JP2010192923A - Light emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new structure of a light emitting element, which improves light distribution characteristic directly above the light emitting element and maintains high light emitting intensity, in the light emitting element which uses a substrate made of a gallium nitride compound semiconductor and uses the substrate back side on which a laminate structure including a light emitting layer is not formed, as a main light-emitting surface side. <P>SOLUTION: A laminate structure composed of an n-type layer 2, a light emitting layer 4, and a p-type layer 6 made of the gallium nitride compound semiconductor are formed on a substrate 1 made of an n-type gallium nitride based compound semiconductor, and an n-type electrode 8 is formed in contact with the surface of the n-type layer 2, which is exposed in one part from the surface of the laminate structure by removing a part thereof. This does not need an electrode arranged on the main light-emitting surface side and makes light distribution directly above the light emitting element uniform. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 light with visible light is basically a light emission composed of an n-type cladding layer and an InGaN layer serving as a light-emitting layer via a buffer layer on a substrate composed 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, Patent Document 1 discloses a blue light-emitting element 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.

  Further, Patent Document 2 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. 3 is a cross-sectional view showing the structure of the 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 layer 12, a light emitting 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.

JP-A-7-94784 JP-A-10-150220

  However, in the gallium nitride compound semiconductor light emitting device having the conventional structure shown in FIG. 3, the substrate 11 made of GaN is transparent to light emitted from the light emitting layer 13, so 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 light emitting layer 13 below this 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 at the top 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 present invention solves the above-mentioned conventional problems. In a light-emitting element 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 characteristic immediately above the light-emitting element is obtained. An object of the present invention is to provide a gallium nitride-based compound semiconductor light-emitting element having a novel structure capable of improving and maintaining high emission intensity.

  In order to solve the above problems, a light emitting diode of the present invention is provided on a first main surface of a substrate made of a light-transmitting n-type gallium nitride compound semiconductor having a first main surface and a second main surface. A stacked structure of at least an n-type layer, a light emitting layer, and a p-type layer made of a gallium nitride compound semiconductor, and the n-side electrode is exposed by removing a part thereof from the surface side of the stacked structure. A gallium nitride-based compound semiconductor light-emitting element provided in contact with the surface of an n-type layer, a p-side electrode provided in contact with the surface of the p-type layer, and the second main surface of the substrate being a main light-emitting surface. It is characterized by being bonded by Au bumps.

  According to such a configuration, it is possible to improve the light distribution characteristic immediately above the light emitting element and to keep the light emission intensity high.

  As described above, according to the present invention, a light-emitting element using a substrate made of a gallium nitride-based compound semiconductor and having a back surface side on which a laminated structure including a light-emitting layer of the substrate is not formed as a main light-emitting surface side Along with improving the light distribution characteristics directly above and maintaining a high emission intensity, a plurality of surface-mounted light-emitting diodes and light-emitting elements that require a uniform light distribution directly above the light-emitting elements are arranged on the substrate. It can be suitably used for applications such as a line light source.

  In addition, since the light emission intensity directly above the light emitting element can be kept high, it can be used for a conventional shell-shaped light emitting diode with a resin lens.

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

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

(Embodiment 1)
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 layer 2 made of GaN, a light emitting layer 4 made of InGaN, and a p-type layer 6 made of AlGaN are sequentially stacked 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 a part of the p-type layer 6, the light emitting layer 4, and the n-type layer 2 is 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 the n-type layer 2.

For the substrate 1, an n-type gallium nitride compound semiconductor (In _a Al _b Ga _1-ab N (where 0 ≦ a ≦ 1, 0 ≦ b ≦ 1, 0 ≦ a + b ≦ 1)) is used. Although it is possible, Al _c Ga _1-c N (where 0 ≦ c ≦ 1) is desirable because good crystallinity is easily obtained. Among these, it is most preferable to use GaN made of GaN that is relatively easy to manufacture and that provides the best 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 approximately 1 × 10 ¹⁶ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ . This is because, when the electron concentration is lower than 1 × 10 ¹⁶ cm ⁻³ , the resistivity is increased, and electrons injected into the substrate 1 tend to hardly spread on the substrate 1, and from 1 × 10 ¹⁹ cm ⁻³ . This is because the crystallinity of the substrate 1 tends to deteriorate due to the high concentration of n-type impurities.

  For the n-type layer 2, an n-type gallium nitride compound semiconductor having a band gap larger than that of the light emitting layer 4 can be used. Thereby, the function as an n-type cladding layer can be imparted 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 laminate of these layers 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 the layer where the n-side electrode 8 is formed, and its electron concentration is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ¹⁹ cm ^−. Desirably less than ³ . This is because, when the electron concentration is lower than 1 × 10 ¹⁷ cm ⁻³ , the ohmic contact resistance with the n-side electrode 8 is increased, and the operating voltage of the light emitting element is increased. This is higher than 1 × 10 ¹⁹ cm ^−3. This is because the crystallinity of the n-type layer 2 tends to deteriorate due to the high concentration of n-type impurities.

  The layer thickness of the n-type layer 2 is preferably 0.1 μm or more. This is because 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 very strict. The upper limit of the thickness of the n-type layer 2 is not particularly limited, but the etching accuracy when forming the exposed surface is eased and the formation time of the n-type layer 2 is not unnecessarily increased to about 5 μm or less. Is desirable.

In order to promote the spread of current (electrons) in the n-type layer 2, the n-type layer 2 is relatively positioned as a current diffusion layer on the light emitting layer 4 side than the layer on which the n-side electrode 8 is formed. It is desirable to provide a layer having a low electron concentration (a layer having a high resistivity) or a layer having a relatively large band gap. By providing these current diffusion layers, electrons temporarily do not easily flow to the light emitting layer 4 side in the n-type layer 2, and the electrons spread uniformly in the surface of the n-type layer 2, and thereby the light-emitting layer 4. This is because the uniform light emission distribution in the light emitting layer 4 becomes uniform, and as a result, uniform surface light emission is obtained on the main light emitting surface on the back surface side of the substrate 1. As a specific configuration, when GaN is used for the substrate 1, GaN is used as the first n-type layer and Al _x Ga _1-x N (provided that 0 is used as the second n-type layer) from the substrate 1 side. ≦ x ≦ 0.2) is desirable. Furthermore, GaN can be provided on the second n-type layer as a third 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 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 to 0.2 μm. This is because if the thickness is less than 0.002 μm, the current spreading effect tends to be small, and if the thickness is more than 0.2 μm, the series resistance of the light emitting element increases and the operating voltage increases. Then, by adjusting the electron concentration according to the thickness of the second n-type layer or the total thickness of the second n-type layer and the third n-type layer, the current spreading effect is achieved in series. The resistance can be reduced. According to the knowledge of the present inventors, it is preferable to increase the electron concentration while increasing the layer thickness.

  For the light emitting layer 4, a gallium nitride 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 not containing Al is used, the emission intensity in the ultraviolet to green wavelength region can be increased. When the light emitting layer 4 contains In, the crystallinity of the light emitting layer 4 can be improved and the light emission efficiency can be further improved by making the film thickness thinner than 0.01 μm to form a single quantum well layer. .

  The light emitting layer 4 has a multiple quantum well structure 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. You can also.

  A p-type gallium nitride compound semiconductor having a band gap larger than that of the light emitting layer 4 can be used for the p-type layer 6. Thereby, the p-type layer 6 can be provided with a function as a p-type cladding layer. As the p-type layer 6, a single layer of GaN, AlGaN, InGaN, InAlGaN or the like, or a laminate of these layers can be used. In particular, it is preferable to use AlGaN as the p-type layer on the side in contact with the light emitting layer 4 because electrons can be efficiently confined in the light emitting layer 4 and the light emission efficiency can be increased.

The p-type layer 6 is doped with a p-type impurity to have p-type conduction. Mg, Zn, Cd, C, or the like can be used as the p-type impurity, but it is preferable to use Mg that can be made p-type relatively easily. The p-type impurity concentration is desirably 1 × 10 ¹⁹ cm ⁻³ or more and less than 5 × 10 ²⁰ cm ⁻³ . When p-type impurity concentration is lower than 1 × 10 ¹⁹ cm ^-3, the ohmic contact resistance between the p-side electrode 7 increases, is because the operating voltage of the light-emitting element is higher than 5 × 10 ²⁰ cm ^-3 Higher, the crystallinity of the p-type layer 6 tends to be deteriorated due to the high concentration of the p-type impurity, and the diffusion of the p-type impurity into the light emitting layer 4 becomes remarkable. This is because of a decrease.

  When the p-type layer 6 is doped with a relatively high concentration of p-type impurity, an intermediate between the light-emitting layer 4 and the p-type layer 6 is used to suppress excessive diffusion of the p-type impurity into the light-emitting layer 4. Layers can also be introduced. For this intermediate layer, InAlGaN can be used. In particular, GaN is preferable because the 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 that diffuse in the direction of the light emitting layer 4. The thickness of the intermediate layer is desirably in the range of 0.001 μm to 0.05 μm. If the thickness is less than 0.001 μm, the effect of suppressing the diffusion of p-type impurities into the light-emitting layer 4 is reduced. If the thickness is more than 0.05 μm, the efficiency of hole injection into the light-emitting layer 4 is lowered, and the light emission efficiency is lowered Because it comes to do.

  The layer thickness of the p-type layer 6 is preferably in the range of 0.05 μm to 0.5 μm. When the thickness is less than 0.05 μm, the constituent metal of the p-side electrode 7 easily enters the light-emitting layer 4 due to electromigration or the like, so that the lifetime of the light-emitting element is likely to be shortened. This is because the voltage drop when passing through the p-type 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.

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

  The n-side electrode 8 is formed on the surface of the n-type layer 2 exposed by removing a part of these from the surface side of the laminated structure formed of the light-emitting layer 4 and the p-type layer 6 formed on the n-type layer 2. Formed in contact. By adopting a configuration in which the n-side electrode 8 is arranged in this way, 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. .

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.
(Embodiment 2)

  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 embodiment mainly shows a growth method of a gallium nitride-based compound semiconductor using a metal organic chemical vapor deposition method, but the growth method is not limited to this, and a molecular beam epitaxy method or an organic method is used. It is also possible to use a metal 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 the present embodiment, the gallium nitride compound semiconductor light emitting element shown in FIG. 2 was produced.

  First, a substrate 1 made of wafer-shaped GaN having a mirror-finished thickness of about 300 μm and a diameter of about 50 mm is placed on a substrate holder in a reaction tube, and then the temperature of the substrate 1 is kept at 1100 ° C. for 10 minutes. By heating the substrate 1 while flowing hydrogen gas at 4 liters / minute, nitrogen gas at 4 liters / minute, and ammonia at 2 liters / minute, dirt and moisture such as organic substances adhering to the surface of the substrate 1 are removed. For cleaning.

Next, while maintaining the temperature of the substrate 1 at 1100 ° C., while flowing nitrogen gas as a carrier gas at 15 liters / minute and hydrogen gas at 4 liters / minute, ammonia is supplied at 2 liters / minute, trimethylgallium (hereinafter, The abbreviated TMG) was supplied at 80 cc mol / min, 10 ppm diluted monosilane at 10 cc / min, and an n-type layer 2 made of Si-doped GaN was grown to a thickness of 2 μm. The n-type layer 2 had an electron concentration of 1 × 10 ¹⁸ cm ⁻³ .

After the n-type layer 2 is grown, the supply of monosilane is stopped while the temperature of the substrate 1 is maintained at 1100 ° C., and ammonia gas is supplied as a carrier gas at a flow rate of 15 liter / minute of nitrogen gas and 4 liter / minute of hydrogen gas. Is supplied at a rate of 2 liter / min, TMG at 40 μmol / min, and trimethylaluminum (hereinafter abbreviated as TMA) at 3 μmol / min to form an n-type layer 3 made of undoped Al _0.05 Ga _0.95 N at 0.05 μm. Grown in thickness. The n-type layer 3 had an electron concentration of 5 × 10 ¹⁶ cm ⁻³ .

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

  After the light emitting layer 4 is grown, the supply of TMI is stopped, the nitrogen gas is supplied as a carrier gas at 15 liters / minute, ammonia is supplied at 6 liters / minute, TMG is supplied at 2 μmol / minute, and the temperature of the substrate 1 is increased to 1050. The intermediate layer 5 made of undoped GaN was grown to a thickness of 0.004 μm while raising the temperature to 0 ° C.

When the substrate temperature reaches 1050 ° C., nitrogen is flown at 15 liters / minute and hydrogen gas is flowed at 4 liters / minute as carrier gas, ammonia is 2 liters / minute, TMG is 40 μmol / minute, TMA is 3 μmol / minute, Biscyclopentadienylmagnesium (hereinafter abbreviated as Cp ₂ Mg) is supplied at a rate of 0.1 μmol / min, and a p-type layer 6 made of Al _0.05 Ga _0.95 N doped with Mg is formed to a thickness of 0.2 μm. I grew up. The Mg concentration of the p-type layer 6 was 1 × 10 ²⁰ cm ⁻³ .

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

After the SiO ₂ film is deposited on the surface of the laminated structure made of the gallium nitride compound semiconductor formed in this way by the CVD method without performing any additional annealing, it is roughly processed by photolithography and wet etching. An SiO ₂ mask for etching was formed by patterning into a shape. Then, a part of the p-type layer 6, the intermediate layer 5, the light emitting layer 4, the n-type layer 3 and the n-type layer 2 is formed at a depth of about 0.5 μm in the direction opposite to the stacking direction by reactive ion etching. Then, the surface of the n-type layer 2 was exposed. Then, an n-side electrode 8 in which 0.1 μm-thick Ti and 0.5 μm-thick Au were laminated was formed on a part of the exposed surface of the n-type layer 2 by photolithography and vapor deposition. Further, after the etching SiO ₂ mask is removed by wet etching, 0.3 μm thick Pt and 0.5 μm thick Au are formed on almost the entire surface of the p-type layer 6 by photolithography and vapor deposition. A p-side electrode 7 made of was formed by vapor deposition.

  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. 2 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 back side of the substrate 1. The light emission output at this time was 3 mW, and the forward operation voltage was 3.4V.

  The gallium nitride-based compound semiconductor light-emitting device of the present invention improves the light distribution characteristics immediately above the light-emitting device and can maintain a high light emission intensity, so that a light-emitting diode that is desired to have a uniform light distribution just above the light-emitting device It is suitable for such as.

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

Claims (1)

On the first main surface of a substrate made of a light-transmitting n-type gallium nitride compound semiconductor having a first main surface and a second main surface, at least an n-type layer made of a gallium nitride compound semiconductor and light emission A stacked structure of a 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 thereof from the surface side of the stacked structure; A light-emitting diode comprising a gallium nitride-based compound semiconductor light-emitting element provided in contact with the surface of the p-type layer and having the second main surface of the substrate as a main light-emitting surface bonded by an Au bump.