Light-emitting diode with an active region made of a multiple-quantum well structure

Abstract

Light-emitting diode (LED), with: a GaN-based N-type compound semiconductor layer (57); a GaN-based P-type compound semiconductor layer (63); and an active region (59) of a multiple quantum well structure with alternately laminated well layers (71) and barrier layers (73, 75, 77, 79), wherein the active region (59) is arranged between the N-type and P-type compound semiconductor layers (57, 63), wherein the barrier layers (73, 75, 77, 79) are relatively thicker than the pot layers (71), wherein the barrier layers (73, 75, 77, 79) positioned between the pot layers (71) have a thinnest barrier layer and a thickest barrier layer, where the thickest barrier layer is 1.3 to 3 times as thick as the thinnest barrier layer, and wherein the barrier layers (73, 75, 77, 79) positioned between the well layers (71) comprise a plurality of relatively thick barrier layers (75) and a plurality of relatively thin barrier layers (73), characterized in that the plurality of relatively thick barrier layers (75) and the plurality of relatively thin barrier layers (73) are arranged alternately.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a light-emitting diode and, more particularly, to a light-emitting diode having an active region of a multiple quantum well structure. 2. Description of the state of the art

[0002] Because Group III element nitrides, such as GaN, AlN, and InGaN, generally exhibit excellent thermal stability and a direct transition energy band structure, they have recently come into the spotlight as materials for light-emitting diodes (LEDs) operating in the blue and ultraviolet regions. In particular, an InGaN compound semiconductor has attracted considerable attention due to its narrow band gap. LEDs using such a GaN-based compound semiconductor are used in various applications, such as large full-color flat-panel displays, backlights, traffic lights, high-density indoor lighting sources, high-resolution output systems, and optical communications.

[0003] Fig. 1 and Fig. Figure 2 is a cross-sectional view and a schematic ribbon model illustrating a conventional LED with an active region composed of a multiple quantum well structure. Fig. 2 (a) simply shows a ribbon model of respective layers, and Fig. Figure 2 (b) shows a band model in an equilibrium state. Fig. 3 is a schematic band model when a forward voltage is applied to the LED of Fig. 2 is created.

[0004] In Fig. 1 and Fig. 2, an LED comprises an N-type semiconductor layer 17, a P-type semiconductor layer 23, and an active region 19 disposed between the N-type and P-type semiconductor layers 17 and 23 to increase the recombination efficiency of electrons and holes, wherein a barrier layer 21 having a relatively wide band gap may be disposed between the P-type semiconductor layer 23 and the active region 19.

[0005] The N-type and P-type semiconductor layers comprise semiconductor layers made of nitrides of Group III elements, e.g., GaN semiconductor layers. The active region 19 is generally formed to have a multiple quantum well structure in which well layers 19a and barrier layers 19b are alternately laminated. In an InGaN LED, an active region of a multiple quantum well structure is generally formed by alternately laminating InGaN well layers 19a and GaN barrier layers 19b. The well layer 19a comprises a semiconductor layer with a smaller band gap than the N-type and P-type semiconductor layers 17 and 19 and the barrier layer 19b, thereby providing quantum wells in which electrons and holes are recombined.

[0006] Here, since polarization is generated by a piezoelectric field in an active region formed of GaN-based semiconductor layers, bands of the well layers 19a are tilted in a direction different from those of the barrier layers 19b, and the polarization is Fig. 2 (b). The polarization induced by the piezoelectric field is commonly known as the Quantum Confined Stark Effect (QCSE). The recombination rate of electrons and holes is reduced due to the QCSE, thereby reducing the photoelectric efficiency.

[0007] In Fig. 3 when a forward voltage V Fis applied to the LED, bands of the N-type semiconductor layer move upward. When a forward voltage similar to or higher than the band gap potential of the P-type semiconductor layer 23 is applied to the LED, the conduction band Ec of the N-type semiconductor layer 17 is positioned higher than that of the P-type semiconductor layer 23. At this time, the closer to the N-type semiconductor layer 17 the depletion layer 19b is positioned in the active region, the higher the conduction band of the depletion layer is positioned, as shown in this figure. The arrangement of the bands of the depletion layers 19b provides a driving force to allow carriers injected from the N-type semiconductor layer 17 to not undergo recombination in the active region 19 but to flow into the P-type semiconductor layer, thus causing carrier spillover to occur, as shown by a dot-dashed arrow.The excessive occurrence of such carrier overflow causes the recombination rate of electrons and holes to deteriorate, thereby reducing the lighting efficiency.

[0008] Meanwhile, the barrier layer 21 is used to reduce carrier overflow. The barrier layer 21 is formed from a semiconductor having a wider band gap to prevent carrier overflow. However, the barrier layer 21 formed from the semiconductor having a wider band gap has an increased lattice mismatch with the P-type semiconductor layer 23, and thus the crystal quality of the P-type semiconductor layer grown on the barrier layer 21 is deteriorated. Therefore, there is a certain limit to prevent carrier overflow with the barrier layer 21.

[0009] As LED applications expand to various fields, including general lighting, the driving voltage applied to an LED is not limited to a conventional forward voltage of 3V or so, but is continuously increased. The increase in the driving voltage causes carrier spillover to increase further, thereby further reducing the lighting efficiency of the LED. Therefore, for an LED driven under high voltage (or high current), it is necessary to develop a new method for preventing carrier spillover in addition to the barrier layer 21 and a method for lowering the driving voltage of the LED.

[0010] Meanwhile, the conventional LED comprises an active region composed of a multiple quantum well structure, which has barrier layers 19b of generally uniform thickness. The thickness of the barrier layers 19b is selected to promote process stability and exhibit optimal lighting characteristics under specific current conditions.

[0011] However, in some cases, the LED can be operated under different current conditions. For example, in the case of an AC LED driven by an AC power source, the LED can be driven by a continuously changing alternating current. In this case, it is difficult for a conventional LED having the barrier layers 19b of the same thickness to exhibit optimal lighting characteristics under both low and high current conditions.

[0012] Furthermore, JP 2005-294813 A discloses a light-emitting diode comprising a GaN-based N-type compound semiconductor layer, a GaN-based P-type compound semiconductor layer, and an active region composed of a multiple quantum well structure with alternately laminated well layers and barrier layers. The barrier layers are relatively thicker than the well layers. Additionally, the barrier layers comprise a plurality of relatively thick barrier layers and a plurality of relatively thin barrier layers. SUMMARY OF THE INVENTION

[0013] Accordingly, it is an object of the present invention to provide an LED in which QCSE and / or carrier spillover is reduced, thereby improving an electron-hole recombination rate.

[0014] Another object of the present invention is to provide an LED capable of reducing the driving voltage of the LED.

[0015] Another object of the present invention is to provide an LED capable of exhibiting effective lighting characteristics under an environment in which operating conditions such as alternating current are changed.

[0016] According to the present invention for achieving the objects, there is provided an LED having the features of claim 1.

[0017] In general, when barrier layers are doped with Si, the driving voltage of the LED can be lowered, but the luminance may be reduced depending on the Si doping. Although the majority of relatively thin barrier layers may be Si-doped barrier layers, the present invention is not limited thereto. That is, the majority of relatively thin barrier layers may be non-Si-doped barrier layers or barrier layers doped with Si at a lower concentration than the majority of relatively thick barrier layers.

[0018] In further embodiments of the present invention, each of the relatively thick barrier layers may be a barrier layer partially doped with Si at a portion thereof closer to the P-type compound semiconductor layer. Furthermore, at least one of the barrier layers positioned between the well layers may comprise an undoped InGaN layer and a Si-doped GaN layer. The Si-doped GaN layer may be positioned closer to the P-type compound semiconductor layer than the undoped InGaN layer. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a sectional view illustrating a conventional LED having an active region of a multiple quantum well structure; Fig. Figure 2 is a schematic ribbon model showing the conventional LED with the active region made of the multiple quantum well structure; Fig. 3 is a schematic band model when a forward bias is applied to the conventional LED with the active region of the multiple quantum well structure; Fig. 4 is a sectional view illustrating an LED having an active region of a multiple quantum well structure according to a first embodiment of the present invention; Fig. 5 is a schematic band model illustrating the LED with the active region of the multiple quantum well structure according to the first embodiment of the present invention; Fig. 6 is a schematic band model when a forward voltage is applied to the LED having the active region of the multiple quantum well structure according to the first embodiment of the present invention; Fig. 7 is a sectional view illustrating an LED having an active region of a multiple quantum well structure according to a second embodiment of the present invention; Fig. 8 is a schematic band model illustrating the LED with the active region of the multiple quantum well structure according to the second embodiment of the present invention; Fig. 9 is a schematic band model when a forward bias is applied to the LED having the active region of the multiple quantum well structure according to the second embodiment of the present invention; Fig. 10 is a sectional view illustrating an LED having an active region of a multiple quantum well structure according to a third embodiment of the present invention; Fig. 11 is a schematic band model illustrating the LED with the active region of the multiple quantum well structure according to the third embodiment of the present invention; Fig. 12 is a schematic band model illustrating an LED having an active region of a multiple quantum well structure according to a fourth embodiment of the present invention; and Fig. 13 is a schematic band model illustrating an LED having an active region of a multiple quantum well structure according to a fifth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided for illustrative purposes only so that a person skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the following embodiments, but may be implemented in other forms. In the drawings, the widths, lengths, thicknesses, and the like of elements may be exaggerated for the purpose of illustration. Like reference numerals indicate like elements throughout the specification and drawings.

[0020] Fig. 4 is a sectional view illustrating an LED having an active region of a multiple quantum well structure according to a first embodiment of the present invention, and Fig. 5 is a schematic band model showing the LED with the active region of the multiple quantum well structure according to the first embodiment of the present invention. Fig. 6 is a schematic band model when a forward voltage is applied to the LED having the active region of the multiple quantum well structure according to the first embodiment of the present invention.

[0021] In Fig. 4, an N-type compound semiconductor layer 57 is positioned on a substrate 51. Furthermore, a buffer layer may be disposed between the substrate 51 and the N-type compound semiconductor layer 57 and may include a low-temperature buffer layer 53 and a high-temperature buffer layer 55. The substrate 51 is not particularly limited but may be, for example, a sapphire substrate, a spinel substrate, a SiC substrate, or the like. Meanwhile, the low-temperature buffer layer 53 may generally be made of Al. x Ga 1-xN(0≤x≤1) and the high-temperature buffer layer 55 may be formed, for example, of undoped GaN or N-type GaN doped with N-type impurities.

[0022] A P-type compound semiconductor layer 63 is positioned over the N-type compound semiconductor layer 57, and an active region 59 is disposed between the N-type and P-type compound semiconductor layers 57 and 63. The N-type compound semiconductor layer and the P-type compound semiconductor layer comprise (Al, In, Ga)N-based semiconductor layers made of Group III nitrides. For example, the N-type and P-type compound semiconductor layers 57 and 63 may be N-type GaN and P-type GaN, or N-type AlGaN and P-type AlGaN, respectively. Furthermore, a barrier layer 61 may be disposed between the P-type compound semiconductor layer 63 and the active region 59. The barrier layer 61 may also be formed of an (Al, In, Ga)N-based Group III nitride semiconductor layer, e.g., AlGaN. A further barrier layer (not shown) may be arranged between the N-type compound semiconductor layer 57 and the active region 59.

[0023] Meanwhile, the active region 59 has a multiple quantum well structure in which well layers 71 and barrier layers 74 are alternately laminated. The well layers 71 are formed of InGaN, and a composition ratio thereof can be selected depending on a desired wavelength of light. At least one of the barrier layers 74 includes an undoped InGaN layer 73 and a Si-doped GaN layer 75. Furthermore, each of the barrier layers 74 positioned between the well layers 71 may include an undoped InGaN layer 73 and a Si-doped GaN layer 75. As shown in the figure, the Si-doped GaN layer 75 is positioned closer to the P-type compound semiconductor layer 63 than the undoped InGaN layer 73. The undoped InGaN layer 73 may be in contact with the well layer 71 positioned on one side of the N-type compound semiconductor layer 57.

[0024] Meanwhile, the Si-doped GaN layer 75 is relatively thinner than the undoped InGaN layer 73. In contrast, it is difficult to prevent carrier spillover because the GaN layer 75 has a relatively wide band gap.

[0025] The InGaN layer 73 may be disposed between the barrier layer 61 or the P-type compound semiconductor layer 63 and the uppermost well layer 71, and an InGaN layer (not shown) may be disposed between the N-type compound semiconductor layer 57 and the lowermost well layer 71. That is, although the well layer 71 has been shown to be in contact with the N-type compound semiconductor layer 57, an InGaN layer 73 may be in contact therewith. Further, although the InGaN layer 73 has been shown to be in contact with the barrier layer 61, a well layer 71 may be in contact therewith.

[0026] In Fig. 5, the active region 59 of the multiple quantum well structure is positioned between the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 63 (or barrier layer 61). The active region 59 is formed by alternately laminating the well layers 71 with a relatively narrow band gap and the barrier layers 74 with a relatively wide band gap.

[0027] At least one of the barrier layers 74 comprises an undoped InGaN layer 73 and a Si-doped GaN layer 75. The GaN layer 75 is in contact with the well layer 71, which is positioned on one side of the P-type compound semiconductor layer 63. Such barrier layers 74 can be formed in multiple layers.

[0028] Furthermore, a barrier layer including the undoped InGaN layer 73 may be disposed between the P-type compound semiconductor layer 63 (or barrier layer 61) and the well layer 71.

[0029] In Fig. 6, bands of the N-type compound semiconductor layer 57 are moved upwards if a forward voltage V F is applied to the LED. When a forward voltage similar to or higher than the band gap potential of the P-type semiconductor layer 63 is applied to the LED, the conduction band Ec of the N-type compound semiconductor layer 57 is positioned higher than that of the P-type compound semiconductor layer 63.

[0030] When a high forward voltage is applied to conventional barrier layers formed of the same material, the conduction band of the barrier layer 19b is positioned higher as in Fig. 3 because the barrier layer 19b is closer to the N-type semiconductor layer 17. The band slope of these conduction bands provides a driving force to allow carriers (electrons) injected from the N-type semiconductor layer 17 to move to the P-type semiconductor layer 23, thereby easily generating carrier spillover.

[0031] However, according to embodiments of the present invention, since each of the barrier layers 74 comprises an InGaN layer and a GaN layer, the movement of electrons is restricted by the bandgap difference between the InGaN layer 73 and the GaN layer 75, thereby preventing carrier spillover. Furthermore, the InGaN layer 73 is formed with a relatively narrow bandgap and is thicker than the GaN layer 75, so that conduction bands in the active region 59 are completely lowered, thereby effectively preventing carrier spillover.

[0032] Furthermore, the GaN layer 75, which is in contact with the well layer 71 positioned on one side of the P-type compound semiconductor layer 63, is doped with Si, so that the influence on a piezoelectric field can be reduced by reducing the stress on the InGaN layer. As a result, the quantum confined Stark effect (QCSE) is reduced, and thus the recombination rate of electrons and holes is improved. Furthermore, some of the undoped InGaN barrier layers are replaced with Si-doped GaN layers, so that the overall electrical resistivity of the barrier layers can be lowered. Accordingly, the driving voltage of the LED according to the present invention can be lowered compared to the conventional LED using undoped InGaN barrier layers.

[0033] Fig. 7 is a sectional view illustrating an LED having an active region of a multiple quantum well structure according to another embodiment of the present invention, and Fig. 8 is a schematic band model illustrating the LED with the active region of the multiple quantum well structure according to the other embodiment of the present invention. Fig. Fig. 9 is a schematic band model when a forward voltage is applied to the LED having the active region of the multiple quantum well structure according to the other embodiment of the present invention. An LED according to this embodiment is connected to the device described with reference to Fig. 4, except for an active region 89. The following description will focus on such differences.

[0034] In Fig. 7, the active region 89 has a multiple quantum well structure in which well layers 71 and barrier layers 84a, 84b, and 83c are alternately laminated. The barrier layers 84a, 84b, and 83c comprise undoped InGaN layers 83a, 83b, and 83c, respectively. Furthermore, at least one of the barrier layers 84a and 84b includes a Si-doped GaN layer 75. Furthermore, each of the barrier layers 84a and 84b positioned between the well layers 71 may include a Si-doped GaN layer 75.

[0035] As shown in the figure, in each of the barrier layers, the Si-doped GaN layer 75 is positioned closer to a P-type compound semiconductor layer 63 than the undoped InGaN layer 83a, 83b, or 83c. Each of the undoped InGaN layers 83a, 83b, and 83c may be in contact with the well layers 71 positioned on one side of an N-type compound semiconductor layer 57 thereof. The Si-doped GaN layer 75 is relatively thinner than the undoped InGaN layers 83a and 83b.

[0036] In Fig. 8, the active region 89 of the multiple quantum well structure is positioned between the N-type compound semiconductor layer 57 and the P-type compound semiconductor layer 63 (or barrier layer 61). The active region 89 is formed by alternately laminating the well layers 71 with a relatively narrow band gap and the barrier layers 84a, 84b, and 83c with a relatively wide band gap. The barrier layers 84a, 84b, and 83c comprise the undoped InGaN layers 83a, 83b, and 83c, respectively, and each of the barrier layers 84a and 84b comprises the Si-doped GaN layer 75.

[0037] The undoped InGaN layers 83a, 83b, and 83c are formed to have a narrower band gap because they are positioned closer to the N-type compound semiconductor layer 57. That is, the band gaps are increased in the order of the undoped InGaN layers 83a, 83b, and 83c. Generally, the band gap of an InGaN layer increases as the composition ratio of Ga increases, and the band gap of the InGaN layer decreases as the composition ratio of In increases. Therefore, by changing the composition ratio of Ga and In, the InGaN layers can be formed to have a narrower band gap because the InGaN layer is closer to the N-type compound semiconductor layer.

[0038] In Fig. 9 if a forward voltage V Fis applied to the LED, bands of the N-type compound semiconductor layer 57 move upward. When a forward voltage similar to or higher than the band gap potential of the P-type semiconductor layer 63 is applied to the LED, the conduction band Ec of the N-type compound semiconductor layer 57 is positioned higher than that of the P-type compound semiconductor layer 63.

[0039] When a high forward voltage is applied to conventional depletion layers formed of the same material, the conduction band of the depletion layer 19b is positioned higher, as shown in Fig. 3 because the barrier layer 19b is closer to the N-type semiconductor layer 17. The band slope of these conduction bands provides a driving force to allow carriers (electrons) injected from the N-type semiconductor layer 17 to move toward the P-type semiconductor layer 23, thereby easily generating carrier spillover.

[0040] However, in the LED according to embodiments of the present invention, since the InGaN layer 83a of the barrier layer 84a near the N-type compound semiconductor layer 57 has a narrower band gap than the InGaN layer 83c near the P-type compound semiconductor layer 63, the band slope of the barrier layers can be reduced even though a high forward voltage is applied to the LED. Specifically, the band gaps of the InGaN layers 83a, 83b, and 83c can be controlled so that the conduction bands of the barrier layers are positioned at generally the same energy level when a forward voltage is applied to the LED. Accordingly, it is possible to reduce the QCSE by the Si-doped GaN layer 75 and remove the driving force that induces carrier spillover in the active region 89, thereby further improving the recombination rate of electrons and holes.

[0041] Although three barrier layers have been illustrated and described in this embodiment, the present invention is not limited thereto. That is, a larger number of barrier layers may be laminated alternately with well layers. Furthermore, several of the barrier layers may each be undoped InGaN layers, and the InGaN layers may be formed to have a narrower band gap because they are positioned closer to the N-type compound semiconductor layer 57.

[0042] Although it has been illustrated and described in the above-mentioned embodiments that all the barrier layers have the same thickness, the present invention is not limited thereto. That is, the barrier layers may be formed to have different thicknesses.

[0043] For example, barrier layers with a relatively thick thickness and barrier layers with a relatively thin thickness may be alternately laminated in the active region. The arrangement of the barrier layers can provide the LED that can exhibit effective lighting characteristics under an environment where operating conditions vary. In such a case, in the barrier layers comprising Si-doped GaN layers and undoped InGaN layers, the GaN layers may be formed to a predetermined thickness, and the InGaN layers may have different thicknesses, and vice versa. Furthermore, when the Si-doped GaN layers have different thicknesses, the doping concentration of Si may be higher because the thickness of the Si-doped GaN layer is thicker. A case where barrier layers have different thicknesses will be described in detail below.

[0044] Fig. 10 is a sectional view illustrating an LED having an active region of a multiple quantum well structure according to another embodiment of the present invention, and Fig. 11 is a schematic ribbon model illustrating the LED with the active region of the multiple quantum well structure according to the further embodiment of the present invention.

[0045] In Fig. 10 and Fig. 11, an N-type compound semiconductor layer 157 is positioned on a substrate 151, as described above. Further, a buffer layer may be disposed between the substrate 151 and the N-type compound semiconductor layer 157. The buffer layer may include a low-temperature buffer layer 153 and a high-temperature buffer layer 155. In addition, a P-type compound semiconductor layer 161 is positioned over the N-type compound semiconductor layer 157, and an active region 159 is disposed between the N-type and P-type compound semiconductor layers 157 and 161. In addition, a barrier layer (not shown) may be disposed between the P-type compound semiconductor layer 161 and the active region 159, and another barrier layer (not shown) may be disposed between the N-type compound semiconductor layer 157 and the active region 159.

[0046] Meanwhile, the active region 159 has a multiple quantum well structure in which well layers 171 and barrier layers 173, 175, 177, and 179 are alternately laminated. The well layers 171 may be formed of InGaN, and a composition range thereof can be selected depending on a desired wavelength of light.

[0047] Meanwhile, each of the barrier layers 173, 175, 177, and 179 may be formed of a (Al, In, Ga)N-based group III nitride semiconductor layer, e.g., an InGaN or GaN layer, having a larger band gap than that of the well layers 171. As described in the previous embodiments, each of the barrier layers may include a Si-doped GaN layer and an undoped InGaN layer.

[0048] In addition, the barrier layers 177 and 179 are relatively thicker than the barrier layers 173 and 175. For example, the barrier layers 177 and 179 may have a thickness 1.3 to 3 times that of the barrier layers 173 and 175. If the barrier layers 177 and 179 are less than 1.3 times as thick as the barrier layers 173 and 175, it is difficult to obtain an effect by thickness control. If the barrier layers 177 and 179 are more than 3 times as thick as the barrier layers 173 and 175, the barrier layers 177 and 179 are excessively thick, and therefore the driving voltage of the LED is excessively increased.

[0049] Meanwhile, all of the barrier layers 173, 175, 177, and 179 are doped with Si, and the driving voltage of the LED is lowered by the Si doping. Further, although all of the barrier layers may be doped with the same concentration, it is preferable that the barrier layers 173 and 175 be doped with a lower concentration than the barrier layers 177 and 179. Conversely, the barrier layers 173 and 175 may not be doped with Si. Since the barrier layers 173 and 175 are relatively thin, an increase in the driving voltage of the LED is not large even though the barrier layers are not doped with Si. Furthermore, the Si doping is omitted to thereby prevent a luminance reduction caused by the Si doping.

[0050] Although Si may be doped throughout the entire thickness of barrier layers 173, 175, 177, or 179, the present invention is not limited thereto. That is, the barrier layers may be partially doped with Si. In such a case, for each Si-doped barrier layer, it is preferable that a portion of the barrier layer closer to the P-type compound semiconductor layer be partially doped with Si to reduce the piezoelectric field.

[0051] In this embodiment, it has been illustrated and described that the relatively thin barrier layers 173 and 175 are arranged close to each other, and the relatively thick barrier layers 177 and 178 are arranged close to each other. As in Fig. 12, however, the relatively thin barrier layers 173 and 175 and the relatively thick barrier layers 177 and 179 may be arranged alternately.

[0052] Although the four barrier layers have been shown and described in this embodiment, the number of barrier layers may be greater than four.

[0053] Fig. 13 is a schematic ribbon model illustrating an LED having an active region of a multiple quantum well structure according to yet another embodiment of the present invention.

[0054] In Fig. 13 the LED is approximately the same as that shown with reference to Fig. 10 and Fig. 11, except for the thicknesses of barrier layers in an active region 159.

[0055] That is, in this embodiment, the thicknesses of barrier layers 183, 185, 187, and 189 positioned between well layers 171 are not constant and vary between the thicknesses of the thinnest barrier layer 183 and the thickest barrier layer 189. Here, the thickness of the thickest barrier layer 189 ranges from 1.3 to 3 times the thickness of the thinnest barrier layer 183.

[0056] In addition, the barrier layers in the active region 159 may be arranged in order of thickness from the thinnest to the thickest or vice versa.

[0057] In this embodiment, an LED capable of emitting light efficiently under varying operating conditions by controlling the thickness of the respective barrier layers in accordance with changes in the operating conditions is provided.

[0058] Meanwhile, barrier layers 183, 185, 187, and 189 may be barrier layers doped with high concentration Si as the thickness is increased. Furthermore, relatively thin barrier layers may not be doped with Si or may be doped with low concentration Si.

[0059] Furthermore, the barrier layers may include a barrier layer partially doped with Si at a portion thereof closer to the P-type compound semiconductor layer. Partial Si doping reduces the stress on the well layers, thereby making it possible to reduce the polarization generated by a piezoelectric field, and the luminance reduction caused by Si doping can be minimized. In this case, each of the barrier layers includes a GaN layer and an undoped InGaN layer. The GaN layer may be positioned close to the P-type compound semiconductor layer, and the GaN layer may be fully or partially doped with Si.

[0060] Although four barrier layers have been illustrated and described in this embodiment, the present invention is not limited thereto. That is, a larger number of barrier layers may be laminated alternately with pot layers.

[0061] According to embodiments of the present invention, an LED comprises barrier layers with undoped InGaN layers and Si-doped GaN layers, so that carrier spillover and QCSE can be reduced, thereby improving the LED's light efficiency and reducing the LED's drive voltage. Furthermore, an LED comprises an active region with relatively thick barrier layers and relatively thin barrier layers, so that effective light characteristics can be achieved under various operating conditions.

Claims

[1] Light-emitting diode (LED), with: a GaN-based N-type compound semiconductor layer (57); a GaN-based P-type compound semiconductor layer (63); and an active region (59) comprising a multiple quantum well structure with alternately laminated well layers (71) and barrier layers (73, 75, 77, 79), the active region (59) being arranged between the N-type and P-type compound semiconductor layers (57, 63), wherein the barrier layers (73, 75, 77, 79) are relatively thicker than the pot layers (71), wherein the barrier layers (73, 75, 77, 79) positioned between the pot layers (71) have a thinnest barrier layer and a thickest barrier layer, where the thickest barrier layer is 1.3 to 3 times as thick as the thinnest barrier layer, and wherein the barrier layers (73, 75, 77, 79) positioned between the well layers (71) comprise a plurality of relatively thick barrier layers (75) and a plurality of relatively thin barrier layers (73), characterized by , that the plurality of relatively thick barrier layers (75) and the plurality of relatively thin barrier layers (73) are arranged alternately. [2] The LED of claim 1, wherein each of the plurality of relatively thick barrier layers (75) is a Si-doped barrier layer. [3] The LED of claim 2, wherein each of the plurality of relatively thin barrier layers (73) is a Si-doped barrier layer. [4] The LED of claim 3, wherein the plurality of relatively thin barrier layers (73) are doped with Si at a lower concentration than the plurality of relatively thick barrier layers (75). [5] The LED of claim 1, wherein each of the plurality of relatively thick barrier layers (75) is a barrier layer partially doped with Si at a portion of the barrier layer closer to the P-type compound semiconductor layer (63).

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