JP2001345476A - Gallium nitride compound semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new structure which can improve the characteristic for distributing luminous intensity of a light emitting element using the rear surface of a substrate composed of a gallium nitride compound semiconductor on which a laminated structure containing a light emitting layer is not formed as its main light emitting surface immediately above the element and, at the same time, can maintain the luminous intensity of the element at a high level. SOLUTION: The characteristic for distributing luminous intensity of the light emitting element immediately above the element can be made uniform by making the electrode to be arranged on the main light emitting surface of the element unnecessary, by providing a laminated structure of an n-type layer 2 composed of a gallium nitride compound semiconductor, the light emitting layer 4, and a p-type layer 6 on the substrate 1 composed of the n-type gallium nitride-based compound semiconductor, and by providing an n-side electrode in contact with the surface of the n-type layer 2 which is exposed by partially removing the layer 2 from the surface side of the laminated structure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a semiconductor light emitting device used for a light emitting diode, and more particularly to a gallium nitride compound light emitting device using a gallium nitride compound semiconductor substrate.

[0002]

2. Description of the Related Art Gallium nitride compound semiconductors have been widely used as semiconductor materials for visible light emitting devices and high-temperature operating electronic devices, and are being developed in the field of blue and green light emitting diodes. .

A gallium nitride-based compound semiconductor light emitting device capable of emitting visible light basically comprises an n-type cladding layer and an InGaN serving as a light emitting layer on a substrate made of sapphire, SiC, or the like via a buffer layer. The mainstream is a laminate of a light-emitting layer made of and a p-type cladding layer. In particular, recently, a double heterostructure grown using a sapphire substrate as a substrate and a low-temperature growth buffer layer made of GaN or AlN by a metal organic chemical vapor deposition method has high luminance and high reliability. It has been widely used for light emitting diodes for outdoor panel displays and the like.

However, recently, a substrate made of GaN has been manufactured, and some gallium nitride-based compound semiconductor light emitting devices using the same have been proposed. For example, Japanese Patent Application Laid-Open No. 7-94784 discloses a blue light-emitting device in which a stacked body including a pn junction is formed on a GaN substrate. According to this publication, a structure in which GaN is used as the substrate and the substrate exists between the electrodes facing each other similarly to other red light-emitting diodes or the like is possible, and the restriction on the electrode position can be eliminated.

Further, Japanese Patent Application Laid-Open No. 10-150220 discloses a light-emitting element that uses a substrate made of n-type GaN and can use the substrate side as a main light-emitting surface side.

FIG. 3 is a cross-sectional view showing the structure of a conventional gallium nitride-based compound semiconductor light emitting device disclosed in the above publication. On a substrate 11 made of n-type GaN, n
12 cladding layers, light emitting layer 13 and p-cladding layer 1
4 are sequentially laminated, an n-side electrode 15 is provided on a part of one surface other than the lamination surface side of the substrate 11, and a p-side electrode 16 is provided over the entire surface on the p-type cladding layer 14. . By mounting the p-side electrode 16 downward,
The surface on which the n-side electrode 15 is provided is defined as the main light emitting surface side, so that surface light emission can be obtained. According to such a configuration, the current-
It is stated that an inexpensive light emitting element with improved light output characteristics can be provided.

[0007]

However, in the gallium nitride-based compound semiconductor light emitting device having the conventional structure shown in FIG. 3, since the substrate 11 made of GaN is transparent to light emitted from the light emitting layer 13, the substrate 11 Can be used as the main light emitting surface. Since the n-side electrode 15 is usually used as a pad for wire bonding, the n-side electrode 15 is formed of a thick film that is not transparent to light emission.

Therefore, light emitted from the light emitting layer 13 below the electrode and traveling toward the main light emitting surface of the substrate 11 is blocked by the thick n-side electrode 15. For this reason,
The light distribution characteristic above the light emitting element has a concave distribution that drops above the region where the n-side electrode 15 is formed. The light distribution characteristic having such a distribution has a problem that it is not desirable in applications that require uniform light distribution characteristics and high luminous intensity right above the light emitting element.

If the size of the n-side electrode 15 is reduced in order to increase the area of the substrate 11 serving as the main light emitting surface in order to avoid such a concave distribution, the work of wire bonding becomes difficult. It is not preferable to reduce the size of No. 15. Therefore, there is a demand for a light-emitting element that can improve the light-emitting characteristics even while ensuring the workability of electrical connection such as bonding.

The present invention solves the above-mentioned conventional problems. In a light-emitting element using a substrate made of a gallium nitride-based compound semiconductor and using the substrate side as a main light-emitting surface, the light-emitting element is disposed directly above the light-emitting element. It is an object of the present invention to provide a gallium nitride-based compound semiconductor light emitting device having a novel structure capable of improving light characteristics and maintaining high light emission intensity.

[0011]

In order to solve the above problems, a gallium nitride based compound semiconductor light emitting device according to the present invention comprises:
On a first main surface of a substrate made of a light-transmitting n-type gallium nitride-based compound semiconductor having a first main surface and a second main surface,
A stacked structure of at least an n-type layer made of a gallium nitride-based compound semiconductor, a light-emitting layer, and a p-type layer is provided, and the n-side electrode is exposed by partially removing the n-side electrode from the surface side of the stacked structure The p-side electrode is provided in contact with the surface of the layer, the p-side electrode is provided in contact with the surface of the p-type layer, and the second main surface of the substrate is a main light emitting surface.

According to such a configuration, the light distribution characteristics right above the light emitting element can be improved, and the emission intensity can be kept high.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the embodiments of the present invention will be described.
This will be described with reference to FIG.

(Embodiment) FIG. 1 is a sectional view showing a structure of a gallium nitride based compound semiconductor light emitting device according to one embodiment of the present invention.

In FIG. 1, an n-type layer 2 made of GaN, a light emitting layer 4 made of InGaN, and a p-type layer 6 made of AlGaN are sequentially laminated on a substrate 1 made of n-type GaN. . A p-side electrode 7 is formed on the surface of the p-type layer 6, and the p-type layer 6, the light emitting layer 4, and a part of the n-type layer 2 are removed from the surface side of the p-type layer 6 by etching. An n-side electrode 8 is formed on the exposed surface of n-type layer 2.

[0016] The substrate 1, n-type gallium nitride-based compound semiconductor _{(In a Al b Ga 1-} ab N ( where, 0 ≦ a ≦ 1,
0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1)) can be used, but Al _c Ga _1-c N (where 0 ≦ c ≦ 1) where good crystallinity is easily obtained is desirable. Among them, it is most preferable to use GaN that is relatively easy to produce and provides the best crystallinity. The substrate 1 is doped with an n-type impurity such as Si or Ge and has an electron concentration controlled in a range of approximately 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . When the electron concentration is lower than 1 × 10 ¹⁶ cm ^-3, the resistivity is high, the electrons injected into the substrate 1 is because it tends to be difficult to spread the substrate 1, from 1 × 10 ¹⁹ cm ^-3 This is because if the n-type impurity is too high, the crystallinity of the substrate 1 tends to deteriorate due to the high concentration of n-type impurities.

As the n-type layer 2, an n-type gallium nitride-based compound semiconductor having a larger band gap than the light-emitting layer 4 can be used. Thereby, the function as an n-type cladding layer can be given to the n-type layer 2. As the n-type layer 2, a single layer of GaN, AlGaN, InGaN, InAlGaN, or the like, or a layer in which these layers are stacked can be used. When GaN is used for the substrate 1, it is desirable to use a GaN layer at least in contact with the substrate 1.

The n-type layer 2 is doped with an n-type impurity such as Si or Ge at least in a layer where the n-side electrode 8 is formed, and has an electron concentration of 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 1
Desirably, it is less than 0 ¹⁹ cm ^-3 . Electron concentration is 1 ×
If it is lower than 10 ¹⁷ cm ^-3 , the ohmic contact resistance with the n-side electrode 8 increases, and the operating voltage of the light emitting element increases. If it is higher than 1 × 10 ¹⁹ cm ^-3 , n
N-type layer 2
This is because the crystallinity tends to deteriorate.

The thickness of the n-type layer 2 is desirably 0.1 μm or more. If the thickness is smaller than 0.1 μm, the etching accuracy when forming an exposed surface for forming the n-side electrode 8 in the n-type layer 2 by etching becomes extremely strict. The upper limit of the thickness of the n-type layer 2 is not particularly limited, but is about 5 μm or less in order to ease the etching accuracy when forming the exposed surface and to prevent the formation time of the n-type layer 2 from becoming unnecessarily long. It is desirable that

The n-type layer 2 has a current (electron) in the n-type layer 2.
In order to promote the spread, a layer having a relatively low electron concentration (a layer having a high resistivity) is provided as a current diffusion layer on the light emitting layer 4 side with respect to the layer on which the n-side electrode 8 is formed, or It is desirable to provide a layer having a relatively large band gap. By providing these current spreading layers, n
In the mold layer 2, electrons are temporarily difficult to flow toward the light emitting layer 4 side, and the electrons are uniformly spread in the plane of the n-type layer 2, whereby uniform injection of electrons into the light emitting layer 4 can be realized. The light emission distribution in the light emitting layer 4 becomes uniform, and as a result, the substrate 1
This is because uniform surface light emission can be obtained on the main light-emitting surface on the back surface side. As a specific configuration, when GaN is used for the substrate 1, GaN is used as the first n-type layer in order from the substrate 1 side.
Is used as a second n-type layer as Al _x Ga ₁ -xN (where 0 ≦ x
≤ 0.2). Further, GaN can be provided as a third n-type layer on the second n-type layer. Here, the first n-type layer is a layer on which the n-side electrode 8 is formed, and the second n-type layer and the third n-type layer are current diffusion layers. The second n-type layer and the third n-type layer may be doped with an n-type impurity or may be undoped. The thickness of the second n-type layer, or the total thickness of the second n-type layer and the third n-type layer, is preferably in the range of 0.002 μm or more and 0.2 μm or less. If the thickness is less than 0.002 μm, the effect of current spreading tends to be small, and
This is because when the thickness is larger than m, the series resistance of the light emitting element increases and the operating voltage increases. Then, by adjusting the electron concentration according to the layer thickness of the second n-type layer or the total layer thickness of the second n-type layer and the third n-type layer, the effect of current spreading can be obtained. Resistance can be reduced. According to the findings of the present inventors, it is preferable to increase the electron concentration while increasing the layer thickness.

As the light emitting layer 4, a gallium nitride-based compound semiconductor having a band gap smaller than that of the n-type layer 2 and the p-type layer 6 can be used. In particular, when InGaN or GaN containing no Al is used, the emission intensity in the ultraviolet to green wavelength range can be increased. When the light emitting layer 4 contains In, the thickness is 0.01 μm
If the single quantum well layer is made thinner, the crystallinity of the light emitting layer 4 can be increased, and the luminous efficiency can be further increased.

The light emitting layer 4 is a multiple quantum well in which a quantum well layer made of InGaN or GaN and a barrier layer made of InGaN, GaN, AlGaN or the like having a larger band gap than the quantum well layer are alternately stacked. It can also be structured.

As the p-type layer 6, a p-type gallium nitride-based compound semiconductor having a larger band gap than the light-emitting layer 4 can be used. Thereby, the function as a p-type cladding layer can be imparted to the p-type layer 6. As the p-type layer 6, a single layer of GaN, AlGaN, InGaN, InAlGaN, or the like, or a layer in which these layers are stacked can be used. In particular, as the p-type layer on the side in contact with the light emitting layer 4, AlGa is used.
It is preferable to use N because electrons can be efficiently confined in the light emitting layer 4 and luminous efficiency can be increased.

The p-type layer 6 is doped with a p-type impurity,
It is p-type conduction. Mg, Zn, and p-type impurities
Cd, C, etc. can be used, but p-type is relatively easily
It is preferable to use Mg that can be used. p-type
The impurity concentration is 1 × 10¹⁹cm ^-35 × 10²⁰cm^-3
It is desirable to be less than. The p-type impurity concentration is 1 × 10
¹⁹cm^-3Lower than the ohmic contact with the p-side electrode 7
Whether the contact resistance increases and the operating voltage of the light emitting element increases
5 × 10²⁰cm^-3Higher than p-type
The doping of the p-type layer 6 due to the highly doped dope
The crystallinity tends to deteriorate, and the p-type
This is because diffusion of impurities becomes remarkable and luminous efficiency decreases.
is there.

When the p-type layer 6 is doped with a relatively high concentration of p-type impurity, the p-type layer 6 is formed between the light-emitting layer 4 and the p-type layer 6 in order to suppress excessive diffusion of the p-type impurity into the light-emitting layer 4. In addition, an intermediate layer may be introduced. In this intermediate layer, InAlG
Although aN can be used, it is particularly preferable to use GaN because crystallinity at the interface with the light emitting layer 4 can be kept good. The intermediate layer is preferably undoped in order to serve as an absorption layer for p-type impurities diffused in the direction of the light emitting layer 4. The thickness of the intermediate layer is 0.0
It is desirable that the thickness be in the range of not less than 01 μm and not more than 0.05 μm. If the thickness is smaller than 0.001 μm, the effect of suppressing the diffusion of the p-type impurity into the light emitting layer 4 becomes small, and
If the thickness is more than m, the efficiency of injecting holes into the light emitting layer 4 decreases, and the light emission efficiency decreases.

The thickness of the p-type layer 6 is preferably in the range from 0.05 μm to 0.5 μm. 0.05
If the thickness is smaller than μm, the constituent metal of the p-side electrode 7 penetrates into the light-emitting layer 4 by electromigration or the like, so that the life of the light-emitting element is easily reduced. If the thickness is larger than 0.5 μm, the current (hole) is p-type. This is because the voltage drop when passing through the layer 6 increases and the operating voltage of the light emitting element increases.

The side of the p-type layer 6 in contact with the p-side electrode 7 can be made of GaN or InGaN having a relatively small band gap. Thereby, the contact resistance with the p-side electrode 7 can be reduced, and the operating voltage can be effectively reduced.

Au, Ni, Pt, P
A single metal such as d or Mg, or an alloy or a laminated structure thereof can be used. In particular, Ag, Pt, Mg, Al, Zn, Rh, Ru, which have high reflectance with respect to the emission wavelength.
When a metal such as Pd is used, light traveling from the light-emitting layer 4 toward the p-side electrode 7 can be reflected and extracted from the back side of the substrate 1, which is preferable in terms of improving light emission intensity.

The n-side electrode 8 is formed by removing a part of the light emitting layer 4 and the p-type layer 6 formed on the n-type layer 2 from the surface side of the laminated structure and exposing the n-type layer 2. Formed in contact with the surface of By arranging the n-side electrode 8 in this manner, the back side of the substrate 1 where the laminated structure is not formed can be used as the main light emitting surface, and uniform surface light emission can be obtained on the main light emitting surface. .

The n-side electrode 8 can be made of a single metal such as Al or Ti, an alloy containing Al, Ti, Au, Ni, V, Cr or the like, or a laminated structure thereof.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a specific example of a method for manufacturing a gallium nitride based compound semiconductor light emitting device of the present invention will be described with reference to the drawings. The following examples mainly show a method for growing a gallium nitride-based compound semiconductor using a metal organic chemical vapor deposition method, but the growth method is not limited to this, and the molecular beam epitaxy method and the organic metal It is also possible to use a molecular beam epitaxy method or the like.

FIG. 2 is a sectional view showing the structure of a gallium nitride based compound semiconductor light emitting device according to another embodiment of the present invention.

In this example, a gallium nitride-based compound semiconductor light emitting device shown in FIG. 2 was manufactured.

First, a mirror-finished surface having a thickness of about 3
After placing a wafer-shaped substrate 1 of 00 μm and a diameter of about 50 mm on a substrate holder in a reaction tube, the temperature of the substrate 1 is maintained at 1100 ° C. for 10 minutes, hydrogen gas is supplied at 4 liter / min, and nitrogen gas is supplied at a rate of 4 l / min. By cleaning the substrate 1 while flowing ammonia at a rate of 2 liters / minute at 2 liters / minute, cleaning for removing dirt such as organic substances and moisture adhering to the surface of the substrate 1 was performed.

Next, while maintaining the temperature of the substrate 1 at 1100 ° C., while supplying nitrogen gas as a carrier gas at 15 liters / minute and hydrogen gas at 4 liters / minute, ammonia is supplied at 2 liters / minute and trimethylgallium is supplied. (Less than,
Abbreviated as TMG. ) At 80 μmol / min, 10 ppm
Dilute monosilane was supplied at a rate of 10 cc / min to grow an n-type layer 2 of GaN doped with Si to a thickness of 2 μm. The electron concentration of the n-type layer 2 is 1 × 10 ¹⁸ cm ⁻³
Met.

After growing the n-type layer 2, the temperature of the substrate 1 is set to 110
While maintaining the temperature at 0 ° C., the supply of monosilane was stopped, and while flowing nitrogen gas as a carrier gas at 15 L / min and hydrogen gas at 4 L / min, ammonia was supplied at 2 L / min, TMG was supplied at 40 μmol / min, and trimethyl was added. Aluminum (hereinafter abbreviated as TMA) at 3 μmol /
The n-type layer 3 made of undoped Al _0.05 Ga _0.95 N was grown to a thickness of 0.05 μm. The electron concentration of this n-type layer 3 was 5 × 10 ¹⁶ cm ⁻³ .

After the growth of the n-type layer 3, the supply of TMG and TMA is stopped, the temperature of the substrate 1 is lowered to 700 ° C., and this temperature is maintained while flowing nitrogen gas as a carrier gas at 15 L / min. , Ammonia at 6 l / min,
TMG was supplied at 4 μmol / min and trimethylindium (hereinafter abbreviated as TMI) at 1 μmol / min to supply a light emitting layer 4 having a single quantum well structure made of undoped In _0.15 Ga _0.85 N of 0.002 μm. Grow in thickness.

After the light emitting layer 4 is grown, the supply of TMI is stopped.
While flowing nitrogen gas as a carrier gas at a rate of 15 liters / minute, ammonia was used at a rate of 6 liters / minute, and TMG was 2 μm.
The intermediate layer 5 made of undoped GaN was grown to a thickness of 0.004 μm while increasing the temperature of the substrate 1 to 1050 ° C. while supplying the solution at ol / min.

When the substrate temperature reaches 1050 ° C., ammonia is supplied at 2 L / min, TMG is supplied at 40 μmol / min, and TMA is supplied at 3 μmo while flowing nitrogen gas as a carrier gas at 15 L / min and hydrogen gas at 4 L / min.
l / min, biscyclopentadienyl magnesium (hereinafter abbreviated as Cp ₂ Mg) at 0.1 μmol / min,
And a p-type layer 6 made of Mg-doped Al _0.05 Ga _0.95 N was grown to a thickness of 0.2 μm. This p
The Mg concentration of the mold layer 6 was 1 × 10 ²⁰ cm ⁻³ .

After growing the p-type layer 6, TMG, TMA and Cp
₂ The supply of Mg was stopped, and the temperature of the substrate 1 was cooled to about room temperature while flowing nitrogen gas at 8 liters / minute and ammonia at 2 liters / minute, and the gallium nitride-based compound semiconductor was stacked on the substrate 1. The removed wafer was taken out of the reaction tube.

The thus-formed lamination structure made of a gallium nitride-based compound semiconductor is not separately annealed, but a SiO ₂ film is deposited on the surface thereof by a CVD method, followed by photolithography and wet etching. To form an SiO ₂ mask for etching. Then, by the reactive ion etching method, the p-type layer 6, the intermediate layer 5, the light-emitting layer 4, the n-type layer 3, and a part of the n-type layer 2 are formed at a depth of about 0.5 μm in a direction opposite to the stacking direction. Then, the surface of the n-type layer 2 was exposed. Then, by photolithography and vapor deposition, a part of the exposed surface of the n-type
An n-side electrode 8 having a thickness of 0.5 μm of Ti and a thickness of 0.5 μm of Au was deposited by vapor deposition. Furthermore, SiO ₂ for etching
After the mask is removed by wet etching, Pt of 0.3 μm thickness and Au of 0.5 μm thickness are formed on almost the entire surface of the p-type layer 6 by photolithography and vapor deposition.
Was formed by vapor deposition.

Thereafter, the back surface of the substrate 1 is polished to 100 μm.
The thickness was adjusted to about m and separated into chips by scribing. Thus, the gallium nitride based compound semiconductor light emitting device shown in FIG. 2 was obtained.

The light emitting device was placed on a Si diode having a pair of positive and negative electrodes with the electrode forming surface facing downward.
Adhered by u bump. At this time, the light emitting element is mounted such that the p-side electrode 7 and the n-side electrode 8 of the light emitting element are connected to the negative electrode and the positive electrode of the Si diode, respectively. Thereafter, the Si diode on which the light emitting element was mounted was mounted on the stem using Ag paste, the positive electrode of the Si diode was connected to the electrode on the stem with a wire, and then resin molded to produce a light emitting diode. When this light-emitting diode was driven with a forward current of 20 mA, it emitted blue light with a peak emission wavelength of 470 nm.
, Uniform surface light emission was obtained from the back side. At this time, the light emission output was 3 mW, and the forward operation voltage was 3.4 V.

[0044]

As described above, according to the present invention, a substrate made of a gallium nitride-based compound semiconductor is used, and the back side of the substrate on which the laminated structure including the light emitting layer is not formed is used as the main light emitting surface. In the device, the light distribution characteristics right above the light emitting element can be improved and the light emission intensity can be kept high. Therefore, a surface mount type light emitting diode or light emitting element on which a uniform light distribution is desired directly above the light emitting element is mounted on the substrate. It can be suitably used for applications such as linear light sources arranged in a plurality.

Further, since the light emission intensity immediately above the light emitting element can be kept high, it can also be used for a conventional light emitting diode with a resin lens having a shell shape.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing the structure of a gallium nitride based compound semiconductor light emitting device according to another embodiment of the present invention.

FIG. 3 is a sectional view showing the structure of a conventional gallium nitride-based compound semiconductor light emitting device.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 n-type layer 3 n-type layer 4 light-emitting layer 5 intermediate layer 6 p-type layer 7 p-side electrode 8 n-side electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuichi Shinagawa 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. F-term (reference) 5F041 CA05 CA13 CA34 CA40 CA91 CA99

Claims (1)

[Claims] 1. A light-transmitting n-type gallium nitride-based compound semiconductor substrate having a first main surface and a second main surface, comprising at least a gallium nitride-based compound semiconductor on a first main surface. A laminated structure of an n-type layer, a light-emitting layer, and a p-type layer is provided, and an n-side electrode is provided in contact with the surface of the n-type layer exposed by removing a part of the laminated structure from the surface side. A gallium nitride-based compound semiconductor light-emitting device, wherein a p-side electrode is provided in contact with the surface of the p-type layer, and the second main surface of the substrate is a main light-emitting surface.