JP2663880B2 - Multiple quantum well structure semiconductor laser - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a long-wavelength band multiple quantum well semiconductor laser, and more particularly to a structure of an active layer thereof.

[0002]

2. Description of the Related Art Conventionally, a semiconductor laser having a multiple quantum well structure (MQW) in a wavelength band of 1.3 μm or 1.55 μm has
Although nGaAsP / InP-based compound semiconductor materials have been used, in these materials, the energy discontinuity of the conduction band is smaller than the value of the valence band energy discontinuity. Sometimes there was a problem with electrons overflowing from the wells to the barrier. Therefore, an increase in the threshold value or a decrease in the efficiency at a high temperature is caused by GaAs.
/ AlGaAs-based compound semiconductor material was larger than a short-wavelength-based semiconductor laser. On the other hand, in recent years B
AlInGaAs / I announced by ellcore
nP MQW Laser (Uncooled Lasers)
for Deployment of Fiber i
n the Loop, OPTICS & PHOTONI
CS NEWS / DECEMBER 1993) uses AlInGaAs for the well and the barrier, so that the band lineup is improved and the temperature dependence of the slope efficiency is extremely improved.

[0003]

SUMMARY OF THE INVENTION However, Bel
Alcore's AlInGaAs / InP based MQW semiconductor lasers have a high Al content in the well, barrier and isolation / confinement heterostructure (SCH) layers.
Since GaAs is used, it is difficult to form a buried structure. Therefore, the oscillation threshold is high because of the ridge waveguide structure, and the characteristics are not so good when compared with a drive current at 5 mW.

SUMMARY OF THE INVENTION An object of the present invention is to solve such a disadvantage of a long wavelength multiple quantum well structure semiconductor laser, to have excellent temperature characteristics and to operate with a low threshold and a low driving current even at a high temperature. An object of the present invention is to provide a 3 μm or 1.55 μm semiconductor laser.

[0005]

According to the present invention, there is provided a semiconductor laser in which an active layer having a multiple quantum well structure is formed on an InP substrate. InGaAs or InG
a well made of an AsP-based semiconductor material and AlInG
A barrier layer made of an aAsP-based semiconductor material and only a portion adjacent to the well are AlInGaAsP, and the remaining portion is an SCH made of an InGaAsP-based semiconductor material.
(Separate Confinment Het
(Electrostructure) layer.

[0006]

The reason why the high-temperature characteristics can be improved by using the barrier layer made of the AlInGaAsP-based semiconductor material according to the present invention will be described below. As described above, a major factor affecting the high-temperature characteristics of the MQW laser is a mechanism in which the injected carriers (in this case, mainly electrons) overflow from the wells to the barrier at a high temperature, thereby lowering the gain of the MQW laser. Conceivable. In the case of a long-wavelength MQW laser, as shown in FIG.
GaAs or InGaAsP and In barrier 16
GaAsP is used. This InGaAs / InGa
AsP heterojunction or InGaAsP / InGa
It is known that, in an AsP-based heterojunction, the value ΔEc / ΔEv of the conduction band energy discontinuity is improved in a direction to increase. Accordingly, a barrier barrier against electrons is increased, so that leakage of electrons from the well to the barrier is suppressed even at a high temperature. As a result, a device having good temperature characteristics can be realized.

When a semiconductor material containing Al is used, burying growth is necessarily difficult. This is because Al is very easily oxidized, so that a thin oxide film is formed on the surface, which hinders buried growth. As shown in FIG. 4, the well 18, the barrier 19 and the S
AlInGaAs containing Al in the entire active layer of CH20 layer
, The burying growth is difficult. On the other hand, in the MQW structure of the present invention, the barrier layer and the SCH
Since Al is included only in a part of the layer, there is an advantage that the buried growth can be performed relatively easily. In fact, an MQW structure consisting of a semiconductor containing Al in both the well and the barrier;
If the MQW structure containing Al in the barrier but not Al in the well is buried and grown under the same conditions, the latter is satisfactorily buried, but in the former, the percentage of buried defects is poor. Very large. This means that the Al oxide film over a wide area of the entire MQW active layer is stable and makes the burying growth difficult.
Since an Al oxide film having a small area such as only a barrier portion is unstable and is easily melted back during burying growth,
There is no particular problem.

Further, although there is no direct relationship with the high temperature characteristics,
By using the AlInGaAsP barrier, the potential barrier of the barrier with respect to holes can be reduced, so that the problem of non-uniform hole injection between wells can also be improved. This means that the number of wells is particularly large (about 7 wells or more).
Because of the problem in QW, normal InGa
In the case of an As (P) / InGaAsP-based MQW laser,
Since the potential barrier of the barrier with respect to the holes is too high, holes injected from the p-InP side are not uniformly distributed in each well, but are distributed more in the p-side well, and in extreme cases, almost all the n-side wells There may be a state where holes are not injected. Therefore, if such a situation occurs, there is a problem that even if the number of wells is increased, improvement in gain cannot be expected much. On the other hand, the structure of the present invention is considered to be effective, and a large differential gain value can be realized in the multilayer MQW by alleviating the non-uniform injection of holes.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. FIG. 1 is a band diagram of an MQW active layer structure of a 1.3 μm long wavelength laser showing one embodiment of the present invention. First, the n-InP (100) substrate 21 is formed on a 50-nm-thick 1.13 μm composition n-InG
An aAsPSCH layer 14 is grown, and a non-doped u-AlInGaAsP barrier 12 having a thickness of 10 nm is further grown. In this case, the composition of Al is 0.05 to
A value of about 0.4 is appropriate. When the amount is too small, the effect of improving the band lineup is small, and when the amount is too large, burying growth cannot be performed well. Further, the composition of other In, Ga, As, and P is determined so as to lattice-match with the InP substrate. On top of this, 1.40 μm with a thickness of about 5 nm
U-InGaAsP well 12 having a wavelength composition of
A 0 nm u-AlInGaAsP barrier 12 is grown for five periods. On top of that, 1.13 μm of 50 nm thickness
A compositional u-InGaAs PSCH layer 14 is grown, and finally a p-InP cladding layer 23 is grown to about 0.6 μm. The well may be InGaAs. The MQW wafer manufactured in this manner is connected to a normal DC-PB as shown in FIG.
Embed in H structure. That is, p-In of the MQW wafer
A photoresist is formed on the surface of the P-cladding layer 23 on the stripe and etched to form a mesa structure at the center. After removing the photoresist, the p-InP current blocking layer 24, n-InP
Current blocking layer 25, p-InP layer 26, P ⁺ InGa
AsP cap layers 27 are sequentially formed. 28 is an MQW active layer. Thereafter, the device is cut out to have an element length of 200 μm, and an end face coating of about 70% and 95% is applied to the entire surface and the rear surface, respectively.

When the high-temperature characteristics of the prototype device were evaluated, the oscillation threshold at 85 ° C. was about 5 mA, and the oscillation threshold at 850 ° C., 5 m
The drive current at the time of W was as good as 20 mA. The characteristic temperature Is of the slope efficiency is also AlGaAs /
It has been improved to 230K, comparable to GaAs lasers.

[0011]

As described above, according to the present invention, AlIn
By using a GaAsP semiconductor material for the barrier, there is an advantage that electrons can be prevented from overflowing into the barrier at a high temperature, and a semiconductor laser having good temperature characteristics can be obtained. Further, the fabrication of the buried structure is relatively easy, so that it also has an advantage that a laser having a small threshold current and a small drive current can be obtained.

[Brief description of the drawings]

FIG. 1 is an MQW of a semiconductor laser according to an embodiment of the present invention.
FIG. 3 is a diagram showing a band diagram of an active layer.

FIG. 2 is a cross-sectional view of an embedded structure of a semiconductor laser according to one embodiment of the present invention.

FIG. 3 shows a band of an MQW active layer of a conventional semiconductor laser;
It is a figure which shows a diagram.

FIG. 4 is a diagram showing a band diagram of an MQW active layer of another conventional semiconductor laser.

[Explanation of symbols]

REFERENCE SIGNS LIST 11 InGaAs well 13 AlInGaAsP barrier 14 InGaAsPSCH layer 21 n-InP substrate 22 MQW layer 23 p-InP cladding layer 24 p-InP current blocking layer 25 n-InP current blocking layer 26 p-InP layer 27 p ⁺ -InGaAsP cap layer 28 MQW active layer

Claims (2)

(57) [Claims] In a semiconductor laser in which an active layer having a multiple quantum well structure is formed on an InP substrate, the active layer having a multiple quantum well structure includes at least InGaAs or InGa.
A well made of an AsP-based semiconductor material and an A containing Al
a barrier layer made of lInGaAsP-based semiconductor material;
A multiple quantum well structure semiconductor laser characterized in that only a part adjacent to the well is AlInGaAsP and the remaining part is a separated confinement heterostructure layer made of an InGaAsP-based semiconductor material. 2. The activity of a multiple quantum well structure on an InP substrate.
Multi-quantum well structure in semiconductor laser forming layers
The active layer is made of at least InGaAs or InGa
A well made of AsP and a well made of AlInGaAsP
Only the barrier layer and a portion adjacent to the well are formed of AlInG.
aAsP, and the rest is made of InGaAsP
A multi-layer structure comprising a separately confined heterostructure layer
Quantum well structure semiconductor laser.