Surface treatment method for group III nitride semiconductor and method for producing the same

Abstract

A surface treatment process of a group III nitride semiconductor, comprising: Providing a group III nitride semiconductor, which includes a first surface and a second surface opposite the first surface, wherein the first surface has a group III polarity and the second surface has a nitrogen polarity; and irradiating the second surface with a laser beam to change the nitrogen polarity of the second surface to the group III polarity; wherein the surface treatment method further comprises forming a crystal defect layer having a defect caused by nitrogen vacancies on the second surface before irradiating the second surface with a laser beam.

Description

Background of the inventionField of the invention

[0001] The present invention relates to a surface treatment method of a group III nitride semiconductor, a method for producing the same, and more particularly to a surface treatment method of a group III nitride semiconductor in which two opposite surfaces have identical polarity and a method for producing the same. Description of related technology

[0002] Generally, a light-emitting device made of a group III nitride semiconductor is used to generate light with blue or green wavelengths. The light-emitting device is made of semiconductor material with a composition comparable to Al. x In y Ga (1-x-y) N, where 0≤x≤1, 0≤y≤1 and 0≤x+y≤1.

[0003] A group III nitride semiconductor can be grown on a heterogeneous substrate, such as a sapphire (α-Al2O3) substrate and a SiC substrate. The sapphire substrate has a hexagonal structure identical to gallium nitride. Furthermore, the sapphire substrate is cheaper than the SiC substrate and stable at high temperatures, so it is mainly used as a growth substrate for the group III nitride semiconductor.

[0004] The Group III nitride semiconductor grown on the sapphire substrate has a wurtzite and non-centrosymmetric crystal structure. Therefore, the Group III nitride semiconductor, such as gallium (Ga) nitride semiconductor, has gallium polarity on one surface (hereinafter referred to as the gallium polarity surface) and nitrogen (N) polarity on another surface (hereinafter referred to as the nitrogen polarity surface). As described above, the two surfaces of the gallium nitride semiconductor exhibit physical differences in terms of etching rate and surface recombination configuration, or defects and surface dislocation due to differences in surface polarity. These physical differences lead to differences in surface properties between the gallium polarity surface and the nitrogen polarity surface.

[0005] This means that the gallium-polarized surface of the gallium nitride semiconductor exhibits better surface flatness than the nitrogen-polarized surface. Furthermore, the gallium-polarized surface exhibits better crystallinity than the nitrogen-polarized surface due to less binding of impurity materials. Accordingly, when the gallium semiconductor is regrown, a newly grown layer grown on the gallium-polarized surface exhibits a flat surface. In contrast, the newly grown layer grown on the nitrogen-polarized surface is affected by surface defects such as hillock, columnar, and pyramidal grains.

[0006] Polarity differences between both surfaces of the gallium nitride semiconductor cause spontaneous polarization, resulting in differences in surface band curvature between the surface with gallium polarity and the surface with nitrogen polarity.

[0007] Furthermore, the surface of the gallium nitride semiconductor with gallium polarity exhibits a low constant voltage due to low ohmic contact resistance and has better electrical properties than the surface with nitrogen polarity. Furthermore, the two surfaces of the gallium nitride semiconductor react differently to an etching solution, such as KOH, due to polarity differences. That is, the surface with gallium polarity hardly reacts with the etching solution, while the surface with nitrogen polarity reacts actively with the etching solution and is thus strongly etched.

[0008] In a Group III nitride semiconductor, as described above, a surface with Group III polarity exhibits better properties in terms of surface flatness, impurity bonding, re-growth properties, electrical properties, and etching properties than a surface with nitrogen polarity. Therefore, there is a need to develop a Group III nitride semiconductor whose two opposing surfaces exhibit Group III polarities.

[0009] US 2008 / 0093618 A1 describes a vertical LED having an n-electrode, an n-type GaN layer formed beneath the n-electrode, and a surface in contact with the n-electrode. The surface has a Ga + N-layer, which contains a larger amount of gallium than nitride.

[0010] In Grandjean, N.; Dussaigne, A.; Pezzagna, S.; Vennéguès, P.: “Control of the polarity of GaN films using an Mg adsorption layer”, Journal of Crystal Growth, 251, 2003, 1-4, 460-464 it is proposed to control the polarity of GaN films using a Mg adsorption layer.

[0011] EP 1 089 329 A1 describes methods for fabricating compound semiconductor devices. A III-V compound semiconductor single-crystal layer is grown on a semiconductor single-crystal substrate. A surface of the compound semiconductor single-crystal layer is irradiated with a laser beam to convert the polarity of the surface.

[0012] JP 2006 - 294 697 A describes an LED comprising a GaN substrate, an inversion layer, a regrown GaN layer, a light-emitting layer, a p-electrode, another light-emitting layer, another p-electrode, and an n-electrode. The regrown GaN layer is formed adjacent to the inversion layer.

[0013] It is an object of the present invention to provide an improved surface treatment method of a group III nitride semiconductor and an improved method for producing a group III nitride semiconductor.

[0014] This object is achieved by the subject matter of the independent patent claims. Preferred embodiments are the subject matter of the subclaims. Summary of the invention

[0015] According to one aspect of the present invention, a surface treatment method in which a second surface opposite to a first surface having a group III polarity and having a nitrogen polarity is irradiated with a laser beam to change the polarity of the second surface to a polarity identical to that of the first surface, and a method for manufacturing the same are provided.

[0016] According to one aspect of the present invention, there is provided a surface treatment method of a group III nitride semiconductor, including providing a group III nitride semiconductor including a first surface having a group III polarity and a second surface opposite to the first surface and having a nitrogen polarity; and irradiating the second surface with a laser beam to change the nitrogen polarity of the second surface to the group III polarity.

[0017] The surface treatment method further includes forming a crystal defect layer having a defect caused by nitrogen vacancies along the second surface before irradiating the second surface with a laser beam. Forming a crystal defect layer may include performing plasma treatment or ion beam irradiation of the second surface.

[0018] The crystal defect layer may contain at least one amorphous region, one polycrystal region, or one Group III-rich region. The crystal defect layer may have a thickness of 5 to 2000 nm.

[0019] The group III nitride semiconductor can be a semiconductor represented by AlxlnyGa(1-xy)N, where 0≤x≤1, 0≤y≤1 and 0≤x+y≤1.

[0020] The Group III nitride semiconductor is a GaN semiconductor, and the Group III polarity is a gallium polarity.

[0021] According to another aspect of the present invention, there is provided a method for manufacturing a group III nitride semiconductor, the method including growing a group III nitride semiconductor on a nitride single crystal growth substrate, the group III nitride semiconductor including a first surface having a group III polarity and a second surface opposite to the first surface, the second surface being in contact with the substrate and having a nitrogen polarity; separating the group III nitride semiconductor from the nitride single crystal growth substrate, and irradiating the second surface with a laser beam to change the nitrogen polarity of the second surface to a group III polarity.

[0022] The method further includes forming a crystal defect layer having a defect caused by nitrogen vacancies on the second surface before irradiating the second surface with a laser beam. Forming a crystal defect layer may include performing plasma treatment or ion beam irradiation of the second surface.

[0023] The crystal defect layer may contain at least one amorphous region, one polycrystal region, or one Group III-rich region. The crystal defect layer may have a thickness of 5 to 2000 nm.

[0024] The group III nitride semiconductor may be a semiconductor formed by Al x In y Ga (1-x-y) N, where 0≤x≤1, 0≤y≤1 and 0≤x+y≤1.

[0025] The group III nitride semiconductor can be a GaN semiconductor, and the group III polarity is a gallium polarity.

[0026] The method may further include growing an additional nitride semiconductor layer on the second surface that is modified to have group III polarity.

[0027] The nitride single crystal growth substrate may be made of a material selected from a group consisting of sapphire, SiC, Si, ZnO, MgAl2O4, MgO, LiAlO2 and LiGaO2. Short description of the drawings

[0028] The above and other aspects, features and other advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1A to 1D illustrate a surface treatment process of a group III nitride semiconductor according to an exemplary embodiment of the invention; Fig. 2A to 2E illustrate a method of manufacturing a group III nitride semiconductor according to an exemplary embodiment of the invention; Fig. 3 represents a group III nitride semiconductor structure; Fig. 4 is a photograph showing a group III nitride semiconductor coated with the Fig. 2A to 2E; Fig. 5 is a photograph showing a group III nitride semiconductor having one surface etched; Fig. 6 represents a group III nitride semiconductor light-emitting device; and Fig. 7 is a diagram showing properties of a Fig. 6 represents the group III nitride semiconductor device shown. Detailed description of the preferred embodiment

[0029] An exemplary embodiment will be described in detail below with reference to the accompanying drawings.

[0030] Fig. 1A to 1D illustrate a surface treatment method of a group III nitride semiconductor according to an exemplary embodiment of the invention. First, as in Fig. 1A, a group III nitride semiconductor 10 is provided. The group III nitride semiconductor 10 may be a single-crystal layer substrate having a semiconductor composition characterized by Al x In y Ga (1-x-y) N, where 0≤x≤1, 0≤y≤1, and 0≤x+y≤1. The III-nitride semiconductor 10 may be a single crystal substrate having a GaN semiconductor composition.

[0031] Furthermore, the group III nitride semiconductor 10 includes a first surface 11 having a group III polarity and a second surface 12 opposite the first surface and having a nitrogen polarity. This means that in the group III nitride semiconductor, group III elements and nitrogen elements have a wurtzite crystal structure. The group III elements are arranged on the first surface 11, and the nitrogen elements are arranged on the second surface 12. This means that the first surface 11 and the second surface 12 each have polarities corresponding to the elements arranged thereon.

[0032] In the following, a surface treatment process in which the second surface 12 is changed from a nitrogen polarity to a group III polarity is described in detail.

[0033] As mentioned with reference to Fig. As can be seen in Figure 1B, a crystal defect layer 13 with defects caused by nitrogen vacancies is formed on the second surface 12. The crystal defect layer 13 may be an amorphous region, a polycrystal region, or a Group III-rich region. The second surface 12 may be formed by performing plasma treatment or ion beam irradiation.

[0034] As described above, when the second surface 12 is plasma-treated or irradiated with ion beams, nitrogen vacancies are generated in a layer extending from the second surface 12 to a certain thickness, thereby forming a crystal defect layer 13 in which the Group III elements and the nitrogen elements are irregularly arranged. The crystal defect layer 13 can be formed to a thickness of 5 to 2000 nm from the second surface 12.

[0035] Then, as in Fig. 1C, is irradiated with a laser beam to change a polarity of the second surface 12 to a group III polarity. That is, the crystal defect layer 13 extending from the second surface 12 to a certain thickness is irradiated with a laser beam. As a result, the group III elements and the nitrogen elements arbitrarily arranged on the crystal defect layer 13 are recrystallized. This changes a crystal arrangement of the group III elements and the nitrogen elements in the crystal defect layer 13, so that the group III elements, rather than the nitrogen elements, can be arranged on the second surface 12. That is, the second surface 12 is changed to have a group III polarity. This is because the group III elements are more stably arranged on the surface than the nitrogen elements.Therefore, the second surface 12 has a group III polarity with a relatively stable crystal structure during the recrystallization of the group III elements and the nitrogen elements.

[0036] The processes described above produce a group III nitride semiconductor 10' as described in Fig. 1D. That is, the Fig. The group III nitride semiconductor 10' shown in Figure 1D includes a first surface 11 having a group III polarity and a second surface 12 opposite the first surface 11 and having a group III polarity. Furthermore, the group III nitride semiconductor 10' includes a polarity reversal layer 13'.

[0037] The polarity reversal layer 13' corresponds to a region of the group III nitride semiconductor 10' located on the second surface 12. The polarity reversal layer 13' is not formed separately from the group III nitride semiconductor 10', but is formed so that it is continuous with the other region of the group III nitride semiconductor 10'.

[0038] The Fig. The group III nitride semiconductor 10' shown in Figure 1D may be structured as described above such that the first surface 11 and the second surface, which are opposite to each other with respect to the polarity inversion layer 13', have an identical group III polarity.

[0039] Fig. 2A to 2E illustrate a method for manufacturing a group III nitride semiconductor according to an exemplary embodiment of the invention. The group III nitride semiconductor 100 is formed as described with reference to Fig. 2A, the nitride single crystal growth substrate 200 is grown in the direction of the arrow. The nitride single crystal growth substrate 200 may be made of a material selected from a group consisting of sapphire, SiC, Si, ZnO, MgAl2O4, MgO, LiAlO2, and LiGaO2. Furthermore, the Group III nitride semiconductor 100 may be formed on the substrate 200 using metal organic chemical vapor deposition (MOCVD), hybrid vapor phase epitaxy (HVPE), and molecular beam epitaxy (MBE).

[0040] The group III nitride semiconductor 100, which is used in Fig. 2A may have a composition determined by Al x In y Ga (1-x-y)N is expressed as 0≤x≤1, 0≤y≤1, and 0≤x+y≤1. Therefore, the group III nitride semiconductor 100 has a crystal structure in which at least one group III element from among aluminum (Al), indium (In), and gallium (Ga) and a nitride element are bonded to each other at a regular interval. Furthermore, the group III nitride semiconductor 100 may have a GaN semiconductor composition containing the gallium element and the nitride element.

[0041] The group III nitride semiconductor 100 contains, as in Fig. 2A, a first surface 110 and a second surface 120, which is in contact with the nitride single-crystal growth substrate 200 and is opposite the first surface 110. Group III elements are arranged on the first surface 110, and therefore, it has a group III polarity. Nitrogen elements are arranged on the second surface 120, and therefore, it has a nitrogen polarity.

[0042] That is, the first surface 110 and the second surface 120 of the group III nitride semiconductor 110 have a crystal structure in which gallium elements as the group III element and nitrogen elements are periodically arranged. Gallium elements are arranged on the first surface 110 of the group III nitride semiconductor 100, so that it has gallium polarity. On the other hand, nitrogen elements are arranged on the second surface 120, which is in contact with the nitride single-crystal substrate 200, so that it has nitrogen polarity.

[0043] Subsequently, when the group III nitride semiconductor 100 is grown as in Fig. 2B, the nitride single-crystal growth substrate 200 is irradiated with a laser beam to separate the group III nitride semiconductor 100 from the nitride single-crystal growth substrate 200. Accordingly, the second surface 120 of the group III nitride semiconductor 100, to which the nitride single-crystal growth substrate 200 is bonded, is exposed.

[0044] Then the Fig. 2C and Fig. 2D are used to change a polarity of the second surface 120 of the group III nitride semiconductor 100. To simplify the description, Fig. 2C and Fig. 2D the group III nitride semiconductor 100 of Fig. 2B, which is rotated so that the second surface 120 faces upwards.

[0045] The crystal defect layer 130 is, as in Fig. 2C, is formed on the second surface 120 of the Group III nitride semiconductor 100. The crystal defect layer 130 contains defects caused by nitrogen vacancies and has a crystal structure in which Group III elements and nitrogen elements are randomly arranged. That is, the crystal defect layer 130 may be at least one of an amorphous region, a polycrystalline region, and a Group III-rich region.

[0046] The crystal defect layer 130 can be formed on the second surface 120 by performing plasma treatment or ion beam irradiation. The crystal defect layer 130 can have a thickness of 500 to 2000 nm by adjusting the time and conditions of the plasma treatment or ion beam irradiation.

[0047] Subsequently, the crystal defect layer 130, as shown in Fig. 2D, the second surface 120 is irradiated with a laser beam to change the nitrogen polarity of the second surface 120 to a group III polarity. That is, by irradiating the laser beam, the group III elements and the nitrogen elements randomly arranged on the crystal defect layer 130 are recrystallized. Accordingly, the group III elements and the nitrogen elements in the crystal defect layer 130 can be rearranged, and the group III elements can be arranged on the second surface 120. That is, the second surface 120 is changed to have the group III polarity.

[0048] As a laser used to rearrange the group III elements and nitrogen elements in the crystal defect layer 130, as described with reference to Fig. 2D, a 193 nm excimer laser, a 248 nm excimer laser, a 308 nm excimer laser, an Nd:YAG laser, a He-Ne laser and an Ar ion laser are used.

[0049] At this time, in order to rearrange the group III elements and the nitrogen elements in the crystal defect layer 130, in addition to the laser beam irradiation, a predetermined heat may be applied using ion beams or heat treatment to the crystal defect layer 130 to enable the group III elements and the nitrogen elements to be rearranged.

[0050] The Fig. The processes shown in Figures 2A to 2D can Fig. 2E shown group III nitride semiconductor 100'. That is, the Fig. The group III nitride semiconductor 100' shown in Figure 2E includes a first surface 110 having a group III polarity, a second surface 120 opposite the first surface 110 and having a group III polarity, and a polarity reversal layer 130' formed to a certain thickness from the second surface 120.

[0051] The polarity reversal layer 130' in Fig. 2E corresponds to a region of a group III nitride semiconductor 100' located at the second surface 120. That is, the polarity reversal layer 130' is not formed separately from the group III nitride semiconductor 100', but is formed via a one-time growth process of the group III nitride semiconductor as shown in Fig. 2A, is formed continuously with the group III nitride semiconductor 100' and is therefore continuous with the other region. The other region may cover a region from a region opposite the second surface 120, ie, the first surface 110, to a boundary of the polarity inversion layer 130'.

[0052] Furthermore, the polarity inversion layer 130' can reverse a crystal arrangement of the other region such that the second surface 120 has a group III polarity that is identical to a polarity of the first surface 110. That is, the polarity inversion layer 130' is recrystallized such that the group III elements and nitrogen elements of the crystal defect layer 130, which are in Fig. 2C and Fig. 2D, with respect to the crystal arrangement. This polarity reversal layer 130' can have a thickness of 5 to 2000 nm.

[0053] The group III nitride semiconductor 100' is contacted with the second surface 120 of the group III nitride semiconductor 100' in Fig. 2E as a growth surface, resulting in a Group III nitride semiconductor structure exhibiting crystallinity and surface flatness. This is described in detail below.

[0054] Fig. 3 represents a group III nitride semiconductor structure. As described with reference to Fig. 3, the group III nitride semiconductor structure 500 includes a first group III nitride semiconductor 100' and a second group III nitride semiconductor 100'-1.

[0055] The first group III nitride semiconductor 100' is identical to the one in Fig. 2E. The first group III nitride semiconductor 100' includes a first surface 110 having a group III polarity and a second surface 120 opposite the first surface 110. Furthermore, the first group III nitride semiconductor 100' includes a polarity reversal layer 130' corresponding to a region located at the second surface 120, which reverses a crystal arrangement of the other region such that the second surface 120 has a polarity identical to a polarity of the first surface 110.

[0056] The second group III nitride semiconductor 100'-1 is formed on the second surface 120 of the first group III nitride semiconductor 100'. The second group III nitride semiconductor 100'-1 can be formed using metal organic chemical vapor deposition (MOCVD), hybrid vapor phase epitaxy (HVPE), and molecular beam epitaxy (MBE). Furthermore, the second group III nitride semiconductor 100'-1 can have a semiconductor composition that is identical to or different from that of the first group III nitride semiconductor 100'.

[0057] As described above, the second group III nitride semiconductor 100'-1 is formed on the second surface 120, which has a group III polarity, and therefore has fewer defects such as hillock, columnar, and pyramidal grains. Accordingly, the second group III nitride semiconductor 100'-1 has better crystallinity and surface flatness compared to the case where the second group III nitride semiconductor 100'-1 is grown on the surface with a nitrogen polarity.

[0058] The second group III nitride semiconductor 100'-1 is, as described with reference to Fig. 3, is depicted as a single layer, but may be composed of a plurality of group III nitride semiconductor layers, each containing an active layer. That is, the plurality of group III nitride semiconductor layers are grown on the second surface 120 of the first group III nitride semiconductor 100' to create a semiconductor light-emitting device. Therefore, the semiconductor light-emitting device fabricated using the second surface 120 with group III polarity exhibits better crystallinity and thus higher light-emitting efficiency.

[0059] Fig. 4 is a photograph that shows one with the Fig. 2A to 2E. That is, Fig. Figure 4 is a section obtained by vertically cutting a group III nitride semiconductor 100' and photographing it. That is, Fig. 4 illustrates a crystal arrangement of a first surface 110, which is a lower surface of the group III nitride semiconductor, and a second surface 120, which is a top surface of the group III nitride semiconductor.

[0060] The group III nitride semiconductor 100' is a GaN semiconductor, and both the first surface 110 and the second surface 120 have a gallium polarity. The second surface 120 is a layer that has a gallium polarity due to a polarity reversal layer 130, through which a polarity has been reversed by crystal rearrangement of gallium elements and nitrogen elements.

[0061] A section A provides, as with reference to the Fig. 4, represents a polarity of the first surface 110, and a section C represents the polarity of the second surface 120. Furthermore, a section B and a section D represent polarities associated with corresponding polarities of section A and section B, respectively.

[0062] First, it can be seen that section A and section C, corresponding to two surfaces of the group III nitride semiconductor 100', have (0002) planes, indicating gallium polarity. That is, the gallium polarity is directed toward the two opposite surfaces of the group III nitride semiconductor 100'. Furthermore, section B and section D have (000-2) planes, indicating nitrogen polarity. That is, the group III nitride semiconductor 100' has a crystal arrangement in which the gallium polarity and the nitrogen polarity are combined. However, the first surface 110 and the second surface 120 have gallium polarity.

[0063] Fig. Figure 5 is a photograph showing a group III nitride semiconductor whose one surface is etched. That is, the Fig. 5 is a GaN semiconductor, and a first region 310 located to the left of the line AA' is a nitride semiconductor formed using the method in Fig. 1B and Fig. 1C shows a surface-treated region, i.e., a region created by etching a region with gallium polarity via polarity reversal. A second region 320, located on the right side, is a region that is not surface-treated and is created by etching a region with nitrogen polarity.

[0064] The group III nitride semiconductor 300 is etched under identical conditions, for example, at an etching temperature and etching time using a KOH etching solution. As a result, the first region 310 with a gallium polarity is barely etched, and a surface of the second region 320 with a nitrogen polarity is etched to form an irregular, rough structure. As described above, it is clearly shown that the polarity of the first region 310 is changed to the gallium polarity by etching the first region 310 and the second region 320.

[0065] Fig. 6 represents a group III nitride semiconductor light emitting device.

[0066] The Fig. The group III nitride semiconductor 400 shown in Figure 6 is a GaN semiconductor and includes a light-emitting structure having a first GaN semiconductor layer 411, an active layer 412, and a second GaN semiconductor layer 413. The group III nitride semiconductor 400 includes a first electrode 420 in contact with the first GaN semiconductor layer 411 and a second electrode 430 formed on the second GaN semiconductor layer 413, and has a vertical structure. Here, both surfaces of the light-emitting structure, namely, a surface of the first GaN semiconductor layer 411 and a surface of the second GaN semiconductor layer 413, have gallium polarity. That is, the first electrode 420 and the second electrode 430 are formed on the light emission structure with a gallium polarity.

[0067] The Fig. The group III nitride semiconductor 400 shown in Figure 6 can be manufactured as follows. First, the first GaN semiconductor layer 411, the active layer 412, and the second GaN semiconductor layer 413 are sequentially layered on a nitride single-crystal substrate, such as a sapphire substrate, to form the light-emitting structure. Further, the second electrode 430 is formed on the second GaN semiconductor layer 413. Furthermore, although not shown, a conductive support substrate may be provided on the second electrode 430 to support the light-emitting structure.

[0068] Subsequently, the light-emitting structure is separated from the nitride single-crystal substrate by general laser lift-off. In this light-emitting structure, a surface 411a of the first GaN semiconductor layer 411, which is bonded to the nitride single-crystal growth substrate, may have a nitrogen polarity, and a surface 413a of the second GaN semiconductor layer 413, located at an uppermost portion, may have a gallium polarity. That is, the two opposite surfaces of the light-emitting structure have different polarities from each other.

[0069] To ensure that both surfaces of this light-emitting structure have a gallium polarity, the surface 411a of the first GaN semiconductor layer 411 is surface-treated with a nitrogen polarity. That is, a crystal defect layer is formed, as shown in Fig. 1B and Fig. 1C, is formed on the surface 411a of the first GaN semiconductor layer 411, and then it is irradiated with a laser beam so that the polarity of the surface 411a is reversed and has a gallium polarity.

[0070] Subsequently, the first electrode 420 is formed on the surface 411a of the first GaN semiconductor layer 411 having a gallium polarity to produce a group III nitride semiconductor light emitting device 400 as shown in Fig. 6. An entire portion of the surface 411a of the first GaN semiconductor layer 411 may have a gallium polarity. Alternatively, only a portion of the surface 411a where the first electrode 420 is to be formed may have a gallium polarity. The surface 411a of the first GaN semiconductor layer 411 has a crystal arrangement that exhibits both a gallium polarity and a nitrogen polarity.

[0071] The Fig. The light-emitting structure shown in Figure 6 includes two surfaces 411a and 413a with gallium polarity. The light-emitting structure is improved with respect to spontaneous polarization caused by polarity differences between the two surfaces. Accordingly, surface band bending characteristics occur equally on both surfaces having gallium polarity. Furthermore, the light-emitting structure has low ohmic contact resistance, so constant voltage and leakage current are reduced. This leads to an improvement in the electrical characteristics of the nitride semiconductor light-emitting device 400. This will be described in detail below.

[0072] Fig. 7 is a diagram showing current-voltage characteristics of a Fig. 6. A first curve 1 represents, as described with reference to Fig. 7, represents the current-voltage characteristics of a group III nitride semiconductor light-emitting device manufactured by a conventional process. A second curve 2 represents the current-voltage characteristics of the Fig. 6. That is, the first curve 1 and the second curve 2 each represent a measurement of a current changing in response to a voltage after the voltage is applied to the light emitting device.

[0073] In technology, an ideal current-voltage characteristic of a semiconductor light-emitting device exhibits nonlinear properties. That is, a very low current flows at a negative voltage and a weak positive voltage, and a current rises rapidly at a given voltage level (approximately 0.7 V or more). The general Group III nitride semiconductor light-emitting device with the current characteristics shown in the first curve (1) is identical to that shown in Fig. 6 Group III nitride semiconductor light-emitting devices are constructed, however, a light-emitting structure of the general light-emitting device has different polarities on its two surfaces. That is, one surface of the light-emitting structure has a gallium polarity, and another surface, opposite to one surface, has a nitrogen polarity. In the light-emitting structure, an electrode formed on the other surface with a nitrogen polarity has a high ohmic contact resistance, thus generating a constant voltage and leakage current. Accordingly, the current-voltage characteristics of the general Group III nitride semiconductor light-emitting device are such that a low current flows only in a voltage range of -0.5 to 0.5 V, as shown in the first curve 1, and a large current flows in the other voltage range, thus generating a leakage current.

[0074] The group III nitride semiconductor light emitting device 400 of Fig. 6, on the other hand, exhibits nonlinear current-voltage characteristics, such that, as shown in a second curve (2), a low current flows at a negative voltage and a current increases rapidly in a voltage range of 1 to 2 V. This resembles an ideal current-voltage characteristic. Therefore, in the group III nitride semiconductor light-emitting device of the present invention, a constant voltage and a leakage current can be reduced, thereby improving the electrical characteristics.

[0075] In a group III nitride semiconductor produced by the method according to exemplary embodiments of the invention, a second surface with a nitrogen polarity opposite a first surface with a group III element polarity is irradiated with a laser beam such that the second surface is changed to have a polarity identical to the first surface. As a result, the opposing surfaces of the group III nitride semiconductor can have an identical group III element polarity.

[0076] When a semiconductor structure, such as a light-emitting device, is fabricated using a second surface surface-treated to have a group III polarity in a group III nitride semiconductor, the crystallinity of the light-emitting device is improved and thus the light-emitting efficiency is improved.

[0077] Furthermore, when the group III nitride semiconductor is regrown using the second surface surface-treated to have group III polarity, a regrown layer having better surface flatness can be formed.

[0078] Furthermore, when an electrode surface-treated to have a group III polarity is formed on the second surface of the group III nitride semiconductor, an ohmic contact resistance at a contact surface is reduced, so that electrical characteristics are improved.

Claims

[1] A surface treatment process of a group III nitride semiconductor, comprising: Providing a group III nitride semiconductor, which includes a first surface and a second surface opposite the first surface, wherein the first surface has a group III polarity and the second surface has a nitrogen polarity; and irradiating the second surface with a laser beam to change the nitrogen polarity of the second surface to the group III polarity; wherein the surface treatment method further comprises forming a crystal defect layer having a defect caused by nitrogen vacancies on the second surface before irradiating the second surface with a laser beam. [2] The surface treatment method according to claim 1, wherein forming a crystal defect layer comprises performing plasma treatment or ion beam irradiation of the second surface. [3] The surface treatment method according to claim 1, wherein the crystal defect layer comprises at least one of an amorphous region, a polycrystal region, and a group III-rich region. [4] The surface treatment method according to claim 1, wherein the crystal defect layer has a thickness of 5 to 2000 nm. [5] The surface treatment method according to claim 1, wherein the group III nitride semiconductor is a semiconductor formed by Al x In y Ga (1-x-y) N, where 0≤x≤1, 0≤y≤1 and 0≤x+y≤1. [6] The surface treatment method according to claim 1, wherein the group III nitride semiconductor is a GaN semiconductor, and the group III polarity is a gallium polarity. [7] A method of manufacturing a group III nitride semiconductor, the method comprising: Growing a group III nitride semiconductor on a nitride single crystal growth substrate, wherein the group III nitride semiconductor includes a first surface having a group III polarity and a second surface opposite the first surface, wherein the second surface is in contact with the substrate and has a nitrogen polarity; Separating the group III nitride semiconductor from the nitride single crystal growth substrate; and irradiating the second surface with a laser beam to change the nitrogen polarity of the second surface to a group III polarity; wherein the method further comprises forming a crystal defect layer having a defect caused by nitrogen vacancies on the second surface before irradiating the second surface with a laser beam. [8] The method of claim 7, wherein forming a crystal defect layer comprises performing plasma treatment or ion beam irradiation of the second surface. [9] The method of claim 7, wherein the crystal defect layer comprises at least one of an amorphous region, a polycrystal region, and a group III-rich region. [10] The method according to claim 7, wherein the crystal defect layer has a thickness of 5 to 2000 nm. [11] The method of claim 7, wherein the group III nitride semiconductor is a semiconductor formed by Al x In y Ga (1-x-y) N, where 0≤x≤1, 0≤y≤1 and 0≤x+y≤1. [12] The method of claim 7, wherein the group III nitride semiconductor is a GaN semiconductor, and the group III polarity is a gallium polarity. [13] The method of claim 7, further comprising growing an additional nitride semiconductor layer on the second surface that has been altered to have group III polarity. [14] The method according to claim 7, wherein the nitride single crystal growth substrate is made of a material selected from a group consisting of sapphire, SiC, Si, ZnO, MgAl2O4, MgO, LiAlO2 and LiGaO2.

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