JP3767621B2 - Semiconductor light emitting device - Google Patents

Description

  The present invention relates to a semiconductor light emitting device using an AlGaInP-based, AlGaAsP-based, and AlGaP-based semiconductor material.

As an example of a conventional semiconductor light emitting diode (LED) using an AlGaInP-based semiconductor material, there is a structure as schematically shown in FIG.
That is, in FIG. 2, 201 is an n-type GaAs substrate, and 202 is a clad layer made of n-type AlGaInP formed on the substrate 201. Reference numeral 203 denotes an active layer made of AlGaInP. Reference numeral 204 denotes a clad layer made of p-type AlGaInP. That is, the mixed crystal ratio is set so that the energy gap of the AlGaInP active layer 203 is smaller than the energy gap of the AlGaInP cladding layers 202 and 204. The p-type AlGaAs current diffusion layer 205 widens the current injected from the electrodes, thereby widening the light emitting region and improving the light extraction efficiency. Reference numeral 206 denotes a contact layer, and 207 and 208 denote electrodes.

  AlGaInP or AlInP (hereinafter, AlGaInP or AlInP is also referred to as an AlGaInP compound) is higher in resistivity and thermal resistance than AlGaAsP or AlGaAs (hereinafter, AlGaAsP or AlGaAs is also referred to as an AlGaAsP compound). There are also disadvantages such as large, and this has caused problems such as increasing the operating voltage of the element and increasing heat generation, which is a major issue in improving the characteristics and reliability of the element . In particular, when the emission density is increased, the above problem becomes more serious.

In addition, zinc (Zn) is generally used as a dopant for the cladding layer of the p-type AlGaInP compound. However, since the activation rate of Zn is low, it is necessary to perform high concentration doping in order to reduce the resistivity. There is. However, in this case, Zn that has not been activated diffuses at a high rate in the AlGaInP-based compound crystal during growth, and the pn junction position may be greatly shifted to the n side from the light emitting layer. In this case, the current-voltage characteristic is abnormal, or the light emission output is reduced. Such Zn diffusion from the p-type AlGaInP-based compound layer becomes conspicuous as the layer thickness of the p-type AlGaInP-based compound layer increases. Further, when a double hetero structure is normally used, a film thickness of about 1 to 2 μm is required for the cladding layer in order to sufficiently confine carriers and light in the active layer. When an AlGaInP-based compound is grown by metal organic vapor phase epitaxy, it is necessary to increase the supply molar ratio (V / III) between the organic metal serving as the group III material and the PH _{3 serving as the} group V material. For this reason, there are problems that the growth rate cannot be increased so much that the growth raw material cost is considerably higher than that of AlGaAs. In particular, in large-scale equipment for mass production capable of simultaneous growth of a large number of sheets, it becomes increasingly serious in terms of detoxification.
Also, a light extraction layer may be provided adjacent to the cladding layer, and the transparency of the light extraction layer with respect to the emission wavelength is important for improving the light extraction efficiency of the LED, but depending on the composition, the transparency is high. However, the specific resistance is high, and current spread may be worsened on the surface.

Therefore, the present inventors use GaAs or GaAsP as a substrate, AlGaInP or GaI.
In a semiconductor light emitting device having an active layer made of nP, the thickness of the Zn-doped p-type AlGaInP compound cladding layer is reduced to such an extent that the device characteristics of the light emitting element are not deteriorated, and Zn diffusion into the active layer and the n-side cladding is reduced. However, if the thickness of the AlGaInP-based clad layer above and below the active layer is reduced, the confinement of carriers and light becomes insufficient and the device characteristics are deteriorated. An AlGaAsP-based compound having a refractive index can be substituted, and an n-type AlGaInP-based clad has a thinner layer thickness because an n-type AlGaAsP-based compound is less susceptible to Zn diffusion than an AlGaInP-based compound having a similar carrier concentration. Is more effective in preventing shift of the pn junction position due to Zn diffusion, In addition, the thinning of the AlGaInP-based cladding layer is effective in reducing operating voltage and thermal resistance, and from the viewpoint of mass production, AlGaInP-based compounds from the viewpoints of growth time, raw material cost, detoxification, etc. The inventors have found that it is more effective to make the layer as thin as possible and to use more AlGaAsP-based compounds, and have reached the present invention. That is, the gist of the present invention is that a first clad layer made of AlGaAsP or AlGaAs of the first conductivity type on a GaAs or GaAsP substrate and made of AlGaInP or AlInP of the first conductivity type adjacent to the first clad layer. A second cladding layer having a thickness of 0.5 μm or less, an active layer having a thickness of 0.1 to 1 μm made of AlGaInP or GaInP of the first or second conductivity type, adjacent to the second cladding layer, Adjacent to the active layer, a third cladding layer made of AlGaInP or AlInP of the second conductivity type and having a thickness of 0.5 μm or less, and made of AlGaP or GaP of the second conductivity type adjacent to the third cladding layer The present invention resides in a semiconductor light emitting device having a light extraction layer.

Hereinafter, the present invention will be described in more detail.
The semiconductor light-emitting device of the present invention includes a first cladding layer made of a first conductivity type AlGaAsP compound using GaAs or GaAsP as a substrate, and a first conductivity type AlGaInP compound adjacent to the first cladding layer. A second cladding layer having a thickness of 0.5 μm or less, an active layer having a thickness of 0.1 to 1 μm made of AlGaInP or GaInP of the first or second conductivity type, adjacent to the second cladding layer, Adjacent to the active layer, a third clad layer made of an AlGaInP-based compound of the second conductivity type and having a thickness of 0.5 μm or less, and adjoining the third clad layer, made of the second conductivity type AlGaP or GaP It is characterized by having a light extraction layer. Note that the content ratio of the constituent elements in each layer of the semiconductor light emitting device of the present invention may be determined in consideration of lattice matching between the substrate and each layer.
Hereinafter, the light-emitting device of the present invention will be described with reference to the element shown in FIG.

FIG. 1 is an example of a semiconductor device of the present invention, and is an explanatory view of the device manufactured in the example. In manufacturing the device of the present invention, a GaAs or GaAsP substrate is used as the substrate 101. A GaAsP substrate is preferred when the aluminum composition of the active layer is lowered due to the emission wavelength or the like. On the substrate, it is preferable to use a buffer layer 102 of about 2 μm or less in order not to bring defects of the substrate into the epitaxial growth layer. On the buffer layer, the first and second cladding layers, the active layer, and the third and fourth cladding layers of the present invention are laminated in this order. The first cladding layer 103 is an AlGaAsP-based compound of the first conductivity type, and the thickness is usually preferably 15 μm or less. A more preferable thickness of the first cladding layer is 0.1 μm or more as a lower limit and 2 μm or less as an upper limit. The carrier concentration is preferably in the range of 5 × 10 ¹⁶ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , particularly preferably 1 × 10 ¹⁷ cm ⁻³ as the lower limit and 1 × 10 ¹⁸ cm ⁻³ as the upper limit. Range.

A second cladding layer 104 made of an AlGaInP-based compound of the first conductivity type and having a thickness of 0.5 μm or less is laminated on the first cladding layer. The more preferable lower limit of the thickness of this layer is 0.01 μm or more, and the upper limit is 0.3 μm. And as the carrier concentration thereof is preferably in the range of ^{5 × 10 16 cm -3 ~3 ×} 10 18 cm -3, particularly preferably,
The lower limit is 1 × 10 ¹⁷ cm ⁻³ and the upper limit is 1 × 10 ¹⁸ cm ⁻³ .

An active layer 105 having a thickness of 0.1 to 1 μm made of AlGaInP or GaInP of the first or second conductivity type is laminated on the second cladding layer. The thickness of the active layer is more preferably 0.2 μm or more as the lower limit and 0.5 μm or less as the upper limit.
The carrier concentration of the active layer is preferably 1 × 10 ¹⁸ cm ⁻³ or less, particularly preferably the lower limit is greater than 1 × 10 ¹⁷ cm ⁻³ and the upper limit is 5 × 10 ¹⁷ cm ⁻³ or less.

On the active layer, a third cladding layer 106 made of an AlGaInP compound of the second conductivity type and having a thickness of 0.5 μm or less is laminated. The carrier concentration is preferably in the range of 5 × 10 ¹⁶ cm ^{−3 to} 3 × 10 ¹⁸ cm ⁻³ , particularly preferably 1 × 10 ¹⁷ cm ⁻³ as the lower limit and 1 × 10 ¹⁸ cm ⁻³ as the upper limit. Range.

Further, a light extraction layer 107 made of AlGaP or GaP of the second conductivity type is laminated on the third cladding layer. In this case, the thickness of the light extraction layer 107 is preferably 1 μm. When the light extraction layer is thick, it is preferable because absorption at the electrode is reduced. However, considering the decrease in efficiency due to light absorption or electrical resistance of the light extraction layer itself, there is no point in providing a very thick light extraction layer, 300 μm or less, More preferably, the thickness is about 100 μm or less. In order to form a light extraction layer having a thickness of about 10 to 1000 μm, a hydride vapor phase growth method is preferably used. In this case, the carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ , particularly preferably 5 × 10 ¹⁷ cm ⁻³ as the lower limit and 5 × 10 ¹⁸ cm as the upper limit. It is in the range of ^-3 .
Since GaP is an indirect transition type material with a wide band gap, it is a very effective light extraction layer with respect to a wavelength in the visible region (550 to 690 nm) that can be realized by the AlGaInP system. Although the same level of transparency as AlxGa1-xAs (X = 0.6 to 0.8) can be realized with a high Al composition, the specific resistance of the AlGaAs layer becomes very high, and current spread is poor on the surface. turn into. Since n-type GaP has better transparency and lower specific resistance than p-type GaP, n-type GaP is preferably used for the light extraction layer.

As the kind of the dopant such as the cladding layer, carbon is preferable as a doping impurity when the p-type layer is an AlGaAs layer, and beryllium and / or as a doping impurity when the p-type layer is an AlGaInP-based compound. Or magnesium is preferable. Silicon is preferable as the n-type doping impurity.
In a more preferred aspect of the present invention, a light reflecting layer is provided between the substrate and the first cladding layer. The light reflecting layer may be made of various known materials that reflect light. Among these, the composition is preferably an AlGaAsP-based compound, and the structure is to provide a Bragg reflecting film.
EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited to an Example, unless the summary is exceeded.

  According to the present invention, by optimizing the structure of the cladding layer sandwiching the active layer made of AlGaInP or GaInP, the characteristics and reliability of the light emitting element can be improved, and the raw material cost can be reduced.

Hereinafter, embodiments of the present invention will be described in detail. In this example, the MOVPE method having excellent film thickness, composition controllability, and mass productivity was used as the crystal growth method. The source gases used were trimethylaluminum (TMA), trimethylgallium (TMG), trimethylindium (TMI), phosphine (PH ₃ ), arsine (AsH ₃ ), and hydrogen (H ₂ ) Gas was used.

The LED of the present invention shown in FIG. 1 was manufactured as an epitaxial wafer according to the following procedure. First, a p-type GaAs buffer layer 102 (thickness 0.5 μm) on a p-type GaAs (100) substrate 101, a Bragg reflection film 108 in which 15 layers of p-type AlGaAs / AlAs are alternately laminated, and p-type Al0.7Ga0.3As. First cladding layer 103 (thickness 1.0 μm), p-type (Al0.7Ga0.3) 0.5In0.5P Second cladding layer 104 (thickness 0.2 μm), p-type (Al0.4Ga0.6) 0.5In0 .5P active layer 105 (thickness 0.3 μm), n-type (Al0.7Ga0.3) 0.5In0.5P third cladding layer 106 (thickness 0.2 μm), n-type GaP light extraction layer 107 (thickness 4 μm) Grown sequentially.
When an LED lamp was produced from the LED wafer grown by the above method, light was emitted at 580 to 590 nm, and a luminance of about 1.5 cd was obtained with a driving current of 20 mA. This is about twice as bright as the conventional structure in which the p-type AlGaInP cladding layer is about 1 μm.

The crystal growth conditions in the above examples are: growth temperature 650 to 800 ° C., pressure 10 ² hPa, V / III ratio 25 to 50 (GaAs, AlGaAs), 500 to 750 (AlGaInP, GaInP) and 50 to 200 (GaP), Growth rate 1-5 μm / hr (GaAs, AlGaAs), 0.5-2 μm / hr (AlGaInP, GaInP) and 0.5-5 μm
/ H (GaP).
In the above embodiment, a p-type substrate is used on the substrate side. However, an epitaxial wafer may be manufactured by inverting the conductivity type of each layer of the above structure using an n-type substrate. Further, the crystal growth method is not limited to the MOVPE method, and the present invention is also very effective in a vapor phase growth method such as an MBE method or a CBE method.

  In an LED, it is usually necessary to grow a relatively thick light extraction layer in order to improve luminance. However, since the light extraction layer takes a long time to grow, if an impurity having a large diffusion coefficient such as zinc or selenium is used as the dopant, the dopant in the cladding layer is opposed to the active layer or through the active layer. The LED layer diffuses to the side layer, and the LED characteristics are greatly deteriorated, and the problem that the reproducibility is greatly impaired is likely to occur. Therefore, by reducing the thickness of the AlGaInP clad layer as much as possible as in the present invention, the total impurity diffusion amount can be reduced, and unnecessary doving for preventing diffusion is unnecessary. In particular, when a thick GaP light extraction layer is regrown by hydride VPE, the present invention is very effective, and crystal quality and device characteristics can be improved particularly well.

  If the active layer is an ultra-thin film such as a quantum well structure, it is more and more necessary to suppress the diffusion of impurities described above. Therefore, in the present invention, carbon is used as the doping impurity of the p-type AlGaAsP-based compound cladding layer, beryllium or magnesium is used as the doping impurity of the p-type AlGaInP-based compound cladding layer, and the n-type AlGaAsP-based compound cladding layer and the n-type AlGaInP-based compound cladding layer. By using silicon as each doping impurity, impurity diffusion can be further reduced, and the yield and reproducibility of device fabrication can be greatly improved.

Furthermore, the surface orientation can be changed from (100) for the suppression of the band gap reduction by ordering of the atomic arrangement peculiar to the AlGaInP compound, that is, the suppression of the longer emission wavelength, or the improvement and stabilization of the surface morphology. [011] It is effective to use a GaAs substrate of the first conductivity type inclined by 5 to 25 degrees in the direction.
In addition, reducing the Al composition of the light emitting layer is important in terms of improving the reliability and life of the device,
This can be easily achieved by using a GaAsP substrate. In this case, an AlGaAsP clad layer or an AlGaAsP light reflecting layer may be used to obtain lattice matching.

  The present invention can greatly reduce the burden on the apparatus such as reduction of growth time and raw material cost and removal, and enables stable production by a large-scale mass production apparatus capable of simultaneously growing a large number of sheets.

FIG. 1 is an explanatory view showing an example of a light emitting device of the present invention. FIG. 2 is an explanatory view showing an example of a conventional light emitting device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Substrate 102 Buffer layer 103 First clad layer 104 Second clad layer 105 Active layer 106 Third clad layer 107 Light extraction layer 201 Substrate 202 Cladding layer 203 Active layer 204 Cladding layer 205 Light extraction layer 206 Contact layer 207 Electrode 208 Electrode

Claims (10)

  A first clad layer made of AlGaAsP or AlGaAs of the first conductivity type on a GaAs or GaAsP substrate, and a first clad layer made of AlGaInP or AlInP of the first conductivity type adjacent to the first clad layer and having a thickness of 0.5 μm or less. Adjacent to the second cladding layer, an active layer made of AlGaInP or GaInP of the first or second conductivity type and having a thickness of 0.1 to 1 μm, adjacent to the active layer, A third clad layer made of two-conductivity type AlGaInP or AlInP and having a thickness of 0.5 μm or less, and a light extraction layer made of second-conductivity type AlGaP or GaP adjacent to the third clad layer A semiconductor light emitting device.   2. The semiconductor light emitting device according to claim 1, wherein the first and second cladding layers are p-type, and the third cladding layer and the light extraction layer are n-type.   2. The semiconductor light emitting device according to claim 1, wherein the first cladding layer is a p-type AlGaAsP or AlGaAs layer, and the p-type layer contains carbon as a doping impurity.   2. The semiconductor light emitting device according to claim 1, wherein the first cladding layer and the second cladding layer are n-type, and the third cladding layer and the light extraction layer are p-type.   The semiconductor light-emitting device according to claim 1, wherein the emission wavelength is 550 to 690 nm.   6. The semiconductor light emitting device according to claim 1, further comprising a light reflecting layer between the substrate and the first cladding layer.   7. The semiconductor light emitting device according to claim 6, wherein the light reflecting layer is made of AlGaAsP or AlGaAs. The p-type layer of the second clad layer and the third clad layer is AlGaInP or AlInP, and the p-type layer contains beryllium and / or magnesium as doping impurities. Semiconductor light emitting device.   9. The semiconductor light emitting device according to claim 1, wherein silicon is used as an n-type doping impurity.   The semiconductor light-emitting device according to claim 1, wherein the light extraction layer having a thickness of 10 to 1000 μm is formed by a hydride vapor phase growth method.

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