JP3975388B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device having a semiconductor region of a gallium nitride compound and having a high external quantum efficiency.
[0002]
[Prior art]
A blue light-emitting element including a light-emitting layer made of a gallium nitride-based compound semiconductor such as GaN, GaAlN, InGaN, or InGaAlN is known as a blue light-emitting diode. In this light-emitting element, a gallium nitride compound semiconductor layer is formed on a low-resistance substrate made of silicon, GaAs, GaP, SiC, or the like, and a pair of electrodes is provided on the upper and lower surfaces of the light-emitting element. In this light emitting device, since the current can flow in the thickness direction of the light emitting device, the resistance value of the current path is lowered as compared with the structure in which the gallium nitride compound semiconductor layer is formed on the insulating substrate made of sapphire or the like. Power consumption and operating voltage can be reduced.
[0003]
[Problems to be solved by the invention]
However, in a blue light emitting device using a low-resistance substrate, light is emitted directly below the bonding electrode disposed on the upper surface of the light-emitting device, and light directed toward the lower surface of the light-emitting device is absorbed by the low-resistance substrate. In this way, the light directed toward the upper surface is absorbed by the electrode, and thus the low-resistance substrate becomes a light absorption layer, so that the external quantum efficiency, which is the ratio between the number of absorbed photons and the number of emitted photons, cannot be increased. there were. In addition, the current that flows directly under the bonding electrode is substantially a reactive current, and the external quantum efficiency cannot be increased.
[0004]
In order to solve this problem, for example, Japanese Patent Laid-Open No. 8-250768 discloses a high resistivity high resistance composed of a silicon oxide film under a light extraction side or light detection side electrode pad of a light emitting element. A semiconductor element in which a region is formed is disclosed. In a light-emitting element in which a gallium nitride-based compound semiconductor region is formed on a light-transmitting sapphire insulating substrate, light passes through the insulating substrate, so that external quantum efficiency can be increased. However, in a light emitting device structure including a light-absorbing low-resistance substrate, when a high-resistance region is formed by a silicon oxide film having a relatively low dielectric breakdown film, dielectric breakdown may occur if the silicon oxide film is formed thin. The effect of blocking the current cannot be obtained, and sufficient improvement cannot be achieved. Therefore, in order to increase the external quantum efficiency, the high resistance region must be formed thick, but when the high resistance region is formed thick and the current is spread around the high resistance region by the transparent electrode, A large level difference occurs in the transparent electrode, resulting in poor coverage. If the transparent electrode is cracked, the current cannot be spread well around the light emitting element, and the external quantum efficiency is lowered.
[0005]
Accordingly, an object of the present invention is to provide a semiconductor light emitting device having a high level of external quantum efficiency.
[0006]
[Means for Solving the Problems]
A semiconductor light-emitting device according to the present invention includes a low-resistance substrate (2) and a first semiconductor of the first conductivity type comprising a gallium nitride-based compound semiconductor formed on one main surface of the low-resistance substrate (2). A semiconductor substrate formed by laminating a region (3), an active layer (4), and a second semiconductor region (5) of the second conductivity type opposite to the first conductivity type made of a gallium nitride compound semiconductor (1) A Schottky barrier electrode layer (6) for forming a Schottky barrier at the interface with the second semiconductor region is formed on a part of one main surface of the semiconductor substrate (1), and the Schottky barrier electrode layer (6) and the semiconductor substrate ( One main surface of 1) is covered with an electrode (7) having optical transparency and conductivity. The Schottky barrier electrode layer (6) is formed in a truncated cone shape having an inclined surface.
[0007]
When a voltage is applied to bias the semiconductor light emitting element in the forward direction, a current flows through the interface between the transparent electrode (7) and the second semiconductor region (5), but the Schottky barrier electrode layer (6) and the second No current substantially flows at the interface with the semiconductor region (5). For this reason, a current flows to the device peripheral side outside the Schottky barrier electrode layer (6) in plan view, and light emission occurs due to carrier recombination at that portion, so the reactive current flowing directly under the bonding electrode is reduced. Thus, it is possible to improve the external quantum efficiency by favorably diffusing current to the peripheral side of the Schottky barrier electrode layer (6) through the transparent electrode (7). In addition, the Schottky barrier electrode layer (6) can alleviate current concentration and prevent electrical degradation of the semiconductor substrate (1).
[0008]
In the embodiment of the present invention, the Schottky barrier electrode layer (6) is one or two selected from Ti, Al, Cr, Ta, and Cu when the second semiconductor region is a p-type semiconductor region. When the second semiconductor region is an n-type semiconductor region, it is formed of one or more metals selected from Pt, Pd, and Au. The light-transmitting electrode (7) is formed of one or more materials selected from Ni, Au, and ITO (indium tin oxide).
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Next, an embodiment of a semiconductor light emitting device according to the present invention applied to a blue light emitting diode device will be described with reference to FIG.
[0010]
As shown in FIG. 1, a blue light emitting diode device according to the present invention includes a low-resistance substrate (2) made of a silicon substrate, an n-type semiconductor region (3) as a first semiconductor region made of GaN (gallium nitride), a semiconductor substrate (1) formed by sequentially stacking an active layer (4) made of p-type InGaN (gallium indium nitride) and a p-type semiconductor region (5) made of GaN as a second semiconductor region; and a semiconductor A Schottky barrier electrode layer (6) formed on the p-type semiconductor region (5) constituting one main surface of the base (1), and on the Schottky barrier electrode (6) and the p-type semiconductor region (5) A transparent electrode (7) formed and a connection electrode (8) formed on the lower surface of the semiconductor substrate (1) are provided. The transparent electrode (7) functions as an anode electrode, and the connection electrode (8) functions as a cathode electrode. The blue light emitting diode element according to the present embodiment is different from the conventional light emitting diode element in that the Schottky barrier electrode layer (6) is provided between the p-type semiconductor region (5) and the transparent electrode (7) in the present embodiment. The point is to form.
[0011]
The low-resistance substrate (2) is composed of a (111) plane n + type silicon single crystal substrate into which, for example, arsenic (As) is introduced as a n-type impurity at a relatively high concentration. The low resistance substrate (2) is a substantial conductor having a resistivity of about 0.0001 to 0.01 Ωcm. In the present embodiment, the low resistance substrate (2) is formed with a thickness of about 350 μm, and the semiconductor region (3-5) formed on the upper surface of the low resistance substrate (2) having sufficient mechanical strength is formed. Good support. The n-type semiconductor region (3), the active layer (4), and the p-type semiconductor region (5) are successively formed on the upper surface of the low-resistance substrate (2) by a known MOCVD method.
[0012]
When manufacturing the semiconductor substrate (1), a buffer layer is formed in advance on the surface of the low-resistance substrate (2), and then the low-resistance substrate (2) is placed in the reaction chamber of the MOCVD (metal organic chemical vapor deposition) apparatus. The low resistance substrate (2) on which the buffer layer (2a) is formed is heated to a temperature of 1040 ° C., and then TMG gas (trimethylgallium gas), NH ₃ (ammonia) gas, SiH is placed in the reaction chamber. ₄ Supply the (silane) gas. For example, the flow rate of the TMG gas supplying Ga about 4.3Myumol / min, the flow rate of NH ₃ gas supplying NH ₃ is about 53.6 mmol / min, the flow rate of the silane gas supplying Si is about 1.5 nmol / min It is. Since silane gas is supplied to the reaction chamber, Si is introduced as an n-type impurity into the formed film, and the upper surface of the buffer layer of the low-resistance substrate (2) has a thickness of about 2.0 to 5.0 μm. An n-type semiconductor region (3) is formed.
[0013]
Further, the impurity concentration of the n-type semiconductor region (3) is about 3 × 10 ¹⁸ cm ^−3, which is considerably lower than the impurity concentration of the low resistance substrate (2). In the present embodiment, the n-type semiconductor region (3) is formed directly on one main surface of the low-resistance substrate (2). In practice, however, the low-resistance substrate (2) and the n-type semiconductor region (3) are formed. A buffer layer (impact mitigation layer) is interposed between the two and the crystal orientation of the low-resistance substrate (2) made of a silicon semiconductor is successfully taken over to form a GaN-based compound semiconductor region on the upper surface. desirable.
[0014]
Subsequently, the low-resistance substrate (2) is heated to a temperature of 800 ° C., the supply of SiH ₄ gas is stopped, and TMI gas (trimethylindium gas) and Cp ₂ are added to the reaction chamber in addition to TMG gas and NH ₃ gas. An active layer (4) having a thickness of about 20 mm made of p-type InGaN is formed on the upper surface of the n-type semiconductor region (3) by supplying Mg gas (bicyclopentaenyl magnesium gas). Since Cp ₂ Mg gas is supplied to the reaction chamber, Mg is introduced as a p-type conductivity impurity into the formed film. For example, the flow rate of TMG gas is 1.1 μmol / min, the flow rate of NH ₃ gas is 67 mmol / min, the flow rate of TMI gas supplying In is about 4.5 μmol / min, and the flow rate of Gp ₂ Mg gas supplying Mg is About 12 nmol / min. The impurity concentration of the active layer (4) is about 3 × 10 ¹⁷ cm ⁻³ .
[0015]
Subsequently, the low-resistance substrate (2) is heated to a temperature of 1040 ° C., TMG gas, NH ₃ gas and Cp ₂ Mg gas are supplied into the reaction chamber, and the upper surface of the active layer (4) is made of p-type GaN. A semiconductor substrate (1) is manufactured by forming a p-type semiconductor region (5) having a thickness of about 0.5 μm. For example, the flow rate of TMG gas is about 4.3 μmol / min, the flow rate of ammonia gas is about 53.6 μmol / min, and the flow rate of Cp ₂ Mg gas is about 0.12 μmol / min. The impurity concentration of the p-type semiconductor region (5) is about 3 × 10 ¹⁸ cm ⁻³ . The n-type semiconductor region (3), the active layer (4) and the p-type semiconductor region (5) formed as described above can be formed on the upper surface of the low-resistance substrate (2) with the crystal orientation aligned. it can.
[0016]
The Schottky barrier electrode layer (6) formed on one main surface of the semiconductor substrate (1) is in contact with the p-type semiconductor region (5) and forms a Schottky barrier (Schottky barrier) at the interface. In the present embodiment, the Schottky barrier electrode layer (6) is configured as a laminated electrode formed by laminating a Ti film (6a) and an Al film (6b), and a side surface of the semiconductor substrate (1 An inclined surface (6c) is formed which extends from the side away from the semiconductor substrate (1) toward one main surface of the semiconductor substrate (1). That is, the Schottky barrier electrode layer (6) is formed in a truncated cone shape at substantially the center on one main surface of the semiconductor substrate (1). When forming the frustoconical Schottky barrier electrode layer (6), a shadow mask having a shape complementary to the frustoconical shape and having an opening inclined at the periphery is disposed on one main surface of the semiconductor substrate, If Ti and Al are sequentially vacuum-deposited through, a Schottky barrier electrode layer (6) having an inclined surface spreading toward the end can be formed. Each of the Ti film and the Al film is a metal film that can form a Schottky barrier at the interface with the p-type semiconductor region (5) made of a GaN semiconductor alone. In this embodiment, the thickness of the Ti film (6a) is about 200 mm, and the thickness of the Al film (6b) is about 5000 mm. The diameter of the Schottky barrier electrode layer (6) is about 120 μm on the upper surface and about 140 μm on the lower surface.
[0017]
The transparent electrode (7) is formed on the upper surface of the p-type semiconductor region (5) constituting the upper surface of the semiconductor substrate (1) and the upper surface of the Schottky barrier electrode layer (6), and makes low resistance contact with both. In the present embodiment, the transparent electrode (7) is configured as a laminated electrode formed by laminating a Ni film (7a) and an Au film (7b). That is, the Ni film (7a) has good low-resistance contact with the gallium nitride compound semiconductor region, and the Au film (7b) has a gallium nitride compound semiconductor region (3-5) compared to the Ni layer (7a). The low resistance contact with respect to is not obtained well, but the conductivity is excellent. For this reason, the transparent electrode (7) can obtain good low-resistance contact with the gallium nitride-based compound semiconductor region (3-5), and can spread the current well around the semiconductor light emitting device. The transparent electrode (7) is formed by, for example, continuously depositing Ni and Au on the entire upper surface of the semiconductor substrate (1) and the upper surface of the Schottky barrier electrode layer (6) by a known vacuum deposition method, and then the semiconductor substrate (1). The Ni film (7a) and the Au film (7b) deposited on the outer edge side of the upper surface can be selectively removed by etching, but the transparent electrode (7) can also be formed by sputtering or the like. . In the present embodiment, since the inclined surface (6c) is formed on the side surface of the Schottky barrier electrode layer (6), the transparent electrode (7) is covered with good coverage on the side surface of the Schottky barrier electrode layer (6). Can do. Therefore, in the vicinity of the rising portion of the Schottky barrier electrode layer (6), it is possible to suppress the generation of cracks and cracks in the transparent electrode (7), and to produce a light emitting element with high reliability and high light emission efficiency with a high yield. . Further, in order to obtain a low resistance contact of the Schottky barrier electrode layer (6) to the p-type semiconductor region (5) and the Schottky barrier electrode layer (6) in a nitrogen atmosphere after vacuum deposition, Heat treatment for about 10 minutes is good. The transparent electrode (7) is a conductive film having a sufficiently low sheet resistance so that a current can be satisfactorily passed also to the outer edge side of the semiconductor substrate (7). In the present embodiment, the Schottky barrier electrode layer (6) and the transparent electrode (7) constitute a bonding electrode. The transparent electrode (7) is transparent to visible light, but is formed of a conductive material.
[0018]
The connection electrode (8) is formed by sequentially vacuum-depositing titanium and nickel on the lower surface of the semiconductor substrate (1), for example, and makes low resistance contact with the low resistance substrate (2). The connection electrode (8) of the blue light emitting diode shown in FIG. 1 is fixed to a support plate (not shown) via, for example, solder or conductive paste, and is composed of a Schottky barrier electrode layer (6) and a transparent electrode (7). One end of a wire (lead fine wire) is connected to the bonding electrode by a known wire bonding method, and the other end of the wire is electrically connected to an external electrode (not shown).
[0019]
In the blue light emitting diode of FIG. 1, a voltage for increasing the potential on the bonding electrode side is provided between the bonding electrode composed of the Schottky barrier electrode layer (6) and the transparent electrode (7) and the connection electrode (8). When applied, holes flow from the p-type semiconductor region (5) into the active layer (4), electrons are injected from the n-type semiconductor region (3) into the active layer (4), and recombination of carriers causes a wavelength around 440 nm. Light is emitted from the active layer (4). At this time, the Schottky barrier electrode layer (6) forms a Schottky barrier at the interface with the p-type semiconductor region (5), and the transparent electrode (7) makes a low-resistance contact with the interface with the p-type semiconductor region (5). . For this reason, when a voltage is applied to bias the semiconductor light emitting element in the forward direction, a current flows through the interface between the transparent electrode (7) and the p-type semiconductor region (5), but the Schottky barrier electrode layer (6) and p No current substantially flows at the interface with the semiconductor region (5). For this reason, a current flows to the device peripheral side outside the Schottky barrier electrode layer (6) in plan view, and light emission occurs due to carrier recombination at that portion, so the reactive current flowing directly under the bonding electrode is reduced. Thus, the current can be diffused favorably to the peripheral side of the Schottky barrier electrode layer (6) via the transparent electrode (7), and the external quantum efficiency can be increased. In addition, the Schottky barrier electrode layer (6) can alleviate current concentration and prevent electrical degradation of the semiconductor substrate (1). The external quantum efficiency of the conventional semiconductor light emitting device is 0.2 to 0.3%, whereas the semiconductor light emitting device according to the present invention has an excellent external quantum efficiency of 6%.
[0020]
The embodiment of the present invention can be modified. For example, the Schottky barrier electrode layer (6) can be formed of other metals such as Cr, Ta and Cu in addition to Ti and Al. The transparent electrode (7) can be formed of ITO (indium tin oxide) or Ni single film. It is not necessary to form the inclined surface (6c) on the side surface of the Schottky barrier electrode layer (6). A metal film for forming a bonding electrode may be further provided on the upper surface of the Schottky barrier electrode layer (6) via the transparent electrode (7). The inclined surface (6c) formed on the side surface of the Schottky barrier electrode layer (6) can be formed without using a shadow mask. For example, after the Schottky barrier electrode layer (6) is deposited on the entire surface of the p-type semiconductor region (5), the Schottky barrier electrode layer (6) may be formed in anticipation of side etching by photolithography and wet etching. The conductivity types of the n-type semiconductor region (3) and the p-type semiconductor region (5) may be reversed. In this case, the Schottky barrier electrode layer (6) can use, for example, Pt, Pd, or Au, and the transparent electrode (7) can be formed of, for example, ITO (indium tin oxide) or Ni. The low resistance substrate (2) may be formed of GaAs, GaP, silicon carbide or the like. The transparent electrode (7) may be formed at a thickness of 100 mm or less, preferably 80 mm or less so that the light transmittance of the transparent electrode (7) can be sufficiently obtained. The transparent electrode (7) may be formed by one layer of the Ni layer (7a) or the Au layer (7b), but the relative contact with the gallium nitride-based compound semiconductor region is good as in the embodiment. It is desirable that the film is composed of a thin first layer (for example, Ni) and a relatively thick second layer (for example, Au) having good conductivity. The thickness of the Schottky barrier electrode layer (6) is preferably 1000 mm or more, and preferably functions as a bonding electrode.
[0021]
【The invention's effect】
In the present invention, the external quantum efficiency of the semiconductor light emitting device can be improved and the reliability can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a semiconductor light emitting device according to the present invention applied to a blue light emitting diode device.
(1) ... Semiconductor substrate, (2) ... Low resistance substrate, (3) ... First semiconductor region (n-type semiconductor region), (4) ... Active layer, (5) ... Second (6) ·· Schottky barrier electrode layer, (6a) · · Ti layer, (6b) · · Al layer, (7) · · transparent electrode, (7a) · · Ni Layer, (7b) ... Au layer, (8) ... connecting electrode,

Claims (4)

A low-resistance substrate, a first semiconductor region of a first conductivity type formed of a gallium nitride-based compound semiconductor formed on one main surface of the low-resistance substrate, an active layer, and a gallium nitride-based compound semiconductor And a semiconductor substrate formed by laminating a second semiconductor region of the second conductivity type opposite to the first conductivity type,
A Schottky barrier electrode layer that forms a Schottky barrier at the interface with the second semiconductor region is formed on a part of one main surface of the semiconductor substrate,
One main surface of the Schottky barrier electrode layer and the semiconductor substrate is covered with an electrode having optical transparency and conductivity,
The semiconductor light emitting device, wherein the Schottky barrier electrode layer is formed in a truncated cone shape having an inclined surface.   2. The semiconductor light emitting element according to claim 1, wherein the Schottky barrier electrode layer is formed of one or more metals selected from Ti, Al, Cr, Ta, Cu, Pt, Pd, and Au.   3. The semiconductor light emitting element according to claim 1, wherein the electrode having optical transparency is formed of one or more substances selected from Ni, Au, and ITO (indium tin oxide).   When a voltage is applied to bias the semiconductor light emitting element in the forward direction, a current flows through the interface between the transparent electrode and the second semiconductor region, and the Schottky barrier electrode layer and the second semiconductor region The semiconductor light-emitting device according to claim 1, wherein substantially no current flows through the interface.

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