JPH07105552B2 - Semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION [Outline] The characteristics of a semiconductor light emitting device are improved by growing a buffer layer of a strained superlattice having different lattice constants on a substrate and forming a semiconductor light emitting element on the buffer layer.

[Industrial application field]

The present invention relates to a semiconductor light emitting device such as a semiconductor laser, and more particularly to a semiconductor light emitting device having a semiconductor layer structure capable of improving its light emitting characteristics.

[Conventional technology]

As a semiconductor laser capable of oscillating a wavelength useful for optical communication, an InP-based semiconductor light emitting device is known.

FIG. 5 shows a cross-sectional structural view of a main part of an InP semiconductor laser as a typical conventional example. Using the InP substrate 41,
As shown in FIG. 5, the light emitting region is formed by the InGaAsP active layer 42,
Both sides are grown by burying with p-InP45 and n-InP46. 43 is p-InP clad layer, 44 is p-InGaAsP
It is a contact layer.

The semiconductor laser shown in FIG. 5 is composed of InGaAsP in the light emitting region.
The current is confined in the light emitting region by utilizing the fact that the built-in voltage of the pn junction of InP in the buried portion is higher than the built-in voltage of the pn junction of the active layer 42.

By the way, in the case of the 1.3 μm band laser used for optical communication, the band gap of In _0.75 Ga _0.25 As _0.55 P _0.45 , which is the light emitting region, is 0.95 eV, and the band gap of InP of the buried layer is 1.35 eV, and the difference is There was only about 0.4 eV, a sufficient built-in voltage was not obtained, and there was a leak current flowing through the InP pn junction.

On the other hand, in order to obtain a sufficient built-in voltage, it is necessary to use a material with a bandgap larger than InP.
It cannot be lattice matched with 1, which is impossible. And InP
The compound semiconductor with the largest bandgap lattice-matched on the substrate 41 is InP (1.35eV), and the compound semiconductor with the smallest bandgap is In _0.53 Ga _0.47 As (0.74
eV). Therefore, in the semiconductor laser using the InP substrate 41, InP is used for the cladding layer 43, and the carrier confinement efficiency cannot be improved any further. Further, in the conventional semiconductor light emitting device, when a visible light laser is constructed, an appropriate substrate cannot be obtained, which is difficult to realize.

As described above, conventionally, the characteristics of the obtained semiconductor laser are limited due to the lattice matching relationship with the substrate,
The desired semiconductor laser could not be obtained.

[Problems to be Solved by the Invention]

Therefore, the present invention is to provide a semiconductor light emitting device having a semiconductor layer structure in which a compound semiconductor having a large energy gap or a small energy gap, which is not lattice-matched to a substrate, can be used as an active layer or a clad layer. is there.

[Means for Solving the Problems]

That is, according to the present invention, on the semiconductor substrate (1), the first lattice constant larger than that of the semiconductor of the semiconductor substrate (1) is provided.
And a second semiconductor having a smaller semiconductor lattice constant than the semiconductor of the semiconductor substrate (1) are alternately laminated, and a buffer layer (2) of the strained superlattice is provided. The present invention provides a semiconductor light emitting device characterized by comprising layers (3, 4, 5) including a semiconductor active layer (4) thereon.

In particular, the present invention uses a strained superlattice layer composed of InGaAsP-based semiconductor layers having different lattice constants for the buffer layer (2), so that InGaP and InGaA having different lattice constants from the semiconductor substrate (1).
s, InGaAsP, GaAsP layers and other high-quality epitaxial crystals are deposited on the substrate to enable the use of a layer with a bandgap larger or smaller than the conventional operating layer as the operating layer, improving the characteristics of the semiconductor light emitting device. It is what makes me.

The structure of the present invention is as follows. That is, on the semiconductor substrate (1), a first InGaAsP-based semiconductor having a lattice constant larger than that of the semiconductor of the semiconductor substrate (1) and a second InGaAsP-based semiconductor having a lattice constant smaller than that of the semiconductor of the semiconductor substrate (1).
A buffer layer (2) of a strained superlattice formed by alternately stacking InGaAsP-based semiconductors is provided, and a layer (3,4,) including a semiconductor active layer (4) is provided on the buffer layer (2) of the strained superlattice. 5) is formed to have a structure as a semiconductor light emitting device.

Alternatively, the semiconductor substrate is an InP substrate (1),
In addition, In _1-x Ga _x As _1-y P, which has a larger lattice constant than InP
_y (0 ≦ x ≦ 1,0 ≦ y ≦ 1) and In _1-u Ga _u As _1-v P _v (0 ≦ u ≦ 1,0 ≦ v ≦ 1) having a smaller lattice constant than InP A strained superlattice buffer layer (2) is provided on which In _1-w Ga _w
P (0 <w <1) or In _1-z Ga _z As (0 <z <1) cladding layer (3,5) and In _1-a Ga _a As _1-b P _b (0 ≦ a ≦ 1 , 0
The semiconductor light emitting device has a structure including an active layer (4) composed of ≦ b ≦ 1) layers.

Alternatively, the semiconductor substrate is a GaAs substrate (11),
In addition, In _1-c Ga _c As _1-d P _{d has} a larger lattice constant than GaAs.
Strain consisting of (0 ≦ c ≦ 1,0 ≦ d ≦ 1) and In _1-e Ga _e As _1-f P _f (0 ≦ e ≦ 1,0 ≦ f ≦ 1) having a smaller lattice constant than GaAs. It has a superlattice buffer layer (12) on which Ga _1-g As _g
P (0 <g <1) or In _1-h Ga _h P (0 <h <1) cladding layer (13,15) and In _1-i Ga _i As _1-j P _j (0 ≦ i ≦ 1 , 0
The semiconductor light emitting device has a structure including an active layer (14) composed of ≦ j ≦ 1) layers.

[Action]

For example, when a strained superlattice buffer layer (2) of InGaAsP layers having different lattice constants is formed on an InP substrate (1), that is, an InGaAsP thin film of a first composition having a larger lattice constant than InP and a lattice constant more than InP. When the InGaAsP thin films of the second composition having a small value are alternately stacked, the strain is relaxed by arranging the atoms so that the strain due to the mismatch of the lattice constants of each layer is relaxed. Then, a semiconductor layer (3,4,5) having a lattice constant different from that of the semiconductor substrate (1) on the strained superlattice
It is possible to prevent the occurrence of defects due to mismatch when growing the.

Embodiments of the present invention will be described below with reference to the drawings.

〔Example〕

As described above, the InGaAsP-based semiconductor laser using the conventional InP substrate 41 is, for example, 0.4 eV between the InGaAsP active layer 42 and the InP clad layer 43 in the case of a laser having a wavelength of 1.3 μm.
Only the energy gap is different. Therefore, the effect of confining carriers is not always sufficient, and some improvement is required to manufacture a high-power laser.

Therefore, in the present invention, as shown in FIG. 1, on the n-InP substrate 1, In _0.4 Ga _0.6 As (thickness ˜100 Å) and In _0.6 Ga
_The strained superlattice buffer layer 2 consisting of two types of crystals of _0.4 As (thickness ~ 100Å) is MBE (Molecular Beam Epitaxy)
Alternatively, it is grown using MOCVD (metal organic chemical vapor deposition). The total thickness of the buffer layer 2 of the strained superlattice is 0.5 to 1 μm.
m. An n-In _0.84 Ga _0.16 P clad layer 3 is grown thereon, and an In _0.4 Ga _0.6 As active layer 4 and a p-In _0.84 Ga _0.16 P clad layer 5 are deposited. The active layer 4 of this composition has a wavelength of 1.3.
Emit light of μm. By using the strained superlattice buffer layer 2, a high-quality In having a lattice constant different from that of the InP substrate 1 is used.
_{The 0.84} Ga _0.16 P layer (3,5) and the In _0.4 Ga _0.6 As layer 4 could be grown.

FIG. 2 shows a quaternary diagram of an InGaAsP-based semiconductor for explaining an embodiment of the present invention. The above embodiment will be explained by using this, and the strained superlattice of this embodiment is lattice-matched to InP. In _0.4 Ga _0.6 As (black triangle) with a larger proportion of Ga and In _0.6 Ga _0.4 As (white triangle) with a smaller proportion of Ga than the InGaAs composition on the equi-lattice constant line marked with a circle (black circle). ) And are alternately grown. Then, a clad layer 3 made of In _0.84 Ga _0.16 P (black square) on the _equilattice constant line (x) of In _0.4 Ga _0.6 As (black triangle) with a large Ga ratio on this strained superlattice Can be grown with good crystallinity.
As is clear from FIG. 2, the band gap of In _0.84 Ga _0.16 P is about 1.55 eV, which is larger than 1.35 eV of InP of InP substrate 1. Then, as shown in FIG. 1, an In _0.4 Ga _0.6 As active layer 4 lattice-matched to the n-In _0.84 Ga _0.16 P clad layer 3 having a large band gap and an upper p-In _0.84 Ga _0.16 P layer are formed on the upper layer.
The clad layer 5 is grown. Then, as shown in FIG. 1B, a laser stripe is formed by etching, and both sides thereof are filled with 6 p-In _0.84 Ga _0.16 P and 7 n-In _0.84 Ga _0.16 P to obtain The semiconductor laser structure is completed. After that, as usual, the n-side electrode and the p-side electrode (not shown) are connected to the n-InP substrate 1 side and the pI of 5 respectively.
n _0.84 Ga _0.16 P Formed on the clad layer.

By adopting such a structure, the energy gap difference between the In _0.4 Ga _0.6 As active layer 4 and the p-In _0.84 Ga _0.16 P cladding layer 5 and the InGaP layers 6 and 7 can be increased to about 0.5 eV. It is possible (see the equal band gap line in FIG. 2), and the current confinement effect can be made larger than in the conventional case.

As a result, the semiconductor laser of the present example was capable of producing a high output of 100 mW, which is larger than the output of 30 mW of the conventional laser with the same bias of 1.3 V as that of the conventional semiconductor laser.

The present invention is not limited to the above-described embodiment, and various configurations are possible. For example, a laser using GaAsP as an active layer is promising as a visible laser, but there is a problem that there is no suitable substrate. Applying the present invention to this, 4 in FIG.
As shown in the original diagram, using a GaAs substrate, In _0.48 Ga _0.52 P (black _circle ) on the GaAs isolattice constant line (white _circle )
In _0.25 Ga _0.75 P (black triangle) with a larger lattice constant,
Lattice constant is small In _0.75 Ga _0.25 P and (open triangle) laminating a strained superlattice grown alternately, the In _0.48 thereon
In _0.25 Ga _0.75 P with larger lattice constant than Ga _0.52 P (black circle)
GaAs in the clad layer and active layer lattice-matched to (black triangle)
By growing _0.6 P _0.4 and the upper cladding layer, a laser using GaAs _0.6 P _0.4 as an active layer can be realized. According to this embodiment, it is possible to form a good quality crystal having no miscibility gap on a GaAs substrate by MBE or MOCVD. FIG. 4 shows the layer structure of the semiconductor laser of this embodiment. 11 is a GaAs substrate, 12 is a strained superlattice buffer layer, 13 is an n-In _0.25 Ga _0.75 P cladding layer, and 14 is GaAs _0.6 P. _{The 0.4} active layer and 15 are P-In _0.25 Ga _0.75 P clad layers, and a semiconductor laser with an oscillation wavelength of 0.65 μm can be obtained.

〔The invention's effect〕

As described above, according to the present invention, it is possible to obtain a semiconductor light emitting device using a semiconductor having a large bandgap or a semiconductor having a small bandgap, which originally does not lattice match with a substrate, in an operation layer. It is possible to obtain an element having no characteristic.

[Brief description of drawings]

1A is a sectional view showing a layer structure of a semiconductor light emitting device according to a first embodiment of the present invention, and FIG. 1B is a schematic sectional structure view of a semiconductor light emitting device according to a first embodiment of the present invention. FIG. 2 shows the relationship between the composition, lattice constant, and band gap of the InGaAsP-based semiconductor for explaining the embodiment of the present invention.
The original diagram, FIG. 3 shows InGaAsP for explaining another embodiment of the present invention.
A quaternary diagram showing the relationship between the composition, lattice constant and bandgap of the system semiconductor, FIG. 4 is a diagram showing the semiconductor layer structure of another embodiment of the present invention, and FIG. 5 is a conventional InP semiconductor laser. It is a principal part sectional structural drawing. 1 …… n-InP substrate 2 …… strained superlattice buffer layer 3 …… n-In _0.84 Ga _0.16 P cladding layer 4 …… In _0.4 Ga _0.6 As active layer 5 …… p-In _0.84 Ga _0.16 P Cladding layer 6 …… p-InGaP 7 …… n-InGaP 11 …… GaAs substrate 12 …… In _0.25 Ga _0.75 P and In _0.75 Ga _0.25 P strain buffer layer 13 …… n-In _0.25 Ga _0.75 P clad layer 14 …… GaAs _0.6 P _0.4 active layer 15 …… p-In _0.25 Ga _0.75 P clad layer 41 …… n-InP substrate 42 …… InGaAsP active layer 43 …… p-InP clad layer 44 …… p- InGaAsP contact layer 45 …… p-InP 46 …… n-InP

Claims (3)

[Claims] 1. A first InGaAsP-based semiconductor having a lattice constant larger than a lattice constant of a semiconductor of the semiconductor substrate and a second lattice smaller than a lattice constant of a semiconductor of the semiconductor substrate on a semiconductor substrate.
A semiconductor light emitting device comprising: a buffer layer of a strained superlattice formed by alternately laminating InGaAsP-based semiconductors; and a layer including a semiconductor active layer formed on the buffer layer of the strained superlattice. . 2. The semiconductor substrate is an InP substrate, on which In _1-x Ga _x As _1-y P _y (0 ≦ x) having a larger lattice constant than InP.
≦ 1,0 ≦ y ≦ 1) and In _1-u G with a lattice constant smaller than InP
A buffer layer of a strained superlattice made of a _u As _1-v P _v (0 ≦ u ≦ 1,0 ≦ v ≦ 1) is provided, and In _1-w Ga _w P (0 <w <1) is provided thereon.
Or In _1-z Ga _z As (0 <z <1) cladding layer and In
The semiconductor light emitting device according to claim 1, further comprising an active layer formed of _{a 1-a} Ga _a As _1-b P _b (0≤a≤1,0≤b≤1) layer. 3. The semiconductor substrate is a GaAs substrate, on which In _1-c Ga _c As _1-d P _d (0 ≦, which has a larger lattice constant than GaAs.
c ≦ 1,0 ≦ d ≦ 1), and In having a smaller lattice constant than GaAs
_1-e Ga _e As _1-f P _f (0 ≤ e ≤ 1, 0 ≤ f ≤ 1) is provided with a strained superlattice buffer layer, and Ga _1-g As _g P (0 <g <
1) or an In _1-h Ga _h P (0 <h <1) clad layer and an In _1-i Ga _i As _1-j P _j (0 ≦ i ≦ 1,0 ≦ j ≦ 1) layer The semiconductor light emitting device according to claim 1, further comprising a layer.