JPH06291366A - Light emitting element of gallium nitride compound semiconductor - Google Patents

Abstract

PURPOSE:To improve an external quantum efficiency of a light emitting element by forming a transparent film, on a surface of the gallium nitride compound semiconductor, of which the refractive index is between the refractive indexes of the compound semiconductor and a sealing material, and suppressing interference of light by multipath reflection inside the semiconductor. CONSTITUTION:A semiconductor wafer of gallium nitride compound, on the sapphire substrate 1 of which, an n-type GaN layer 2, a Zn doped InGaN layer 3 and a p-type GaN layer 4 are formed, is prepared. Forming a predetermined pattern of the p-type GaN layer 4, ohmic electrodes are formed on the p-type GaN layer 4 and the n-type GaN laer 2. Then masking a part of the electrode, a transparent film 5 of SnO2 is formed by deposition on the surface of the p-type GaN layer 4. The refractive index of the transparent film 5 at the wavelength of the light emission of the gallium nitride compound semiconductor is between the refractive indexes of the gallium nitride compound semiconductor and sealing material 6. Then the wafer is cut off into chips, after wire-bonding, each chip is sealed with epoxy resin, thus fabricating the light emitting elements.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a sapphire substrate on which a gallium nitride compound semiconductor represented by the general formula In _X Al _Y Ga _1-XY N (0≤X <1, 0≤Y <1) is laminated. The present invention relates to a gallium nitride-based compound semiconductor light emitting device obtained by encapsulating the chip with an encapsulating material such as epoxy resin.

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN, In
A gallium nitride-based compound semiconductor such as AlGaN has a direct transition, its band gap changes from 1.95 eV to 6 eV, and its emission color ranges from ultraviolet to red. Therefore, a material for a light emitting element such as a light emitting diode or a laser diode. Is seen as promising. The light emitting device made of the gallium nitride-based compound semiconductor generally uses n-type and p-type on a sapphire substrate by using a vapor phase growth method such as MOCVD or MBE.
Alternatively, it can be obtained by growing and stacking into n-type and i-type, taking out the electrodes from the respective layers, fixing them to a lead frame as a chip, and finally sealing with a resin such as epoxy.

However, since the gallium nitride-based compound semiconductor light-emitting device has a so-called heteroepitaxial structure in which a completely different material called a gallium nitride-based compound semiconductor is laminated on the sapphire substrate as described above, other GaAs and GaP are used. As compared with a light emitting device laminated on the same material, the external quantum efficiency is deteriorated due to the difference in refractive index between the substrate and the epitaxial film. Specifically, due to the difference in refractive index between the sapphire substrate and the gallium nitride-based compound semiconductor, or the gallium nitride-based compound semiconductor and the resin mold that seals the light-emitting element, the light emission of the gallium-nitride-based compound semiconductor is reflected multiple times at their interfaces. However, the reflected light is absorbed inside the gallium nitride-based compound semiconductor, and there is a problem that the emitted light cannot be efficiently extracted to the outside.

[0004]

If the multiple reflections between the gallium nitride-based compound semiconductor and the substrate, the sealing material, or the atmosphere can be suppressed and the interference can be reduced, the external quantum efficiency can be improved and the luminous efficiency can be improved. Can be improved. Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to suppress gallium nitride compound semiconductor light emission by suppressing interference caused by multiple reflection of light inside the gallium nitride compound semiconductor. It is to improve the external quantum efficiency of the device.

[0005]

[Means for Solving the Problems] We have conducted a number of experiments to suppress multiple reflections inside the gallium nitride-based compound semiconductor and to increase the external quantum efficiency. It has been newly found that the above problem can be solved by forming a transparent optical thin film having a refractive index between the refractive index of the semiconductor and the surface of the gallium nitride-based compound semiconductor. That is, the gallium nitride-based compound semiconductor light-emitting device of the present invention is a light-emitting device obtained by encapsulating a chip, in which a gallium nitride-based compound semiconductor is laminated on a sapphire substrate, with an encapsulating material. A transparent thin film having a refractive index at the emission wavelength of the gallium nitride compound semiconductor between the refractive index of the gallium nitride compound semiconductor and the refractive index of the sealing material is formed.

Although the refractive index is slightly different depending on the wavelength, as a material of the transparent thin film formed on the surface of the gallium nitride compound semiconductor, the refractive index is between the refractive index of the gallium nitride compound semiconductor and the sealing material, Any transparent material may be used. Specifically, the gallium nitride-based compound semiconductor used for the light emitting device has a refractive index of about 2,
Since the epoxy resin generally used as a sealing material has a refractive index of about 1.5, a material between 2 and 1.5 is, for example, Al ₂ O ₃ (refractive index 1.6
2), MgO (1.75), SnO ₂ (1.9), La
F ₃ (1.59), CeF ₃ (1.63) and the like can be mentioned as preferable materials, and these materials can be used, for example, on the surface of a gallium nitride-based compound semiconductor by using an apparatus such as vapor deposition, sputtering, or plasma CVD. Can be formed.

Further, assuming that the thickness of the transparent thin film is t, the emission wavelength of the gallium nitride compound semiconductor is λ, and the refractive index of the transparent thin film at λ is n, t = Aλ / (4
n) (however, A is a natural number). By forming the transparent thin film with this film thickness, the transparent thin film satisfies the condition of antireflection coating for the light of the emission wavelength λ, and the light can be transmitted to the sealing resin without being reflected at the interface. The A value is not particularly limited,
It is more preferable to select a natural number of 5 or less because the film thickness can be formed thinner and the amount of light emission absorbed is reduced.

[0008]

1 shows the structure of a gallium nitride-based compound semiconductor light emitting device according to one embodiment of the present invention. 1 is a sapphire substrate, 2 is an n-type GaN layer, 3 is Zn-doped InGaN
Layer 4 is a Mg-doped p-type GaN layer, 5 is a transparent thin film made of SnO ₂ , and 6 is an encapsulating material made of an epoxy resin for encapsulating the whole. In the light emitting device of this structure, the light emitting layer is Zn-doped InGaN. It corresponds to layer 3. Sapphire has a refractive index of about 1.6, gallium nitride-based compound semiconductor has a refractive index of about 2, and epoxy resin has a refractive index of about 1.5.
In the conventional light emitting device, as shown in FIG. 2, the sapphire substrate 1, the gallium nitride compound semiconductors 2, 3,
4, the epoxy resin 6 and the respective materials have different refractive indexes, so that part of the light emitted from the InGaN layer 3 is p-type GaN.
The light is reflected at the interface between the layer 4 and the epoxy resin, and the reflected light is reflected at the interface between the sapphire substrate 1 and the n-type GaN layer 2, resulting in multiple reflection, and gradually the gallium nitride-based compound semiconductor layers 2, 3, 4, It is absorbed in and attenuated. Since the gallium nitride-based compound semiconductors 2, 3, and 4 may be regarded as having almost the same refractive index, the multiple reflection at the interface between the semiconductor layers may be regarded as zero (0).
On the other hand, as in the present invention (FIGS. 1 and 3), Mg-doped p-type G
On the aN layer, a SnO ₂ film 5 having a refractive index between the gallium nitride compound semiconductor and the epoxy resin (refractive index 1.
9), the SnO ₂ film 5 is formed as shown in FIG.
Serves as a buffer layer, and the reflection of light at the interface can be reduced. In particular, the thickness t of the SnO ₂ film 5 is t = λ / (4
By setting the thickness to n), the SnO ₂ film 5 acts as a non-reflective coating, and reflection can be almost eliminated. More conveniently, when a transparent thin film having conductivity such as SnO ₂ is formed, it can be electrically connected to an ohmic-contacted electrode, and p-type G
It can act as an entire surface electrode of the aN layer 4.

[0009]

[Example 1] A GaN buffer layer and Si-doped n-type GaN are formed on a sapphire substrate by MOCVD.
A gallium nitride-based compound semiconductor wafer is prepared in which a layer, a Zn-doped InGaN layer, and a Mg-doped GaN layer are sequentially grown and laminated. Next, a predetermined pattern is formed on the p-type GaN layer, which is the uppermost layer of this wafer, by a photolithography technique, and the p-type GaN layer is partially etched to expose an n-type GaN layer for forming electrodes. After that, ohmic electrodes are attached to the p-type GaN layer and the n-type GaN layer. When the emission wavelength of this gallium nitride-based compound semiconductor was measured by energizing both electrodes, it was 470n.
It had a peak at m.

Next, after masking a part of the electrode, a transparent thin film made of SnO ₂ is formed on the surface of the p-type GaN layer by vapor deposition. The film thickness is 470 nm, the refractive index of the gallium nitride-based compound semiconductor is about 2, the refractive index of SnO ₂ is 1.9, and t = 470 / (4 × 1.9)
It was set to about 620 angstroms.

Next, the mask of the electrode is peeled off, and the wafer is cut into 0.5 mm square chips. Finally, the chip is placed on a lead frame according to a conventional method and wire-bonded, and then sealed with an epoxy resin to obtain a light emitting device (blue light emitting diode) of the present invention. The emission spectrum of this light emitting diode is shown in FIG. On the other hand, for comparison,
The spectrum of a conventional light emitting diode obtained in the same manner without forming the transparent thin film is also shown in FIG. 4 (b).

As shown in this figure, in the spectrum of the conventional light emitting diode, in addition to the main emission peak, a plurality of peaks due to the interference effect of multiple reflection appears. On the other hand, in the spectrum of the light emitting diode of the present invention, the peak of the interference effect due to multiple reflection does not appear, and it is understood that the emission intensity is improved by 10% or more as compared with the conventional one.

[Embodiment 2] A GaN buffer layer, a Si-doped n-type GaN layer, and a Mg-doped G layer on a sapphire substrate.
The aN layer and the aN layer are sequentially grown and laminated, and the main emission wavelength is 4
A gallium nitride-based compound semiconductor wafer having a thickness of 30 nm is prepared.

After etching the p-type GaN layer in the same manner as in Example 1, a transparent thin film made of Al ₂ O ₃ is formed on the surface of the p-type GaN layer by vapor deposition as well. The transparent thin film has a thickness of Al ₂ O ₃ of 1.6 because
670 angstrom at t = 430 / (4 × 1.6).

Thereafter, a blue light emitting diode was prepared in the same manner as in Example 1 and its spectrum was measured. The result is shown in FIG. For comparison, a blue light emitting diode without a transparent thin film was similarly prepared, and its spectrum is shown in FIG. 5 (d).

Also in this figure, as in FIG. 4, a plurality of peaks due to interference of multiple reflections appear in the emission spectrum of the conventional light emitting diode in which the transparent thin film is not formed. On the other hand, from the spectrum of the light emitting diode of the present invention, a plurality of peaks disappeared and the emission intensity was improved by 10% or more.

[0017]

As described above, in the gallium nitride compound semiconductor light emitting device of the present invention, a transparent thin film having a function of suppressing the interference of multiple reflection generated inside the semiconductor is formed on the surface of the gallium nitride compound semiconductor. Therefore, the light emission of the gallium nitride-based compound semiconductor can be effectively extracted to the outside, and the external quantum efficiency of the light emitting device is improved. Also,
A light-emitting device made of a material other than a gallium nitride-based compound semiconductor does not have a heteroepitaxial structure, so providing such a thin film is less effective, but a gallium nitride-based compound semiconductor light-emitting device having a heteroepitaxial structure is a transparent thin film. The effect is remarkable.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a part of the structure of a gallium nitride-based compound semiconductor light emitting device according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view illustrating an optical path of a conventional light emitting element.

FIG. 3 is a schematic cross-sectional view illustrating an optical path of a light emitting device of the present invention.

FIG. 4 is a diagram showing a spectrum of a light emitting element according to an embodiment of the present invention and a spectrum of a conventional light emitting element for comparison.

FIG. 5 is a diagram showing a spectrum of a light emitting element according to an embodiment of the present invention and a spectrum of a conventional light emitting element for comparison.

[Explanation of symbols]

1 ... Sapphire substrate 2 ... n-type GaN layer 3 ... Zn-doped InGaN layer 4 ... p-type GaN layer 5 ... Transparent thin film 6 ... Encapsulating resin

Claims (3)

[Claims] 1. A light-emitting device comprising a sapphire substrate and a chip in which a gallium nitride-based compound semiconductor is stacked and sealed with a sealing material, wherein the gallium nitride-based compound semiconductor surface emits light of the gallium nitride-based compound semiconductor. A gallium nitride-based compound semiconductor light-emitting device, wherein a transparent thin film having a refractive index at a wavelength between the refractive index of a gallium nitride-based compound semiconductor and the refractive index of a sealing material is formed. 2. The transparent thin film has a film thickness of t,
When the emission wavelength of the gallium nitride compound semiconductor is λ and the refractive index of the transparent thin film at λ is n, t = Aλ / (4n)
The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the gallium nitride-based compound semiconductor light emitting device is formed in a relationship of (where A is a natural number). 3. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the transparent thin film has conductivity.