JP2009027022A - Nitride semiconductor light-emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor light-emitting element capable of preventing a defect, and emitting light with high efficiency, even if the emission wavelength is made long by maintaining very small lattice mismatches of a quantum-well structure in the active layer. <P>SOLUTION: Since a well layer in the active layer having the quantum well structure is prepared by Al<SB>W1</SB>B<SB>X1</SB>In<SB>Y1</SB>Ga<SB>Z1</SB>N(W1+X1+Y1+Z1=1), containing at least boron and indium, so that it is formed to have the emission wavelength which is not shorter than 365 nm, the active layer is formed so that the lattice matching of the well layer and GaN can be achieved or the lattice mismatching of the well layer and GaN can be made very small, and the emission wavelength can also be long. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor light emitting device using a ternary mixed crystal of AlBInGaN.

  As a semiconductor light emitting element such as a semiconductor laser element or a light emitting diode that emits blue to green or violet light, there is a nitride semiconductor light emitting element. When manufacturing a nitride semiconductor light emitting device, a GaN-based semiconductor layer is epitaxially grown on a substrate made of sapphire, GaN, SiC, Si, or the like.

  For example, an n-type GaN contact layer, an InGaN well layer, and a quantum well active layer by a GaN barrier layer are sequentially formed on a sapphire substrate using MOCVD (metal organic chemical vapor deposition), and a p-type is formed on the active layer. An AlGaN block layer, a p-type GaN contact layer, and the like are sequentially formed.

  From the p-type GaN contact layer to a partial region of the n-type GaN contact layer is removed by etching, the n-type GaN contact layer is exposed, and an n-electrode is formed on the exposed upper surface of the n-type GaN contact layer. A p-electrode is formed on the upper surface of the contact layer.

  FIG. 7 is a unit cell diagram showing the plane orientation of a hexagonal crystal having a wurtzite structure, such as a sapphire single crystal or a GaN single crystal. Here, the expressions C-plane and a-axis can be expressed by a so-called Miller index. For example, the C-plane is expressed as a (0001) plane. In FIG. 4, the hatched surface is the A-plane (11-20), and the M-plane (10-10) is a hexagonal crystal column. For example, the {11-20} plane and the {10-10} plane are generic names including the plane equivalent to the (11-20) plane and the (10-10) plane due to the symmetry of the crystal. . Further, the a axis indicates the vertical direction of the A plane, the m axis indicates the vertical direction of the M plane, and the c axis indicates the vertical direction of the C plane.

  As described above, when the GaN-based semiconductor layer is stacked on the sapphire substrate, the C-plane (0001) of the sapphire substrate is used, and the GaN-based semiconductor stacked on the (0001) -oriented sapphire substrate is (0001). ) Orientation wurtzite type crystal structure, Ga element has a crystal polarity in which the growth surface direction (C-plane growth).

  At the stacked interface of the GaN-based semiconductor layers stacked in this way, spontaneous polarization occurs due to the wurtzite structure in which there is no symmetry in the c-axis direction and the front and back surfaces of the epitaxial film grown on the C plane are generated. Piezoelectric polarization due to the interfacial stress occurs and an electric field is generated at the laminated interface due to these polarization charges. The interfacial stress changes due to lattice mismatch due to lattice defects. When the lattice mismatch increases, the interfacial stress increases and piezo polarization increases.

  Since the spontaneous polarization and piezo polarization are generated at the heterojunction interface of the GaN-based semiconductor layer, they are also generated in the InGaN / GaN quantum well active layer, and carriers are polarized by the electric field generated in the quantum well. There has been a problem that it causes a reduction and a red shift of the emission wavelength (shift to the longer wavelength side).

Therefore, the crystal growth surface of the sapphire substrate or the like is a nonpolar surface (nonpolar surface) such as the M surface or the A surface in the unit cell diagram of FIG. 4, or the (10-1-1) surface, (10-1-3). And a semipolar plane (semipolar plane) such as a (11-22) plane, and a growth plane of the InGaN / GaN quantum well active layer is a nonpolar plane or a semipolar plane. There has been proposed a structure that eliminates the effects of spontaneous polarization and piezo-polarization at the interface, thereby reducing the luminous efficiency and the red shift of the emission wavelength (see, for example, Patent Document 1).
JP 2006-128661 A

  However, even if spontaneous polarization and piezoelectric polarization are suppressed, the lattice mismatch between GaN and InGaN occurs because the quantum well structure of the GaN barrier layer and the InGaN well layer is used. In addition, there is a demand for longer emission wavelengths of nitride semiconductor light emitting devices. In order to increase the wavelength, the In composition ratio of the InGaN well layer must be increased. The difference between the lattice constant and the lattice constant increases, and the difference in lattice constant reaches about 10% at the maximum. This lattice mismatch becomes a factor for generating defects, lowers the internal quantum efficiency of the active layer, and reduces the light emission efficiency.

  In addition, when the nonpolar plane or the semipolar plane is used as the crystal growth plane, the red shift effect as in the C plane growth is lost. Therefore, when the wavelength is increased, the InGaN is more effective than in the C plane growth. There was a problem that the In composition ratio of the well layer had to be increased, the difference in lattice constant with the GaN barrier layer was increased, and the luminous efficiency was drastically reduced.

  The present invention was devised to solve the above-described problems, and by maintaining a state in which the lattice mismatch of the quantum well structure in the active layer is very small, the occurrence of defects is prevented, and the emission wavelength is increased. An object of the present invention is to provide a nitride semiconductor light emitting device capable of emitting light with high efficiency even when the wavelength is increased.

In order to achieve the above object, the invention according to claim 1 is a nitride semiconductor light emitting device including an active layer having a quantum well structure, wherein the well layer in the active layer contains at least boron and indium. A nitride semiconductor light-emitting element formed of Al _W1 B _X1 In _Y1 Ga _Z1 N (W1 + X1 + Y1 + Z1 = 1) and having an emission wavelength of 365 nm or more.

Further, the invention according to claim 2 is that In _Y3 Ga _Z3 N (0 ≦ Y3 ≦ 1, Z3 = 1−Y3) configured so that the lattice constant of the well layer has the same band gap as the well layer. The nitride semiconductor light emitting device according to claim 1, wherein the nitride semiconductor light emitting device is formed smaller than a lattice constant of the nitride semiconductor light emitting device.

  The invention according to claim 3 is the nitride semiconductor light emitting device according to claim 1, wherein the well layer has a lattice mismatch with GaN within ± 1.5%.

  The invention according to claim 4 is the nitride semiconductor light emitting device according to claim 1, wherein the well layer is lattice-matched with GaN.

Further, the invention of claim 5, wherein the barrier layer in the active _layer, Al _W2 is formed by _{B X2 In Y2 Ga Z2 N (} W2 + X2 + Y2 + Z2 = 1), and the band gap than the well layer is constituted largely The nitride semiconductor light-emitting device according to claim 1.

  The invention according to claim 6 is the nitride semiconductor light emitting device according to claim 5, wherein the barrier layer has a lattice mismatch with GaN within ± 1.5%.

The invention according to claim 7 is the nitride semiconductor light emitting device according to claim 5, wherein the barrier layer is lattice-matched with GaN.

According to the present invention, in the active layer having the quantum well structure, the well layer in the active layer is Al _W1 B _X1 In _Y1 Ga _Z1 N (W1 + X1 + Y1 + Z1 = 1) containing at least boron and indium, and the emission wavelength is Since it is formed to be 365 nm or more, it is configured so that the well layer and GaN can be lattice-matched, or the lattice mismatch between the well layer and GaN can be extremely reduced, and the emission wavelength is increased. Can also be possible.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a structural example of the nitride semiconductor light emitting device of the present invention, and FIG. 2 is an enlarged detailed view of the active layer 4 of FIG. FIG. 1 shows the band gap (energy gap), emission wavelength, and lattice constant in a nitride semiconductor combining Al (aluminum), B (boron), In (indium), Ga (gallium), and N (nitrogen). The relationship is shown.

  As a configuration example of the nitride semiconductor light emitting device, an AlN buffer layer 2, an n-type GaN contact layer 3, an active layer 4, a p-type AlGaN (electron) block layer 8, and a p-type GaN contact layer 5 are formed on a sapphire substrate 1. Are sequentially stacked, and a part of the p-type GaN contact layer 5 is mesa-etched to form an n-electrode 7 on the surface where the n-type GaN contact layer 3 is exposed. A p-electrode 6 is formed on the p-type GaN contact layer 5.

  The active layer 4 is an active layer having a quantum well structure, and has a structure in which a well layer (well layer) is sandwiched between barrier layers (barrier layers) having a larger band gap than the well layer. ing. The quantum well structure may be multiplexed instead of one. In this case, an MQW (Multi Quantum Well), that is, a multiple quantum well structure is formed.

In the present invention, the entire active layer 4 is made of ternary mixed crystal AlBInGaN of Al (aluminum), B (boron), In (indium), Ga (gallium), and N (nitrogen), and the well layer 4b is made of Al _W1 B. _X1 In _Y1 Ga _Z1 N (W1 + X1 + Y1 + Z1 = 1, 0 ≦ W1 <1, 0 <X1 <1, 0 <Y1 <1, 0 ≦ Z1 <1), the barrier layer (barrier layer) 4a is made of Al _W2 B _X2 In _Y2 The quantum well structure was Ga _{2 Z 2} N (W 2 + X 2 + Y 2 + Z 2 = 1, 0 ≦ W 2 ≦ 1, 0 ≦ X 2 ≦ 1, 0 ≦ Y 2 ≦ 1, 0 ≦ Z 2 ≦ 1).

That is, the well layer 4b is composed of at least B (boron) and In containing _{(indium) Al W1 B X1 In Y1 Ga} Z1 N (W1 + X1 + Y1 + Z1 = 1), the barrier layer 4a is _Al W2 _B X2 _In Y2 _{Ga Z2} N (W2 + X2 + Y2 + Z2 = 1). Therefore, the minimum configuration of the well layer 4b and the barrier layer 4a is that the well layer 4b is BInN (W1 = 0, Z1 = 0) and the barrier layer 4a is GaN (above W2 = X2 = Y2 = 0).

  As shown in FIG. 2, a barrier layer 4a is disposed on the side where the active layer 4 is in contact with the n-type GaN contact layer 3, and a well layer 4b is stacked thereon. The barrier layer 4a and the well layer 4b Are stacked alternately for several periods, the last barrier layer 4a is formed, and the p-type AlGaN block layer 8 is stacked on the last barrier layer 4a.

  Further, the barrier layer 4a needs to have a higher band gap energy than the well layer 4b. In general, the In composition ratio of the barrier layer 4a is made smaller than that of the well layer 4b so that Y1> Y2.

Next, the left vertical axis in FIG. 1 is the band gap (energy gap) (unit is eV), the right vertical axis is the emission wavelength (unit is nm), the horizontal axis is the lattice constant in the a-axis direction (unit is angstrom: Å). Moreover, the straight line graph described in FIG. 1 shows data in the case of a ternary mixed crystal of the AlBInGaN. For example, the straight line 11 starts from a binary mixed crystal of BN in the upper left and ends with a binary mixed crystal of InN in the lower right. Here, the straight line 11 connecting BN and InN represents data obtained by changing the composition ratio X from 0 to _{1 in a} ternary mixed crystal of B _X In _1-X N.

Similarly, the straight line 13 connecting the AlN point and the GaN point is a straight line connecting the AlN point and the InN point in the composition ratio X of 0 to _{1 in the} ternary mixed crystal of Al _X Ga ₁ -XN. 14 is an Al _X In _1- XN ternary mixed crystal, the composition ratio X is 0 to 1, and a straight line 12 connecting the GaN point and the InN point is In _X Ga _1-X N ternary mixed. The data when the composition ratio X is changed from 0 to 1 in the crystal is shown.

Therefore, a hatched region 20 surrounded by the straight line 13, the straight line 12, and the straight line 14 represents a mixed crystal of AlN, GaN, and InN, that is, a quaternary mixed crystal region of AlInGaN. This is Stated examples of the barrier layer _4a, in _{Al W2 B X2 In Y2 Ga Z2} N (W2 + X2 + Y2 + Z2 = 1), the boron component was 0 (X2 = 0) in particular equal.

  On the other hand, a region 10 indicated by scattered points is surrounded by a broken line connecting the straight line 11, the straight line 12, the straight line 13, BN, and AlN, and the AlBnGaN quaternary mixed crystal region to the AlInGaN quaternary mixed crystal region. Represents the area minus. This corresponds to a composition range that can be newly constructed by adding B to the AlInGaN quaternary mixed crystal.

  Here, when the band gap at each point of BN, GaN, InN, and AlN in FIG. 1 is shown, the band gap Eg (GaN) of BN is 5.8 eV, and the band gap Eg (GaN) of GaN is 3.39 eV, InN. The band gap Eg (InN) of A is 0.65 eV, and the band gap Eg (AlN) of AlN is 6.2 eV.

  On the other hand, the lattice constant of each point in the a-axis direction is as follows. The lattice constant a (BN) of BN is 2.504Å, the lattice constant a (GaN) of GaN is 3.189Å, and the lattice constant a (InN) of InN. Is 3.5378Å, and the lattice constant a (AlN) of AlN is 3.112Å.

  The emission wavelength corresponding to the band gap of 3.39 eV of GaN is 365 nm from the right vertical axis of FIG. The emission wavelength at the intersection of the lattice constant 3.189ＧａＮ of GaN and the straight line 11 is 515 nm. Therefore, it is possible to produce a well layer lattice-matched with GaN, and the composition range of the lattice-matched well layer is wide, and the range is a range of a straight line 15 indicated by a dotted line in FIG. This range corresponds to an emission wavelength of 365 nm to 515 nm. Therefore, by changing the composition ratio of the well layer, the emission wavelength can be changed in the range of 365 nm to 515 nm while lattice-matching the well layer to GaN.

  On the other hand, in the case of the conventional InGaN / GaN quantum well structure, as can be seen from the straight line 12, in the range of the emission wavelength of 365 nm or more, there is no lattice matching region between InGaN and GaN, and the composition ratio of In is As it becomes larger, the lattice mismatch with GaN becomes larger. This is the same even when the well layer is made of a quaternary mixed crystal with AlInGaN. As can be seen from the region 20 where the emission wavelength is 365 nm or more, there is no portion that lattice matches with GaN.

4, 5 and 6 show the same band gap (energy gap) in a nitride semiconductor combining Al (aluminum), B (boron), In (indium), Ga (gallium), and N (nitrogen) as in FIG. The relationship between the emission wavelength and the lattice constant is shown, and the scale and unit of the vertical and horizontal axes are the same. Here, the hatched area in FIG. 4 is the invention described in claim 1, that is, the well layer in the active layer is Al _W1 B _X1 In _Y1 Ga _Z1 N (W1 + X1 + Y1 + Z1 = 1) containing at least boron and indium. Further, it corresponds to forming the emission wavelength to be 365 nm or more. In this case, the shaded area in FIG. 4 does not include the line 14.

On the other hand, the hatched area in FIG. 5 is the In _Y3 Ga _Z3 N (0 ≦ Y3 ≦ 1, in which the lattice constant of the well layer has the same band gap as the well layer in the hatched area in FIG. It is smaller than the lattice constant of Z3 = 1−Y3), that is, it corresponds to the invention described in claim 2. In this case, the shaded area in FIG. 5 does not include the straight line 12.

Thus, when prepared by adjusting the respective composition of _{Al W1 B X1 In Y1 Ga Z1} N so that the well layer 4b and the emission wavelength 365nm or more, the composition range of the well layer 4b, as in FIG. 4, the light emitting This is a region represented by oblique lines below the dotted line indicating the wavelength of 365 nm. On the other hand, the barrier layer 4a can be formed with a composition in a range in which the region 10 and the region 20 are added together. Even when each composition is configured so that the well layer 4b has an emission wavelength of 365 nm or longer, the barrier layer 4a can be determined so as to be lattice-matched to the well layer 4b, and the band of the barrier layer 4a in a lattice-matched state. The gap can be made larger than that of the well layer 4b, and the emission wavelength can be changed in a lattice-matched state.

  However, the relationship diagram of FIG. 1 does not consider the bowing parameter. Therefore, when the bowing parameter is considered, the emission wavelength can be set to 515 nm or more in a state where the well layer 4b lattice-matched with GaN is used. .

  As described above, the active layer in the nitride semiconductor light emitting device of the present invention can be formed so that the well layer can lattice match with GaN, or the lattice constant of the well layer is very close to the lattice constant of GaN. In addition, the emission wavelength can be changed in the range of 365 nm to 515 nm (when the bowing parameter is considered, 515 nm or more).

  As can be seen from FIG. 1, the barrier layer 4a and the well layer 4b can be configured so that the lattice mismatch with GaN is within ± 1.5%. Here, the lattice mismatch with GaN is within ± 1.5% when the lattice constant of the barrier layer 4a or the well layer 4b is L and the lattice constant of GaN is A. | (LA) / L | ≦ 0.015. Since the lattice constant A of GaN is 3.189Å as described above, when the range of L is specifically calculated, 3.142Å ≦ L ≦ 3.238Å. FIG. 6 shows a region where the lattice mismatch between the well layer 4b and GaN falls within a range of ± 1.5%, based on the calculation result, with hatching.

  Therefore, even if the C-plane growth described in the prior art is performed, the stress on the well layer working due to lattice mismatch is reduced, so that the generation of dislocations is suppressed and piezo polarization is suppressed, resulting in a decrease in luminous efficiency. do not do. Further, when the crystal growth surface of the active layer 4 is a nonpolar surface or a semipolar surface, the lattice mismatch with GaN is intentionally shifted within a range of ± 1.5% from the lattice constant of GaN. Thus, biaxial stress can be exerted on the well layer to provide polarization characteristics.

Next, a method for manufacturing the nitride semiconductor light emitting device of FIG. 3 will be briefly described. As a manufacturing method, growth is performed by a well-known MOCVD method or the like. For example, after the C-plane sapphire substrate 1 is heated to about 1100 ° C. and thermally cleaned, the substrate temperature is lowered to about 1000 ° C., the AlN buffer layer 2 is 100 to 500 nm, and the Si-doped n-type GaN contact layer 3 is formed. The active layer 4 having an MQW structure is formed by laminating about 1 to 5 μm and then lowering the substrate temperature to about 800 ° C. After that, the Mg-doped p-type AlGaN blocking layer 8 functioning as an electron blocking layer is formed with the substrate temperature kept unchanged, and then the Mg-doped p-type GaN contact layer 5 is laminated by about 0.2 to 1 μm. As described above, the active layer 4 has the well layer Al _W1 B _X1 In _Y1 Ga _Z1 N (W1 + X1 + Y1 + Z1 = 1, 0 ≦ W1 <1, 0 <X1 <1, 0 <Y1 <1, 0 ≦ Z1 <1) The barrier layers Al _W2 B _X2 In _Y2 Ga _Z2 N (W2 + X2 + Y2 + Z2 = 1, 0 ≦ W2 ≦ 1, 0 ≦ X2 ≦ 1, 0 ≦ Y2 ≦ 1, 0 ≦ Z2 ≦ 1) are alternately stacked.

  After the p-type GaN contact layer 5 is formed, the p-type GaN contact layer 5 to the n-type GaN contact layer 3 are removed by mesa etching by reactive ion etching or the like to expose the surface of the n-type GaN contact layer 3. Let Thereafter, an n electrode 7 is formed on the exposed n-type GaN contact layer 3 surface by evaporation, and a p-electrode 6 is formed on the p-type GaN contact layer 5 by evaporation.

Note that the manufacturing of the semiconductor layers described above, the ammonia with hydrogen / nitrogen carrier gas triethyl gallium as a source gas of Ga (TEGa) or trimethyl gallium (TMG), as a source gas of nitrogen (NH _3), Reactive gases corresponding to the components of each semiconductor layer, such as trimethylaluminum (TMA), which is a source gas of Al, trimethylindium (TMIn), which is a source gas of In, and triethylboron (TEB), which is a source gas of B, n-type Necessary gases such as silane (SiH ₄ ) as a dopant gas in the case of making p-type and cyclopentadiethylmagnesium (CP ₂ Mg) as a dopant gas in the case of making the p-type are supplied, and about 650 ° C. to 1000 ° C. By sequentially growing in a range, a semiconductor layer having a desired composition and a desired composition is obtained. It can be formed on the main thickness.

The relationship between the band gap of the semiconductor layer in the active layer used for the nitride semiconductor light emitting element of this invention, the light emission wavelength, and a lattice constant is shown. It is a figure which shows the expansion detail of the active layer of FIG. It is a figure which shows an example of a structure of the nitride semiconductor light-emitting device. It is a figure which shows the structure range of the well layer equivalent to the invention of Claim 1. It is a figure which shows the structure range of the well layer equivalent to the invention of Claim 2. FIG. 5 is a diagram showing a region where the lattice mismatch with GaN is within ± 1.5% in the shaded region of FIG. 4. It is a unit cell figure which shows the hexagonal system surface orientation.

Explanation of symbols

1 Sapphire substrate 2 AlN buffer layer 3 n-type GaN contact layer 4 active layer 5 p-type GaN contact layer 6 p-electrode 7 n-electrode 8 p-type AlGaN block layer

Claims (7)

A nitride semiconductor light emitting device including an active layer having a quantum well structure,
The well layer in the active layer is formed of Al _W1 B _X1 In _Y1 Ga _Z1 N (W1 + X1 + Y1 + Z1 = 1) containing at least boron and indium, and has an emission wavelength of 365 nm or more. Semiconductor light emitting device. The lattice constant of the well layer, is smaller than the lattice constant of being configured to be the same band gap as the well layer _{In Y3 Ga Z3 N (0 ≦} Y3 ≦ 1, Z3 = 1-Y3) The nitride semiconductor light-emitting device according to claim 1.   2. The nitride semiconductor light emitting device according to claim 1, wherein the well layer has a lattice mismatch with GaN within ± 1.5%.   2. The nitride semiconductor light emitting device according to claim 1, wherein the well layer is lattice-matched with GaN. Barrier layer in the active layer _is formed of _{Al W2 B X2 In Y2 Ga Z2} N (W2 + X2 + Y2 + Z2 = 1), and nitride of claim 1, wherein the band gap is configured larger than the well layer Semiconductor light emitting device.   6. The nitride semiconductor light emitting device according to claim 5, wherein the barrier layer has a lattice mismatch with GaN within ± 1.5%.   6. The nitride semiconductor light emitting device according to claim 5, wherein the barrier layer is lattice-matched with GaN.

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