JPH04152583A - Distorted quantum well semiconductor laser - Google Patents

Abstract

PURPOSE:To simultaneously utilize the quantum size effect and the distortion effect by having an active layer with at least one distorted quantum well layer, a special relationship between the lattice constant of this distorted quantum well layer and the semiconductor substrate, and the distorted quantum well layer formed by four-section mixed crystals. CONSTITUTION:The MOCVD method is used to grow in order a distorted quantum well active layer 2 and a p-InP layer 3 on an n-InP substrate 1. This distorted quantum well layer 2 has a thickness of 4nm or larger and a 4-section structure that consists of a 5-7nm In0.9Ga0.1As0.7P0.3 distorted quantum well active layer 2a (distortion amount +1.8%) and a non-distorted InGaAs barrier layer 2b. After that, in order to keep the active layer width at about 1mum, a reverse mesa-shaped mesa stripe is formed, this is filled by a p-InP layer 4 and an n-InP layer 5 to create a BH structure, and a p electrode 6 and an n electrode 7 are formed. A relationship of (aw-as)/as>=0.8% is established between the distorted quantum well layer 2 lattice constant aw and the semiconductor substrate 1 lattice constant as.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser for optical fiber communication, and particularly to a semiconductor laser for use in post-10 Gbit/s ultra-high-speed optical communication or coherent multiplex optical communication. It is.

[Conventional technology]

Strained quantum well semiconductor lasers are attracting attention as a successor to multiple quantum well (MQW) lasers from the perspective of semiconductor lasers for next-generation optical communication applications. Especially wavelength 1.5~1.6μm
The strained quantum well of the conventional strained quantum well laser is InG.
It was formed of aAs ternary mixed crystal. For example, Electronics Letters, Vol. 26, pp. 465-467 (1990)
l, 26. P, 465-467 (1990)).

[Problem to be solved by the invention]

However, in the above conventional technology, the strained quantum well layer is formed of InGaAs with a film thickness of 2.5 nm, and the strain amount is +
1.53%, and the biggest problem with this structure was that the strained quantum well layer was too thin, reducing the quantum size effect.

The above problem will be further explained using FIG. 7.

The figure shows the calculated value of the quantum well film thickness dependence of the square root of the differential gain, which is an index of the quantum size effect. As the quantum well film thickness decreases, the differential gain increases, but reaches a maximum value between 5 and 7 nm, and rapidly decreases below 4 nm. This is because if the quantum well layer is too thin, the wave function of electrons leaks into the Kana River layer.

This is because the confinement of electrons in the quantum well layer becomes worse.

Therefore, in the conventional technology described above, the strain effect is exhibited as shown in Figure 8, reflecting the strain amount of about 1.55, but since the quantum well layer film thickness is thin at 2.5 nm, it is difficult to fully bring out the quantum size effect. I can't.

The above problem arises because the strained quantum well is made of InGaAs, so one emission wavelength is used for optical fiber communication.
This is due to the fact that a thin quantum well layer had to be used in order to achieve a thickness of 5 to 1.6 μm.

In other words, InGa with a strain amount of +1% or more that produces a sufficient strain effect.
In the As ternary mixed crystal, when the quantum well film thickness is set to 5 to 7 nm to produce sufficient quantum effects, the emission wavelength is 1.7 nm.
Therefore, with the conventional technology, it was impossible to realize a strained quantum well laser having both a quantum effect and a strain effect.

An object of the present invention is to provide a strained quantum well semiconductor laser that can exhibit both a quantum size effect and a strain effect.

[Means to solve the problem]

In order to achieve the above object, the present inventors have developed an InGaA
I has a wider forbidden band width than s, that is, one emission wavelength shorter than I.
We have found that it is extremely effective to introduce nGaAsP or InGaA (lAs) quaternary mixed crystal into the strained quantum well layer.
The amount of strain in the GaAsP or InGaA Q As quaternary mixed crystal strained quantum valve layer must be set to at least +0.8%, as shown in the dependence of the square root of the differential gain on the amount of strain in Figure 8. , +0.8% or more, the increase in differential gain due to the distortion effect appears significantly. Furthermore, in order to fully bring out the quantum size effect, the thickness of the strained quantum well layer should be at least 4 nm or more, preferably 5 nm or more.
Set to 7nm.

[Effect]

With the above configuration, light is emitted at a wavelength of 1.5 to 1.6 μm,
In addition, a strained quantum well semiconductor laser having a strain amount of +0.8% or more and a strained quantum well layer having a thickness of 4 nm or more, or 5 to 7 nm could be manufactured. This means that the forbidden band width is larger than that of InGaAs4.
Original mixed crystal (InGaAsP.

Since the material itself has a shorter emission wavelength than InGaAs, it is possible to achieve an emission wavelength of 1.5 to 1.6 μm in a somewhat thick (5 to 7 nm) strained quantum well layer. It became.

The scope of application of InGaAsP and InGaA QAs quaternary mixed crystals to the strained quantum well layer in the present invention is explained in the fourth section.
This is shown in the quaternary mixed crystal phase diagram shown in FIG. First, for In, -xGaxAs, -yPy, O<x<0.2
5,0.15゜y<0.55, and (A Q v
Gal-V) V>0.2, 0.2 for WIn1-wAs
The range of <W<0.4 is the quaternary composition of the present invention.

As described above, a strained quantum well semiconductor laser that has both quantum size effect and strain effect was realized.

Furthermore, modulation doping (P or n-type) to this strained quantum well is extremely effective, and we succeeded in simultaneously bringing out the three effects of strain effect, quantum size effect, and modulation doping effect.

〔Example〕

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

Example 1 FIG. 1 is a sectional view of a strained quantum well semiconductor laser according to the present invention. A strained quantum well active layer 2 and a p-InP layer 3 were successively grown on an n-InP substrate 1 by MOCVD. Here, the strained quantum well active layer 2 consists of a strained quantum well layer 2a (strain amount +1.8%) and a film thickness of 15 nm. strain-free InGaAsP barrier layer 2b (15-1.32 m)
It has a four-periodic structure.

Thereafter, an inverted mesa-like mesa stripe is formed so that the active layer width is about 1 μm, and the p-InP layer 4 and the n-InP layer 4 are
It was filled with a P layer 5 to form a BH structure. Furthermore, the p-electrode 6.
An n-electrode 7 was formed to provide a resonator with a length of about 300 μm.

The prototype device oscillated with an extremely small threshold current of approximately 2 mA, reflecting sufficient strain effects and quantum size effects, and exhibited an extremely high relaxation oscillation frequency of 30 GHz when the optical output was 10 mW.

Embodiment 2 Another embodiment of the present invention is shown in the cross-sectional view of FIG.
This will be explained using the cross-sectional view of Figure (b) (line AA' in (a)). n-In with periodic 240 nm diffraction grating 8
On the P substrate 1, n-InGsAsP (unstrained, 18~1
．． 2 μm) light guide layer, 5.5 nm thick In, -9
2GaD-asAso +5SPD +3S strained quantum well layer (strain amount: +1.5%) and InGaAs with a film thickness of 10 nm
A strained quantum well active layer 2 and a p-InP layer 3 consisting of a 2-10 periodic structure of a P barrier layer (unstrained, λt~1.25 μm) were grown in sequence by gas source MBE.

Next, after forming a reverse mesa stripe with a width of 1 μm in the active layer, F
An e-doped InP layer (film thickness ~4 μm) 10 was buried and grown by MOCVD. Finally, p electrode 6. After forming the n-electrode 7, the resonator length was about 200 μm.

The prototype device oscillated at approximately 1.5 mA and obtained a single spectrum with a width mode suppression ratio of 40 dB or more at a wavelength of 1.55 μm, reflecting the DFB structure using the diffraction grating. In addition, reflecting sufficient quantum effects and strain effects, the relaxation oscillation frequency at an optical output of 10 mW is approximately 30 GHz, and the Fe-doped InP
Reflecting the low capacity structure due to embedding, the 300bi
Ultra high speed operation of t/s is now possible. Also, at that time 2
The chirping amount for 0 dB down was approximately 2 people, which is an order of magnitude lower than the conventional value. Furthermore, the spectral linewidth at an optical output of 20 mW was extremely small at 50 kHz.

Example 3 FIG. 3 shows another example according to the present invention, in which InGaA
It uses QAs and is further subjected to modulation doping. A film with a thickness of 4 to 7 nm (A Q0.
, Gaw, s). , 3 I naw7A S strained quantum well layer 11a (strain amount: +1.2%) and InGaA Q As barrier layer 11b with a film thickness of 20 nm (unstrained, λg=1
．． Modulation doped strained quantum well active layer 11 consisting of a 2 to 8 periodic structure of 2 μm), p - I n P cladding layer 3, n -
InP layers 12 were grown sequentially by MOCVD. At this time, either Mg or Be is added to the barrier layer by 2
10"an-3 doping. After this, S i O2
A film 13 is formed, a 5in2 layer is selectively removed, a Zn diffusion region 14 is provided, and a p-electrode 6. A gain waveguide stripe type was used in which an n-electrode 7 was formed.

In the prototype device, effects that simultaneously reflected the three factors of the strain element, quantum size effect, and modulation doping effect were remarkable, and the relaxation oscillation frequency showed a large value of 50 GHz at an optical output of 10 mW.

Embodiment 4 FIG. 6 is a schematic diagram of an embodiment in which the strained quantum well semiconductor laser of the present invention is applied to optical communication. A pie-eye power source 15 and a signal source 17 are connected to the strained quantum well semiconductor laser 15, and the laser beam is modulated by these. The laser beam 22 passes through an optical fiber 18, and the emitted light 19 is sent to a photodetector 20.
The signal is converted into an electrical signal and processed by the decoder 21.

In this example, the speed is 400 bit/s, and the fiber length is 40
km [Effects of the Invention] According to the present invention, the strain effect and quantum size effect of a strained quantum well semiconductor laser can be simultaneously brought out, and the semiconductor laser can be made to operate at an ultra-high speed. It had great effects as a light source for optical communications.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views of laser devices according to embodiments of the present invention, FIGS. 4 and 5 are diagrams showing compositional regions of quaternary mixed crystal strained quantum valve layers according to the present invention, and FIG. is a schematic diagram of an embodiment of the optical communication system of the present invention, and FIGS. 7 and 8 are characteristic diagrams explaining the present invention in detail. 2...Strained quantum well active layer, 8...Diffraction grating, 11.
... Hendaiku No. 1 construction map 1-χ crkuχ A, 5l-y

Claims (1)

[Claims] 1. A semiconductor laser having at least an active layer that generates light and a cladding layer that confines light on a semiconductor substrate, wherein the active layer has at least one strained quantum well layer;
Between the lattice constant a_w of the strained quantum well layer and the lattice constant a_s of the semiconductor substrate, (a_w-a_s)/a_s≧0.
．． A strained quantum well semiconductor laser having a relationship of 8% and having a strained quantum well layer formed of a quaternary mixed crystal. 2. The strained quantum well semiconductor laser according to claim 1, wherein the emission wavelength is within a range of 1.5 to 1.6 μm. 3. In a semiconductor laser having at least an active layer that generates light and a cladding layer that confines light on a semiconductor substrate, the active layer emits light in the wavelength range of 1.5 to 1.6 μm, and the active layer has at least one strain quantum layer. The lattice constant a_w of the strained quantum well layer consisting of wells and the lattice constant a_s of the semiconductor substrate
A strained quantum well semiconductor laser characterized in that there is a relationship of (a_w−a_s)/a_s≧0.8%, and the film thickness of the strained quantum well layer is 4 nm or more. 4. The strained quantum well semiconductor laser according to claim 3, wherein the strained quantum well layer has a thickness in a range of 5 to 7 nm. 5. The laser according to claims 1 to 4, wherein the barrier layer adjacent to the strained quantum well layer has a thickness of 1×10^1^0 cm^-
A strained quantum well semiconductor laser characterized by having a region doped with conductivity type impurities at a density of ^3 or more. 6. In the laser according to claims 1 to 5, the resonator for returning light has a reflecting surface made of a cleavage plane, or is formed on a light guide layer adjacent to at least one side above and below the active layer. A strained quantum well semiconductor laser characterized by having a diffraction grating. 7. A strained quantum well semiconductor laser according to claim 1, wherein the semiconductor substrate is made of InP and the strained quantum well layer is made of InGaAsP or InGaAlAs. 8. The quaternary composition of InGaAsP according to claim 7 is
When _1_-_xGa_xAs_1_-_yP_y, x and y are 0<x<0.25, 0.15<y<0.5
A strained quantum well semiconductor laser characterized by satisfying the following range. 9. The quaternary composition of InGaAlAs according to claim 7 is (A
1. A strained quantum well semiconductor laser characterized in that V and W satisfy the range of V>0.2 and 0.2<W0.4 when 1_VGa_1_-_V)_WIn_1_-_WAs. 10. A strained quantum well semiconductor laser according to any one of claims 1 to 9, means for inputting an electric signal to the strained quantum well semiconductor laser, and means for transmitting laser light from the strained quantum well semiconductor laser. and a receiving section that receives the laser beam.