JPS61154191A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain low threshold current in an SCH structure and to obtain a semiconductor laser element having excellent temperature characteristics, by using a semiconductor super lattice for light confining layers. CONSTITUTION:A P-type doped, semiconductor super-lattice light confining layer 24 comprises AlAs and GaAs. Two very thin single crystal semiconductor layers comprising AlAs and GaAs in an Angstrom order are alternately laminated in said layer 24. An N-type doped, semiconductor super-lattice light confining layer 26 comprises AlAs and GaAs. The interfaces between an active layer 25 and the light confining layer 24 and between the layer 25 and the layer 26 have heterogeneous interfaces. The light confinement is achieved by the conventional method. Meanwhile, in carrier confinement, the confinement can be performed, with sufficiently large energy difference being provided in comparison with the conventional method. Thus, a semiconductor laser characterized by small leak current, low threshold current, excellent temperature characteristics and small spread of a beam can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a semiconductor laser device, and particularly to improving the performance of a laser having an SCH structure in which optical confinement and carrier confinement are performed separately.

[Conventional technology]

Figure 3 shows, for example, J, Appl, Phys, average, 322
(1974), the conventional 5eparate Co
nfinement Hetero -5tructu
2 is a cross-sectional view of a re (S CH) laser, in which 1 is an upper electrode, 2 is a P+-GaAs contact layer, 3 is a p AlxGa1-zAs cladding layer, and 4 is a p
-AlyGaHb-3As optical confinement layer, 5 is GaAs
The active layer 6 is an n-AjlyGal-pAS optical confinement layer, and the interface between the active layer 5 and the optical confinement layer 4.6 is a heterointerface. 7 is a n-AlxGa1z As cladding layer, 8 is an n+-GaAs substrate, and 9 is a lower electrode. However, the mixed crystal ratio x of Aj+ in the above AJGaAs layer
, y is x>y. Moreover, FIG. 4 is a diagram showing the energy gap and refractive index distribution.

Next, the operation will be explained. When a current of a threshold value or more is passed between the electrodes 1 and 9, electrons are trapped in the active layer 5. In this way, carriers are formed in a thin active layer 5q! -1 light can be effectively confined in the wider optical confinement layer 4.6, and therefore a semiconductor laser with a lower threshold current can be obtained.

[Problem that the invention seeks to solve]

However, in the conventional SCH laser, in order to create the optical confinement layer as described above, A11 y Ga with a smaller Aj+ composition than the cladding layer made of AlxGa1-χAs is used.
(Carrier confinement must be carried out at -1A s, and in this case, as the composition ratio y of AβGaAs is increased, the energy gap becomes larger and the refractive index becomes smaller. Both the energy gap and the refractive index determine the composition ratio y. Therefore, for example, when determining the refractive index of the optical confinement layer in order to effectively confine light, it is necessary to maintain a sufficient energy gap between the optical confinement layer and the active layer. There were problems such as carrier leakage to the optical confinement layer and poor temperature characteristics such as threshold current.

The present invention has been made to solve the above-mentioned problems, and aims to provide a semiconductor laser device having an SCH structure that can obtain a low threshold current and have good temperature characteristics.

It uses a 44-dimensional semiconductor superlattice formed by alternately stacking two extremely thin semiconductor layers.

[Function] In this invention, since a semiconductor superlattice is used for the optical confinement layer in the semiconductor laser device with the SCH structure, a smooth hetero interface between the active layer and the optical confinement eyebrow can be obtained, and the optical confinement layer has a smooth heterointerface. This can be achieved by being able to change the energy gap and refractive index independently. Therefore, for example, if the effective energy gap of the semiconductor superlattice used for the optical confinement layer is larger than the energy gap of the active layer by a predetermined value, carriers will be confined in the active layer, and in this case, the optical confinement layer will refract the carriers. When the refractive index is made larger than the refractive index of the cladding layer, light is effectively confined in the optical confinement layer and the active layer.

〔Example〕

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

As mentioned above, the present invention uses a semiconductor superlattice for the optical confinement layer, and this allows the energy level and refractive index of the optical confinement layer to be changed independently.
As an example, FIG. 1 shows an embodiment in which the effective energy gap of the optical confinement layer and the energy gap of the cladding layer are approximately the same. In FIG. 1, 21 is an upper electrode;
22 is a P10 a As contact layer, 23 is a p-A
JxGa7-zAs cladding layer, 24 is A! As and Ga
This is a p-type doped semiconductor superlattice optical confinement layer made of As.
Two single crystal semiconductor layers of aAs are alternately stacked. 25 is a GaAs active layer, 26 is AlAs and Ga
This is an n-type doped semiconductor superlattice optical confinement layer made of As, and includes an active layer 25 and an optical confinement layer 24.26.
The interface with this is a hetero interface. 27 is n-AIt
xGa, -, xAsAs cladding 28 is n''-GaAs
The substrate 29 is a lower electrode. In addition, FIG. 2 shows the active layer 25.
．． Semiconductor superlattice optical confinement layer 24, 26, cladding layer 2
It shows the energy gap and refractive index distribution of 3.27. In the energy gap diagram, the effective energy gap of the semiconductor superlattice optical confinement layers 24 and 26 is shown by a dotted line.

Next, the operation will be explained.

In this device, a semiconductor superlattice layer is used as the optical confinement layer 24, 26 between the active layer 25 and the cladding layer 23.
It is almost the same as l-zAs23.27. Therefore, there is an energy gap difference of more than a predetermined value between the optical confinement layer 24, 26 and the active layer 25, and after the carriers fall into the active layer 25, the carriers enter the optical confinement layer
, 26 (leakage), and has a sufficient confinement effect on the carrier. On the other hand, the refractive index of the semiconductor superlattice optical confinement layer 24.26 is larger than that of the cladding layer (Aj! The light is trapped by the optical confinement layer 24.26. It can be effectively confined in the three layers of the active layer 25.

In this way, optical confinement is the same as the conventional method,
On the other hand, regarding carrier confinement, it is possible to confine carriers with a sufficiently large energy difference compared to conventional methods, so a semiconductor laser with low leakage current, low threshold current, and good temperature characteristics and small beam spread can be obtained. Since the semiconductor superlattice layer is inserted between the layer 25 and the cladding layers 23 and 27, a smooth heterointerface is formed.

Furthermore, since the period of the semiconductor superlattice optical confinement layer, that is, the thickness of each layer, is generally 100 Å or less, the active layer thickness can also be made thin as long as it is not smaller than the period, in which case quantum effects Furthermore, it is possible to fabricate a semiconductor laser with low threshold current, good temperature characteristics, and small beam spread.

In addition, in the above embodiment, IA s is used as the optical confinement layer.
/ GaAs superlattice was used, but AfGaAs/
G a A s superlattice or more generally AJX
Gal-z As/AjlyGa7-) As (x#y
) Similar effects can be obtained using a superlattice.

In addition, in the above embodiment, the optical confinement layer using a semiconductor superlattice was made to have almost the same effective energy gap as the cladding layer, but even though the effective energy gap of the optical confinement layer is lower than that of the cladding layer to some extent, As long as it is larger than that of the active layer by a predetermined value or more, a carrier confinement effect can be obtained. Furthermore, since the present invention uses a semiconductor superlattice in the optical confinement layer to obtain a smooth hetero-interface, it is within the scope of the present invention to make the refractive index of the optical confinement layer almost the same as that of the cladding layer. include.

〔Effect of the invention〕

As described above, according to the present invention, since a semiconductor superlattice is used for the optical confinement layer, a semiconductor laser device with a smooth active layer interface can be obtained, and the effective energy gap of optical confinement debris can be reduced by reducing the effective energy gap between the active layer and the active layer. If it is larger than that by a predetermined value or more, the threshold current is low and the temperature characteristics are good (,
This has the effect of providing a semiconductor laser element with small beam spread.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention, FIG. 2 is a diagram showing its energy gap and refractive index distribution, FIG. 3 is a sectional view of a conventional SCH semiconductor laser, and FIG. The figure shows the energy gap and refractive index distribution. 25...active layer, 24...p-type doped A!
Semiconductor superlattice optical confinement layer consisting of As and GaAs, 2
6...AJ doped to n-type! Semiconductor superlattice optical confinement layer made of As and GaAS, 23.27...Crabt layer. In the drawings, the same reference numerals indicate the same or equivalent parts.

Claims (11)

[Claims] (1) Optical confinement and carrier confinement are performed separately
CH(Separate Confinement H
It is characterized by using a semiconductor superlattice formed by alternately stacking two extremely thin semiconductor layers made of different semiconductors in the optical confinement layer placed above and below the active layer. A semiconductor laser device. (2) The semiconductor laser device according to claim 1, wherein the semiconductor superlattice used for the optical confinement layer has an effective energy gap that is larger than the energy gap of the active layer by a predetermined value or more. (3) The SCH structure is characterized by comprising a first semiconductor and a second semiconductor, and the two ultrathin semiconductor layers of the semiconductor superlattice used for the optical confinement layer are comprised of the first semiconductor and the second semiconductor. A semiconductor laser device according to claim 1 or 2. (4) The semiconductor laser device according to claim 3, wherein the first semiconductor is AlAs and the second semiconductor is GaAs. (5) The semiconductor laser device according to claim 4, wherein the active layer is thin enough to produce a quantum size effect. (6) The SCH structure is composed of a first semiconductor and a mixed crystal semiconductor consisting of the first semiconductor and a second semiconductor, and the two ultrathin semiconductor layers of the semiconductor superlattice used as the optical confinement layer are 3. The semiconductor laser device according to claim 1, comprising a semiconductor and a second semiconductor, the first semiconductor and a mixed crystal semiconductor, or the second semiconductor and a mixed crystal semiconductor. (7) The first semiconductor is AlAs, the second semiconductor is GaAs, and the two ultrathin semiconductor layers of the semiconductor superlattice are made of AlGaAs/GaAs. The semiconductor laser device described in . (8) The semiconductor laser device according to claim 7, wherein the active layer is thin enough to produce a quantum size effect. (9) The SCH structure is made of a first mixed crystal semiconductor made of a first semiconductor and a second semiconductor, and a second mixed crystal semiconductor made of the first semiconductor and a second semiconductor and having a different composition from the first mixed crystal semiconductor. The two ultrathin semiconductor layers of the semiconductor superlattice used for the optical confinement layer are the first mixed crystal semiconductor and the second semiconductor layer.
The semiconductor laser device according to claim 1 or 2, characterized in that it is made of a mixed crystal semiconductor. (10) The first mixed crystal semiconductor is AlxGa_1_-_x
As, and the second mixed crystal semiconductor is AlyGa_1_-
_yAs, and the two ultrathin semiconductor layers of the semiconductor superlattice are AlxGa_1_-_yAs/AlyGa_1_
-_xAs (x≠y), the semiconductor laser device according to claim 9. (11) The semiconductor laser device according to claim 10, wherein the active layer is thin enough to produce a quantum size effect.