JPH07231115A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To provide a light emitting element, wherein light having a sub-peak wavelength is suppressed with the simple structure, by providing the new constitution, which can suppress the generation of the light having the sub-peak wavelength. CONSTITUTION:An absorbing layer 2 is provided between a substrate B and a P-N junction part 1 in this structure. The band-gap of the absorbing layer 2 is substantially equal to the energy of main-peak light. It is preferable that a suppressing layer 3 comprising a material, whose carrier concentration is 5X10<17>cm<-3> and the band gap is smaller than the energy of light passing through the absorbing layer, is provided on the substrate side of the absorbing layer 2. The suppressing layer 3 can be the layer, which is also used as the substrate B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device such as a light emitting diode or a semiconductor laser, and more particularly, to a light emitting device capable of suppressing harmful light emission in other wavelength bands besides the main wavelength of light emission. Concerning the structure of.

[0002]

2. Description of the Related Art Light emission from a semiconductor light emitting device (hereinafter referred to as "light emitting device") such as a light emitting diode (LED) or a semiconductor laser is forward to a pn junction formed in one semiconductor crystal material. Is a light-emission phenomenon caused by the recombination of free electrons and holes to release energy when a voltage is applied to it. The center wavelength of the intended light emission is almost determined by the band gap of the semiconductor crystal material used as the active layer. It is a thing. Further, the light is often not only a central wavelength but also a light emission having a peak at the central wavelength over a specific wavelength range. Hereinafter, the center wavelength of the target light emission is referred to as "main peak wavelength", and the light including the above-described light emission over a specific wavelength range centered on the main peak wavelength is referred to as "main peak wavelength light". In the light emitting element, in addition to the main peak wavelength, there may be a problem in that light emission also exists in other wavelength bands apart from this. (Hereinafter, the center wavelength of such light emission is referred to as "sub-peak wavelength".) For example, AlGa on a GaAs substrate
Red L crystal-grown with As pn junction as light emitting layer
Explaining the case of ED, the main peak wavelength is 6
880 to 900 n, while 50 to 670 nm
An example of a phenomenon is known in which light emission having a sub-peak wavelength near m is observed.

Sub-peak wavelength light is light emission in a wavelength band that is unexpected for the purpose of designing a light emitting device. Therefore,
If a light emitting element that causes such light emission is used for a light source of, for example, a photoelectric sensor, malfunction occurs and various problems occur. It is known that the cause of generation of the sub-peak wavelength light is photoluminescence, which is generated by the crystal substrate being excited by the irradiation of the main peak wavelength light. In order to deal with this phenomenon, conventionally, the carrier concentration of the substrate is set to about 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ , or a thin layer having a similar carrier concentration is provided on the substrate to detect the sub-peak wavelength light. Was used as a layer for suppressing the intensity of photoluminescence.

[0004]

The object of the present invention is to provide a new structure capable of suppressing the generation of sub-peak wavelength light.
An object of the present invention is to provide a light emitting device having a simple structure in which sub-peak wavelength light is suppressed.

[0005]

Means for Solving the Problems The present inventor has focused on the band gap of a layer in which sub-peak wavelength light is generated, and by making the band gap and the energy of the main peak wavelength light substantially equal, The inventors have found that wavelength light can be effectively suppressed and completed the present invention. That is, the light emitting device of the present invention has the following constitution. (1) A p-type or n-type conductive semiconductor layer for absorbing light, which is provided above the substrate (hereinafter referred to as “absorption layer”)
And a pn junction having a conductivity type different from that of the absorption layer provided above the absorption layer, and the band gap of the absorption layer is substantially equal to the energy of light emitted from the pn junction. A semiconductor light-emitting device characterized by being the same. (2) The absorption layer is composed of a portion having a band gap substantially equal to the energy of light emitted from the pn junction and a portion having a band gap larger than the band gap (1). Semiconductor light emitting device. (3) The semiconductor light emitting device according to (1), wherein the carrier concentration of the absorption layer is 5 × 10 ¹⁷ cm ⁻³ or less. (4) The semiconductor light emitting device according to (1), wherein the absorption layer has a thickness of 1 μm to 40 μm, and the absorption layer is formed by a slow cooling method of a liquid phase epitaxial method. (5) A semiconductor layer for suppressing photoluminescence (hereinafter referred to as “suppression layer”) is provided on the substrate side with respect to the absorption layer, and the suppression layer has the same conductivity type as the absorption layer and has a carrier concentration of The semiconductor light emitting device according to (1), which is 5 × 10 ¹⁷ cm ⁻³ or less and has a bandgap smaller than the energy of light emitted from the pn junction. (6) The semiconductor light emitting device according to (5), wherein the suppression layer also serves as the substrate. (7) The dopant of the absorption layer and / or the suppression layer is Z
The semiconductor light emitting device according to (5), wherein n is n.

The term "pn junction" as used herein means a pn junction composed of two layers such as a homojunction or a heterojunction, a double heterojunction, or a junction having one or multiple quantum well structures. means.

The absorption layer and the suppression layer may be provided on either the p-type side or the n-type side with respect to the joint surface of the pn junction, but the conduction type of these layers is provided. The conductivity type is the same as the conductivity type of the pn junction on the closed side. For example, if the absorption layer is provided on the p-type side with respect to the pn junction surface, the conductivity type of the layer is p-type. Hereinafter, in the present specification, a case where the absorption layer and the suppression layer are provided on the p-type side with respect to the pn junction surface will be described for convenience.

The substrate is pn with a matching lattice constant and the like.
It can serve as a basis for crystal growth of the bonding portion, the absorption layer, and the like. When the substrate is a semiconductor, its conductivity type is the same as the conductivity type of the pn junction on the side where the substrate is provided, like the absorption layer.

The band gap is a width of an energy state in which electrons cannot be taken in a solid, and is also called an energy gap or a forbidden band width. As shown in FIG. 4, not only the band gap E1 of the intrinsic semiconductor but also the band gaps E2, E3 between the impurity band formed by impurities and the intrinsic semiconductor band, and the impurity band It also includes a band gap E4 between them.

The energy of light is the wavelength λ of the light.
Is an amount determined by the above formula and is represented by “hc / λ”. However, h is Planck's constant and c is the speed of light.

[0011]

The function of the structure of the light emitting device of the present invention will be described in brief. First, the relationship between the energy of the light and the band gap of the semiconductor layer when the light passes through the semiconductor layer will be described. When light having a specific wavelength passes through the semiconductor layer, and the energy of the light is smaller than the band gap of the semiconductor layer, the light simply passes through the semiconductor layer. On the other hand, when the energy of the light is larger than the band gap of the semiconductor layer, the light is absorbed by the semiconductor layer. In addition, the absorbed light excites the semiconductor layer and generates sub-peak wavelength light determined by the band gap of the semiconductor layer. Main peak wavelength light L targeted by the present invention
As described above, 1 includes not only light having a single wavelength, but also a case where the light is a set of lights distributed in a specific range around the main peak wavelength. With respect to such light, the following structure suppresses the generation of sub-peak wavelength light.

The basic structure of the light emitting device of the present invention is shown in FIG.
As shown in (a), the main peak wavelength light L1 first emitted from the pn junction 1 is received by the absorption layer 2 having a band gap substantially equal to the energy of the light of the central wavelength. In the figure, a is an external world from which light should be emitted, B is a substrate, and light is indicated by a thick arrow. In addition, parts such as electrodes are omitted. With the above structure, light having an energy larger than the band gap of the absorption layer 2, that is, light on the short wavelength side including the central wavelength λ of the main peak wavelength light L1 is absorbed by the absorption layer 2 and the absorption layer 2 is excited. And emits photoluminescence L2. However, as described above, by setting the band gap of the absorption layer 2 to be substantially equal to the energy of the light of the main peak wavelength, this photoluminescence L2 is the same as the light L1 of the main peak wavelength. It becomes the light of the central wavelength. Therefore, even if photoluminescence occurs, the main peak wavelength light is emitted, and the sub peak wavelength light is suppressed.

On the other hand, as shown in FIG. 1 (b), the absorption layer 2
Light with energy smaller than the band gap of
Of the main peak wavelength light L1, the light L1a on the longer wavelength side than the central wavelength λ is not absorbed by the absorption layer 2 and passes through the absorption layer 2 with some attenuation. The present invention proposes that the passing light L1a is received by the suppression layer 3 having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or less and a band gap smaller than the energy of the light L1a, as a preferable structure. It is a thing. With the structure in which this suppression layer is provided, the suppression of the sub-peak wavelength light becomes more sufficient, as described below.

In FIG. 1B, the absorption layer 2 is formed on the suppression layer 3.
When the light L1a that has passed through is reached, since the band gap of the suppression layer 3 is smaller than the energy of the light L1a, all the light L1a is absorbed without passing through this layer, and the photoluminescence L2a is absorbed. , That is,
Harmful sub-peak wavelength light is generated. However, the suppression layer 3
The intensity of the passing light L1a that reaches the first light emission L1a is about half that of the first light emission L1 and the carrier concentration of the suppression layer is 5 × 10 ^17.
Since it is specified to be as low as cm ⁻³ or less, the intensity of the generated sub-peak wavelength light L2a is also at an extremely low level. In addition,
The suppression layer 3 is irradiated with not only the passing light L1a but also the main peak wavelength light L2 generated as photoluminescence in the absorption layer 2, but the photoluminescence L2 is a weak light originally generated secondarily. Therefore, the photoluminescence L3 tertiaryly generated in the suppression layer due to the irradiation of the photoluminescence L2 is a slight amount and is not a problem. Therefore, only the photoluminescence L2a generated in the suppression layer 3 by the light L1a that has passed through the absorption layer 2 becomes the sub-peak wavelength light of the substantial amount, and the result is sufficiently suppressed as a whole.

"The band gap of the absorption layer is substantially equal to the energy of light emitted from the pn junction."
Does not mean only when the bandgap E _g of the absorption layer and the energy hc / λ of the light of the central wavelength λ emitted from the pn junction are theoretically completely equal,
It includes that these two energy states that should be set to be equal to each other should be values that are close to each other within an allowable range of about ± 0.03 eV in actual use.

The bandgap of the absorption layer 2 does not need to be uniform in the thickness direction, and a partial layer in the absorption layer has a bandgap substantially equal to the energy of light emitted from the pn junction. I wish I had it. For example, depending on the crystal growth method of the absorption layer, the composition ratio gradually changes in the thickness direction and the band gap is not uniform. In that case, a band having a band gap larger than that of the light is emitted so that the portions other than the layer having a band gap substantially equal to the energy of the light emitted from the pn junction are layers through which the light simply passes. A gap is preferable.

The phrase "the bandgap of the suppression layer is smaller than the energy possessed by the light arriving from the pn junction" means that the bandgap has a size capable of absorbing substantially all the light passing through the absorption layer. Say. The suppression layer is not limited to the mode in which it is provided between the absorption layer and the substrate, and the suppression layer may also serve as the substrate.

[0018]

EXAMPLES The present invention will be described in more detail with reference to examples. [Embodiment 1] FIG. 2 is a diagram schematically showing the structure of an LED which is an embodiment of the light emitting device of the present invention. As shown in the figure, the structure of the LED includes a substrate B, a suppression layer 3 provided on the substrate, an absorption layer 2 provided on the suppression layer,
The pn junction 1 is provided on the absorption layer. Further, X and Y are positive and negative electrodes, respectively. Note that Zn was used as a dopant for the suppression layer and the absorption layer.

The pn junction 1 is composed of a well-known semiconductor crystal capable of obtaining a light emission phenomenon whether visible or invisible by a forward current. Further, as described above, in addition to the homojunction / heterojunction, it may have a double heterojunction, and among them, one or multiple quantum well structures. In this embodiment, two types of structure examples are shown as the structure of the pn junction 1. That is, the n-type layer 1a and the p-type layer 1b
And a simple single-hetero structure example consisting of and a double-hetero structure example having an active layer 1c between them. However, in FIG. 1, the active layer 1c is represented by a boundary line between the n-type layer 1a and the p-type layer 1b. Table 1 shows examples of combinations of materials used for the pn junction.

Any material can be used as the material for forming the absorption layer 2 as long as it has a band gap substantially equal to the energy of the main peak wavelength light, but in practical use. Is a combination using a semiconductor material having a bandgap substantially equal to the bandgap of the semiconductor material forming the pn junction portion 1. In particular, among the semiconductor materials forming the pn junction portion, a portion related to light emission. By making the semiconductor composition and the material composition of the absorption layer exactly the same, it is preferable to make the bandgap of the absorption layer and the energy of the light emitted from the pn junction easily equal. Is. Table 1 shows the materials used for the second semiconductor layer, p
It is shown corresponding to the material of the n-junction.

The carrier concentration of the absorption layer is not particularly limited, but by setting it within the range of about 1 × 10 ^{16 to} 5 × 10 ¹⁷ cm ^-3 , diffusion of the dopant into the adjacent suppression layer is suppressed, and the suppression is suppressed. It is preferable because the carrier concentration in the layer can be prevented from increasing. In particular, when the dopant is Zn, the diffusion rate is high, so the carrier concentration in the absorption layer is preferably within the above range.

The thickness of the absorption layer is not particularly limited, but it is preferably thin from the viewpoint of reducing the fluctuation of the composition ratio in the thickness direction which occurs in the case of a multi-element mixed crystal and shortening the growth time. 1 μm to 40 μm, particularly 1 μm to 20
μm is preferred.

The suppression layer 3 is a layer for appropriately attenuating the light not absorbed by the absorption layer 2, as described above,
The band gap is set to a value smaller than the energy of the light passing through the absorption layer 2 and the carrier concentration is set to 5 × 10 ¹⁷ cm ⁻³ or less so that all the passing light is absorbed and a small amount of photo is generated. It functions to generate luminescence. The lower limit of the carrier concentration of the suppression layer 3 is preferably 1 × 10 ¹⁷ cm ⁻³ or more in consideration of the contact resistance value of the ohmic electrode when an electrode is provided on the suppression layer 3, If it is not necessary to provide an electrode, consider the stability and reproducibility of crystal growth and use 5 x 1
It is preferably 0 ¹⁶ cm ^-3 or more.

As a material for forming the suppressing layer, any material may be used as long as it has a band gap smaller than the energy of light passing through the absorption layer 2 as described above. In particular,
The composition ratio may be determined so that the band gap is smaller than that of the material forming the pn junction 1. The materials used for the suppression layer are shown in Table 1 as a suitable combination of the material for the pn junction 1 and the material for the absorption layer 2.

The substrate B is a crystal that serves as a basis for growing the above various semiconductor crystal layers. The material of the substrate B is
In addition to single-element semiconductors, compound semiconductors, crystals that have good lattice constant matching with semiconductor crystals to be grown, such as insulators such as sapphire Good. The materials used for the substrate B are shown in Table 1 as a suitable combination of the materials from the pn junction 3 to the absorption layer 1.

[0026]

[Table 1]

The numbers in parentheses in the table are carrier concentrations (unit: cm ^-3 ) of each layer.

As a method of forming the suppression layer, the absorption layer, and the pn junction on the substrate, a film formation method capable of epitaxial growth is preferable. In addition to the LPE method (liquid phase epitaxial growth method), a CVD method (chemical vapor deposition method) is also available. ), MOCVD method (metalorganic vapor phase epitaxy method), VPE method (vapor phase epitaxy method), MBE method (molecular beam epitaxy method), etc. Compared with this, it is preferably used because it is highly safe and can be easily produced in small or large quantities. In this example, the crystal growth of the suppression layer and the absorption layer was performed by the LPE method by the slow cooling method, and the thickness of the suppression layer was 15 μm and the thickness of the absorption layer was 5 μm.

The substance used as a dopant for imparting a desired carrier concentration to the absorption layer 2 and the suppression layer 3 is not particularly limited, but Zn is Te or Si.
It is preferable because it has a better diffusibility into the material than other substances, and it is easy to accurately obtain the target carrier concentration.

Example 2 A light emitting device according to this example is
As shown in FIG. 3, when the carrier concentration of the substrate B in Example 1 was 5 × 10 ¹⁷ cm ⁻³ or less, the suppression layer 3 was formed on the substrate B.
It has a structure that doubles as. Thus, a structure that does not increase the number of stacked layers can be obtained with a greater suppression effect than before, and a preferable structure can be obtained. In this embodiment, Table 2 shows a preferable combination of materials used for each layer from the pn junction 1 to the substrate B (= suppressing layer 3).
Shown in.

[0031]

[Table 2]

The light emitting devices shown in the above Examples 1 and 2 show a simple example of the pn junction, and by substituting these into various junction structures such as a quantum well structure, the sub-peak wavelength can be reduced. Various suppressed light emitting devices can be obtained.

[Performance Test] The light emitting devices according to the above-described examples were actually caused to emit light, and the degree of suppression of the sub-peak wavelength was examined by analyzing this light. The structure of the light emitting element was the light emitting diode shown in Example 2 and FIG. 2, and the material used for each layer was the combination shown in the second of Table 2. That is, n-type layer 1a; Al _0.7 Ga _0.3 As (1 × 10 ¹⁸ ) active layer 1c; Al _0.35 Ga _0.65 As (3 × 10 ¹⁷ ) p-type layer 1b; Al _0.7 Ga _0.3 As (3 × 10 ¹⁷ ) absorption Layer 2; Al _0.35 Ga _0.65 As (5 × 10 ¹⁷ ), suppression layer 3 (= substrate); GaAs (5 × 10 ¹⁷ ). (The number in parentheses is the carrier concentration of each layer (unit: cm ⁻³ ).) As a result of measuring light emission by the light emitting diode having the above-mentioned configuration,
88 for the main peak wavelength of 650 to 670 nm
Although sub-peak wavelength light was observed in the wavelength band of 0 to 900 nm, its intensity was 0.5% or less of the main peak wavelength, and it was confirmed that it was sufficiently effectively suppressed. Further, when the structures of the light emitting devices shown in Examples 1 and 2 were measured by using the combinations of materials shown in Tables 1 and 2, the same effect of suppressing the sub-peak wavelength as the above was confirmed.

[0034]

The light-emitting device of the present invention has a novel absorption layer that absorbs light having a main peak wavelength and that the photoluminescence generated has a center wavelength that is substantially the same as that of the main peak wavelength light. According to the configuration, it is possible to provide a light emitting device with a simple structure, in which light with sub-peak wavelength is suppressed. In particular, in addition to the absorption layer, the light that has not been absorbed by the absorption layer and passes through is configured to be received by the suppression layer having a low carrier concentration and a small band gap, thereby absorbing all the light that has passed through the absorption layer, Only weak sub-peak wavelength light can be generated. Therefore,
It is possible to set the intensity of the sub-peak wavelength light as the entire light emitting element to 0.5% or less of the intensity of the main peak wavelength light. By effectively suppressing the sub-peak wavelength light in the light emitting device according to the present invention, it has become possible to solve problems such as malfunction of the sensor.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing the principle of suppressing sub-peak wavelength light in a light emitting device of the present invention.

FIG. 2 shows an L manufactured as an example of a light emitting device of the present invention.
It is a figure which shows the structure of ED typically.

FIG. 3 is a diagram schematically showing a configuration of an LED manufactured as another embodiment of the light emitting device of the present invention.

FIG. 4 is a diagram schematically showing a band gap range in the present specification.

[Explanation of symbols]

 1 pn junction 2 absorption layer 3 suppression layer B substrate

Claims (7)

[Claims] 1. A p-type or n-type conductive semiconductor layer for light absorption provided above a substrate, and a semiconductor layer provided above the semiconductor layer for light absorption and having an upper side above the semiconductor layer for light absorption. And a pn junction having different conductivity types, and the band gap of the semiconductor layer for absorbing light is substantially equal to the energy of light emitted from the pn junction. . 2. A semiconductor layer for absorbing light is composed of a bandgap portion substantially equal to the energy of light emitted from a pn junction and a bandgap portion larger than the bandgap. The semiconductor light emitting device according to claim 1. 3. The carrier concentration of the semiconductor layer for absorbing light is 5
The semiconductor light emitting device according to claim 1, which has a ^{density of not} more than × 10 ¹⁷ cm ^-3 . 4. A semiconductor layer for absorbing light is 1 μm to 40 μm.
2. The semiconductor light emitting device according to claim 1, wherein the semiconductor layer is formed by a slow cooling method of a liquid phase epitaxial method. 5. A semiconductor layer for suppressing photoluminescence is provided on the substrate side of the semiconductor layer for absorbing light, and the semiconductor layer for suppressing photoluminescence has the same conductivity type as the semiconductor layer for absorbing light. 2. The semiconductor light emitting device according to claim 1, wherein the carrier concentration is 5 × 10 ¹⁷ cm ⁻³ or less, and the band gap is smaller than the energy of light reaching from the pn junction. 6. The semiconductor light emitting device according to claim 5, wherein the semiconductor layer for suppressing photoluminescence also serves as a substrate. 7. The dopant of the semiconductor layer for absorbing light and / or the semiconductor layer for suppressing photoluminescence is Zn.
The semiconductor light emitting device according to claim 5.