Light-emitting devices

Abstract

Light emitting device (1) comprising: a carrier (20); a first semiconductor structure (11a) formed on the carrier (20) with a first active layer (112); a second semiconductor structure (15a) having a second active layer (152) formed between the carrier (20) and the first semiconductor structure (11a); a tunnel junction (14) formed between the first semiconductor structure (11a) and the second semiconductor structure (15a); a lower electrode (22) arranged on a rear side of the carrier (20) and electrically connected to the first semiconductor structure (11a) and the second semiconductor structure (15a); and a third upper electrode (16) on an upper surface (15s) of the second semiconductor structure (15a); wherein the first active layer (112) is configured to emit a first light having a first dominant wavelength during normal operation, wherein a diode character of the second semiconductor structure (15a) is permanently broken as a result of a reverse bias at the third upper electrode (16) and the lower electrode (22), so that the second active layer (152) does not emit light during normal operation.

Description

Technical area

[0001] The disclosure relates to light emitting devices. Description of the state of the art

[0002] A light-emitting diode (LED) is widely used as a semiconductor lighting source. The light-emitting diode (LED) generally comprises a p-type semiconductor layer, an n-type semiconductor layer, and an active layer between the p-type semiconductor layer and the n-type semiconductor layer for emitting light. The principle of an LED is to convert electrical energy into optical energy by applying an electric current to the LED and injecting electrons and holes into the active layer. The combination of electrons and holes in the active layer consequently emits light.

[0003] Other relevant light emitting devices are described in HAN, J. [et al.]: Advances in AIGaInN Blue and Ultraviolet Light Emitters, published in IEEE Journal on Selected Topic in Quantum Electronics, Vol. 8, 2002, No. 2, pp. 289-297, US 5 999 553 A, JP H10- 256 597 A and US 2012 / 0 025 237 A1.

[0004] Compared to the prior art, the present invention solves the problem of providing light-emitting devices in which electrically segmented multi-wavelengths above other wavelengths can be emitted using more favorable manufacturing processes. Summary of Revelation

[0005] This object is achieved by light-emitting devices according to the independent claims. Preferred embodiments are specified in the respective dependent claims. Brief description of the drawings Fig. 1A-1D show a process flow of a manufacturing method of a light emitting device according to an embodiment of the present disclosure; Fig. 2 shows a sectional view of a light emitting device according to a first embodiment of the present disclosure; and Fig. 3 shows a sectional view of a light emitting device according to a second embodiment of the present disclosure. Detailed description of the present disclosure

[0006] Fig. 1A-1D show a process flow of a method for manufacturing a light-emitting device 1 according to an embodiment of the present disclosure. As in Fig. As shown in Figure 1A, the method for manufacturing the light-emitting device 1 includes a step of epitaxially growing a first semiconductor stack 11 on a growth substrate 10 by an epitaxial growth method such as a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, or a hydride vapor phase epitaxy (HVPE) method. The growth substrate 10 comprises a single crystal material having a single crystal plane on which the first semiconductor stack 11 can be epitaxially grown, wherein the single crystal plane includes a sapphire C plane, a sapphire R plane, or a sapphire A plane. In another example, the growth substrate 10 comprises a metal oxide or a semiconductor material such as silicon carbide (SiC), silicon, ZnO, GaAs, or GaN.The first semiconductor stack 11 includes a first semiconductor layer 111 having a first conductivity type, a second semiconductor layer 113 having a second conductivity type different from the first conductivity type, and a first active layer 112 formed between the first semiconductor layer 111 and the second semiconductor layer 113. The first active layer 112 includes a single heterostructure (SH), a double heterostructure (DH), or a multiple quantum well (MQW) structure. In one embodiment, the first semiconductor layer 111 is an n-type semiconductor layer for providing electrons, and the second semiconductor layer 113 is a p-type semiconductor layer for providing holes. Holes and electrons combine in the first active layer 112 to emit light under a drive current.Alternatively, the first semiconductor layer 111 may be a p-type semiconductor layer, and the second semiconductor layer 113 may be an n-type semiconductor layer. The material of the first active layer 112 comprises In. x Ga y Al 1-x-y )N for emitting light with a dominant wavelength in the ultraviolet to green spectral range, In x Ga y Al (1-x-y) P for emitting light with a dominant wavelength in the yellow to red spectral range or In x Ga y Al (1-x-y) As for emitting light with a dominant wavelength in the infrared spectral range.

[0007] Next, the method includes a step of epitaxially growing a reflective layer 13 on the first semiconductor stack 11. The reflective layer 13 comprises a DBR structure and a group III-V semiconductor material. The reflective layer 13 has a conductivity type that is the same as that of the second semiconductor layer 113 of the first semiconductor stack 11. Next, a tunnel junction 14 comprising a group III-V semiconductor material is epitaxially grown on the first semiconductor stack 11. The tunnel junction 14 includes a pn junction formed by a first heavily doped layer of a first conductivity type, for example, an n-type conductive semiconductor layer, and a second heavily doped layer of a second conductivity type, for example, a p-type semiconductor layer.The heavily doped n-type conductive semiconductor layer and the heavily doped p-type layer have a doping concentration that is at least one order of magnitude higher than that of the semiconductor layers of the first semiconductor stack 11. These heavily doped layers of the tunnel junction 14 are preferably provided with a doping concentration greater than 10. 18 / cm 3doped, thus creating a low electrical contact resistance during operation. The low-resistance tunnel junction 14 is provided to be an electrical junction between the first semiconductor structure 11a and another semiconductor structure deposited thereon in the subsequent process. A side of the tunnel junction 14 adjacent to the second semiconductor layer 113 or the reflective layer 13 comprises a conductivity type the same as that of the second semiconductor layer 113 or the reflective layer 13. An opposite side of the tunnel junction 14, remote from the second semiconductor layer 113 or the reflective layer 13, comprises a conductivity type opposite to that of the second semiconductor layer 113 or the reflective layer 13.

[0008] Then, an etch stop layer 23 is epitaxially grown on the first semiconductor stack 11. Next, a second semiconductor stack 15 is epitaxially grown on the etch stop layer 23 by an epitaxial growth method such as a metal organic chemical vapor deposition (MOXVD) method, a molecular beam epitaxy (MBE) method, or a hydride vapor phase epitaxy (HVPE) method. The second semiconductor stack 15 includes a third semiconductor layer 151 having a first conductivity type, a fourth semiconductor layer 153 having a second conductivity type different from the first conductivity type, and a second active layer 152 formed between the third semiconductor layer 151 and the fourth semiconductor layer 153. The second active layer 152 includes a single heterostructure (SH), a double heterostructure (DH), or a multiple quantum well (MQW) structure.In one embodiment, the third semiconductor layer 151 is an n-type semiconductor layer for providing electrons, and the fourth semiconductor layer 153 is a p-type semiconductor layer for providing holes. Holes and electrons combine in the second active layer 152 to emit light under a drive current. Alternatively, the third semiconductor layer 151 may be a p-type semiconductor layer, and the fourth semiconductor layer 153 may be an n-type semiconductor layer. The material of the second active layer 152 comprises In. x Ga y Al (1-x-y) N to emit light with a dominant wavelength in the ultraviolet to green spectral range, In x Ga y Al (1-x-y) P for emitting light with a dominant wavelength in the yellow to red spectral range or In x Ga y Al (1-x-y)As for emitting light with a dominant wavelength in the infrared spectral range.

[0009] The first semiconductor stack 11, the reflection layer 13, the tunnel junction 14, the etch stop layer 23 and the second semiconductor stack 15 are continuously deposited on the grown substrate in an epitaxial chamber to prevent them from being contaminated and to ensure high quality of the semiconductor layers thus stacked.

[0010] As in Fig. 1B, the method for manufacturing the light-emitting device 1 further includes a bonding step of reversely mounting the multilayer structure formed by the above steps to a carrier 20 by bonding the fourth semiconductor layer 153 of the second semiconductor stack 15 to the carrier 20 through an adhesive layer 21 and a thermal pressing process, wherein the carrier 20 includes a first region and a second region adjacent to the first region. The bonding layer is made of an adhesive material. A material of the carrier 20 and the adhesive layer 21 includes a conductive material such as metal or solder. In a variant of the embodiment, the carrier 20 includes a thermally conductive material or an insulating material. Next, the growth substrate 10 is removed after the fourth semiconductor layer 153 of the second semiconductor stack 15 is bonded to the carrier 20.

[0011] As in Fig. 1C, the method for manufacturing the light-emitting device 1 further includes forming a patterned mask (not shown) on the first semiconductor stack 11 by a photolithographic process and etching the first semiconductor stack 11 over the second region of the carrier, such as a portion of the first semiconductor stack 11, the reflective layer 13, and the tunnel junction 14 not covered by the patterned mask, by chemical wet etching or dry etching to expose the etch stop layer 23 while maintaining the first semiconductor stack 11 over the first region of the carrier 20. The etch stop layer 23 is formed of a group III-V material, such as InGaP, at a relatively lower etch rate than the first semiconductor stack 11 in the etching step.The portion of the first semiconductor stack 11 covered with the patterned mask is retained on the second semiconductor stack 15 to form a first semiconductor structure 11a.

[0012] As in Fig. 1D, the method of manufacturing the light-emitting device 1 further comprises forming a groove 30 through the exposed etch stop layer 23 and the second semiconductor stack 15. The groove 30 divides the second semiconductor stack 15 into a second semiconductor structure 15a and a third semiconductor structure 15b, wherein the second semiconductor structure 15a is formed between the carrier 20 and the first semiconductor structure 11a, and the third semiconductor structure 15b is formed above the carrier 20 and is spaced from the second semiconductor structure 15a.

[0013] As in Fig. 2 or Fig. Next, as shown in Figure 3, a lower electrode 22 is disposed on the back side of the carrier 20 so that it is electrically connected to each of the first semiconductor structure 11a, the second semiconductor structure 15a, and the third semiconductor structure 15b. A first upper electrode 17 and a second upper electrode 18 are formed on the front side of the first semiconductor structure 11a and the front side of the third semiconductor structure 15b, respectively.

[0014] Next, alternative examples of the method for manufacturing the light emitting device 1 in Fig. 2 or Fig. 3 shown.

[0015] See Fig. 2 for a first example of the method for manufacturing the light-emitting device 1. The method further comprises forming a third upper electrode 16 on an exposed surface 15s of the second semiconductor structure 15a and applying an electric current across the third upper electrode 16 and the lower electrode 22 to break the diode nature of the second semiconductor structure 15a. In particular, a reverse bias voltage is applied across the third upper electrode 16 and the lower electrode 22 to permanently break the diode nature of the second semiconductor structure 15a, so that the second active layer 152 of the second semiconductor structure 15a is unable to emit light. In particular, an electric current in the range of 80 A / cm 2 up to 200 A / cm 2into the second semiconductor structure 15a for a period of between 0.1 and 0.5 seconds across the third upper electrode 16 and the lower electrode 22 to break the diode behavior of the second semiconductor structure 15a. Consequently, the second semiconductor structure 15a becomes and functions as a resistor with a resistance value lower than 200 ohms, preferably lower than 100 ohms, more preferably lower than 10 ohms, and therefore the second MQW structure of the second active layer 152 of the second semiconductor structure 15a is substantially non-luminous, even when the second semiconductor structure 15a is forward biased. After completing all the process steps described above, the light-emitting device 1 of the first embodiment of the present disclosure is formed as shown in Fig. 2 shown.

[0016] See Fig. 3 for a second example of the method for manufacturing the light-emitting device 1. The method further comprises forming a third upper electrode 16 directly on an upper surface 15s and a side surface 15s' of the second semiconductor structure 15a to short-circuit the second semiconductor structure 15a, and therefore, a drive current between the first upper surface 17 and the lower electrode 22 bypasses the second active layer 152 of the second semiconductor structure 15a to render the second active layer 152 of the second semiconductor structure 15a incapable of emitting light during normal operation. After completing all the process steps described above, the light-emitting device 1 of the second embodiment of the present disclosure is formed as shown in Fig. 3 shown.

[0017] The first upper electrode 17, the second upper electrode 18, the lower electrode 22, and the third upper electrode 16 comprise a metal material with low electrical resistance, such as Au, Al, Pt, Cr, Ti, Ni, W, or the combination thereof, and can be formed from a monolayer or multiple layers. A thickness of the first upper electrode 17, the second upper electrode 18, the lower electrode 22, or the third upper electrode 16 is about 0.1 to 10 micrometers. The first upper electrode 17 and the second upper electrode 18 each have a shape such as a rectangle, polygon, circle, or ellipse from a plan view of the light-emitting device 1. The first upper electrode 17, the second upper electrode 18, the lower electrode 22, and the third upper electrode 16 can be formed by sputtering, vapor deposition, or plating.

[0018] Fig. 2 shows a sectional view of the light-emitting device 1 according to the first embodiment of the present disclosure. The light-emitting device 1 includes a first light-emitting element 1a and a second light-emitting element 1b. The first light-emitting element 1a includes the first semiconductor structure 11a and the second semiconductor structure 15a, and the second light-emitting element 1b includes the third semiconductor structure 15b. The first light-emitting element 1a and the second light-emitting element 1b are both formed on the carrier 20. The first light-emitting element 1a includes the first semiconductor structure 11a and the second semiconductor structure 15a formed between the first semiconductor structure 11a and the carrier 20.The first active layer 112 of the first semiconductor structure 11a of the first light-emitting element 1a comprises an MQW structure that is driven by the first upper electrode 17 and the lower electrode 22 to emit light having a first dominant wavelength λ1. The second active layer 152 of the second semiconductor structure 15a of the first light-emitting element 1a comprises a second MQW structure that does not emit light when the first light-emitting element 1a is driven to emit light having a first dominant wavelength λ1.The second light-emitting element 1b comprises a third semiconductor structure 15b formed above the carrier 20 and adjacent to the first light-emitting element 1a, wherein the second active layer 152 of the third semiconductor structure 15b comprises a third MQW structure having the same material composition and the same layer sequence as the second MQW structure of the second semiconductor structure 15a, and the third MQW structure is controlled by the second upper electrode 18 and the lower electrode 22 to emit light having a second dominant wavelength λ2. The first MQW structure of the first semiconductor structure 11a comprises a material or a material composition that is different from that of the second MQW structure of the second semiconductor structure 15a or the third MQW structure of the third semiconductor structure 15b. The first dominant wavelength λ1 is different from the second dominant wavelength λ2.In one example of the embodiment, the first dominant wavelength λ1 is greater than the second dominant wavelength λ2. In another example of the embodiment, the first dominant wavelength λ1 is in the infrared range and the second dominant wavelength λ2 is in the red range. In another example of the embodiment, the first dominant wavelength λ1 and the second dominant wavelength λ2 are both in the red range.

[0019] The third upper electrode 16 is formed on the surface 15s of the second semiconductor structure 15a. The first upper electrode 17 and the lower electrode 22 supply a first electric current to forward-bias the first MQW structure of the first active layer 112 of the first semiconductor structure 11a to emit light having a first dominant wavelength λ1. The second upper electrode 18 and the lower electrode 22 supply a second electric current to forward-bias the third MQW structure of the second active layer 152 of the third semiconductor structure 15b to emit light having a second dominant wavelength λ2, where λ1 is different from λ2.Specifically, the first light-emitting element 1a emits only the first dominant wavelength generated in the first MQW structure under an electric current 100 flowing in series through the first MQW structure and the second MQW structure, wherein the second MQW structure of the second active layer 152 of the second semiconductor structure 15a is not luminous even when the second semiconductor structure 15a is forward biased.

[0020] Fig. 3 shows a sectional view of a light emitting device 1 according to the second embodiment of the present disclosure. Fig. 3, which are designated by the same symbols as those shown in Fig. 2 include the same structure, material and functions and will not be discussed again.

[0021] As in Fig. 3, the first semiconductor structure 11a and the second semiconductor structure 15a of the first light-emitting element 1a form a stepped shape on a surface 15s of the second semiconductor structure 15a. The third upper electrode 16 includes a contact 161 formed on the upper surface 15s of the second semiconductor structure 15a and a bridge 162 coated on a side surface 15s' of the second semiconductor structure 15a. Specifically, the third upper electrode 16 abuts the surface of the second semiconductor structure 15a. The contact 161 is disposed on the surface 15s of the second semiconductor structure 15a, and the bridge 162 extends from the contact 161 to the carrier 20 or the adhesive layer 21. The second MQW structure of the second active layer 152 of the second semiconductor structure 15a is short-circuited by the third upper electrode 16 and blocked from emitting light.The third upper electrode 16 comprises a metal material with low electrical resistance, such as Au, Al, Pt, Cr, Ti, Ni, W, or a combination thereof, and may be formed from a single layer or multiple layers. The third upper electrode 16 creates an electrical series connection between the first upper electrode 17 and the lower electrode 22. The third upper electrode 16 is formed directly on the upper surface and the side surface of the second semiconductor structure 15a to short-circuit the second semiconductor structure 15a, and therefore, a drive current between the first upper electrode 17 and the lower electrode 22 bypasses the second active layer 152 of the second semiconductor structure 15a to render the second active layer 152 of the second semiconductor structure 15a incapable of emitting light during normal operation.The first MQW structure of the first active layer 112 of the first semiconductor structure 11a is driven by the first upper electrode 17 and the lower electrode 22 to emit light having the first dominant wavelength λ1. Specifically, the first light-emitting element 1a emits only the first dominant wavelength λ1 generated in the first MQW structure under an electric current 200 flowing in series through the first MQW structure and the second MQW structure, with the second MQW structure being non-luminous.

[0022] As in Fig. 2-3, the light-emitting device 1 includes the adhesive layer 21 comprising a metal material such as Cu, Al, Pt, Ti, W, Ag, or the combination thereof. The adhesive layer 21 is formed between the first light-emitting element 1a and the support 20 and / or between the second light-emitting element 1b and the support 20 to reflect the light generated in the first active layer 112 of the first light-emitting element 1a toward the light-harvesting surface of the first light-emitting element 1a away from the support 20 and / or the light generated in the second active layer 152 of the second light-emitting element 1b toward a light-harvesting surface of the second light-emitting element 1b. In one embodiment of the present disclosure, the light-harvesting efficiency of the first light-emitting element 1a and the second light-emitting element 1b can be improved by the adhesive layer.

[0023] Furthermore, the diode nature of the second semiconductor structure 15a of the first light-emitting element 1a in the first embodiment cannot be completely broken, or the short circuit formed by the third upper electrode 16 (contact 161 and bridge 162) in the second embodiment cannot completely block the electric current flowing through the second active layer 152 of the second semiconductor structure 15a of the first light-emitting element 1a. Some dark light with weak optical output may be generated and emitted from the second active layer 152 of the second semiconductor structure 15a of the first light-emitting element 1a. Consequently, the reflection layer 13 is formed between the first semiconductor layer 151 of the second semiconductor structure 15a of the first light-emitting element 1a and the second semiconductor layer 113 of the first semiconductor structure 11a of the first light-emitting element 1a, as shown in Fig. 2 and Fig. 3, to reflect the light generated in the first active layer 112 of the first semiconductor structure 11a of the first light-emitting element 1a toward a light-harvesting surface of the first semiconductor structure 11a of the first light-emitting element 1a and to reflect the light generated in the second active layer 152 of the second semiconductor structure 15a of the first light-emitting element 1a away from the light-harvesting surface of the first semiconductor structure 11a of the first light-emitting element 1a. In these cases, the second active layer 152 of the second semiconductor structure 15a of the first light-emitting element 1a emits an optical output power that is less than 10% of a total optical output power of the light-emitting device 1.

Claims

[1] Light emitting device (1) comprising: a carrier (20); a first semiconductor structure (11a) formed on the carrier (20) with a first active layer (112); a second semiconductor structure (15a) having a second active layer (152) formed between the carrier (20) and the first semiconductor structure (11a); a tunnel junction (14) formed between the first semiconductor structure (11a) and the second semiconductor structure (15a); a lower electrode (22) arranged on a rear side of the carrier (20) and electrically connected to the first semiconductor structure (11a) and the second semiconductor structure (15a); and a third upper electrode (16) on an upper surface (15s) of the second semiconductor structure (15a); wherein the first active layer (112) is configured to emit a first light having a first dominant wavelength during normal operation, wherein a diode character of the second semiconductor structure (15a) is permanently broken as a result of a reverse bias at the third upper electrode (16) and the lower electrode (22), so that the second active layer (152) does not emit light during normal operation. [2] The light emitting device (1) according to claim 1, further comprising a reflection layer (13) arranged between the first semiconductor structure (11a) and the second semiconductor structure (15a), which reflection layer comprises a DBR structure and a group III-V semiconductor material, wherein the first semiconductor structure (11a) comprises a first semiconductor layer (111) having a first conductivity type and a second semiconductor layer (113) having a second conductivity type different from the first conductivity type, and the DBR structure has the same conductivity type as the second semiconductor layer (113). [3] The light emitting device (1) according to claim 1 or 2, wherein the first semiconductor structure (11a) comprises a first n-type semiconductor layer, a first p-type semiconductor layer, and the first active layer (112) disposed between the first n-type semiconductor layer and the first p-type semiconductor layer, and wherein the second semiconductor structure (15a) comprises a second n-type semiconductor layer, a second p-type semiconductor layer, and the second active layer (152) disposed between the second n-type semiconductor layer and the second p-type semiconductor layer. [4] A light emitting device (1) according to any preceding claim, further comprising a first upper electrode (17) formed on the first semiconductor structure (11a). [5] The light-emitting device (1) according to claim 1, wherein the first semiconductor structure (11a) comprises a first semiconductor layer (111) and a second semiconductor layer (113), and the first active layer (112) is arranged between the first semiconductor layer (111) and the second semiconductor layer (113); wherein the tunnel junction (14) comprises a first heavily doped layer and a second heavily doped layer having different conductivity types, and the doping concentration of the first heavily doped layer and / or the second heavily doped layer is at least one order of magnitude higher than that of the first semiconductor layer (111), the second semiconductor layer (113), or the first active layer (112). [6] Light emitting device (1) according to one of the preceding claims, wherein the second semiconductor structure (15a) has a resistance of less than 200 ohms. [7] Light emitting device (1) according to one of the preceding claims, wherein the first active layer (112) In x Ga y Al 1-x-y As (0 ≤ x, y ≤ 1), and the second active layer (152) In a Ga b Al 1-a-b P (0 ≤ a, b ≤ 1). [8] Light emitting device (1) comprising: a carrier (20); a first semiconductor structure (11a) formed on the carrier (20) with a first active layer (112); a second semiconductor structure (15a) having a second active layer (152) formed between the carrier (20) and the first semiconductor structure (11a); a lower electrode (22) arranged on a back side of the carrier (20) and electrically connected to the first semiconductor structure (11a) and the second semiconductor structure (15a); a tunnel junction (14) formed between the first semiconductor structure (11a) and the second semiconductor structure (15a); a reflection layer (13) arranged between the first semiconductor structure (11a) and the second semiconductor structure (15a), which comprises a DBR structure and a group III-V semiconductor material, wherein the first semiconductor structure (11a) comprises a first semiconductor layer (111) having a first conductivity type and a second semiconductor layer (113) having a second conductivity type different from the first conductivity type, and the DBR structure has the same conductivity type as the second semiconductor layer (113); and a third upper electrode (16) formed directly on an upper surface (15s) and on a side surface (15s') of the second semiconductor structure (15a) to short-circuit the second semiconductor structure (15a) so that the second active layer (152) does not emit light in a normal operation. [9] The light emitting device (1) according to claim 8, further comprising an etching top layer (23) formed between the first semiconductor structure (11a) and the second semiconductor structure (15a). [10] The light emitting device (1) according to claim 8 or 9, further comprising an adhesive layer (21) formed between the carrier (20) and the second semiconductor structure (15a).

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