Source: https://patents.google.com/patent/RU2561761C1/en
Timestamp: 2020-01-25 19:06:31
Document Index: 263453144

Matched Legal Cases: ['art 11', 'art 11', 'art 11', 'art 11', 'art 11', 'art 11']

RU2561761C1 - Nitride semiconductor ultraviolet light-emitting element - Google Patents
RU2561761C1
RU2561761C1 RU2014109007/28A RU2014109007A RU2561761C1 RU 2561761 C1 RU2561761 C1 RU 2561761C1 RU 2014109007/28 A RU2014109007/28 A RU 2014109007/28A RU 2014109007 A RU2014109007 A RU 2014109007A RU 2561761 C1 RU2561761 C1 RU 2561761C1
RU2014109007/28A
Сирил ПЕРНО
Акира ХИРАНО
Соко Кагаку Ко., Лтд.
2011-08-09 Application filed by Соко Кагаку Ко., Лтд. filed Critical Соко Кагаку Ко., Лтд.
2015-09-10 Publication of RU2561761C1 publication Critical patent/RU2561761C1/en
239000011247 coating layers Substances 0 abstract 5
SUBSTANCE: nitride semiconductor ultraviolet light-emitting element comprises: a base structure which includes a sapphire substrate (0001) and an AlN layer formed on the substrate; and a section of the structure of the light-emitting element, which includes an n-type coating layer of an n-type AlGaN semiconductor layer, an active layer, having an AlGaN semiconductor layer, a p-type coating layer of a p-type AlGaN semiconductor layer, wherein said n-type coating layer, active layer and p-type coating layer are formed on the base section of the structure. The plane (0001) of the substrate is inclined at an angle of 0.6-3.0°, and the molar ratio of AlN of the n-type coating layer is equal to greater than 50%.
EFFECT: invention improves the crystal quality of an AlGaN-based semiconductor layer formed on a sapphire substrate by optimising the inclination angle, and increases light-emitting output of the nitride semiconductor ultraviolet light-emitting element.
The present invention relates to a nitride semiconductor light emitting element obtained by forming an n-type coating layer, an active layer and a p-type coating layer, each of which is an AlGaN-based semiconductor layer, over a sapphire substrate (0001), and, more particularly, a nitride semiconductor ultraviolet light emitting element having a wavelength region of maximum radiation in the ultraviolet region.
Typically, there are a large number of light emitting structures in which nitride semiconductor light emitting elements, such as LED diodes (light emitting diodes) or semiconductor lasers, use a sapphire substrate (0001) as a substrate, and a plurality of layers of the nitride semiconductor are formed on the substrate by epitaxial growth. The nitride semiconductor layer is expressed in the general formula Al 1-xy Ga x In y N (0≤x≤1, 0≤y≤1, 0≤x + y≤1).
As the sapphire substrate (0001), in general, a slightly inclined substrate having a surface (0001) slightly inclined by an inclination angle of approximately 0.05 ° to 0.5 ° than a non-inclined substrate having a surface (0001) is used which is not inclined at all, with an inclination angle of zero degrees, under the assumption that the surface property or crystallinity of the nitride semiconductor layer to be epitaxially grown is increased (for example, see the following Patent Document 1 and Patent Document 2).
The structure of the light emitting element has a double heterostructure in which the active layer is located between the n-type nitride semiconductor layer and the p-type nitride semiconductor. The active layer is composed by a nitride semiconductor layer having a single quantum well (SQW) structure or a multiple quantum well (MQW) structure. In the case where the active layer is an AlGaN-based semiconductor layer, it is possible to control the energy of the energy gap within the range, the lower and upper limits of which are the energy of the energy gap, which can be taken away by GaN and AlN, respectively (approximately 3.4 eV and approximately 6, 2 eV) by adjusting the mole fraction of AlN (which is also referred to as the compositional ratio of AlN). Thus, it is possible to obtain an ultraviolet light emitting element having a radiation wavelength of from about 200 nm to 365 nm.
Patent Document 1: JP 2000-156341A
Patent Document 2: JP 2001-158691A
The following can be regarded as the state of the art in which a sapphire substrate (0001) is generally used having an angle of inclination of approximately 0.05 ° to 0.5 °.
As schematically shown in FIG. 1, the slightly inclined substrate is a stepped substrate having a step S between the terrace surfaces T obtained by inclining the surfaces (0001). If the inclination angle θ increases, the width W of the terrace surface T decreases. As shown in FIG. 1, the tilt angle θ is defined as the angle formed by the line connecting the upper ends or lower ends of the steps S and the terass surface T. RMS (rms) value of the concave-convex parts of the surface of the nitride semiconductor layer formed on a common sapphire substrate (0001), having an inclination angle of about 0.05 ° to 0.5 ° is usually equal to or less than 0.4 nm. When the angle of inclination increases to exceed 0.5 °, however, it is possible that the RMS value may increase to exceed 0.4 nm. On the other hand, the film thickness of the quantum well layer constituting the active layer is usually equal to or less than 5 nm. If the tilt angle is excessively increased, the fluctuation in the film thickness of the quantum well layer increases, so that the light emission performance of the light emitting element can be affected.
In the case where the surface of the substrate is stepped, in addition, the nitride semiconductor layer to be grown on it is also stepped to follow the property of the surface of the substrate. Since Ga has a great ability to migrate, it easily moves to the terass surface on the lower side behind the stepped part. For this reason, the separation of Ga occurs in the composition of the nitride semiconductor layer, which is growing. In an AlGaN-based semiconductor, therefore, an AlGaN region having a high molar fraction of AlN and an AlGaN region having a low molar fraction of AlN are formed along the stepped portion. As a result, if the tilt angle increases, it is possible that light emission from the active layer may have a more widely scattered wavelength distribution and separated peaks of the radiation wavelength.
As described above, a nitride semiconductor light emitting element using a sapphire substrate (0001) and having an inclination angle of about 0.05 ° to 0.5 ° is generally used, and mainly adapted for a light emitting element having a larger a radiation wavelength of less than approximately 365 nm when the active layer is constituted by a GaN or InGaN based semiconductor (for example, see Patent Document 1 and Patent Document 2). In an ultraviolet light emitting element having a shorter emission wavelength than approximately 365 nm, it has not been studied enough in the past whether the tilt angle within the range of about 0.05 ° to 0.5 ° is optimal or not.
In considering the aforementioned problem, an object of the present invention is to improve the crystal quality of an AlGaN based semiconductor layer formed on a (0001) sapphire substrate by optimizing the tilt angle, and to increase the light emitting output of the nitride semiconductor ultraviolet light emitting element.
The inventors of the present invention conducted a serious study and found that an excellent light-emitting yield is obtained in a state in which the full width at the half maximum level (FWHM) of the torsion strain distribution estimated by the X-ray rolling curve (XRC) method, an AlGaN layer formed on a sapphire substrate ( 0001) is equal to or less than a predetermined value in the relation between the crystallinity shown by FWHM and the light emitting output of the ultraviolet light element, emerging from the structure of the light-emitting element containing AlGaN, and additionally found that the angle of inclination at which the FWHM in the distribution of torsion strain is equal to or less than a predetermined value has a dependence of the molar fraction of AlN on AlGaN to be used in the coating layer n -type.
The present invention was created on the basis of the aforementioned new knowledge and provides a nitride semiconductor ultraviolet light emitting element including: an underlying part of the structure including a sapphire substrate (0001) and an AlN layer formed on the surface (0001) of the substrate; and a part of the structure of the light emitting element, including an n-type coating layer of an AlGaN-based n-type semiconductor layer, an active layer having an AlGaN-based semiconductor layer, and a p-type coating layer of an AlGaN-based p-type semiconductor layer, a part of the structure of the light-emitting element formed on the surface of the crystal of the underlying part of the structure, while the surface (0001) of the substrate is inclined at an angle of inclination that is equal to or greater than 0.6 ° and equal to or less than it is 3.0 °, and the molar fraction of the AlN layer of the n-type coating is equal to or greater than 50%.
According to the present invention, an AlGaN-based semiconductor is a Group III nitride semiconductor, which is based on a triple (or double) composition expressed in the general formula Al x Ga 1-x N (x represents the mole fraction of AlN, 0≤x≤1), and has an energy gap energy within the range whose lower and upper limits are the energy gap energies (approximately 3.4 eV and approximately 6.2 eV) for GaN (x = 0) and AlN (x = 1), respectively. As long as the condition relating to the energy of the energy gap is satisfied, this also includes the case when a very small amount of In is contained.
According to the nitride semiconductor ultraviolet light emitting element having the property described above, in the case where the molar fraction of the AlN layer of the n-type coating is equal to or greater than 50%, it is possible to significantly increase the probability that the FWHM in the distribution of torsion strain showing the crystallinity of the AlGaN layer The n-type, which is the top layer on the AlN layer of the underlying part of the structure, can be equal to or less than a predetermined value, thereby increasing light emitting in running with high yield within the range of 0,6 ° to 3,0 °, which is much greater than the range of the tilt angle to be used, in general, in the prior art.
In addition, in the nitride semiconductor ultraviolet light-emitting element, the tilt angle is preferably equal to or greater than 1.0 ° and equal to or less than 2.5 °. Therefore, it is possible to further improve the crystallinity of the AlGaN layer, thereby stably increasing the light emitting yield with a higher yield.
In addition, in the nitride semiconductor ultraviolet light-emitting element, the wavelength of the maximum radiation is preferably equal to or less than 300 nm. As described above, since the sapphire substrate (0001) within a range in which the angle of inclination is equal to or greater than 0.6 ° and equal to or less than 3.0 ° has a stepped surface (0001), the separation of Ga occurs in a semiconductor an AlGaN layer formed on the substrate so that the radiation wavelength distribution is scattered. The scattering of the distribution of the radiation wavelength tends to increase if the radiation wavelength increases, as will be described below. If the wavelength of the maximum radiation is equal to or less than 300 nm, the scattering distribution of the radiation wavelength (full width at the half maximum level) is controlled so that it is approximately 20 nm or less in the case where the inclination angle is 1 °. Therefore, the separation of the peak wavelength of the radiation is not formed.
In addition, in the nitride semiconductor ultraviolet light-emitting element, the film thickness of the AlN layer formed on the substrate of the underlying part of the structure is preferably equal to or greater than 2.2 μm and equal to or less than 6.6 μm. In the AlN layer of the underlying part of the structure, which has a larger film thickness, the crystallinity of the n-type AlGaN layer formed on the upper layer tends to improve more significantly. On the other hand, if the film thickness increases excessively, there is a tendency that the likelihood of a crack in the underlying part of the structure increases. By setting the film thickness equal to or greater than 2.2 μm and equal to or less than 6.6 μm, it is possible to obtain an increase effect in the light emitting output more reliably.
FIG. 1 is an illustrative view schematically showing a state of a surface of a sapphire substrate substrate (0001) inclined at an inclination angle θ.
FIG. 2 is a sectional view showing a main part schematically illustrating a layered structure according to one embodiment of a nitride semiconductor ultraviolet light emitting element in accordance with the present invention.
FIG. 3 is a plan view schematically showing a planar structure according to an embodiment of a nitride semiconductor ultraviolet light emitting element in accordance with the present invention.
FIG. 4 is a characteristic diagram showing a relationship between FWHM in a distribution of torsion strain of an n-type coating layer and a light emitting output.
FIG. 5 is a characteristic diagram showing a relationship between the tilt angle of a sapphire substrate (0001) and FWHM in a distribution of torsion strain of an n-type coating layer.
FIG. 6 is a characteristic diagram showing the relationship between the FWHM for the distribution of the torsion strain of the n-type coating layer and the FWHM for the distribution of the torsion strain of the AlN layer depending on the difference in the tilt angle of the sapphire substrate (0001).
FIG. 7 is a characteristic diagram showing the relationship between the molar fraction of AlN of the n-type coating layer and FWHM in the distribution of torsion strain.
FIG. 8 is a characteristic diagram showing a relationship between a film thickness of an AlN layer and an FWHM in a distribution of torsion strain of an n-type coating layer.
FIG. 9 is a characteristic diagram showing the relationship between the light emitting output and the direct current according to each of Example 1 and Comparative Examples 1 and 3.
FIG. 10 is a characteristic diagram showing radiation wavelength characteristics according to Example 1 and Comparative Examples 1 and 3.
FIG. 11 is a characteristic diagram showing a relationship between a light emitting output and a direct current according to each of examples 2 and 3 and comparative example 2.
FIG. 12 is a characteristic diagram showing radiation wavelength characteristics according to examples 2 and 3 and comparative example 2.
FIG. 13 is a table showing the FWHM in the distribution of torsion strain of the n-type coating layer, the light emitting output at a forward current of 100 mA, and the FWHM of the radiation wavelength distribution according to each of Examples 1 to 3 and Comparative Examples 1 to 3.
One embodiment of a nitride semiconductor ultraviolet light emitting element according to the present invention (which will be referred to below as a "light emitting element") will be described based on the drawings. As shown in the drawings, which are used in the following description, the main parts are enlarged and the contents of the invention are thus shown schematically for easy understanding of the description. For this reason, the dimensional relationship of each part is not always equal to the dimensional relationship of the actual element. In the present embodiment, a description will be given on the assumption that the light emitting element is a light emitting diode.
As shown in FIG. 2, the light emitting element 1 according to the present embodiment has a layered structure in which a substrate obtained by growing an AlN layer 3 and an AlGaN layer 4 on a sapphire substrate 2 (0001) is used as a pattern 5 (corresponding to the underlying part of the structure), and n-type coating layer 6 formed from n-type AlGaN, active layer 7, electron blocking layer 8 having a higher Al molar fraction than active layer 7 and formed from p-type AlGaN, p-type coating layer 9 formed from AlGaN p-type, and the contact layer 10 p-t IPs formed from p-type GaN are layered on template 5 in order. A portion of the active layer 7, the electron blocking layer 8, the p-type coating layer 9 and the p-type contact layer 10 provided on the n-type coating layer 6 is removed by reactive ion etching or the like until a partial surface of the layer 6 is shown n-type coatings. Part 11 of the structure of the light-emitting element from the n-type coating layer 6 to the p-type contact layer 10 is formed in the first region R1 provided on the n-type coating layer 6. Additionally, p electrode 12 formed of Ni / Au is formed on the surface of the p-type contact layer 10 and n electrode 13 formed of Ti / Al / Ti / Au is formed on a part of the surface of the second region R2 other than the first region R1 n-type coating layer 6, for example. In the present embodiment, an AlN layer 3 is used depending on the crystal growth at a temperature of about 1150 to 1300 ° C.
In the present embodiment, for the reason that will be described later, a slightly inclined substrate obtained by tilting the surface (0001) of the substrate by an angle of inclination that is equal to or greater than 0.6 ° and equal to or less than 3.0 °, used as sapphire substrate 2 (0001). It is more preferable that the inclination angle of the slightly inclined substrate is equal to or greater than 1.0 ° and equal to or less than 2.5 °. The direction of inclination of the angle of inclination may be the direction of the m-axis, the direction of the a-axis or their intermediate direction.
As an example, the active layer 7 has a single layer quantum well structure composed by an n-type AlGaN barrier layer 7a having a film thickness of 10 nm and an AlGaN well layer 7b having a film thickness of 3.5 nm. The active layer 7 may have a double heterojunction structure in which the active layer 7 is placed between n-type and p-type AlGaN layers having high molar fractions of Al on the lower layer and the upper layer, or may have a multiple quantum well structure in which a single layer structure The quantum well is multilayer.
Each AlGaN layer is formed by a well-known epitaxial growth method, such as an organometallic gas phase epitaxy (MOVPE) method or a molecular beam epitaxy (MBE) method, and Si is used as a donor impurity of an n-type layer, for example, and Mg is used as an acceptor impurities of the p-type layer. The AlN layer and the AlGaN layer, which do not determine the type of conductivity, are undoped layers in which the impurity is not embedded. Referring to the molar fractions of AlN of the n-type AlGaN layer and the active layer, as an example, the AlGaN layer 4, the n-type coating layer 6 and the barrier layer 7a have molar fractions of AlN that are equal to or greater than 50% and equal to or less than than 100% (more preferably equal to or greater than 55% and equal to or less than 90%), and the pit layer 7b has a mole fraction of AlN that is equal to or greater than 30% and is equal to or less than 80% (more preferably is equal to or greater than 35% and is equal to or less than 70%). In the present embodiment, it is assumed that the wavelength of the maximum radiation of the light emitting element 1 is equal to or greater than 223 nm and is equal to or less than 300 nm. In the present embodiment, it is assumed that the light emitting element 1 is a back-side type element in which light emission from the active layer 7 is taken from the side of the sapphire substrate 2. For this reason, it is necessary to set the mole fraction of AlN of the AlGaN layer 4 so that it is larger than the molar fraction of the pit layer 7b. As an example, the molar fractions of AlN of the AlGaN layer 4 and the n-type coating layer 6 are set equal to each other. The mole fraction of AlN layer 4 of AlGaN can be set to be larger than the mole fraction of AlN layer 6 of the n-type coating.
Referring to the film thicknesses of the corresponding AlGaN layers in terms of the structure of the light emitting element other than the active layer 7, for example, the n-type coating layer 6 has a thickness of 2000 nm, the electron blocking layer 8 has a thickness of 2 nm, the coating layer 9 of p The β-type has a thickness of 540 nm, and the p-type contact layer 10 has a thickness of 200 nm. Referring to pattern 5, moreover, the AlN layer 3 preferably has a film thickness set equal to or greater than 2200 nm and equal to or less than 6600 nm, and more preferably equal to or greater than 3000 nm and equal to or less than 6000 nm. AlGaN layer 4 has a film thickness set equal to or greater than 200 nm and equal to or less than 300 nm, for example. In the present embodiment, the n-type coating layer 6 as an AlGaN layer is formed on the AlGaN layer 4. For this reason, the conductivity type of the AlGaN layer 4 is not an undoped layer, but may be of an n-type layer, and the AlGaN layer 4 may be combined with the n-type coating layer 6 to form the pattern 5 by only AlN layer 3.
FIG. 3 shows an example of a pattern of a light emitting element 1 visible on a plane. FIG. 3 shows the first region R1 and the second region R2 before the formation of the p electrode 12 and n of the electrode 13. As an example, p electrode 12 is formed over the almost complete surface of the first region R1 and n electrode 13 is formed over the almost full surface of the second region R2. Moreover, the chip size of the light emitting element 1 used in the examples that will be described below has a length and width of 800 μm, and the first region R1 has a region of approximately 168,000 μm 2 . The first region R1 shown in FIG. 2 is part of the first region R1 shown in FIG. 3.
The respective layers of the pattern 5 and the structure part 11 of the light-emitting element in the light-emitting element 1 are formed by a well-known extension method, as described above, and the p electrode 12 and n electrode 13 are formed respectively as follows. After the photoresist, which is to be the inverse circuit of each electrode, is formed, the multilayer metal film of each electrode is deposited by the electron beam evaporation deposition method or the like, and the photoresist is removed by peeling to separate the multilayer metal film on the photoresist, and heat treatment is performed by RTA (fast by thermal annealing) or the like, if necessary.
Next, a description will be given for measurement data, which are the basis of the present invention. FIG. 4 shows the first measurement data that are the basis of the present invention. In particular, FIG. 4 is a graph of FWHM measurement values for the distribution of torsion strain obtained by evaluating the crystallinity of the n-type AlGaN layer of the n-type coating layer 6 by the XRC method, and the light emitting yield for samples in which the maximum emission wavelength of the light emitting element 1 having the structures shown in FIG. 2 and 3, is in the range from 255 nm to 300 nm. In FIG. 4, the abscissa axis shows FWHM (unit: arcsec) and the ordinate axis shows the light-emitting output (unit: mW). Each of the sapphire substrates (0001) used for the samples has a tilt angle within the range of 0.15 ° to 2.0 °.
From the measurement result in FIG. Figure 4 shows that there is a tendency that the light emitting yield decreases if the FWHM in the distribution of torsion strain increases and exceeds approximately 550 arcsec, and the light emitting output does not increase even if the FWHM in the distribution of torsion strain decreases more significantly within a range of approximately 550 arcsec or less. In other words, it is obvious that the crystallinity of the n-type AlGaN layer is sufficient if FWHM is obtained with a torsion strain distribution of approximately 550 arcsec or less.
FIG. 5 shows the second measurement data, which are the basis of the present invention. In particular, FIG. 5 is a graph of the minimum value and the median in the FWHM measurement values for the distribution of torsion strain at each tilt angle for six types of samples in which the n-type coating layer 6 has a mole fraction of AlN of 50% or more and a tilt angle of 0, 3 °, 0.6 °, 1.0 °, 1.5 °, 2.0 ° and 3.0 °. However, only the minimum value for a tilt angle of 3.0 ° is displayed. The structure of the measurement data samples shown in FIG. 5 is the same as the samples of the measurement data shown in FIG. 4, except that the semiconductor layers, which should be the upper layers on the n-type coating layer 6, and the corresponding electrodes are not formed.
Obviously from the measurement result in FIG. 5, FWHM in the distribution of torsion strain decreases if the angle of inclination increases from 0.3 ° to 1.5 °, and vice versa FWHM in the distribution of torsion strain increases if the angle of inclination increases from 1.5 ° to 3.0 °. Moreover, it is obvious that the FWHM in the distribution of torsion strain is equal to or less than approximately 550 arcsec within a range in which the tilt angle is equal to or greater than 0.6 ° and equal to or less than 3.0 °, and the light emitting output may increase by comparison with the measurement result of FIG. four.
FIG. 6 shows third measurement data that are the basis of the present invention. In particular, FIG. 6 is a graph of FWHM measurement values for the distribution of torsion strain of each of the AlN layer 3 and the n-type coating layer 6 at each angle of inclination for three types of samples in which the n-type coating layer 6 has a molar fraction of AlN equal to 50% or more, and an inclination angle of 0.15 °, 0.3 °, and 1.0 ° (sample structures are the same as sample structures of the measurement data shown in Fig. 5). In FIG. 6, the ordinate axis shows the FWHM of the n-type coating layer 6 and the abscissa axis shows the FWHM of the AlN layer 3. The solid line drawn obliquely in FIG. 6 is a line connecting the points where the FWHM values of the AlN layer 3 and the n-type coating layer 6 have the same value, and shows that crystallinity increases more significantly in the n-type coating layer 6, which should be the top layer on AlN layer 3 in the samples on the lower side of the solid line, and vice versa, crystallinity decreases more significantly in the n-type coating layer 6, which should be the upper layer on AlN layer 3 in the samples on the upper side of the solid line.
Obviously from the measurement result in FIG. 6, the FWHM of AlN layer 3 is distributed in 564 to 679 arcsec, and the FWHM of layer n of the n-type coating varies from 558 to 719 arcsec in samples having an inclination angle of 0.15 °, and crystallinity decreases in most samples. It is obvious that the FWHM of AlN layer 3 is distributed in from 402 to 773 arcsec and the FWHM of layer n of the n-type coating varies from 517 to 733 arcsec in samples having an inclination angle of 0.3 °, and crystallinity decreases in about half of the samples and crystallinity increases in about the other half of the samples. On the other hand, it is obvious that the FWHM of the AlN layer 3 is distributed in from 410 to 683 arcsec and the FWHM of the n-type coating layer 6 varies from 394 to 568 arcsec in samples having an inclination angle of 1.0 °, and the crystallinity increases in most samples, and FWHM is equal to or less than approximately 550 arcsec in almost all samples.
FIG. 7 shows fourth measurement data that are the basis of the present invention. FIG. 7 is a graph of FWHM measurement values for the distribution of the torsion strain of the n-type coating layer 6 for three types of samples having an inclination angle of 0.15 °, 0.3 °, and 1.0 ° (sample structures are the same as the data samples measurements shown in Fig. 5 and 6), in which the molar fraction of AlN layer 6 of the n-type coating changes completely within the range from 19.2% to 84%. In FIG. 7, the ordinate axis shows the FWHM of the n-type coating layer 6 and the abscissa axis shows the mole fraction of the AlN of the n-type coating layer 6.
From the measurement result in FIG. 7 it can be seen that a sample having an inclination angle of 0.15 ° tends to increase FWHM during distribution of torsional deformation and the crystallinity of the n-type coating layer 6 decreases with an increase in the molar fraction of AlN of the n-type coating layer 6 within the range, in which the molar fraction of AlN is equal to or less than about 40%, and vice versa, the FWHM decreases during torsion distribution and the crystallinity of the n-type coating layer 6 increases with an increase in the molar fraction of AlN within the range in which the molar fraction of AlN is equal to or greater shey than about 40%, and is further necessary to limit the mole fraction of AlN, so that it was equal to or less than about 28% in order to implement the FWHM of approximately 550 arcsec or less. A sample having an inclination angle of 0.3 ° tends to slightly increase the FWHM upon distribution of torsion strain and the crystallinity of the n-type coating layer 6 decreases with increasing in molar fraction of AlN within the range in which the molar fraction of AlN of coating layer 6 n the α-type is equal to or less than about 35%, and vice versa, the FWHM decreases with torsional strain distribution and the crystallinity of the n-type coating layer 6 increases with increasing in the molar fraction of AlN within the range in which the molar fraction of AlN is equal to or greater than about 35%. Although it is necessary to limit the mole fraction of AlN so that it is equal to or greater than approximately 55%, in order to realize FWHM of approximately 550 arcsec or less in a sample having an inclination angle of 0.3 °, it is not possible to expect high yields. On the other hand, it is obvious that a sample having an inclination angle of 1.0 ° has a tendency that the FWHM decreases during distribution of torsion strain and the crystallinity of the n-type coating layer 6 increases with an increase in the molar fraction of AlN of the n-type coating layer 6 within a range in which the mole fraction of AlN is equal to or greater than about 30%, and further, FWHM of about 550 arcsec or less can be realized with high production within a range in which the mole fraction of AlN of the n-type coating layer 6 is equal to or more hours I eat about 50%.
From the measurement results shown in FIG. 4 to 7, it is obvious that the n-type coating layer 6 having an FWHM with a torsional strain distribution of approximately 550 arcsec or less and excellent crystallinity can be realized with high yield, so that a high light-emitting yield can be stably obtained since the molar fraction The AlN of the n-type coating layer 6 is set equal to or greater than 50% and the tilt angle of the sapphire substrate (0001) is set equal to or greater than 0.6 ° and equal to or less than 3.0 ° in the light emitting element 1 according to the present embodiment.
From the measurement result shown in FIG. 5, it is obvious that, moreover, it is possible to further reduce the FWHM when the torsion strain distribution is from approximately 550 arcsec, thereby obtaining a high light-emitting yield more stably by setting the tilt angle of the sapphire substrate (0001) in the range from 1.0 ° to 2.5 ° .
From the measurement result shown in FIG. 7, it is obvious that it is further preferred that the angle of inclination of the sapphire substrate (0001) is small, i.e., approximately 0.15 °, in the case where the mole fraction of AlN of the n-type coating layer 6 is equal to or less than 28%, that is, the radiation wavelength from the active layer 7 is also large in the same nitride semiconductor ultraviolet light-emitting element, and vice versa, it is preferable that the angle of inclination significantly exceeds the commonly used range so that it is equal to or less than 0.6 ° and was equal to or less than 3.0 ° if the molar fraction of AlN of the n-type coating layer 6 is equal to or greater than 50%, that is, the radiation wavelength from the active layer 7 is small (approximately 300 nm or less).
FIG. 8 shows the measurement result for the dependence of the film thickness of the AlN layer for samples in which the molar fraction of AlN layer 6 of the n-type coating is equal to or greater than 50% and the angle of inclination is 1.0 ° (the structure of each of the samples is the same as the structure each of the samples of the measurement data shown in Fig. 5 to 7). It is apparent that approximately 550 arcsec or less can be realized as FWHM in the distribution of the torsion strain of the n-type coating layer 6 with its film thickness within the range of 2200 nm to 6600 nm.
Further, FIG. 9 to 12 show the results obtained by measuring the light emitting outputs and wavelength distributions in two examples 1 and 2 of the light emitting element 1 according to the present embodiment, in which the tilt angle of the sapphire substrate 2 (0001) is 1.0 °, and example 3 of the light emitting element 1 according to the present embodiment, in which the angle of inclination is 0.6 °, and two comparative examples 1 and 2, in which the angle of inclination of sapphire substrate 2 (0001) is 0.3 °, and comparative example 3, in which the angle of inclination is 0.15 °. In example 1 and comparative examples 1 and 3, only the tilt angles differ from each other, other element structures are the same, the molar fractions of AlN of the n-type coating layer 6 and the well layer 7b are 60% and 35%, respectively, and the radiation wavelengths are approximately equal to each other (first group of radiation wavelength). In examples 2 and 3 and comparative example 2, only the tilt angles are different from each other, other element structures are the same, the molar fractions of AlN of the n-type coating layer 6 and the well layer 7b are 70% and 55%, respectively, and the radiation wavelength are approximately equal to each other (second group of radiation wavelength).
FIG. 9 shows a characteristic of the light emitting output, showing the relationship between the light emitting output and the direct current in each of Example 1 and comparative examples 1 and 3, and FIG. 10 shows a characteristic of the radiation wavelength according to each of example 1 and comparative examples 1 and 3. FIG. 11 shows a characteristic of the light emitting output, showing the relationship between the light emitting output and the direct current in each of examples 2 and 3 and comparative example 2, and FIG. 12 shows a characteristic of the radiation wavelength according to each of examples 2 and 3 and comparative example 2. In FIG. 10 and 12, the ordinate axis for the characteristic of the radiation wavelength shows the radiation intensity normalized by setting the peak output equal to unity. Moreover, FIG. 13 collectively shows, in the table, the FWHM for the distribution of the torsion strain of the n-type coating layer 6, the light emitting output at a forward current of 100 mA, and the FWHM of the radiation wavelength distribution according to each of examples 1 to 3 and comparative examples 1 to 3 .
From FIG. 9 and 11, it is obvious that the light-emitting output increases when the tilt angle increases in the respective groups of the radiation wavelength, even if the same direct current is applied.
Additionally, is apparent from FIG. 10 and 12, that the radiation wavelength distribution is scattered when the angle of inclination increases and exceeds 0.3 ° in the corresponding radiation wavelength groups. In the two groups of radiation wavelengths, it is obvious that the scattering of the distribution of the radiation wavelength is suppressed in the second group of the radiation wavelength having a shorter radiation wavelength. Although there is a tendency that the maximum radiation wavelength increases when the tilt angle increases in the respective radiation wavelength groups, it is obvious that a change in the maximum radiation wavelength is suppressed with a smaller radiation wavelength. In detail, in FIG. 10, in example 1 with an inclination angle of 1.0 °, in comparison with comparative example 3 with an inclination angle of 0.15 °, the wavelength of the maximum radiation is greater by approximately 15 nm, i.e., approximately 300 nm, the distribution FWHM value the radiation wavelength is increased to be approximately 18 nm, which is approximately 1.5 times greater than this value in comparative example 3, and the separation of the peak radiation wavelength is not observed. In FIG. 12, in Example 2 having a tilt angle of 1.0 °, compared with comparative example 2 with a tilt angle of 0.3 °, the wavelength of the maximum radiation is slightly larger by about 2.0 nm, i.e., approximately 260 nm, the FWHM value of the radiation wavelength distribution increases to be approximately 12 nm, which is approximately 1.2 times larger than this value in comparative example 2, and the increase is suppressed to be approximately 1.2 times larger than in comparative example 2.
The scattering of the wavelength distribution of the radiation observed in FIG. 10 and 12, is caused by an increase in the step of sapphire substrate 2 (0001), the occurrence of Ga separation in the AlGaN layer in the active layer 7 of part 11 of the light-emitting element structure formed on the substrate 2, and the formation of an AlGaN region having a high molar fraction of AlN and an AlGaN region having a low mole fraction of AlN along the stepped portion when the angle of inclination increases, as described above.
From the measurement data, the following is obvious. In the case where the molar fraction of AlN of the n-type coating layer 6 is equal to or greater than 50%, that is, the radiation wavelength from the active layer 7 is small (approximately 300 nm or less), the light-emitting yield can be increased by setting the angle of inclination of the sapphire substrate (0001) to be equal to or greater than 0.6 ° and equal to or less than 3.0 ° significantly outside the commonly used range, although an increase in the FWHM of the radiation wavelength distribution is slightly caused.
An embodiment of the light emitting element 1 has been described in detail above. Although a description has been given by adopting part 11 of the structure of the light emitting element shown in FIG. 2, as an example of a part of the structure of the light emitting element constituting the light emitting element 1 in the embodiment, the layered structure, electrode structure, film thickness, mole fraction AlN of the AlGaN layer and the like are illustrative in the description and the structure part 11 of the light emitting element is not limited to the said specific example. Additionally, the shape of the light emitting element 1 visible on a plane is not limited to the shape shown in FIG. 3.
In particular, the measurement data shown in FIG. 5 to 8 relate to samples in which the structure of the upper layer element on the n-type coating layer 6 is not formed, and show that the relationship between the tilt angle and the crystallinity of the n-type coating layer 6 (FWHM in the distribution of torsion strain) is established, if the molar fraction of AlN of the n-type coating layer 6 is equal to or greater than 50%, regardless of the structure of the element of part 11 of the structure of the light-emitting element. An increase in the light-emitting characteristic with an improvement in crystallinity of the n-type coating layer 6 can also be expected in other structures of the light-emitting element.
The nitride semiconductor ultraviolet light emitting element according to the present invention can be used in a light emitting diode in which the mole fraction of the n-type AlN coating layer is equal to or greater than 50% or the like, and is effective for improving the light emitting output.
Description of Reference Positions
1: nitride semiconductor ultraviolet light emitting element
2: sapphire substrate (0001)
5: template (underlying part of the structure)
6: n-type coating layer (n-type AlGaN)
7a: barrier layer
7b: pit layer
9: p-type coating layer (p-type AlGaN)
10: p-layer contact (p-type GaN)
11: part of the structure of the light emitting element
12: p-electrode
13: n-electrode
R1: first area
R2: second area
1. Nitride semiconductor ultraviolet light-emitting element containing:
an underlying portion of the structure including a sapphire substrate (0001) and an AlN layer formed on the surface (0001) of the substrate; and
a part of the structure of the light emitting element, including an n-type coating layer of an AlGaN-based n-type semiconductor layer, an active layer having an AlGaN-based semiconductor layer, and a p-type coating layer of an AlGaN-based p-type semiconductor layer, and part of the structure a light-emitting element is formed on the surface of the crystal of the underlying part of the structure,
wherein the surface (0001) of the substrate is inclined at an inclination angle that is equal to or greater than 0.6 ° and equal to or less than 3.0 °, and
the mole fraction of the AlN layer of the n-type coating is equal to or greater than 50%.
2. The nitride semiconductor ultraviolet light emitting element according to claim 1, in which the angle of inclination is equal to or greater than 1.0 ° and equal to or less than 2.5 °.
3. The nitride semiconductor ultraviolet light emitting element according to claim 1 or 2, in which the wavelength of the maximum radiation is equal to or less than 300 nm.
4. The nitride semiconductor ultraviolet light emitting element according to claim 1 or 2, wherein the film thickness of the AlN layer formed on the substrate of the underlying part of the structure is equal to or greater than 2.2 μm and equal to or less than 6.6 μm.
5. The nitride semiconductor ultraviolet light emitting element according to claim 3, wherein the film thickness of the AlN layer formed on the substrate of the underlying part of the structure is equal to or greater than 2.2 μm and equal to or less than 6.6 μm.
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2017-06-21 PD4A Correction of name of patent owner