RU2494498C2 - Semiconductor light-emitting device - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: semiconductor light-emitting device according to the invention comprises: a substrate; a first layer of an n-type conductivity semiconductor formed on the substrate; a second layer of a p-type conductivity semiconductor; an active layer between the first and second layers; a conducting layer on the second layer; a first contact deposited on the substrate; a second contact deposited on the conducting layer, wherein the substrate has at least one through-hole made in form of a truncated inverted pyramid. The first, second, active and conducting layers are deposited on both the horizontal portions of the substrate and the inner faces of the holes.

EFFECT: high efficiency of semiconductor light-emitting devices, while suppressing negative effects associated with vertices of inverted surface pyramids.

19 cl, 3 ex, 5 dwg

Description

FIELD OF THE INVENTION

The invention relates to the field of light-emitting devices, in particular to light-emitting semiconductor diodes with high efficiency.

BACKGROUND

A semiconductor LED chip is a major component of solid state lighting technology. The voltage applied between the two contacts of the LED chips induces an electric current through the pn junction, and the LED chip emits light due to radiative recombination of electrons and holes.

The advantages of LED chips are a long service life, high reliability, high coefficient of electro-optical conversion and low electrical energy consumption.

LED chips emitting infrared, red and green light have been produced and sold for a very long time, while the technology for the production of LED chips based on the third group nitrides (III nitrides) emitting ultraviolet, blue, green and white light has improved significantly recently (US 7642108 US 7335920, US 7365369, US 7531841, US 6614060). As a result, LED chips are widespread and are used in various fields, including lighting.

Usually, LED chips are made using planar technology for growing crystals from the gas phase, and have flat upper and lower surfaces through which light comes out.

The flat surfaces of the LED chip cause the light emitted at an angle greater than the angle of total internal reflection, cannot go outside and absorbed inside the LED chip, which reduces its efficiency.

To overcome this drawback, in US 5087949, it was proposed to use LED chips in the form of convex truncated pyramids containing inclined planes through which light can leave the LED chip without experiencing total internal reflection.

However, the use of LED chips in the form of a single convex truncated pyramid requires a significantly higher consumption of semiconductor material compared to a conventional thin-film flat chip, as well as the need for expensive cutting of V-grooves.

To overcome these problems in US 7446345 and US 7611917 it was proposed to use LED chips containing multiple V-shaped surface defects (pits) in the form of inverted pyramids. In LED chips with multiple pits, a layered LED structure including an active layer with quantum wells is grown on the flat areas of the LED chips and also extends into the inverted surface pyramids formed by V-shaped surface pits. After growing the active layer, the inverted surface pyramids are healed and a flat chip surface is formed. This approach allows you to increase the active layer area per unit area of the chip, and thereby increase the internal quantum yield of the LED chip, however, the light extraction efficiency does not increase.

The increase in light extraction while increasing the quantum yield can be achieved using LED chips with ungrown inverted surface pyramids formed by V-shaped surface pits, as was proposed in articles by T. Wunderer, M. Feneberg, F. Lipskil, J. Wang, R.A.R. Leutel, S. Schwaiger, K. Thonke, A. Chuvilin, U. Kaiser, S. Metzner, F. Bertram, J. Christen, G.J. Beirne, M. Jetter, P. Michler, L. Schade, C. Vierheilig, U.T. Schwarz, A.D. Drager, A. Hangleiter, and F. Scholz, Phys. Status Solidi B, 1-12 (2010) and T. Wunderer, J. Wang, F. Lipskil, S. Schwaiger, A. Chuvilin, U. Kaiser, S. Metzner, F. Bertram, J. Christen, SSShirokov, Ae Yunovich and F. Scholz, Phys. Status Solidi C7, 2140-2143 (2010).

However, the use of complete inverted pyramids, as suggested above, has a significant drawback due to the fact that inverted surface pyramids serve as a drain for dislocations, contaminants, and other defects. As a result, the positive effect of increasing the active layer area per unit area of the chip is compensated by a decrease in the internal quantum yield due to the accumulation of defects near the vertices of the inverted surface pyramids. In addition, the increase in the coefficient of light extraction due to the presence of inclined planes in inverted pyramids is limited by the fact that light is strongly absorbed near the vertices of the pyramids, where the inclined planes are conjugated with each other.

The present invention is to increase the efficiency of light-emitting semiconductor devices while suppressing the negative effects associated with the vertices of inverted surface pyramids.

SUMMARY OF THE INVENTION

To solve this problem, a light emitting semiconductor device is proposed, comprising:

- substrate;

- the first layer of a semiconductor with n-type conductivity formed on a substrate;

- a second p-type semiconductor layer;

- an active layer located between the first and second layers;

- a conductive layer located on the second layer,

- the first contact deposited on the substrate,

a second contact applied to the conductive layer,

moreover, the substrate contains at least one through hole made in the form of a truncated inverted pyramid, while the first, second, active and conductive layers are deposited on both horizontal sections of the substrate and on the inner faces of the holes.

Preferably, the number of faces of said pyramids ranges from 3 to 24, the length of the side of the base of the pyramids ranges from 10 μm to 1 mm, the angle of inclination of the side faces of these pyramids with respect to the surface of the substrate ranges from 10 ° to 90 °, height the cut off part of the pyramid is from 5% to 50% of its full height, and the thickness of the substrate lies in the range from 10 μm to 1 mm.

Preferably, the through holes are arranged in the form of a two-dimensional lattice.

The substrate may be made of gallium nitride, or of silicon carbide, or of aluminum oxide.

In a preferred embodiment, the conductive layer is transparent or translucent. Preferably, the conductive layer may be made of indium oxide with tin (ITO) or of metal with a thickness of 50 to 400 Angstroms.

The first layer of n-type semiconductor can be made of gallium nitride doped with silicon.

The second layer of p-type semiconductor can be made of gallium nitride doped with magnesium.

The active layer can be made of gallium nitride (GaN) and a solid solution of boron-aluminum-gallium-indium nitride (B _x Al _y Ga _z In _1-z N).

Preferably, the active layer is made integral and consists of layers of a semiconductor with a zinc blende phase structure and layers with a wurtzite phase structure.

In a preferred embodiment, the active layer may contain many quantum wells made of a solid solution of boron-aluminum-gallium-indium nitride (B _x Al _y Ga _z In _1-z N).

In another preferred embodiment, the active layer contains one wide well and many quantum wells made of a solid solution of boron-aluminum-gallium-indium nitride (B _x Al _y Ga _z In _1-z N).

The light emitting device may further comprise a phosphor layer located on the upper surface of the chip to convert blue light to white light.

The light-emitting device may further comprise an optical light diffuser located on the upper surface of the chip to produce white light from a mixture of multi-colored light fluxes emitted from the faces of the pyramids and from flat areas outside the pyramids.

Preferably, the second contact applied to the conductive layer is non-continuous with partial light transmission.

The present invention provides LED chips with a set of through holes in the form of truncated inverted pyramids, on the side faces of which a layered LED structure is formed. In such chips there is no peak collecting dislocations, contaminants and other defects.

The basis of the proposed light-emitting semiconductor device is a conductive semiconductor substrate containing through holes made in the form of truncated inverted pyramids extending to the upper and lower surfaces of the LED chip.

In the truncated inverted pyramids, there is no peak at which inclined faces meet and dislocations, contaminants and other defects are collected. Inclined faces close to the holes on the bottom surface of the flat chip. Holes provide free exit of light from the LED chip to the outside without strong absorption at the tops of the pyramids.

The present invention differs from existing analogues in that the LED chip is not continuous, but contains through holes, which are made in the form of truncated inverted pyramids.

The use of truncated pyramids makes it possible to avoid contact of the active layer with the region close to the top of the pyramid, where the increased rate of nonradiative recombination due to the presence of dislocations and contaminants reduces the internal quantum yield and reduces the coefficient of conversion of electric energy into light. At the same time, with regard to light extraction, the use of inverted truncated pyramids is as effective as convex truncated pyramids, and the coefficient of light extraction in LED chips with inverted truncated pyramids significantly exceeds the corresponding coefficient for LED chips with inverted full pyramids.

In addition, the use of a non-continuous LED chip with through holes allows to significantly improve its cooling by pumping air, inert gas or liquid through these holes. As a result, the LED chip can operate at high current densities, give more light power and have a higher brightness.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by the drawings shown in FIGS. 1-5.

Figure 1 presents a diagram of a conductive substrate of an LED chip with a set of through holes in the form of truncated inverted pyramids.

Figure 2 presents a diagram of a truncated inverted pyramid with a layered LED structure formed on its side faces.

Figure 3 presents a sectional diagram, in the region of one of the truncated inverted pyramids, the LED chip of example 1. which generates blue light.

Figure 4 presents a sectional diagram in the region of one of the truncated inverted pyramids, the LED chip from example 2. which generates white light using a phosphor.

5 is a sectional diagram, in the region of one of the truncated inverted pyramids, of the LED chip from Example 3. which generates white light without using a phosphor.

DETAILED DESCRIPTION OF THE INVENTION

The basis of the proposed light-emitting semiconductor device is a conductive semiconductor substrate 100 containing through holes 101 made in the form of truncated inverted pyramids. Figure 1.

On the faces 104 of the truncated inverted pyramids 101, an LED structure 200 is formed as shown in FIG. 2. The LED structure 200 consists of a first semiconductor layer 201 with n-type conductivity, a second p-type semiconductor layer 203, an active layer 202 located between the first and second layers, and a transparent conductive layer 204 located on the second conductivity semiconductor layer 203 p-type.

The conductive substrate 100 contains at least one through hole made in the form of a truncated inverted pyramid, with the first 201, second 203, active 202 and conductive 204 layers applied both to the horizontal sections of the substrate and to the inner faces of the through holes 101, made in the form of truncated inverted pyramids, as shown in the section diagram of the LED chip 300 in the region of one of the truncated inverted pyramids. Figure 3.

Two metal contacts 302 and 303, which provide current supply to the LED structure, are applied from below to the substrate 100 and from above to a horizontal portion of the transparent conductive layer 204, see FIG. 3.

The present invention will be explained below with a few examples of options for its implementation. It should be noted that the following description of these embodiments is merely illustrative and not exhaustive.

Example 1. An LED chip with eleven holes in the shape of an inverted truncated. hexagonal pyramids generating blue light.

A general diagram of a conductive arm 100 of an LED chip generating blue light is shown in FIG. The substrate of the LED chip consists of a rectangular plate of a semiconductor crystal of gallium nitride with a size of 3 × 2 mm, and with a thickness of 200 μm and a surface perpendicular to the crystalline axis with [0 0 0 1]. Eleven holes were formed on the plate in the form of inverted truncated hexagonal pyramids with faces coinciding with the crystal planes {1 -1 0 1} and the angle of inclination of the side faces with respect to the plane (0 0 0 1), θ = 61.96 °, with the sides of the base, oriented along the crystalline directions <1 1 -2 0>, and with the length of the sides of the base R _b = 200 μm. Inverted truncated hexagonal pyramids are packed in a triangular two-dimensional lattice with a period of 500 μm.

The cross-sectional diagram of the LED chip 300 in the region of one of the truncated inverted pyramids is shown in FIG. 3. The layered structure of the LED chip consists of a conductive substrate 100 of n-type gallium nitride with a thickness of 100 μm, on which a metal contact 302 is applied from below, a layer 201 of high-quality n-type gallium nitride with a thickness of 2 μm, an undoped active layer 202 GaN with a thickness of 0.1 μm with five In _0.2 Ga _0.8 N quantum wells with a width of 2 nm, a p-type 203 GaN layer 0.1 μm thick with an Al _0.4 Ga _0.6 N 5 nm barrier at the interface with the active layer 202, a conducting layer of indium oxide tin 204 (ITO ) 1 μm thick, on which a metal contact 303 is applied on top.

When a constant voltage is applied, current flows between the contacts 302 and 303 in the LED chip 300, while the electrons from the contact 302 first flow into the conductive substrate 100 of n-type gallium nitride, then into the layer 201 of high-quality n-type gallium nitride, and then fall into the active layer 202 of undoped GaN with five In _0.2 Ga _0.8 N quantum wells 2 nm wide, where they recombine with holes, emitting blue light. In turn, holes from the conducting layer of indium oxide tin (ITO) 204, which forms a transparent ohmic contact, flow into the p-type GaN layer 203, overcome the Al _0.4 Ga _0.6 N barrier preventing electron leakage into the p-type GaN layer 203, and also fall into the active layer of an undoped 202 GaN layer with five In _0.2 Ga _0.8 N quantum wells 2 nm wide, where they recombine with electrons, emitting blue light.

Due to the presence of inclined planes with a large angle of inclination θ = 61.96 ° in the inverted pyramids, the light extraction coefficient from the LED chip 300 is significantly higher than the light extraction coefficient for a conventional flat chip.

In addition, in five In _0.2 Ga _0.8 N quantum wells with a width of 2 nm, formed in a layer of 202 undoped GaN, on the side faces of the pyramid formed by the {1 -1 0 1} crystal planes, due to the rotation of these planes relative to the polar plane (О 0 0 1), the built-in electric field associated with spontaneous and piezoelectric polarization is strongly suppressed, which helps to increase the internal quantum yield of light from the active layer 202.

Also, the use of truncated pyramids makes it possible to avoid contact of the active layer with the region close to the top of the pyramid, where the increased rate of nonradiative recombination due to the presence of dislocations and contaminants reduces the internal quantum yield and reduces the coefficient of conversion of electric energy into light.

Example 2. An eight-hole LED chip in the shape of an inverted truncated hexagonal pyramid that generates white light using a phosphor.

The general layout of the substrate 100 of an LED chip generating white light is shown in FIG. The position of the LED chip consists of a rectangular plate of a semiconductor crystal of gallium nitride with a size of 1 × 1 mm and a thickness of 200 μm and a surface perpendicular to the crystalline axis with [0 0 0 1]. Eight holes are formed on the plate in the form of inverted truncated hexagonal pyramids with faces coinciding with the crystal planes {3 3 -6 2} and the angle of inclination of the side faces with respect to the plane (0 0 0 1), θ = 78.42 °, with sides the base, oriented along the crystalline directions <1 -1 0 0>, and with the length of the sides of the base R _b = 100 μm. Inverted truncated hexagonal pyramids are packed in a triangular two-dimensional lattice with a period of 300 μm.

A section diagram of a LED chip 300 in the region of one of the truncated inverted pyramids is shown in FIG. 4. The layered structure of the LED chip consists of a conductive substrate 100 of n-type gallium nitride with a thickness of 100 μm, on which a metal contact 302 is applied from below, a layer 201 of high-quality n-type gallium nitride with a thickness of 2 μm, an unalloyed layer of 202 GaN with a thickness of 0.1 μm, with one a wide In _0.1 Ga _0.9 N well with a width of 20 nm and three In _0.2 Ga _0.8 N quantum wells with a width of 2 nm, a p-type 203 GaN layer 0.1 μm thick, a conductive indium oxide layer 204 with tin (ITO) 1 μm thick, on which is placed on top of a metal contact 303, on which lies the phosphor layer 401.

The LED chip 300 is mounted in an LED or LED lamp on a mirror reflective surface, such as a polished aluminum or copper plate.

When a constant voltage is applied between the contacts 302 and 303, current flows in the LED chip 300, while the electrons from the contact 302 first flow into the conductive substrate 100 of n-type gallium nitride, then into the layer 201 of high-quality gallium nitride of the n-type, and then fall into active layer 202 of undoped GaN, where they are first captured in a wide In _0.1 Ga _0.9 N well with a width of 20 nm, and then tunnel into three In _0.2 Ga _0.8 N quantum wells with a width of 2 nm, where they recombine with holes, emitting blue light. In turn, holes from the conducting layer of indium oxide tin (ITO) 204, which forms a transparent ohmic contact, flow into the p-type GaN layer 203, fall into the undoped GaN active layer 202, and are captured by two 2 nm wide In _0.2 Ga _0.8 N quantum wells, where they recombine with electrons, emitting blue light. The blue light emitted by the LED chip 300 enters the phosphor layer 401, either immediately or after several reflections from the lower mirror surface and the side faces of the inverted truncated pyramid. In the phosphor layer 401, blue light excites the phosphor and is converted to white light.

Due to the presence of inclined planes with a large angle of inclination θ = 78.42 ° in the inverted pyramids, the light extraction coefficient from the LED chip 300 is significantly higher than the light extraction coefficient for a conventional flat chip.

In addition, in three In _0.2 Ga _0.8 N quantum wells 2 nm wide, formed in a layer of 202 undoped GaN, on the lateral faces of the pyramids formed by {3 3 -6 2} crystal planes, due to the rotation of these planes relative to the polar plane (0 0 0 1), the built-in electric field associated with spontaneous and piezoelectric polarization is strongly suppressed, which helps to increase the internal quantum yield of light from the active layer 202.

Also, the use of truncated pyramids makes it possible to avoid contact of the active layer with the region close to the top of the pyramid, where the increased rate of nonradiative recombination due to the presence of dislocations and contaminants reduces the internal quantum yield and reduces the coefficient of conversion of electric energy into light.

Example 3. An LED chip with eight holes in the form of inverted truncated hexagonal pyramids that generates white light without using a phosphor.

The general layout of the substrate 100 of an LED chip generating white light is shown in FIG. The substrate of the LED chip consists of a rectangular plate of a gallium nitride semiconductor crystal with a size of 2 × 2 mm, and with a thickness of 100 μm and a surface perpendicular to the crystal axis with [0 0 0 1]. Eight inverted truncated hexagonal pyramids with faces coinciding with the crystal planes {1 1 -2 2} and an angle of inclination of the side faces with respect to the plane (0 0 0 1), θ = 58.41 °, with the sides of the base, are formed on the plate oriented along the crystalline directions <1 -1 0 0>, and with the length of the side of the base R _b = 150 microns. Inverted truncated hexagonal pyramids are packed in a triangular two-dimensional lattice with a period of 500 μm.

Figure 5 shows a sectional diagram of an LED chip 300 in the region of one of the truncated inverted pyramids. The layered structure of the LED chip consists of a conductive substrate 100 of n-type gallium nitride with a thickness of 100 μm, on which a metal contact 302 is applied from below, a layer 201 of high-quality n-type gallium nitride with a thickness of 2 μm, an undoped GaN layer 202 with a thickness of 0.1 μm, with one a wide In _0.1 Ga _0.9 N well with a width of 20 nm and three In _0.15 Ga _0.85 N quantum wells with a variable width of 2 nm at the faces of inverted truncated hexagonal pyramids coinciding with the crystal planes {1 1 -2 2} and 4 nm outside the pyramids on horizontal crystalline plane (0 0 0 1), p-type GaN layer 203 0.1 μm thick, indium tin layer 204 (ITO) 20 μm thick, on which a metal mesh contact 501 is applied, electrically connected to a reinforced metal contact 303 on which the optical light diffuser 502 is located.

Installation of the LED chip 300 in an LED or LED lamp is performed on a mirror reflective surface, for example, a polished aluminum or copper plate.

When a constant voltage is applied, current flows between the contacts 302 and 303 in the LED chip 300, while the electrons from the contact 302 first flow to the n-type gallium nitride conductive substrate 100, then to the high-quality n-type gallium nitride layer 201, and then fall into the active layer 202 of undoped GaN, where they are first captured into a wide In _0.1 Ga _0.9 N well with a width of 20 nm, and then tunnel into three In _0.2 Ga _0.8 N quantum wells with a width of 2 nm on the faces of the pyramids and 4 nm on the horizontal plane sections outside the pyramids, where recombine with holes, emit I have blue light on the faces of the pyramids and yellow on sections of the horizontal plane outside the pyramids. In turn, holes from the conducting layer of indium oxide tin (ITO) 204, which forms a transparent ohmic contact, flow into the p-type GaN layer 203, fall into the undoped GaN active layer 202, and are captured by three variable width In _0.2 Ga _0.8 N quantum wells where they recombine with the electrons, emitting blue and yellow light. The blue and yellow light emitted by the LED chip 300 enters the optical light diffuser 502 either immediately or after several reflections from the lower mirror surface and the side faces of the inverted truncated th pyramids. In the optical light diffuser 502, blue and yellow light are mixed and converted to white light.

Due to the presence of inclined planes with a large angle of inclination θ = 58.41 ° in the inverted pyramids, the light extraction coefficient from the LED chip 300 is significantly higher than the light extraction coefficient for a conventional flat chip.

In addition, in three In _0.2 Ga _0.8 N quantum wells, 2 nm wide, formed in a layer 202 of undoped GaN, on the side faces of the pyramids formed by the {1 1 -2 2} crystal planes, due to the rotation of these planes relative to the polar plane ( 0 0 0 1), the built-in electric field associated with spontaneous and piezoelectric polarization is strongly suppressed, which helps to increase the internal quantum yield of light from the active layer 202.

Also, the use of truncated pyramids makes it possible to avoid contact of the active layer with the region close to the top of the pyramid, where the increased rate of nonradiative recombination due to the presence of dislocations and contaminants reduces the internal quantum yield and reduces the coefficient of conversion of electric energy into light.

Although the present invention has been described and illustrated by examples of embodiments of the invention, it should be noted that the present invention is in no way limited to the examples given.

Claims (19)

1. A light emitting semiconductor device, comprising:
- substrate;
- the first layer of a semiconductor with n-type conductivity formed on a substrate;
- a second p-type semiconductor layer;
- an active layer located between the first and second layers;
- a conductive layer located on the second layer,
- the first contact deposited on the substrate,
- a second contact deposited on the conductive layer, and the substrate contains at least one through hole made in the form of a truncated inverted pyramid, while the first, second, active and conductive layers are applied both to horizontal sections of the substrate and to the inner faces holes. 2. The light-emitting semiconductor device according to claim 1, in which the number of faces of the pyramids lies in the range from 3 to 24, the length of the side of the base of the pyramids lies in the range of 10 μm to 1 mm, the angle of inclination of the side faces of the pyramids with respect to the surface of the substrate lies in the range from 10 to 90 °, the height of the cut off part of the pyramid is from 5 to 50% of its full height. 3. The light emitting semiconductor device according to claim 1, in which the through holes are arranged in the form of a two-dimensional lattice. 4. The light emitting semiconductor device according to claim 1, in which the thickness of the substrate lies in the range from 10 μm to 1 mm 5. The light emitting semiconductor device according to claim 1, in which the substrate is made of gallium nitride. 6. The light emitting semiconductor device according to claim 1, in which the substrate is made of silicon carbide. 7. The light emitting semiconductor device according to claim 1, wherein the substrate is made of alumina. 8. The light emitting semiconductor device according to claim 1, in which the conductive layer is transparent or translucent. 9. The light emitting semiconductor device of claim 8, wherein the conductive layer is made of indium tin oxide (ITO). 10. The light emitting semiconductor device of claim 8, in which the conductive layer is made of metal with a thickness of from 50 to 400 Å. 11. The light-emitting semiconductor device according to claim 1, in which the first layer of a semiconductor with n-type conductivity is made of gallium nitride doped with silicon. 12. The light-emitting semiconductor device according to claim 1, wherein the second p-type semiconductor layer is made of magnesium doped gallium nitride. 13. The light-emitting semiconductor device according to claim 1, in which the active layer is made of gallium nitride (GaN) and a solid solution of boron nitride - aluminum - gallium - indium (B _x Al _y Ga _z In _1-z N). 14. The light-emitting semiconductor device according to claim 1, in which the active layer is made composite, consisting of layers of a semiconductor with a zinc blende phase structure and layers with a wurtzite phase structure. 15. The light emitting semiconductor device according to claim 1, in which the active layer contains many quantum wells made of a solid solution of boron nitride - aluminum - gallium - indium (B _x Al _y Ga _z In _1-z N). 16. The light-emitting semiconductor device according to claim 1, in which the active layer contains one wide well and many quantum wells made of a solid solution of boron nitride - aluminum - gallium indium (B _x Al _y Ga _z In _1-z N). 17. The light-emitting semiconductor device according to claim 1, in which it further comprises a phosphor layer located on the upper surface of the chip, for the conversion of blue light into white light. 18. The light-emitting semiconductor device according to claim 1, in which it further comprises an optical light diffuser located on the upper surface of the chip, to obtain white light from a mixture of multi-colored light fluxes emitted from the faces of the pyramids and from flat areas outside the pyramids. 19. The light-emitting semiconductor device according to claim 1, in which the second contact is made continuous with the possibility of partial transmission of light.

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