JP2012060163A - Method for manufacturing group iii nitride semiconductor light-emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a group III nitride semiconductor light-emitting element having good ohmic contact.SOLUTION: In the group III nitride semiconductor element, a junction JC is inclined with respect to the reference surface perpendicular to a c axis of a gallium nitride-based semiconductor layer, and an electrode is joined to a semipolar plane of the gallium nitride-based semiconductor layer. However the oxygen concentration decreases in the gallium nitride-based semiconductor layer grown so as to form the junction JC. Since the electrode forms the junction on the semipolar plane of the gallium nitride-based semiconductor layer, a metal/semiconductor junction exhibits good ohmic characteristics.

Description

  The present invention relates to a method for manufacturing a group III nitride semiconductor light emitting device, and a group III nitride semiconductor light emitting device.

  Patent Document 1 describes a method for producing a group III-V nitride semiconductor. According to this method, it is possible to manufacture an ohmic electrode capable of obtaining a low contact resistance with high reproducibility.

  Non-Patent Document 1 describes ohmic contact to p-type GaN. A metal made of Ni / Au is deposited on the p-type GaN. Thereafter, metallic nickel is converted into NiO together with an amorphous Ni—Ga—O phase and large Au grains by heat treatment.

JP 2008-300421 A

Jin-Kuo Ho et al., JOURNAL OF APPLIED PHYSICS, VOL. 86, No. 8, 1999, “Low-resistance ohmic contacts to p-type GaN achieved by the oxidation of Ni / Au films”

  It is desired to obtain a better ohmic contact with a non-c surface of a gallium nitride based semiconductor such as gallium nitride. According to the inventor's knowledge, a non-c plane of a gallium nitride semiconductor such as gallium nitride, that is, a semipolar plane, is easily oxidized as compared to the c plane when exposed to an atmosphere containing oxygen.

  This finding indicates that it is important to reduce the oxygen concentration on the surface of the gallium nitride semiconductor to which the electrode film is bonded. However, oxygen is easily mixed in the manufacturing process. Moreover, according to another knowledge of the inventor, it is not easy to break the bond between oxygen and gallium in the semipolar plane. Thus, it is considered that the reduction of the oxygen concentration at the metal / semiconductor interface is deeply related to the intrinsic property of the semipolar plane of the gallium nitride based semiconductor layer.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for manufacturing a group III nitride semiconductor light emitting device having good ohmic contact. Another object of the present invention is to provide a group III nitride semiconductor light emitting device having good ohmic contact.

  One aspect of the present invention is a method of manufacturing a group III nitride semiconductor light emitting device. This method includes a step of exposing the epitaxial substrate to a gallium atmosphere without forming a group III nitride semiconductor at a substrate temperature of 300 ° C. or higher in a vacuum chamber. The principal surface of the epitaxial substrate has a semipolar principal surface made of a gallium nitride semiconductor, and the epitaxial substrate includes an active layer made of a group III nitride semiconductor.

One aspect of the present invention is a method of manufacturing a group III nitride semiconductor light emitting device. The method includes (a) exposing the epitaxial substrate to a gallium atmosphere at a substrate temperature of 300 ° C. or higher in the vacuum chamber without forming a group III nitride semiconductor, and (b) in the vacuum chamber. Forming a substrate product by forming a conductive film for an electrode on the main surface of the epitaxial substrate. The principal surface of the epitaxial substrate has a semipolar principal surface made of a gallium nitride semiconductor, and the epitaxial substrate includes an active layer made of a group III nitride semiconductor.
According to this manufacturing method, the epitaxial substrate is exposed to a gallium atmosphere without forming a group III nitride semiconductor at a substrate temperature of 300 ° C. or higher in a vacuum chamber. Prior to this exposure step, an oxide is formed on the surface of the group III nitride semiconductor of the epitaxial substrate. However, in the exposure step, gallium is supplied to the semipolar main surface of the gallium nitride semiconductor and the surface of the semipolar main surface The gallium oxide is reduced to be modified to a gallium oxide having a low melting point. The reaction at this time is expressed as follows.
Ga ₂ O ₃ + 4Ga → 3Ga ₂ O.
The gallium oxide Ga ₂ O is released from the gallium nitride semiconductor into the hollow of the vacuum chamber by the action of the substrate temperature in the exposure step according to its melting point. Therefore, prior to the semipolar main surface forming a junction with the electrode film, the oxygen concentration in the vicinity of the semipolar main surface can be reduced by gallium irradiation to the semipolar main surface rich in oxygen bonding. Therefore, a group III nitride semiconductor light emitting device having good ohmic contact can be manufactured.

  The manufacturing method according to one aspect of the present invention may further include a step of growing the semiconductor region on the main surface of the substrate to form the epitaxial substrate. The main surface of the substrate is made of a group III nitride semiconductor. The semiconductor region includes a first conductivity type group III nitride semiconductor layer, the active layer, and a second conductivity type group III nitride semiconductor layer, the epitaxial substrate includes the substrate, and the main region of the substrate The plane is inclined at an angle in the range of not less than 10 degrees and not more than 80 degrees from the plane orthogonal to the reference axis extending along the c-axis of the group III nitride semiconductor, and the main surface of the epitaxial substrate is the group III nitride It is preferable to incline at an angle in the range of 10 degrees to 80 degrees from a plane orthogonal to the reference axis extending along the c-axis of the physical semiconductor.

  According to this manufacturing method, when the tilt angle is in the range of 10 degrees or more and 80 degrees or less, the semipolar plane of the gallium nitride semiconductor is rich in oxygen bonding. Therefore, it is important to reduce oxygen during the formation of the ohmic electrode.

  In the manufacturing method according to one aspect of the present invention, the epitaxial substrate includes a p-type gallium nitride based semiconductor layer provided on the active layer, and the p-type gallium nitride based semiconductor layer includes magnesium as a dopant, The main surface of the p-type gallium nitride based semiconductor layer preferably constitutes the main surface of the epitaxial substrate.

  According to this manufacturing method, an electrode that makes ohmic contact with the p-type gallium nitride based semiconductor layer can be formed.

  In the manufacturing method according to one aspect of the present invention, the conductive film preferably includes any one of Au, Pd, Ni, Rh, Al, Ti, Zn, Cu, In, Ta, Pt, and Tl. In this manufacturing method, it is preferable to include at least one of Au, Pd, Ni, Rh, Al, Ti, Zn, Cu, In, Ta, Pt, and Tl.

  In the manufacturing method according to one aspect of the present invention, the substrate temperature is preferably equal to or lower than a minimum temperature of film formation temperatures in the formation of the epitaxial substrate. According to this manufacturing method, it is possible to reduce thermal stress on the active layer that may occur due to the modification process in the exposing step.

In the manufacturing method according to one aspect of the present invention, the minimum temperature is preferably 900 degrees Celsius or less. According to this manufacturing method, it is possible to reduce the oxygen concentration on the semipolar principal surface by utilizing the fact that gallium oxide has various melting points. Examples of gallium oxide include the following. Ga ₂ O ₃ has a relatively high melting point (eg, 1725 degrees Celsius, 1 atmosphere, RT), while Ga ₂ O has a relatively low melting point (eg, 500 degrees Celsius, 1 × 10 ⁻⁶ Torr).

  In the manufacturing method according to one aspect of the present invention, the active layer preferably includes an InGaN layer, and the substrate temperature of the epitaxial substrate is preferably equal to or lower than a growth temperature of the InGaN layer of the active layer. According to this manufacturing method, the quality of the InGaN layer of the active layer can be prevented from being deteriorated by the heat treatment in the exposing step.

  The manufacturing method according to an aspect of the present invention may further include a step of forming a pattern on the electrode after the substrate product is taken out of the vacuum chamber. This method is preferable because the alloy for the electrode is not formed after the conductive film is formed. According to this manufacturing method, it is possible not to perform alloying for the electrodes.

  In the manufacturing method according to one aspect of the present invention, the group III nitride semiconductor of the substrate is preferably GaN. In the manufacturing method according to one aspect of the present invention, the main surface of the epitaxial substrate is preferably made of GaN.

  The manufacturing method according to one aspect of the present invention further includes a step of forming a group III nitride semiconductor on the active layer after the epitaxial substrate is placed in the vacuum chamber to form the epitaxial substrate. Can be provided. According to this manufacturing method, the oxygen concentration of the group III nitride semiconductor grown by this film formation can be reduced.

  In the manufacturing method according to one aspect of the present invention, it is preferable that the conductive film is formed without forming a group III nitride semiconductor after exposing the epitaxial substrate to a gallium atmosphere. According to this manufacturing method, the ohmic electrode can be formed on the semipolar surface provided by the modification.

  In the manufacturing method according to one aspect of the present invention, the main surface of the epitaxial substrate has an angle in the range of not less than 63 degrees and not more than 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor. It is preferable to incline at. The semipolar plane in this angular range has a step that is susceptible to oxidation.

In the manufacturing method according to one aspect of the present invention, the oxygen concentration in the gallium nitride-based semiconductor layer in contact with the conductive film may be 1 × 10 ¹⁸ cm ⁻³ or less. According to this manufacturing method, the oxygen concentration in the gallium nitride based semiconductor region where the electrode forms a junction can be reduced.

  A group III nitride semiconductor light emitting device according to another aspect of the present invention includes: (a) a first conductivity type group III nitride semiconductor layer; and (b) a main surface of the first conductivity type group III nitride semiconductor layer. An active layer provided thereon, (c) a group III nitride semiconductor layer provided on a main surface of the active layer, and (d) an electrode forming a junction with the group III nitride semiconductor layer. . The group III nitride semiconductor layer has a second conductivity type, and the junction is inclined with respect to a reference plane orthogonal to the c-axis of the first conductivity type group III nitride semiconductor layer.

  According to this group III nitride semiconductor light emitting device, the junction is inclined with respect to the reference plane orthogonal to the c-axis of the first conductivity type group III nitride semiconductor layer, so that the electrode is the second group III nitride. Bonding to the semipolar surface of the nitride semiconductor layer. Since the electrode forms a junction with this semipolar plane, this junction exhibits good ohmic characteristics.

  In the group III nitride semiconductor light emitting device according to another aspect of the present invention, the junction can be inclined at an angle in a range of 10 degrees to 80 degrees from a plane orthogonal to the reference axis. According to this group III nitride semiconductor light emitting device, the semipolar plane inclined at an angle in the range of 10 degrees or more and 80 degrees or less is more easily oxidized than the c plane (polar plane). Applies to

  In the group III nitride semiconductor light emitting device according to another aspect of the present invention, the electrode includes any one of Au, Pd, Ni, Rh, Al, Ti, Zn, Cu, In, Ta, Pt, and Tl. Can do. This group III nitride semiconductor light emitting device preferably includes at least one of Au, Pd, Ni, Rh, Al, Ti, Zn, Cu, In, Ta, Pt, and Tl.

  The group III nitride semiconductor light emitting device according to another aspect of the present invention may further include a support base having a main surface made of a group III nitride semiconductor. The main surface of the support base is inclined at an angle in the range of 10 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor, and the first conductivity type group III The nitride semiconductor layer, the active layer, and the group III nitride semiconductor layer are arranged in the direction of the normal line of the main surface of the support base.

  According to this group III nitride semiconductor light emitting device, good ohmic contact is achieved on the semipolar upper surface of the semiconductor stack including the semiconductor layers arranged in order on the semipolar surface inclined at an angle in the range of 10 degrees to 80 degrees. Provided.

  In the group III nitride semiconductor light emitting device according to another aspect of the present invention, the group III nitride semiconductor of the support base is preferably GaN. In the group III nitride semiconductor light emitting device according to another aspect of the present invention, the main surface of the group III nitride semiconductor layer is preferably made of GaN.

  In the group III nitride semiconductor light-emitting device according to another aspect of the present invention, the active layer includes a gallium nitride based semiconductor layer containing indium as a group III constituent element, and the active layer has a wavelength range of 360 nm to 600 nm. Are provided so as to have a peak emission wavelength.

  According to this group III nitride semiconductor light emitting device, the driving voltage in the wavelength range of 360 nm or more and 600 nm or less can be lowered.

  The above and other objects, features, and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments of the present invention, which proceeds with reference to the accompanying drawings.

  As described above, according to one aspect of the present invention, there is provided a method for manufacturing a group III nitride semiconductor light emitting device having good ohmic contact. In addition, according to another aspect of the present invention, a group III nitride semiconductor light emitting device having a good ohmic contact is provided.

FIG. 1 is a drawing schematically showing main steps in a method for manufacturing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 2 is a drawing schematically showing main steps in the method of manufacturing the group III nitride semiconductor light emitting device according to the present embodiment. FIG. 3 is a drawing schematically showing main steps in the method for manufacturing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 4 is a drawing schematically showing main steps in the method for manufacturing a group III nitride semiconductor light emitting device according to the present embodiment. FIG. 5 is a drawing showing a transmission electron microscope (TEM) image near the interface between the GaN region and the metal (gold). FIG. 6 is a drawing showing the results of measuring the oxygen concentration in the underlying gallium nitride based semiconductor region for electrode formation by a secondary ion mass spectrometry (SIMS) method. FIG. 7 is a diagram showing current-voltage characteristics.

  The knowledge of the present invention can be easily understood by considering the following detailed description with reference to the accompanying drawings shown as examples. Subsequently, a method for manufacturing a group III nitride semiconductor light emitting device of the present invention and an embodiment relating to the group III nitride semiconductor light emitting device will be described with reference to the accompanying drawings. Where possible, the same parts are denoted by the same reference numerals.

  1 to 4 are drawings schematically showing main steps in a method for manufacturing a group III nitride semiconductor light emitting device according to the present embodiment. As shown in FIG. 1A, the substrate 11 is prepared in step S101. The substrate 11 has a main surface 11a made of a group III nitride semiconductor. Main surface 11a is inclined with respect to a plane perpendicular to a reference axis (indicated by vector VC) extending in the direction of the c-axis of the group III nitride semiconductor, and thus exhibits semipolarity. The group III nitride semiconductor of the substrate 11 can be made of, for example, GaN.

  As shown in FIG. 1B, in step S102, a semiconductor stack 13 for a semiconductor light emitting device is grown on a substrate 11 in a growth furnace 10a to form an epitaxial substrate E. One embodiment will be described. After the substrate 11 is placed in the growth furnace 10a, ammonia and hydrogen are supplied to the growth furnace 10a to perform thermal cleaning of the main surface 11a of the substrate 11. Thereafter, in the growth furnace 10a, a plurality of group III nitride semiconductor layers are grown in order on the main surface 11a of the substrate 11. As the growth method for the growth furnace 10a, for example, a metal organic chemical vapor deposition method can be used.

  The semiconductor stack 13 includes a first conductivity type group III nitride semiconductor layer such as an n-type group III nitride semiconductor region 15, an active layer 17, and a second conductivity type group III nitride such as a p-type group III nitride semiconductor region 19. A physical semiconductor layer. The n-type group III nitride semiconductor region 15 can be made of, for example, GaN, AlGaN, InAlGaN, or the like. The p-type group III nitride semiconductor region 19 can be made of, for example, GaN, AlGaN, InAlGaN, or the like, and can include an electron block layer 27 and a p-type cladding layer 29. The p-type group III nitride semiconductor region 19 can include a p-type contact layer if necessary. The active layer 17 has, for example, a quantum well structure 21, and the quantum well structure 21 can include alternately arranged barrier layers 23 and well layers 25. The band gap of the barrier layer 23 is larger than the band gap of the well layer 25. The barrier layer 23 can be made of, for example, GaN, InGaN, InAlGaN, or the like, and the well layer 25 can be made of, for example, GaN, InGaN, InAlGaN, or the like.

  In step S102, the semiconductor stack 13 is grown on the main surface 11a of the substrate 11 to form an epitaxial substrate. The main surface 11a of the substrate 11 has a reference axis extending along the c-axis of the group III nitride semiconductor. It is preferable to incline at an angle in the range of 10 degrees to 80 degrees from the plane orthogonal to Cx. In addition, the main surface of the epitaxial substrate E is preferably inclined at an angle in the range of 10 degrees or more and 80 degrees or less from the plane orthogonal to the reference axis Cx. When these inclination angles are in the range of 10 degrees or more and 80 degrees or less, the semipolar plane of the gallium nitride-based semiconductor is rich in oxygen bonding. Therefore, it is important to reduce oxygen during the formation of the ohmic electrode.

  The inclination angle on the main surface of the epitaxial substrate E is preferably inclined at an angle in the range of not less than 63 degrees and not more than 80 degrees from a plane orthogonal to the reference axis extending along the c-axis of the group III nitride semiconductor. The semipolar plane in this angular range has a step that is susceptible to oxidation.

  As shown in part (c) of FIG. 1, in step S103, when the epitaxial substrate E is taken out of the growth furnace 10a, the epitaxial substrate E is exposed to the atmosphere containing oxygen. As a result, native oxide gallium oxide 12 is formed on the gallium nitride based semiconductor surface exposed on the surface of the epitaxial substrate E.

  After removing the epitaxial substrate E from the growth furnace 10a, as shown in FIG. 2A, the epitaxial substrate E is placed in the processing apparatus 10b in step S104.

Next, as shown in FIG. 2B, in step S105, the epitaxial substrate E is heated by the processing apparatus 10b. In an example of the heating conditions, the heating temperature is, for example, 750 degrees Celsius, the heat treatment time is 30 minutes, and the heat treatment atmosphere is, for example, a Ga atmosphere. This temperature range can be, for example, 300 degrees Celsius or more, and if the temperature is below this temperature, the Ga oxide Ga ₂ O ₃ is not reduced to Ga ₂ O having a higher vapor pressure. Also, this temperature range can be, for example, a range of 900 degrees Celsius or less, in order to avoid damage to the active layer 17. The atmosphere of the heat treatment can be, for example, a Ga atmosphere.

After the epitaxial substrate E is heated, without breaking the vacuum, as shown in FIG. 2C, in step S106, an atmosphere containing gallium is formed in the chamber of the processing apparatus 10b, and this atmosphere is epitaxially formed. The surface 13a of the substrate E is exposed. The atmosphere of this treatment preferably does not contain nitrogen in order to avoid the growth of a gallium nitride based semiconductor. This is because the range of the substrate temperature in this process can be, for example, 300 degrees Celsius or more, and when the temperature is below this temperature, the Ga oxide Ga ₂ O ₃ is not reduced to Ga ₂ O having a higher vapor pressure. Also, this temperature range can be, for example, a range of 900 degrees Celsius or less, in order to avoid damage to the active layer 17. The duration for this heat treatment is, for example, 30 minutes.

  The substrate temperature for the heating step and the exposing step is preferably equal to or lower than the lowest temperature among the film formation temperatures in the formation of the epitaxial substrate E. It is possible to reduce thermal stress on the active layer that may be caused by the modification treatment in the heating step and the exposing step. When the active layer includes an InGaN layer, the substrate temperature of the epitaxial substrate E is preferably equal to or lower than the growth temperature of the InGaN well layer of the active layer, for example. It can be avoided that the quality of the InGaN layer of the active layer is deteriorated by the heat treatment in the heating process and the exposing process.

  In one embodiment of this process, the surface 13a of the epitaxial substrate E can be exposed by irradiating the surface 13a with the gallium flux 31.

There are various forms of compounds of gallium and oxygen. Gallium oxide has various melting points. By utilizing this difference in melting point, the oxygen concentration on the semipolar main surface can be reduced. Examples of gallium oxide include the following. The melting point of Ga ₂ O ₃ (eg, 1725 degrees Celsius, 1 atmosphere, RT) is relatively high, but the melting point of Ga ₂ O (eg, 500 degrees Celsius, 1 × 10 ⁻⁶ Torr) is relatively low.

  In the process so far, after the epitaxial substrate E is disposed in the vacuum chamber of the processing apparatus 10b, the modification process by heating and Ga irradiation has been performed. Thereafter, if necessary, as shown in FIG. 3A, in step S107, the vacuum is not broken on the semiconductor stack 13 including the active layer 17 in the vacuum chamber of the processing apparatus 10b. The gallium nitride based semiconductor layer 33 can be grown to form a new epitaxial substrate E2. According to this method, the oxygen concentration of the group III nitride semiconductor grown by this film formation can be reduced.

Since a metal for an electrode is deposited on the gallium nitride based semiconductor layer 33 in a later step, the gallium nitride based semiconductor layer 33 has a desired conductivity type dopant, for example, a p-type dopant such as magnesium or zinc. Is preferably added. The p-type dopant concentration can be, for example, 1 × 10 ¹⁶ cm ⁻³ or more and 1 × 10 ²¹ cm ⁻³ or less. According to this manufacturing method, an electrode that makes ohmic contact with the p-type gallium nitride based semiconductor layer can be formed.

  After removing the gallium atmosphere, as shown in FIG. 3B, in step S107, the conductive film 35 for the electrode is formed on the main surface of the epitaxial substrate E2 in the vacuum chamber of the processing apparatus 10b without breaking the vacuum. To form a substrate product SP.

According to this manufacturing method, the epitaxial substrate E is exposed to a gallium atmosphere at a substrate temperature of 300 degrees Celsius or higher in the vacuum chamber of the processing apparatus 10b without forming a group III nitride semiconductor. Prior to this exposure step, gallium oxide Ga ₂ O ₃ is formed on the surface of the group III nitride semiconductor of the epitaxial substrate E. However, in the exposure step, gallium is supplied to the gallium nitride semiconductor semipolar main surface 13a and oxidized. Gallium Ga ₂ O ₃ is modified to be modified to Ga oxide Ga ₂ O having a low melting point on the semipolar main surface. The Ga oxide Ga ₂ O is released from the surface of the gallium nitride semiconductor into the hollow of the vacuum chamber of the growth reactor 10a by the effect of the substrate temperature in the exposing step according to the melting point. Therefore, prior to forming the junction with the electrode film, the semipolar main surface 13a can reduce the oxygen concentration in the vicinity of the semipolar main surface by irradiating the semipolar main surface 13a rich in oxygen with Ga. Therefore, a group III nitride semiconductor light emitting device having good ohmic contact can be manufactured.

  In the present embodiment, after the epitaxial substrate E is exposed to the gallium atmosphere, a metal film such as the conductive film 35 may be formed without forming the group III nitride semiconductor. According to this method, an ohmic electrode can be formed on the semipolar surface 13a provided by the modification.

  The conductive film 35 preferably contains any of Au, Pd, Ni, Rh, Al, Ti, Zn, Cu, In, Ta, Pt, and Tl. In this manufacturing method, it is preferable to include at least one of Au, Pd, Ni, Rh, Al, Ti, Zn, Cu, In, Ta, Pt, and Tl.

  As shown in part (c) of FIG. 3, when the epitaxial substrate E2 is taken out from the processing apparatus 10b in step S109, the epitaxial substrate E2 is exposed to the atmosphere containing oxygen. However, since the semipolar plane made of the gallium nitride semiconductor is already covered with the conductive film 35, the metal film is exposed on the surface of the substrate product SP. After the substrate product SP is taken out from the processing apparatus 10b, it is placed in an atmosphere containing oxygen as shown in part (c) of FIG.

  After the substrate product SP is taken out from the vacuum chamber of the processing apparatus 10b, a pattern is formed on the conductive film 35 to form the electrode 37 in step S110 as shown in FIG. 4A. This method does not perform alloying for the electrode 37 after the conductive film 35 is formed. By not performing the alloy for the electrode 37, there is an advantage that electrode deterioration due to heating and interface abnormality between the electrode and the semiconductor are prevented.

  As shown in part (b) of FIG. 4, in step S <b> 111, the electrode 39 is formed on the back surface 11 b of the substrate 11. Prior to the formation of the electrode 39, the back surface of the substrate 11 can be polished to obtain a desired thickness to form a polished back surface. Through these steps, the substrate product SP3 is produced.

  Thereafter, the substrate product SP3 is separated to obtain a group III nitride semiconductor light emitting device 41. The group III nitride semiconductor light emitting device 41 includes a first conductivity type group III nitride semiconductor layer 43, an active layer 45 provided on the main surface of the first conductivity type group III nitride semiconductor layer 43, and an active layer. The first group III nitride semiconductor layer 49 provided on the main surface 45 and the second group III nitride semiconductor layer 51 provided on the main surface of the first group III nitride semiconductor layer 49. And an electrode 53 provided on the main surface of the second group III nitride semiconductor layer 51. The second group III nitride semiconductor layer 51 forms a first junction J1 with the first group III nitride semiconductor layer 49. The electrode 53, the second group III nitride semiconductor layer 51, and the second junction J2 are formed.

  The first and second junctions J1 and J2 are inclined with respect to a reference plane orthogonal to the c-axis VC43 of the first conductivity type group III nitride semiconductor layer 43. The main surface of the active layer 45 is inclined with respect to a reference plane orthogonal to the c-axis VC 43 of the first conductivity type group III nitride semiconductor layer 43. The well layer 45b and the barrier layer 45a constituting the active layer 45 extend along a plane inclined with respect to a reference plane orthogonal to the c-axis VC43 of the first conductivity type group III nitride semiconductor layer 43. The first and second group III nitride semiconductor layers 49 and 51 have the second conductivity type.

  According to this group III nitride semiconductor light emitting device 41, since the second junction J2 is inclined with respect to the reference plane orthogonal to the c-axis VC43, the electrode 53 is formed on the second group III nitride semiconductor layer 51. Join the semipolar surface. Since the electrode 53 forms a junction with the semipolar surface 51a, the second junction J2 exhibits good ohmic characteristics.

  The first and second joints J1 and J2 are substantially parallel to the main surface 55a, and the first and second joints J1 and J2 are 10 degrees or more and 80 degrees or less from the plane orthogonal to the reference axis. It is preferable to incline at an angle in the range.

  The group III nitride semiconductor light emitting device 41 can further include a support base 55, and the support base 55 has a main surface 55a made of a group III nitride semiconductor. The main surface 55a of the support base 55 is inclined at an angle in the range of 10 degrees to 80 degrees from a plane orthogonal to the reference axis extending along the c-axis VC55 of the group III nitride semiconductor. The group III nitride semiconductor layer 43, the active layer 45, the first group III nitride semiconductor layer 49, and the second group III nitride semiconductor layer 51 are in the direction of the normal line Nx of the main surface 55a of the support base 55. Arranged.

  The main surface 55a of the support base 55 is preferably inclined at an angle in the range of not less than 63 degrees and not more than 80 degrees from a plane orthogonal to the reference axis extending along the c-axis of the group III nitride semiconductor. The semipolar plane in this angular range has a step that is susceptible to oxidation.

In order to obtain good ohmic properties, the oxygen concentration in the second group III nitride semiconductor layer 51 is preferably 1 × 10 ¹⁸ cm ⁻³ or less.

  The active layer 45 includes a gallium nitride based semiconductor layer containing indium as a group III constituent element, and the active layer 45 is provided to have a peak emission wavelength in a wavelength range of, for example, 500 nm or more and 540 nm or less.

  FIG. 5 is a drawing showing a transmission electron microscope (TEM) image near the interface between a GaN region and an electrode (metal). Referring to part (a) of FIG. 5, a bond formed when a gold (Au) film is formed on the c-plane is shown. Referring to part (b) of FIG. 5, a bond formed when a gold film is formed on the {20-21} plane is shown. In the junction of the part (b) in FIG. 5, a dark layer is observed at the interface between gold (Au) and {20-21} -GaN, and this dark layer is the interface of the interface in the part (b) in FIG. Thick compared to the dark layer. This dark layer shows the oxide at the interface. As understood from FIG. 5, the oxide layer is thicker on the semipolar plane than on the c-plane.

Example 1
FIG. 6 is a drawing showing the results of measuring the oxygen concentration in the underlying gallium nitride based semiconductor region for electrode formation by a secondary ion mass spectrometry (SIMS) method. The following device structures were prepared for evaluation of secondary ion mass spectrometry. The following layers are arranged in order on the {20-21} GaN substrate in the method from the left side to the right side of the horizontal axis (in the direction of depth 0.3 μm to 0.7 μm).
ud-GaN: 630 nm.
p-GaN: 50 nm.
p-GaN: 400 nm.
n-GaN: 1000 nm.
Epitaxial substrates up to the broken line JC shown in FIG. 6 are prepared. The epitaxial substrate includes a {20-21} GaN substrate, an n-type GaN layer (1000 nm), a p-type GaN layer (400 nm), and a p-type GaN layer (50 nm). An n-type GaN layer (1000 nm), a p-type GaN layer (400 nm), and a p-type GaN layer (50 nm) are grown on a {20-21} GaN substrate. The surface of the p-type GaN layer (50 nm) is exposed to an atmosphere containing oxygen. Epi substrates A1 and A2 having the above structure were prepared. After placing the epi substrate A1 on the molecular epitaxy (MBE) apparatus, an undoped GaN (630 nm) layer is grown on the p-type GaN layer (50 nm) by the MBE method without irradiating Ga flux to form the epi substrate B1. did. In addition, after the epi substrate A2 is arranged in the molecular epitaxy (MBE) apparatus, after irradiating the Ga flux, an undoped GaN (630 nm) layer is grown on the p-type GaN layer (50 nm) by the MBE method, and the epi substrate B2 Formed.

Examples of conditions for gallium irradiation are as follows.
Substrate temperature: 750 degrees Celsius.
Ga flux amount: 1.4 × 10 ⁻⁶ Torr (1 Torr is converted to 133.322 Pascal).
Irradiation time: 30 minutes.

Referring to FIG. 6, on the surface of the measurement result B1 without Ga flux irradiation, and oxygen peaks in the SIMS analysis (peak value close to 1 × ¹⁰ 20 ^{cm -3} exceed ^{1 × 10 19 cm -3),} MBE method A flat oxygen concentration (steady value greater than 1 × 10 ¹⁸ cm ⁻³ ) is observed in the GaN layer grown at 1.

Further, referring to FIG. 6, no oxygen peak was observed in the surface of the measurement result B2 with Ga flux irradiation in SIMS analysis, and the oxygen peak in the measurement result B1 (1 × 10 ¹⁹ cm ⁻³ exceeded 1 × The peak value close to 10 ²⁰ cm ⁻³ ) has disappeared.

  The result of FIG. 6 shows that gallium oxide formed by exposure to the atmosphere containing oxygen can be reduced by performing irradiation with Ga flux. By forming the conductive film subsequent to the irradiation of the Ga flux, the conductive film for the electrode can be formed on the semipolar surface where the amount of gallium oxide is reduced. Further, by forming a gallium nitride based semiconductor film following the irradiation of the Ga flux, the oxygen concentration in the semiconductor film can be reduced, and the semipolar plane of the gallium nitride based semiconductor film having a low oxygen concentration is provided for the electrode. A conductive film can be formed.

  FIG. 7 is a diagram showing current-voltage characteristics. Part (a) of FIG. 7 shows the device structure used for the measurement. The epitaxial substrate includes a {20-21} GaN substrate, an n-type GaN layer (1000 nm), a p-type GaN layer (400 nm), a first p-type GaN layer (50 nm), and a second p-type GaN layer (50 nm). An n-type GaN layer (1000 nm), a p-type GaN layer (400 nm), a first p-type GaN layer (50 nm), and a second p-type GaN layer (50 nm) are grown on a {20-21} GaN substrate. The surface of the first p-type GaN layer (50 nm) is exposed to an atmosphere containing oxygen. A second p-type GaN layer (50 nm) is grown on the first p-type GaN layer (50 nm) using an MBE device without irradiating Ga flux, and a gold electrode is formed on the second p-type GaN layer (50 nm). The substrate product C1 was formed by forming. In addition, after irradiating the Ga flux using the MBE apparatus, the second p-type GaN layer (50 nm) is continuously grown, and a gold electrode is formed on the second p-type GaN layer (50 nm) to obtain the substrate product C2. Produced. Substrate products C1 and C2 having the above structure including a gold electrode having a thickness of 2000 nm were prepared.

As shown in part (b) of FIG. 7, it is understood that application of Ga flux can improve ohmic characteristics and reduce drive voltage. According to the present embodiment, the contact resistance is 1 × 10 ⁻³ Ω · cm ² or less. Note that the reactivity of gold is low, and therefore the use of a gold electrode is suitable for investigating the influence of an oxide film. Therefore, the electrode material is not limited to gold.

  The oxygen profile in the gallium nitride-based semiconductor to which the electrodes are joined changes with Ga irradiation. Specifically, the amount of oxide film at the electrode / semiconductor film interface is reduced by Ga irradiation. In addition to the experiments disclosed in this specification, various experiments have been conducted. The oxygen concentration at the metal / semiconductor interface, including the results of these experiments, is determined in the gallium nitride-based semiconductor layer to which the metal is bonded ( The oxygen concentration is 10 times or less at a depth of 100 nm from the interface. The type of semiconductor layer has not changed.

(Example 2)
The inventors estimated the relationship between the degree of vacuum in Ga irradiation and the substrate temperature by simulation. The simulation was derived using a chemical reaction / equilibrium calculation software called HSC Chemistry manufactured by Outotec Research Oy. The estimate is shown below.
Atmospheric pressure, heating temperature (Celsius).
7.50E-02, over 1070 degrees Celsius.
7.50E-03, 860 degrees Celsius or higher.
7.50E-04, over 710 degrees Celsius.
7.50E-05, 610 degrees Celsius or higher.
7.50E-06, 540 degrees Celsius or higher.
7.50E-07, 490 degrees Celsius or higher.
7.50E-08, 450 degrees Celsius or higher.
7.50E-09, 400 degrees Celsius or higher.
7.50E-10, over 370 degrees Celsius.
7.50E-11, 340 degrees Celsius or higher.
7.50E-12, over 310 degrees Celsius.
7.50E-13, 290 degrees Celsius or higher.
The display “7.50E-13” indicates “7.50 × 10 ⁻¹³ ”. According to this estimate, the substrate temperature can be reduced as the value of the degree of vacuum during Ga irradiation is reduced (high vacuum).

  While the principles of the invention have been illustrated and described in the preferred embodiments, it will be appreciated by those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. The present invention is not limited to the specific configuration disclosed in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.

  As described above, according to the present embodiment, there is provided a method for manufacturing a group III nitride semiconductor light emitting device having good ohmic contact. Further, according to the present embodiment, a group III nitride semiconductor light emitting device having a good ohmic contact is provided.

DESCRIPTION OF SYMBOLS 10a ... Growth furnace, 10b ... Processing apparatus, 11 ... Substrate, 12 ... Natural oxide gallium oxide, 13 ... Semiconductor lamination, 13a ... Surface of semiconductor lamination, E, E2 ... Epitaxial substrate, 15 ... N-type group III nitride semiconductor Region, 17 ... active layer, 19 ... p-type group III nitride semiconductor region, 21 ... quantum well structure, 23 ... barrier layer, 25 ... well layer, 27 ... electron block layer, 29 ... p-type cladding layer, 31 ... gallium Flux, 33 ... Gallium nitride semiconductor layer, 35 ... Conductive film, SP3 ... Substrate product, 41 ... Group III nitride semiconductor light emitting device, 43 ... First conductivity type group III nitride semiconductor layer, 45 ... First conductivity type Group III nitride semiconductor layer, 47 ... active layer, 49 ... first group III nitride semiconductor layer, 51 ... second group III nitride semiconductor layer, 53 ... electrode, J1, J2 ... junction, 55 ... support base .

Claims (14)

A method of manufacturing a group III nitride semiconductor light emitting device,
A step of exposing the epitaxial substrate to a gallium atmosphere without forming a group III nitride semiconductor at a substrate temperature of 300 ° C. or more in a vacuum chamber;
The epitaxial substrate has a semipolar main surface made of a gallium nitride semiconductor,
The method of manufacturing a group III nitride semiconductor light emitting device, wherein the epitaxial substrate includes an active layer made of a group III nitride semiconductor. A method of manufacturing a group III nitride semiconductor light emitting device,
Exposing the epitaxial substrate to a gallium atmosphere without forming a group III nitride semiconductor at a substrate temperature of 300 degrees Celsius or higher in a vacuum chamber;
Forming a substrate product by forming a conductive film for an electrode on the principal surface of the epitaxial substrate; and
With
The main surface of the epitaxial substrate has a semipolar main surface made of a gallium nitride semiconductor,
The method of manufacturing a group III nitride semiconductor light emitting device, wherein the epitaxial substrate includes an active layer made of a group III nitride semiconductor.   3. The group III nitride semiconductor light emitting device according to claim 2, wherein the conductive film includes any one of Au, Pd, Ni, Rh, Al, Ti, Zn, Cu, In, Ta, Pt, and Tl. how to. After removing the substrate product from the vacuum chamber, further comprising forming an electrode by patterning the conductive film;
4. The method for manufacturing a group III nitride semiconductor light-emitting device according to claim 2, wherein the electrode is not alloyed after the conductive film is formed.   The film formation of the conductive film is performed without performing a film formation of a group III nitride semiconductor after the epitaxial substrate is exposed to a gallium atmosphere. A method of manufacturing a group III nitride semiconductor light emitting device. Further comprising the step of growing a semiconductor region on the main surface of the substrate to form the epitaxial substrate;
The main surface of the substrate is made of a group III nitride semiconductor,
The semiconductor region includes a first conductivity type group III nitride semiconductor layer, the active layer, and a second conductivity type group III nitride semiconductor layer,
The epitaxial substrate includes the substrate,
The main surface of the substrate is inclined at an angle in the range of 10 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor,
The main surface of the epitaxial substrate is inclined at an angle in a range of 10 degrees to 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor. A method for producing a group III nitride semiconductor light-emitting device according to any one of the above. The epitaxial substrate includes a p-type gallium nitride based semiconductor layer provided on the active layer,
The p-type gallium nitride based semiconductor layer contains magnesium as a dopant,
The method for producing a group III nitride semiconductor light-emitting device according to claim 1, wherein a main surface of the p-type gallium nitride based semiconductor layer constitutes the main surface of the epitaxial substrate. .   The method for producing a group III nitride semiconductor light-emitting device according to claim 1, wherein the substrate temperature is equal to or lower than a lowest temperature among film formation temperatures in the formation of the epitaxial substrate. .   The method for producing a group III nitride semiconductor light-emitting device according to any one of claims 1 to 8, wherein the substrate temperature is 900 degrees Celsius or less. The active layer includes an InGaN layer;
The method for manufacturing a group III nitride semiconductor light-emitting device according to claim 1, wherein the substrate temperature of the epitaxial substrate is equal to or lower than a growth temperature of the InGaN layer of the active layer. . The group III nitride semiconductor of the substrate is GaN;
The method for producing a group III nitride semiconductor light-emitting device according to claim 1, wherein the main surface of the epitaxial substrate is made of GaN.   The main surface of the epitaxial substrate is inclined at an angle in a range of not less than 63 degrees and not more than 80 degrees from a plane orthogonal to a reference axis extending along the c-axis of the group III nitride semiconductor. A method for producing a group III nitride semiconductor light-emitting device according to any one of the above.   13. The method according to claim 1, further comprising a step of forming a gallium nitride-based semiconductor on the active layer in the vacuum chamber after the epitaxial substrate is exposed to a gallium atmosphere. A method for manufacturing a Group III nitride semiconductor light emitting device. The oxygen concentration in the gallium nitride based semiconductor layer formed in the vacuum chamber after exposing the epitaxial substrate to a gallium atmosphere is 1 × 10 ¹⁸ cm ⁻³ or less. A method for producing the group III nitride semiconductor light-emitting device described in the item.

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