# Patent

## Title
Light-emitting device having active layers stacked alternately

## Abstract

A light-emitting device comprises a substrate, and a light-emitting structure formed on the substrate. The light-emitting structure comprises a first active layer emitting the light with a first wavelength, and a second active layer emitting the light with a second wavelength. The light-emitting structure is formed by the first active layer and the second active layer stacked alternately.

## Background
RELATED APPLICATIONS
The present application claims the right of priority based on Taiwan Patent Application No. 099142743 entitled “LIGHT-EMITTING DEVICE”, filed on Dec. 7, 2010, and is incorporated herein by reference in its entirety and assigned to the assignee herein.
TECHNICAL FIELD
The present application relates to a light-emitting device, and more particularly, to a light-emitting device having a first active layer and a second active layer stacked alternately.
BACKGROUND
Recently the light-emitting diode (LED) becomes one of the solid state lighting sources having an extremely potential due to the epitaxy and process technology progress. LED can only be driven by direct current due to physical mechanism restriction, therefore the alternating current provided directly from the power plant is transferred to the direct-current used by LED in any lighting design for LED light source. The above electronic devices for rectification and voltage adjustment increase the cost and decrease the efficiency of the alternating current transfer to direct current, not mention to its big volume. The above disadvantages can influence the reliability and life-time of the LED used in illumination application in daily life.
ACLED devices do not need the electronics devices for rectification and/or voltage adjustment and can be directly operated under alternating current, so the ACLED devices are highly possible to be the mainstream products of the solid state lighting source in stationary position in the future.
Because of the current leakage, the luminous intensity of LED drops when the temperature is increased. To alleviate the current leakage problems, the carrier concentration of the p-type confining layer is usually increased, or a material with higher level energy gap material is grown to increase the confining ability of the electrons. In most situations, the increasing degree of the carrier concentration of the p-type confining layer is limited, and when the carrier concentration of the p-type confining layer is increased, the light emitting quality is affected because the higher carrier concentration forces the p-type carrier move towards the active layer which has lower carrier concentration.
SUMMARY
A light-emitting device, comprising a substrate; and a light-emitting structure on the substrate, comprising a first active layer and a second active layer stacked alternately, wherein the light-emitting device has a first temperature coefficient when the light-emitting structure is formed by a first manufacturing process, and has a second temperature coefficient when the light-emitting structure is formed by a second manufacturing process, wherein the absolute value of the difference between the first temperature coefficient and the second temperature coefficient is smaller than 0.12%/K.



BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this application are more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
FIG. 1 is a diagram of a light-emitting structure in accordance with the first embodiment of the present application;
FIG. 2 is a diagram of a light-emitting structure in accordance with the second embodiment of the present application;
FIG. 3 is a diagram of a light-emitting structure in accordance with the third embodiment of the present application;
FIG. 4 is a diagram showing a backlight module device in accordance with the fourth embodiment of the present application; and
FIG. 5 is a diagram showing an illumination device in accordance with the fifth embodiment of the present application.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present application provides a method to grow two active layers having different wavelengths in the light-emitting structure to solve the luminous intensity of a light-emitting device decreased as the temperature increased. In light of the energy state theory, the probability of an electron occupied the lower energy level (i.e. the longer wavelength) of the active layer is higher. When the energy of an electron is increased as the temperature is increased, the probability of an electron jumping from the lower energy level to the higher energy level is increased, so a higher energy level (i.e. the shorter wavelength) of the active layer is provided for electrons to jump.
The temperature coefficient (TC) is usually referred to indicate the decreased degree of the luminous intensity of the light-emitting device as the temperature increases. The definition is described below: if the flux of a light-emitting device is f1 lm at T1 temperature, the flux is f2 lm at T2 temperature, and if the flux of the T1 temperature is normalized to 1, the flux of the T2 temperature is normalized to (f2/f1), the temperature coefficient (TC) of the light-emitting device can be indicated by the below equation, and the value is smaller than 0:

TC=((f2/f1)−1)/(T2−T1)  equation (1)

FIG. 1 shows a diagram of a light-emitting structure 12 in the epitaxial structure 100 of the light-emitting device 1 in accordance with the first embodiment of the present application, wherein the light-emitting structure 12 is between a first conductivity type semiconductor layer 11 and a second conductivity type semiconductor layer 13. In the present embodiment, the structure of the light-emitting device 1 comprises a growth substrate (not shown in the figure), a first conductivity type semiconductor layer 11, a light-emitting structure 12, and a second conductivity type semiconductor layer 13 on the growth substrate formed in sequence. The material of the growth substrate can be gallium arsenic, sapphire, silicon carbide, gallium nitride, aluminum nitride, silicon, and germanium. The light-emitting structure 12 is formed by a first active layer 100a and a second active layer 100b stacked alternately, wherein the first active layer 100a is a quantum well structure and can emit a first light-emitting wavelength λ1, the second active layer 100b is a quantum well structure and can emit a second light-emitting wavelength λ2. The λ1 is larger than the λ2. The light-emitting structure is formed by an III-V group semiconductor material, wherein the material of the III-V group semiconductor can be AlGaInP series compound, AlGaInN series compound, or a combination of the two compounds.
Concluding from many experiment data, the light-emitting structure 12 is formed by the first active layer 100a and the second active layer 100b stacked alternately, and when the total layers of the first active layer 100a and the second active layer 100b is 23n (n is an integer number greater than 0) with d layers of the second active layer 100b interlaced between every two of the first active layers 100a (4n≦d≦10n), the absolute value of the difference of the measured temperature coefficients of the light-emitting devices 1 having the light-emitting structures 12 formed by different manufacturing processes is smaller than 0.12%/K. One reason is when there are too many layers of the first active layer 100a which can emit the longer first wavelength λ1, the electrons do not necessarily fill up the whole energy level positions so the distribution of the electrons is not uniform; when there are too few layer, the energy level positions for electron occupation is not enough.
In the present embodiment, the first active layer 100a can emit the light with a wavelength of 610 nm, the second active layer 100b can emit the light with a wavelength of 600 nm, and the total layers of the first active layer 100a and the second active layer 100b is 23 (n=1) with d layers of the second active layer 100b interlaced between every two of the first active layers 100a (4≦d≦10). For example, the light-emitting structure 12 is formed by one layer of the first active layer 100a/seven layers of the second active layer 100b/one layer of the first active layer 100a/seven layers of the second active layer 100b/one layer of the first active layer 100a/six layers of the second active layer 100b stacked in sequence. The measured flux is 155.7 lm at 25° C., and the measured flux is 81.6 lm at 100° C. for the light-emitting device 1 comprising the light-emitting structure 12 formed by a first manufacturing process. The first temperature coefficient (TC1) calculated by the equation (1) is −0.65%/K. The measured flux is 1445 lm at 25° C., and the measured flux is 636 lm at 100° C. for the light-emitting device 1 formed by a second manufacturing process. The second temperature coefficient (TC2) calculated by the equation (1) is −0.75%/K. The absolute value of the difference between the first temperature coefficient (TC1) and the second temperature coefficient (TC2) is 0.1%/K. The first manufacturing process and the second manufacturing process comprise different parameters, manufacture conditions of the exposure, developing, etching, evaporation, polish, and cutting, and so on. It is found that in the present embodiment the temperature coefficient of light-emitting structure formed by two active layers with different light-emitting wavelengths stacked alternately is not affected by the manufacturing processes, which means the electrons can distribute uniformly in the light-emitting structure of the light-emitting device.
FIG. 2 shows a diagram of a light-emitting structure 12 in the epitaxial structure 200 of the light-emitting device 1 in accordance with the second embodiment of the present application, wherein the light-emitting structure 12 is between a first conductivity type semiconductor layer 11 and a second conductivity type semiconductor layer 13. In the present embodiment, the light-emitting structure 12 is formed by a first active layer 100a and a second active layer 100b stacked alternately, wherein the first active layer 100a is a quantum well structure and can emit a first light-emitting wavelength λ1, the second active layer 100b is a quantum well structure and can emit a second light-emitting wavelength λ2. The λ1 is larger than the λ2. The light-emitting structure is formed by an III-V group semiconductor material, wherein the material of the III-V group semiconductor can be AlGaInP series compound, AlGaInN series compound, or a combination of the two compounds.
In the present embodiment, the first active layer 100a can emit the light with a wavelength of 610 nm, the second active layer 100b can emit the light with a wavelength of 600 nm, and the total layers of the first active layer 100a and the second active layer 100b is 23 (n=1) with d layers of the second active layer 100b interlaced between every two of the first active layers 100a (4≦d≦10). For example, the light-emitting structure 12 is formed by one layer of the first active layer 100a/ten layers of the second active layer 100b/one layer of the first active layer 100a/ten layers of the second active layer 100b/one layer of the first active layer 100a stacked in sequence. The measured flux is 139.1 lm at 25° C., and the measured flux is 72.4 lm at 100° C. for the light-emitting device 1 comprising the light-emitting structure 12 formed by a first manufacturing process. The first temperature coefficient (TC1) calculated by the equation (1) is −0.66%/K. The measured flux is 1477.4 lm at 25° C., and the measured flux is 624.8 lm at 100° C. for the light-emitting device 1 formed by a second manufacturing process. The second temperature coefficient (TC2) calculated by the equation (1) is −0.77%/K. The absolute value of the difference between the first temperature coefficient (TC1) and the second temperature coefficient (TC2) is 0.11%/K. The first manufacturing process and the second manufacturing process comprise different parameters, manufacture conditions of the exposure, developing, etching, evaporation, polish, and cutting, and so on. It is found in the present embodiment that the temperature coefficient of light-emitting structure formed by two different wavelength active layers stacked alternately is not affected by the manufacturing process even the stacked layers of the two active layers are different, which means the electrons can distribute uniformly in the light-emitting structure of the light-emitting device.
FIG. 3 shows a diagram of a light-emitting structure 12 in the epitaxial structure 300 of the light-emitting device 1 in accordance with the third embodiment of the present application, wherein the light-emitting structure 12 is between a first conductivity type semiconductor layer 11 and a second conductivity type semiconductor layer 13. In the present embodiment, the light-emitting structure 12 is formed by a first active layer 100a and a second active layer 100b stacked alternately, wherein the first active layer 100a is a quantum well structure and can emit a first light-emitting wavelength λ1, the second active layer 100b is a quantum well structure and can emit a second light-emitting wavelength λ2, and the λ1 is larger than the λ2. The light-emitting structure is formed by an III-V group semiconductor material, wherein the material of the III-V group semiconductor can be AlGaInP series compound, AlGaInN series compound, or a combination of the two compounds.
In the present embodiment, the first active layer 100a can emit the light with a wavelength of 610 nm, the second active layer 100b can emit the light with a wavelength of 600 nm, and the total layers of the first active layer 100a and the second active layer 100b is 23 (n=1) with d layers of the second active layer 100b interlaced between every two of the first active layers 100a (4≦d≦10). For example, the light-emitting structure 12 is formed by one layer of the first active layer 100a/five layers of the second active layer 100b/one layer of the first active layer 100a/five layers of the second active layer 100b/one layer of the first active layer 100a/five layers of the second active layer 100b/one layer of the first active layer 100a/four layers of the second active layer 100b stacked in sequence. The measured flux is 134.1 lm at 25° C., and the measured flux is 67.3 lm at 100° C. for the light-emitting device 1 comprising the light-emitting structure 12 formed by a first manufacturing process. The first temperature coefficient (TC1) calculated by the equation (1) is −0.68%/K. The measured flux is 1343.5 lm at 25° C., and the measured flux is 646.4 lm at 100° C. for the light-emitting device 1 formed by a second manufacturing process. The second temperature coefficient (TC2) calculated by the equation (1) is −0.69%/K. The absolute value of the difference between the first temperature coefficient (TC1) and the second temperature coefficient (TC2) is 0.01%/K. The first manufacturing process and the second manufacturing process comprise different parameters, manufacture conditions of the exposure, developing, etching, evaporation, polish, and cutting, and so on. It is found in the present embodiment that the temperature coefficient of light-emitting structure formed by two active layers with emitting different light-emitting wavelength stacked alternately is not affected by the manufacturing process even the stacked layers of the two active layers are different, which means the electrons can distribute uniformly in the light-emitting structure of the light-emitting device.
FIG. 4 shows a backlight module device 400 in accordance with the fourth embodiment of the present application. The backlight module device 400 comprises a light source device 410 having the light-emitting device 1 in one of the above mentioned embodiments, an optics device 420 deposited on the light extraction pathway of the light source device 410, and a power supply system 430 which provides a predetermined power to the light source device 410.
FIG. 5 shows an illumination device 500 in accordance with the fifth embodiment of the present application. The illumination device 500 can be automobile lamps, street lights, flashlights, indicator lights and so forth. The illumination device 500 comprises a light source device 510 having the light-emitting device 1 in one of the above mentioned embodiments, a power supply system 520 which provides a predetermined power to the light source device 410, and a control element 530 which controls the current driven into the light source device 510.
As is understood by a person skilled in the art, the foregoing preferred embodiments of the present application are illustrated of the present application rather than limiting of the present application. It is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.

## Claims

1. A light-emitting device, comprising:
a substrate;
a first conductivity type semiconductor layer on the substrate;
a light-emitting structure on the first conductivity type semiconductor layer, comprising:
a plurality of first active layers, each of first active layers having a quantum well structure and emitting a light with a first light-emitting wavelength; and
a plurality of second active layers, each of second active layers having a quantum well structure and emitting a light with a second light-emitting wavelength; and

a second conductivity type semiconductor layer on the light-emitting structure,
wherein the first active layers and the second active layers are stacked alternately, and wherein the first light-emitting wavelength is larger than the second light-emitting wavelength
wherein the first active layer is a single layer, and the second active layer comprises multiple layers, and
wherein the first light-emitting wavelength is the same for each of the first active layers and the second light-emitting wavelength is the same for each of the second active layers.

2. The light-emitting device according to claim 1, wherein a number of the total layers of the first active layers and the second active layers is 23n, wherein n is an integer number greater than 0.

3. The light-emitting device according to claim 2, wherein d layers of the second active layers are disposed between every two layers of the first active layers, wherein 4n≦d≦10n.

4. The light-emitting device according to claim 1, wherein the substrate comprises gallium arsenic.

5. The light-emitting device according to claim 1, wherein a material of the light-emitting structure can be AlGaInP series compound, AlGaInN series compound, or a combination of the two compounds.

6. A backlight module device, comprising:
a light source device having a light-emitting device made according to claim 1;
an optics device deposited on a light extraction pathway of the light source device; and
a power supply system to provide a predetermined power to the light source device.

7. An illumination device, comprising:
a light source device having a light-emitting device made according to claim 1;
a power supply system to provide a predetermined power of the light source device; and
a control element to control the current driven into the light source device.

8. The light-emitting device according to claim 1, wherein the substrate comprises sapphire.

9. The light-emitting device according to claim 1, wherein the substrate comprises silicon carbide.

10. The light-emitting device according to claim 1, wherein the substrate comprises gallium nitride.

11. The light-emitting device according to claim 1, wherein the substrate comprises aluminum nitride.

12. The light-emitting device according to claim 1, wherein the substrate comprises silicon.