Light emitting diode chip and fabrication method

A light emitting diode chip includes an epitaxial layer with a plurality of recess portions and protrusion portions over the top layer; a light transmission layer, located between top ends of adjacent protrusion portions and forming holes with the recess portions. The light transmission layer has a horizontal dimension larger than a width of the top ends of two adjacent protrusion portions, and serves as current blocking layer; a current spreading layer covering the surface of the light transmission layer and the surface of an epitaxial layer of a non-mask light transmission layer. As the refractive index of the light transmission layer is between those of the epitaxial layer and the hole, indicating a difference of refractive index between the light transmission layer and the epitaxial layer, the probability of scattering generated when light from a luminescent layer emits upwards can be increased, thus avoiding light absorption by electrodes and improving light extraction efficiency.

BACKGROUND

Featured with small size, high efficiency and long service life, light emitting diode is widely used in fields like traffic light and outdoor full color display and is becoming a study hot point in electronics field.

To get high-luminance LED, the key is to improve the internal and external quantum efficiency. The light extraction efficiency of chip is a main factor constraining the external quantum efficiency. As the refractive indices of epitaxial material, substrate material and air differ a lot, the light produced at the light emitting layer will be totally reflected at the material interfaces with different refractive indices and cannot be exported from the chip. Therefore, study on improving light emitting efficiency of LED is active, mainly including: change of chip's geometric profile, use of inverted pyramid structure, resonant cavity or photonic crystal. It can be seen that chip structure design is of great importance to improve the light-emitting efficiency of LED.

Chinese Patent Application No. 200910037641.3 discloses a light emitting diode with current blocking layer, comprising a substrate, an N-type semiconductor material layer formed on the front side of the substrate, a light emitting layer formed on the N-type semiconductor material layer, a P-type semiconductor material layer formed on the light emitting layer, a transparent electrode layer formed on the P-type semiconductor material layer, an anode metal electrode bonding line layer formed on the transparent electrode layer and a cathode metal electrode bonding line layer formed on the N-type semiconductor material layer, bonding lines formed on the anode metal electrode bonding line layer and the cathode metal electrode bonding line layer, and a current blocking layer at the local position under the anode metal electrode bonding line layer and between the transparent electrode layer and the P-type semiconductor material layer.

SUMMARY

The inventors of the present disclosure have recognized that the current blocking layer in existing technologies can be configured to reduce current accumulation under the wafer electrode and further the absorption of light by the electrode, but make a limited increase of light emitting efficiency due to the failure to fully reflect the light by the current blocking layer.

The technical problem to be solved by some embodiments of the present disclosure is to improve the above limitations of the prior art, thus further improve the current blocking/spreading property, increase light emitting efficiency and luminance of light emitting diode chip and cut production cost.

The technical schemes below are adopted in some embodiments of the present disclosure to solve the technical problems:

Various embodiments disclosed herein provide a light emitting diode chip, comprising an epitaxial layer, which includes from the bottom up at least a type I semiconductor layer, a light emitting layer and a type II semiconductor layer and with a plurality of recess portions and protrusion portions on the top layer; a light transmission layer, located between the top ends of the adjacent protrusion portions and forming holes with the recess portions the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions.

Some embodiments provide another light emitting diode chip, comprising an epitaxial layer which includes from the bottom up at least a type I semiconductor layer, a light emitting layer and a type II semiconductor layer and with a plurality of recess portions and protrusion portions at the central part area on the top layer; a dielectric layer, located between the top ends of the adjacent protrusion portions and forming holes with the recess portions the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions; a current spreading layer covering the surface of the dielectric layer and the surface of the epitaxial layer of non-mask dielectric layer; a first electrode formed on a current spreading layer and vertically corresponding to the dielectric layer.

Various embodiments also provide a fabrication method of a light emitting diode, comprising the following steps: (1) a substrate is provided; (2) an epitaxial layer is formed on the substrate, which includes from the bottom up at least an epitaxial layer with a plurality of recess portions and protrusion portions on the top layer; (3) a light transmission layer formed on the epitaxial layer, specifically, located between the top ends of the adjacent protrusion portions and forming holes with the recess portions the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions; (4) a current spreading layer in film structure and continuously distributed, covering the surface of the light transmission layer and the surface of an epitaxial layer of a non-mask light transmission layer.

Following Step (4), the fabrication method can further comprise (5) directly fabricating the first electrode and the second electrode, respectively arranged above part of the current spreading layer and below the substrate, or (5) firstly removing part of the epitaxial layer to expose part of the type I semiconductor layer, and then (6) fabricating the first electrode and the second electrode, respectively arranged above part of the current spreading layer and above part of the type I semiconductor layer.

Some embodiments also provide another fabrication method of light emitting diode, comprising the following steps: (1) a substrate is provided; (2) an epitaxial layer is formed on the substrate, composed of from the bottom up at least a type I semiconductor layer, a light emitting layer and a type II semiconductor layer and with a plurality of recess portions and protrusion portions at the central part area on the top layer; (3) a dielectric layer formed on the epitaxial layer, specifically, located between the top ends of the adjacent protrusion portions and forming holes with the recess portions the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions; (4) a current spreading layer in film structure and continuously distributed, covering the surface of the dielectric layer and the surface of the epitaxial layer of non-mask dielectric layer;

Following Step (4), the fabrication method can further comprise (5) directly fabricating a first electrode and a second electrode, respectively arranged above part of the current spreading layer and below the substrate, or (5) firstly removing part of the epitaxial layer to expose part of the type I semiconductor layer, and then (6) fabricating a first electrode and a second electrode, respectively arranged above part of the current spreading layer and part of the type I semiconductor layer.

Preferably, a hollow cell is left between two adjacent transmission layers.

Preferably, the light transmission layer is periodically distributed.

Preferably, the light transmission layer is of nanoball or nanoline or nanorod structure.

Preferably, the light transmission layer is made of dielectric layer or conducting layer or the combination of the two.

Preferably, the dielectric layer is made of SiO2or SiNxor Al2O3or TiO2or AN or the combination of them.

Preferably, the conducting layer is made of ITO or ZnO or CTO or InO or In doped with ZnO or Al doped with ZnO or Ga doped with ZnO or the combination of them.

Preferably, the refractive index of the light transmission layer is between those of the epitaxial layer and the air.

Preferably, the light emitting diode chip also comprises the current spreading layer, covering the surface of the dielectric layer and the surface of the epitaxial layer of the non-mask dielectric layer.

Preferably, the current spreading layer is of a continuously distributed film structure.

Preferably, the current spreading layer is made of ITO or ZnO or CTO or InO or In doped with ZnO or Al doped with ZnO or Ga doped with ZnO or the combination of them.

Preferably, the light emitting diode chip also comprises the substrate positioned oppositely to the epitaxial layer; and the substrate is epitaxial substrate or thermal conducting substrate or electro conducting substrate or insulating substrate.

Preferably, the light emitting diode chip also comprises a first electrode and a second electrode, respectively arranged above part of the light transmission layer and below the substrate.

Preferably, the light emitting diode chip also comprises the first electrode and the second electrode, respectively arranged above part of the current spreading layer and below the substrate.

Preferably, the light emitting diode chip also comprises the first electrode and the second electrode, respectively arranged above part of the light transmission layer and part of the type I semiconductor layer.

The disclosure has at least the following beneficial effects: by controlling the position relation between the light transmission layer and the epitaxial layer with protruded and recessed micro structure, the light transmission layer is placed between the top ends of two adjacent protrusion portions of the epitaxial layer and forms with the recessed part a hole structure which functions as a current blocking layer; the light transmission layer is a dielectric layer to block current and so current accumulation under chip electrode is eliminated to a great extent; the light transmission layer is also an electro conducting layer to diffuse current and so current injection efficiency is improved and working voltage of devices is decreased; as the refractive index of the light transmission layer is between those of the epitaxial layer and the hole (the air), indicating a difference of refractive index between the light transmission layer and the epitaxial layer, the probability of scattering generated when the light rays from a luminescent layer emits upwards can be increased, thus avoiding the absorption of light by electrode and further improving light extraction efficiency. In addition, metal film as a reflecting layer is not needed, cutting production cost.

DETAILED DESCRIPTION

Further detailed description will be made to the disclosure with the following embodiments.

A fabrication procedure of the light emitting diode chip, comprising:

Step 1: as shown inFIG. 1, a substrate101is provided, where the substrate can be an epitaxial substrate, a thermal conducting substrate, an electro conducting substrate or an insulating substrate. In this embodiment, preferably, silicon (Si) is used as an epitaxial substrate, and in other embodiments, the substrate can be an Al2O3substrate, a SiC substrate, a GaN substrate, a GaAs substrate, a GaP substrate, an AlN substrate or a Cu substrate. Through metal organic chemical vapor phase deposition (MOCVD), an epitaxial layer102is formed on the substrate, on which from bottom upwards a first semiconductor layer103, a light emitting layer104and a second semiconductor layer105are stacked, with the first semiconductor layer103electrically opposite to the second semiconductor layer105, i.e., when the first semiconductor layer 1-3 is N-type, the second semiconductor layer105is P-type, vice versa; in this embodiment, the first semiconductor layer103is an N-type GaN layer, the second semiconductor layer105is a P-type GaN layer, and the light emitting layer104is a multi-quantum well (MQW) made of InGaN/GaN. In other embodiments, the first semiconductor layer103, the second semiconductor layer105and the light emitting layer104can be made up of other components than the above;

Step 2: as shown inFIG. 2, etching process is adopted to form a protruded and recessed micro structure on the top layer of the epitaxial layer, comprising a plurality of protrusion portions106and recess portions107, and the etching process is not limited to dry etching, and wet etching is also an option. The protruded and recessed micro structure can also be formed during the epitaxial layer fabricating process by adjusting the technological parameters, rather than being limited to the chip fabricating process. It should be noted that the position of the protruded and recessed micro structure is not limited to the inside of the epitaxial layer; rather, it can be formed on the surface of the epitaxial layer by introducing other protruded and recessed micro structure like periodic array-shaped dielectric layer.

Step 3: as shown inFIG. 3, nano-imprinting process is adopted to form a light transmission layer108on the epitaxial layer102, specifically, between the top ends of two adjacent protrusion portions106, forming holes109with the recess portions107the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions; adjacent light transmission layers contacts each other by dot, line or plane, or are separate from each other, and in this embodiment, adjacent light transmission layers108do not contact each other but being distributed periodically with an interval of 200 nm, thus forming a hollow cell110; the light transmission layer is of nano ball or nano line or nano column structure, and in this embodiment, the light transmission layer108is preferably of nano ball structure with wire diameter of 10-500 nm, preferably 200 nm; the light transmission layer108is made of dielectric layer or conducting layer, and in this embodiment, the conducting layer is preferably a conducting layer, made of ITO or ZnO or CTO or InO or In doped with ZnO or Al doped with ZnO or Ga doped with ZnO, preferably made of ITO in this embodiment, and the refractive index of the light transmission layer is between those of the epitaxial layer and the air.

Step 4: as shown inFIG. 4, a current spreading layer111in film structure and continuously distributed covers the surface of the light transmission layer108and the surface of the epitaxial layer of the non-mask light transmission layer108, and the current spreading layer is made of ITO or ZnO or CTO or InO or In doped with ZnO or Al doped with ZnO or Ga doped with ZnO, preferably made of ITO in this embodiment, the same as the light transmission layer108, so avoiding internal damage of the light emitting diode and guaranteeing low working voltage while having good light intensity of the light emitting diode. The current spreading layer111can be formed by vacuum evaporation or electronic beam evaporation or radio frequency (RF) or sputtering or plasma chemical vapor deposition (PECVD), preferably by sputtering in this embodiment.

Step 5: as shown inFIG. 5, P electrode112and N electrode113are fabricated above part of the current spreading layer111and below the substrate101, and it should be noted that since the substrate101is made of silicon substrate with electrical conductivity, N electrode113below the substrate101can be spared.

As shown inFIG. 5, the light emitting diode chip made by the above method has a structure composed of the silicon substrate101at the bottom; the epitaxial layer102with protruded and recessed micro structure and formed on the silicon substrate101, comprising from bottom upwards the first semiconductor layer103, the light emitting layer104and the second semiconductor layer105and the top layer, namely, the second semiconductor layer105, having a plurality of protrusion portions106and recess portions107on the surface; ITO light transmission layer108in nano ball structure, located between the top ends of adjacent protrusion portions106and forming holes109with the recess portions107, the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions, adjacent light transmission layers distributed periodically without contacting, thus forming the hollow cell110; ITO current spreading layer111in film structure and continuously distributed, covering the surface of the light transmission layer and the surface of the epitaxial layer of the non-mask light transmission layer; P electrode112, formed on part of the ITO current spreading layer111; and N electrode113, formed below the silicon substrate101.

The structure of the above light emitting diode chip adopts the combination of the light transmission layer and the epitaxial layer with protruded and recessed micro structure, having the light transmission layer located between the top ends of the adjacent protrusion portions and forming holes with the recess portions as the current blocking layer; the light transmission layer diffuses current and so current injection efficiency is improved, working voltage of devices is decreased and finally LED luminous efficiency and brightness are improved.

As shown inFIG. 6, different from Embodiment 1, this embodiment discloses a light emitting diode chip in structure with electrodes on the same surface. In this embodiment, sapphire substrate is adopted as the epitaxial substrate201, and P electrode212and N electrode213are respectively made above part of the current spreading layer211and the exposed first semiconductor layer203.

As shown inFIG. 7, different from Embodiment 2, the top layer of the epitaxial layer of this embodiment adopts a protruded and recessed micro structure, the recessed part307is on the same surface as the surface of the second semiconductor layer305, while the protruded part206of Embodiment 2 is on the same surface as the surface of the second semiconductor layer205.

As shown inFIG. 8, different from Embodiment 2, the protruded and recessed micro structure on the top layer of the epitaxial layer of this embodiment is formed by the periodically arranged dielectric layer408with low refractive index, and the dielectric layer408is made of SiO2or SiNxor Al2O3or TiO2or AlN or the combination of them, preferably in this embodiment made of SiO2. As the light transmission layer409is placed between the top ends of two adjacent protrusion portions406and forms with the recessed part407a hole structure408, the hole408functions as a current blocking layer, and in addition, the dielectric layer408of protruded and recessed micro structure also can block the current, and the combination of the hole and the dielectric layer will greatly eliminate current accumulation under the chip electrode.

As shown inFIG. 9, different from Embodiment 3, the light transmission layer is composed of the first light transmission layer and the second light transmission layer, the first light transmission layer508is made of dielectric layer and on the protruded and recessed micro structure on the top layer of the epitaxial layer, and the second light transmission layer509is made of electro conducting layer and on the surface of the second semiconductor layer of the epitaxial layer. As the first light transmission layer508is placed between the top ends of two adjacent protrusion portions506and forms with the recessed part a hole structure510, the hole510functions as the current blocking layer, and in addition the first light transmission layer508made of the dielectric layer408also can block the current, the combination of the hole and the dielectric layer will greatly eliminate current accumulation under the chip electrode.

Step 1: as shown inFIG. 10, the Al2O3substrate601is provided, and the epitaxial layer602is formed on the substrate by MOCVD method, on which the first semiconductor layer603, the light emitting layer604and the second semiconductor layer605are from bottom upwards stacked.

Step 2: as shown inFIG. 11, etching process is adopted to form a protruded and recessed micro structure on the central part area of the top layer of the epitaxial layer, comprising a plurality of protrusion portions606and recess portions607.

Step 3: as shown inFIG. 12, nano-imprinting process is adopted to form the dielectric layer608on the epitaxial layer602, specifically, between the top ends of two adjacent protrusion portions606, forming holes609with the recess portions607the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions; the dielectric layer608is made of SiO2or SiNxor Al2O3or TiO2or AlN or the combination of them, preferably in this embodiment made of SiO2and the refractive index between those of the epitaxial layer and the air.

Step 4: as shown inFIG. 13, the current spreading layer610in film structure and continuously distributed covers the surface of the light transmission layer608and the surface of the epitaxial layer of the non-mask dielectric layer608, and the current spreading layer is made of ITO or ZnO or CTO or InO or In doped with ZnO or Al doped with ZnO or Ga doped with ZnO, preferably made of ZnO in this embodiment.

Step 5: as shown inFIG. 14, as insulative Al2O3substrate is adopted as the substrate601in this embodiment, and electrodes on the same surface are needed, dry etching process is adopted to etch from the current spreading layer610to the first semiconductor layer603, and so part of the first semiconductor layer603platform is exposed for subsequent N electrode fabrication.

It should be noted that the exposed first semiconductor layer platform in the embodiment is formed in Step 5, yet it can be done before the forming of the current spreading layer and the etching process is not limited to dry etching, rather, wet etching is also an option.

Step 6: as shown inFIG. 15, P electrode611and N electrode612are fabricated above part of the current spreading layer610and the exposed first semiconductor layer603.

As shown inFIG. 15, the light emitting diode chip made by the above method has a structure composed of the sapphire substrate601at the bottom; the epitaxial layer602with protruded and recessed micro structure and formed on the sapphire substrate601, comprising from bottom upwards the first semiconductor layer603, the light emitting layer604and the second semiconductor layer605, and the second semiconductor layer605has a plurality of protrusion portions606and recess portions607on the surface; SiO2dielectric layer608in nano ball structure, located between the top ends of adjacent protrusion portions606and forming holes609with the recess portions607, the horizontal size of which is larger than the width of the top ends of two adjacent protrusion portions606, adjacent dielectric layers608distributed periodically and contacting with each other; ZnO current spreading layer111with a thin film structure in continuous distribution, covering the surface of the dielectric layer608and the surface of the epitaxial layer102of the non-mask dielectric layer608; P electrode611, formed on part of the current spreading layer610, and vertically corresponding to the dielectric layer608; and N electrode612, formed above the exposed first semiconductor layer603.

As shown in the light path inFIG. 15, by utilizing that the refractive index of the dielectric layer vertically under P electrode is between those of the epitaxial layer and the hole, indicating a difference of refractive index between the dielectric layer and the epitaxial layer, the light emitting diode chip structure as abovementioned can increase the probability of scattering generated when the light rays from a luminescent layer emits upwards, thus avoiding the absorption of light by electrode and further improving light extraction efficiency. In addition, metal film as a reflecting layer is not needed, cutting production cost. As the dielectric layer is placed between the top ends of two adjacent protrusion portions and forms with the recessed part a hole structure, the hole functions as a current blocking layer, and further, the dielectric layer itself can also block the current, and the combination of the hole and the dielectric layer will greatly eliminate current accumulation under the chip electrode.

As shown inFIG. 16, different from Embodiment 6, the diffusing materials doped in the dielectric layer708in this embodiment further enhance the diffusion effect of the dielectric layer. As the dielectric layer708doped with diffusing materials also functions as the blocking layer and the reflecting layer, the combined structure of the dielectric layer708with the hole709further raises the blocking and reflection effect under the P electrode in the vertical direction, thus improving the uniformity of current distribution and increasing light extraction efficiency to the greatest extent.

As shown inFIG. 17, different from Embodiment 6, this embodiment discloses a light emitting diode chip with a vertical structure. In this embodiment, Cu substrate is adopted as the thermal dissipation substrate801, N electrode812is formed on the back of the thermal dissipation substrate801, forming an LED apparatus with a vertical structure. The light path of this embodiment is similar to that shown inFIG. 15, so details are not provided here.