JP3986703B2 - Epitaxial wafer and light emitting device for AlGaInP light emitting device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an epitaxial wafer for an AlGaInP-based light emitting device (having a wavelength of 650 nm (red) to 550 nm (yellowish green)) and a light emitting device.
[0002]
[Prior art]
Recently, the demand for high-intensity red and yellow light-emitting diodes as light-emitting elements manufactured using AlGaInP-based epitaxial wafers has been greatly increased. The main demand is traffic signals, automobile tail lamps, fog lamps, outdoor display boards, full-color displays, etc.
[0003]
FIG. 3 is a structural diagram of an epitaxial wafer for an AlGaInP light emitting diode having an emission wavelength of 590 nm.
[0004]
The epitaxial wafer shown in FIG. 1 has an n-type GaAs buffer layer 2, an n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 3, an undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 on an n-type GaAs substrate 1. A P active layer 4, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P layer 5 and a p-type GaP window layer 6 are epitaxially grown sequentially.
[0005]
All the epitaxial layers 2 to 6 are grown by metal organic chemical vapor deposition (hereinafter referred to as “MOVPE”). As the window layer of the light emitting diode, an AlGaAs layer (Al composition of 0.6 or more) may be used. From the viewpoint of light extraction efficiency and ease of deterioration, GaP has a large band gap and is not easily oxidized. The layer is more suitable as a window layer.
[0006]
[Problems to be solved by the invention]
However, the GaP window layer has the following problems.
[0007]
Figure 4 is an illustration of the band structure in the vicinity of the hetero interface of the p-type GaP window layer 6 and the p-type AlGaInP cladding layer 5 of AlGaInP-based light-emitting diode epitaxial wafer shown in FIG. In the figure, an arrow A indicates the direction of movement of holes when a forward voltage is applied.
[0008]
The p-type GaP window layer 6 and the p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 5 have a large potential barrier (inside the broken-line circle B) due to the difference in electron affinity (band discontinuity). The electric potential barrier prevents the movement of holes). This potential barrier becomes a factor that hinders the movement of holes from the p-type GaP window layer 6 to the p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 5 when the light emitting diode is energized. As a result, the forward voltage of the light emitting diode (operating voltage: voltage at 20 mA energization) becomes high. In general, a light emitting diode having a high forward voltage has low reliability. In a light emitting diode using the p-type GaP window layer 6, it is a big problem to reduce the forward voltage.
[0009]
Accordingly, an object of the present invention is to provide an epitaxial wafer for an AlGaInP-based light emitting device and a light emitting device that can solve the above-described problems and obtain a light emitting device having a low forward voltage.
[0010]
[Means for Solving the Problems]
An epitaxial wafer for an AlGaInP-based light-emitting element according to the present invention includes an n-type cladding layer made of at least an AlGaInP-based compound semiconductor on an electrically conductive substrate, and an AlGaInP-based compound semiconductor having a smaller band gap energy than the n-type cladding layer. An undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer, and a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer made of a p-type AlGaInP compound semiconductor having a composition with a larger band gap energy than the active layer, In an epitaxial wafer for an AlGaInP light emitting element in which a p-type GaP window layer made of GaP is laminated, the band gap energy between the p-type cladding layer and the p-type window layer is larger than that of the active layer, P-type (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P intervening layer is provided.
[0011]
In addition to the above configuration, the epitaxial wafer for an AlGaInP-based light emitting device of the present invention has a p-type (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P intervening layer having a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less. Is preferred.
[0012]
The light-emitting element of the present invention includes an n-type cladding layer made of at least an AlGaInP-based compound semiconductor on an electrically conductive substrate, and an undoped (Al _0.1 layer made of an AlGaInP-based compound semiconductor having a smaller band gap energy than the n-type cladding layer. A Ga _0.9 ) _0.5 In _0.5 P active layer, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer made of a p-type AlGaInP-based compound semiconductor having a larger band gap energy than the active layer, and a p-type made of GaP. In a light emitting device in which an electrode is provided on a stacked body in which a GaP window layer is stacked, a material having a band gap energy larger than that of the active layer and smaller than that of the p type cladding layer between the p type cladding layer and the p type window layer. der which p-type _{(Al 0.1 Ga 0.9) 0.5 in} 0.5 P intermediate layer is provided consisting of .
[0013]
In addition to the above structure, in the light-emitting element of the present invention, the carrier concentration of the p-type (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P intervening layer is preferably 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less. .
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of an epitaxial wafer for an AlGaInP-based light emitting device and a light emitting device of the present invention will be described. Incidentally, using the same reference numerals are given to the same members as the conventional example shown in FIG.
[0015]
The feature of the epitaxial wafer for an AlGaInP-based light emitting device of the present invention is that an intervening layer having a band gap smaller than that of the p-type AlGaInP layer is provided between the p-type AlGaInP cladding layer 5 and the p-type GaP window layer 6. .
[0016]
【Example】
FIG. 1 is a structural view showing an embodiment of an epitaxial wafer for an AlGaInP light emitting device of the present invention. In the present embodiment, the case of an epitaxial wafer for red light emitting diodes having an emission wavelength of around 625 nm will be described.
[0017]
An epitaxial wafer for an AlGaInP-based light emitting device shown in FIG. 1 is formed on an n-type GaAs substrate 1 by an MOVPE method using an n-type (Se-doped) GaAs buffer layer 2 and an n-type (Se-doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 3, undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer (hereinafter referred to as “active layer”) 4, p-type (Zn doped) (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer (hereinafter referred to as “active layer”) 5 is sequentially grown, and a p-type (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P layer as an intervening layer which is a main part of the present invention is formed on the p-type cladding layer 5. (Hereinafter referred to as “forward voltage reduction layer”) 7 is formed of epitaxial layers 2 to 7 in which 100 nm is grown by MOVPE and p-type (Zn-doped) GaP window layer 6 is grown by 10 μm. . As a comparative example, a p-type (Zn-doped) GaP film was grown by 10 μm without forming a forward voltage reduction layer.
[0018]
All epitaxial layers 2 to 7 are grown at a growth temperature of 700 ° C., a growth pressure of 50 Torr, a growth rate of each epitaxial layer 2 to 7 is 0.3 to 3.0 nm / s, and a V / III ratio is 100 to 600. It was. Thereafter, the epitaxial wafer was processed to produce a light emitting diode.
[0019]
The chip size of the light emitting diode was 300 μm square, an n-type electrode was formed on the entire lower surface of the chip, and a circular p-type electrode having a diameter of 150 μm was formed on the upper surface of the chip. For the n-type electrode, gold germanium, nickel, and gold were deposited in the order of 60 nm, 10 nm, and 500 nm, respectively, and for the p-type electrode, gold zinc, nickel, and gold were deposited in the order of 60 nm, 10 nm, and 1000 nm, respectively. Furthermore, this chip was assembled into a stem, and resin molding was performed, and the light emission characteristics and voltage-current characteristics of the light emitting diode were examined.
[0020]
FIG. 2 is a light emission characteristic diagram of the light-emitting element of the present invention, in which the horizontal axis indicates the forward voltage, and the vertical axis indicates the forward current.
[0021]
In the figure, the solid line shows the light emission characteristics of the light emitting element of the present invention (with the forward voltage reduction layer 7 made of (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P), and the broken line shows the light emission characteristics of the conventional light emitting element. Show.
[0022]
The forward voltage of the light emitting diode using the AlGaInP-based light emitting element epitaxial wafer of the present invention can be greatly reduced to 1.80 V with respect to the forward voltage of 2.40 V of the conventional light emitting diode.
[0023]
The minimum value of the forward voltage of the light emitting diode is determined by the band gap of the active layer 4, and this value of 1.80 V in the forward voltage is the band gap of the active layer 4 of the epitaxial wafer for AlGaInP-based light emitting device of the present invention. (In other words, it is substantially equal to the forward voltage when the AlGaAs window layer is used) . Providing the forward voltage reduction layer 7 did not lower the luminance as compared with the conventional light emitting device.
[0024]
(Grounds for optimal conditions)
When the bandgap is provided a small forward voltage reduction layer 7 than the active layer 4, the light from the active layer 4 is absorbed by the forward voltage reduction layer 7, LED light extraction efficiency becomes extremely poor. Therefore, the band gap of the forward voltage reduction layer 7 is preferably smaller than that of the p-type cladding layer 5 and larger than that of the active layer 4.
[0025]
The conductivity type of the forward voltage reduction layer 7 is preferably the same p-type as the p-type cladding layer 5 and the p-type GaP window layer, and the carrier concentration thereof is 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ^−. It is preferably ³ or less. When the carrier concentration of the forward voltage reduction layer 7 is 5 × 10 ¹⁷ cm ⁻³ or less, the resistivity of the forward voltage reduction layer 7 becomes high and the forward voltage becomes high. On the other hand, when the carrier concentration is 5 × 10 ¹⁸ cm ⁻³ or more, defects in the crystal increase and the light emission efficiency is lowered.
[0026]
The forward voltage reduction layer 7 is preferably lattice-matched with the p-type cladding layer 5 serving as a base. If the lattice matching is not achieved, defects will occur in the epitaxial layer, causing problems such as a decrease in light emission efficiency and clouding of the surface of the p-type GaP window layer 6.
[0027]
In this embodiment, the case of an epitaxial wafer and a light-emitting element using an n-type conductive substrate has been described. can get.
[0028]
【The invention's effect】
In short, according to the present invention, the following excellent effects are exhibited.
[0029]
It is possible to provide an AlGaInP light-emitting element epitaxial wafer and a light-emitting element from which a light-emitting element having a low forward voltage can be obtained.
[Brief description of the drawings]
FIG. 1 is a structural diagram showing an example of an epitaxial wafer for an AlGaInP light emitting element according to the present invention.
FIG. 2 is a light emission characteristic diagram of the light emitting device of the present invention.
FIG. 3 is a structural diagram of an epitaxial wafer for an AlGaInP light emitting diode having an emission wavelength of 590 nm.
4 is an explanatory diagram of a band structure in the vicinity of a heterointerface between a p-type GaP window layer and a p-type AlGaInP clad layer of the epitaxial wafer for AlGaInP-based light emitting diodes shown in FIG. 3;
[Explanation of symbols]
1 Substrate (n-type GaAs substrate)
2 n-type GaAs buffer layer 3 n-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 4 undoped (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P active layer (active layer)
5 p-type AlGaInP cladding layer (p-type cladding layer)
6 p-type GaP window layer 7 Intervening layer (forward voltage reduction layer)

Claims (4)

An n-type cladding layer made of at least an AlGaInP-based compound semiconductor and an undoped (Al _0.1 Ga _0.9 ) _0.5 In _{0.5 made of} an AlGaInP-based compound semiconductor having a smaller band gap energy than the n-type cladding layer on a conductive substrate. A P-type active layer, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer made of a p-type AlGaInP-based compound semiconductor having a larger band gap energy than the active layer, and a p-type GaP window layer made of GaP. in laminated AlGaInP-based light emitting device epitaxial wafer, between the p-type cladding layer and the p-type window layer, a band gap energy larger than the active layer, made of less material than the p-type cladding layer p provided type _{(Al 0.1 Ga 0.9) 0.5 In} 0.5 P intermediate layer AlGaInP-based light emitting device epitaxial wafer, characterized by being. 2. The epitaxial wafer for an AlGaInP-based light emitting device according to claim 1, wherein a carrier concentration of the p-type (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P intervening layer is 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less. . An n-type cladding layer made of at least an AlGaInP-based compound semiconductor and an undoped (Al _0.1 Ga _0.9 ) _0.5 In _{0.5 made of} an AlGaInP-based compound semiconductor having a smaller band gap energy than the n-type cladding layer on a conductive substrate. A P-type active layer, a p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer made of a p-type AlGaInP-based compound semiconductor having a larger band gap energy than the active layer, and a p-type GaP window layer made of GaP. In a light emitting device in which an electrode is provided on a stacked laminate, a band gap energy between the p-type cladding layer and the p-type window layer is larger than that of the active layer and smaller than that of the p-type cladding layer. JP that p-type _{(Al 0.1 Ga 0.9) 0.5 in} 0.5 P intermediate layer is provided comprising The light-emitting element to be. 4. The light emitting device according to claim 3, wherein the p-type (Al _0.1 Ga _0.9 ) _0.5 In _0.5 P intervening layer has a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ or more and 5 × 10 ¹⁸ cm ⁻³ or less.

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