JPH0690021A - Pn-junction type light emitting diode using silicon carbide - Google Patents

Abstract

PURPOSE:To realize a brighter pn-junction type light emitting diode of silicon carbide by laminating multiple silicon carbide semiconductor layers on a silicon carbide substrate and then providing a part of its top surface with an annular ohmic electrode. CONSTITUTION:A pn-junction type light emitting diode includes an insulating film layer 15, and a silicon carbide top face layer 14 and an electrode 16 form an ohmic contact at the periphery of insulating film layer, not at the central part of silicon carbide top face layer. With the electrode 16 provided not at the central part of element but near the end face, the light emission from the light emitting area near the end face will not be obstructed by an upper electrode, and further, that from direct under the electrode can be, with an emission path shown with an arrow, effectively taken out from the surface and end face into the outside, for a high luminance of light emitting diode. As an insulating film layer material, silicon dioxide (SiO2) or silicon nitride (Si3N4) is used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a pn junction type light emitting diode using silicon carbide, and more particularly to an electrode structure of a high brightness blue light emitting diode.

[0002]

2. Description of the Related Art A light emitting diode is used as a light source for reading and recording information in various display devices because it is a light emitting source which is small in size, consumes less power, and can stably emit high brightness light. Visible light emitting diodes that have been widely put into practical use so far can emit high-luminance red to green light. On the other hand, currently developed blue visible light emitting diodes still have low brightness and have not yet been put to practical use, but silicon carbide is regarded as a promising material for the light emitting diodes. .

As shown in FIG. 8, a general light emitting diode has a structure in which a substrate is on the lower side, a growth thin film layer having a light emitting layer is on the upper side, and light emission is taken out from the upper portion. Then, a current diffusion layer having a low resistance is provided on the outermost surface of the growth layer in order to flow the current not only directly under the electrode but also in the entire region of the pn junction in the chip to enhance the efficiency of extracting light to the outside.

Recently, the present inventors have found that chemical vapor deposition (C
VD method) was used to invent a method (Japanese Patent Application No. 2-129918) for producing a pn junction type light emitting diode capable of stably emitting blue visible light with high brightness and with good controllability and mass productivity. Furthermore, even in a pn junction type light emitting diode using a silicon carbide material, it has been found that a low resistance p-type growth layer can be obtained by using a silicon carbide Si surface as a growth substrate surface, and this is used as a current diffusion layer. Invented a high brightness pn junction type blue light emitting diode.

[0005]

In the conventional light emitting diode having the current spreading layer 84 as shown in FIG.
A current also flows under 6 and the light emitting region also exists under the electrode. However, light emission from just below the electrode is blocked by the upper electrode, and it is difficult to effectively extract the light to the outside of the element. Therefore, the current in the region eventually becomes a reactive current. Such an invalid current has been a major obstacle to realizing higher brightness of the blue light emitting diode.

It is an object of the present invention to solve the above problems and to provide an electrode structure of a pn junction type light emitting diode which is effective for high brightness.

[0007]

According to the present invention, in a pn junction type light emitting diode having a silicon carbide substrate and a silicon carbide semiconductor layer, the outermost surface of the silicon carbide semiconductor layer in which a plurality of silicon carbide semiconductor layers are laminated on the substrate is provided. It is characterized by having an annular ohmic electrode in part.

Further, in a pn junction type light emitting diode having a silicon carbide substrate and a silicon carbide semiconductor layer, an insulating thin film is formed on a part of the outermost surface of the silicon carbide semiconductor layer in which a plurality of silicon carbide semiconductor layers are laminated on the substrate. A thin film having an ohmic electrode having a ring shape on a contact surface with the outermost surface of the silicon carbide semiconductor layer on the thin film, and the insulating thin film has a smaller area covering the outermost surface of the silicon carbide semiconductor layer than the ohmic electrode. Is characterized in that.

Preferably, the outermost surface of the silicon carbide semiconductor layer is p
A layered film of titanium (Ti) and aluminum (Al) is used for the ohmic electrode with the silicon carbide semiconductor layer.

In the structure using an insulating thin film, a thin film of an insulating material of silicon dioxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ) is used between the outermost surface of the silicon carbide semiconductor layer and the ohmic electrode. It is characterized by

[0011]

The function of the present invention will be described below in comparison with the conventional example. 1 and 2 show a pn junction type light emitting diode according to the present invention and a conventional general pn junction type light emitting diode, respectively. Since the pn junction type light emitting diode of the present invention shown in FIG. 1 has the insulating thin film layer 15, the silicon carbide outermost surface layer 14 and the electrode 16 are not in the central portion of the silicon carbide outermost surface layer but in the periphery of the insulating thin film layer. 2 forms ohmic contact, and in the conventional pn junction type light emitting diode shown in FIG. 2, the ohmic contact is formed by the electrode formed in the central portion of the silicon carbide outermost surface layer 24 of the device.

In the structure shown in FIG. 2, the region where the injected current most effectively works is just below the electrode, but light emission in this region is blocked by the upper electrode 26 and cannot be effectively taken out to the outside, resulting in a reactive current. Become. Areas other than directly below the electrode, such as the end face of the mesa, can be extracted with light because they are not blocked by the upper electrode, but a small diffusion current contributes to light emission. The efficiency is remarkably deteriorated, and it is difficult to increase the brightness.

Therefore, by arranging the electrode 16 in the vicinity of the end face rather than in the center of the device as shown in FIG. 1, light emission from the light emitting region near the end face is rarely blocked by the upper electrode. The light emitted from just below the electrode can be effectively taken out from the surface or the end face through the light emitting path shown by the arrow in the figure, so that the brightness of the light emitting diode can be increased.

Further, by designing the resistivity and film thickness of the silicon carbide current diffusion layer, it becomes possible to concentrate the light emitting region only in the vicinity of the end face of the pn junction in the chip.

[0015]

EXAMPLES Examples of the present invention will be described below.

Example 1 In this example, a pn junction type blue light emitting diode using a 6H type silicon carbide (hereinafter abbreviated as SiC (forbidden band width about 3 eV)) substrate was manufactured. FIG. 3 is a sectional view showing the structure of a pn junction type blue light emitting diode according to the first embodiment of the present invention.

The pn-junction type blue light emitting diode of the present embodiment is composed of a 6H-type n-SiC single crystal substrate 31 and n-Si.
The C single crystal layers 32 and 33 and the p-SiC single crystal layer 34 are sequentially stacked to form a pn junction between the n-SiC single crystal layer 33 and the p-SiC single crystal layer 34. The pn junction has a mesa-etched structure, and the p-SiC single crystal layer 34 is formed.
An insulating thin film layer 35 made of silicon dioxide (SiO ₂ ), which is an upper layer of Ti, and Ti which covers the layer and has a larger area than the layer.
And a p-type ohmic electrode 36 made of a laminate of Al.

FIG. 4 shows the vapor phase growth (CV) used in this embodiment.
D) Schematic of the device. The growth process of the pn junction type blue light emitting diode will be described with reference to the drawing. The vapor phase growth apparatus includes a cylindrical reaction tube 100 made of quartz and a flange 108 attached to the opening thereof, and the support rod 102 projectingly provided inside the quartz reaction tube 100. A sample table 101 is attached to the tip of the. The sample stage 101 and the support rod 102 are both made of graphite, and the sample stage 101 may be installed horizontally or appropriately inclined.

The reaction tube 100 has a double tube structure, and a work coil 103 is wound around the outer circumference of the outer tube. Sample table 1
The silicon carbide sample 104 placed on 01 is heated to a predetermined temperature by the high frequency current applied to the work coil 103. A branch pipe 105 is provided on one side of the reaction tube 100, and the branch pipe 105 serves as an inlet for the raw material gas, the carrier gas, and the impurity gas. The outer tube of the reaction tube 100 having the double structure is provided with branch tubes 106 and 107, and the reaction tube 100 can be cooled by flowing cooling water therethrough.

The opening of the reaction tube 100 is closed by a stainless steel flange 108, and is sealed by a stopper plate 113, a bolt 109, a nut 110, and an O-ring 111 arranged on the periphery of the opening. A branch pipe 112 is provided near the center of the flange 108, and the reaction gas introduced from the branch pipe 105 is discharged.

The pn junction type light emitting diode of this embodiment shown in FIG. 3 was manufactured as follows using the vapor phase growth apparatus. First, as shown in FIG. 4, a 6H-type n-SiC single crystal substrate (dimensions of about 1 cm × 1 c) was placed on the sample table 101.
m) The sample 31 was placed. On the growth surface of the substrate sample 31,
The plane orientation is <11-20 from the (0001) Si plane direction.
A surface inclined about 5 degrees in the> direction was used.

Then, a high frequency current is supplied to the work coil 103 while flowing from the branch pipe 105 into the reaction tube 100 at a rate of 1 × 10 ⁴ cc / min using hydrogen gas as a carrier gas in the vapor phase growth apparatus. Then, the n-SiC single crystal substrate 31 was heated to 1,400 to 1,500 ° C. Then, by adding the source gas and the impurity gas to the carrier gas, the n-SiC single crystal substrate 31 is formed.
The single crystal layers 32 and 33 and the p-SiC single crystal layer 34 were sequentially grown to form a pn junction.

In this example, monosilane (SiH ₄ ) gas and propane (C ₃ H ₈ ) gas were used as the source gas. The flow rate of the raw material gas was about 1 cc / min. Further, as an impurity gas, trimethylaluminum (Al (CH ₃ ) ₃ ) is added to add an aluminum acceptor.
Gas was used, and nitrogen (N ₂ ) gas was used for adding the nitrogen donor.

First, the n-SiC single crystal layer 32 is doped with nitrogen gas as an impurity gas at a rate of 1 to 5 cc / min, and has a carrier concentration in the range of 5 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ . An n-SiC single crystal layer was obtained. 1 ~ as film thickness
It was grown to about 5 μm.

Then, nitrogen gas was added at a rate of 1 to 10 cc / min and trimethylaluminum was added at a rate of 0.05 to 0.4 cc / min to grow a layer 33 to which nitrogen and aluminum were simultaneously added. This layer was an n-type layer having a higher nitrogen content than aluminum, and the carrier concentration was set in the range of 1 × 10 ^{16 to} 3 × 10 ¹⁸ cm ⁻³ . This layer became a light emitting layer and was grown to a film thickness of 3 to 10 μm.

Then, by adding only trimethylaluminum at a rate of 0.15 to 0.5 cc / min,
P-S with a carrier concentration of 2 × 10 ^{17 to} 5 × 10 ¹⁸ cm ^-3
The iC single crystal 34 was grown to a film thickness of 3 μm.

After the growth, the substrate sample 31 is taken out from the reaction tube 21, and the n-SiC single crystal films 32 and 33 and the p-SiC single crystal film 34 are selectively etched by the dry etching method, as shown in FIG. Such a mesa structure was formed.
Due to this etching, one pn junction is about 170 μm
It became × 170 μm square. As the etching gas, carbon tetrafluoride (CF ₄ ) gas and oxygen (O ₂ ) gas were used.

Further, a polycrystalline silicon film of about 400 nm is deposited on the single crystal by a vapor phase growth method using silane gas, and the film is thermally oxidized in wet oxygen at 1100 ° C. for 1 hour to have a thickness of about 1 μm. A SiO ₂ film 35 was obtained.
The SiO ₂ film of 100 μm × 100 μm square is left in the center of the mesa, and the others are removed by etching.
A p-type ohmic electrode 36 having a m × 130 μm square Ti and Al stack was formed.

Finally, an n-side ohmic electrode 37 made of Ni was formed on the back surface of the n-SiC single crystal substrate 31 to obtain the pn junction type light emitting diode shown in FIG.

When an operating voltage of about 3.2 V was applied to the obtained light emitting diode, a current of 20 mA flowed and blue light emission with a peak wavelength of about 465 nm was obtained. In the light emitting diode obtained in this example, the light extraction efficiency was improved, so that the brightness was about 2.5 times that of the conventional structure.

<Embodiment 2> FIG. 5 is a sectional view showing the structure of a pn junction blue light emitting diode according to a second embodiment of the present invention. In this example, a pn junction type blue light emitting diode using 6H type SiC was manufactured. In this example, a plane whose plane orientation was inclined from the (000-1) C plane direction to the <11-20> direction by about 5 degrees was used as the growth surface of the substrate sample. The growth apparatus and growth method were the same as in Example 1, and an n-SiC single crystal layer 53 having a carrier concentration in the range of 5 × 10 ^{17 to} 5 × 10 ¹⁸ cm ⁻³ was grown on the substrate sample 51 to about 1 to 5 μm. .

Then, only trimethylaluminum is added to give a carrier concentration of 5 × 10 ^{15 to} 3 × 10 ¹⁷ cm ^-3.
Of p-SiC single crystal layer 54 of about 5 μm was grown. This p-type layer becomes a light emitting layer. After the growth, in the step of forming a SiO ₂ film, the SiC single crystal film is directly subjected to thermal oxidation in wet oxygen for 7 hours to form S having a thickness of about 0.6 μm.
An iO ₂ film 55 is formed, and a 150 μm square contact forming hole that leaves a 100 μm square SiO ₂ film in the center of the chip is removed by etching to form a 150 μm square p-type ohmic electrode 56 made of a Ti / Al stack. A pn junction type light emitting diode shown in FIG. 5 was obtained.

When an operating voltage of about 3.2 V was applied to the obtained light emitting diode, a current of 20 mA flowed and blue light emission with a peak wavelength of about 455 nm was obtained. The light emitting diode obtained in this example has a brightness of about 5 times that of the conventional structure.

<Embodiment 3> FIG. 6 is a sectional view showing the structure of a pn junction ultraviolet light emitting diode according to a third embodiment of the present invention. In this example, a pn junction type violet light emitting diode using 4H type SiC was manufactured. In this example, as the growth surface of the substrate sample, a surface whose plane orientation was inclined from the (0001) Si surface direction to the <11-20> direction by about 5 degrees was used.
The growth apparatus and the growth direction were the same as in Example 1, and the carrier concentration was 5 × 10 ^{16 to} 5 × 1 on the substrate sample 61.
About 5 μm of n-type SiC63 single crystal layer in the range of 0 ¹⁷ cm ⁻³
I grew it. This n-type layer becomes a light emitting layer.

Then, only trimethylaluminum was added to grow a p-type SiC single crystal layer 64 having a carrier concentration of 5 × 10 ^{17 to} 5 × 10 ¹⁸ cm ^-3 by about 4 μm. A pn junction type light emitting diode as shown in FIG. 6 is obtained by the same steps as in Example 1 except that Si ₃ N ₄ is formed as the post-growth insulating film 65 by plasma CVD to a thickness of about 1.5 μm. It was

When an operating voltage of about 3.4 V was applied to the obtained light emitting diode, a current of 20 mA flowed and ultraviolet emission having a peak wavelength of about 394 nm was obtained. The light emitting diode obtained in this example provided about three times the output as compared with the conventional structure.

<Embodiment 4> The pn of the fourth embodiment of the present invention.
The structure of the junction blue light emitting diode is similar to that of FIG. In this example, the same steps as in Example 1 were carried out except that 15R type SiC was used as the substrate sample 71.
A pn junction type light emitting diode was obtained.

When an operating voltage of about 3.1 V was applied to the obtained light emitting diode, a current of 20 mA flowed and blue light emission with a peak wavelength of about 475 nm was obtained. The light emitting diode obtained in this example has a brightness about 2.5 times higher than that of the conventional structure.

Although the first to fourth embodiments of the present invention described above are only for the mesa-shaped structure, the structure without the mesa-shaped structure as shown in FIG. 7 can also improve the emission luminance as compared with the conventional structure. Became.

In Examples 1 to 4 of the present invention described above, the ohmic electrode is provided after the insulating thin film is laminated on a part of the uppermost surface layer of the silicon carbide semiconductor layer, but the insulating thin film is not laminated. The structure may be such that the ohmic electrode is directly provided and the annular ohmic electrode is provided on a part of the outermost surface layer of the silicon carbide semiconductor layer.

[0041]

According to the pn junction type light emitting diode of the present invention, high brightness of the pn junction type light emitting diode using silicon carbide can be achieved.

According to this, for example, it is possible to increase the number of colors of the display portion in various display devices and to increase the speed and density of information recording and reading in various information processing devices using light emitting diodes as light sources. Moreover, since it can be mass-produced, the application field of the light emitting diode is dramatically expanded.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a light emission path of a silicon carbide pn junction type light emitting diode according to the present invention.

FIG. 2 is a cross-sectional view showing a light emitting path of a conventional silicon carbide pn junction type light emitting diode.

FIG. 3 is a sectional view of a silicon carbide pn junction type light emitting diode according to Example 1 of the present invention.

FIG. 4 is a structural cross-sectional view showing an example of a vapor phase growth apparatus used for manufacturing a silicon carbide pn junction type light emitting diode of the present invention.

FIG. 5 is a sectional view of a silicon carbide pn junction type light emitting diode according to Example 2 of the present invention.

FIG. 6 is a sectional view of a silicon carbide pn junction type light emitting diode according to Example 3 of the present invention.

FIG. 7 is a sectional view of a silicon carbide pn junction type light emitting diode according to Example 4 of the present invention.

FIG. 8 is a structure of a conventional general light emitting diode.

[Explanation of symbols]

11, 21, 31, 51, 61, 71, 81 n-silicon carbide single crystal substrate 12, 22, 32, 33, 53, 63, 72, 73, 8
2 n-silicon carbide single crystal layer 13, 23, 34, 54, 64, 74, 83 p-silicon carbide single crystal layer 14, 24, 84 p-silicon carbide current diffusion layer 15, 35, 55, 65, 75 insulation Film 16, 26, 36, 56, 66, 76, 86 p-side ohmic electrode 17, 27, 37, 57, 67, 77, 87 n-side ohmic electrode

Claims (5)

[Claims] 1. A pn junction type light emitting diode having a silicon carbide substrate and a silicon carbide semiconductor layer, wherein an annular ohmic electrode is provided on a part of an outermost surface of the silicon carbide semiconductor layer in which a plurality of silicon carbide semiconductor layers are laminated on the substrate. A pn junction type light emitting diode having. 2. A pn junction type light emitting diode having a silicon carbide substrate and a silicon carbide semiconductor layer, wherein an insulating thin film is provided on a part of an outermost surface of the silicon carbide semiconductor layer in which a plurality of silicon carbide semiconductor layers are laminated on the substrate. An ohmic electrode having a ring shape on the contact surface with the outermost surface of the silicon carbide semiconductor layer is formed on the thin film, and the insulating thin film has a smaller area covering the outermost surface of the silicon carbide semiconductor layer than the ohmic electrode. A pn junction type light emitting diode. 3. A silicon carbide semiconductor layer outermost surface is a p-type silicon carbide surface layer, and a laminated film of titanium (Ti) and aluminum (Al) is used for an ohmic electrode with the silicon carbide semiconductor layer. P of Claim 1 or Claim 2
n-junction type light emitting diode. 4. The silicon carbide semiconductor layer outermost surface is a p-type silicon carbide surface layer, and silicon dioxide (SiO ₂ ) is used for an insulating thin film between the silicon carbide growth layer and the ohmic electrode. The pn junction type light emitting diode according to claim 2. 5. The silicon carbide semiconductor layer outermost surface is a p-type silicon carbide surface layer, and silicon nitride (Si ₃ N ₄ ) is used for the insulating thin film between the silicon carbide growth layer and the ohmic electrode. The pn junction type light emitting diode according to claim 2.