JP5974980B2 - Nitride semiconductor light emitting device - Google Patents

Description

  The present invention relates to a nitride semiconductor light emitting device having a light emitting layer between an n type nitride semiconductor layer and a p type nitride semiconductor layer.

  Since light emitting elements using nitride semiconductors can control the emission wavelength according to the materials used, they are currently used in various fields, and their research and development are also being actively conducted (for example, patents). Reference 1).

  A conventional nitride semiconductor light emitting device has a structure in which a p-side contact layer overdoped with Mg, a p-type nitride semiconductor layer doped with Mg, a light emitting layer, and an n-type nitride semiconductor layer doped with Si are sequentially stacked. doing.

JP 2007-59830 A

  Conventionally, the p-side contact layer is heavily doped in order to improve the contact property with the electrode formed on the p-side contact layer and realize ohmic connection. More specifically, a configuration is adopted in which ITO or Ni, which is a degenerate semiconductor, is provided as a contact electrode on the p-side contact layer, and a metal electrode (Ag, Al) is further provided on the contact electrode.

  However, in the conventional nitride semiconductor light emitting device described above, the contact electrode made of ITO or Ni used for making contact with the p-side contact layer doped with Mg at a high concentration absorbs light of a short wavelength. Therefore, there is a problem that the light emission intensity in the short wavelength region is lowered. For example, since ITO has an absorption edge near 365 nm and Ni has an absorption edge on the longer wavelength side than ITO, there is a strong concern that the emission intensity in the ultraviolet wavelength region is reduced.

  The present invention realizes a nitride semiconductor light emitting device having contact characteristics equivalent to those of a conventional nitride semiconductor light emitting device without using a contact electrode formed of a material such as ITO or Ni, thereby transmitting in the ultraviolet wavelength region. The object is to realize an element with a high rate.

  If a metal electrode can be formed directly on the p-type contact layer without providing a contact electrode made of ITO or Ni, the above problem of absorption of short wavelength light by the material forming the contact electrode is solved. The However, with conventional techniques, it has been considered that good ohmic characteristics cannot be realized when a metal electrode is directly formed on the p-type contact layer without providing such a contact electrode. The present inventor has made an excellent study between a semiconductor layer and a metal electrode by providing a contact layer (semiconductor layer) by a method different from that of a conventional nitride semiconductor light-emitting device, without providing a contact electrode, through intensive research. Thus, a nitride semiconductor light emitting device exhibiting contact characteristics has been realized.

That is, the nitride semiconductor light emitting device of the present invention is
In a nitride semiconductor light emitting device having a light emitting layer between an n type nitride semiconductor layer and a p type nitride semiconductor layer,
A first contact layer made of a nitride semiconductor layer in contact with the p-type nitride semiconductor layer and doped with a first impurity material at a higher concentration than the p-type nitride semiconductor layer;
Al _X Ga _Y In _Z N (0 ≦ X ≦ 1) in contact with the first contact layer and doped with at least one second impurity material of any one of Zn, Cd, Be, Sr, Ca and C , 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, and X + Y + Z = 1).

Al _X Ga _Y In _ZN (0 ≦ X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1) constituting the second contact layer is a trace amount of other substances (Sb, etc.) May be contained.

  The second impurity material doped into the second contact layer (one or more of Zn, Cd, Be, Sr, Ca and C) is generally doped when forming the p-type nitride semiconductor layer. A deeper impurity level is formed than the material (Mg). More specifically, the activation energy of the second impurity material doped to the second contact layer is higher than the activation energy of the first impurity material doped to the first contact layer. The second impurity material may be selected. For example, when both the first contact layer and the second contact layer are made of GaN, the activation energy of Mg is 140 meV, whereas Zn is 350 meV.

  In the second contact layer, since a deep level is formed by the second impurity material, even if an impurity is added to the semiconductor layer at an effective density or higher, it is not ionized, and carriers are not located in the valence band but between the sites formed by the impurity. Conduct hopping conduction. When a voltage is applied between the elements, electrons that are trapped in a deep level and cannot move are thermally excited at a level capable of tunneling under the influence of an electric field, and then tunnel hopping. It is considered that the carrier can move with high efficiency.

  In order to realize hopping conduction, it is necessary to apply an electric field to the second contact layer. When the nitride semiconductor light emitting device emits light, an electric field is inevitably applied to the second contact layer because a voltage is applied to cause a current to flow through the light emitting layer. Here, according to the current-voltage characteristics (IV characteristics) of the light emitting layer, current does not flow until the rising voltage in the initial stage, and when a voltage higher than that voltage is applied, current starts to flow through the light emitting layer and emits light. Is started. By applying the voltage at this initial stage, an electric field necessary for realizing hopping conduction is applied to the second contact layer, so that a driving voltage for flowing a current necessary for the light emitting layer is increased as compared with the conventional case. There is no problem.

  According to this configuration, contact characteristics equivalent to those of a conventional configuration having a contact electrode made of ITO or Ni are realized without having a contact electrode. For this reason, since the metal electrode can be formed in contact with the second contact layer, the problem of the conventional nitride semiconductor light emitting device that the emission intensity in the short wavelength region is reduced is solved.

In particular, Zn can be suitably used as the second impurity material. In this case, better contact characteristics can be realized by setting the concentration of Zn to be doped to 1 × 10 ¹⁹ / cm ^{3 to} 5 × 10 ²¹ / cm ³ . In order to realize hopping conduction, it is necessary to narrow the interval between the levels, so that it is preferable to set the impurity concentration to be equal to or higher than the effective state density. Further, it is considered that when doping is performed at an excessively high concentration, the crystallinity of the Al _X Ga _Y In _ZN material forming the second contact layer is deteriorated and the resistance is substantially increased. For this reason, it is preferable to dope the second contact layer with a concentration in the above range.

  In addition to the above configuration, the nitride semiconductor light emitting device of the present invention has a configuration in which a metal electrode containing at least one of Ag (including an Ag alloy) and Al is in contact with the second contact layer. Can do.

Since the second contact layer has good ohmic characteristics, a metal electrode can be formed in direct contact with the second contact layer. In particular, by using Ag (including an Ag alloy) or Al having high reflectivity as the metal electrode, light emitted from the light emitting layer to the p-type nitride semiconductor layer side is reflected in the light extraction direction. The function as a reflective electrode can be realized. In particular, when the nitride semiconductor light emitting device of the present invention is realized as a light source for deep ultraviolet light, the p-type nitride semiconductor layer, the first contact layer, and the second contact layer are all made of Al _X Ga _Y In _Z N (0 <X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1), and the metal electrode is preferably made of Al. Thereby, it is not necessary to form the contact electrode with a material having an absorption edge longer than the emission wavelength, such as ITO or Ni, and thus a deep ultraviolet light source element with high light extraction efficiency can be realized. At this time, the composition ratios of Al _X Ga _Y In _Z N constituting the p-type nitride semiconductor layer, the first contact layer, and the second contact layer are not necessarily all common. Different ratios may be used.

  According to the nitride semiconductor light emitting device of the present invention, a device having contact characteristics equivalent to those of a conventional nitride semiconductor light emitting device can be realized without using a contact electrode formed of a material such as ITO or Ni.

1 is a schematic cross-sectional view showing a schematic configuration of a nitride semiconductor light emitting device according to a first embodiment of the present invention. It is a schematic cross section which shows schematic structure of a prior art example and a comparative example. It is a graph which shows the current-voltage characteristic in each element of an Example, a prior art example, and a comparative example. 10 is a table showing the results of verifying contact characteristics when the concentration of Zn doped in the second contact layer is changed in the element 1 of the example. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 1st Embodiment. It is a schematic cross section which shows schematic structure of the nitride semiconductor light-emitting device of 2nd Embodiment of this invention. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 2nd Embodiment. It is a part of process sectional drawing of the nitride semiconductor light-emitting device of 2nd Embodiment.

[First Embodiment]
An example of the structure of the nitride semiconductor light emitting device according to the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of a nitride semiconductor light emitting device 1. In the following, the expression “AlGaN” is described by omitting the composition ratio of Al and Ga, and does not indicate that the composition ratio is 1: 1. Moreover, the arrow in FIG. 1 has shown the extraction direction of light.

<Construction>
The nitride semiconductor light emitting device 1 includes a support substrate 11, a conductive layer 20, an insulating layer 21, a semiconductor layer 30, an electrode 42 and a bonding electrode 43. The semiconductor layer 30 includes a p-type nitride semiconductor layer 31, a first contact layer 32, a light emitting layer 33, a second contact layer 34, and an n-type nitride semiconductor layer 35.

(Support substrate 11)
The support substrate 11 is composed of a conductive substrate such as CuW, W, or Mo, or a semiconductor substrate such as Si.

(Conductive layer 20)
A conductive layer 20 having a multilayer structure is formed on the support substrate 11. In this embodiment, the conductive layer 20 includes a solder layer 13, a solder layer 15, a protective layer 17, and a metal electrode 19.

  The solder layer 13 and the solder layer 15 are made of, for example, Au—Sn, Au—In, Au—Cu—Sn, Cu—Sn, Pd—Sn, Sn, or the like. As will be described later, the solder layer 13 and the solder layer 15 are bonded together after the solder layer 13 formed on the support substrate 11 and the solder layer 15 formed on another substrate are opposed to each other. It is formed by.

  The protective layer 17 is made of, for example, a Pt-based metal (an alloy of Ti and Pt), W, Mo, or the like. As will be described later, when bonding is performed via a solder layer, the material constituting the solder diffuses to the metal electrode 19 side described later, and functions to prevent a decrease in luminous efficiency due to a drop in reflectance.

  The metal electrode 19 is made of, for example, Ag (including an Ag alloy), Al, or the like. It is assumed that the nitride semiconductor light emitting device 1 takes out the light emitted from the light emitting layer 33 of the semiconductor layer 30 in the upward direction on the paper of FIG. 1, and the metal electrode 19 radiates downward from the light emitting layer 33 on the paper surface. It has a role as a reflective electrode that reflects the emitted light upward, and fulfills a function of increasing luminous efficiency. In the nitride semiconductor light emitting device 1, a contact electrode such as ITO or Ni for improving the contact property is not formed on the metal electrode 19.

  Note that the conductive layer 20 is partially in contact with the semiconductor layer 30, and when a voltage is applied between the support substrate 11 and the bonding electrode 43, the support substrate 11, the conductive layer 20, the semiconductor layer 30, and the bonding electrode A current path that flows to the bonding wire 45 through 43 is formed.

(Insulating layer 21)
Insulating layer 21 is composed for example _{SiO 2, SiN, Zr 2 O} 3, AlN, etc. _Al 2 _{O 3.} The insulating layer 21 has an upper surface in contact with the semiconductor layer 30, more specifically, a bottom surface of the second contact layer 34. As will be described later, the insulating layer 21 has a function as an etching stopper layer at the time of element isolation (step S7), and also has a function of spreading current in a direction parallel to the substrate surface of the support substrate 11.

(Semiconductor layer 30)
As described above, the semiconductor layer 30 includes the p-type nitride semiconductor layer 31, the first contact layer 32, the light emitting layer 33, the second contact layer 34, and the n-type nitride semiconductor layer 35.

(N-type nitride semiconductor layer 35)
In the present embodiment, the n-type nitride semiconductor layer 35 is composed of Al _n Ga _1-n N (0 ≦ n ≦ 1). At least the n-type nitride semiconductor layer 35 is doped with n-type impurities such as Si, Ge, S, Se, Sn, and Te, and is preferably doped with Si.

  In the example of FIG. 1, the n-type nitride semiconductor layer 35 has irregularities on the upper surface. This is because the light emitted upward from the light emitting layer 33 (and the reflected light emitted upward from the metal electrode 19) is reduced in the amount of light reflected downward on the surface of the n-type nitride semiconductor layer 35, The purpose is to increase the amount of light extracted outside the element.

  The n-type nitride semiconductor layer 35 is configured with a film thickness of about 0.5 μm to 1 μm. As described above, in the case where irregularities are formed on the upper surface of the n-type nitride semiconductor layer 35, the n-type nitride semiconductor layer 35 extends from the irregular recesses (valleys) to the interface with the light emitting layer 33. The thickness of the n-type nitride semiconductor layer 35 may be from the convex / concave portion (mountain portion) to the interface with the light emitting layer 33.

(Light emitting layer 33)
The light emitting layer 33 is formed of a semiconductor layer having a multiple quantum well structure in which, for example, a well layer made of InGaN and a barrier layer made of AlGaN are repeated. These layers may be undoped or p-type or n-type doped.

(P-type nitride semiconductor layer 31, first contact layer 32)
The p-type nitride semiconductor layer 31 and the first contact layer 32 are made of, for example, Al _m Ga _1-m N (0 ≦ m ≦ 1). The semiconductor materials constituting the p-type nitride semiconductor layer 31 and the first contact layer 32 may be different. That is, as an example, the p-type nitride semiconductor layer 31 may be made of AlGaN, and the first contact layer 32 may be made of GaN.

Here, the first contact layer 32 is more highly doped than the p-type nitride semiconductor layer 31. For example, the impurity concentration of the p-type nitride semiconductor layer 31 is about 1 × 10 ¹⁹ / cm ³ or more and 5 × 10 ¹⁹ / cm ³ or less, and the first contact layer 32 is 5 × 10 ¹⁹ / cm ³ or more, 5 × 10 ²⁰ / cm ³ or less Any of these layers may have Mg as a dopant.

(Second contact layer 34)
Second contact layer 34, Zn, Cd, Be, Sr , any one or more of the second impurity material of Ca and _{C-doped, Al X Ga Y In Z N} (0 ≦ X ≦ 1,0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, X + Y + Z = 1). For example, the impurity concentration of the second contact layer 34 is about 1 × 10 ¹⁹ / cm ³ or more and about 5 × 10 ²¹ / cm ³ or less. Specifically, it can be a Ga N doped with Zn as an example. Here, as the impurity material doped into the second contact layer 34 (corresponding to “second impurity material”), the impurity material doped into the first contact layer 32 (corresponding to “first impurity material”) is the first contact. Any material that forms an impurity level deeper than the impurity level formed in the layer 32 may be used. As an example, when the first contact layer 32 is doped with Mg, when the second contact layer 34 is doped with Zn, the impurity levels formed in the second contact layer 34 are the impurities formed in the first contact layer 32. The position is deeper than the level.

  As will be described later with reference to the embodiment, the nitride semiconductor light emitting device 1 uses the hopping conduction in the second contact layer 34 to achieve a good ohmic connection between the semiconductor layer 30 and the metal electrode 19 even without the contact electrode. It is a structure that is formed and can realize low-voltage driving. As the second impurity material doped in the second contact layer 34, a material that forms a deep level as described above is used. The first contact layer 32 is configured to have an intermediate level between the Fermi levels because the Fermi levels of the p-type nitride semiconductor layer 31 and the second contact layer 34 are separated from each other. preferable.

(Electrode 42, Bonding electrode 43)
The electrode 42 and the bonding electrode 43 are formed in the upper layer of the n-type nitride semiconductor layer 35 and are made of, for example, Cr—Au. More specifically, the electrode 42 and the bonding electrode 43 are formed in the upper layer of the n-type nitride semiconductor layer 35 in the position directly above the region where the bottom surface of the semiconductor layer 30 and the top surface of the insulating layer 21 are in contact. . As a result, a material with low conductivity is formed below the electrode, so that an effect of spreading the current in the light emitting layer 33 in the horizontal direction when a current is applied can be obtained.

  A bonding wire 45 made of, for example, Au or Cu is connected to the bonding electrode 43, and the other end of the wire is connected to a power supply pattern (not shown) of the substrate on which the nitride semiconductor light emitting element 1 is disposed. Is done.

<Verification of contactability>
With respect to the point that the nitride semiconductor light emitting device 1 of the present invention can realize a good contact layer equivalent to the conventional one without providing ITO or Ni, a description will be given with reference to Examples.

(Example)
The nitride semiconductor light emitting device 1 shown in FIG. 1 was taken as an example. Here, the semiconductor layer 30 includes an n-type nitride semiconductor layer 35 made of Al _0.06 Ga _0.94 N having a Si concentration of 3 × 10 ¹⁹ / cm ³ , a well layer made of InGaN, and an n-type AlGaN. A light-emitting layer 33 having a 15-cycle multi-quantum well structure, and a p-type nitride semiconductor layer 31 composed of Al _0.06 Ga _0.94 N having an Mg concentration of about 3 × 10 ¹⁹ / cm ^3. A first contact layer 32 made of GaN having an Mg concentration of about 1 × 10 ²⁰ / cm ³ , and a second contact layer 34 made of GaN having a Zn concentration of about 1 × 10 ²⁰ / cm ³ It was. Further, the metal electrode 19 was made of Ag.

(Conventional example)
FIG. 2A schematically shows a configuration of a conventional element 80. In the element 80 of this conventional example, the first contact layer 32 is in contact with the conductive layer 20a without including the second contact layer 34 as compared with the embodiment. More specifically, the conductive layer 20 a includes a contact electrode 83 made of Ni in addition to the metal electrode 19, and the contact electrode 83 is in contact with the first contact layer 32. Other configurations are the same as those in the example.

(Comparative example)
FIG. 2B schematically shows the configuration of the element 81 of the comparative example. The element 81 of this comparative example has a configuration in which the contact electrode 83 is not provided for the element 80 of the conventional example. That is, the first contact layer 32 is in contact with the conductive layer 20, more specifically, the metal electrode 19.

(inspection result)
FIG. 3 shows current I and voltage V when voltage V is applied between bonding electrode 43 and support substrate 11 for device 1 of the example, device 80 of the conventional example, and device 81 of the comparative example. Is a graph of the relationship.

  According to FIG. 3, the element 1 of the example has a configuration in which the first contact layer 32 is not in contact with the metal electrode 19 without the contact electrode 83, as in the conventional element 80 having the contact electrode 83. A lower voltage can be realized than the element 81 of a certain comparative example. Therefore, according to the configuration of the present invention, it can be seen that good contact property equivalent to or higher than that of the conventional element 80 having the contact electrode 83 can be realized without forming the contact electrode 83.

  This is presumably due to the following reasons. Since the first contact layer 32 is doped with Mg at a high concentration, a shallow impurity level is formed, and the acceptor is ionized at room temperature. Further, Ag formed as the metal electrode 19 has a small work function. For this reason, when Ag (metal electrode 19) is brought into direct contact with the first contact layer 32 as in the comparative example, a large external voltage is required to cause a tunnel effect to flow current. Therefore, conventionally, in order to reduce the external voltage, a contact electrode 83 formed of Ni or the like has been interposed. As in the element 80 of the conventional example, the contact electrode 83 is formed, NiO is formed by annealing in an oxygen atmosphere, and the work function difference from the first contact layer 32 is reduced. The external voltage can be lowered.

On the other hand, the element 1 of the example has the second contact layer 34 doped with Zn. Zn, unlike Mg, forms an impurity level at a deep level from the valence band in Al _X Ga _Y In _ZN . For this reason, the acceptor is not ionized, and even if an impurity is added to the semiconductor layer at an effective density or higher, the energy level is localized. Therefore, carriers do not valence band, but hop conduction between the sites formed by the impurity. . That is, electrons trapped in a deep level and cannot move are thermally excited at a level capable of tunneling by an applied electric field and then tunnel hopped, so that the conventional example does not have the contact electrode 83. It is considered that the operating voltage could be reduced as in the case of the element 80.

  Further, by doping a material (second impurity material) that forms a deep level, such as Zn, the energy level is localized even when doped at a high concentration, and hopping conduction can be realized. On the other hand, since the width of the depletion layer can be narrowed by doping at a high concentration, an effect of facilitating movement of carriers to the metal electrode 19 side by tunneling can be obtained.

FIG. 4 shows the results of verifying the contact characteristics when the concentration of Zn doped in the second contact layer 34 is changed in the element 1 of the example. In the case of 8 × 10 ¹⁸ / cm ³ , the contact characteristics deteriorated, and in the case of 1 × 10 ¹⁹ / cm ³ , the contact characteristics were better than in the case of 8 × 10 ¹⁸ / cm ³ . Further, when the concentration was 5 × 10 ¹⁹ / cm ³ , 1 × 10 ²⁰ / cm ³ , 5 × 10 ²⁰ / cm ³ , and 1 × 10 ²¹ / cm ³ , extremely good contact characteristics were obtained. . When the concentration is 5 × 10 ²¹ / cm ³ , the contact characteristics are the same as the case of 1 × 10 ¹⁹ / cm ³ , and when the concentration is higher (1 × 10 ²² / cm ³ ), the contact characteristics deteriorate. did.

In the case where the Zn concentration is 8 × 10 ¹⁸ / cm ³ , it is assumed that as a result of the concentration being too low, the discrete level of localized impurity levels is high, and carrier hopping conduction is not efficiently performed. Is done. In addition, when the Zn concentration is 1 × 10 ²² / cm ³ , the resistance has increased due to the crystallinity of Al _X Ga _Y In _ZN being deteriorated by doping at a very high concentration. It is guessed.

Therefore, according to the experimental results shown in FIG. 4, the Zn concentration doped in the second contact layer 34 is preferably 1 × 10 ¹⁹ / cm ^{3 to} 5 × 10 ²¹ / cm ³ , and more preferably 5 × 10 10. ^{19 / cm 3 ~1 × 10 21} / cm 3 is said to be more preferable.

  As described above, according to the element 1 of Example 1, the contact electrode 83 using ITO having an absorption edge near 365 nm or Ni having an absorption edge longer than that is used without using the contact electrode 83. Since the contact characteristics can be realized, the contact electrode 83 is not necessary. Thereby, absorption of ultraviolet light in the contact electrode 83 is suppressed, and an ultraviolet light emitting element with improved light extraction efficiency is realized.

<Other configuration>
Both the first contact layer 32 and the second contact layer 34 may be formed of AlGaN having a predetermined composition ratio, and the metal electrode 19 may be formed of Al. Al X _Ga Y _In Z _N by increasing the composition ratio of Al in, it is possible to shift the absorption edge on the shorter wavelength side, the nitride semiconductor light emitting element 1, forming a device that emits deep ultraviolet light Can do. In this case, since the contact electrode 83 formed of Ni, ITO or the like is not necessary, absorption of deep ultraviolet light in the contact electrode 83 is suppressed, and a deep ultraviolet light emitting element with improved light extraction efficiency is realized. .

<Manufacturing process>
Next, a manufacturing process of the nitride semiconductor light emitting device 1 shown in FIG. 1 will be described. This manufacturing process is merely an example, and the gas flow rate, the furnace temperature, the furnace pressure, and the like may be appropriately adjusted.

(Step S1)
As shown in FIG. 5A, the epi layer 40 is formed on the sapphire substrate 61. This step S1 is performed by the following procedure, for example.

<Preparation of sapphire substrate 61>
First, the c-plane sapphire substrate 61 is cleaned. More specifically, for this cleaning, for example, a c-plane sapphire substrate 61 is placed in a processing furnace of a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, and hydrogen having a flow rate of 10 slm is placed in the processing furnace. While flowing the gas, the temperature in the furnace is raised to, for example, 1150 ° C.

<Formation of undoped layer 36>
Next, a low-temperature buffer layer made of GaN is formed on the surface of the c-plane sapphire substrate 61, and a base layer made of GaN is further formed thereon. These low-temperature buffer layer and underlayer correspond to the undoped layer 36.

  A more specific method for forming the undoped layer 36 is, for example, as follows. First, the furnace pressure of the МОCVD apparatus is 100 kPa, and the furnace temperature is 480 ° C. Then, while flowing nitrogen gas and hydrogen gas with a flow rate of 5 slm respectively as carrier gas into the processing furnace, trimethylgallium (TMG) with a flow rate of 50 μmol / min and ammonia with a flow rate of 250,000 μmol / min are used as the raw material gas in the processing furnace. For 68 seconds. As a result, a low-temperature buffer layer made of GaN having a thickness of 20 nm is formed on the surface of the c-plane sapphire substrate 61.

  Next, the furnace temperature of the MOCVD apparatus is raised to 1150 ° C. Then, while flowing nitrogen gas having a flow rate of 20 slm and hydrogen gas having a flow rate of 15 slm as a carrier gas in the processing furnace, TMG having a flow rate of 100 μmol / min and ammonia having a flow rate of 250,000 μmol / min are introduced into the processing furnace as source gases. Feed for 30 minutes. As a result, a base layer made of GaN having a thickness of 1.7 μm is formed on the surface of the first buffer layer.

<Formation of n-type Nitride Semiconductor Layer 35>
Next, an n-type nitride semiconductor layer 35 having a composition of Al _n Ga _1-n N (0 ≦ n ≦ 1) is formed on the undoped layer 36.

A more specific method for forming the n-type nitride semiconductor layer 35 is, for example, as follows. First, with the furnace temperature kept at 1150 ° C., the furnace pressure of the MOCVD apparatus is set to 30 kPa. Then, while flowing nitrogen gas having a flow rate of 20 slm and hydrogen gas having a flow rate of 15 slm as a carrier gas into the processing furnace, TMG having a flow rate of 94 μmol / min, trimethylaluminum (TMA) having a flow rate of 6 μmol / min, Ammonia with a flow rate of 250,000 μmol / min and tetraethylsilane with a flow rate of 0.025 μmol / min are supplied into the treatment furnace for 60 minutes. Thereby, for example, an n-type nitride semiconductor layer 35 having a composition of Al _0.06 Ga _0.94 N, a Si concentration of 3 × 10 ¹⁹ / cm ³ and a thickness of 2 μm is formed in the upper layer of the undoped layer 36. Is done. Then, the n-AlGaN layer having a thickness of 2 μm is shaved with an ICP device so that the thickness becomes about 0.8 μm, and the thickness of the n-type nitride semiconductor layer 35 is adjusted.

  Thereafter, the supply of TMA is stopped, and other source gases are supplied for 6 seconds, thereby forming a protective layer made of n-type GaN having a thickness of 5 nm on the n-type nitride semiconductor layer 35. It may be a thing.

  As the n-type impurity contained in the n-type nitride semiconductor layer 35, silicon (Si), germanium (Ge), sulfur (S), selenium (Se), tin (Sn), tellurium (Te), or the like is used. be able to. Among these, silicon (Si) is particularly preferable.

<Formation of the light emitting layer 33>
Next, a light emitting layer 33 having a multiple quantum well structure in which a well layer made of InGaN and a barrier layer made of n-type AlGaN are periodically repeated is formed on the n-type nitride semiconductor layer 35.

  Specifically, first, the furnace pressure of the MOCVD apparatus is set to 100 kPa, and the furnace temperature is set to 830 ° C. Then, while flowing nitrogen gas having a flow rate of 15 slm and hydrogen gas having a flow rate of 1 slm as a carrier gas in the processing furnace, TMG having a flow rate of 10 μmol / min, trimethylindium (TMI) having a flow rate of 12 μmol / min, and A step of supplying ammonia at a flow rate of 300,000 μmol / min into the processing furnace for 48 seconds is performed. Thereafter, TMG having a flow rate of 10 μmol / min, TMA having a flow rate of 1.6 μmol / min, tetraethylsilane having a flow rate of 0.002 μmol / min, and ammonia having a flow rate of 300,000 μmol / min are supplied into the processing furnace for 120 seconds. Hereinafter, by repeating these two steps, the light-emitting layer 33 having a multi-quantum well structure of 15 periods with a well layer made of InGaN having a thickness of 2 nm and a barrier layer made of n-type AlGaN having a thickness of 7 nm is formed into an n-type. It is formed on the surface of the nitride semiconductor layer 35.

<Formation of p-type nitride semiconductor layer 31>
Next, a p-type nitride semiconductor layer 31 composed of Al _m Ga _1-m N (0 ≦ m ≦ 1) is formed on the light emitting layer 33.

Specifically, the furnace pressure of the MOCVD apparatus is maintained at 100 kPa, and the furnace temperature is raised to 1025 ° C. while nitrogen gas having a flow rate of 15 slm and hydrogen gas having a flow rate of 25 slm are supplied as carrier gases in the processing furnace. To do. Thereafter, as source gases, TMG with a flow rate of 35 μmol / min, TMA with a flow rate of 20 μmol / min, ammonia with a flow rate of 250,000 μmol / min, and biscyclopentadiene with a flow rate of 0.1 μmol / min for doping p-type impurities. Enilmagnesium (CP ₂ Mg) is fed into the processing furnace for 60 seconds. Thereby, a hole supply layer having a composition of Al _0.3 Ga _0.7 N having a thickness of 20 nm is formed on the surface of the light emitting layer 33. After that, by changing the flow rate of TMG to 9 μmol / min and supplying the source gas for 360 seconds, a hole supply layer having a composition of Al _0.13 Ga _0.87 N having a thickness of 120 nm is formed. A p-type nitride semiconductor layer 31 is formed by these hole supply layers. The p-type impurity (Mg) concentration of the p-type nitride semiconductor layer 31 is about 3 × 10 ¹⁹ / cm ³ .

<Formation of First Contact Layer 32>
Thereafter, the supply of TMA is stopped, the flow rate of CP ₂ Mg is changed to 0.2 μmol / min, and the source gas is supplied for 20 seconds, whereby the first contact layer 32 made of p ⁺ GaN having a thickness of 5 nm is formed. Form. The p-type impurity (Mg) concentration of the first contact layer 32 is about 1 × 10 ²⁰ / cm ³ .

<Formation of Second Contact Layer 34>
Next, the supply of CP ₂ Mg is stopped, and in addition to the source gas, the second flow of diethyl zinc is supplied for 20 seconds in a state where the flow rate of diethyl zinc is 0.2 μmol / min. A contact layer 34 is formed. In addition to Zn, Cd, Be, Sr, Ca, C, etc. can be used as the dopant of the second contact layer 34. The impurity (Zn) concentration of the second contact layer 34 is about 1 × 10 ²⁰ / cm ³ .

  In this way, an epitaxial layer comprising the undoped layer 36, the n-type nitride semiconductor layer 35, the light emitting layer 33, the p-type nitride semiconductor layer 31, the first contact layer 32, and the second contact layer 34 on the sapphire substrate 61. 40 is formed.

(Step S2)
Next, an activation process is performed on the wafer obtained in step S1. More specifically, activation is performed at 650 ° C. for 15 minutes in a nitrogen atmosphere using an RTA (Rapid Thermal Anneal) device.

(Step S3)
Next, as shown in FIG. 5B, the insulating layer 21 is formed at a predetermined position on the p-type nitride semiconductor layer 31. More specifically, it is preferable to form the insulating layer 21 at a position located below a region where the power supply terminal 42 is formed in a later step. As the insulating layer 21, for example, SiO ₂ is formed to a thickness of about 200 nm. Note that the material for forming the film may be an insulating material, such as SiN or Al ₂ O ₃ .

(Step S4)
As shown in FIG. 5C, the conductive layer 20 is formed so as to cover the upper surfaces of the p-type nitride semiconductor layer 31 and the insulating layer 21. Here, the conductive layer 20 having a multilayer structure including the metal electrode 19, the protective layer 17, and the solder layer 15 is formed.

  A more specific method for forming the conductive layer 20 is, for example, as follows. First, Ag is formed on the entire surface so as to cover the upper surfaces of the second contact layer 34 and the insulating layer 21 by a sputtering apparatus, and the metal electrode 19 is formed. As described above, in the configuration of the present embodiment, since the deep impurity level is formed in the second contact layer 34 by Zn doping, the direct contact with the semiconductor layer without forming a contact electrode such as Ti or ITO. Good contact characteristics can be obtained by contacting Ag.

  Next, the protective layer 17 is formed by depositing 100 nm-thick Ti and 200 nm-thickness Pt on the upper surface (Ag surface) of the metal electrode 19 with an electron beam evaporation apparatus (EB apparatus) for three periods. . Further, after depositing Ti with a thickness of 10 nm on the upper surface (Pt surface) of the protective layer 17, Au-Sn solder composed of Au 80% Sn 20% is deposited with a thickness of 3 μm, thereby forming the solder layer 15. Form.

  In the step of forming the solder layer 15, the solder layer 13 may also be formed on the upper surface of the support substrate 11 prepared separately from the sapphire substrate 61 (see FIG. 5D). The solder layer 13 may be made of the same material as the solder layer 15, and is bonded to the solder layer 13 in the next step, whereby the sapphire substrate 61 and the support substrate 11 are bonded together. For example, CuW is used as the support substrate 11 as described in the section of the structure.

(Step S5)
Next, as shown in FIG. 5E, the sapphire substrate 61 and the support substrate 11 are bonded together. More specifically, the solder layer 15 and the solder layer 13 formed on the upper layer of the support substrate 11 are bonded together at a temperature of 280 ° C. and a pressure of 0.2 MPa.

(Step S6)
Next, as shown in FIG. 5F, the sapphire substrate 61 is peeled off. More specifically, the interface between the sapphire substrate 61 and the epi layer 40 is decomposed by irradiating a KrF excimer laser from the sapphire substrate 61 side with the sapphire substrate 61 facing upward and the support substrate 11 facing downward. Then, the sapphire substrate 61 is peeled off. While the laser passes through the sapphire 61, the underlying GaN (undoped layer 36) absorbs the laser, so that this interface is heated to decompose GaN. As a result, the sapphire substrate 61 is peeled off.

  Thereafter, GaN (undoped layer 36) remaining on the wafer is removed by wet etching using hydrochloric acid or the like, or dry etching using an ICP apparatus, and the n-type nitride semiconductor layer 35 is exposed. In this step S6, the undoped layer 36 is removed, and the second contact layer 34, the first contact layer 32, the p-type nitride semiconductor layer 31, the light emitting layer 33, and the n-type nitride semiconductor layer 35 are stacked in this order. The formed semiconductor layer 30 remains.

(Step S7)
Next, as shown in FIG. 5G, adjacent elements are separated. Specifically, the semiconductor layer 30 is etched using an ICP device until the upper surface of the insulating layer 21 is exposed in a boundary region with an adjacent element. As described above, the insulating layer 21 also functions as a stopper during etching.

(Step S8)
Next, as shown in FIG. 5H, irregularities are formed on the surface of the n-type nitride semiconductor layer 35. Specifically, the unevenness is formed by immersing an alkaline solution such as KOH. At this time, unevenness may not be formed in a portion where the electrode 42 and the bonding electrode 43 are formed later. By not forming irregularities at these locations, the surface of the n-type nitride semiconductor layer 35 where the electrodes are to be formed is maintained in a flat state. By maintaining the surface of the n-type nitride semiconductor layer 35 where the electrode is formed in a flat state, the bonding electrode 43 and the n-type nitride semiconductor layer 35 are formed particularly when wire bonding is performed after the bonding electrode 43 is formed. The effect of preventing the generation of voids at the interface can be obtained.

(Step S9)
Next, as shown in FIG. 5I, an electrode 42 and a bonding electrode 43 are formed on the upper surface of the n-type nitride semiconductor layer 35. More specifically, after forming an electrode made of Cr having a thickness of 100 nm and Au having a thickness of 3 μm, sintering is performed at 250 ° C. for 1 minute in a nitrogen atmosphere.

As a subsequent process, the exposed element side surface and the element upper surface other than the electrode 42 and the bonding electrode 43 are covered with an insulating layer 41. More specifically, an SiO ₂ film is formed by an EB apparatus. An SiN film may be formed. Then, the elements are separated from each other by, for example, a laser dicing apparatus, the back surface of the support substrate 11 is joined to the package by, for example, Ag paste, and wire bonding is performed on the bonding electrode 43. For example, wire bonding is performed by connecting a wire 45 made of Au to a bonding region of Φ100 μm with a load of 50 g. Thereby, the nitride semiconductor light emitting device 1 shown in FIG. 1 is formed.

<Other manufacturing process>
When the first contact layer 32 and the second contact layer 34 are formed of AlGaN , the following method can be adopted in step S1. First, after the p-type nitride semiconductor layer 31 is formed, the flow rate of CP ₂ Mg is changed to 0.2 μmol / min and a source gas is supplied for 20 seconds, whereby p ⁺ Al _0.13 Ga ₀ having a thickness of 5 nm is supplied. _A first contact layer 32 made of _.87N is formed. Next, the supply of CP ₂ Mg is stopped, diethyl zinc is changed to 0.2 μmol / min, and the raw material gas is supplied for 20 seconds, whereby the Zn-doped Al _0.13 Ga _0.87 N having a thickness of 5 nm is formed. A second contact layer 34 is formed.

[Second Embodiment]
An example of the structure of the nitride semiconductor light emitting device according to the second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a schematic cross-sectional view of the nitride semiconductor light emitting device 1a of the second embodiment. In addition, about the same material as 1st Embodiment, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted. Moreover, the arrow in FIG. 6 has shown the extraction direction of light, and the light extraction direction is reverse with the nitride semiconductor light-emitting device 1a shown in FIG.

<Construction>
A sapphire substrate 61, a semiconductor layer 30a, metal electrodes 19, 19a, a power supply terminal 51, and a power supply terminal 52 are provided. The semiconductor layer 30 a includes a p-type nitride semiconductor layer 31, a first contact layer 32, a light emitting layer 33, a second contact layer 34, an n-type nitride semiconductor layer 35, and an undoped layer 36. The nitride semiconductor light emitting device 1a is assumed to extract light downward in the drawing.

  In this embodiment, in order to distinguish from the metal electrode 19 formed on the upper surface of the p-side semiconductor layer 30 in the first embodiment, the metal electrode formed on the upper surface of the n-side semiconductor layer 30 is referred to as “metal electrode 19a”. However, they may be made of the same material.

  Also in this configuration, as in the first embodiment, the contact property is improved because the metal electrode 19 formed of Ag or the like is directly formed on the upper surface of the second contact layer 34, so that good contact characteristics can be obtained. Therefore, it is not necessary to form a contact electrode made of Ni or ITO. Thereby, even when the light from the light emitting layer 33 is emitted upward, the light that has reached the metal electrode 19 without being absorbed by the contact electrode can be reflected downward (in the extraction direction). Extraction efficiency is improved.

<Manufacturing process>
With respect to the manufacturing process of the nitride semiconductor light emitting device 1a shown in FIG. 6, only portions different from the device 1 of the first embodiment will be described.

  Step S1 and step S2 are executed as in the first embodiment.

(Step S10)
After step S2 (see FIG. 5A), as shown in FIG. 7A, the second contact layer 34, the first contact layer 32, and the p-type nitride semiconductor are used until a partial upper surface of the n-type nitride semiconductor layer 35 is exposed. The layer 31 and the light emitting layer 33 are removed by dry etching using an ICP device. In step S3, the n-type nitride semiconductor layer 35 may be partially removed by etching.

(Step S11)
As shown in FIG. 7B, the metal electrode 19 and the metal electrode 19a are formed by depositing Ag on the upper surface of the second contact layer 34 and the exposed upper surface of the n-type nitride semiconductor layer 35. Also in this embodiment, since a deep impurity level is formed in the second contact layer 34 by Zn doping, the second contact layer 34 and Ag are brought into contact without forming a contact electrode such as Ni or ITO. As a result, good contact characteristics can be obtained.

In the present configuration, it is preferable that at least the upper surface portion of the n-type nitride semiconductor layer 35 is made of AlGaN having a high concentration of n-type impurity concentration higher than 1 × 10 ¹⁹ / cm ³ . Thereby, the favorable contact characteristic of the n-type nitride semiconductor layer 35 and the metal electrode 19a is also realizable.

(Step S12)
Thereafter, a power supply terminal 51 is formed on the upper surface of the n-side metal electrode 19a, and a power supply terminal 52 is formed on the upper surface of the p-side metal electrode 19. More specifically, after forming a conductive material film (for example, a material film made of Cr with a thickness of 100 nm and Au with a thickness of 3 μm) to form the power supply terminals 51 and 52, the power supply terminals 51 and 52 are formed by lift-off. To do. Thereafter, sintering is performed at 250 ° C. for 1 minute in a nitrogen atmosphere.

  Then, by connecting the substrate 55 and the power supply terminal 51 via the bonding electrode 53 and connecting the substrate 55 and the power supply terminal 52 via the bonding electrode 54, the nitride semiconductor light emitting element 1a shown in FIG. 2 is formed. The

[Another embodiment]
Hereinafter, another embodiment will be described.

<1> In the above-described manufacturing process, the case where the second contact layer 34 is GaN or AlGaN doped with Zn has been described. However, based on the same principle, the second contact layer 34 is formed of Al _X Ga _Y In _Z N (0 ≦ ≤) doped with at least one second impurity material of Zn, Cd, Be, Sr, Ca, and C. In the case where X ≦ 1, 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, and X + Y + Z = 1), the contact property with the metal electrode 19 can be improved.

Furthermore, even when the second contact layer 34 is made of Al _X Ga _Y In _Z N containing a trace amount of another substance (such as Sb), the same effect is exhibited. It is not intended to exclude an element in which the second contact layer 34 is formed of such a material from the scope of rights.

  <2> In the first embodiment, a conductive oxide film layer may be formed instead of the insulating layer 21. When the conductive oxide film layer is provided, the conductivity is higher than that of the insulating layer 21, so that current easily flows in the semiconductor layer 30 in the vertical direction. However, the conductive layer is more conductive than a normal conductive material (metal or the like). Since the rate is significantly low, the effect of spreading the current in the horizontal direction is realized.

  The insulating layer 21 and the conductive oxide film layer are preferably formed immediately below the electrodes (42, 43) in the sense of spreading the current in the horizontal direction. It does not mean that an element having no conductive oxide film layer is excluded from the scope of rights.

  <3> The structure shown in FIG. 1 and FIG. 6 and the manufacturing method shown in FIG. 5A to FIG. 5I and FIG. 7A and FIG. 7B are examples of preferred embodiments, and all of these configurations and processes are provided. It doesn't mean you have to.

  For example, in the first embodiment, the solder layer 13 and the solder layer 15 are formed so as to efficiently bond two substrates, and if the bonding of two substrates can be realized, the nitride semiconductor It is not always necessary to realize the function of the light emitting element.

  Similarly, the protective layer 17 is preferably provided from the viewpoint of preventing the diffusion of the solder material and the unevenness of the surface of the n-type nitride semiconductor layer 35 from the viewpoint of improving the light extraction efficiency. It is not intended to exclude an element having a configuration not provided from the scope of rights.

  <4> In the first embodiment, the solder layer is formed on both the sapphire substrate 61 and the support substrate 11 (solder layers 13 and 15). After forming the solder layer on only one of them, the two substrates are bonded together. It doesn't matter. Further, although the protective layer 17 is formed on the sapphire substrate 61 side, it may be formed on the support substrate 11 side. That is, instead of the configuration shown in FIG. 5D, the protective layer 17 formed on the support substrate 11 and the solder layer 13 formed thereon may be bonded to the sapphire substrate 61 in step S5.

DESCRIPTION OF SYMBOLS 1, 1a: Nitride semiconductor light emitting element 11: Support substrate 13: Solder layer 15: Solder layer 17: Protective layer 19, 19a: Metal electrode 20, 20a: Conductive layer 21: Insulating layer 30, 30a: Semiconductor layer 31: p Type nitride semiconductor layer 32: first contact layer 33: light emitting layer 34: second contact layer 35: n-type nitride semiconductor layer 36: undoped layer 40: epi layer 41: insulating layer 42: electrode 43: bonding electrode 45: Bonding electrodes 51, 52: Power supply terminals 53, 54: Bonding electrodes 55: Substrate 61: Sapphire substrate 80: Conventional element 81: Comparative element 83: Contact electrode

Claims (6)

In a nitride semiconductor light emitting device having a light emitting layer between an n type nitride semiconductor layer and a p type nitride semiconductor layer,
A first contact layer made of a nitride semiconductor layer in contact with the p-type nitride semiconductor layer and doped with a first impurity material at a higher concentration than the p-type nitride semiconductor layer;
Al _X Ga _Y In _Z N (0 ≦ X ≦ 1) in contact with the first contact layer and doped with at least one second impurity material of any one of Zn, Cd, Be, Sr, Ca and C , 0 ≦ Y ≦ 1, 0 ≦ Z ≦ 1, and X + Y + Z = 1).   The impurity level in the second contact layer formed of the second impurity material is deeper than the impurity level in the first contact layer formed of the first impurity material. The nitride semiconductor light emitting device according to claim 1.   The nitride semiconductor light emitting device according to claim 1, wherein the second impurity material is Zn. 4. The nitride semiconductor light emitting device according to claim 3, wherein the impurity concentration of the second contact layer is 1 × 10 ¹⁹ / cm ^{3 to} 5 × 10 ²¹ / cm ³ .   The nitride semiconductor light emitting device according to claim 3, wherein the first impurity material is Mg.   6. The nitride semiconductor light-emitting element according to claim 1, wherein the nitride semiconductor light-emitting element has a metal electrode containing at least one of Ag, an Ag alloy, and Al in contact with the second contact layer.

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