JP2006013473A - Group iii nitride semiconductor light emitting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a group III nitride semiconductor light emitting element which assures lower forward voltage and has excellent light emitting efficiency by utilizing a Ge-doped n-type group III nitride semiconductor layer having a lower resistance and ensures excellent flatness. <P>SOLUTION: The group III nitride semiconductor light emitting element includes a light emitting layer which is bonded with a crystal layer formed of an n-type or p-type group III nitride semiconductor. The n-type group III nitride semiconductor layer is provided in which germanium (Ge) is added and resistivity is 1×10<SP>-1</SP>to 1×10<SP>-3</SP>Ωcm. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a group III nitride semiconductor light emitting device using a low resistance n-type group III nitride semiconductor layer having a region where germanium (Ge) is irregularly added (doping).

Conventionally, a group III nitride semiconductor is a functional material for forming a group III nitride semiconductor light emitting device having a pn junction structure such as a light emitting diode (LED) or a laser diode (LD) that emits visible light having a short wavelength. (See, for example, Patent Document 1). For example, in constructing an LED that emits light in the near ultraviolet band, blue band, or green band, an n-type or p-type aluminum gallium nitride (compositional formula Al _x Ga _y N: 0 ≦ x, y ≦ 1, x + y = 1) is used to construct a clad layer (see, for example, Patent Document 2). Further, gallium indium nitride (compositional formula Ga _y In _z N: 0 ≦ y, z ≦ 1, y + z = 1) is used to form an active layer (light emitting layer) (for example, Patent Document 3). reference).

In a conventional group III nitride semiconductor light emitting device, an n-type or p-type group III nitride semiconductor layer is generally bonded to the light emitting layer. This is because a light emitting part having a hetero junction structure is formed in order to obtain high intensity light emission. For example, in order to form a light emitting part having a double hetero (DH) junction structure, the light emitting layer has conventionally been made of Ga _y In _z N (0 ≦ y, z ≦ 1, y + z = 1) or the like, and is n-type or p-type. A type III nitride semiconductor layer is bonded as a clad layer or the like (see, for example, Non-Patent Document 1).

For example, an n-type group III nitride semiconductor layer disposed between the substrate and the light emitting layer has heretofore been composed exclusively of a group III nitride semiconductor to which silicon (Si) is added. By adjusting the doping amount of silicon, for example, having a controlled resistivity, n-type _{Al x Ga y N (0 ≦} x, y ≦ 1, x + y = 1) layer is utilized (e.g., Patent Documents 4).

  However, there is a problem that cracks occur when a large amount of silicon (Si) is doped to vapor-phase grow a low-resistance n-type group III nitride semiconductor layer. (For example, refer nonpatent literature 2). That is, the conventional technical means for doping silicon cannot stably obtain an n-type group III nitride semiconductor layer having low resistance and continuity.

  On the other hand, Ge is known as an n-type impurity other than silicon (Si) (see, for example, Patent Document 5). However, compared with the case of Si, doping efficiency is low (see Non-Patent Document 3), which is disadvantageous for obtaining a low-resistance n-type Group III nitride semiconductor layer. In addition, when Ge is doped at a high concentration, a small hole (pit) that impairs flatness is generated on the surface of the n-type group III nitride semiconductor layer (see Non-Patent Document 4).

JP 2000-332364 A JP 2003-229645 A Japanese Patent Publication No.55-3834 Japanese Patent No. 3383242 Japanese Patent Laid-Open No. 4-170397 Isao Akasaki, “III-V Group Compound Semiconductor”, published on May 20, 1995, Bafukan Co., Ltd., Chapter 13 H. Murakami et al., J. Crystal Growth, 115 (1991), 648 3 Jpn. J. et al. Appl. Phys. , 31 (9A) (1992), 2883 Group III Nitride Semiconductor Compounds (CLARENDON Press. (OXFORD), 1998), p. 104

  By using a Ge-doped n-type group III nitride semiconductor layer having low resistance and excellent flatness, a group III nitride semiconductor light-emitting device having a low forward voltage and excellent luminous efficiency is obtained.

The present invention relates to a group III nitride semiconductor light emitting device having a light emitting layer bonded to a crystal layer made of an n-type or p type group III nitride semiconductor, to which Ge is added, and the resistivity is 1 × 10 ⁻¹ to A gist of a group III nitride semiconductor light-emitting device comprising an n-type group III nitride semiconductor layer of 1 × 10 ⁻³ Ωcm.

In a preferred embodiment of the present invention, the n-type group III nitride semiconductor has a composition formula of Al _x Ga _y In _z N _1-a M _a (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1). And x + y + z = 1, and M represents a Group V element different from nitrogen (N), and 0 ≦ a <1. Furthermore, in a preferred aspect of the present invention, the n-type nitride semiconductor layer to which Ge is added is a group III nitride semiconductor layer including a region in which the atomic concentration of Ge is periodically changed. In a preferred embodiment of the present invention, the region where the atomic concentration of Ge is periodically changed includes a group III nitride semiconductor layer to which Ge is added, and an undoped (unadded) group III nitride semiconductor layer. Are alternately and periodically stacked. In another preferred embodiment of the present invention, the layer thickness of the group III nitride semiconductor layer to which Ge is added is equal to or less than that of the undoped group III nitride semiconductor layer. In a preferred embodiment of the present invention, the concentration of Ge atoms in the group III nitride semiconductor layer to which Ge is added is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. Furthermore, in another preferred embodiment of the present invention, the n-type group III nitride semiconductor layer is disposed between the substrate and the light emitting layer.
That is, the present invention relates to the following.
(1) In a group III nitride semiconductor light-emitting device having a light emitting layer bonded to a crystal layer made of an n-type or p-type group III nitride semiconductor, germanium (Ge) is added, and the resistivity is 1 × 10 ^{− A} group III nitride semiconductor light-emitting device comprising an n-type group III nitride semiconductor layer of ¹ to 1 × 10 ⁻³ Ωcm.
(2) The n-type group III nitride semiconductor has a composition formula Al _x Ga _y In _z N _1-a M _a (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, and x + y + z = And M represents a Group V element different from nitrogen (N), and 0 ≦ a <1.) The Group III nitride semiconductor light-emitting device according to (1).
(3) The group III nitride according to (1) or (2), wherein the n-type nitride semiconductor layer to which Ge is added is a group III nitride semiconductor layer including a region in which the atomic concentration of Ge is periodically changed. Nitride semiconductor light emitting device.
(4) The region in which the atomic concentration of Ge is periodically changed has a structure in which a group III nitride semiconductor layer to which Ge is added and an undoped group III nitride semiconductor layer are alternately and periodically stacked. The group III nitride semiconductor light-emitting device according to (3).
(5) The group III nitride semiconductor according to any one of (1) to (4), wherein the layer thickness of the group III nitride semiconductor layer to which Ge is added is equal to or less than the layer thickness of the undoped group III nitride semiconductor layer. Light emitting element.
(6) The concentration of Ge atoms in the group III nitride semiconductor layer to which Ge is added is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. The group III nitride semiconductor light-emitting device described.
(7) The group III nitride semiconductor light emitting device according to any one of (1) to (6), wherein the n-type group III nitride semiconductor layer is disposed between the substrate and the light emitting layer.
(8) The group III according to any one of (3) to (7), wherein the total thickness of the region in which the atomic concentration of Ge is periodically changed is 0.1 μm or more and 10 μm or less Nitride semiconductor light emitting device.
(9) The group III according to any one of (3) to (8), wherein the layer thickness for one period of the region where the atomic concentration of Ge is periodically changed is 1 nm or more and 1000 nm or less Nitride semiconductor light emitting device.
(10) A method for manufacturing a group III nitride semiconductor light-emitting device having a light emitting layer bonded to a crystal layer made of an n-type or p-type group III nitride semiconductor, wherein Ge is added to the n-type group III nitride A method of manufacturing a group III nitride semiconductor light-emitting device, wherein a Ge source is periodically changed and supplied to a reaction system when growing a compound semiconductor layer.

  In the Ge-doped n-type group III nitride semiconductor layer of the present invention, the pits generated in the low-resistance Ge atom high-concentration layer are filled with the Ge-atom low-concentration layer. Yes and excellent in flatness. Therefore, the light emitting device of the present invention using such a Ge-doped n-type group III nitride semiconductor layer has a low forward voltage and excellent light emission efficiency.

The n-type Group III nitride semiconductor layer including a region in which the Ge atom concentration is periodically changed according to the present invention has a relatively high melting point and heat-resistant sapphire (α-Al ₂ O ₃ single crystal), Oxide single crystal materials such as zinc oxide (ZnO) or gallium oxide / lithium (composition formula LiGaO ₂ ), IV such as silicon (Si) single crystal (silicon), cubic or hexagonal crystal silicon carbide (SiC), etc. It forms on the board | substrate which consists of a group semiconductor single crystal. As the substrate material, a III-V compound semiconductor single crystal material such as gallium phosphide (GaP) can also be used. An optically transparent single crystal material that can transmit light emitted from the light emitting layer can be effectively used as a substrate. Sapphire is preferable.

The n-type group III nitride semiconductor layer including the region doped (doped) with Ge is preferably composed of Al _x Ga _y In _z N _1-a M _a (0 ≦ x ≦ 1, 0 ≦ y ≦ 1). 0 ≦ z ≦ 1 and x + y + z = 1, and M represents a group V element different from nitrogen, and 0 ≦ a <1. Here, examples of M in the composition formula include P, As, Sb, and the like.

When there is a lattice mismatch between the crystal substrate and the group III nitride semiconductor layer formed thereon, a low-temperature buffer layer or a high-temperature buffer layer that relaxes the mismatch and provides an upper layer with excellent crystallinity is interposed. It is a good idea to stack them together. The buffer layer can be made of, for example, aluminum gallium nitride (compositional formula Al _x Ga _y In _z N: 0 ≦ x, y, z ≦ 1 and x + y + z = 1).

  The n-type group III nitride semiconductor layer including a region in which the Ge atom concentration is periodically changed according to the present invention is a metal organic chemical vapor deposition method (abbreviated as MOCVD, MOVPE, OMVPE, etc.), molecule. It can be formed by a vapor phase growth method such as a line epitaxial method (MBE) method, a halogen vapor phase growth method, or a hydride (hydride) vapor phase growth method. Among these, the MOCVD method is preferable.

In MOCVD, hydrogen (H ₂ ) or nitrogen (N ₂ ) is used as a carrier gas, trimethyl gallium (TMG) or triethyl gallium (TEG) is used as a Ga source which is a group III source, trimethyl aluminum (TMA) or triethyl aluminum is used as an Al source. (TEA), trimethylindium (TMI) or triethylindium (TEI) is used as the In source, and ammonia (NH ₃ ) or hydrazine (N ₂ H ₄ ) is used as the nitrogen source.

As an addition source of Ge, an organic Ge compound such as germane gas (GeH ₄ ), tetramethyl germanium (molecular formula: (CH ₃ ) ₄ Ge) or tetraethyl germanium ((C ₂ H ₅ ) ₄ Ge) can be used. In the MBE method, elemental Ge can also be used as a doping source.

In the MOCVD method, an n-type group III nitride semiconductor layer including a region in which the Ge atom concentration is periodically changed is 900 ° C. or higher and 1250 ° C. or lower using (CH ₃ ) ₄ Ge on a sapphire substrate. It is preferable to form by.

The resistivity of the n-type group III nitride semiconductor layer including the region in which the Ge atom concentration is periodically changed is suitably 1 × 10 ⁻¹ to 1 × 10 ⁻³ Ωcm. Preferably, it is 1 × 10 ^{−2 to} 3 × 10 ⁻³ Ωcm, and more preferably 3 × 10 ^{−2 to} 5 × 10 ⁻³ Ωcm. If the resistivity is larger than 1 × 10 ⁻¹ Ωcm, the resistance is increased and the drive voltage of the device is increased, which is not preferable. On the other hand, if it is smaller than 1 × 10 ⁻³ Ωcm, a small hole (pit) is generated and the flatness is impaired.

  The resistivity of the n-type group III nitride semiconductor layer including the region in which the Ge atom concentration is periodically changed has a predetermined range depending on a mixing ratio of the Ge doping source and another source gas in the vapor phase growth process. Value can be set. Moreover, you may set to the value of a predetermined range by adjusting a growth temperature, a growth pressure, a periodic film thickness, etc. instead of a mixing ratio.

  The region in which the Ge atom concentration is periodically changed is formed by periodically changing the supply amount of the Ge doping source to the vapor phase growth reaction system during the vapor phase growth of the group III nitride semiconductor layer. To do. For example, after forming an undoped thin layer without supplying a Ge doping source to the vapor phase growth region, a large amount of Ge doping source is instantaneously supplied to the vapor phase growth region to contain a high concentration of Ge atoms. A thin layer is formed. If the supply amount of the Ge doping source to the vapor phase growth reaction system is increased or decreased, a region in which the Ge atom concentration is periodically changed can be formed. After growing a thin layer with a low Ge atom concentration, the growth is interrupted until the growth conditions such as the V / III ratio can be adjusted so that the Ge atom is suitable for adding a high concentration of Ge atoms. A thin layer containing a high concentration is formed by bonding.

  An n-type Group III nitride semiconductor thin layer containing Ge atoms at a high concentration and an n-type Group III nitride semiconductor thin layer having a Ge atom concentration lower than that are alternately and periodically stacked. In the case of forming a region in which the atomic concentration is periodically changed, the entire layer thickness of the region in which the Ge atom concentration is periodically changed is preferably 0.1 μm or more and 10 μm or less. Preferably, they are 0.3 micrometer or more and 5 micrometers or less, More preferably, they are 0.5 micrometer or more and 3 micrometers or less. When the layer thickness is less than 0.1 μm, it becomes difficult to obtain a low-resistance n-type group III nitride semiconductor layer. Moreover, the effect obtained even if it exceeds 10 μm does not change.

  The sum of the layer thickness of the n-type group III nitride semiconductor layer containing Ge at a high concentration and the layer thickness of the n-type group III nitride semiconductor layer containing Ge at a low concentration, that is, the periodic layer thickness is 1 nm or more and 1000 nm or less. Suitable. Preferably, they are 4 nm or more and 400 nm or less, More preferably, they are 6 nm or more and 100 nm or less. If the total layer thickness is less than 1 nm, it is difficult to obtain the effect of periodically laminating the Ge-doped layer. On the other hand, if it exceeds 1000 nm, the formation of pits may not be suppressed or the resistance may be increased.

  That is, when the high-concentration Ge-doped layer in one cycle is thicker than the low-concentration Ge-doped layer, pit formation cannot be suppressed and flatness is difficult to obtain. On the other hand, when the low-concentration Ge-doped layer in one cycle is equal to or thicker than the high-concentration Ge-doped layer, the flatness is good. Therefore, the thickness of the low-concentration Ge-doped layer is preferably equal to or greater than the thickness of the thin layer doped with Ge. In order to make the Ge atom concentration smaller, when it is composed of an undoped n-type group III nitride semiconductor thin layer, it fills the pits existing on the surface of the n-type group III nitride semiconductor thin layer containing Ge atoms at a high concentration. The effect is further enhanced, and it is effective to obtain a Ge-doped group III nitride semiconductor thin layer having a flat surface.

  However, if the low-concentration layer is too thick, the resistance is increased and it becomes difficult to obtain a good n-type group III nitride semiconductor layer. That is, if the low concentration layer is large, it is disadvantageous to obtain a group III nitride semiconductor light emitting device having a low forward voltage (so-called Vf) or a low threshold voltage (so-called Vth). Therefore, it is appropriate that the thickness of the thin n-type group III nitride semiconductor thin layer having a low Ge atom concentration is 500 nm or less. In addition, it is desirable to reduce the layer thickness as the Ge concentration of the low concentration layer is small and the carrier concentration is low.

  The number of cycles to be laminated is suitably 1 or more and 10,000 or less. Preferably it is 10 or more and 1000 or less, More preferably, it is 20 or more and 200 or less. For example, a joined body of a high-concentration Ge-doped GaN layer having a layer thickness of 10 nm and a low-concentration Ge-doped GaN layer having a layer thickness of 10 nm is laminated as a single cycle for a total of 100 cycles. A region in which the Ge atom concentration is periodically changed to 2 μm is formed.

  The thickness of the n-type group III nitride semiconductor layer containing Ge at a high concentration is suitably 0.5 nm or more and 500 nm or less. Preferably, they are 2 nm or more and 200 nm or less, More preferably, they are 3 nm or more and 50 nm or less. If the layer thickness is less than 0.5 nm, Ge doping is not sufficient and the resistance tends to increase. On the other hand, if it exceeds 500 nm, the pits are not completely filled with the low-concentration layer, or if the low-concentration layer is sufficiently thick for filling, there is a possibility that the resistance will be increased.

  The layer thickness of the n-type group III nitride semiconductor layer containing Ge at a low concentration is suitably 0.5 nm or more and 500 nm or less. Preferably, they are 2 nm or more and 200 nm or less, More preferably, they are 3 nm or more and 50 nm or less. If the layer thickness is less than 0.5 nm, the pits formed by the Ge-doped layer cannot be sufficiently filled and the flatness may be impaired. Therefore, it is preferably thicker than the thickness of the n-type group III nitride semiconductor layer containing Ge at a high concentration. However, if it exceeds 500 nm, the resistance is increased, which is not preferable.

The concentration of Ge atoms in the n-type group III nitride semiconductor layer containing Ge at a high concentration is suitably 5 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less. Preferably, it is 1 × 10 ¹⁸ cm ⁻³ or more and 3 × 10 ¹⁹ cm ⁻³ or less, and more preferably 3 × 10 ¹⁸ cm ⁻³ or more and 2 × 10 ¹⁹ cm ⁻³ or less. The concentration of Ge atoms in the n-type Group III nitride semiconductor layer containing Ge at a high concentration is not necessarily constant, and the concentration may be changed continuously or discontinuously.

The concentration of Ge atoms inside the n-type group III nitride semiconductor layer containing Ge at a low concentration is lower than the concentration of Ge atoms inside the n-type group III nitride semiconductor layer containing Ge at a high concentration, and It is suitable that it is not less than the lower limit of quantification by the following analytical method and not more than 2 × 10 ¹⁹ cm ⁻³ . Preferably, it is not less than the lower limit of quantification and not more than 1 × 10 ¹⁹ cm ⁻³ , more preferably not less than the lower limit of quantification and not more than 5 × 10 ¹⁸ cm ⁻³ . Further, the Ge atom concentration inside the n-type group III nitride semiconductor layer containing Ge at a low concentration is not necessarily constant, and the concentration may be changed continuously or discontinuously. If the concentration of Ge atoms exceeds 2 × 10 ¹⁹ cm ⁻³ , the density of small holes on the surface increases rapidly, which is not preferable.

  The concentration of Ge atoms can be measured, for example, by secondary ion mass spectrometry (SIMS). This is a technique for performing mass analysis on an element ionized and ejected by irradiating the surface of a sample with primary ions, and the concentration distribution in the depth direction of a specific element can be observed and quantified. This method is also effective for the Ge element present in the group III nitride semiconductor layer.

When the concentration of the high-concentration Ge-doped layer is 5 × 10 ¹⁷ cm ⁻³ or more, it can contribute to constructing an LED having a low forward voltage. On the other hand, assuming that 1 × 10 ²⁰ cm ⁻³ , the entire carrier concentration in the region where the Ge atom concentration is periodically changed is approximately (3-4) × 10 ¹⁹ cm ⁻³ . Doping Ge beyond this atomic concentration is not preferable because the density of pores on the surface increases rapidly.

  A region in which the concentration of Ge atoms is periodically changed can be disposed anywhere in the n-type group III nitride semiconductor layer. For example, it is directly bonded to the surface of the crystal substrate. Further, it is provided by being bonded onto a buffer layer provided on the surface of the crystal substrate. An n-type group III nitride semiconductor excellent in crystallinity if a region in which the concentration of Ge atoms is periodically changed is provided under the n-type group III nitride semiconductor layer adjacent to the crystal substrate or the buffer layer. A layer is obtained. This is because by providing a region in which the concentration of Ge atoms is periodically changed, propagation upward of the layer such as misfit dislocation based on lattice mismatch with the crystal substrate is suppressed. In this case, the periodic layer thickness may be increased from 0.5 μm to 5 μm.

  In a region where the concentration of Ge atoms is periodically changed, propagation of dislocations penetrating from below can be suppressed. For this reason, when a region in which the concentration of Ge atoms is periodically changed is provided as an underlayer for forming a light emitting layer above the n-type group III nitride semiconductor layer, a light emitting layer having excellent crystallinity is formed. Is effective. Therefore, it is possible to contribute to obtaining a group III nitride semiconductor light emitting device having high emission intensity.

  The light emitting layer preferably has a quantum well structure, more preferably a multiple quantum well structure.

  The p-type layer is usually 0.01 to 1 μm in thickness, and includes a p-cladding layer in contact with the light-emitting layer and a p-contact layer for forming a positive electrode. The p-cladding layer and the p-contact layer can be combined. The p-clad layer is formed using GaN, AlGaN or the like, and doped with Mg as a p-dopant. It is desirable to form the outermost surface as a high carrier concentration layer so that contact with the electrode can be easily made, but most layers may have high resistance. That is, there is no problem even if the amount of the dopant is reduced, and there is no problem even if hydrogen that is supposed to inhibit the activation of the dopant is included. Rather, it is desirable because the reverse breakdown voltage of the element is improved.

  As for the p-cladding layer, layers having different compositions and lattice constants may be alternately stacked a plurality of times. At that time, in addition to the composition, the amount and thickness of the dopant may be changed depending on the layer to be stacked.

  GaN, AlGaN, InGaN or the like can be used for the p contact layer, and Mg is doped as an impurity. Group III nitride semiconductor doped with Mg is usually high resistance when taken out from the reactor, but p conductivity can be obtained by applying activation treatment such as annealing treatment, electron beam irradiation treatment, microwave irradiation treatment, etc. However, as described above, it may be used without performing the activation process.

  Further, boron phosphide doped with p-type impurities can also be used as the p-contact layer. Boron phosphide doped with p-type impurities exhibits p-conductivity without any treatment for p-type conversion as described above.

  The growth method of the group III nitride semiconductor constituting these underlayer, light emitting layer, and p-type layer is not particularly limited, and a well-known method such as MBE, MOCVD, HVPE, etc. is used under well-known conditions in the same manner as the n-type layer. be able to. Of these, the MOCVD method is preferable.

  As the negative electrode, negative electrodes having various compositions and structures are well known, and these known negative electrodes can be used without any limitation. As a negative electrode contact material in contact with the n-contact layer, in addition to Al, Ti, Ni, Au, etc., Cr, W, V, etc. can be used. Needless to say, the entire negative electrode can have a multilayer structure to provide bonding properties and the like. In particular, it is preferable to cover the outermost surface with Au in order to facilitate bonding.

  As the positive electrode, positive electrodes having various compositions and structures are well known, and these known positive electrodes can be used without any limitation.

  The translucent positive electrode material may include Pt, Pd, Au, Cr, Ni, Cu, Co, and the like. Further, it is known that the translucency is improved by using a structure in which a part thereof is oxidized. In addition to the above materials, Rh, Ag, Al, or the like can be used as the reflective positive electrode material.

  These positive electrodes can be formed by a method such as sputtering or vacuum deposition. When sputtering is used in particular, ohmic contact can be obtained by appropriately controlling the sputtering conditions without performing annealing after forming the electrode film.

  As a structure of the light emitting element, a flip chip type element including a reflective positive electrode may be used, or a face-up type element including a translucent positive electrode, a lattice type, or a comb type positive electrode may be used.

Example 1
The Ge doped layer according to the present invention formed on the sapphire substrate will be specifically described.

  FIG. 1 schematically shows a cross-sectional structure of an epitaxial multilayer structure 21 described in this example.

  The epitaxial laminated structure was formed by the following procedure using a general low pressure MOCVD means. First, the (0001) -sapphire substrate 1 was placed on a susceptor made of high-purity graphite for semiconductors heated to a film forming temperature by a high-frequency (RF) induction heater. After placing, nitrogen gas was circulated in a stainless steel vapor phase growth reactor to purge the inside of the furnace.

After flowing nitrogen gas through the vapor phase growth reactor for 8 minutes, the induction heating type heater was operated, and the temperature of the substrate 1 was raised from room temperature to 600 ° C. in 10 minutes. While maintaining the temperature of the substrate 1 at 600 ° C., hydrogen gas and nitrogen gas were circulated to set the pressure in the vapor phase growth reactor to 1.5 × 10 ⁴ pascals (Pa). The surface of the substrate 1 was thermally cleaned by allowing it to stand for 2 minutes under this temperature and pressure. After the thermal cleaning was completed, the supply of nitrogen gas into the vapor phase growth reactor was stopped. The supply of hydrogen gas was continued.

  Thereafter, the temperature of the substrate 1 was raised to 1120 ° C. in a hydrogen atmosphere. After confirming that the temperature was stabilized at 1120 ° C., hydrogen gas accompanied by vapor of trimethylaluminum (TMAl) was supplied into the vapor phase growth reactor for 8 minutes 30 seconds. As a result, it is reacted with nitrogen (N) atoms generated by decomposition of deposition deposits containing nitrogen (N), which has been attached to the inner wall of the vapor phase growth reactor, to a thickness of several nm on the sapphire substrate 1. An aluminum nitride (AlN) thin film 2 was deposited. After stopping the supply of hydrogen gas accompanying the vapor of TMAl into the vapor phase growth reactor and terminating the growth of the AlN thin film 2, it waits for 4 minutes and completely discharges the TMAl remaining in the vapor phase growth reactor. did.

Subsequently, after 4 minutes had passed since the supply of ammonia (NH ₃ ) gas into the vapor phase growth reactor, the temperature of the susceptor was lowered to 1040 ° C. while continuing the circulation of the ammonia gas. After confirming that the temperature of the susceptor reached 1040 ° C., wait for a while for the temperature to stabilize, then start supplying trimethylgallium (TMGa) into the vapor phase growth reactor, and undoped GaN layer 3 Grow for 1 hour. The undoped GaN layer 3 has a thickness of 2 μm.

Next, the wafer temperature was raised to 1120 ° C., and when the temperature was stabilized, tetramethyl germanium ((CH ₃ ) ₄ Ge) was passed for 18 seconds and then stopped for 18 seconds. This cycle was repeated 100 times to form a Ge-doped GaN layer 4 in which the Ge concentration of 2.0 μm changes periodically.

  After the growth of the Ge-doped GaN layer 4 was finished, the energization to the induction heating type heater was stopped, and the temperature of the substrate 1 was lowered to room temperature in about 20 minutes. During the temperature drop, the atmosphere in the vapor phase growth reactor was composed only of nitrogen. After confirming that the temperature of the substrate 1 was lowered to room temperature, the laminated structure was taken out from the vapor phase growth reactor.

As a result, an N-type GaN layer having a flat surface with a pit density of 200 pieces / cm ² or less was obtained for the Ge-doped GaN layer whose carrier concentration by hole measurement was 7 × 10 ¹⁸ cm ⁻³ . The resistivity of this Ge-doped GaN layer was 8 × 10 ⁻³ Ωcm. As a result of SIMS analysis, the Ge concentration of the high-concentration Ge-doped layer was 1.2 × 10 ¹⁹ cm ⁻³ , and the Ge concentration of the low-concentration Ge-doped layer was 1 × 10 ¹⁸ cm ⁻³ . The periodic layer thickness was 20 nm.
Example 2
In Example 1, a Ge-doped GaN in which tetramethylgermanium or less ((CH ₃ ) ₄ Ge) was passed for 18 seconds and then stopped for 18 seconds was repeated 100 times, and the Ge concentration of 2.0 μm changed periodically. A Ge-doped GaN layer was formed under the same conditions as in Example 1 except that the layer 4 was formed.

As a result, the carrier concentration by hole measurement was 2 × 10 ¹⁹ cm ⁻³ and the pit density was 400 / cm ² . The resistivity of this Ge-doped GaN layer was 2.5 × 10 ⁻³ Ωcm. As a result of SIMS analysis, the Ge concentration of the high-concentration Ge-doped layer was 4 × 10 ¹⁹ cm ⁻³ , and the Ge concentration of the low-concentration Ge-doped layer was 3 × 10 ¹⁸ cm ⁻³ . The periodic layer thickness was 20 nm.

  As in the first and second embodiments, the resistivity of the Ge-doped GaN layer can be changed by controlling the supply amount (unit: mol / min) of the gas containing Ge. In this embodiment, the supply amount of the raw material gas containing Ge is controlled. However, the supply amount of the raw material gas to be supplied may be controlled at the same time, and the resistivity is changed by controlling the mixing ratio between the two. Also good. It is also possible to control the resistivity by changing the conditions (for example, temperature and pressure) under which the efficiency with which the dopant raw material is taken into the crystal changes.

Further, it is possible to control the resistivity obtained by averaging the entire contact layer by controlling the film thicknesses of the high concentration doped layer and the low concentration doped layer.
Example 3
The present invention will be specifically described by taking as an example the case where a light emitting layer is laminated on the Ge-doped GaN layer of Example 1 to constitute a group III nitride semiconductor light emitting diode.

  FIG. 2 schematically shows a cross-sectional structure of an epitaxial multilayer structure 22 for producing the LED described in this example.

After the Ge-doped GaN layer was laminated in the same manner as in Example 1, an undoped n-type Al _0.07 Ga _0.93 N cladding layer 5 was deposited at 1060 ° C. The thickness of the cladding layer 5 was 12.5 nm.

Next, the temperature of the substrate 1 is set to 730 ° C., and the multi-quantum well structure light emitting layer 6 having a five-period structure including the barrier layer 6a made of Al ₀₀₃ Ga _0.97 N and the well layer 6b made of In _0.25 Ga _0.75 N is undoped. The n-type Al _0.07 Ga _0.93 N clad layer 5 was provided. In the light emitting layer 6 having a multiple quantum well structure, first, an Al ₀₀₃ Ga _0.97 N barrier layer 6 a was provided to be joined to the undoped n-type Al _0.07 Ga _0.93 N cladding layer 5.

The Al ₀₀₃ Ga _0.97 N barrier layer 6a was grown using trimethylaluminum (TMAl) as an aluminum source and triethylgallium (TEGa) as a gallium source. The layer thickness was 8 nm and was undoped.

The In _0.25 Ga _0.75 N well layer 6b was grown using triethylgallium (TEGa) as a gallium source and trimethylindium (TMIn) as an indium source. The layer thickness was 2.5 nm and was undoped.

On the light emitting layer 6 having a multiple quantum well structure, a p-type Al _0.07 Ga _0.93 N cladding layer 7 doped with magnesium (Mg) was formed. The layer thickness was 10 nm. On the p-type Al _0.07 Ga _0.93 N cladding layer 7, a p-type GaN contact layer 8 doped with Mg was further formed. Bis-cyclopentadienyl Mg (bis-Cp ₂ Mg) was used as the Mg doping source. Mg was added so that the hole concentration of the p-type GaN contact layer 8 was 8 × 10 ¹⁷ cm ⁻³ . The layer thickness of the p-type GaN contact layer 8 was 100 nm.

  After completing the growth of the p-type GaN contact layer 8, the energization of the induction heater was stopped, and the temperature of the substrate 1 was lowered to room temperature in about 20 minutes. During the temperature drop, the atmosphere in the vapor phase growth reactor was composed only of nitrogen. After confirming that the temperature of the substrate 1 was lowered to room temperature, the laminated structure 22 was taken out from the vapor phase growth reactor. At this point, the p-type GaN contact layer 8 already showed p-type conductivity without performing an annealing process to electrically activate the p-type carrier (Mg).

  Next, the surface of the highly Ge-doped GaN layer 4 was exposed only to a region where the n-type ohmic electrode 9 was to be formed by using a known photolithography technique and a general dry etching technique. On the exposed surface of the Ge-doped n-type GaN layer 4, an n-type ohmic electrode 9 in which titanium (Ti) and gold (Au) were laminated on the surface side was formed. The entire surface of the p-type GaN contact layer 8 that forms the surface of the remaining laminated structure 22 is made of nickel (Ni) in order from the surface side by using a general vacuum deposition means, a known photolithography means, and the like. ) And gold (Au) are stacked to form a p-type ohmic electrode 10.

  Next, it is cut into a square LED chip (not shown) in a plan view of 350 μm square, placed on a lead frame (not shown), and a gold wire (not shown) is connected to the lead frame. Thus, the element driving current can be passed from the lead frame to the LED chip (not shown).

An element driving current was passed in the forward direction between the n-type and p-type ohmic electrodes 9 and 10 via the lead frame. When the forward current was 20 mA, the forward voltage was 3.5V. Further, the central wavelength of emitted blue band light emitted when a forward current of 20 mA was passed was 460 nm. Also, the intensity of light emission measured using a common integrating sphere reached 5 mW, resulting in a Group III nitride semiconductor LED that provides high intensity light emission.
Example 4
A group III nitride semiconductor light-emitting device was produced in the same manner as in Example 3 except that the laminated structure produced in Example 2 was used. When the forward voltage and the light emission intensity were measured in the same manner as in Example 3, they were 3.5 V and 4.8 mW. The center wavelength of blue band emission was 455 nm.
Comparative Example 1
In Example 1, instead of alternately laminating the layers that circulate (CH ₃ ) ₄ Ge and the layers that do not circulate, (CH ₃ ) ₄ Ge is continuously circulated to form the Ge-doped N-type GaN layer 2. FIG. 3 schematically shows a cross-sectional structure of the epitaxial multilayer structure 23 having the same structure as that of Example 1 except that the thickness is 0 μm.

As a result, when the carrier concentration was adjusted to 1 × 10 ¹⁹ cm ⁻³ , the pit density was as high as 1 × 10 ⁶ cm ⁻³ and a flat surface could not be obtained.
Comparative Example 2
For the structure of Example 3, tetramethylgermanium (hereinafter (CH ₃ ) ₄ Ge) was passed for 18 seconds, and then stopped for 18 seconds. This cycle is repeated 100 times, and instead of forming the Ge-doped GaN layer 4 in which the Ge concentration of 2.0 μm changes periodically, (CH ₃ ) ₄ Ge is continuously circulated in the same manner as in Comparative Example 1 to form Ge A doped N-type GaN layer 11 was formed to 2.0 μm. Thereafter, an n-type cladding layer 5, a multiple quantum well structure light emitting layer 6, a p-type Al _0.07 Ga _0.93 N cladding layer 7 and a p-type GaN contact layer 8 are formed under the same conditions as in Example 3. Further, Example 3 The electrodes were formed, mounted on the lead frame, and connected under the same conditions as above to produce an LED (FIG. 4 Epitaxial Laminate Structure 24 for Producing LED). As a result, the emission intensity measured using a general integrating sphere was only 0.4 mW as a characteristic when a forward current of 20 mA was applied.
Comparative Example 3
In Example 3, a Ge-doped GaN in which tetramethylgermanium (hereinafter referred to as (CH ₃ ) ₄ Ge) was passed for 18 seconds and then stopped for 18 seconds was repeated 100 times, and the Ge concentration of 2.0 μm changed periodically. Instead of forming the layer 4, a GaN layer 12 in which Si is uniformly doped with 7 × 10 ¹⁸ cm ⁻³ is laminated. Thereafter, an undoped AlGaN cladding layer 5, a multiple quantum well structure light emitting layer 6, a p-type Al _0.07 Ga _0.93 N cladding layer 7 and a p-type GaN contact layer 8 are formed under the same conditions as in Example 3. Further, Example 3 An electrode was formed, placed on a lead frame, and connected under the same conditions as in Example 1 to produce an LED (FIG. 5 Epitaxial Laminate Structure 25 for Producing LED). As a result, the forward voltage when the forward current was 20 mA was 3.5V. Further, the central wavelength of emitted blue band light emitted when a forward current of 20 mA was passed was 460 nm. As a characteristic when a forward current of 20 mA was applied, the emission intensity measured using a general integrating sphere was reduced by 20% compared to the case where 4 mW and Ge doping were used for the GaN layer 4.

  The light emitting device of the present invention using a Ge-doped n-type group III nitride semiconductor layer has a low forward voltage and excellent luminous efficiency.

A cross-sectional structure of the epitaxial multilayer structure 21 is schematically shown. A cross-sectional structure of the epitaxial multilayer structure 22 is schematically shown. A cross-sectional structure of the epitaxial multilayer structure 23 is schematically shown. Epitaxial laminated structure 24 for producing LED. Epitaxial laminated structure 25 for producing LED.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 AlN thin film layer 3 Undoped GaN layer 4 Ge doped GaN layer 6 Light emitting layer with multiple quantum well structure 7 p-type AlGaN cladding layer 8 p-type GaN contact layer 9 n-type ohmic electrode 10 p-type ohmic electrode

Claims (10)

In a group III nitride semiconductor light-emitting device having a light emitting layer bonded to a crystal layer made of an n-type or p-type group III nitride semiconductor, germanium (Ge) is added, and the resistivity is 1 × 10 ⁻¹ to 1 A group III nitride semiconductor light emitting device comprising an n-type group III nitride semiconductor layer of × 10 ⁻³ Ωcm. n-type Group III nitride semiconductor, is a composition formula _{Al x Ga y In z N 1} -a M a ( and by 0 ≦ x ≦ 1,0 ≦ y ≦ 1,0 ≦ z ≦ 1, x + y + z = 1 The group III nitride semiconductor light-emitting device according to claim 1, wherein M represents a group V element different from nitrogen (N), and 0 ≦ a <1.   3. The group III nitride semiconductor light-emitting device according to claim 1, wherein the n-type nitride semiconductor layer to which Ge is added is a group III nitride semiconductor layer including a region in which the atomic concentration of Ge is periodically changed. .   The region where the atomic concentration of Ge is periodically changed is composed of a structure in which a group III nitride semiconductor layer doped with Ge and an undoped group III nitride semiconductor layer are alternately stacked periodically. The group III nitride semiconductor light-emitting device according to claim 3.   The group III nitride semiconductor light-emitting device according to any one of claims 1 to 4, wherein a layer thickness of the group III nitride semiconductor layer to which Ge is added is equal to or less than a layer thickness of the undoped group III nitride semiconductor layer. The group III nitride semiconductor layer to which Ge is added has a concentration of Ge atoms of 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ²⁰ cm ⁻³ or less, according to claim 1. Group nitride semiconductor light emitting device.   The group III nitride semiconductor light-emitting device according to claim 1, wherein the n-type group III nitride semiconductor layer is disposed between the substrate and the light emitting layer.   The group III nitride semiconductor according to any one of claims 3 to 7, wherein the total layer thickness of the region in which the atomic concentration of Ge is periodically changed is 0.1 µm or more and 10 µm or less. Light emitting element.   The group III nitride semiconductor according to any one of claims 3 to 8, wherein a layer thickness of one period of the region in which the atomic concentration of Ge is periodically changed is 1 nm or more and 1000 nm or less. Light emitting element.   A method of manufacturing a group III nitride semiconductor light-emitting device having a light emitting layer bonded to a crystal layer made of an n-type or p-type group III nitride semiconductor, wherein the n-type group III nitride semiconductor layer is doped with Ge A method of manufacturing a group III nitride semiconductor light-emitting device, wherein the Ge source is periodically changed and supplied to the reaction system when growing the substrate.

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