JP3697749B2 - Semiconductor light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor light emitting device using AlGaInP-based and AlGaAsP-based semiconductor materials.
[0002]
[Prior art]
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.
[0003]
[Problems to be solved by the invention]
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.
[0004]
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.
[0005]
[Means for Solving the Problems]
Therefore, the present inventors reduced the thickness of the Zn-doped p-type AlGaInP-based compound cladding layer to such an extent that the element characteristics of the light-emitting element are not deteriorated in a semiconductor light-emitting device having an active layer made of AlGaInP or GaInP, The idea is to reduce Zn diffusion into the n-side cladding. However, if the thickness of the AlGaInP-based compound cladding layer above and below the active layer is reduced, the confinement of carriers and light becomes insufficient and the device characteristics deteriorate. Therefore, the shortage can be replaced with an AlGaAsP-based compound having substantially the same band gap and refractive index, and n-type AlGaAsP-based compounds are less susceptible to Zn diffusion than AlGaInP-based compounds having similar carrier concentrations. The thinner the n-type AlGaInP-based compound cladding, the more Zn diffusion From the viewpoint of mass production, it is effective to prevent the pn junction position from being shifted, and further, the thinning of the AlGaInP-based compound clad layer is effective in reducing the operating voltage and the thermal resistance. The present inventors have found that it is more effective to make the AlGaInP-based compound layer as thin as possible and use more AlGaAsP-based compounds in terms of growth time, raw material cost, detoxification, and the like. That is, the gist of the present invention is that a first cladding layer made of AlGaAsP or AlGaAs of the first conductivity type, and a thickness of 0.5 μm or less made of AlGaInP or AlInP of the first conductivity type adjacent to the first cladding layer. Adjacent to the second cladding layer, an active layer made of AlGaInP or GaInP of the first or second conductivity type with a thickness of 0.1 to 1 μm, and 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 a fourth cladding layer made of AlGaAsP or AlGaAs of the second conductivity type adjacent to the third cladding layer. And a light-emitting diode having a light extraction layer substantially transparent to the wavelength of the active layer between the electrode formed on the light extraction side and the fourth cladding layer. It resides in the de.
[0006]
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, and a thickness of 0.5 μm or less made of a first conductivity type AlGaInP compound adjacent to the first cladding layer. Adjacent to the second cladding layer, an active layer made of AlGaInP or GaInP of the first or second conductivity type with a thickness of 0.1 to 1 μm, and adjacent to the active layer A third cladding layer made of a second conductivity type AlGaInP-based compound having a thickness of 0.5 μm or less, and a fourth cladding layer made of a second conductivity type AlGaAsP-based compound adjacent to the third cladding layer. and, and, between the formed on the light extraction side electrode 4 cladding layer, and characterized in that have a substantially transparent light extraction layer for the wavelength of the active layer.
[0007]
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. 1, which is an example of an embodiment realized as a light-emitting diode (LED).
[0008]
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. When manufacturing the apparatus of the present invention, it is usually constructed on a single crystal substrate. The substrate 101 is not particularly limited, but a GaAs substrate is usually used. Further, when the aluminum composition of the active layer is lowered due to the emission wavelength or the like, a GaAsP substrate is suitable. 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.
[0009]
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. 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.
[0010]
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 1 × 10 ¹⁷ cm ⁻³ or more as the lower limit and 5 × 10 ¹⁷ cm ⁻³ or less as the upper limit.
[0011]
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.
[0012]
Furthermore, a fourth cladding layer 107 made of an AlGaAsP-based compound of the second conductivity type is laminated on the third cladding layer. The thickness is preferably in the range of 0.5 to 3 μm, and the more preferable range is 0.8 μm as the lower limit and 1.5 μm as the upper limit. The carrier concentration is preferably in the range of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ , particularly preferably in the range of 3 × 10 ¹⁷ cm ⁻³ as the lower limit and 3 × 10 ¹⁸ cm ⁻³ as the upper limit. It is. The fourth clad layer may have the same composition as the light extraction layer 108 described later. In this case, the total thickness of the fourth clad layer and the light extraction layer is preferably 1 μm or more, more preferably 1 to 300 μm, most preferably Preferably it is 1-100 micrometers. 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 . From the viewpoint of manufacturing, it is preferable that the fourth cladding layer and the light extraction layer are manufactured as one continuous layer with the same composition.
[0013]
A preferred light extraction layer for use in the present invention is a compound single crystal layer having an indirect transition type band structure, preferably having a thickness of 1 to 50 μm, and more preferably having a lower limit of 5 μm and an upper limit of 15 μm. 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 for visible wavelengths (550 to 690 nm) that can be realized with an AlGaInP system. A certain amount of transparency can be realized even with Al _x Ga _1-x As (X = 0.6 to 0.8) with a high Al composition, but the resistivity of the GaP-based layer is lower than that of such an AlGaAs layer. The current spread at the surface is good. In addition, since n-type GaP is more transparent than p-type GaP and has a lower specific resistance, it is preferable to use n-type GaP for the light extraction layer.
[0014]
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, the light reflecting layer 108 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.
[0015]
For the other layers, the contact layer 109 and the like may be formed according to a conventional method.
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.
[0016]
【Example】
Hereinafter, embodiments of the present invention will be described in detail. In this example, a 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.
[0017]
The LED of the present invention shown in FIG. 1 was manufactured as an epitaxial wafer according to the following procedure. First, an n-type GaAs buffer layer 102 (thickness 0.5 μm) on an n-type GaAs (100) substrate 101, a Bragg reflection film 108 in which 15 layers of AlGaAs / AlAs are alternately stacked, and an n-type Al _0.7 Ga _0.3 As first cladding Layer 103 (thickness 1.0 μm), n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P second clad layer 104 (thickness 0.2 μm), and active layer 105 (Al _0.2 Ga _0.8 ) _0.5 In _0.5 P (thickness 0) .3 μm), p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P third cladding layer 106 (thickness 0.2 μm), p-type Al _0.7 Ga _0.3 As fourth cladding + light extraction layer 107 (thickness 10 μm), p-type A GaAs cap layer 109 (thickness 2 μm) was sequentially grown.
[0018]
The crystal growth conditions in the above examples are: growth temperature 650-750 ° C., pressure 10 ² hPa, V / III ratio 25-50 (AlGaAs) and 500-750 (AlGaInP, GaInP), growth rate 1-15 μm / hr (AlGaAs ) And 0.5-2 μm / hr (AlGaInP, GaInP).
When an LED lamp was fabricated from the LED wafer grown by the above method, light was emitted at 630 to 640 nm, and a luminance of about 3 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.
[0019]
In the above embodiment, an n-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 a p-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.
[0020]
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, or the reproducibility is greatly impaired. Therefore, by reducing the thickness of the AlGaInP cladding 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. Therefore, the carrier concentration of the n-type cladding layer can be suppressed to 1 × 10 ¹⁸ cm ⁻³ or less, and the crystal quality and device characteristics can be improved.
[0021]
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 as 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.
[0022]
Furthermore, the surface orientation can be changed from (100) for the suppression of band gap reduction by ordering of atomic arrangement peculiar to AlGaInP compounds, that is, suppression of longer emission wavelength, or improvement and stabilization of 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.
Further, reduction of the Al composition of the light emitting layer is important in terms of improving the reliability and life of the device, but 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.
[0023]
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.
[0024]
【The invention's effect】
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.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an example of a light-emitting element of the present invention.
FIG. 2 is an explanatory view showing an example of a conventional light emitting device.
[Explanation of symbols]
101 Substrate 102 Buffer layer 103 First cladding layer 104 Second cladding layer 105 Active layer 106 Third cladding layer 107 Fourth cladding layer 108 Light reflecting layer 109 Contact layer 201 Substrate 202 Cladding layer 203 Active layer 204 Cladding layer 205 Current diffusion layer 206 Contact layer 207 Electrode 208 Electrode

Claims (8)

A first cladding layer made of AlGaAsP or AlGaAs of the first conductivity type, adjacent to the first cladding layer, a second cladding layer made of the first conductivity type AlGaInP or AlInP, and adjacent to the second cladding layer An active layer made of AlGaInP or GaInP of the first or second conductivity type, a third clad layer made of AlGaInP or AlInP of the second conductivity type adjacent to the active layer, and a third clad layer adjacent to, a light emitting diode which have a fourth cladding layer formed of AlGaAsP or AlGaAs of a second conductivity type, the thickness of the second cladding layer 0.5μm or less, the thickness of the third cladding layer is 0.5μm And a light extraction layer substantially transparent to the wavelength of the active layer between the electrode formed on the light extraction side and the fourth cladding layer. A light emitting diode . The light emitting diode according to claim 1, wherein the active layer has a thickness of 0.1 to 1 μm. The light- emitting diode according to claim 1, wherein the light extraction layer is a compound single crystal layer having an indirect transition band structure. The light emitting diode according to claim 1, further comprising a light reflecting layer between the substrate and the first cladding layer. 5. The light emitting diode according to claim 4, wherein the light reflecting layer is made of AlGaAsP or AlGaAs. The light emitting diode according to any one of claims 1 to 5, wherein, of the first cladding layer and the fourth cladding layer, the p-type layer is an AlGaAsP or AlGaAs layer, and the p-type layer contains carbon as a doping impurity. 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. Light emitting diode . 8. The light emitting diode according to claim 1, wherein silicon is used as an n-type doping impurity.

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