JPH05218591A - Semiconductor laser element and semiconductor photo detector - Google Patents

Abstract

PURPOSE:To provide a 1.5mum band InGaAs/InAlAs quantum well semiconductor laser element having a low oscillation threshold current density, and a 1.5mum band semiconductor photo detector having high-sensitivity and a large SN ratio. CONSTITUTION:Concerning a semiconductor laser element having an activated layer 14 composed of an InAlAs barrier layer and an InGaAs quantum well layer formed on an InP substrate 11, the surface azimuth of the InP substrate 11 is a (111) B surface or a tilted (111) B surface in the (100) direction or (110) direction by at most 10 degrees. And concerning a semiconductor photo detector having a carrier multiplication layer and an InGaAs photo absorption layer formed in order on an InP substrate 11, the surface azimuth of the InP substrate 11 is the (111) B surface or a tilted (111) B surface in the (100) direction or in the (110) direction by at most 10 degrees.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device which emits light in the 1.5 .mu.m band and a semiconductor light receiving device having a light receiving sensitivity in the same wavelength range.

[0002]

2. Description of the Related Art A quartz optical fiber used for long-distance optical communication has a minimum loss at a wavelength of 1.55 μm. Therefore,
A high-performance semiconductor laser device that emits light in the 1.5 μm band,
A semiconductor light receiving element having high sensitivity in the same wavelength range is required. Conventionally, a quantum well semiconductor laser device in the 1.3 to 1.5 μm band has been manufactured by laminating InGaAsP-based materials that are lattice-matched on an InP substrate by MOCVD. Recently, InGa containing no P by the MBE method
Development of a semiconductor laser device in this wavelength band is actively carried out using an As / InAlAs-based material. The reason is that in this semiconductor laser device, InGaAsP
Well layer / InGaAsP barrier layer system quantum well (1.3 μm
Band) and the InGaAsP well layer / InGaAsP barrier layer system quantum well (1.5 μm band), the conduction band discontinuity ΔE _{c in the} energy band is larger, so a semiconductor laser device with a low oscillation threshold can be obtained. Because there is a nature. On the other hand, as a conventional 1.5 μm band semiconductor light receiving element, Ge or InGa in which the light absorption layer is p-type doped is used.
A photodiode is used that uses an As system to generate electrons by absorbing light and take out a photocurrent through a pn junction. The Ge layer is formed on the Ge substrate by InGaA.
The s-based layer is formed on the InP substrate that is lattice-matched. Recently, when high speed and large capacity are required for optical communication, a reverse bias voltage is applied to a non-doped layer provided between pn junctions.
Carriers are amplified by an avalanche phenomenon, and an avalanche photodiode (APD) having an improved SN ratio has come to be used. Particularly in the InGaAs system, a superlattice of InGaAs and InAlAs is introduced into this non-doped layer, and the fact that the conduction band discontinuity ΔE _c in the energy band is larger than that in the valence band is used to multiply only the electrons. Therefore, research on a superlattice avalanche photodiode having an improved SN ratio has been actively conducted. The above-mentioned semiconductor laser device and semiconductor light-receiving device are formed on the (100) plane where crystals easily grow.

[0003]

However, the above-mentioned semiconductor laser device and semiconductor light-receiving device have the following problems, respectively. That is, 1) In the InGaAs / InAlAs-based quantum well semiconductor laser device, it was difficult to epitaxially grow an InAlAs layer having high optical quality. Therefore, the oscillation threshold current density is about 0.8 to 2.4 KA / cm ² , which is higher than that of the InGaAsP system and has not reached the expected low value. 2) In the APD using Ge as the light absorption layer, a large SN ratio cannot be obtained because the multiplication ratio of electrons and holes is small. In the InGaAs system, the multiplication ratio of electrons and holes is increased to about 20 due to the superlattice.
Since the light absorption layer has low sensitivity, few electron-hole pairs are generated. Therefore, in long-distance optical communication, not only a semiconductor laser device with high emission intensity is required and many repeaters are required, but also shot noise caused by fluctuations in the amount of electron-hole pairs generated is large. There was a problem of becoming.

[0004]

SUMMARY OF THE INVENTION The present invention provides a semiconductor laser device and a semiconductor light receiving device that solve the above problems. An InAlAs barrier layer and an In layer are formed on an InP substrate.
In a semiconductor laser device having an active layer formed of a GaAs quantum well layer, the plane orientation of the InP substrate is (111) B.
Plane, or (111) B plane is (100) direction or (1
In the semiconductor photodetector in which the carrier multiplication layer and the InGaAs light absorption layer are sequentially formed on the InP substrate, the semiconductor laser device having the plane orientation tilted at most 10 ° in the 10) direction is the plane orientation of the InP substrate. Is the (111) B plane, or the (111) B plane is the (100) direction or (110)
A second aspect of the present invention is a semiconductor light receiving element having a plane orientation inclined by at most 10 ° in the direction.

[0005]

In the present invention, InAlAs and In are formed on the InP substrate.
This is based on the following new experimental facts regarding the case of forming a quantum well made of GaAs. That is, the photoluminescence (PL) intensity and InP of this quantum well
Examining the relationship between the substrate plane orientations, the plane orientation in which the (111) B plane or the (111) B plane is tilted at most 10 ° in the (100) direction or the (110) direction as compared with the (100) substrate plane orientation Then, the PL intensity becomes extremely large. The reason for this is that the quantum wells of the (111) B-plane and the plane orientation near the (111) B-plane have a smaller effective in-plane effective mass than the (100) -plane quantum well, so that the energy consumption is easier than that of the (100) -plane quantum well. It is considered that this is because the band can be filled with carriers to obtain a gain. Therefore, when a quantum well made of InAlAs and InGaAs is formed as an active layer on these plane orientations, it can be expected that the oscillation threshold current density is lowered. InAl on these plane orientations
When a quantum well made of As and InGaAs is formed as a light absorption layer, many electron-hole pairs are generated and the light receiving sensitivity becomes high. It should be noted that In _X Ga _1-X A constituting the active layer, the light absorption layer, and the carrier multiplication layer, which are the quantum well layers, are formed.
It is desirable that the composition of s be 0.3 ≦ X ≦ 0.7.
The reason is that on the InP substrate, In _X Ga _1-X As is X =
This is because it becomes more difficult to perform epitaxial growth without introducing dislocations as the lattice matching with the substrate becomes 0.53 and the deviation from this composition increases. In particular, when X <0.3 and X> 0.7, the film thickness (critical film thickness) that can be epitaxially grown without dislocations is about several tens of liters, which makes it difficult to manufacture a superlattice.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. The present invention is based on the following experimental facts. FIG. 3 shows InGa formed on an InP substrate.
4 shows the relationship between the PL intensity of an As / InAlAs-based quantum well and the substrate surface orientation. The sample used has the structure shown in FIG. 4 and was manufactured as follows. That is, M
InP substrate 1 having (100) plane orientation and (111) B plane orientation tilted by 2 ° in the (100) direction by BE method
Was attached to a molybdenum block (not shown), and crystal growth was simultaneously performed thereon. First, the surface oxide film is removed by a normal preheating process, and then a 0.7 μm InAlAs buffer layer 2 is laminated, and then 200 μm.
Å In _0.52 Al _0.48 As barrier layer 3 is sandwiched between 10, 2
In _0.53 Ga _0.47 As with thickness of 0, 30, 50, 80 Å
The quantum well layers 4 were sequentially stacked. For these samples,
The result of measuring the PL intensity at 77K is shown in FIG. The respective emission peak wavelengths are 80,
It corresponds to light emission from the quantum well layer 4 having a thickness of 50, 30, and 20Å, and then corresponds to the In _0.52 Al _0.48 As barrier layer 3 and the InP substrate 1. Comparing the emission peak intensities, for example, in the quantum well layer 4 of 80 Å, (11
1) The intensity of the B2 ° off face is about 8 times stronger than that of the (100) face, and the intensity of other emission peaks is also stronger for the (111) B2 ° off face than the (100) face. The following examples are based on new findings from the above experimental facts. Example 1. FIG. 1 is a sectional view of an embodiment of a semiconductor laser device according to the present invention. In the figure, 11 is an n-InP substrate,
12 is a 1.5 μm thick n-In _0.52 Al _0.48 As cladding layer (Si-doped: 1 × 10 ¹⁸ cm ⁻³ ), 13 and 15
Is a 500 Å-thick undoped In _0.5 (Ga _Y A
The GRIN-SCH layer made of 1 _1-Y ) _0.5 As, 14 is In _X Ga _1-X As (0.3 ≦ X) having a thickness of 10 to 200 Å.
≦ 0.7) Quantum well layer and In _0.52 with a thickness of 30 to 200 Å
An active layer composed of multiple quantum well layers made of Al _0.48 As barrier layer, and 16 is p-In _0.52 Al having a thickness of 1.5 μm.
_0.48 As clad layer (Be-doped: 1 × 10 ¹⁸ c
m ^-3 ), 17 is p-In _0.53 Ga _0.47 having a thickness of 0.5 μm.
As cap layer (Be-doped: 1 × 10 ¹⁷ cm ⁻³ ), 1
8 is an ohmic electrode. The plane orientation of the n-InP substrate 11 was the (111) B plane which was off by 2 ° in the (100) direction. p-InGaAs cap layer 17 and InAlA
The s clad layers 12 and 16 are lattice-matched with the InP substrate 11 within 0.1%. The oscillation threshold current density of the semiconductor laser device thus obtained is 1.0 kA / cm ² on the (100) substrate surface.
0.5 kA / cm ^{2 on} (111) B2 ° off-plane
And improved. The present invention is not limited to the above embodiment, and the plane orientation of the (111) B substrate may be off by at most 10 ° in the (100) direction or the (110) direction. Further, the device structure is not limited to a broad contact, and may be one having a current constriction due to an oxide stripe or a buried type. Further, the active layer is not limited to having a composition that is lattice-matched with the InP substrate, but may be strained, the number of InGaAs well layers may be 1 to 15, and the optical confinement layer may be only the GRIN layer. Without I
SCH layer made of nGaAlAs and InGaAs / In
An AlAs superlattice SCH layer may be used. Example 2. FIG. 2 is a sectional view of an embodiment of the semiconductor light receiving element according to the present invention. In the figure, 21 is S-doped n-InP
A substrate, 22 is a Si-doped n-InGaAs layer, 23 is an electron multiplication layer made of non-doped InGaAs / InAlAs superlattice, 24 is a Be-doped p-InGaAs light absorption layer, 25 is an n-electrode, and 26 is a p-electrode. Si-doped n
The plane direction of the -InP substrate 21 was the (111) B plane which was off by 2 ° in the (100) direction. The present invention is not limited to the above embodiment, and the plane orientation of the (111) B substrate may be off by at most 10 ° in the (100) direction or the (110) direction, and the electron multiplication layer is super A non-doped InGaAs layer may be used instead of the lattice, or may be omitted.

[0007]

As described above, according to the present invention, I
In a semiconductor laser device in which an active layer composed of an InAlAs barrier layer and an InGaAs quantum well layer is formed on an nP substrate, the plane orientation of the InP substrate is the (111) B plane, or the (111) B plane is the (100) direction or ( Since the plane orientation is tilted at most 10 ° in the 110) direction, there is an excellent effect that the oscillation threshold current density is lowered. Also, In
In a semiconductor light receiving element in which a carrier multiplication layer and an InGaAs light absorption layer are sequentially formed on a P substrate, the plane direction of the InP substrate is (111) B plane or (111) B plane is (10).
Since the plane orientation is tilted at most 10 ° in the 0) direction or the (110) direction, there is an excellent effect that the light receiving sensitivity and the SN ratio are improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of a semiconductor laser device according to the present invention.

FIG. 2 is a sectional view of an embodiment of a semiconductor light receiving element according to the present invention.

FIG. 3 is a diagram showing experimental results on the relationship between PL intensity and substrate surface orientation.

FIG. 4 is a cross-sectional view of a sample used in the above experiment.

[Explanation of symbols]

1, 11, 21 Substrate 2 Buffer layer 3 Barrier layer 4 Quantum well layer 12, 16 Cladding layer 13, 15 GIN layer 14 Active layer 17 Cap layer 18, 25, 26 Electrode 22 Si-doped n-InGaAs
Layer 23 Electron multiplication layer 24 Light absorption layer

Claims (4)

[Claims] 1. In a semiconductor laser device in which an active layer including an InAlAs barrier layer and an InGaAs quantum well layer is formed on an InP substrate, the plane direction of the InP substrate is (11).
1) A semiconductor laser device characterized in that the B plane or the (111) B plane has a plane orientation inclined at most 10 ° in the (100) direction or the (110) direction. 2. A carrier multiplication layer, In, on an InP substrate.
In a semiconductor light receiving device in which a GaAs light absorption layer is sequentially formed, the plane orientation of the InP substrate is (111) B plane or (1)
11) A semiconductor light-receiving element characterized in that the plane B has a plane orientation inclined by at most 10 ° in the (100) direction or the (110) direction. 3. The InGaAs quantum well layer is In _x Ga.
_2. The semiconductor laser device according to claim _{1, which is made of 1-X} As (0.3≤X≤0.7). 4. The InGaAs light absorbing layer is made of In _X Ga _{1 -X.}
As (0.3 ≦ X ≦ 0.7), and the carrier multiplication layer is composed of In _Y Ga _{1 -Y} As (0.3 ≦ Y ≦ 0.7) and In _Z.
3. The semiconductor light receiving element according to claim 2, comprising a superlattice made of Al1 _- ZAs (0.3≤Z≤0.7).