JP2004304090A - Light emitting diode - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a light emitting diode which has a large light emitting output and a low operating voltage and also is strong in an overvoltage. <P>SOLUTION: The light emitting diode has an active layer 104 composed of at least an InGaAlP based material on a first conductive type semiconductor substrate 101, a second conductive type upper clad layer 105 which is formed on this active layer and is composed of InGaAlP having a greater band cap than the active layer, and a second conductive type current diffusion layer which is formed thereon and is composed of GaP. The second conductive type current diffusion layer has a structure in which a GaP layer 107a of a low carrier concentration in which a carrier concentration is 1×10<SP>17</SP>cm<SP>-3</SP>or less is sandwiched between GaP layers 106 and 107b of a higher carrier concentration. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a light-emitting diode having a high light-emitting output, a low operating voltage, and a high resistance to overvoltage.
[0002]
[Prior art]
AlGaInP-based light emitting diodes (LEDs) are widely used as light sources for various displays. In particular, light sources for outdoor displays and traffic signals are required to have high output, high reliability, and low cost.
[0003]
As a measure for obtaining a high output, for example, an active layer (light-emitting layer) located above the active layer is made thicker by a layer that is almost transparent to light emission (a so-called current diffusion layer). For example, AlGaAs disclosed in Japanese Patent Application Laid-Open No. 3-171679 (Patent Document 1), GaP disclosed in US Pat. No. 5,008,718 (Patent Document 2), and the like are widely used.
[0004]
As another measure for obtaining a high output, as disclosed in, for example, Japanese Patent Application Laid-Open No. 3-283674 (Patent Document 3), a second cladding layer having a small resistivity is inserted to promote current diffusion. There is a method of increasing the output by using this method.
[0005]
As another measure for obtaining high output, for example, as disclosed in JP-A-4-87379 (Patent Document 4), current diffusion is promoted by inserting a layer having a low carrier concentration on the substrate side. There is a method of increasing the output by using this method.
[0006]
As another measure for obtaining a high output, for example, as disclosed in JP-A-4-229665 (Patent Document 5), a method for increasing the output by providing a current blocking layer and increasing the concentration of current is disclosed. There is.
[0007]
As another measure for obtaining high output, for example, as disclosed in Japanese Patent Application Laid-Open No. 7-202264 (Patent Document 6), current diffusion is enhanced by inserting a low potential and high conductivity layer. Then, there is a method of increasing the output.
[0008]
Japanese Patent Application Laid-Open No. 9-260724 (Patent Document 7) discloses that an intermediate layer made of AlInAs, GaAs, or AlGaInP is interposed between an AlGaInP layer and a GaP layer to suppress an increase in operating voltage by smoothing an energy band profile. Is disclosed.
[0009]
[Patent Document 1]
JP-A-3-171679
[Patent Document 2]
US Patent No. US5088718
[Patent Document 3]
JP-A-3-283674
[Patent Document 4]
JP-A-4-87379
[Patent Document 5]
JP-A-4-229665
[Patent Document 6]
JP-A-7-202264
[Patent Document 7]
JP-A-9-260724
[Problems to be solved by the invention]
However, in the methods of Patent Documents 1 to 6 described above, although a desired effect is obtained from the viewpoint of increasing the output, when an excessive voltage is applied to the element, the current exponentially increases with respect to the voltage due to the characteristics of the diode. Therefore, there is a problem that it is easily broken. For example, since the band gap of the active layer of a light emitting diode device having a light emission wavelength of 650 nm is about 1.9 eV, when the voltage applied to the device exceeds about 1.9 V, the current flowing through the device increases exponentially, and finally. The device is destroyed. Although depending on the heat dissipation design of the elements, many elements will be destroyed if the forward voltage exceeds about 3V.
[0017]
From the viewpoint of reliability, GaP which does not contain easily oxidizable Al in the current diffusion layer is more advantageous, but a notch is generated in the energy band profile at the hetero interface between GaP and AlGaInP, and the operating voltage is increased. There's a problem. For this reason, for example, as disclosed in Patent Document 7, there is a method in which an intermediate layer is interposed between an AlGaInP layer and a GaP layer to smoothen an energy band profile and suppress an increase in operating voltage. As a result, the operating voltage could be reduced, but it is preferable to lower the operating voltage as much as possible.
[0018]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to eliminate such conventional disadvantages, and to provide a light-emitting diode having a large light-emitting output, a low operating voltage, and being resistant to overvoltage.
[0019]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is configured as follows.
[0020]
The light emitting diode according to the first aspect of the present invention provides an active layer made of at least an InGaAlP-based material on a semiconductor substrate of a first conductivity type, and an InGaAlP formed on the active layer and having a larger band gap than the active layer. In a light emitting diode having a second conductivity type cladding layer made of GaP and a second conductivity type current spreading layer made of GaP formed thereon, the second conductivity type current spreading layer has a carrier concentration of 1%. It has a structure in which a GaP layer having a low carrier concentration of × 10 ¹⁷ cm ⁻³ or less is sandwiched between GaP layers having a higher carrier concentration.
[0021]
This is an LED in which the second conductivity type GaP current diffusion layer has a high resistance layer in a GaP layer, for example, and is resistant to overvoltage. Typically, the carrier concentration is 1 × 10 ¹⁷ cm. ^The low carrier concentration layer portion of ⁻³ or less is sandwiched between the high carrier concentration layer portions of 1 × 10 ¹⁸ cm ⁻³ or more.
[0022]
According to a second aspect of the present invention, there is provided a light emitting diode comprising: an active layer made of at least an InGaAlP-based material on a semiconductor substrate of a first conductivity type; and an InGaAlP formed on the active layer and having a larger band gap than the active layer. In the light emitting diode having a second conductivity type cladding layer made of GaP and a second conductivity type current diffusion layer made of GaP formed thereon, the second conductivity type current diffusion layer has a different carrier concentration. The first GaP layer of the first GaP layer in contact with the second conductivity type clad layer has a carrier concentration of 3 × 10 ¹⁸ cm ⁻³ or more. second GaP layer, a GaP layer with a low carrier concentration in which the carrier concentration is 1 × ¹⁰ 17 ^{cm -3,} a high carrier concentration carrier concentration of 1 × ¹⁰ 18 ^{cm -3} or more of Characterized in that it is formed as a layered structure including a GaP layer (multilayer structure of two or more layers).
[0023]
According to a third aspect of the present invention, in the light emitting diode according to the second aspect, the second GaP layer includes a low carrier concentration layer having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a carrier concentration of 1 × 10 ^18. It is characterized by being formed as a multilayer structure of three or more layers including a high carrier concentration layer of cm ^-3 or more.
[0024]
According to a fourth aspect of the present invention, in the light emitting diode according to the second or third aspect, the semiconductor substrate of the first conductivity type comprises a GaAs substrate or a Ge substrate having n-type conductivity.
[0025]
A light emitting diode according to a fifth aspect of the present invention is a light emitting diode, comprising: an n-type lower cladding layer made of at least an InGaAlP-based material on an n-type GaAs substrate or a Ge substrate; An active layer made of a base material, a p-type upper cladding layer made of InGaAlP having a bandgap energy larger than that of the active layer, and a p-type cladding layer formed on the p-type cladding layer, which is thicker than the p-type cladding layer. In the light emitting diode having a GaP layer, the p-type GaP layer is composed of a plurality of layers having different carrier concentrations, and the GaP layer in contact with the p-type upper cladding layer has a carrier concentration of 3 × 10 ^18. cm- ³ or more as a first GaP layer having a carrier concentration of 1 × on the first GaP layer. A second GaP layer having a multilayer structure including a GaP layer having a low carrier concentration of 10 ¹⁷ cm ⁻³ or less and a GaP layer of a high concentration carrier having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more is formed. It is characterized by having.
[0026]
The invention according to claims 1 to 4 has a stacked structure including not only a single hetero structure but also a first conductive type lower clad layer and a second conductive type upper clad layer sandwiching an active layer from both sides. (Double hetero structure). On the other hand, the invention according to claim 5 specifies the form of the double hetero structure.
[0027]
<Action>
In order to increase the light emission luminance of the LED, it is necessary to improve the current dispersion. In order to improve the current distribution, it is necessary to effectively utilize the flow due to the electric field which is the driving force for generating the flow of electricity and the flow due to the concentration diffusion. In order to conduct electricity using the effect of the electric field, the voltage must be increased, and the driving voltage is increased.
[0028]
When the low carrier concentration layer is sandwiched between the high carrier concentration layers as in the present invention, the low carrier concentration layer becomes a potential barrier, and the flowing carriers are stopped by the barrier, and the current spreads laterally. If the potential is increased, the current is sufficiently diffused, but a voltage that exceeds the potential is required, and the driving voltage increases. Therefore, by lowering this potential and increasing the number of layers, it is possible to cause current dispersion while keeping the drive voltage low.
[0029]
When a voltage is applied to the barrier thus manufactured and the current-voltage characteristics are measured, the barrier functions as a series resistance component. Therefore, even if a voltage of, for example, about 3 to 5 V is applied, the current value does not suddenly increase. With the GaP layer in which the above measures are taken, it is possible to obtain an LED having a large output, a low operating voltage, and a high resistance to overvoltage.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional disadvantages, and has as its object to obtain a light emitting diode having a large light emitting output, a low operating voltage, and a high resistance to overvoltage. In a typical embodiment of the present invention, the first conductivity type is n-type, and a semiconductor substrate made of a GaAs substrate or a Ge substrate having n-type conductivity, and an InGaAlP-based material formed on the semiconductor substrate. An active layer formed on the active layer, a p-type conductive cladding layer made of AlGaInP having a band gap larger than that of the active layer, and a p-type conductive layer formed on the p-type conductive cladding layer. In a light-emitting diode having a p-type conductivity GaP layer thicker than a cladding layer, the p-type conductivity GaP layer is composed of a plurality of layers having different carrier concentrations, and a carrier of the GaP layer in contact with the p-type conductivity cladding layer. A first GaP layer having a concentration of 3 × 10 ¹⁸ cm ⁻³ or more, a GaP layer having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less, and a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less are formed on the first GaP layer. A structure in which a second GaP layer having a multilayer structure of a GaP layer of × 10 ¹⁸ cm ⁻³ or more is provided, thereby achieving a desired light emitting diode.
[0031]
FIG. 1 shows a configuration of a light emitting diode according to an embodiment of the present invention. This light-emitting diode has a stacked structure formed of a semiconductor substrate 101 made of a GaAs substrate or a Ge substrate having n-type conductivity and an n-type AlGaAs buffer layer 102 on the semiconductor substrate. An n-type lower cladding layer 103 made of a material, an active layer (light emitting layer) 104 made of an InGaAlP-based material having a smaller band gap energy than the cladding layer, and a band formed on the active layer, which is smaller than the active layer. A p-type upper cladding layer 105 made of AlGaInP having a large gap, and a current diffusion layer formed on the p-type upper cladding layer 105 and made of a p-type GaP layer thicker than the p-type upper cladding layer 105. Having. In the light emitting diode, the p-type GaP current diffusion layer includes a plurality of layers having different carrier concentrations, here, a first GaP layer 106 and a second GaP layer 107. In the case of this embodiment, the first GaP layer 106 on the side in contact with the p-type upper cladding layer 105 is made of a GaP layer having a carrier concentration of 3 × 10 ¹⁸ cm ⁻³ or more. The second GaP layer 107 formed on the first GaP layer has a low carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a low carrier concentration of 1 × 10 ¹⁷ cm ^{−3. It} has a multilayer structure (here, a two-layer structure) including the GaP layer 107b having a high carrier concentration of ¹⁸ cm ⁻³ or more.
[0032]
In order to confirm the effect of the present invention, for the LED having the above configuration, the forward voltage of the LED at the time of 20 mA current was changed by changing the carrier concentration of the first GaP layer 106 in contact with the p-type upper cladding layer 105. As a result of the examination, as shown in FIG. 2, the forward voltage monotonously decreased with an increase in the carrier concentration, and when the carrier concentration exceeded 3 × 10 ¹⁸ cm ⁻³ , the forward voltage became almost constant. As a result, if the carrier concentration of the first GaP layer 106 in contact with the p-type upper cladding layer 105 is 3 × 10 ¹⁸ cm ⁻³ or more, a sufficient effect for obtaining a low forward voltage can be obtained. I understood. The unit on the horizontal axis in the figure is, for example, 1E + 18, which represents 1 × 10 ¹⁸ cm ⁻³ .
[0033]
Further, of the second GaP layers 107, a prototype having a structure in which the carrier concentration of the GaP layer 107a having a low carrier concentration was reduced from 1 × 10 ¹⁸ cm ⁻³ to 1 × 10 ¹⁷ cm ⁻³ was prototyped. The voltage characteristics were examined. FIG. 3 shows current-voltage characteristics when the carrier concentration of the low carrier concentration GaP layer 107a is changed to 1 × 10 ¹⁸ cm ⁻³ , 5 × 10 ¹⁷ cm ⁻³ , and 1 × 10 ¹⁷ cm ⁻³ . As a result of examining the current-voltage characteristics, as shown in FIG. 3, it was found that the element breakdown voltage when a high voltage was applied increased as the carrier concentration in the low carrier concentration portion decreased. From this, it was found that the carrier concentration of the low carrier concentration GaP layer 107a in the second GaP layer 107 is preferably 1 × 10 ¹⁷ cm ⁻³ or less.
[0034]
[Example]
An LED having a (Al _0.1 Ga _0.9 ) _0.5 In _0.5 active layer and a GaP window layer (current diffusion layer) on a Ge substrate by MOVPE was produced.
[0035]
An n-type Ge single crystal substrate was used as the semiconductor substrate 101, and triethylgallium or trimethylgallium, trimethylaluminum, and trimethylindium were used as Ga, Al, and In raw materials. Phosphine (PH ₃ ) was used as the P raw material. Arsine (AsH ₃ ) was used as the As raw material. The composition of the active layer may be an appropriate composition according to the emission wavelength, or may be a quantum well structure.
[0036]
First, a semiconductor substrate (Ge substrate) 101 was placed in a growth furnace, and an AlGaAs buffer layer 102 having n-type conductivity and a thickness of 0.5 μm was formed at a substrate temperature of 700 ° C. At this time, triethylgallium and arsine were used as Ga and As raw materials. The plane orientation of the substrate used was a (100) substrate, but the plane orientation is not particularly limited. Next, while keeping the substrate temperature at 700 ° C., the (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P lower cladding layer 103 having n-type conductivity and a thickness of 1.0 μm is undoped. (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer 104 having a thickness of 0.5 μm, having p-type conductivity and having a thickness of 1.0 μm (Al _0.7 Ga _{0) .3)} were successively formed a _0.5 an In _0.5 P upper cladding layer 105.
[0037]
Next, the substrate temperature was set to 600 to 650 ° C., and a first GaP layer 106 having a thickness of 0.5 μm was formed. The first GaP layer 106 was doped with C to have a carrier concentration of 3 × 10 ^{18 to} 3 × 10 ¹⁹ cm ⁻³ .
[0038]
Next, the substrate temperature is set to 700 ° C., the GaP layer 107a having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a thickness of 0.5 μm is set, and then the substrate temperature is set to 600 to 650 ° C. × ¹⁰ 18 ^{cm -3} or more in thickness to form a GaP layer 107b of 10 [mu] m, and these and second GaP layer 107. The second GaP layer 107 may have a multilayer structure of three or more layers including a layer having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a layer having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more.
[0039]
An LED chip was manufactured from the LED epitaxial wafer thus obtained. The size of the chip is 300 μm square, and the lower electrode 108 made of an Au—Ge—Ni alloy is formed on the entire lower surface of the chip corresponding to the substrate 101 side of the epitaxial wafer, and the Au—Be—Ni alloy is formed on the second GaP layer 107 side. A circular upper electrode 109 having a diameter of 150 μm was formed.
[0040]
This LED chip was assembled on a stem, and the IL (current-emission output) characteristic and the IV (current-voltage) characteristic were examined. It was compared with a prototype LED having a conventional structure for comparative reference. That is, the structure except for the GaP layer is the same, and the total thickness of the GaP layer portion is the same, but the low carrier concentration layer (in the embodiment, the carrier concentration of the second GaP layer 107 is 1 × 10 ¹⁷ An LED having a structure without the GaP layer 107 a) of cm ⁻³ or less was manufactured and compared with the present example. As a result, the IL characteristics were almost the same as shown in FIG.
[0041]
Further, when the blocking breakdown voltage was examined for reliability, as shown in the IV characteristic diagram of FIG. 5, the element breakdown voltage at the time of applying a high voltage could be increased from 3 V of the conventional example to 5 V or more.
[0042]
In the above embodiment, the Ge substrate is used as the semiconductor substrate 101, but the effects of the present invention can be obtained even when a GaAs substrate is used.
[0043]
【The invention's effect】
As described above, according to the present invention, an active layer made of at least an InGaAlP-based material is formed on a semiconductor substrate of a first conductivity type, and a band gap is formed on the active layer and is larger than the active layer. In a light emitting diode having a second conductivity type cladding layer made of InGaAlP and a second conductivity type current diffusion layer made of GaP formed thereon, the second conductivity type current diffusion layer has a carrier concentration of Since a GaP layer having a low carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less is sandwiched between GaP layers having a higher carrier concentration, light emission output is large, operating voltage is low, and light emission is strong against overvoltage. By providing a diode, in particular, a light-emitting diode that is resistant to overvoltage such that the element is not destroyed even when the forward voltage exceeds approximately 3 V can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a light emitting diode of the present invention.
FIG. 2 is a diagram showing the relationship between the carrier concentration of a portion of a GaP layer in contact with a p-type cladding layer and the operating voltage of an LED when a current of 20 mA is applied.
FIG. 3 is a diagram showing current-voltage characteristics of three LEDs of the second GaP layer having different carrier concentrations in a low carrier concentration portion.
FIG. 4 is a diagram showing current-emission output characteristics of a light-emitting diode of the present invention in comparison with a conventional example.
FIG. 5 is a diagram showing current-voltage characteristics of a light emitting diode of the present invention in comparison with a conventional example.
[Explanation of symbols]
101 semiconductor substrate 102 buffer layer 103 lower cladding layer 104 active layer (light emitting layer)
105 upper cladding layer 106 first GaP layer 107 second GaP layer 107a low carrier concentration GaP layer 107b high carrier concentration GaP layer 108 lower electrode 109 upper electrode

Claims (5)

An active layer made of at least an InGaAlP-based material on a semiconductor substrate of the first conductivity type; a cladding layer of a second conductivity type made of InGaAlP having a larger band gap than the active layer formed on the active layer; A light-emitting diode having a second conductivity type current diffusion layer made of GaP formed thereon;
The current diffusion layer of the second conductivity type has a structure in which a low carrier concentration GaP layer having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less is sandwiched between GaP layers having a higher carrier concentration. Light emitting diode. An active layer made of at least an InGaAlP-based material on a semiconductor substrate of the first conductivity type; a cladding layer of a second conductivity type made of InGaAlP having a larger band gap than the active layer formed on the active layer; A light-emitting diode having a second conductivity type current diffusion layer made of GaP formed thereon;
The second conductivity type current diffusion layer includes a first GaP layer and a second GaP layer having different carrier concentrations;
The carrier concentration of the first GaP layer on the side in contact with the second conductivity type cladding layer is 3 × 10 ¹⁸ cm ⁻³ or more;
The second GaP layer thereon is composed of a low carrier concentration GaP layer having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a high carrier concentration GaP layer having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more. A light-emitting diode, which is formed as a layer structure including: The light emitting diode according to claim 2,
The second GaP layer has three or more layers including a low carrier concentration layer having a carrier concentration of 1 × 10 ¹⁷ cm ⁻³ or less and a high carrier concentration layer having a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ or more. A light emitting diode formed as a structure. The light emitting diode according to claim 2 or 3,
A light emitting diode, wherein the semiconductor substrate of the first conductivity type comprises a GaAs substrate or a Ge substrate having n-type conductivity. An n-type lower cladding layer made of at least an InGaAlP-based material, an active layer made of an InGaAlP-based material having a smaller band gap energy than the cladding layer, and a semiconductor substrate made of an n-type GaAs substrate or a Ge substrate. In a light emitting diode having a p-type upper cladding layer made of InGaAlP having a larger band gap energy and a p-type GaP layer formed on the p-type cladding layer and having a thickness larger than that of the p-type cladding layer,
The p-type GaP layer is composed of a plurality of layers having different carrier concentrations;
The GaP layer of the side in contact with the p-type upper cladding layer is formed as a first GaP layer having a carrier concentration of 3 × 10 ¹⁸ cm ⁻³ or more,
This first GaP layer, a GaP layer with a low carrier concentration in which the carrier concentration is 1 × ¹⁰ 17 ^{cm -3,} the carrier concentration of 1 × ¹⁰ 18 ^{cm -3} or more high-concentration carrier and a GaP layer A light emitting diode, wherein a second GaP layer having a multilayer structure is formed.

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