JP3299739B2 - Light emitting element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light-emitting element,
The present invention relates to an improvement in luminous efficiency of a light-emitting element formed by laminating N and AlGaN.

[0002]

2. Description of the Related Art Blue (emission wavelength: 450 n) using GaN
m) to green (emission wavelength: 500 nm) light emitting diode (LED) is considered to be applied to traffic signals, outdoor displays, and the like. The material of this LED is specifically InGaN. However, in order to shorten the emission wavelength and obtain light emission in, for example, an ultraviolet region, it is necessary to reduce the In composition and approach GaN. However, it is known that when the composition of In is reduced, the luminous efficiency is significantly deteriorated, and an LED having a wavelength shorter than 370 nm and having practical efficiency has not yet been developed.

[0003] An LED that emits light in the ultraviolet region is expected to be applied to many fields, and is expected to be used, for example, as a light source for optical recording and reproduction or as a light source for optical communication.

[0004]

On the other hand, GaN and AlG
It has been reported that the emission wavelength can be shortened to 340 nm without lowering the emission efficiency by employing a multilayer structure in which aN is laminated. In the case where InGaN is used as the light emitting layer, the luminous efficiency is extremely high despite the extremely high dislocation density due to the fluctuation of the composition of In. As described above, the shortest wavelength is obtained when the In composition is 0,
Since the composition fluctuation does not occur in GaN, the luminous efficiency is significantly reduced due to the influence of dislocation. AlG with In replaced with Al
In the case of aN, although the emission wavelength is shortened, the composition efficiency of Al does not fluctuate, so that the emission efficiency is reduced. However, by forming a superlattice structure by alternately laminating very thin (about 2 to 3 nm) GaN and AlGaN, the thickness of each layer slightly fluctuates, so that the same effect as the composition fluctuation is obtained. ,
It is considered that the luminous efficiency does not deteriorate unlike the single-layer AlGaN.

As described above, the superlattice structure in which GaN / AlGaN is stacked is considered promising. However, as described above, in order to be put to practical use as a light source for optical communication or a reading light source for a recording medium, it is necessary to further improve the structure. Improvement in luminous efficiency or luminous intensity is required.

In particular, when a light-emitting device is configured with a GaN / AlGaN structure, it is necessary to form a PN junction, and a structure that enhances luminous efficiency or a structure that effectively extracts emitted light to the outside is required. .

The present invention has been made in view of the above-mentioned problems of the related art, and an object of the present invention is to provide a light emitting device having excellent luminous efficiency.

[0008]

[0009]

[0010]

In order to achieve the above object, the present invention relates to a light emitting device comprising a GaN-based compound semiconductor and a PN junction, wherein the N-type semiconductor layer comprises GaN and AlG.
aN are alternately stacked, and a tunnel effect is generated at the interface between the N-type semiconductor layer and the P-type semiconductor layer.
It is characterized in that AlGaN having a moderate thickness is formed.
AlG formed at the interface between the N-type semiconductor layer and the P-type semiconductor layer
aN forms an energy barrier against electrons (AlGaN also functions as a barrier against holes, but its size is smaller than electrons), and suppresses the movement of electrons from the N-type semiconductor layer to the P-type semiconductor layer. As a result, light emission in the N-type semiconductor can be promoted.

Further, the present invention is a light emitting device in which a GaN-based compound semiconductor is PN-junctioned, wherein the P-type and N-type semiconductor layers are formed by alternately stacking GaN and AlGaN. The thickness of AlGaN is set so as to satisfy the Bragg condition with respect to electrons injected into the P-type semiconductor layer, and is set so as not to satisfy the Bragg condition with respect to holes injected into the N-type semiconductor. It is characterized by the following. The electrons injected into the P-type semiconductor layer have a de Broglie wavelength according to the energy level, and the film thickness of each of the GaN / AlGaN laminated structures (specifically, superlattice) is different from the de Broglie wavelength by the Bragg condition. When satisfies, the electrons are totally reflected at the interface of the superlattice. on the other hand,
Since the holes have an energy level different from that of the electrons, the Bragg condition is not satisfied, the holes move from the P-type semiconductor layer into the N-type semiconductor layer, and recombine with the electrons in the N-type semiconductor layer to emit light. Since the energy level of electrons changes according to the bias voltage applied to the light emitting element, phenomenologically,
It can be said that the film thickness is set so as to Bragg-reflect electrons in the P-type semiconductor layer at the driving voltage V of the light-emitting element and cause recombination in the N-type semiconductor layer. Alternatively, a periodic energy barrier is formed by adjusting the thickness of the P-type semiconductor layer, and Bragg reflection is caused on the energy of electrons injected into the P-type semiconductor layer when a bias voltage is applied. Dominantly (ie, P
It can also be said that recombination occurs (at a greater rate than in the type semiconductor layer).

[0012] In the light emitting device of the present invention, further, a substrate, an N-type AlGaN layer formed on the substrate and adjacent to the N-type semiconductor layer, and a P-type semiconductor layer formed on the P-type semiconductor layer.
Type AlGaN ohmic layer. By forming both the buffer layer and the ohmic layer of AlGaN, absorption of light in the ultraviolet region emitted from the N-type semiconductor layer can be suppressed, and luminous efficiency can be improved.

Further, in the light emitting device of the present invention, further, a substrate, an N-type GaN layer formed on the substrate,
A Bragg reflection layer formed on the N-type GaN layer and adjacent to the N-type semiconductor layer, wherein the Bragg reflection layer can reflect light emitted from the PN junction. Light in the ultraviolet region emitted from the N-type semiconductor layer is reflected by the Bragg reflection layer, and absorption in the GaN layer can be suppressed.

Further, in the light emitting device of the present invention, the N
It is preferable that at least either GaN or AlGaN of the type semiconductor layer is doped with Si. The applicant of the present application has confirmed that the light emission intensity of the N-type semiconductor layer is increased by doping with Si, whereby the light emission efficiency of the light emitting element can be improved.

Further, in the light emitting device of the present invention, the N
The GaN of the type semiconductor layer is doped with Si and In,
Preferably, the AlGaN is doped with In. The present applicant has doped GaN with Si and In,
It has been confirmed that doping GaN with In increases the light emission intensity of the N-type semiconductor layer, whereby the light emission efficiency of the light emitting element can be improved.

Further, in the light emitting device of the present invention, the N
It is preferable that Si is formed at the interface between the GaN and the AlGaN in the semiconductor layer. Si formed at the interface between GaN and AlGaN causes lattice mismatch, and GaN / AlGaN
AlGaN causes local thickness fluctuations. As a result, fluctuation of the band gap is caused in GaN / AlGaN, and the luminous efficiency can be improved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a configuration of a light emitting device according to the present embodiment. N-type G on sapphire substrate 10
The aN layer 12 is formed, for example, to about 2 μm. N-type GaN
An N-type GaN-based layer 14 is further formed on the layer 12 as an N-type semiconductor layer, and a P-type GaN-based layer 16 is further laminated. A PN junction is formed at the interface between the N-type GaN-based layer 14 and the P-type GaN-based layer 16, and holes are injected from the P-type GaN-based layer 16 into the N-type GaN-based layer 14 by applying a predetermined voltage to emit light. I do. The N-type GaN-based layer 14 is composed of GaN and A
Superlattice structure (SLS strained
layer superlattice). In addition, the P-type GaN-based layer 16 can also have a superlattice structure in which GaN and AlGaN are alternately stacked. Of course, P-type GaN
The system layer 16 may not have a super lattice structure. Although not shown, a P-type GaN ohmic layer is formed on the P-type GaN-based layer 16 and is connected to an electrode by an ohmic contact.

FIG. 2 shows the N-type GaN-based layer 1 shown in FIG.
4 are shown. GaN14a and AlGa
Is a superlattice structure of alternately laminated N14b, G aN
14a is doped with In and Si, and AlGaN
14b is doped with In. Here, “doping” in the specification of the present application means that the material is introduced into the reaction tube during the layer growth process. The specific creation method is as follows. That is, after a substrate is placed in a reaction tube and an N-type GaN layer 12 is formed, a gas containing TMG, NH ₃ , H ₂ and In and Si, for example, TMIn or SiH ₄ is introduced into the reaction tube to form an N-type GaN layer. GaN 14a doped with Si is formed by MOCVD. And G
When forming AlGaN 14b on aN 14a, T
MG and TMAl are introduced into the reaction tube, and a gas containing In, for example, TMIn is introduced to form InGaN-doped AlGaN 14b. The amount of In or Si introduced is, for example, TMIn = 1.8 μmol / min, SiH
₄ = 446 μmol / min. Ga
The thickness of each of N14a and AlGaN14b is about 2 nm
These sets are formed in a total of about 250 pitches (only three pitches are shown in the figure for simplicity). The thickness of the superlattice layer is determined by the diffusion length of the injected carriers. On the other hand, if the thickness of the superlattice exceeds 1 μm, cracks occur. Therefore, the thickness of the superlattice layer is 1 nm or more and does not cause cracks.
It can be.

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

FIG. 3 shows the structure of the light emitting device according to this embodiment. In the configuration shown in FIG.
Although the P-type GaN-based layer 16 is formed adjacent to the N-type layer 14, in the present embodiment, the N-type GaN-based layer 14 and the P-type GaN
An AlGaN layer 15 is formed at the interface of the system layer 16. Al
The GaN layer 15 is formed thin enough to cause a tunnel effect, preferably 1 to 50 nm, more preferably 2 to 50 nm.
About 10 nm. As the N-type GaN-based layer 14, the N-type GaN-based layer shown in FIG. 2 can be used. When a forward bias is applied in such a configuration, N-type Ga
The band gaps of the N-based layer 14 and the P-type GaN-based layer 16 are narrower than the undoped AlGaN single layer, and the AlGaN layer 15 acts as an energy barrier for electrons. The AlGaN layer 15 acts as an energy barrier not only for electrons but also for holes. However, as shown in FIG. 4 , since the barrier for electrons is larger than the barrier for holes, the AlGaN layer 15 has more holes and the P-type GaN-based layer 16 has an N-type. Ga
It is implanted into the N-based layer 14. Therefore, light can be emitted from the N-type GaN-based layer 14 having high luminous efficiency.

In FIG. 3 , instead of the AlGaN layer 15, AlGaN doped with Mg or Zn may be used to increase the resistance.

FIG. 3 shows an N-type GaN-based layer 1.
At the interface between the P-type GaN-based layer 4 and the P-type GaN-based layer 16, the injection of holes is promoted by forming a layer having a larger energy barrier for electrons than for holes. By alternately stacking GaN and AlGaN to form a superlattice structure and adjusting the film thickness of GaN and AlGaN, electrons can be confined in the N-type GaN-based layer 14 and the injection of holes can be promoted.

[0035] Since electrons and holes are both also the nature of the wave (de Broglie waves or matter wave), is in a layer having a periodic energy, such as shown in FIG. 5 is reflected at each interface. When the Bragg condition is satisfied with respect to the de Broglie wavelength whose energy cycle is determined by the energy level of the electrons, the light is totally reflected and cannot move. Since the effective mass and the height of the energy barrier are different between electrons and holes, if the energy barrier and the period of the P-type GaN-based layer 16 are set so as to satisfy the Bragg condition for electrons, the electrons are injected into the P-type GaN-based layer 16. The electrons are totally reflected and cannot move in the P-type GaN-based layer 16, but holes are injected into the N-type GaN-based layer 14 without being totally reflected because the Bragg condition is not satisfied. As described above, GaN and Al in the P-type GaN-based layer 16 are
By setting the thickness of GaN so that the Bragg condition is satisfied with respect to the injected electrons, the N-type GaN-based layer 14 is formed.
Then, recombination of holes and electrons is caused to emit light. The specific conditions are as follows.

[0036]

(Equation 1)

(Equation 2) Where m ^* is the effective mass of an electron or hole,
E is the energy of electrons or holes, L is the thickness of the barrier (B) and well (W), U0 is the energy height of the barrier, h is Planck's constant, and m and n are integers.

The GaN of the P-type GaN-based layer 16 formed by alternately stacking GaN and AlGaN functions as a well layer (subscript w), and AlGaN functions as a barrier layer (subscript B). The specific thickness of GaN and AlGaN varies depending on the Al composition x of AlGaN. For example, x = 0.15, Δ
If Eg = 200 meV and ΔEc = 140 meV,
Lw (thickness of GaN as a well layer) = 1.8 ± 0.5 n
m, LB (thickness of AlGaN as a barrier layer) = 1 ±
It is about 0.5 nm.

FIG. 6 shows the structure of a light emitting device according to still another embodiment . In the configuration shown in FIG. 1, a PN junction layer is formed on the N-type GaN layer 12, and a Ga layer is formed thereon.
Although an N-ohmic layer is formed, GaN is opaque to light in the ultraviolet region (UV), and light emitted from the active layer may be absorbed by GaN, resulting in lower efficiency.

Therefore, in this embodiment, the luminous efficiency in the active layer is improved, and absorption in a layer adjacent to the active layer is also prevented. Specifically, as shown in FIG.
An AlGaN layer 13 (for example, 1.5 μm) is formed, and a P-type AlGa is formed as an ohmic layer on the PN junction layer.
An N ohmic layer 17 is formed. AlG compared to GaN
Since aN is relatively transparent to UV, it can suppress UV absorption from the active layer.

FIG. 7 shows the structure of a light emitting device according to still another embodiment . In the present embodiment, a Bragg reflection layer 18 for Bragg-reflecting light emitted at the interface between the N-type GaN layer 12 and the N-type GaN-based layer 14 in the configuration of FIG. A P-type AlGaN ohmic layer 17 transparent to UV is formed. The Bragg reflection layer 18 is formed by adjusting GaN and AlGaN to a quarter wavelength with respect to the wavelength of light (UV) from the active layer and stacking the layers.
Prevent UV absorption in the N layer. In addition, G
Since the P-type AlGaN ohmic layer 17 is formed instead of the aN ohmic layer, absorption of UV can be prevented.

Although the embodiments of the present invention have been described above, the present invention is not limited to these, and various modifications are possible. For example, as shown in FIG. 1, a sapphire substrate / N-type GaN layer / N-type GaN-based layer / P-type G
and aN based layer / P-type ohmic So構 granulation, then paste the another substrate on the surface removal of the sapphire substrate and the N-type GaN layer 12 by polishing or the like or light irradiation, N-type GaN
Absorption in layer 12 may be prevented.

[0042]

According to the present invention, light emission efficiency can be increased by causing light emission in the N-type semiconductor layer at the PN junction. Further, absorption of light emitted from the active layer can be suppressed, and luminous efficiency can be increased.

[Brief description of the drawings]

1 is an overall configuration diagram of a light emitting device related to the embodiment.

FIG. 2 is a basic configuration diagram of an N-type GaN-based layer in FIG.

FIG. 3 is an overall configuration diagram of a light emitting device according to an embodiment.
You.

FIG. 4 is an explanatory diagram of bands of electrons and holes.

FIG. 5 shows the relationship between de Broglie waves and periodic energy barriers.
FIG.

FIG. 6 is an overall configuration diagram of another light emitting element according to the embodiment.
is there.

FIG. 7 is an overall explanatory diagram of another light emitting element according to the embodiment.
is there.

[Explanation of symbols]

10 sapphire substrate, 12 N-type GaN layer, 14 N
-Type GaN-based layer, 16P-type GaN-based layer.

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-5-308154 (JP, A) JP-A-6-151967 (JP, A) JP-A-8-213655 (JP, A) JP-A-8-213 264832 (JP, A) JP-A-9-172200 (JP, A) JP-A-9-219538 (JP, A) JP-A-9-227298 (JP, A) JP-A-10-32347 (JP, A) JP-A-10-51030 (JP, A) JP-A-10-209493 (JP, A) JP-A-11-126925 (JP, A) JP-A-11-145057 (JP, A) JP-A-11-186605 JP-A-11-346032 (JP, A) JP-A-11-346035 (JP, A) JP-A-2000-82843 (JP, A) JP-A-2000-91633 (JP, A) JP-A-2000 -91640 (JP, A) JP 2001-168389 (JP, A) JP 2001-177188 (JP, A) JP 2001-177189 (JP, A) 2001-177190 (JP, A) JP 2001-177191 (JP, A) JP 2001-203387 (JP, A) JP 2001-24221 (JP, A) JP 2001-230500 (JP, A) JP-A-10-252585 (JP, A) JP-A-10-41549 (JP, A) JP-A-2001-97800 (JP, A) JP-A-2000-91629 (JP, A) JP-A-11-168240 (JP, A) JP-A-11-186600 (JP, A) JP-A-11-186607 (JP, A) JP-A-11-168241 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 33/00 C23C 16/00-16/56 H01L 21/205

Claims (7)

(57) [Claims] 1. A light emitting device comprising a GaN-based compound semiconductor and a PN junction, wherein the N-type semiconductor layer is formed by alternately stacking GaN and AlGaN, and wherein the N-type semiconductor layer and the P-type semiconductor Tunnel effect at layer interface
A light-emitting element characterized in that AlGaN is formed in such a thickness as to cause generation of AlGaN. 2. A light emitting device comprising a GaN-based compound semiconductor and a PN junction, wherein the P-type and N-type semiconductor layers alternately include GaN and AlGaN.
GaN and AlGaN
Of the thickness of the electron injection into the P-type semiconductor layer
The N-type semiconductor is set so as to satisfy the Bragg condition.
Set not to fill holes injected into the layer
Emitting element characterized by being. 3. A device as claimed in any of claims 1, further comprising: a substrate, formed on said substrate, adjacent to the N-type semiconductor layer N
A light emitting device comprising: a p-type AlGaN layer; and a p-type AlGaN ohmic layer formed on the p-type semiconductor layer. 4. The light emitting device according to claim 1, further comprising: a substrate; an N-type GaN layer formed on the substrate; and an N-type GaN layer formed on the N-type GaN layer. And a Bragg reflection layer adjacent to the mold semiconductor layer, wherein the Bragg reflection layer reflects light emitted from the PN junction. 5. A device as claimed in any of claims 1-4, the light emitting element Si to at least one of the GaN or AlGaN of the N-type semiconductor layer is characterized in that it is doped. 6. The device as claimed in any of claims 1-4, emitting said GaN on Si and In of the N-type semiconductor layer is doped, In the AlGaN is characterized in that it is doped element. 7. A device as claimed in any of claims. 1 to 4, S in the interface of the GaN and AlGaN of the N-type semiconductor layer
A light emitting device, wherein i is formed.