JP2008147504A - Led epitaxial wafer, and led manufactured using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED epitaxial wafer which has a uniform luminance characteristic distribution in a wafer surface even when the number of times of crystal growth becomes large and deposits stick on a holder, and to provide an LED manufactured using the same. <P>SOLUTION: The LED epitaxial wafer is constituted by providing, on a substrate 2, an active layer 6 which emits light, a light guide-out surface for guiding the light emitted by the active layer 6 out, and a DBR layer 4 which is provided between a substrate 2 and the active layer 6 for reflecting the light emitted by the active layer 6 to the light guide-out side. The DBR layer 4 is so designed that a reflection wavelength of the DBR layer 4 becomes equal to a light emission wavelength of the active layer 6 on a wafer outer peripheral side, and then formed so that the difference between the light emission wavelength of the active layer 6 and the reflection wavelength of the DBR layer 4 becomes minimum on the wafer outer peripheral side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an LED epitaxial wafer and an LED manufactured using the same, and more particularly to an LED epitaxial wafer having a uniform and uniform luminance characteristic distribution in the wafer surface.

  In recent years, light-emitting diodes are rapidly spreading in mobile phones, liquid crystal displays, traffic lights, in-vehicle, and other illumination applications. An LED is a lamp in which an epitaxial wafer on which a compound semiconductor has been grown on a substrate so as to form a PN junction or a PIN junction is formed into an electrode by a process, formed into a chip, wired by wire bonding, and molded by resin. . In traffic lights, car tail lamps, and the like, a plurality of LEDs are often used as a display (display). In such applications, high brightness is required. Many have reflective layers.

  FIG. 2 shows a schematic cross-sectional view of an example in which a p-type semiconductor is located on the wafer surface in the layer structure of an LED having a DBR layer.

  Of the light emitted from the active layer 6, the light emitted to the second electrode 10 side (upper side) is a p-cladding layer 7 designed to be transparent to the emission wavelength, p-current diffusion. The light passes through the layer 8 and the p-contact layer 9 and is emitted from a gap where the second electrode 10 is not formed. On the other hand, the light emitted from the active layer 6 to the first electrode 1 side (lower side) is reflected by the DBR layer 4 and emitted to the second electrode 10 side (upper side), and the second electrode 10 is also formed. Radiated from the gap that is not. 3 is an n-buffer layer and 5 is an n-cladding layer.

  Here, when there is no DBR layer 4 below the active layer 6, light emitted from the active layer 6 to the first electrode 1 side is mainly absorbed by the substrate 2, so that the light is reflected upward. It is not emitted from the upper surface. Therefore, the DBR layer 4 is an effective means for increasing the brightness of the LED.

  In order to grow such a DBR layer, the growth of a thin layer having a thickness of several tens of nanometers can be controlled, and an MOVPE method that does not require an ultra-high vacuum and is excellent in mass productivity is often used. . The MOVPE method is a method in which an organic metal (hereinafter referred to as MO) and gas are supplied into a reaction furnace, a thermal decomposition reaction is caused on a substrate heated to a high temperature, and a crystal (epitaxial layer) is grown on the substrate. is there.

  FIG. 3 is a longitudinal sectional view of the reactor in the MOVPE apparatus, and FIG. 4 is a view taken along line 4-4 in FIG.

  As shown in FIG. 3, a holder 12 on which a substrate (GaAs substrate) 11 is set is placed in a hole of a disk 14 connected to a shaft 13. A gear 15 is formed on the outer periphery of the holder 12, and the gear 15 is engaged with external teeth 16 provided around the disk 14 and fixed to the reaction furnace 21. As shown in FIG. 4, when the shaft 13 rotates in a certain direction, the disk 14 also rotates in the same direction. However, the external teeth 16 around the disk 14 are fixed to the reaction furnace 21 and thus do not rotate. The holder 12 engaged with 16 rotates in the opposite direction in the hole of the disk 14. As a result, each holder 12 (substrate 11) revolves around the shaft 13 while rotating around the hole of the disk 14. Such a reactor is called a self-revolving converter. Comparing this revolving furnace with a revolving furnace in which the holder 12 does not have a gear 15 mechanism and only revolves around the shaft 13, the revolving furnace is superior in uniformity of the layer thickness in the wafer surface. ing.

Japanese Patent No. 2778868

  When a plurality of LEDs are used as a display device, it is necessary that the brightness of all the LEDs is uniform. Therefore, in manufacturing, it is important to increase the productivity of LEDs that a chip can be obtained from the entire wafer surface at a desired luminance level or higher and with a uniform luminance within the wafer surface.

  By the way, when the MOVPE method described above is used, if the number of times of crystal growth is repeated, deposits adhere to the holder for setting the wafer, and the flow of MO and gas is blocked particularly at the periphery (outer peripheral side) of the wafer. For this reason, on the outer peripheral side of the wafer, the supply of MO and gas is reduced and the epitaxial growth is hindered, the layer thickness on the outer peripheral side of the wafer becomes thinner than that in the central portion, and the luminance characteristic distribution in the wafer surface deteriorates.

  As described above, the revolution furnace makes the layer thickness distribution on the wafer concentric circle (circumferential direction) uniform by rotating the wafer, and the layer thickness uniformity in the wafer surface is superior to the revolution furnace. However, a layer thickness distribution is unavoidable at the wafer center and the outer peripheral side (radial direction).

  Usually, as shown in FIG. 5, the wafer is designed so that the emission wavelength of the active layer and the reflection wavelength of the DBR layer coincide with each other at the center of the wafer. For this reason, since the layer thickness on the outer peripheral side of the wafer becomes thin due to the deposit, the difference between the emission wavelength of the active layer and the reflection wavelength of the DBR layer becomes remarkable, and the luminance decreases from the center of the wafer toward the outer peripheral side. Will have an in-plane distribution. In particular, the shorter the emission wavelength of the active layer (LED), the more susceptible to changes in layer thickness.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an LED epitaxial wafer having a uniform luminance characteristic distribution within the wafer surface and an LED manufactured using the same even when the number of crystal growths is repeated and the deposit is attached to the holder. There is to do.

  In order to achieve the above object, an invention according to claim 1 comprises an active layer for emitting light on a substrate, a light extraction surface for extracting light emitted from the active layer, the substrate, and the substrate. In an LED epitaxial wafer provided between the active layers and provided with a DBR layer for reflecting the light emitted from the active layer to the light extraction surface side, the reflection wavelength of the DBR layer is the active wavelength on the outer peripheral side of the wafer. The LED epitaxial wafer is characterized in that the DBR layer is designed so as to match the emission wavelength of the layer and formed so that the difference between the emission wavelength of the active layer and the reflection wavelength of the DBR layer is minimized on the outer peripheral side of the wafer.

  According to a second aspect of the present invention, an active layer for emitting light, a light extraction surface for extracting light emitted from the active layer, and an active layer provided between the substrate and the active layer are provided on the substrate. In an LED epitaxial wafer provided with a DBR layer for reflecting light emitted from the layer to the light extraction surface side, on the outer periphery side of the wafer, the emission wavelength of the active layer is active so as to match the reflection wavelength of the DBR layer The LED epitaxial wafer is characterized in that the layer is designed so that the difference between the emission wavelength of the active layer and the reflection wavelength of the DBR layer is minimized on the outer peripheral side of the wafer.

In the invention of claim 3, the difference between the emission wavelength of the active layer and the reflection wavelength of the DBR layer on the wafer outer peripheral side is:
−10 nm ≦ (emission peak wavelength of active layer) − (reflection peak wavelength of DBR layer) ≦ 10 nm (1)
The LED epitaxial wafer according to claim 1, wherein the DBR layer or the active layer is designed so as to satisfy the above.

According to a fourth aspect of the invention, the substrate is a GaAs substrate, and the active layer is an (Al _x1 Ga ₁ -x1) _y1 In ₁ -y1 P well layer (0 ≦ x1 ≦ 0.5, 0.4 ≦ y1 ≦ 0. 6) and (it was Al _x2 Ga _1-x2) Repeat _y2 In _1-y2 P barrier layer (0 <x2 ≦ 1, x1 < unit semiconductor which has x2,0.4 ≦ y2 ≦ 0.6) the superposed laminated 2. A multiple quantum well (MQW) structure, wherein the DBR layer has a multilayer structure in which unit semiconductors in which an Al _x3 Ga _1-x3 As (0 ≦ x3 ≦ 0.6) semiconductor and an AlInP semiconductor are stacked are repeatedly stacked. 3. The LED epitaxial wafer according to any one of 3 above.

  The invention according to claim 5 is an LED manufactured using the LED epitaxial wafer according to any one of claims 1 to 4.

  According to the present invention, it is possible to manufacture an LED epitaxial wafer having a uniform luminance characteristic distribution in the wafer surface.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows the emission wavelength distribution of the active layer and the reflection wavelength distribution of the DBR layer in the wafer plane of the LED epitaxial wafer according to the preferred embodiment of the present invention.

  The layer structure of the LED epitaxial wafer according to the present embodiment is such that an n-buffer layer 3, a DBR layer 4, an n-clad layer 5, an active layer 6, and a p-clad are formed on the upper surface of the substrate 2 shown in FIG. A layer 7, a p-current diffusion layer 8, and a p-contact layer (light extraction surface) 9 are provided.

  The substrate 2 is a GaAs substrate, the active layer 6 is a multi-layered structure in which unit semiconductors obtained by superimposing undoped GaInP semiconductors and AlGaInP semiconductors are stacked, and the DBR layer 4 is composed of Si-doped GaAs semiconductors and AlInP semiconductors. The stacked unit semiconductors constitute one pair, and are configured in a multilayer structure in which the pairs are repeatedly stacked.

As shown in FIG. 1, the DBR layer 4 is arranged so that the reflection wavelength of the DBR layer 4 matches the emission wavelength of the active layer 6 on the wafer outer peripheral side, that is, the emission wavelength of the active layer 6 and the reflection wavelength of the DBR layer 4. The difference is designed to be the smallest on the outer periphery side of the wafer.
−10 nm ≦ (emission peak wavelength of active layer) − (reflection peak wavelength of DBR layer) ≦ 10 nm (1)
Designed to meet. At this time, the wavelength difference between the emission wavelength of the active layer 6 and the reflection wavelength of the DBR layer 4 at the wafer center also satisfies the above equation (1), and the maximum wavelength difference is 10 nm or less.

  After the LED epitaxial wafer according to the present embodiment is used, the first electrode layer (not shown) is provided on the lower surface of the substrate 2 and the second electrode layer (not shown) is provided on the upper surface of the p-contact layer 9. The first electrode 1 and the second electrode 10 are formed through a photolithography process and an etching process, and then a chip is formed through a dicing process. Each chip and a frame are wired by wire bonding, and then molded by resin. Is obtained.

  Next, the operation of the present embodiment will be described.

  First, the relationship between the layer thickness and reflection wavelength of the DBR layer 4 and the layer thickness and emission wavelength of the active layer 6 will be described.

a) DBR layer The layer thickness d of the epitaxial layer constituting the DBR layer 4 is:
Layer thickness d = wavelength λ / (4 × refractive index n of epitaxial layer) to be reflected (2)
It is expressed by the relational expression.

  Therefore, as the layer thickness d of the epitaxial layer on the outer peripheral side of the wafer is reduced by increasing the number of times of crystal growth, the value of the wavelength λ to be reflected also decreases. Here, if the light emission wavelength of the LED does not match the wavelength λ desired to be reflected in the above equation (2), the DBR layer 4 does not function effectively as a reflective film of the LED, so that the light emission output of the LED is reduced. Become.

b) Active layer In the case of the active layer 6 made of multiple quantum wells (MQW), there is a correlation between the layer thickness and the emission wavelength. The MQW has a structure in which two epitaxial layers called a well layer and a barrier layer (having a larger band gap than the well layer) are alternately stacked. When the thickness of the well layer is reduced, the wavelength becomes shorter. The longer the layer, the longer the wavelength.

  Here, for example, consider a case where the epitaxial layers of the DBR layer 4 and the active layer 6 become thin as a whole. When the layer thickness of the epitaxial layer constituting the DBR layer 4 is reduced by 5%, the reflection wavelength of the DBR layer 4 is shifted to the short wavelength side by about 30 nm (λ = 560 to 650 nm in the above equation (2), and the layer thickness is 5 % When thinned). On the other hand, even if the thickness of the epitaxial layer constituting the active layer 6 is reduced by 5%, the emission wavelength of the active layer 6 is shifted to the short wavelength side at most several nm. For these reasons, if the thickness of each epitaxial layer of the DBR layer 4 and the active layer 6 becomes thinner than the original design by increasing the number of times of crystal growth, the emission wavelength of the active layer 6 on the outer peripheral side of the wafer The deviation of the reflection wavelength of the DBR layer 4 increases, and the light emission output of the LED decreases. For example, the deposition of the deposit on the holder 12 shown in FIG. 2 reduces the supply of MO and gas on the wafer outer peripheral side, and the layer thickness on the wafer outer peripheral side becomes thinner. The influence is shown in FIG. As described above, the reflection wavelength of the DBR layer 4 is more easily received than the emission wavelength of the active layer 6. As a result, in a wafer whose emission wavelength is designed at the center of the wafer, when deposition of deposits progresses, the reflection peak wavelength of the DBR layer 4 becomes a short wave on the outer peripheral side of the wafer, and is far from the design value.

  Therefore, in the LED epitaxial wafer according to the present embodiment, the emission wavelength of the active layer 6 is designed at the center of the wafer, and the reflection wavelength of the DBR layer 4 is designed according to the emission wavelength of the active layer 6 on the outer periphery side of the wafer. Thus, the luminance distribution is made uniform in the LED epitaxial wafer surface.

  Specifically, the reflection wavelength of the DBR layer 4 is designed to match the emission wavelength of the active layer 6 on the outer peripheral side of the wafer, and the difference between the emission wavelength of the active layer 6 at the wafer center and the reflection wavelength of the DBR layer 4 is 10 nm. The following conditions are optimum conditions for making the luminance distribution in the wafer surface constant.

  In this way, by designing the reflection wavelength of the DBR layer 4 in accordance with the emission wavelength of the active layer 6 on the outer peripheral side of the wafer, the thickness of the deposit is deteriorated by increasing the number of times of crystal growth and originally deteriorating the luminance distribution in the wafer surface. Even in this region, since the optimum reflection condition can be obtained on the outer peripheral side of the wafer, it is possible to compensate for the decrease in luminance on the outer peripheral side of the wafer due to the deposition of the deposit on the holder. Therefore, an LED epitaxial wafer having a constant luminance distribution can be obtained. As a result, a constant luminance is maintained in each LED manufactured using the LED epitaxial wafer. That is, by using the LED epitaxial wafer according to the present embodiment having a high uniformity of luminance distribution, a chip can be obtained from the entire epitaxial wafer over the desired luminance level and with good luminance uniformity within the wafer surface. It is possible to omit the luminance rank sorting step in the chip manufacturing process, and the productivity of the LED is improved.

  In the LED epitaxial wafer according to the present embodiment, the case where the reflection wavelength of the DBR layer 4 is designed according to the emission wavelength of the active layer 6 on the outer peripheral side of the wafer has been described as an example. A similar effect can be obtained by designing the emission wavelength to match the reflection wavelength of the DBR layer 4 on the outer peripheral side of the wafer.

Carrier concentration of 1 × 10 ¹⁸ cm ^-3, the top surface of the Si-doped GaAs substrate of 3 inches in diameter, first, a carrier concentration of 1 × 10 ¹⁸ cm ^-3, film thickness 200 nm, to form a Si-doped consisting GaAs n-buffer layer .

Next, the upper surface of the n- buffer layer, a carrier concentration of 1 × 10 ¹⁸ cm ^-3, Si doped GaAs semiconductor and the carrier concentration of the film thickness 45nm 1 × 10 ¹⁸ cm ^-3, the Si-doped AlInP semiconductor having a film thickness of 50nm One unit of the stacked unit semiconductors was used, and 20 pairs were repeatedly stacked to form a DBR layer. On the upper surface of the DBR layer, an n-cladding layer made of Si-doped AlInP with a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ and a film thickness of 500 nm was formed.

Next, a unit semiconductor in which an undoped GaInP semiconductor having a thickness of 5 nm and an undoped (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P semiconductor having a thickness of 10 nm are superposed on the upper surface of the n-cladding layer is taken as one pair. 50 pairs were repeatedly laminated to form an active layer.

Thereafter, on the upper surface of the active layer, a p-cladding layer made of Zn-doped AlInP with a carrier concentration of 1 × 10 ¹⁸ cm ⁻³ and a film thickness of 500 nm, a carrier concentration of 5 × 10 ¹⁸ cm ⁻³ , a film thickness of 10000 nm and a Zn-doped layer. A p-current diffusion layer made of GaP, a carrier concentration of 1 × 10 ¹⁹ cm ⁻³ , a film thickness of 10 nm, and a p-contact layer made of Zn-doped GaAs were formed to produce an epitaxial wafer (3 inches in diameter). The reflection wavelength of the DBR layer in the wafer surface (Max-Min) was 8 nm, and the emission wavelength of the active layer in the wafer surface (Max-Min) was 3 nm.

  Table 1 shows the layer structure of the obtained epitaxial wafer.

  In this epitaxial wafer, the DBR layer is designed so that the DBR layer on the outer peripheral side of the epitaxial wafer is anticipated to be thin, and the emission wavelength of the active layer on the outer peripheral side of the wafer matches the reflection wavelength of the DBR layer. Therefore, the difference between the emission wavelength of the active layer and the reflection wavelength of the DBR layer was as small as 10 nm or less at both the wafer center and the wafer outer peripheral side, and the luminance distribution was uniform.

It is a figure which shows the light emission wavelength distribution of the active layer in the wafer surface, and the reflection wavelength distribution of a DBR layer in the LED epitaxial wafer which concerns on suitable one Embodiment of this invention. It is sectional drawing which shows the layer structure of LED which has a DBR layer. It is a longitudinal cross-sectional view of the reaction furnace (self-revolving converter) in a MOVPE apparatus. Fig. 4 is a view taken along line 4-4 in Fig. 3. It is a figure which shows the light emission wavelength distribution of the active layer in the wafer surface, and the reflection wavelength distribution of a DBR layer in the conventional LED epitaxial wafer.

Explanation of symbols

2 Substrate 4 DBR layer 6 Active layer

Claims (5)

  An active layer for emitting light, a light extraction surface for extracting light emitted from the active layer, and a light emitted from the active layer provided between the substrate and the active layer on the substrate. In an LED epitaxial wafer provided with a DBR layer for reflection on the light extraction surface side, the DBR layer is designed on the outer periphery side of the wafer so that the reflection wavelength of the DBR layer matches the emission wavelength of the active layer. An LED epitaxial wafer characterized in that the difference between the emission wavelength of light and the reflection wavelength of the DBR layer is minimized on the outer peripheral side of the wafer.   An active layer for emitting light, a light extraction surface for extracting light emitted from the active layer, and a light emitted from the active layer provided between the substrate and the active layer on the substrate. In an LED epitaxial wafer provided with a DBR layer for reflection on the light extraction surface side, the active layer is designed so that the emission wavelength of the active layer matches the reflection wavelength of the DBR layer on the outer periphery side of the wafer. An LED epitaxial wafer characterized in that the difference between the emission wavelength of light and the reflection wavelength of the DBR layer is minimized on the outer peripheral side of the wafer. On the wafer outer peripheral side, the difference between the emission wavelength of the active layer and the reflection wavelength of the DBR layer is
−10 nm ≦ (emission peak wavelength of active layer) − (reflection peak wavelength of DBR layer) ≦ 10 nm (1)
The LED epitaxial wafer according to claim 1 or 2, wherein the DBR layer or the active layer is designed to satisfy the following. The substrate is a GaAs substrate, the active layer is (Al _x1 Ga _1-x1 ) _y1 In ₁ -y1 P well layer (0 ≦ x1 ≦ 0.5, 0.4 ≦ y1 ≦ 0.6) and (Al _x2 Ga _1-x2 ) _y2 In _1-y2 Multiple quantum well (MQW) structure in which unit semiconductors laminated with P barrier layers (0 <x2 ≦ 1, x1 <x2, 0.4 ≦ y2 ≦ 0.6) are repeatedly stacked 4. The LED according to claim 1, wherein the DBR layer has a multilayer structure in which a unit semiconductor in which an Al _x3 Ga _1-x3 As (0 ≦ x3 ≦ 0.6) semiconductor and an AlInP semiconductor are stacked is repeatedly stacked. Epitaxial wafer.   An LED manufactured using the LED epitaxial wafer according to claim 1.

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