JP2004172382A - Nitride semiconductor light emitting element and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize the reduction of an oscillation threshold and the improvement of yield by improving light emitting efficiency at the central wavelength of a laser. <P>SOLUTION: A nitride semiconductor light emitting element is configured by successively setting a lower cladding layer constituted of a nitride semiconductor containing Al and Ga, a lower guide layer constituted of a nitride semiconductor primarily containing In and Ga, and an active layer containing a nitride semiconductor primarily containing In and Ga on a substrate. Further, in the element the lower guide layer is provided with a first layer, and a second layer whose content of In is larger than that of the first layer successively from the active layer. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a nitride semiconductor light emitting device with improved luminous efficiency of an active layer and a method for manufacturing the same.
[0002]
[Prior art]
The nitride semiconductor light emitting device has an oscillation wavelength of about 400 nm, and is being developed for an optical disk system. In addition, since it is durable up to a high output, application fields such as a high power light source and a pulse oscillator are widely studied. Reduction of the oscillation threshold is an important problem when used in various applications, and various improvements such as improvement of a substrate, an epitaxial growth technique, and a multiple quantum well active layer have been made. FIG. 14 shows the structure of a conventional improved nitride semiconductor light emitting device (see Patent Document 1).
[0003]
As shown in FIG. 14, this light-emitting element has a buffer layer 452, an n-type contact layer 453, a second n-type cladding layer 454, a first n-type cladding layer 455, an active layer 456, a sapphire substrate 451. One p-type cladding layer 457, a second p-type cladding layer 458, and a p-type contact layer 459 are sequentially laminated. By providing the first n-type cladding layer 455 or the first p-type cladding layer 457 made of a nitride semiconductor containing In and Ga, the crystallinity of the active layer 456 is improved and the light emission efficiency is increased.
[0004]
However, when the nitride semiconductor light emitting device according to the precedent is operated at an oscillation threshold or less and the emission spectrum is observed from the back surface of the wafer with a spot size of several μm, some characteristics are observed. When the measurement is performed while changing the spot position in the laser resonator, the wavelength at which the maximum intensity is obtained varies, and the full width at half maximum of the emission spectrum is wide, and a subpeak is often observed in a long wavelength region of 440 nm or more. Such a nitride semiconductor light-emitting device has a lower threshold for stimulated emission than a nitride semiconductor light-emitting device having a light emission spectrum having a single peak and a narrow full width at half maximum, and thus has a high oscillation threshold.
[0005]
Further, a light emitting device provided with an n-guide layer made of a nitride semiconductor containing In and Ga according to the precedent example has already been disclosed, and it is difficult to find a case where an active layer made of InGaN is provided on a layer made of GaN or AlGaN. Thus, the deterioration of crystallinity is suppressed (see Patent Document 1, Patent Document 2, and Patent Document 3). However, as a result of a detailed study by the present researcher, these structures are not sufficiently effective.
[0006]
[Patent Document 1]
JP-A-8-228025
[0007]
[Patent Document 2]
JP-A-9-266327
[0008]
[Patent Document 3]
JP-A-11-330614
[0009]
[Problems to be solved by the invention]
It is an object of the present invention to reduce the oscillation threshold and improve the yield by improving the luminous efficiency at the center wavelength of a laser.
[0010]
[Means for Solving the Problems]
The nitride semiconductor light-emitting device of the present invention has a lower cladding layer made of a nitride semiconductor containing Al and Ga, a lower guide layer made of a nitride semiconductor mainly containing In and Ga, and In and Ga. And an active layer containing a nitride semiconductor mainly containing a first layer. The lower guide layer is composed of a first layer in order from the active layer and a second layer having a higher In content than the first layer. And a layer.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
In the nitride semiconductor light emitting device according to the present invention, the lower guide layer laminated between the lower clad layer and the active layer includes, in order from the active layer, a first layer and a second layer having a higher In content than the first layer. And a layer of As a result of examining the structure of the lower layer of the active layer, a lower guide layer made of a nitride semiconductor mainly containing In and Ga is provided between the n-cladding layer and the active layer. There are a first layer and a second layer in order, and the In content of the second layer is made substantially equal to the In content of the well layer in the active layer, so that the emission spectrum from the active layer is simple. The peak and full width at half maximum are narrowed, and the oscillation threshold can be lowered. The second layer may or may not have an n-type impurity added.
[0012]
When the second layer is very close to the active layer, part of the carriers injected from the p-type electrode and the n-type electrode are recombined in the second layer, so that the second layer also functions as a light-emitting layer. . Further, when the substantial band gap of the active layer is different from the substantial band gap of the second layer, the stimulated emission probability of one of the two layers is reduced. Even if the band gaps are almost the same, the second layer has low luminous efficiency due to the influence of the base, and the volume of the luminescent layer increases, so that the oscillation threshold current increases. As described above, it is preferable that the distance between the active layer and the well layer on the substrate side in the active layer is set to 20 nm or more so that the holes injected from the p-type electrode do not flow into the second layer.
[0013]
The active layer mainly contains In and Ga, the epitaxial growth temperature is about 650 ° C. to 850 ° C., and the layer adjacent to the active layer is generally made of Al and Ga, or a nitride semiconductor mainly containing Ga. In many cases, the epitaxial growth temperature is 900 ° C. or higher, and the present invention is also performed at 1075 ° C. Note that “mainly contained” described in the present specification means that at least 99% of the described raw material is contained, and impurities to be added may be different. For example, it means that 1% or less of Al may be mixed in the active layer. The active layer refers to a layer that directly contributes to light emission. The quantum well may refer to a layer in consideration of the spread of electrons, but may include only a well layer or a barrier layer unless otherwise specified. In a multiple quantum well formed by several quantum wells, the quantum well may be from well layers located at both ends to a well layer, or may be from a barrier layer to a barrier layer.
[0014]
In order for the active layer to have good light-emitting characteristics, the lattice constant of Ga or a layer composed of a nitride semiconductor mainly containing Al and Ga and the lattice constant of an active layer composed of a nitride semiconductor mainly containing In and Ga are determined. Due to the difference, it is necessary to reduce the distortion caused in the active layer, the temperature change after the active layer is grown, and the influence of the thermal history. In order to reduce the distortion of the active layer, a lower guide layer serving as a buffer is provided below the active layer, and the lower guide layer is a layer made of a nitride semiconductor mainly containing In and Ga. It is necessary to provide a second layer close to the In content of the well layer in the active layer. After the growth of the active layer, there is a carrier block layer made of a nitride semiconductor mainly containing Al and Ga (Al content is 0.15 or more, preferably 0.2 or more), and mainly contains Ga. A p-type guide layer, a p-type clad layer mainly containing Al and Ga, and a p-type contact layer made of a nitride semiconductor mainly containing Ga are provided. Since these layers are often epitaxially grown at 900 ° C. or higher, they change the state of the active layer to some extent.
[0015]
By the way, in a nitride layer containing In such as an active layer, In tends to be in an energy-stable segregated state, and the diffusion of In in the layer is controlled by appropriately controlling the growth rate of the active layer. During breaks, segregation can be actively adjusted. On the other hand, since the temperature change after the active layer growth also changes the segregation state of In in the active layer, especially the step of raising or lowering the growth temperature not only makes it difficult to maintain the characteristics of the active layer, make worse.
[0016]
For example, in the case where a p-type guide layer mainly containing In and Ga is provided at a growth temperature of 650 ° C. or more and 850 ° C. or less after growth of the carrier block layer, at least one temperature decrease and temperature increase after growth of the active layer A process occurs. It is very difficult for a manufactured nitride semiconductor light emitting device to grow an active layer stably, the oscillation wavelength varies between lots, within the same wafer, and the yield tends to decrease. As described above, it is desirable not to provide a low-temperature growth process, particularly a layer that grows at 830 ° C. or lower, after the temperature raising step after the active layer is grown. Therefore, in this specification, an asymmetric guide layer structure in which a lower guide layer made of a nitride semiconductor mainly containing In and Ga is provided only in the n-layer is provided. When the photon distribution is biased, it is effective to provide a layer made of a nitride semiconductor mainly containing In and Ga between the active layer and the carrier block layer.
[0017]
There is an n-type cladding layer made of a nitride semiconductor mainly containing Al and Ga on a GaN substrate, and an n-type guide layer made of a nitride semiconductor mainly containing Ga is laminated by several tens of nm. The n-type guide layer may be omitted.) Then, after the growth temperature is lowered to about 730 ° C., a second layer including a nitride layer mainly containing In and Ga is provided. . The growth temperature of the second layer is desirably about 650 ° C. to 830 ° C. Here, the substrate is not limited to GaN, but may be sapphire, SiC, GaAs, Si, ZrB.₂And so on. However, for these substrates, an appropriate nitride layer is inserted below the n-type cladding layer.
[0018]
After the growth of the second layer, the first layer is stacked at a growth temperature of 830 ° C. or lower. The first layer is a nitride semiconductor mainly containing In and Ga. The growth temperature in the process from the start of the growth of the lower guide layer to the start of the growth of the active layer is 830 ° C. or less, and the change in the growth temperature is 80 ° C. or less. Thus, the strain applied to the active layer from the nitride semiconductor layer mainly containing Al and Ga below the substrate and the active layer, or the layer mainly containing Ga can be reduced. In particular, the content of the second layer is substantially the same as that of the active layer, and the active layer laminated after the growth of the second layer can be grown under a condition with little distortion. It is desirable that the second layer hardly absorbs laser light because the increase in internal loss is suppressed. However, even if the second layer has a substantially small band gap to absorb laser light, If the carrier lifetime of the layer is almost the same as that of the active layer, or if it is sufficiently long, the absorption characteristics are quickly saturated as the semiconductor light emitting device oscillates. Rise can be ignored. When the manufactured nitride semiconductor light emitting device is operated below the threshold, the emission spectrum is monomodal, the full width at half maximum is narrowed, and the luminous efficiency is improved.
[0019]
The first layer may or may not be doped with an n-type impurity such as Si, but it is desirable that the second layer and the active layer are separated by at least 20 nm or more. The spacing refers to the distance from the top of the top well layer in the second layer to the bottom of the bottom well layer in the active layer. Note that the growth of both the first layer and the second layer may be interrupted at intervals of several nm to several tens nm. Thereby, the morphology during the growth is improved, so that a good growth of the active layer becomes possible. The effects of the present invention can be obtained regardless of the number of well layers and the well width of the active layer.
[0020]
Embodiment 1
In a nitride semiconductor light emitting device, a lower guide layer is provided between a lower clad layer and an active layer, and the lower guide layer has a first layer and a second layer, thereby improving luminous efficiency during current injection. can do. FIG. 1A is a cross-sectional view of the semiconductor light emitting device manufactured in the first embodiment as viewed from the resonator direction. This light emitting device includes an n-type electrode 1, an n-GaN substrate 2, an n-GaN layer 3, an n-AlGaN cladding layer 4, an n-GaN guide layer 5, an n-InGaN third layer 6, and an n-InGaN second layer. Layer 7, n-InGaN first layer 8, n-InGaN active layer 9, p-AlGaN carrier block layer 10, p-GaN guide layer 11, p-AlGaN cladding layer 12, p-GaN contact layer 13, insulating It comprises a layer 14 and a p-type electrode 15. The n-InGaN active layer 9 includes a barrier layer and a well layer, and has a multiple quantum well (MQW) structure. FIG. 1B is a schematic diagram showing the energy level of each layer of the light emitting device manufactured in the first embodiment. The third layer 6 and the first layer 8 have the same In content.
[0021]
The epitaxial growth method described in this specification is a method for growing a crystal film on a substrate, and includes a VPE (vapor phase epitaxial) method, a CVD (chemical vapor deposition) method, and a MOVPE (organic metal vapor phase) method. Epitaxial), MOCVD (Metal Organic Chemical Vapor Deposition), Halide-VPE (Halogen Chemical Vapor Deposition), MBE (Molecular Beam Epitaxy), MOMBE (Metal Organic Molecular Beam Epitaxy), GSMBE (Gas Raw Material) Molecular beam epitaxy) and CBE (chemical beam epitaxy).
[0022]
When the change in the full width at half maximum of the spontaneous emission light was examined by changing the content ratio of In in the second layer by SIMS (FIG. 3), when the active layer was a quantum well layer, the change in In of the second layer was confirmed. Content In_{(X) 2}Is the In content rate In of the well layer in the active layer In_{(X) 0}When the value is within the following range, the full width at half maximum is narrowed, and the luminous efficiency is improved. In_{(X) 2}−0.10 ≦ In_{(X) 0}≤In_{(X) 2}+0.10
Layer thickness d of the second layer in the first embodiment₂Is the thickness d of the well layer in the active layer.₀Is similar to When the emission spectrum from the second layer and the emission spectrum from the active layer are compared by PL (photoluminescence) measurement, the full width at half maximum becomes narrowest at almost the same time. Therefore, the condition under which the effect of improving the characteristics of the active layer is seen is that the substantial band gap of the active layer is changed to Eg.₀And the substantial band gap of the second layer is Eg₂When
Eg₀−0.35 eV ≦ Eg₂
Since it is more desirable that the second layer hardly absorbs laser light,
Eg₀−0.05 eV ≦ Eg₂
Is more desirable.
[0023]
Regarding the position of the second layer, the distance from the top of the second layer (p-type electrode side) to the bottom of the active layer (bottom of the well layer on the n-type electrode side) is L.₁Then
L₁<20 nm
At this time, spontaneous emission light (EL: electroluminescence) from the second layer is observed at the time of current injection. Normally, the mobility of holes is low in the n-InGaN first layer 8, but in the above range, holes seem to be injected into the second layer 7, and the oscillation threshold increases. Therefore, L₁Is
L₁≧ 20nm
Is desirable. On the other hand, when the distance between the second layer and the active layer is increased, the full width at half maximum of the spontaneous emission light increases, and the crystallinity of the active layer deteriorates. Therefore,
L₁≤500nm
It is desirable that
[0024]
The growth temperature of the n-InGaN third layer 6 and the n-InGaN first layer 8 will be discussed. Here, the growth temperature refers to the temperature of the wafer during growth. When the growth temperatures of the second layer 7 and the active layer 9 were fixed and the growth temperatures of the n-InGaN third layer 6 and the n-InGaN first layer 8 were changed, the growth of the third layer was started. The change ΔT in the growth temperature from the start of the growth of the lower guide layer to the start of the growth of the active layer until the end of the growth of the first layer,
ΔT> 80 ° C
Then, the full width at half maximum of the spontaneous emission light increases, and as shown in FIG. 5, a light emission component is observed at 440 nm or more, and the light emission intensity decreases. This component is considered to be the effect of the band tail of the active layer or the fluctuation of the In content. Therefore,
ΔT ≦ 80 ° C
It is necessary to
[0025]
It can be seen that when the growth temperature of the second layer 7 and the active layer 9 is increased, the half width of the spontaneous emission increases even within the range of the temperature difference. Therefore, all the growth temperatures T of each layer from the start of the growth of the n-InGaN lower guide layer to the start of the growth of the active layer are T ≦ 830 ° C.
It is necessary to
[0026]
Layer thickness d of second layer 7₂As a result, if the above conditions are satisfied, the effect of the present specification can be expected. Specific layer thickness d of the second layer₂Is preferably 0.5 nm to 20 nm if the second layer is a single quantum well. If the thickness of the second layer is less than 0.5 nm, the atomic radius of In is larger than that of Ga and N, so that it is difficult to form the layer, and it is difficult to expect the above effect. On the other hand, when the thickness is larger than 20 nm, if the content of In is substantially the same as that of the active layer, the substantial band gap becomes small, so that the internal loss α_i[Cm^-1], The internal loss α_i[Cm^-1] Is suppressed, the In content is reduced, and the effect of the present invention is reduced.
[0027]
Consider the third layer 6. When the third layer 6 is omitted, the internal loss α of the nitride semiconductor light emitting device_i[Cm^-1] Increases. It is considered that absorption occurs at the interface between the n-GaN guide layer 5 and the second layer 7. It is considered that when the second layer having a large In content and the n-GaN guide layer 5 are adjacent to each other as described above, a lattice mismatch is large and a region having poor crystallinity is formed at the interface. Therefore, it is desirable to have the third layer 8 having a smaller In content than the second layer 7. On the other hand, the thickness d of the third layer₃Is a parameter to be defined by the confinement coefficient of the active layer and the vertical transverse mode, and is not defined by the effects described in this specification. The lower guide layer referred to here is a layer sandwiched between the active layer 9 and the n-GaN guide layer 5 (or the n-AlGaN cladding layer 4 if there is no n-GaN guide layer). It is a nitride layer mainly contained and includes a third layer 6, a second layer 7, and a first layer 8. However, when the third layer 6 is omitted, the second layer 7 and the first layer 8 are included.
[0028]
Even if the layer structure between the n-guide layer and the substrate, such as the n-AlGaN cladding layer 4, changes, the effect of the present specification can be expected. In addition, even when In is removed from the n-InGaN third layer 6 and the n-InGaN first layer 8, improvement in the full width at half maximum of spontaneous emission light and luminous efficiency can be expected by the n-InGaN second layer 7. However, the effect is smaller than that of the light emitting device of the present invention. On the other hand, although the GaN substrate is used in the first embodiment, sapphire, SiC, GaAs, Si, ZrB₂Even with such a substrate, the effect can be expected. Usually, when these substrates are used, a buffer layer is provided on the substrate, and an n-type nitride layer containing Al and Ga is provided thereon.
[0029]
The nitride semiconductor light emitting device according to the present invention has a ridge structure. In this structure, a refractive index waveguide structure is formed by current constriction by the ridge portion and a built-in refractive index difference. However, the effect of the present invention is not limited to the ridge structure, but may be a gain waveguide structure using a stripe electrode, or the same refractive index in which the insulating layer of the ridge structure is composed of Al and Ga or a layer mainly containing Ga. May be a buried structure or a block structure, and a known light confinement technology of a semiconductor light emitting device can be applied. However, it is necessary to slightly adjust the thickness of each layer so that the light confinement coefficient of the second layer does not change. However, in the first embodiment, the layer whose thickness is particularly defined, that is, the first layer 8 and the second layer The layer 7 and the third layer 6 follow the above-mentioned range.
[0030]
Embodiment 2
When the second layer in the first embodiment has a multiple quantum well structure, the nitride semiconductor light emitting device has a monomodal spontaneous emission spectrum when operated at a threshold or less, has a narrow full width at half maximum, and It is desirable because luminous efficiency is improved. FIG. 6 is a schematic diagram showing the energy level of each layer in the present structure. This light emitting device includes an n-AlGaN cladding layer 604, an n-GaN guide layer 605, an n-InGaN third layer 606, an n-InGaN second layer 607, an n-InGaN first layer 608, An n-InGaN active layer 609, a p-AlGaN carrier block layer 610, a p-GaN guide layer 611, and a p-AlGaN cladding layer 612 are formed.
[0031]
In the second layer 607 comprising multiple quantum wells, the In content of the well layer is set to In._{(X) 2 ｀}And the In content of the well layer in the active layer 609 is In_{(X) 0}Then
In_{(X) 2 ｀}−0.10 ≦ In_{(X) 0}≤In_{(X) 2 ｀}+0.10
If so, it is desirable because the effects of the present specification can be expected. In addition, the substantial band gap Eg of the second layer 607_{2 ｀}And the substantial band gap of the active layer 609 is Eg₀Then
Eg₀−0.35 eV ≦ Eg_{2 ｀}
Is desirable, and it is more desirable that the second layer hardly absorbs laser light.
Eg₀−0.05 eV ≦ Eg_{2 ｀}
Is more desirable.
[0032]
The bandgap of the first layer 608 is set to Eg₁, The band gap of the third layer 606 is set to Eg.₃Then
Eg₁> Eg_{2 ｀}
Eg₃> Eg_{2 ｀}
And the distance from the uppermost part (p-type electrode side) of the second layer 607 made of multiple quantum wells to the lowermost part of the active layer (end of the well layer on the n-type electrode side) is L._{1 ｀}given that,
20 nm ≦ L_{1 ｀}≤500nm
Is desirable.
[0033]
On the other hand, the thickness d of one well layer of the second layer composed of multiple quantum wells_{2 ｀}After examining,
0.5 nm ≦ d_{2 ｀}≤20nm
Is desirable. This is because the atomic radius of In is larger than that of Ga and N as described above, so that it is difficult to form a layer.
[0034]
Embodiment 3
In the third embodiment, a structure in which the n-GaN guide layer in the first embodiment is omitted will be discussed. FIG. 7A is a cross-sectional view when the semiconductor light emitting device is viewed from the resonator direction. FIG. 7B is a schematic diagram showing the energy level of each layer in the present structure. This light emitting device includes an n-type electrode 701, an n-GaN substrate 702, an n-GaN layer 703, an n-AlGaN cladding layer 704, an n-InGaN third layer 706, an n-InGaN second layer 707, and n-InGaN First layer 708, n-InGaN active layer 709, p-AlGaN carrier block layer 710, p-GaN guide layer 711, p-AlGaN cladding layer 712, p-GaN contact layer 713, insulating layer 714, and p-type electrode 715 Consists of
[0035]
Changing the thickness of the n-GaN guide layer in the first embodiment changes the light confinement coefficient of the active layer. Since the third layer, the second layer, and the first layer also function as n-side light guide layers, propagating light is confined around the active layer without the n-GaN guide layer. In particular, when the first to third layers are thick, it is preferable not to provide the n-GaN guide layer because the confinement coefficient of the active layer can be increased. The nitride semiconductor light-emitting device manufactured in this manner has a monomodal spontaneous emission spectrum when operated at a threshold or less, and improves luminous efficiency.
[0036]
Embodiment 4
In the fourth embodiment, a structure in which the In content of the n-InGaN first layer in the first embodiment is changed will be examined. FIG. 8A is a cross-sectional view of a semiconductor light emitting device in which the In content of the n-InGaN first layer is reduced, as viewed from the resonator direction. FIG. 8B is a schematic diagram showing the energy level of each layer in the present structure. This light emitting device includes an n-type electrode 801, an n-GaN substrate 802, an n-GaN layer 803, an n-AlGaN cladding layer 804, an n-GaN guide layer 805, an n-InGaN third layer 806, and an n-InGaN second layer 806. Layer 807, n-InGaN first layer 808, n-InGaN active layer 809, p-AlGaN carrier block layer 810, p-GaN guide layer 811, p-AlGaN cladding layer 812, p-GaN contact layer 813, insulation It comprises a layer 814 and a p-type electrode 815.
[0037]
FIG. 9A is a cross-sectional view of a semiconductor light emitting device in which the content of In in the n-InGaN first layer is increased, as viewed from the resonator direction. FIG. 9B is a schematic diagram showing the energy level of each layer in the present structure. This light emitting device includes an n-type electrode 901, an n-GaN substrate 902, an n-GaN layer 903, an n-AlGaN cladding layer 904, an n-GaN guide layer 905, an n-InGaN third layer 906, and an n-InGaN second layer 906. Layer 907, n-InGaN first layer 908, n-InGaN active layer 909, p-AlGaN carrier block layer 910, p-GaN guide layer 911, p-AlGaN cladding layer 912, p-GaN contact layer 913, insulation It comprises a layer 914 and a p-type electrode 915.
[0038]
FIG. 10A is a cross-sectional view of a semiconductor light emitting device in which the In-content of the n-InGaN first layer is not unity and has two or more regions having different In-contents, as viewed from the resonator direction. It is. FIG. 10B is a schematic diagram showing the energy level of each layer in the present structure. This light emitting device includes an n-type electrode 101, an n-GaN substrate 102, an n-GaN layer 103, an n-AlGaN cladding layer 104, an n-GaN guide layer 105, an n-InGaN third layer 106, and an n-InGaN second layer 106. Layer 107, n-InGaN first layer 108, n-InGaN active layer 109, p-AlGaN carrier block layer 110, p-GaN guide layer 111, p-AlGaN cladding layer 112, p-GaN contact layer 113, insulation It comprises a layer 114 and a p-type electrode 115.
[0039]
FIG. 11A is a cross-sectional view of a semiconductor light emitting device in which the In content of the n-InGaN first layer is continuously changing, as viewed from the resonator direction. FIG. 11B is a schematic diagram showing the energy level of each layer in the present structure. The light emitting device includes an n-type electrode 151, an n-GaN substrate 152, an n-GaN layer 153, an n-AlGaN cladding layer 154, an n-GaN guide layer 155, an n-InGaN third layer 156, and an n-InGaN second layer 156. 157, n-InGaN first layer 158, n-InGaN active layer 159, p-AlGaN carrier block layer 160, p-GaN guide layer 161, p-AlGaN cladding layer 162, p-GaN contact layer 163, insulation It comprises a layer 164 and a p-type electrode 165.
[0040]
The substantial band gap of the first layer is Eg₁And the substantial band gap of the active layer is Eg₀In order to obtain a carrier confinement effect in the active layer,
Eg₀<Eg₁
Is desirable. Further, the content of In in the first layer is changed to In._{(X) 1}And the content In of the barrier layer in the active layer In_{(X) 0 ｀}When
In_{(X) 0 ｀}−0.02 ≦ In_{(X) 1}≤In_{(X) 0 ｀}+0.02
0 ≦ In_{(X) 1}
Is desirable.
[0041]
The nitride semiconductor light-emitting device manufactured in this way has a single-peak spontaneous emission spectrum when operated at a threshold or less, and is expected to improve luminous efficiency. In the n-InGaN first layer, In is slightly mixed with In in order to minimize a change in growth temperature during the growth process in growing the active layer from the second layer. Therefore, the content of the first layer is not limited to a narrow range, but the content of In in the first layer is increased in that the carrier confinement effect in the active layer can be enhanced and the threshold can be reduced. It is desirable that the content of In in the well layer is smaller than that.
[0042]
Embodiment 5
In the fifth embodiment, a structure in which the third layer in the first embodiment includes a fourth layer having a higher In content than the third layer will be described. FIG. 12A is a cross-sectional view when the semiconductor light emitting device is viewed from the resonator direction. FIG. 12B is a schematic diagram showing the energy level of each layer in the present structure. The light emitting device includes an n-type electrode 251, an n-GaN substrate 252, an n-GaN layer 253, an n-AlGaN cladding layer 254, an n-GaN guide layer 255, an n-InGaN third layer 256, and an n-InGaN fourth layer 256. Layer 250, n-InGaN second layer 257, n-InGaN first layer 258, n-InGaN active layer 259, p-AlGaN carrier block layer 260, p-GaN guide layer 261, p-AlGaN cladding layer 262 , A p-GaN contact layer 263, an insulating layer 264 and a p-type electrode 265.
[0043]
In the first embodiment, the second layer also serves to alleviate the strain applied to the active layer from the substrate, the n-AlGaN cladding layer and the n-GaN guide layer, and the fourth layer 250 in the fifth embodiment It promotes the effect. Specifically, the substantial band gap of the fourth layer 250 is changed to Eg.₄And the content of In in the fourth layer is In_{(X) 4}When
In_{(X) 3}<In_{(X) 4}
And
In_{(X) 0}−0.10 ≦ In_{(X) 4}≤In_{(X) 0}+0.10
Is desirable. Conditions under which the effect of improving the characteristics of the active layer can be seen are as follows:
Eg₀−0.35 eV ≦ Eg₄
Since it is better that the second layer hardly absorbs laser light,
Eg₀−0.05 eV ≦ Eg₄
Is more desirable.
[0044]
The nitride semiconductor light-emitting device manufactured in this manner promotes the narrowing of the full width at half maximum of the spontaneous emission light observed in the operation below the threshold value as compared with the first embodiment. Although the fourth layer 250 is formed of a single quantum well in the fifth embodiment, it may be formed of a multiple quantum well structure or a plurality of layers having substantially different band gaps. Each layer has the above Eg₄And In_{(X) 4}It suffices if the condition described above is satisfied.
[0045]
Embodiment 6
In the sixth embodiment, a structure having a p-InGaN fifth layer between the active layer and the p-type carrier block layer in the first embodiment will be examined. FIG. 13A is a cross-sectional view of the semiconductor light emitting device having the p-InGaN fifth layer when viewed from the resonator direction. FIG. 13B is a schematic diagram showing the energy level of each layer in the present structure. The light emitting device includes an n-type electrode 351, an n-GaN substrate 352, an n-GaN layer 353, an n-AlGaN cladding layer 354, an n-GaN guide layer 355, an n-InGaN third layer 356, and an n-InGaN second layer 356. Layer 357, n-InGaN first layer 358, n-InGaN active layer 359, p-InGaN fifth layer 350, p-AlGaN carrier block layer 360, p-GaN guide layer 361, p-AlGaN cladding layer 362 , A p-GaN contact layer 363, an insulating layer 364 and a p-type electrode 365.
[0046]
In the structure according to the first embodiment, the guide layer below the active layer is made of a nitride semiconductor mainly containing In and Ga, and the guide layer above the active layer is made of a nitride semiconductor mainly containing Ga. The two guide layers have different refractive indexes, and the latter has a lower refractive index. The light distribution in the vertical direction is pulled toward the substrate by such an asymmetric guide layer. When the center of the light distribution deviates from the position of the active layer, the light confinement coefficient of the active layer becomes small, so that the oscillation threshold increases. Therefore, when the fifth layer made of a nitride semiconductor mainly containing In and Ga is provided on the active layer adjacent to the active layer, the active layer can be closer to the center of the vertical light distribution. , Which is desirable in that the threshold value can be reduced.
[0047]
It is better to increase the mobility of holes in the fifth layer, and it is effective to add a p-type impurity such as Mg. The effect can be expected even if the fifth layer is an n-type or non-doped layer. On the other hand, after the growth of the p-type carrier block layer, the substrate temperature was lowered, and a p-type nitride layer containing In and Ga was provided. The peak did not become a peak, and the threshold increased. This is probably because the segregation of In occurred in the active layer due to the temperature history after the growth of the active layer.
[0048]
【Example】
Example 1
In this example, a nitride semiconductor light emitting device as shown in FIG. 1 was manufactured. First, the n-GaN substrate 2 is set in the MOCVD apparatus, and NH3 as a group V raw material is set.₃A GaN buffer layer was grown to a thickness of 25 nm at a growth temperature of 550 ° C. using a group III material TMGa. Next, at a growth temperature of 1075 ° C., SiH₄To the n-GaN layer 3 (Si impurity concentration 1 × 10¹⁸/ Cm³) Was formed at 3 μm. Subsequently, 1.5 μm thick n-Al_0.1Ga_0.9N cladding layer 4 (Si impurity concentration 1 × 10¹⁸/ Cm³) Was grown, and then the n-GaN guide layer 5 was grown to 0.05 μm.
[0049]
Thereafter, the substrate temperature was lowered to 725 ° C., and n-In_0.02Ga_0.98An N third layer 6 (non-doped) is grown to a thickness of 8 nm, and n-In_0.14Ga_0.86N second layer 7 (non-doped) is grown to a thickness of 4 nm, and n-In_0.02Ga_0.98An N first layer 8 (non-doped) was grown to a thickness of 46 nm. After the growth of the second layer, or between the third layer and the first layer, the growth may be interrupted for 1 second to 180 seconds at intervals of about several nm. Thereby, the flatness of each layer is improved, and the luminescence half width is reduced. Each of the third layer 6, the second layer 7, and the first layer 8 has an impurity concentration of 1 × 10¹⁷/ Cm³From 1 × 10²²/ Cm³You may add in the range of the extent.
[0050]
Then, a 4 nm thick In_0.15Ga_0.85N well layer and 8 nm thick In_0.02Ga_0.98A three-period active layer (multiple quantum well structure) 9 composed of an N barrier layer was grown in the order of well layer / barrier layer / well layer / barrier layer / well layer / barrier layer. The growth may be interrupted for 1 second to 180 seconds between the barrier layer and the well layer or between the well layer and the barrier layer. As a result, the flatness of each layer is improved, and the light emission half width is reduced.
[0051]
Next, the substrate temperature was raised again to 1050 ° C., and the 18 nm-thick p-Al_0.3Ga_0.7An N carrier block layer 10 and a p-GaN guide layer 11 having a thickness of 0.1 μm were grown. 5 × 10 Mg as a p-type impurity¹⁹/ Cm³~ 2 × 10²⁰/ Cm³Was added. Subsequently, at a substrate temperature of 1050 ° C., a 0.5 μm-thick p-Al_0.1Ga_0.9An N-cladding layer 12 and a 0.1 μm-thick p-GaN contact layer 13 were grown. 5 × 10 Mg as a p-type impurity¹⁹/ Cm³~ 2 × 10²⁰/ Cm³Was added. TMGa, TMAl, TMIn, NH₃, Cp₂Mg, SiH₄Was used.
[0052]
After the formation of the p-GaN contact layer 13, a ridge structure was formed by dry etching, and a p-type electrode 15 made of Pd / Mo / Au was formed on the upper surface of the insulating layer 14. For the insulating layer, SiO₂Was used, but ZrO₂, SiO, Ta₂O₅, TiO₂, Al₂O₃Or a mixture thereof. Further, even a semiconductor such as AlGaN can be used to adjust the refractive index. Thereafter, a part of the GaN substrate 2 was removed from the rear surface side by polishing or etching, and the thickness of the wafer was adjusted to be as thin as about 100 μm to 200 μm. This is a step for easily dividing the wafer into individual laser chips in a later step. In particular, when the laser end face mirror is also formed at the time of division, it is desirable to adjust the thickness to about 80 μm to 150 μm. In this embodiment, the thickness of the wafer is adjusted to about 120 μm by using a grinder and a polishing machine, but it may be adjusted only by a polishing machine. The back surface of the wafer was polished with a polishing machine and flattened.
[0053]
After polishing, a thin metal film was deposited on the back surface of the GaN substrate 2 to obtain an n-type electrode 1. The n-type electrode 1 had a layer structure of Hf / Al / Mo / Pt / Au from the substrate side. In order to form such a thin metal film with good controllability of the film thickness, a vacuum deposition method is suitable. In this embodiment, the vacuum deposition method was used. However, it goes without saying that another method such as an ion plating method or a sputtering method may be used. In order to improve the characteristics of the p-type and n-type electrodes, annealing was performed at 500 ° C. after forming the metal film to obtain a good ohmic electrode. The annealing may be performed after the formation of the p-type electrode and after the formation of the n-type electrode, respectively, or after the formation of Hf / Al in the n-type electrode, may be performed to form Mo / Pt / Au. .
[0054]
The semiconductor light emitting device thus manufactured was divided by the following method. First, a scribe line was formed at the diamond point from the surface, and the wafer was divided along the scribe line by appropriately applying force to the wafer. The scribe line may be inserted from the back side.Other methods include a dicing method of making a cut or cut using a wire saw or a thin blade, irradiation of a laser beam such as an excimer laser, and subsequent rapid cooling, followed by rapid cooling. A laser scribing method using a scribe line as a scribe line or a laser ablation method that irradiates a high energy density laser beam and evaporates this part to perform grooving is also applied to the chip. Can be divided.
[0055]
After the division, a reflectivity was changed by providing a dielectric multilayer film on the end face forming the Fabry-Perot resonator. Such a reflective film is formed according to the system, and is not absolutely determined. Generally, however, it is desirable that the rear surface has a rear reflective film of 80% or more. In particular, when a light receiving element for detecting light output is not provided further behind the rear surface, it is preferable to provide a reflection film of 90% or more. As a result, the photon density in the semiconductor light emitting device is improved, so that the oscillation threshold value is reduced. Such a high reflection film may be formed by alternately forming a material having a low refractive index and a material having a high refractive index with a layer thickness of 4 / λ.₂, TiO₂, Ta₂O₅, Al₂O₃, ZrO₂Are used.
[0056]
By the way, in order to increase the external differential efficiency, the reflectance of the end surface on the emission surface side may be reduced. However, it is difficult to design a low-reflection film having less wavelength dispersion as compared with a high-reflection film. In particular, at a wavelength near 405 nm, SiO or TiO is used as the above-mentioned dielectric.₂And ZrO₂By providing a multilayer film made of at least three or more materials to which a mixture or the like is added, design becomes easy. On the other hand, if attention is paid to low-output noise characteristics, it is also useful to slightly increase the reflectivity of the end face composed of the cleavage interface by about 22%, and it is preferable to provide a front reflection film of 50% or less.
[0057]
Next, the laser chip was mounted on a heat sink by a die bonding method to obtain a semiconductor laser device. The chip was firmly bonded by junk-up with the n-type electrode side as the bonding surface. The heat sink here is a stem or the like. Note that the junction may be junction-down with the p-type electrode side as a bonding surface. In this case, the p-type electrode structure is Pd / Mo / Pt / Au or Pd / Mo / Ni / Au. Good.
[0058]
Various characteristics of the nitride semiconductor light emitting device thus manufactured were examined. The resonator length of the nitride semiconductor light emitting device was 500 μm, and the stripe width was 1.5 μm. Continuous oscillation was performed at a threshold of 33 mA at room temperature of 25 ° C., and the oscillation wavelength was 405 ± 5 nm. This device was operated at a threshold value or less, and the spectrum of spontaneous emission light was observed as shown in FIG. When the full width at half maximum of the spontaneous emission light was examined, it was 13.5 nm, and there was almost no light emission at 440 nm or more.
[0059]
Comparative Example 1
A nitride semiconductor light emitting device was manufactured in the same manner as in Example 1 except that only the second layer in Example 1 was eliminated, and various characteristics were examined. As a result, continuous oscillation was performed at a room temperature of 25 ° C. with a threshold value of 42 mA, and the oscillation wavelength was 405 ± 5 nm. The device was operated below the threshold, and the spectrum of spontaneous emission light as shown in FIG. 4 was observed. When the full width at half maximum of the spontaneous emission light was examined, it was 17.5 nm, and the emission intensity was reduced. The increase in the oscillation threshold was considered to be a decrease in the crystallinity of the active layer or a change in strain.
[0060]
The embodiments and examples disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.
[0061]
【The invention's effect】
According to the present invention, the emission threshold can be reduced and the yield can be improved by improving the luminous efficiency at the center wavelength of the laser.
[Brief description of the drawings]
FIGS. 1A and 1B are diagrams showing a nitride semiconductor light emitting device according to a first embodiment of the present invention, in which FIG. 1A is a cross-sectional view as viewed from a resonator direction, and FIG. 1B shows an energy level of each layer. It is a schematic diagram.
FIG. 2 is a diagram showing a spectrum of spontaneous emission light of the nitride semiconductor light emitting device in Example 1 of the present invention.
FIG. 3 is a diagram showing a change in full width at half maximum of spontaneous emission light when the In content of the second layer is changed in the first embodiment of the present invention.
FIG. 4 is a diagram showing a spectrum of spontaneous emission light of the nitride semiconductor light emitting device in Comparative Example 1.
FIG. 5 is a diagram showing spontaneous emission light (spectrum) of a nitride semiconductor light emitting device when a change in growth temperature is higher than 80 ° C.
FIG. 6 is a schematic diagram showing an energy level of each layer according to the second embodiment of the present invention.
FIGS. 7A and 7B are diagrams showing a nitride semiconductor light emitting device according to a third embodiment of the present invention, wherein FIG. 7A is a cross-sectional view when viewed from the direction of a resonator, and FIG. It is a schematic diagram.
8A and 8B are diagrams showing a nitride semiconductor light emitting device according to a fourth embodiment of the present invention, wherein FIG. 8A is a cross-sectional view when viewed from the direction of a resonator, and FIG. 8B shows the energy level of each layer. It is a schematic diagram.
9A and 9B are diagrams showing a nitride semiconductor light emitting device according to a fourth embodiment of the present invention, in which FIG. 9A is a cross-sectional view as viewed from the direction of the resonator, and FIG. 9B shows the energy level of each layer. It is a schematic diagram.
FIGS. 10A and 10B are diagrams showing a nitride semiconductor light emitting device according to a fourth embodiment of the present invention, wherein FIG. 10A is a cross-sectional view when viewed from the direction of the resonator, and FIG. 10B shows the energy level of each layer. It is a schematic diagram.
FIGS. 11A and 11B are diagrams showing a nitride semiconductor light emitting device according to a fourth embodiment of the present invention, in which FIG. 11A is a cross-sectional view as viewed from the direction of a resonator, and FIG. 11B shows the energy level of each layer. It is a schematic diagram.
12A and 12B are diagrams showing a nitride semiconductor light emitting device according to a fifth embodiment of the present invention, in which FIG. 12A is a cross-sectional view when viewed from the direction of a resonator, and FIG. 12B shows the energy level of each layer. It is a schematic diagram.
13A and 13B are diagrams showing a nitride semiconductor light emitting device according to a sixth embodiment of the present invention, wherein FIG. 13A is a cross-sectional view as viewed from the direction of a resonator, and FIG. 13B shows an energy level of each layer. It is a schematic diagram.
FIG. 14 is a sectional view of a conventional nitride semiconductor light emitting device.
[Explanation of symbols]
1 n-type electrode, 2 n-GaN substrate, 3 n-GaN layer, 4 n-AlGaN cladding layer, 5 n-GaN guide layer, 6 n-InGaN third layer, 7 n-InGaN second layer, 8 n-InGaN first layer, 9 n-InGaN active layer, 10 p-AlGaN carrier block layer, 11 p-GaN guide layer, 12 p-AlGaN cladding layer, 13 p-GaN contact layer, 14 insulating layer, 15 p-type Electrodes, 250 n-InGaN fourth layer, 350 p-InGaN fifth layer.

Claims (10)

Including a lower clad layer made of a nitride semiconductor containing Al and Ga, a lower guide layer made of a nitride semiconductor mainly containing In and Ga, and a nitride semiconductor mainly containing In and Ga A nitride semiconductor light-emitting device having an active layer and a substrate successively provided on a substrate, wherein the lower guide layer has a first layer in order from the active layer and an In content higher than that of the first layer. A nitride semiconductor light emitting device comprising: a second layer. From the second layer, the distance L ₁ to the well layer of the substrate side of the active layer,
L ₁ ≧ 20 nm
The nitride semiconductor light emitting device according to claim 1, wherein The active layer is a quantum well active layer, wherein the content of In in the second layer is In _{(x) 2,} and the content of In in the well layer in the active layer is In _{(x) 0.} ,
_{In (x) 2 -0.10 ≦ In} (x) 0 ≦ In (x) 2 +0.10
The nitride semiconductor light emitting device according to claim 1, wherein: 4. The nitride semiconductor light emitting device according to claim 1, wherein the content of In in the first layer is smaller than the content of In in the well layer in the active layer. 5. The lower guide layer includes, in order from the active layer, a first layer, a second layer, and a third layer having a lower In content than the second layer. Item 3. The nitride semiconductor light emitting device according to item 1. The nitride semiconductor light-emitting device according to claim 5, wherein the third layer includes a fourth layer having a higher In content than the third layer. The second layer is a multiple quantum well layer, and the content of In in the well layer in the second layer is In _{(x) 2 ｀,} and the content of In in the well layer in the active layer is In _{( x) When 0} ,
In _(x) 2｀−0.10 ≦ In _{(x) 0} ≦ In _{(x) 2 ｀} + 0.10
The nitride semiconductor light emitting device according to claim 1, wherein: The nitride according to claim 1, further comprising a fifth layer made of a nitride semiconductor mainly containing In and Ga on the active layer, adjacent to the active layer. Semiconductor light emitting device. The change ΔT in the growth temperature from the start of the growth of the lower guide layer to the start of the growth of the active layer is:
ΔT ≦ 80 ° C
The method for manufacturing a nitride semiconductor light emitting device according to claim 1, wherein 2. The method according to claim 1, wherein a growth temperature of each layer from the start of the growth of the lower guide layer to the start of the growth of the active layer is 830 ° C. or less. 3.

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