JP6019541B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device.

  As a semiconductor light emitting device, a structure in which an n-type GaN layer is provided on a sapphire substrate and a multiple quantum well layer formed by alternately stacking GaN and InGaN on the sapphire substrate is known.

In Patent Document 1, an n-type GaN layer is provided on a sapphire substrate via a buffer layer, and non-doped In _a Ga _1-a N (0.01 ≦ a ≦ 0.05) is formed thereon. A strain relaxation layer having a thickness of 180 nm formed in step (b) is provided, and a multiple quantum well layer formed by alternately stacking GaN and InGaN is provided on the strain relaxation layer, and the heat of the sapphire substrate and the multiple quantum well layer is provided. A semiconductor light emitting device is disclosed in which stress due to strain generated by a difference in expansion coefficient is relaxed by a strain relaxation layer.

Japanese Patent Laid-Open No. 11-233824

The present invention comprises a GaN layer whose main surface is a nonpolar or semipolar surface,
In _x Ga _1-x N (0 <x <0.1) is formed by epitaxial growth directly on the GaN layer, and includes an n-type dopant-containing InGaN layer having a thickness of 0.2 μm or more,
A multiple quantum well layer formed by epitaxial growth directly on the InGaN layer and including a well layer formed of InGaN;
With
The InGaN layer is a semiconductor light emitting device in which strain due to lattice mismatch with the GaN layer is completely or partially relaxed.

It is sectional drawing of the semiconductor light-emitting device concerning embodiment. (A)-(e) is explanatory drawing of the manufacturing method of the semiconductor light-emitting device based on embodiment. It is a graph which shows the relationship between the content rate x of In of an InGaN layer, and the magnification of PL emitted light intensity on the basis of a reference. It is a graph which shows the relationship between the thickness of an n-type InGaN layer, and the full width at half maximum of light emission intensity distribution.

  Hereinafter, embodiments will be described in detail based on the drawings.

(Semiconductor light emitting device)
FIG. 1 shows a semiconductor light emitting device 10 according to an embodiment. The semiconductor light emitting device 10 according to the present embodiment is suitably used, for example, as a semiconductor laser or a light emitting diode.

  The semiconductor light emitting device 10 according to this embodiment includes a u-GaN layer 12, an n-type GaN layer 13, an n-type InGaN layer 14, a multiple quantum well layer 15, a p-type AlGaN layer 16, and a p-type GaN on a substrate 11. The layer 17 is sequentially stacked, and the n-type electrode 18 and the p-type electrode 19 are respectively provided on the n-type InGaN layer 14 exposed by etching and the p-type GaN layer 17.

Here, as the substrate 11, for example, a sapphire substrate (single crystal substrate having a corundum structure of Al ₂ O ₃ ) is typically exemplified, and other examples include a ZnO substrate and a SiC substrate. The substrate 11 may be a processed substrate in which fine irregularities are formed on the substrate surface by etching or the like, and silicon oxynitride (SiO _x N _y ) or aluminum nitride (AlN) or the like is partially formed on the substrate surface. It may be a processed substrate provided with fine irregularities. For example, the substrate 11 is formed in a rectangular plate shape in the state of the light emitting element, and has a vertical and horizontal length of 200 to 1000 μm and a thickness of 50 to 300 μm.

  The main surface of the substrate 11 is a plane <{11-20} plane>, c plane <{0001} plane>, m plane <{1-100} plane>, n plane <{1-123} plane> and r. Any of the planes <{1-102} plane>, or a crystal plane with another plane orientation may be used.

  The crystal growth surface of the substrate 11 may be a main surface, or may be an uneven side surface of a processed substrate. Crystal growth planes of the substrate 11 are a plane <{11-20} plane>, c plane <{0001} plane>, m plane <{1-100} plane>, n plane <{1-123} plane> and It may be any of the r-plane <{1-102} plane>, or may be a crystal plane with another plane orientation.

  The u-GaN layer 12 is formed by epitaxially growing GaN from the crystal growth surface of the substrate 11 without containing a dopant. The thickness of the u-GaN layer 12 is, for example, 2 to 20 μm.

  The main surface of the u-GaN layer 12 is a nonpolar plane or a semipolar plane, and may be a {11-22} plane, or a crystal plane with another plane orientation such as a {10-11} plane. There may be.

The n-type GaN layer 13 may or may not be present. The n-type GaN layer 13 is formed by epitaxially growing GaN in the same plane direction as the u-GaN layer 12 including an n-type dopant immediately above the u-GaN layer 12. Nonpolar or semipolar surface. Examples of the n-type dopant include Si and Ge. The concentration of the n-type dopant is, for example, 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ / cm ³ . The thickness of the n-type GaN layer 13 is, for example, 2 to 10 μm.

The n-type InGaN layer 14 is formed immediately above the n-type GaN layer 13 when there is the n-type GaN layer 13, and when not present, the n-type GaN layer 13 includes In _x Ga _1-x N containing an n-type dopant. Therefore, the main surface is a nonpolar surface or a semipolar surface.

In _x Ga _1-x N forming the n-type InGaN layer 14 has an In content ratio of 0 <x <0.1, preferably 0 <x <0.05, and more preferably 0.01. <X <0.05. Examples of the n-type dopant include Si and Ge as in the case of the n-type GaN layer 13. The concentration of the n-type dopant is, for example, 1.0 × 10 ^{17 to} 1.0 × 10 ²⁰ / cm ³ . The n-type InGaN layer 14 may be composed of a single layer, or may be composed of a plurality of layers having different n-type dopant types and concentrations.

  The thickness of the n-type InGaN layer 14 is 0.2 μm or more, preferably 0.2 to 10 μm, and more preferably 0.5 to 5 μm.

  In the n-type InGaN layer 14 having the above-described configuration, strain due to lattice mismatch with the n-type GaN layer 13 is completely or partially relaxed. Here, in this application, “complete relaxation” means that the InGaN layer is 100% relaxed with respect to the underlying GaN layer, and “partial relaxation” is defined as a relaxation rate> 0. To do.

  The multiple quantum well layer 15 is formed by epitaxially growing a semiconductor in the same plane orientation as the n-type InGaN layer 14 immediately above the n-type InGaN layer 14, and thus the main surface is a nonpolar or semipolar surface. And it has the alternately laminated structure of the barrier layer 15a and the well layer 15b. The number of barrier layers 15a and well layers 15b is, for example, 3 to 15. The multiple quantum well layer 15 constitutes a light emitting layer, and its light emission wavelength is a wavelength in the visible region, specifically, 360 to 640 nm in the light emitting region of InGaN. The multiple quantum well layer 15 is preferably configured to emit purple, blue, or green light, and more preferably configured to emit purple light. Here, the purple emission wavelength range is 380 to 450 nm, the blue emission wavelength range is 450 to 495 nm, and the green emission wavelength range is 495 to 570 nm.

The well layer 15b is made of In _y Ga _1-y N, and y is preferably larger than x. The thickness of the well layer 15b is, for example, 1 to 20 nm.

  Examples of the semiconductor forming the barrier layer 15a include GaN having a band gap larger than that of the well layer 15b. The thickness of the barrier layer 15a is, for example, 5 to 20 nm.

The p-type AlGaN layer 16 is formed immediately above the multiple quantum well layer 15 by epitaxially growing Al _z Ga _1-z N containing a p-type dopant in the same plane orientation as the multiple quantum well layer 15. Therefore, the main surface is a nonpolar surface or a semipolar surface. Al _z Ga _1-z N forming the p-type AlGaN layer 16 has an Al content ratio of, for example, 0.05 <z <0.3. Examples of the p-type dopant include Mg and C. In the case of a p-type dopant, since the acceptor level is deep and the dopant concentration and the free hole concentration differ greatly, the free hole concentration measured by the Hall effect is used as the content evaluation index. Is, for example, 1.0 × 10 ^{17 to} 5 × 10 ¹⁸ / cm ³ . The p-type AlGaN layer 16 may be composed of a single layer, or may be composed of a plurality of layers having different types and concentrations of p-type dopants. The thickness of the p-type AlGaN layer 16 is, for example, 10 to 30 nm.

The p-type GaN layer 17 is formed directly on the p-type AlGaN layer 16 by epitaxially growing GaN in the same plane orientation as that of the p-type AlGaN layer 16 including the p-type dopant. Nonpolar or semipolar surface. Examples of the p-type dopant include Mg and C as in the case of the p-type AlGaN layer 16. The free hole concentration measured by the Hall effect measurement is, for example, 2.0 × 10 ¹⁷ to 10 × 10 ¹⁷ / cm ³ . The p-type GaN layer 17 may be composed of a single layer, or may be composed of a plurality of layers having different types and concentrations of the p-type dopant. The thickness of the p-type GaN layer 17 is, for example, 50 to 200 nm.

  The p-type layer is not limited to the p-type AlGaN layer 16 and the p-type GaN layer 17, and may be a special structure such as an InGaN / GaN superlattice structure.

  Examples of the constituent electrode material of the n-type electrode 18 include a laminated structure such as Cr / Au, Ti / Al, Ti / Al / Mo / Au, Hf / Au, or an alloy. The thickness of the n-type electrode 18 is, for example, Ti / Al (10 nm / 500 nm).

  Examples of the p-type electrode 19 include a laminated structure such as Pd / Pt / Au, Ni / Au, and Pd / Mo / Au, an alloy, or an oxide-based transparent conductive material such as ITO (indium tin oxide). It is done. The thickness of the p-type electrode 19 is, for example, 10 to 200 nm for ITO. A pad electrode for wire bonding is necessary on the p-type electrode 19, and in many cases, it is made of the same material system as that of the n-type electrode 18.

  By the way, a semiconductor light emitting device using a group III nitride semiconductor whose main surface is a nonpolar surface is expected to have high luminous efficiency because of its physical properties, but actually, InGaN contained in a multiple quantum well layer. There is a problem that the well layer formed in (1) has a structural defect such that defects are likely to enter, and the advantages of the physical properties are not fully utilized.

On the other hand, in the semiconductor light emitting device 10 according to this embodiment having the above-described configuration, an InGaN layer is interposed between the n-type GaN layer 13 and the multiple quantum well layer 15, and therefore, dislocations in the light emitting layer are eliminated. Occurrence is suppressed. Further, In _x Ga _1-x N (0 <x <0.1) is provided between the n-type GaN layer 13 whose main surface containing the n-type dopant is a nonpolar plane or a semipolar plane and the multiple quantum well layer 15. ) Is formed by epitaxial growth, and an n-type InGaN layer 14 having a thickness of 0.2 μm or more containing an n-type dopant of the same type as that of the n-type GaN layer 13 is interposed, and the n-type InGaN layer 14 is n The strain due to lattice mismatch with the n-type GaN layer 13 is completely or partially relaxed, so that the defects do not become threading dislocations. Therefore, the defect density of the n-type InGaN layer 14 is equal to that of the underlying n-type GaN layer 13. Thus, high luminous efficiency can be obtained. Specifically, the full width at half maximum of the emission intensity distribution with respect to the emission wavelength of the multiple quantum well layer 15 is preferably 40 nm or less, and more preferably 35 nm or less. Even if the n-type GaN layer 13 is not provided and the n-type InGaN layer 14 is interposed between the u-GaN layer 12 and the multiple quantum well layer 15, the same effect can be obtained.

(Manufacturing method of semiconductor light emitting device)
Next, a method for manufacturing the semiconductor light emitting device 10 according to this embodiment will be described with reference to FIGS.

  In the method for manufacturing the semiconductor light emitting device 10 according to the present embodiment, the u-GaN layer 12, the n-type GaN layer 13 (Si-doped), the n-type InGaN layer 14 (Si-doped), and the light emitting layer on the wafer 11 ′. Each semiconductor layer of the quantum well layer 15 (barrier layer 15a: GaN, well layer 15b: InGaN), p-type AlGaN layer 16 (Mg-doped), and p-type GaN layer 17 (Mg-doped) is sequentially formed, and then etched. The n-type GaN layer 13 is exposed, and an n-type electrode 18 and a p-type electrode 19 are formed on the n-type InGaN layer 14 and the p-type GaN layer 17, respectively.

<Wafer preparation>
A wafer 11 ′ is prepared. The wafer 11 ′ has a thickness of 0.3 to 3.0 mm and a diameter of 50 to 300 mm, although it varies depending on the diameter. In the case of the wafer 11 ′ having a diameter of 50 mm, 5000 to 12000 semiconductor light emitting elements 10 can be formed on one wafer.

  On the surface of the wafer 11 ′, a number of fine irregularities on the order of submicron are formed and processed by etching or deposition of silicon oxynitride (SiOxNy) as necessary.

<Formation of semiconductor layer>
The following semiconductor layers can be formed by metalorganic vapor phase epitaxy (MOVPE), halogen vapor phase epitaxy (VPE), molecular beam epitaxy (MBE), hydride vapor phase epitaxy (HVPE). Of these, metal organic vapor phase epitaxy is the most common. Below, the formation method of each semiconductor layer using a metal organic chemical vapor deposition method is demonstrated.

  The MOVPE apparatus used for forming each semiconductor layer includes a wafer transfer system, a wafer heating system, a gas supply system, and a gas exhaust system, which are electronically controlled. The wafer heating system is composed of a thermocouple, a resistance heater, and a carbon or SiC susceptor provided thereon. In the wafer heating system, the MOVPE apparatus is configured to grow a semiconductor layer with a reactive gas on a wafer 11 'set on a susceptor of a quartz tray to be conveyed.

-U-GaN layer-
After the wafer 11 ′ was set on the quartz tray using the MOVPE apparatus, the wafer 11 ′ was heated to 1050 to 1150 ° C. and the pressure in the reaction vessel was set to 10 to 100 kPa, and was set in the reaction vessel. H ₂ is circulated as a carrier gas in the flow channel, and this state is maintained for several minutes to thermally clean the wafer 11 ′.

Next, the temperature of the wafer 11 ′ is set to 1050 to 1150 ° C., the pressure in the reaction vessel is set to 10 to 100 kPa, and the carrier gas H ₂ is flowed into the reaction vessel at a flow rate of about 10 L / min (hereinafter, the gas flow rate is a reference). In this state, the V group element supply source (NH ₃ ) and the Group III element supply source (TMG) are supplied as reaction gases. The flow rate is 0.1-5 L / min and 50-150 μmol / min.

  At this time, starting from the crystal growth surface of the wafer 11 ′, undoped GaN is epitaxially grown thereon, and as shown in FIG. 2A, the u-GaN layer 12 is formed on the wafer 11 ′. .

  In the case where the low temperature buffer layer is formed before the u-GaN layer 12 is formed, the temperature of the wafer 11 ′ is set to 400 to 500 ° C., and GaN is crystal-grown.

-N-type GaN layer-
The pressure in the reaction vessel is set to 10 to 100 kPa, and the carrier gas H ₂ is circulated in the reaction vessel at a flow rate of ₅ to 15 L / min, and as a reaction gas, a group V element supply source (NH ₃ ), Group III element supply source 1 (TMG) and n-type dopant supply source (SiH ₄ ) are supplied at flow rates of 0.1 to 5 L / min, 50 to 150 μmol / min, and 1 to 5 × 10 ⁻³ μmol, respectively. / Min.

  At this time, as shown in FIG. 2B, n-type GaN is epitaxially grown immediately above the u-GaN layer 12 to form an n-type GaN layer 13.

-N-type InGaN layer-
The temperature of the wafer 11 ′ is set to about 600 to 850 ° C., the pressure in the reaction vessel is set to 10 to 100 kPa, and a carrier gas N ₂ is circulated in the reaction vessel, while supplying a group V element as a reaction gas. A source (NH ₃ ), a group III element source 1 (TMG), a group III element source 2 (TMI), and an n-type dopant source (SiH ₄ ) are supplied.

  At this time, as shown in FIG. 2C, n-type InGaN is epitaxially grown immediately above the n-type GaN layer 13 to form the n-type InGaN layer 14.

-Multiple quantum well layer-
The temperature of the wafer 11 ′ is set to about 600 to 850 ° C., the pressure in the reaction vessel is set to 10 to 100 kPa, and a carrier gas N 2 is circulated in the reaction vessel, and as a reaction gas, a group V element supply source is provided. (NH ₃ ) and a group III element supply source (TMG) are supplied at respective supply flow rates. At this time, GaN epitaxially grows immediately above the n-type InGaN layer 14 to form the barrier layer 15a.

Next, a Group V element supply source (NH ₃ ), a Group III element supply source 1 (TMG), and a Group III element supply source 2 (TMI) are flowed. At this time, InGaN is epitaxially grown immediately above the GaN barrier layer 15a to form the well layer 15b.

  Then, the same operation as described above is repeated alternately to form the multiple quantum well layer 15 by alternately forming the barrier layer 15a and the well layer 15b as shown in FIG. 2 (d). The emission wavelength of the multiple quantum well layer 15 depends on the well width of the well layer 15b (the thickness of the well layer 15b) and the InN mixed crystal ratio, and the higher the InN mixed crystal ratio, the longer the emission wavelength. The InN mixed crystal ratio is determined by the TMI molar flow rate / (TMG molar flow rate + TMI molar flow rate), the V / III ratio, and the growth temperature.

-P-type AlGaN layer and p-type GaN layer-
The temperature of the wafer 11 ′ is set to 800 to 1100 ° C., the pressure in the reaction vessel is set to 10 to 100 kPa, and the carrier gas H ₂ is circulated in the reaction vessel, while supplying a group V element as a reaction gas. A source (NH ₃ ), a group III element supply source 1 (TMG), a group III element supply source 3 (TMA), and a p-type dopant supply source (Cp ₂ Mg) are flowed.

  At this time, as shown in FIG. 2 (e), p-type AlGaN is epitaxially grown immediately above the multiple quantum well layer 15 to form a p-type AlGaN layer 16.

Subsequently, a group V element supply source (NH ₃ ), a group III element supply source 1 (TMG), and a p-type dopant supply source (Cp ₂ Mg) are flowed as reaction gases.

  At this time, as shown in FIG. 2E, the p-type GaN is epitaxially grown immediately above the p-type AlGaN layer 16 to form the p-type GaN layer 17.

<Formation of electrode>
The n-type GaN layer 13 is exposed by partially reactive ion etching of the wafer 11 ′ on which the semiconductor layer is formed, and the n-type InGaN layer 14 is exposed by a method such as vacuum deposition, sputtering, or CVD (Chemical Vapor Deposition). An n-type electrode 18 is formed on the substrate. A p-type electrode 19 is formed on the p-type GaN layer 17. A transparent conductive film such as ITO may be interposed between the p-type GaN layer 17 and the p-type electrode 19.

  Finally, the wafer 11 ′ is cleaved to be divided into individual semiconductor light emitting elements 10.

(Test evaluation 1)
A semiconductor light emitting device having the same configuration as that of the above embodiment was manufactured.

  As the substrate, a processed substrate of a sapphire substrate whose main surface having fine irregularities formed on the surface was an r-plane was used. Then, on the sapphire substrate, a u-GaN layer whose principal surface is a {11-22} plane is grown through a low-temperature buffer layer, and a semiconductor is epitaxially grown thereon to form an n-type GaN layer, n A type InGaN layer, a multiple quantum well layer, a p-type AlGaN layer, and a p-type GaN layer were sequentially stacked. Accordingly, the main surface of each layer is the {11-22} plane.

  As the semiconductor light emitting device, a plurality of types in which the light emission wavelength of the multiple quantum well layer was 420 nm (purple) and the In content ratio x in the n-type InGaN layer was varied were produced. Similarly, for each of the light emission wavelength of 450 nm (blue) and the light emission wavelength of 520 nm (green), a plurality of types in which the In content ratio x in the n-type InGaN layer was varied were produced. A semiconductor light emitting device without a reference n-type InGaN layer was also produced.

  And about each semiconductor light emitting element, PL emitted light intensity was measured and the magnification of PL emitted light intensity on the basis of a reference was calculated.

  FIG. 3 shows the relationship between the In content ratio x in the InGaN layer and the PL emission intensity magnification with reference to the reference.

  According to this, in the range where the In content ratio x in the n-type InGaN layer is in the range of 0 <x <0.1, it is understood that the PL emission intensity magnification is larger than 1, and thus high luminous efficiency can be obtained. . In particular, it can be seen that remarkably high luminous efficiency can be obtained in the range of 0.01 <x <0.05 and those that emit purple light.

  Further, when reciprocal lattice space mapping measurement was performed for each semiconductor light emitting element, at least the In content ratio x in the n-type InGaN layer is in the range of 0 <x <0.15, the n-type InGaN layer is n It was confirmed that the strain due to lattice mismatch with the type GaN layer was completely or partially relaxed.

(Test evaluation 2)
In the same manner as in Test Evaluation 1, a semiconductor light-emitting element of the same kind that emits blue-green light with a variable thickness of the n-type InGaN layer was produced. The In content ratio x was set to 0.02. In addition, a semiconductor light emitting device without a reference n-type InGaN layer was also produced. For each semiconductor light emitting device, the full width at half maximum of the emission intensity distribution with respect to the emission wavelength of the multiple quantum well layer at the time of current injection of 20 mA was obtained.

  FIG. 4 shows the relationship between the thickness of the n-type InGaN layer and the full width at half maximum of the emission intensity distribution.

  According to FIG. 4, in the reference semiconductor light emitting device, the full width at half maximum of the light emission intensity distribution is a little over 40 nm (white circle in FIG. 4), but when the thickness of the n-type InGaN layer is 0.2 μm or more, light emission It can be seen that the full width at half maximum of the intensity distribution is 40 nm or less, and at 0.3 μm or more, the full width at half maximum of the emission intensity distribution is 35 nm or less, and about 1.0 nm at 1.0 μm. That is, this indicates that the high light emission efficiency of the semiconductor light emitting device can be obtained when the thickness of the n-type InGaN layer is 0.2 μm or more.

  The present invention is useful for semiconductor light emitting devices.

DESCRIPTION OF SYMBOLS 10 Semiconductor light-emitting device 11 Substrate 11 ′ Wafer 12 u-GaN layer 13 n-type GaN layer 14 n-type InGaN layer 15 Multiple quantum well layer 15a Barrier layer 15b Well layer 16 p-type AlGaN layer 17 p-type GaN layer 18 n-type electrode 19 p-type electrode

Claims (3)

A GaN layer whose principal surface is a {11-22} plane;
In _x Ga _1-x N (0.01 <x <0.05) is formed by epitaxial growth directly on the GaN layer, and includes an n-type dopant-containing InGaN layer having a thickness of 0.2 μm or more,
A multiple quantum well layer formed by epitaxial growth directly on the InGaN layer and configured to emit purple light including a well layer formed of InGaN;
With
In the InGaN layer, distortion due to lattice mismatch with the GaN layer is completely or partially relaxed,
A semiconductor light emitting device wherein the full width at half maximum of the emission intensity distribution with respect to the emission wavelength of the multiple quantum well layer is 40 nm or less. The semiconductor light emitting device according to claim 1,
A semiconductor light-emitting device further comprising a substrate provided with the GaN layer. The semiconductor light emitting device according to claim 7,
A semiconductor light emitting device wherein the substrate is a sapphire substrate.

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