JP2001036131A - AlGaInP LIGHT EMITTING DIODE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce forward voltage and uniform and improve the light emitting efficiency by providing a specific layer in a light emitting part and an oxide layer in a window layer respectively, allowing a layer including a metallic element between the light emitting part and window layer to have a non- covering area on a laminated plane, and providing an electrode thereon. SOLUTION: A thin film 106 made of Ni is adhered to the surface of a p-type (Al0.7Ga0.3)0.5In0.5P upper clad layer 105 through a general vacuum evaporation system. A widow layer 107 formed of n-type conductive zinc oxide film is jointed with a metal thin film 106. An insulation film having a smaller refractive index than the zinc oxide is laminated as a surface protective film 108 of the oxide window layer 107 on the surface of the window layer 107. Then, a silicon nitride protective film 108 is removed and the zinc oxide layer forming the window layer 107 is exposed, so that a p-type electrode 109 of double-layered structure, where a lower bottom part 109a in contact with the zinc oxide layer is set to be Ti and an upper layer part 109b is made of Al is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high brightness AlGaInP light emitting diode having an oxide window layer having good ohmic contact.

[0002]

2. Description of the Related Art (Al _X Ga _{1 -x} ) _Y In _{1 -Y} P (0 ≦ X ≦
1, 0 <Y ≦ 1) (hereinafter abbreviated as AlGaInP) in a multi-element mixed crystal, and in particular, the indium composition ratio (= 1−Y) is set to 0.5 (Al _X Ga _{1 -X} ) _0.5 In _0.5 P (0 ≦ X ≦
1) has an advantage of achieving good lattice matching with gallium arsenide (GaAs) single crystal (Appl. Phys. L).
ett. , 57 (27) (1990), 2937-29.
See page 39). For this reason, it is used as a constituent layer of a light-emitting element such as a light-emitting diode (LED) or a laser diode (LD) that emits green to red-orange colors (Appl. Phys. Lett., 64 (21)).
(1994), pages 2839-2841).

[0003] Conventional pn junction type double hetero (D
H) In a high-brightness LED having a structure, it is customary to arrange a window layer (window layer) above a DH structure light-emitting portion provided with an AlGaInP light-emitting layer (SPI)
E, Vol. 3002 (1997), pp. 110-118). The window layer needs to be made of a semiconductor material that is hard to absorb the light emitted from the light emitting layer, is transparent to the light emission, and has a large band gap in order to improve the light extraction efficiency. In addition, the window layer is a crystal layer that also plays a role of widely diffusing an element operating current in order to enlarge a light emitting area. Therefore, the window layer is usually made of a material having as low a resistance as possible.

Conventionally, there is an example in which a window layer is made of a transparent oxide. For example, US Pat. No. 5,481,12
In the AlGaInPLED of the invention of No. 2, the indium tin oxide (indium) is formed on the p-type ohmic contact layer.
A window layer composed of a -tin oxide (abbreviated as ITO) layer is arranged. Further, means for providing a transparent coating made of indium oxide, tin oxide, zinc oxide or magnesium oxide is disclosed (see JP-A-11-17220).

Further, the ITO layer is made of AlGaInPLED.
(Zn) or gold (Au) provided on the entire surface of the laminated surface of the p-type III-V compound semiconductor crystal layer constituting
-A technique of providing via a Zn alloy film is disclosed (see Japanese Patent Application Laid-Open No. 11-4020). AlGaIn
Such a metal or alloy film is a good conductor as compared with the semiconductor crystal material constituting the PLED. Therefore, the element operating current flowing from the electrode laid on the ITO window layer is changed to Al
There is an advantage that it can be diffused in a wide range in a plane toward the GaInP light emitting portion.

[0006]

In an LED of a type in which light is emitted to the outside from the oxide window layer side, light emitted from a region below an electrode provided on the window layer is shielded by the electrode and efficiently emitted to the outside. Can not be taken out. Therefore, the operating current flowing in the projection region of the electrode provided in the direction of extracting light emission does not contribute to the improvement of the external luminous efficiency and is wasted.

In the conventional invention described in Japanese Patent Application Laid-Open No. 11-4020, a metal film is arranged on the entire surface immediately below the oxide window layer. That is, the element operation current is also made to flow in a region where light emission is shielded by the electrode. For this reason, there is a problem that efficient high brightness cannot be sufficiently achieved.

According to the present invention, there is provided an AlGaInPLED having a stacked structure of an oxide window layer / a metal (alloy) layer / a p-type group III-V compound semiconductor LED constituent layer. With AlGaInPL
Provide ED.

[0009]

Means for Solving the Problems The inventor of the present invention has arrived at the present invention as a result of intensive studies to solve the above-mentioned problems.
That is, the present invention provides [1] a light emitting diode having a light emitting portion, a window layer, and an electrode, wherein the light emitting portion is (Al _X Ga _{1 -x} )
_A window layer including an oxide layer, a layer including a metal element between the light emitting portion and the window layer, the layer including a _Y In _1-Y P (0 ≦ X ≦ 1, 0 <Y ≦ 1) layer; A p-side-up type light-emitting diode, characterized in that the layer containing a metal element has an uncovered region on the stacking plane and has an electrode on the uncovered region, [2]
The p-side-up type light emitting diode according to claim 1, wherein the layer containing the metal element is in ohmic contact with the layer on the light emitting section side, [3] the layer containing the metal element contains nickel. The p-side-up type light emitting diode according to [1] or [2], wherein [4] the layer containing a metal element contains nickel oxide. [5] The p-side-up light-emitting diode according to any one of [1] to [4], wherein the window layer contains zinc oxide. .

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a so-called p-side layer in which a group III-V compound semiconductor crystal layer disposed above an AlGaInP light-emitting layer in a direction in which light is emitted is formed of a p-type layer. Up-type AlGaInPLED
It is intended for.

A layer containing a metal element according to the embodiment of the present invention (hereinafter abbreviated as a metal layer) is a p-side-up type Al
P-type I which constitutes a GaInPLED and is also a layer to be deposited with a window layer containing an oxide (hereinafter abbreviated as an oxide window layer)
It can be formed on the surface of the II-V compound semiconductor crystal layer by the following method. (1) After a metal layer is once deposited on the entire surface of the layer to be deposited,
A method of selectively removing a metal layer corresponding to a region where an electrode is to be formed using a known patterning technique in accordance with the bottom surface shape of the electrode. (2) On a surface of the layer to be deposited, a region where an electrode is to be formed is coated in advance with a coating material such as a photoresist material in a plane shape corresponding to the bottom shape of the electrode, and then a metal layer is applied. A method of partially removing only a metal layer existing in a region where an electrode is to be formed by using a lift-off method or the like.

The planar shape of the region where the metal layer is selectively removed is preferably similar to the planar shape of the electrode. For example, in the case of a circular electrode, it is desirable that the region from which the metal layer is removed is also circular. In addition, it is desirable that the center of the planar shape of the electrode and the center of the region where the metal layer is removed be substantially matched. The plane area of the region from which the metal layer is removed is substantially the same as the bottom area of the electrode. If the area of the region where the metal layer is removed is extremely large compared to the bottom area of the electrode, the area of the high-resistance junction region between the oxide window layer and the LED constituent layer increases, and the region where the operating current can flow Will shrink. Therefore, there is a problem in increasing the brightness. The plane area of the region from which the metal layer is removed is desirably approximately 0.7 to 1.2 times the bottom area of the electrode.

In the present invention, the metal layer is formed of p-type III-V
A more preferable oxide window layer can be obtained by using a metal that makes ohmic contact with a layer on the light emitting portion side such as a group III compound semiconductor crystal. Metals that can form an ohmic junction with the p-type III-V compound semiconductor crystal layer include well-known gold-zinc (A
u-Zn) alloy. In addition, there is a simple metal such as nickel (Ni). Nickel-aluminum (Ni
-Al) alloy, nickel-gold (Ni-Au), nickel-titanium (Ni-Ti), nickel-silver (Ni-A
g), nickel-molybdenum (Ni-Mo), nickel-copper (Ni-Cu), and other alloys containing Ni. These metal layers can be applied using a general vacuum deposition method, a high frequency sputtering method, or the like.

It is preferable that the metal layer be made of Ni or nickel oxide (NiO) because good ohmic contact with the III-V compound semiconductor constituent layer is exhibited. In particular, NiO
In the case where is used, an oxide window layer having excellent translucency is formed.

The metal layer made of NiO can be applied using, for example, a target material made of NiO. III
After a film made of Ni alone is deposited on the surface of the -V compound semiconductor constituent layer, the film can be formed by oxidizing the film. Further, after depositing a film composed of a single element of Ni, an oxide layer serving as a window layer is successively deposited thereon, and thereafter, if heat treatment is performed, Ni contained in the oxide layer is reduced by oxygen contained in the oxide layer.
The film is oxidized and converted to NiO.

The oxide window layer is made of, for example, zinc oxide (Zn).
O), tin oxide (SnO)_Two), Indium oxide (In)
_TwoO_Three), Titanium oxide (TiO, TiO_Two), Gallium oxide
(Ga_TwoO _Three), NiO, manganese oxide (MnO), acid
It can be made of copper oxide (CuO) or the like. In addition, such as ITO
It can be composed of a composite oxide. In particular, AlGaInP emission
The red-orange light emitted from the layer can be sufficiently transmitted.
Less than about 2 electron volts (eV)
The above oxide is preferably used as a constituent material of the window layer.
You. The bandgap is so large, and the specific resistance
About 1 milliohm centimeter (mΩ · cm) or
The lower resistivity, conductive oxide material is LED
Window that doubles as a current spreading layer that spreads the operating current in two dimensions
Advantageously available as a layer.

The window layer can also be formed by stacking a plurality of oxide crystal layers. If a crystal layer made of an oxide having a different refractive index is gradually layered so that the refractive index gradually becomes smaller upward, a more convenient window layer can be formed to transmit light emitted from the light emitting layer. . For example, there is an example of a layered window layer in which the lower layer is made of ITO and the upper layer is made of a zinc oxide layer.

In the present invention in which an oxide window layer is provided on a p-type group III-V compound semiconductor constituent layer, the oxide window layer is
Conveniently, the composition is mainly composed of ZnO. III-
In a group V compound semiconductor crystal, zinc behaves as a p-type impurity. Therefore, if the zinc constituting the zinc oxide is p
Even if it penetrates into the group III-V compound semiconductor constituent layer,
II-V compound semiconductors are advantageous because they can maintain p-type conduction. The oxide mainly composed of ZnO refers to an oxide containing the same substance as a main component. For example, there are composite oxides such as indium / zinc oxide and gallium / zinc oxide.

[0019]

EXAMPLE In this example, the epitaxial laminated structure 2 was used.
AlGaInPL with a window layer made of ZnO
The present invention will be described in detail using the ED 10 as an example. FIG. 1 is a schematic sectional view of an LED 10 according to the present embodiment.

The laminated structure 20 is made of silicon (Si) doped n
-Type GaAs single crystal substrate 101, Si-doped n-type GaAs
Buffer layer 102, Si-doped n-type (Al _0.7 Ga _0.3 ) _0.5
An In _{0 .5} P lower cladding layer 103, an undoped (Al _0.2
Ga _0.8 ) _0.5 In _0.5 P light emitting layer 104 and magnesium (Mg) doped p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P
The upper clad layer 105 was used. Each of the epitaxial constituent layers 102 to 105 is composed of trimethylgallium ((CH ₃ ) ₃ Ga) / trimethyl aluminum ((CH
₃ ) ₃ Al) / trimethylindium ((CH ₃ ) ₃ In)
/ Phosphine (PH ₃ ) based 7 pressure reduction MO-VPE method
Grow at 30 ° C. Doping source of magnesium bis - cyclopentadienyl _{Mg (bis- (C 5 H 5} ) 2
Mg). The silicon doping source is disilane (S
disilane containing i ₂ H ₆₎ at a concentration of about 10 vol ppm - was hydrogen mixed gas.

As the substrate 101, a GaAs single crystal inclined by 4 ° in the <011> direction was used. The carrier concentration of the substrate 101 was about 2 × 10 ¹⁹ cm ⁻³ , and the layer thickness was about 300 μm. The layer thickness (d) of the GaAs buffer layer 102 is 1.5 μm
And the carrier concentration (n) was about 2 × 10 ¹⁸ cm ⁻³ . The lower cladding layer 103 has d = 3.5 μm and n =
It was 3 × 10 ¹⁸ cm ⁻³ . The light emitting layer 104 has d = 0.2 μm
m and the carrier concentration (p) = 1 × 10 ¹⁷ cm ⁻³ . The upper cladding layer 105 has d = 1 μm and p = 7 ×
It was set to 10 ¹⁷ cm ^-3 .

On the surface of the p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P upper cladding layer 105, a film 106 made of Ni was applied by a general vacuum deposition method. The film thickness is about 10n
m. It was visually recognized that the Ni film 106 immediately after the deposition was gray. Using a general photolithography technique, the Ni film 106 in a region where an electrode is to be formed is made similar to the shape of the bottom surface of the electrode to be formed on the oxide window layer later.
Was selectively removed over a circular area of 130 μm in diameter. The center of the planar shape of the electrode substantially coincided with the center of the region where the Ni film 106 was removed.

On the metal layer 106, a window layer 107 made of a zinc oxide film exhibiting n-type conductivity was bonded. The oxide window layer 107 was formed from Al-doped zinc oxide having a specific resistance of about 9 × 10 ⁻⁴ Ω · cm by a high-frequency magnetron sputtering method. The thickness of the zinc oxide layer deposited at about 300 ° C. was about 0.25 μm.

On the surface of the window layer 107, an insulating film made of Si ₃ N ₄ (refractive index: about 1.9) having a smaller refractive index than zinc oxide (refractive index = 2.0) is formed. 107 was deposited as a surface protective film 108. Silicon nitride protective film 108
Was deposited by a known plasma CVD method using monosilane (SiH ₄ ) and ammonia (NH ₃ ) as raw materials. The layer thickness was about 0.15 μm.

On the back surface of the n-type GaAs substrate 101, a gold (Au) -germanium (Ge) alloy (Au 95% by weight)
-Ge 5% by weight) The film was applied by a general vacuum evaporation method. The film thickness was about 0.5 μm. Thereafter, an alloying treatment was performed at 430 ° C. for 10 minutes in a stream of argon (Ar) to form an n-type ohmic electrode 110.

After the alloy processing,
It was visually observed that the Ni film 106 was decolorized and became substantially transparent. It is considered that this is because the Ni film 106 was converted to nickel oxide (NiO) by oxygen contained in the zinc oxide film 107 as the upper layer of the Ni film 106.

Next, the silicon nitride protective film 108 in the region where the p-type electrode 109 is to be formed was partially removed by using a known photolithography technique. Silicon nitride protective film 10
8 is removed, and a lower bottom portion 109a in contact with the zinc oxide layer is formed in a region where the zinc oxide layer forming the window layer 107 is exposed.
Then, a p-type electrode 109 having a multilayer structure in which the upper layer portion 109b was made of Al was formed. The p-type electrode 109 has a diameter of about 120
A circular electrode having a thickness of μm was used.

P-type electrode 109 and n-type ohmic electrode 1
When a current of 20 milliamperes (mA) was passed in the forward direction between 10 and 10, red-orange light was emitted almost uniformly from almost the entire surface of the window layer 107. The emission wavelength measured by the spectrometer was about 618 nm. The half width of the light emission spectrum was about 19 nm, and light emission having excellent monochromaticity was obtained. In addition, the provision of the metal layer 106 allows the upper clad layer 1
The ohmic junction between the layer 05 and the window layer 107 became good. For this reason, the forward voltage (ｍ20 mA) was reduced to 2.1 volts (V) on average. The forward voltage between the LEDs was accommodated in a uniform range of 2.1V ± 0.1V. The emission intensity reached about 66 millicandela (mcd).

Comparative Example An n-type (Al _0.7 Ga _0.3 ) forming the outermost surface of the epitaxial laminated structure described in Example 1.
_On the surface of the _0.5 In _0.5 P upper cladding layer, Ni (Ni
O) An AlGaInPLED was formed by directly bonding an oxide window layer made of zinc oxide without an intervening film.

Al formed by the method described in Example 1
The GaInPLED had a high forward voltage of about 6 V when the forward current was 20 mA. Oxide window layer and I
This is because ohmic contact between both layers is poor because no metal layer is interposed between the II-V compound semiconductor constituent layer and the II-V compound semiconductor constituent layer. The central wavelength of light emission was about 618 nm, almost as in Example 1. No light emission was observed from almost the entirety of the oxide window layer, and only light emission was observed from the very outer periphery of the electrode on the window layer. Since the light emitting area was extremely limited, the light emitting intensity in a chip state was only about 20 mcd. As described in the present comparative example, the conventional configuration in which the metal layer is not disposed at a specific position related to the planar shape of the electrode has a disadvantage in obtaining a high-luminance AlGaInPLED because of its excellent ohmic contact and low forward voltage. Proof that there is.

[0031]

According to the present invention, an AlGaInPLED is provided.
A good ohmic contact property can be obtained with the oxide window layer, and an operating current can be diffused to the light-emitting surface, so that a high-luminance element having a low forward voltage, uniformity, and excellent luminous efficiency can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of the LED described in Example 1.

DESCRIPTION OF SYMBOLS 10 AlGaInPLED 20 laminated structure 101 GaAs single crystal substrate 102 GaAs buffer layer 103 lower cladding layer 104 light emitting layer 105 upper cladding layer 106 metal layer 107 oxide window layer 108 protective film 109 p-type electrode 109a p-type electrode Lower bottom layer 109b p-type electrode upper layer 110 n-type ohmic electrode

Claims (5)

[Claims] 1. A light emitting diode having a light emitting part, a window layer, and an electrode, wherein the light emitting part is (Al _X Ga _{1 -x} ) _Y In _{1 -Y} P
(0 ≦ X ≦ 1, 0 <Y ≦ 1) layer, the window layer includes an oxide layer, and a layer including a metal element between the light emitting portion and the window layer.
A p-side-up type light-emitting diode, wherein the layer containing a metal element has an uncovered region on a stack plane and has an electrode on the uncovered region. 2. The p-side-up type light-emitting diode according to claim 1, wherein the layer containing a metal element is in ohmic contact with the layer on the light-emitting portion side. 3. The p-side-up type light emitting diode according to claim 1, wherein the layer containing a metal element contains nickel. 4. The p-side-up type light emitting diode according to claim 1, wherein the layer containing a metal element contains nickel oxide. 5. The light emitting diode according to claim 1, wherein said window layer contains zinc oxide.