LIGHT-EMITTING DEVICE
A light-emitting device includes: a light-emitting stack formed on a first conductivity type contact layer and including an active layer and a second conductivity type semiconductor layer on the active layer; a first trench dividing the light-emitting stack into a first portion and a second portion, wherein the first trench includes a bottom exposing a top surface of the first conductivity type contact layer; a non-conductive material layer formed in the first trench and being a film conformal to a profile of the first trench; a connecting layer formed in the first trench and electrically connecting the first and the second portions of the light-emitting stack, wherein the connecting layer is a film conformal to a profile of the non-conductive material layer; and a first electrode formed on the first conductivity type contact layer and electrically connected to the first conductivity type semiconductor layer.
This application a continuation application of U.S. patent application Ser. No. 13/614,405, entitled “LIGHT-EMITTING DEVICE”, filed on Sep. 13, 2012, which is incorporated by reference herein in its entirety.
TECHNICAL FIELDThe application relates to a light-emitting device, in particular to a light-emitting diode with uniform light emission.
DESCRIPTION OF BACKGROUND ARTA light-emitting diode (LED) is known for its high energy efficiency and is introduced to various fields of use. The theory for a light-emitting diode (LED) to emit light is that when a forward voltage power is applied to a p-n junction, the electrons are driven from the n-type semiconductor and the holes are driven from the p-type semiconductor, and these carriers are combined in the active layer to emit light. The efficiency of an LED depends on the combination rate of the electrons from the n-type semiconductor and the holes from the p-type semiconductor. However, due to the poor current spreading, especially in the p-type semiconductor, the efficiency is reduced. An electrode with an extending part such as a finger-type electrode is commonly used to improve the poor current spreading. In addition, a transparent conductive layer is disposed between the finger-type electrode and the p-type semiconductor as an ohmic contact layer to improve the current spreading.
To solve the problem described above, a conventional light-emitting diode with the finger-type p-electrode shown in
As illustrated in
A light-emitting device is disclosed and comprises: a substrate; a first conductivity type contact layer on the substrate; a light-emitting stack on the first conductivity type contact layer, comprising an active layer and a second conductivity type semiconductor layer on the active layer; a first trench dividing the light-emitting stack into a first portion and a second portion, wherein each of the first portion and the second portion comprises a portion of the active layer and a portion of the second conductivity type semiconductor layer and the first trench comprises a bottom exposing a top surface of the first conductivity type contact layer; a non-conductive material layer formed in the first trench and being a film conformal to a profile of the first trench; a connecting layer formed in the first trench and electrically connecting the first and the second portions of the light-emitting stack, where in the connecting layer is a film conformal to a profile of the non-conductive material layer; and a first electrode formed on the first conductivity type contact layer and electrically connected to the first conductivity type semiconductor layer.
The conductive structure 320 comprises a transparent conductive layer 321 of a first conductive material over the light-emitting stack 310, and a connecting layer 322 of a second conductive material. The transparent conductive layer 321 comprises a first block 321a and a second block 321b which is adjacent to but separated from the first block 321a by a first trench 307. That is, the first trench 307 divides the transparent conductive layer 321 into the first block 321a and the second block 321b. The first trench 307 may be formed by an etching process to remove the part between the first block 321a and the second block 321b of the transparent conductive layer 321. In this embodiment, a non-conductive material such as SiNx, SiOx, and SOG is further provided and fills the first trench 307. In this embodiment, the transparent conductive layer 321 may comprise a transparent conductive oxide layer, for example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), ZTO (Zinc Tin Oxide), AZO (Al-doped ZnO), GZO (Ga-doped ZnO), IGZO (Indium Gallium Zinc Oxide), CTO (Cadmium Stannate, Cd2SnO4), ZTO (Zinc Stannate, Zn2SnO4), and CIO (Cadmium Indate, CdIn2O4).
The connecting layer 322 over the transparent conductive layer 321 comprises a second conductive material and electrically connects the two blocks 321a and 321b of the transparent conductive layer 321. The second conductive material comprises conductivity which is different from that of first conductive material of the transparent conductive layer 321. Preferably, the second conductive material comprises conductivity greater than that of the first conductive material. For example, in this embodiment the connecting layer 322 may comprises a metal material, or metal alloy or a mixture thereof. The metal material may comprise copper (Cu), aluminum (Al), indium (In), tin (Sn), gold (Au), platinum (Pt), zinc (Zn), silver (Ag), titanium (Ti), lead (Pb), palladium (Pd), germanium (Ge), nickel (Ni), chromium (Cr), cadmium (Cd), and cobalt (Co). The first block 321a and the second block 321b of the transparent conductive layer 321 are electrically connected by the connecting layer 322 so that the first block 321a, the second block 321b, and the connecting layer 322 form a first current path.
The first conductivity type contact layer 311 is disposed between the substrate 300 and the first conductivity type semiconductor layer 301. The conductivity of the first conductivity type contact layer 311 is different from the conductivity of the first conductivity type semiconductor layer 301. In this embodiment, the conductivity of the first conductivity type contact layer 311 is greater than the conductivity of the first conductivity type semiconductor layer 301. For example, the conductivity of the first conductivity type contact layer 311 comprises the same material as that of the first conductivity type semiconductor layer 301, but has a higher impurity doping level than that of the first conductivity type semiconductor layer 301. In this embodiment, the first conductivity type semiconductor layer 301 is doped to a concentration of about 5×1017(atoms/cm3), while the first conductivity type contact layer 311 is doped to a concentration of about 5×1018(atoms/cm3). The first electrode 305 is electrically connected to the first conductivity type contact layer 311 to be electrically connected to the first conductivity type semiconductor layer 301, and the second electrode 306 is electrically connected to the conductive structure 320, or more specifically to the second block 321b of the transparent conductive layer 321 to be electrically connected to the second conductivity type semiconductor layer 303. The second electrode 306 may be formed simultaneously with the connecting layer 322. That is, the second electrode 306 comprises the second conductive material.
The resistance for each part of the light-emitting device 30 is shown by a resistor. For example, the resistance for a portion of the first conductivity type contact layer 311 which is substantially under the first block 321a is indicated by a resistor Rc, and the resistance for a portion of the first conductivity type contact layer 311 which is substantially under the second block 321b is indicated by a resistor Rd. The equivalent resistance model of the light-emitting device 30 is therefore shown as
The first block 321a, the second block 321b, and the connecting layer 322 form a resistor R1 (and R1=Ra+Rt+Rb) serially connected with the diode D1 and the second electrode 306. The second block 321b forms a resistor R2(=Rb) serially connected with the diode D2 and the second electrode 306. A resistor R3(=Rc) is serially connected with the diode D1 and the first electrode 305. In addition, as the first electrode 305 does not comprise any extending electrode, for the diode D2, the current flows through substantially the whole first conductivity type contact layer 311 (with a resistance Rc+Rd) before entering the first electrode 305. That is, a resistor R4(=Rc+Rd) is substantially in serial connection with the diode D2 and the first electrode 305. When the total serial resistance for the respective current paths through the two diodes D1 and D2 are compared, obviously, the resistor R1(=Ra+Rt+Rb) for the current path through the diode D1 is larger than the resistor R2(=Rb) for the current path through the diode D2. However, the resistor R3(=Rc) for the current path through the diode D1 is smaller than the resistor R4(=Rc+Rd) for the current path through the diode D2. The person of ordinary skill in the art therefore can modify the structure of the light-emitting device 30 so that the respective total serial resistances for the two current paths through the diodes D1 and D2 are substantially the same. Because the two diodes D1 and D2 form two light-emitting diodes in parallel connection between the first electrode 305 and the second electrode 306, a current flow through the diode D1 is substantially equal to that through the diode D2, that is, a current flow through the portion of the light-emitting stack 310 which is substantially under the first block 321a is substantially equal to a current flow through the portion of the light-emitting stack 310 substantially under the second block 321b. This solves the current crowding problem and brings a uniform light emission and high luminous efficiency. The modification of the structure of the light-emitting device 30 can be, for example, through the selection of the materials or the dimensions of the first block 321a, the second block 321b, and the connecting layer 322.
As the above illustration, this embodiment is useful to solve the current crowding problem when the light-emitting device comprises a rectangular shape from the top view, and especially useful when the first electrode is disposed substantially at one end along the longitudinal direction of the rectangle, as shown in
For a light-emitting device comprising a longer rectangle, that is, a rectangle with a higher ratio of the length to the width, the above first embodiment can be employed by analogy to divide the transparent conductive layer 321 into more blocks, and the whole light-emitting stack 310 is divided into more than two portions to form more diodes in the equivalent circuit model, wherein each of which constitutes a current path between the two electrodes.
The element corresponding to the same element in
Though the embodiments described above are illustrated by a horizontal type LED and specific materials, it will be apparent that other alternatives, modifications and materials may be made to the embodiments without escaping the spirit and scope of the application.
Claims
1. A light-emitting device, comprising:
- a substrate;
- a first conductivity type contact layer on the substrate;
- a light-emitting stack on the first conductivity type contact layer, comprising an active layer and a second conductivity type semiconductor layer on the active layer;
- a first trench dividing the light-emitting stack into a first portion and a second portion, wherein each of the first portion and the second portion comprises a portion of the active layer and a portion of the second conductivity type semiconductor layer and the first trench comprises a bottom exposing a top surface of the first conductivity type contact layer;
- a non-conductive material layer formed in the first trench and being a film conformal to a profile of the first trench;
- a connecting layer formed in the first trench and electrically connecting the first and the second portions of the light-emitting stack, where in the connecting layer is a film conformal to a profile of the non-conductive material layer; and
- a first electrode formed on the first conductivity type contact layer and electrically connected to the first conductivity type semiconductor layer.
2. The light-emitting device as claimed in claim 1, further comprising a transparent conductive layer on the light-emitting stack.
3. The light-emitting device as claimed in claim 2, further comprising a second trench dividing the transparent conductive layer into a first block and a second block.
4. The light-emitting device as claimed in claim 3, wherein the non-conductive material layer is conformal to a profile of the second trench.
5. The light-emitting device as claimed in claim 3, wherein the connecting layer contacts the first block and the second block.
6. The light-emitting device as claimed in claim 1, further comprising a first conductivity type semiconductor layer between the first conductivity type contact layer and the active layer, and the first conductivity type contact layer comprises the same material as that of the first conductivity type semiconductor layer.
7. The light-emitting device as claimed in claim 6, wherein the first conductivity type contact layer has a higher doping level than that of the first conductivity type semiconductor layer.
8. The light-emitting device as claimed in claim 1, wherein the connecting layer comprises a first segment between the first portion and the second portion and a secondary segment on one of the first portion and the second portion.
9. The light-emitting device as claimed in claim 8, wherein a shape of the secondary segment comprises a curve.
10. The light-emitting device as claimed in claim 1, wherein a shape of the light-emitting device from its top view is a rectangle having a longitudinal direction, and the first electrode is disposed near one end of the longitudinal direction of the rectangle.
11. The light-emitting device as claimed in claim 10, wherein a ratio of a length to a width of the rectangle is not smaller than 2.
12. The light-emitting device as claimed in claim 6, wherein the first conductivity type contact layer is exposed by the first trench.
13. The light-emitting device as claimed in claim 1, further comprising a second electrode on one of the first portion and the second portion.
14. The light-emitting device as claimed in claim 13, wherein the second electrode comprises the same material as that of the connecting layer.
15. The light-emitting device as claimed in claim 1, wherein a first current flow through the first portion is equal to a second current flow through the second portion when driving the light-emitting device.
16. The light-emitting device as claimed in claim 2, wherein the conductivity of the connecting layer is larger than the conductivity of the transparent conductive layer.
17. The light-emitting device as claimed in claim 3, wherein a shape of the first trench and a shape of the second trench in a cross section of the light-emitting device are different.
18. The light-emitting device as claimed in claim 3, wherein the first trench comprises a first width along a horizontal direction perpendicular to a stacking direction of the first conductivity type semiconductor layer, the active layer and the second conductivity type semiconductor layer from a cross section view of the light-emitting device, and the second trench comprises a second width along the horizontal direction perpendicular to the stacking direction from the cross section view of the light-emitting device, and the second width is larger than the first width.
Type: Application
Filed: Apr 10, 2019
Publication Date: Aug 1, 2019
Inventors: Chen OU (Hsinchu), Liang-Sheng CHI (Hsinchu), Chun-WEI CHANG (Hsinchu), Chih-Wei WU (Hsinchu)
Application Number: 16/380,115