JP2005094043A - Gallium nitride compound semiconductor light emitting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new structure capable of improving light distribution property immediately above a light emitting device and maintaining high emission intensity using a substrate composed of a gallium nitride compound semiconductor in the light emitting device having this substrate side as a main light emitting surface side. <P>SOLUTION: In a semiconductor light emitting device, a laminate structure of an n-type cladding layer 2, an active layer 3, and a p-type cladding layer composed of a gallium nitride compound semiconductor is provided on a substrate 1 composed of an n-type gallium nitride compound semiconductor. The emitting device has an electrode connected to the substrate 1. An electrode arranged at a main light emitting surface side can be made unnecessary and light distribution immediately above the light emitting device can be made uniform by placing the electrode directly in contact with the front surface of the substrate 1 which is exposed by removing from the front surface side of the laminate structure a portion of the laminate structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  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 substrate made of a gallium nitride compound semiconductor.

  Gallium nitride compound semiconductors are 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 has an n-type cladding layer and an active layer made of InGaN serving as a light emitting layer through a buffer layer on a substrate made of sapphire or SiC. The mainstream is a laminate of a layer and a p-type cladding layer. In particular, in recent years, a double heterostructure grown using a sapphire substrate and a low temperature growth buffer layer made of GaN, AlN, or the like by metalorganic vapor phase epitaxy has high brightness and high reliability. It has been widely used for light-emitting diodes for outdoor panel displays.

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

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

FIG. 2 is a cross-sectional view showing the structure of a conventional gallium nitride compound semiconductor light emitting device disclosed in the above publication. On the substrate 11 made of n-type GaN, an n-type cladding 12 layer, an active layer 13 and a p-type cladding layer 14 are sequentially stacked. The n-side electrode 15 is provided in the part, and the p-side electrode 16 is provided over the entire surface of 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 the main light emitting surface side, and surface emission can be obtained. According to such a configuration, an inexpensive light-emitting element with improved current-light output characteristics can be provided.
Japanese Patent Laid-Open No. 7-94784 Japanese Patent Laid-Open No. 10-150220

  In the light emitting device having the structure shown in FIG. 2, since the substrate 11 made of GaN is transparent to light emitted from the active layer 13, the side of the n-side electrode 15 provided on the substrate 11 can be the main light emitting surface. . Since the n-side electrode 15 is normally used as a wire bonding pad, the n-side electrode 15 is formed of a thick film that is not permeable to light emission.

  Therefore, the light emitted from the active 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 falls in the upper part of the region where the n-side electrode 15 is formed. Such a distribution of light distribution characteristics has a problem that it is not desirable in applications that require uniform light distribution characteristics and high light emission intensity directly 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 wire bonding operation becomes difficult. It is not preferable to reduce the value. Therefore, there is a demand for a light-emitting element that can improve light-emitting characteristics even when workability of electrical connection such as bonding is ensured.

  The problem to be solved in the present invention is to improve the light distribution characteristics immediately above the light emitting element and to improve the light emission intensity in a light emitting element using a substrate made of a gallium nitride compound semiconductor and having the substrate side as the main light emitting surface side. It is to provide a novel structure that can maintain high.

  In the present invention, a laminated structure of an n-type cladding layer, an active layer, and a p-type cladding layer made of a gallium nitride compound semiconductor is provided on a substrate made of an n-type gallium nitride compound semiconductor, and is connected to the substrate. A semiconductor light emitting device having an electrode to be provided, wherein the electrode is provided in direct contact with the surface of the substrate exposed by removing a part thereof from the surface side of the laminated structure. .

In the present invention, the n-type cladding layer has an electron concentration of 1 × 10 ¹⁶ cm ⁻³ or more and less than 1 × 10 ¹⁷ cm ⁻³ .

  According to such a configuration, in the light-emitting element in which the substrate side is the main light-emitting surface side, it is possible to improve the light distribution characteristics directly above the light-emitting element and to keep the emission intensity high.

As described above, according to the present invention, in a light emitting device using a substrate made of a gallium nitride compound semiconductor and having the substrate side as a main light emitting surface side, the light distribution characteristics immediately above the light emitting device are improved and light emission is achieved. Since the strength can be kept high, it can be suitably used for applications such as surface-mounted light-emitting diodes that require a uniform light distribution directly above the light-emitting elements and line light sources in which a plurality of light-emitting elements are arranged on a substrate. it can.
Further, since the light emission intensity directly above the light emitting element can be maintained, it can be used for a conventional shell-shaped light emitting diode with a resin lens.
Furthermore, by specifying the conditions of the arrangement of the n-side electrode and the electron concentration of the n-type cladding layer, current spreading in the n-type substrate and the n-type cladding layer is ensured, so the size of the n-side electrode is reduced. Is possible. For this reason, since the electrical connection by Au bumps etc. can be used, the restrictions of workability, such as wire bonding by an electrode size, are eliminated, and the workability of electrical connection is ensured.

  In the first aspect of the present invention, a laminated structure of an n-type cladding layer, an active layer, and a p-type cladding layer made of a gallium nitride compound semiconductor is provided on a substrate made of an n-type gallium nitride compound semiconductor. A semiconductor light emitting device having an electrode connected to the substrate, wherein the electrode is provided in direct contact with the surface of the substrate exposed by removing a part thereof from the surface side of the stacked structure. When the substrate side is the main light emitting surface side, the light distribution characteristics directly above the light emitting element can be made substantially uniform.

The invention according to claim 2 is the invention according to claim 1, wherein the n-type cladding layer has an electron concentration of 1 × 10 ¹⁶ cm ⁻³ or more and less than 1 × 10 ¹⁷ cm ^−3. This is characterized by the fact that electrons injected from the n-side electrode into the substrate easily spread at the interface between the substrate and the n-type cladding layer.

  The invention according to claim 3 is the invention according to claim 2, wherein the n-type cladding layer is made of GaN, and the crystallinity of the n-type cladding layer is good. In addition, the electron concentration can be easily controlled within the above range.

  A specific example of the embodiment of the present invention will be described below with reference to FIG.

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

  In FIG. 1, an n-type cladding layer 2 made of GaN, an active layer 3 made of InGaN, a first p-type cladding layer 4 made of GaN, and a first layer made of AlGaN are formed on a substrate 1 made of n-type GaN. Two p-type cladding layers 5 and a p-type contact layer 6 made of InGaN are sequentially stacked. A p-side electrode 7 is formed on the surface of the p-type contact layer 6. From the surface side of the p-type contact layer 6, the p-type contact layer 6, the second p-type cladding layer 5, and the first p-type cladding layer are formed. 4, the active layer 3, the n-type cladding layer 2, and a part of the substrate 1 are removed by etching, and an n-side electrode 8 is formed on the surface of the substrate 1 exposed.

For the substrate 1, an n-type gallium nitride compound semiconductor can be used. Among them, it is preferable to use a material made of GaN that is relatively easy to manufacture and can be obtained with relatively good crystallinity. The substrate 1 is doped with an n-type impurity such as Si or Ge, and its electron concentration is controlled in the range of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . This is because when the electron concentration is lower than 1 × 10 ¹⁷ cm ⁻³ , the resistivity is increased and the electrons injected into the substrate 1 tend to be difficult to spread on the substrate 1, which is more than 1 × 10 ¹⁹ cm ^−3. This is because if it is high, the crystallinity of the substrate 1 tends to deteriorate due to the high concentration of n-type impurities.

For the n-type cladding layer 2, an n-type gallium nitride compound semiconductor having a band gap larger than that of the active layer 3 can be used, and its electron concentration is 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ¹⁷ cm ^−. Desirably less than ³ . By specifying the electron concentration within this range, the difference in electron concentration with respect to the substrate 1, that is, the difference in resistivity can be increased. Since it spreads sufficiently in the plane, and uniform injection of electrons into the active layer 3 can be realized, the emission distribution in the active layer 3 becomes uniform, and as a result, uniform surface emission on the main light emitting surface on the substrate 1 side. This is because

GaN, AlGaN, InGaN, or the like can be used for the n-type cladding layer 2, but when GaN is used for the substrate 1, it is desirable to use GaN doped with n-type impurities or undoped. This is because gallium nitride-based compound semiconductors exhibit n-type conductivity even in an undoped state, and among them, GaN can easily control the electron concentration by doping with n-type impurities. Moreover, if the electron concentration is within the above range,
Since it is possible to prevent the crystallinity of the n-type cladding layer 2 from being lowered by doping with an n-type impurity, the crystallinity of the active layer 3 grown thereon can be prevented from being lowered and the luminous efficiency can be kept high. Is also preferable.

  The layer thickness of the n-type cladding layer 2 is desirably in the range of 0.05 μm to 0.5 μm. This is because if the thickness is less than 0.05 μm, the effect of current spreading tends to be small, and if it is thicker than 0.5 μm, 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 n-type cladding layer 2, it is possible to reduce the series resistance while exhibiting the effect of current spreading. According to the knowledge of the present inventors, it is preferable to increase the thickness of the n-type cladding layer 2 and increase the electron concentration within the above range.

  As the active layer 3, a gallium nitride compound semiconductor containing In and having a band gap smaller than that of the n-type cladding layer 2 and the first and second p-type cladding layers 4 and 5 can be used. In particular, when InGaN containing no Al is used, the light emission intensity in the blue to green wavelength region can be increased. Furthermore, when the film thickness is made thinner than 100 nm to form a single quantum well structure, the crystallinity of the active layer 3 can be enhanced, and the light emission efficiency can be further enhanced.

  The active layer 3 is a multiple quantum well in which a quantum well layer made of InGaN having a thickness less than 100 nm and a barrier layer made of InGaN, GaN or the like having a larger band gap than the quantum well layer are alternately stacked. It can also be a structure.

  For the first p-type cladding layer 4, a gallium nitride compound semiconductor having a band gap larger than that of the active layer 3 can be used. In particular, the use of GaN is preferable because the crystallinity at the interface with the active layer 3 can be kept good.

  The first p-type cladding layer 4 is doped with a p-type impurity so that the conductivity type is p-type. This p-type impurity can be doped by flowing a p-type impurity source gas during crystal growth, but the second p-type cladding layer 5 grown on the first p-type cladding layer 4 is doped. When the doped p-type impurity is diffused and doped, the luminous efficiency can be increased.

  The layer thickness of the first p-type cladding layer 4 is preferably in the range of 30 nm to 60 nm.

  For the second p-type cladding layer 5, a gallium nitride compound semiconductor having a band gap larger than that of the active layer 3 can be used. In particular, it is preferable to use AlGaN having a band gap larger than that of the first p-type cladding layer 4 because electrons can be efficiently confined in the active layer 3 and luminous efficiency can be increased. Furthermore, the light emission efficiency can be increased by adopting a structure in which the composition is changed so that the Al composition converges from the side in contact with the first p-type cladding layer 4 to the side in contact with the p-type contact layer 6. At the same time, the operating voltage can be reduced, which is preferable.

  The layer thickness of the second p-type cladding layer 5 is preferably in the range of 0.03 μm to 0.3 μm.

  GaN, InGaN, or AlGaN can be used for the p-type contact layer 6, but GaN or InGaN that can reduce the contact resistance with the p-side electrode 7 is preferably used. In particular, when the second p-type cladding layer 5 made of AlGaN having a composition gradient and the p-type contact layer 6 made of InGaN are used in combination, the luminous efficiency can be improved and the operating voltage can be reduced simultaneously. .

  The layer thickness of the p-type contact layer 6 is preferably in the range of 0.02 μm to 0.2 μm.

  Mg, Zn, Cd, C, or the like can be used as the p-type impurity doped in the first p-type cladding layer 4, the second p-type cladding layer 5, and the p-type contact layer 6, but relatively easily. It is preferable to use Mg that can be made p-type.

  For the p-side electrode 7, a single metal such as Au, Ni, Pt, Pd, or Mg, or an alloy or a laminated structure thereof can be used. In particular, when a metal such as Pt or Mg having a high reflectance with respect to the emission wavelength is used, the light traveling from the active layer 3 toward the p-side electrode 7 can be reflected and extracted from the substrate 1 side. It is preferable in terms of improvement.

The n-side electrode 8 has a laminated structure comprising an n-type cladding layer 2, an active layer 3, a first p-type cladding layer 4, a second p-type cladding layer 5 and a p-type contact layer 6 formed on the substrate 1. It is formed in direct contact with the surface of the substrate 1 exposed by removing some of these from the surface side. By adopting a configuration in which the n-side electrode 8 is arranged in this manner, the surface side of the substrate 1 on which the laminated structure is not formed can be a main light emitting surface, and the above-described n-type cladding layer 2, substrate 1, Due to the current spreading effect at the interface, uniform surface emission can be obtained on this main light emitting surface.

  For the n-side electrode 8, 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 can be used.

  Hereinafter, specific examples of the method for producing 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 growth method of a gallium nitride-based compound semiconductor using a metal organic vapor phase growth method, but the growth method is not limited to this, and a molecular beam epitaxy method or an organic metal It is also possible to use a molecular beam epitaxy method or the like.

  Example In this example, the gallium nitride compound semiconductor light emitting device shown in FIG. 1 was fabricated.

  First, a substrate 1 made of GaN having a mirror-finished surface is placed on a substrate holder in a reaction tube, and then the substrate 1 is heated while flowing hydrogen gas while keeping the surface temperature of the substrate 1 at 1100 ° C. for 10 minutes. Thus, cleaning for removing dirt such as organic substances and moisture adhering to the surface of the substrate 1 was performed.

  Subsequently, the surface temperature of the substrate 1 is maintained at 1100 ° C. for 5 minutes, and the crystallinity of the surface of the substrate 1 is improved while flowing hydrogen gas, nitrogen gas, and ammonia.

Next, after the surface temperature of the substrate 1 is lowered to 1050 ° C., a carrier gas for TMG containing trimethylgallium (TMG) and SiH, which is a Si source, are supplied while flowing nitrogen gas and hydrogen gas as main carrier gases. _The n-type cladding layer 2 made of GaN doped with Si was grown to a thickness of 0.2 μm. The n-type cladding layer 2 had an electron concentration of 3 × 10 ¹⁶ cm ⁻³ .

After the n-type cladding layer 2 is grown, the TMG carrier gas and the SiH ₄ gas are stopped, the substrate temperature is lowered to 750 ° C., and nitrogen gas is flowed as the main carrier gas at 750 ° C. An active layer 3 having a single quantum well structure made of undoped In _0.2 Ga _0.8 N was grown to a thickness of 3 nm while flowing a carrier gas and a carrier gas for TMI.

After the active layer 3 is grown, the TMI carrier gas is stopped, and the substrate temperature is raised toward 1050 ° C. while flowing the TMG carrier gas, and then undoped GaN is grown to a thickness of 4 nm to obtain the substrate. When the temperature reaches 1050 ° C., it is newly grown while flowing a nitrogen gas and a hydrogen gas as main carrier gases, a carrier gas for TMA, and a carrier gas for Cp ₂ Mg as an Mg source. A second p-type cladding layer 5 made of AlGaN doped with is grown to a thickness of 0.1 μm. During the growth of AlGaN, the carrier gas for TMA was decreased linearly with time, while the carrier gas for TMG was increased linearly with time to change the composition from Al _0.15 Ga _0.85 N to Al _0.01 Ga _0.99 N. A second p-type cladding layer 5 was grown as a gradient composition AlGaN.

  Thereafter, the carrier gas for TMG and the carrier gas for TMA are stopped, the substrate temperature is kept at 1050 ° C., Mg is diffused from undoped AlGaN to Mg, and the first p-type cladding Layer 4 was formed.

After forming the first p-type cladding layer 4 and the second p-type cladding layer 5, the substrate temperature is lowered to 800 ° C., and at 800 ° C., a new carrier gas for TMG, a carrier gas for TMI, and Cp _{2 The} p-type contact layer 6 made of In _0.05 Ga _0.95 N doped with Mg was grown to a thickness of 0.1 μm while flowing with a carrier gas for ₂ Mg.

After the growth of the p-type contact layer 6, the TMG carrier gas, the TMI carrier gas, and the Cp ₂ Mg carrier gas are stopped, and the wafer is cooled to about room temperature while flowing the main carrier gas and ammonia as they are. Was removed from the reaction tube.

Next, an SiO ₂ film was deposited on the surface of the p-type contact layer 6 by the CVD method, and then patterned into a predetermined shape by photolithography to form an etching mask. The p-type contact layer 6, the second p-type cladding layer 5, the first p-type cladding layer 4, the active layer 3, the n-type cladding layer 2, and a part of the substrate 1 are about 0. The surface of the substrate 1 was exposed by removing in a direction opposite to the stacking direction at a depth of 5 μm. Then, an n-side electrode 8 made of Al was vapor-deposited on the surface of the substrate 1 exposed by photolithography and vapor deposition. Further, a p-side electrode 7 made of Pt and Au was deposited on the surface of the p-type contact layer 6 in the same manner.

  Thereafter, the back surface of the substrate 1 was polished and adjusted to a thickness of about 100 μm, and separated into chips by scribing. In this manner, the gallium nitride compound semiconductor light emitting device shown in FIG. 1 was obtained.

  This light emitting element was bonded by Au bumps on a Si diode having a pair of positive and negative electrodes with the electrode formation surface side facing down. At this time, the light-emitting element is mounted so 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 placed on the stem with 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, light was emitted in blue with a peak emission wavelength of 470 nm, and uniform surface light emission was obtained from the substrate 1 side. The light emission output at this time was 1.1 mW, and the forward operation voltage was 3.4V.

Sectional drawing which shows the structure of the gallium nitride compound semiconductor light-emitting device based on one embodiment of this invention Sectional drawing which shows the structure of the conventional gallium nitride compound semiconductor light emitting element

Explanation of symbols

1 substrate 2 n-type cladding layer 3 active layer 4 first p-type cladding layer 5 second p-type cladding layer 6 p-type contact layer 7 p-side electrode 8 n-side electrode

Claims (3)

A stacked structure of an n-type cladding layer, an active layer, and a p-type cladding layer made of a gallium nitride compound semiconductor is provided on a substrate made of an n-type gallium nitride compound semiconductor, and an electrode connected to the substrate is provided. A gallium nitride-based compound, characterized in that the electrode is provided in direct contact with the surface of the substrate exposed by removing a part of the electrode from the surface side of the laminated structure. Semiconductor light emitting device. 2. The gallium nitride compound semiconductor light-emitting element according to claim 1, wherein the n-type cladding layer has an electron concentration of 1 × 10 ¹⁶ cm ⁻³ or more and less than 1 × 10 ¹⁷ cm ⁻³ . 3. The gallium nitride compound semiconductor light emitting device according to claim 2, wherein the n-type cladding layer is made of GaN.

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