JPH07135370A - Strained quantum well semiconductor laser and its fabrication - Google Patents

Abstract

PURPOSE:To provide a stained quantum well semiconductor laser in which high optical output characteristics are realized by fabricating a strained quantum well using a mixed crystal containing Al or an InAsP mixed crystal. CONSTITUTION:A first waveguide layer 2, a multiple quantum well 5 comprising a strained well layer 3 and a barrier layer 4, and a second optical guide layer 6 are grown on a semiconductor single crystal substrate 1. An AlInGaAsP mixed crystal or an InAsP mixed crystal is employed in the strained well layer in order to inhibit relaxing of strain due to ordering and to increase the discontinuity of conductive band thus realizing high optical output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a strained quantum well capable of effectively confining strain in a well layer of a strained quantum well by using, for example, AlGaInAs as a mixed crystal containing Al which hardly causes ordering. The present invention relates to a semiconductor laser and a manufacturing method thereof.

[0002]

2. Description of the Related Art The structure of a conventional strained quantum well is shown in FIG. 3 (Temkin et al., Journal of Crystal Growth J. Cryst. Growth, 93,
353 (1988)). 1 is an InP single crystal substrate, 2 is a first optical waveguide layer, 3 is a strain well layer, 4 is a barrier layer, 5 is a multiple quantum well consisting of the strain well layer 3 and the barrier layer 4, and 6 is a second optical waveguide Layer, 10 is an active layer region composed of multiple quantum wells 6 and two optical waveguide layers 2 and 6, 7 is a current confinement layer, 8 is a p-side electrode, 9
Is an n-side electrode.

The operation of the conventional strained quantum well laser configured as described above will be described. Current is p-side electrode 8
To the n-side electrode 9 causes laser oscillation in the multiple quantum well portion 5. The strain well layer 3 has a mixed crystal composition of In0.7Ga0.3As and is supplied with gas so as to have a compressive strain of 1% to perform MOVPE crystal growth.

[0004]

However, in the structure shown in FIG. 3, ordering occurs because In0.7Ga0.3As is used for the strain well layer 3. That is, InAs
And GaAs are regularly arranged to generate strain because the mixed crystal grows without changing the bond angle between the group 3 element and the group 5 element. Strain generation in the crystal is suppressed even in the mixed crystal composition. Will be done. In particular, very clear ordering is observed in In0.5Ga0.5As, but in In0.7Ga0.3As, ordering also occurs locally, so the threshold current density is reduced and the external differential quantum efficiency and relaxation oscillation frequency are reduced. However, there is a problem that the improvement of the laser characteristics due to the distortion such as the improvement of the above is small.

This is because, firstly, when ordering occurs, the bond angle between elements does not change, so that even if a mixed crystal having a composition in which strain is introduced is grown, no strain actually occurs in the crystal. Is. Secondly, as shown in Fig. 4, In0.7Ga
Since the energy discontinuity in the conduction band occupying the energy gap of the 0.3As mixed crystal is as small as Ec = 0.2Eg, the electron energy becomes larger than the barrier height when a current is injected into the laser, causing carrier overflow. Is generated and contributes to laser oscillation.
There was also a problem that the light output of the laser was saturated because the light emission of 2 also occurred.

In view of the above point, the present invention uses a strained quantum well structure with a mixed crystal containing Al such as AlGaInAs or an InAsP mixed crystal in place of In0.7Ga0.3As to suppress ordering and effectively suppress strain. It is an object of the present invention to provide a semiconductor laser that can be generated in a layer and can increase the band discontinuity of the conduction band and can operate at high light output at high speed, and a method for manufacturing the same.

[0007]

In order to solve the above problems, the present invention solves the above problems by using a semiconductor single crystal substrate, a first optical waveguide layer laminated on the substrate, a strained quantum well layer, and a second optical waveguide. A strained quantum well semiconductor laser including a layer and using a mixed crystal containing Al for a well layer forming the strained quantum well layer.

In addition, AlxG is used as a well layer forming the strained quantum well layer.
A strained quantum well semiconductor laser using an ayIn (1-xy) AszP (1-z) (0.01 <x <0.9) mixed crystal and an InGaAsP-based mixed crystal for the barrier layer is provided.

In addition, a semiconductor single crystal substrate, a first optical waveguide layer laminated on the substrate, a strain quantum well layer, and a second optical waveguide layer are included in a well layer forming the strain quantum well layer. The strained quantum well semiconductor laser uses an InAsP mixed crystal.

Further, a first optical waveguide, a strained quantum well layer in which well layers and barrier layers having different lattice constants are alternately laminated, a second optical waveguide layer, and a cladding layer are formed on a semiconductor single crystal substrate. A first crystal growth step of stacking, an etching step of etching in a stripe shape, and a second crystal growth step of growing a current block layer on the stripe are included, and a mixed crystal containing Al as the well layer is crystal-grown. A method of manufacturing a strained quantum well semiconductor laser.

[0011]

With the above-mentioned structure, the present invention can suppress the ordering peculiar to InGaAs used in the well layer of the conventional laser and obtain a large strain effect. That is, when the lattice strain is not introduced into the well layer with respect to the substrate, the composition is In0.53Ga0.47As, which is close to the composition of In0.5Ga0.5As, so most of them are ordered. Here, the In—As bond having a large lattice constant is oriented in the crystal growth direction in spite of increasing the In composition because a compressive strain is introduced, and the crystal is grown in the growth direction without causing strain with the substrate. The lattice constant of is large. This is because InAs and GaAs are blended almost equally, and when the atoms are alternately arranged, the enthalpy decreases, the total internal energy decreases, and the order becomes stable and ordering occurs. The internal energy will be examined in detail below. The total internal energy is represented by E = H-TS.

H is enthalpy, T is temperature, and S is entropy. The random presence of InAs and GaAs generally increases the entropy S more than the increase the enthalpy H, so that the internal energy E is reduced and a more random arrangement occurs. This is particularly noticeable during growth at a large temperature T, and in the growth where lattice strain is not introduced, ordering is hardly observed.

However, the enthalpy H is greatly increased by introducing the lattice strain. When the atoms are arranged randomly, the lattice strain increases and the enthalpy increases sharply as compared with the case where ordering occurs, canceling the effect due to the increase in entropy. As a result, the internal energy becomes large and becomes unstable, so that the amount of ordering becomes large so that the internal energy becomes small. Eventually, ordering will occur to the extent that it balances the effect of lattice distortion.

Now, by adding Al to the InGaAs layer, Al0.5Ga is maintained while keeping the energy band width constant.
0.2In0.3As In this case, since there are three types of Group 3 elements, the larger the entropy, the more stable the internal energy of the crystal and the suppression of ordering. As a result of suppressing the ordering, the strained crystal cannot grow while being lattice-matched with the substrate, and the strain corresponding to the lattice mismatch between the strained crystal and the substrate is generated in the crystal.

Further, by increasing the Al composition, Al0.8In
With 0.2 As, the energy discontinuity in the conduction band between the well layer and the barrier layer can be increased while keeping the energy band width constant. Therefore, the electrons injected into the laser exist in the strain well layer, and the electrons do not overflow into the barrier layer or the waveguide layer, so that the supplied electrons are effectively extracted as light. Especially when the light output becomes large, the electron overflow becomes a problem, and the light output is distorted even if the supply flow rate is increased, but when the energy discontinuity in the conduction band is large, the light output is not saturated up to a high light output. It will be possible.

[0016]

1 is a block diagram of a strained quantum well semiconductor laser according to an embodiment of the present invention. 1 is a Sn-doped InP semiconductor single crystal substrate, 2 is InGaAsP (λg =
1.05) First optical waveguide layer, 3 is Al0.8In0.2As strain well layer, 4 is InGaAsP (λg = 1.30) barrier layer, and 5 is a multiple quantum well including strain well layer 3 and barrier layer 4. , 6 is InGa
AsP (λg = 1.05) Second optical waveguide layer, 7 is p-InP, n
-InP, p-InP current confinement layer, 8 is a p-side electrode, and 9 is an n-side electrode. Here, by using a mixed crystal of Al0.8In0.2As, which is an Al compound, instead of Ga in the strained quantum well layer 3, Al and I
Ordering was suppressed because the composition of n can be made very different from 4: 1. As a result of the measurement, In
In a GaAs strained quantum well, Cu-
Au type ordering was confirmed, but Al _0.8 I
In the n _0.2 As strained quantum well, diffraction due to ordering was not confirmed, and the influence due to ordering could be suppressed by using an Al compound. . The oscillation wavelength of the laser is 1.55 μm, and the maximum optical output is 300 mW and InGa
It is 1.2 times higher than that of As strained quantum wells. It is considered that this is because the ordering was suppressed, the strain effect was generated, and the band discontinuity of the conduction band was increased, so that the electron leakage was reduced.

A maximum optical output of 360 mW was obtained by using Al0.7In0.3As0.4P0.6 as the crystal composition of the strained quantum well for a laser having an oscillation wavelength of 1.3 μm. The relaxation oscillation frequency was 3 GHz / mA ^1/2 and the line width increase coefficient was 1.5.

On the other hand, when InAsP was used as the strain well layer of the strain quantum well for 1.3 μm laser, the maximum light output was 280 mW due to the ordering suppressing effect and the band discontinuity expanding effect. When the InGaAsP mixed crystal is used, the composition of the crystal can be known only by the lattice mismatch rate, which has an advantage that the condition for crystal growth can be easily set.

As described above, according to this embodiment, AlG
By creating strained quantum wells using aInAsP mixed crystals, we realized a laser that suppresses ordering and increases band discontinuity in the conduction band, thereby increasing optical output and achieving high-speed operation and long-distance transmission. You can do it.

FIG. 2 shows a method of manufacturing a strained quantum well in this embodiment. InP as a semiconductor single crystal substrate
First crystal growth step (a) of growing the first optical waveguide layer 2, the Al _0.8 In _0.2 As strain well layer 3, the barrier layer 4, the multiple quantum well 5, and the second optical waveguide layer 6 on the substrate 1. And a second crystal growth step of growing the current confinement layer 7 and (b), and an electrode forming step (c) of forming the p-side electrode 8 and the n-side electrode 9. Particularly, in order to obtain the strain well layer 3 having good crystallinity, the growth temperature needs to be 650 ° C. or higher. As the semiconductor single crystal substrate, an InP substrate whose crystal surface is 2 ° off from the (001) plane was used.

In this embodiment, the laser structure is S
Although the CH (spectrum confinment heterostructure) structure is used, other laser structures such as a waveguide structure may be used. In addition, the mixed crystal composition of Al0.8In0.2As and Al0.7In0.3As0.4
P0.6, InAs0.4P0.6, etc. were used, but since the mixed crystal composition differs depending on the target laser oscillation wavelength and the thickness of the strain well layer,
It is necessary to set the composition according to each application. Further, although the present laser is of the Fabry-Perot type, even a high value-added laser such as a DFB or DBR type laser can realize the characteristic improvement as an active layer. Incidentally, not only the laser but also the light receiving element and the high speed electronic element such as the HFET can be applied to improve the characteristics.

[0022]

As described above, according to the present invention,
By using a mixed crystal containing Al or an InAsP-based mixed crystal as the strained quantum well layer, ordering is suppressed, band discontinuity is increased, optical output is increased, and a strained quantum that realizes high-speed operation and long-distance communication. A well semiconductor laser can be provided, and its practical effect is extremely large.

[Brief description of drawings]

FIG. 1 is a structural sectional view of a strained quantum well semiconductor laser according to an embodiment of the present invention.

FIG. 2 is a process sectional view showing a method of manufacturing a strained quantum well laser in an example of the present invention.

FIG. 3 is a structural diagram of a conventional strained quantum well laser.

FIG. 4 is an energy band structure diagram of a conventional strained quantum well laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Single crystal substrate 2 1st waveguide layer 3 Strain well layer 4 Barrier layer 5 Strain quantum well structure 6 1st waveguide layer 7 Current confinement layer 8 p side electrode 9 n side electrode

Claims (4)

[Claims] 1. A well layer that comprises a semiconductor single crystal substrate, a first optical waveguide layer laminated on the substrate, a strain quantum well layer, and a second optical waveguide layer, and constitutes the strain quantum well layer. To Al
A strained quantum well semiconductor laser characterized by using a mixed crystal containing. 2. AlxGayIn is used as a well layer constituting a strained quantum well layer.
2. The strained quantum well semiconductor laser according to claim 1, wherein a (1-xy) AszP (1-z) (0.01 <x <0.9) mixed crystal is used and an InGaAsP-based mixed crystal is used for the barrier layer. 3. A well layer that comprises a semiconductor single crystal substrate, a first optical waveguide layer laminated on the substrate, a strain quantum well layer, and a second optical waveguide layer, and constitutes the strain quantum well layer. To In
A strained quantum well semiconductor laser characterized by using an AsP mixed crystal. 4. A first optical waveguide on a semiconductor single crystal substrate,
A strained quantum well layer in which well layers and barrier layers having different lattice constants are alternately laminated, a first crystal growth step of laminating a second optical waveguide layer, and a cladding layer, and an etching step of etching in a stripe shape. And a second crystal growth step of growing a current blocking layer on the stripe, and performing crystal growth of a mixed crystal containing Al as the well layer, the method of manufacturing a strained quantum well semiconductor laser.