has a crystal orientation <010> of the substrate and a crystal orientation <11-20> of the buffer layer and the single crystal thin film when the (801) plane is the main surface. The semiconductor device is characterized in that it is parallel and the buffer layer and the single crystal thin film have Ga polarity .

According to this configuration, by providing the buffer layer made of the GaN-based compound on the substrate made of the β-Ga ₂ O ₃ based single crystal, the wurtzite structure is formed on the β-Ga ₂ O ₃ based crystal structure. When a single crystal thin film made of a GaN-based compound is grown, the lattice mismatch is further reduced to grow. As a result, a decrease in crystal quality can be suppressed, and a single crystal thin film made of a high quality GaN compound can be obtained.

In order to achieve the above object, the present invention provides a step of preparing a substrate made of a β-Ga ₂ O ₃ single crystal having a main surface, and the c-axis is formed on the main surface of the substrate. A step of forming a buffer layer made of a wurtzite-type GaN-based compound that is substantially perpendicular to the substrate, a step of annealing the buffer layer, and a c-axis is substantially perpendicular to the main surface on the buffer layer. And a step of forming a single crystal thin film made of a wurtzite structure GaN-based compound , wherein the substrate has a (801) plane as the main surface, the crystal orientation <010> of the substrate, the buffer layer, and the crystal orientation of the single crystal thin film <11-20> are substantially parallel, the buffer layer and the single crystal thin film is to provide a method of manufacturing a semiconductor device characterized by have a Ga polarity.

  ADVANTAGE OF THE INVENTION According to this invention, the light emitting element provided with the single crystal thin film which consists of a GaN-type compound with high crystal quality can be obtained.

[First Embodiment]
<Configuration of light emitting element>
FIG. 1 is a schematic perspective view of a light emitting device according to a first embodiment of the present invention. The light emitting element 10 includes a substrate 11 (hereinafter referred to as “Ga ₂ O ₃ substrate”) 11 made of β-Ga ₂ O ₃ exhibiting n-type conductivity, and a buffer is formed on the Ga ₂ O ₃ substrate 11. Layer 12, n-GaN cladding layer 13 exhibiting n-type conductivity, InGaN light-emitting layer 14 having a multiple quantum well structure (MQW), p-AlGaN cladding layer 15 exhibiting p-type conductivity, and p-type conductivity The p-GaN contact layer 16 exhibiting properties is sequentially stacked, the p-electrode 17 is formed on the upper surface of the p-GaN contact layer 16, and the n-electrode 18 is formed on the lower surface of the Ga ₂ O ₃ substrate 11.

The Ga ₂ O ₃ substrate 11 is made of a β-Ga ₂ O ₃ single crystal and has transparency. The Ga ₂ O ₃ substrate 11 has a (100) plane as a main surface, and the main surfaces are a buffer layer 12 made of GaN, an n-GaN cladding layer 13, an InGaN light emitting layer 14, a p-AlGaN cladding layer 15, and a p-GaN. It becomes a growth surface of a semiconductor layer such as the contact layer 16.

The Ga ₂ O ₃ substrate 11 is basically made of β-Ga ₂ O ₃ single crystal as described above, but is made of Cu, Ag, Zn, Cd, Al, In, Si, Ge, and Sn. You may comprise with the oxide which has as a main component Ga which added 1 or more types chosen from the group which consists of. By adding these elements, the lattice constant or band gap energy can be controlled. For example, by adding elements of Al and In, (Ga _x Al _y In _(1-xy) ) ₂ O ₃ (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) The Ga ₂ O ₃ substrate 11 represented by

The buffer layer 12 is a so-called low-temperature buffer layer formed on the Ga ₂ O ₃ substrate 11 by MOCVD. The thickness of the buffer layer 12 does not need to be increased, and is 1000 nm or less, preferably 200 nm or less. With this thickness, the GaN layer formed on the buffer layer 12 can take over the influence of the crystal lattice of the substrate. Here, the buffer layer 12 is made of a wurtzite structure GaN-based compound, and the c-axis of the GaN-based compound is substantially perpendicular to the main surface of the Ga ₂ O ₃ substrate 11. In addition, as long as it is the same as or approximates to the lattice constant of β-Ga ₂ O ₃ constituting the Ga ₂ O ₃ substrate 11, it may be formed not only on the main surface but also on other surfaces.

A GaN-based compound thin film including the n-GaN cladding layer 13, the InGaN light emitting layer 14, the p-AlGaN cladding layer 15, the p-GaN contact layer 16, and the like is formed by the MOCVD method in the same manner as the buffer layer 12. This GaN-based compound thin film may contain an additive such as a group III element such as B, Al, In, or Tl. For example, by adding elements of Al and In, the general formula Ga _x Al _y In _(1-xy) N (where 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) The represented GaN-based compound thin film can be used.

  Further, instead of the n-GaN clad layer 13 described above, a thin film made of InGaN, AlGaN or InGaAlN may be grown. Since these are almost the same as the lattice constant of GaN, lattice mismatch is unlikely to occur, and the crystal quality is not easily lowered.

  The InGaN light emitting layer 14 is formed of, for example, a semiconductor made of non-doped InGaN to which no impurity is added, and has a single quantum well or multiple quantum well structure (MQW). The emission wavelength can be changed by changing the band gap of the InGaN light-emitting layer 14 by adjusting the composition ratio of In and Ga or by using p-type or n-type conductivity.

  The p electrode 17 is formed on the p-GaN contact layer 16 with a material that can provide ohmic contact by vapor deposition, sputtering, or the like. As a material of the p-electrode 17, a simple metal such as Au, Al, Be, Ni, Pt, In, Sn, Cr, Ti, Zn, or at least two kinds of alloys thereof (for example, Au—Zn alloy, Au—Be Alloys), those forming these in a two-layer structure (for example, Ni / Au), ITO, or the like can be used.

The n-electrode 18 is formed on the lower surface of the Ga ₂ O ₃ substrate 11 with a material that can provide ohmic contact by vapor deposition, sputtering, or the like. As a material for the n-electrode 18, a simple metal such as Au, Al, Co, Ge, Ti, Sn, In, Ni, Pt, W, Mo, Cr, Cu, Pb, or at least two kinds of these alloys (for example, (Au—Ge alloy), those formed in a two-layer structure (for example, Al / Ti, Au / Ni, Au / Co), ITO, or the like can be used.

<Substrate formation method>
Next, a method for forming the Ga ₂ O ₃ substrate 11 will be described. That is, a β-Ga ₂ O ₃ single crystal as a material of the Ga ₂ O ₃ substrate 11 is produced by an FZ (floating zone) method, and the β-Ga ₂ O ₃ single crystal is cut into a predetermined size to obtain a substrate. Make it.

Hereinafter, the manufacturing method of a board | substrate is demonstrated in detail. First, a β-Ga ₂ O ₃ seed crystal and a β-Ga ₂ O ₃ polycrystalline material are prepared. As the β-Ga ₂ O ₃ seed crystal, a β-Ga ₂ O ₃ single crystal is cut out along the heel interface and formed into a predetermined size. The β-Ga ₂ O ₃ polycrystalline material is obtained, for example, by filling a rubber tube with 4N purity Ga ₂ O ₃ powder, cold-compressing it at 500 MPa, and sintering at 1500 ° C. for 10 hours. .

Next, in an atmosphere of a mixed gas of nitrogen and oxygen (changed between 100% nitrogen and 100% oxygen) having a total pressure of 1 to 2 atm in a quartz tube, a β-Ga ₂ O ₃ seed crystal and β The tips of the —Ga ₂ O ₃ polycrystalline material are brought into contact with each other, and the contact portions are heated and melted. When the melted β-Ga ₂ O ₃ polycrystalline material is cooled, the β-Ga ₂ O ₃ single crystal is in the same direction as the axial direction of the β-Ga ₂ O ₃ seed crystal (a-axis, b-axis, or c direction). Furthermore, the β-Ga ₂ O ₃ polycrystal is dissolved in a direction away from the seed crystal, and the dissolved β-Ga ₂ O ₃ polycrystal is cooled to obtain a β-Ga ₂ O ₃ single crystal. The β-Ga ₂ O ₃ single crystal is cleaved along, for example, the (100) plane, and cut into a predetermined size to produce the Ga ₂ O ₃ substrate 11. As a result of measuring the specific resistance of the Ga ₂ O ₃ substrate 11 thus produced, a value of 0.1 Ω · cm or less was obtained at room temperature.

<Method for forming buffer layer>
Next, a method for forming the buffer layer 12 by the MOCVD method will be described. First, the Ga ₂ O ₃ substrate 11 is held in the reaction container so that the main surface on which the buffer layer 12 is to be formed appears. Then, the temperature of the surface of the _Ga 2 _{O 3} substrate 11 is 400 ° C. to 700 ° C., preferably to regulate the temperature in the reaction vessel so as to be 600 ℃ ± 50 ℃. The inside of the reaction vessel is depressurized to 100 torr, and TMG (trimethylgallium) as a Ga feedstock and NH ₃ as a nitrogen source are supplied into the reaction vessel together with He as a carrier gas, 0.1 to 1000 nm, preferably A buffer layer 12 made of GaN having a thickness of 200 nm or less is grown. The plane orientation of the Ga ₂ O ₃ substrate 11 on which the buffer layer 12 is grown is the (100) plane. The reason why hydrogen is not used as the carrier gas is that the Ga ₂ O ₃ substrate 11 is etched by hydrogen, resulting in poor flatness and it is difficult to grow a thin film thereon. When the crystal orientation of β-Ga ₂ O ₃ is <010> when the buffer layer 12 is kept at 1080 ° C. and a so-called high-temperature annealing treatment is performed and the (100) plane of the substrate is the main surface, The crystal orientation of GaN is <11-20>, which is almost parallel. Even when the (801) plane is inclined by 13.52 ° with respect to the (100) plane, when the crystal orientation of β-Ga ₂ O ₃ is <010>, the crystal orientation of GaN is <11-20> and become almost parallel.

<Method for forming GaN-based compound thin film>
The GaN-based compound thin films of the n-GaN cladding layer 13, the InGaN light emitting layer 14, the p-AlGaN cladding layer 15, and the p-GaN contact layer 16 are formed by the MOCVD method in the same manner as the buffer layer 12 is formed. In order to form the n-GaN cladding layer 13 and the p-GaN cladding layer 15, TMG and NH ₃ are used as source gases, and in order to form the InGaN light-emitting layer 14, TMI (trimethylindium), TMG are used as source gases. In order to form the p-AlGaN cladding layer 15 using (trimethylgallium) and NH ₃ , TMA, TMG, and NH ₃ are used as source gases. The carrier gas is an inert gas such as He for the reasons described above. In this case, the growth of the GaN-based compound thin film is promoted by a predetermined temperature range. At this time, the GaN-based compound thin film has Ga polarity.

<Formation of thin films with different carrier concentrations>
In order to change the carrier concentration of GaN as in the case of the n-GaN cladding layer 13 and the p-GaN contact layer 16 by the MOCVD apparatus, the amount of n-type dopant or p-type dopant added to GaN is changed.

  That is, in order to form thin films having different carrier concentrations, for example, the n-GaN clad layer 13 and the p-GaN contact layer 16 by the MOCVD apparatus, the following process is performed.

First, the n-GaN cladding layer 13 will be described. In the reaction vessel, the Ga ₂ O ₃ substrate 11 is held such that the surface on which the thin film is formed faces up. Then, the temperature in the reaction vessel for example, as 1080 ° C., TMG and 54 × ^{10 -6} mol / min, TMA (trimethyl aluminum) and 6 × ^{10 -6} mol / min, monosilane (SiH ₄₎ and 22 × 10 ^{- A} flow rate of ¹¹ mol / min is applied for 60 minutes to grow Si-doped Ga _0.9 Al _0.1 N (n-GaN cladding layer 13) with a thickness of 3 μm. Note that the temperature, the TMA concentration, and the like can be increased or decreased within a range that does not affect the film growth.

Next, the p-GaN contact layer 16 will be described. The temperature in the reaction vessel is, for example, 1080 ° C., TMG is flowed at 54 × 10 ⁻⁶ mol / min together with bisdiclopentadienylmagnesium (Cp ₂ Mg), and Mg-doped GaN (p-GaN contact layer 16) is flown. Growing with a film thickness of 1 μm. Note that the temperature, the TMA concentration, and the like can be increased or decreased within a range that does not affect the film growth.

  Instead of the n-GaN cladding layer 13, InGaN, AlGaN, or InGaAlN may be grown. In the case of InGaN and AlGaN, the lattice constant with the buffer layer 12 can be substantially matched, and in the case of InAlGaN, the lattice constant with the buffer layer 12 can be matched.

<Effect of the first embodiment>
The light emitting device 10 according to the first embodiment has the following effects.
(A) On the (100) plane and the (801) plane of the β-Ga ₂ O ₃ single crystal of the Ga ₂ O ₃ substrate 11, the unit cell has a hexagonal prism shape, which is close to the wurtzite structure that is the crystal structure of GaN. To do. A single crystal thin film of GaN is grown so that the crystal orientation <11-20> of the wurtzite structure and the crystal orientation <010> of the Ga ₂ O ₃ substrate 11 are substantially parallel. At this time, a GaN-based compound single crystal thin film having substantially the same lattice constant and good crystallinity can be obtained. Therefore, deterioration of crystal quality can be suppressed, and a light-emitting element with improved light emission efficiency can be obtained.
(B) Since the Ga ₂ O ₃ substrate 11 and the buffer layer 12 have translucency and conductivity, a light-emitting diode having a vertical electrode structure can be formed. As a result, the entire light-emitting element 10 Therefore, the current density can be lowered, and the lifetime of the light emitting element 10 can be extended.
(C) Since the light-emitting element 10 has a multiple quantum well structure, the probability that the electrons and holes serving as carriers are confined in the InGaN light-emitting layer 14 and recombined increases, so that the light emission rate is greatly increased. To improve.
(D) Since the Ga surface of the buffer layer 12 can be easily exposed, other thin films can be grown on this surface by MOCVD.

2A and 2B show a light-emitting element according to Example 1, where FIG. 2A is a schematic view seen from the top surface of the light-emitting element, and FIG. 2B is a side view.
The Ga ₂ O ₃ substrate 11 is obtained by growing a β-Ga ₂ O ₃ single crystal in the planar direction along the b-axis and the c-axis and growing in the thickness direction along the a-axis direction.

The GaN-based compound thin film layer 23 includes an n-GaN cladding layer 13, an InGaN light emitting layer 14, a p-AlGaN cladding layer 15, and a p-GaN contact on the (100) plane and the (801) plane of the Ga ₂ O ₃ substrate 11. A GaN-based compound thin film such as the layer 16 is grown in the <010> direction along the b-axis, and is grown in the thickness direction of the substrate 11.

According to Example 1, when the crystal orientation of β-Ga ₂ O _{3 on} the crystal surface of the (100) plane and the (801) plane of the Ga ₂ O ₃ substrate 11 is <010>, The crystal orientation is <11-20> and is almost parallel.

[Other embodiments]
Although the FZ method has been described as the growth method of the Ga ₂ O ₃ substrate 11, β-Ga manufactured by the FZ method can be applied even if another growth method such as an EFG (Edge-defined Film-fed Growth method) method is applied. ₂ O ₃ can be produced similar _beta-Ga 2 _{O 3} single crystal and the single crystal can be produced _Ga 2 _{O 3} substrate 11 by cutting it.

  Also, the MOCVD method has been described as a method for growing a GaN-based compound thin film. However, even if another growth method such as a PLD (Pulsed Laser Deposition) method or MBE (Molecular Beam Epitaxy) method is applied, it is the same as that by the MOCVD method. Can be epitaxially grown.

  Note that the light-emitting element 10 according to the present invention is not limited to a light-emitting diode or a laser diode, but can also be applied to a semiconductor such as a transistor, a thyristor, or a diode. Specifically, a field effect transistor, a photodiode, a solar cell, etc. are mentioned, for example.

It is a typical perspective view of the light emitting element which concerns on embodiment of this invention. The light emitting element which concerns on Example 1 is shown, (a) is the schematic seen from the upper surface of the light emitting element, (b) is a side view. It is sectional drawing which shows the conventional semiconductor layer.

Explanation of symbols

10 light-emitting element 11 _Ga 2 _{O 3} substrate 12 GaN layer 13 n-GaN cladding layer 14 InGaN light-emitting layer 15 p-AlGaN cladding layer 16 p-GaN contact layer 17 n electrode 18 p electrode 23 GaN-based compound thin film layer 30 semiconductor layer 31 Al ₂ O ₃ substrate 32 buffer layer 33 GaN growth layer

Claims (2)

A substrate made of a β-Ga ₂ O ₃ single crystal having a main surface;
An annealed buffer layer made of a wurtzite structure GaN-based compound formed on the main surface of the substrate and having a c-axis substantially perpendicular to the main surface ; a c-axis formed on the buffer layer; Comprising a single crystal thin film made of a wurtzite structure GaN-based compound that is substantially perpendicular to the main surface ,
When the substrate has the (801) plane as the main surface, the crystal orientation <010> of the substrate is substantially parallel to the crystal orientation <11-20> of the buffer layer and the single crystal thin film,
The buffer layer and the single crystal thin film have a Ga polarity . Preparing a substrate made of a β-Ga ₂ O ₃ based single crystal having a main surface;
Forming a buffer layer made of a wurtzite structure GaN-based compound having a c-axis substantially perpendicular to the main surface on the main surface of the substrate;
Annealing the buffer layer;
Forming a single crystal thin film made of a wurtzite type GaN-based compound having a c-axis substantially perpendicular to the main surface on the buffer layer;
With
When the substrate has the (801) plane as the main surface, the crystal orientation <010> of the substrate is substantially parallel to the crystal orientation <11-20> of the buffer layer and the single crystal thin film,
The buffer layer and the single crystal thin film, a method of manufacturing a semiconductor device characterized by have a Ga polarity.