JP2763102B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a semiconductor laser device for long wavelength optical communication using a double hetero junction structure.

(Prior Art) In general, in an injection type semiconductor laser device using a double heterojunction structure, holes are injected into an active layer from a p− type semiconductor layer sandwiching an active layer, and an n− type semiconductor layer sandwiches an active layer. Then, holes are accumulated in the active layer using the valence band discontinuity of the active layer as a barrier. On the other hand, electrons are injected into the active layer from the n− type semiconductor layer sandwiching the active layer, and electrons are accumulated in the active layer using the conduction band discontinuity between the p− type semiconductor layer sandwiching the active layer and the active layer as a barrier.
Holes and electrons recombine in the active layer to emit light. Light is concentrated in the vicinity of the active region due to the difference in the refractive index between the active region of the active layer and the upper, lower, left and right crystals of the active region. In a semiconductor laser device having a normal structure, the material of the n-type semiconductor layer and the material of the p-type semiconductor layer sandwiching the active region are the same, so that the active region is
The conduction band discontinuity of the n-type semiconductor layer, the conduction band discontinuity of the active region and the n-type semiconductor layer are the same, and the valence band discontinuity of the active region and the n-type semiconductor layer, the active region and the p-type semiconductor layer Have the same valence band discontinuity. Therefore, p-
The overflow of electrons into the semiconductor layer or the overflow of holes from the active region to the n − -type semiconductor layer occurred, resulting in poor current confinement efficiency in the active layer. In particular, in the InP-based semiconductor laser region where the conduction band discontinuity with the active region cladding layer is small, this tendency is remarkable in a semiconductor laser having an active layer thickness of several hundred angstroms or less.

(Problems to be Solved by the Invention) As described above, in the present invention, the overflow area of electrons from the active layer to the p − type semiconductor layer reduces the overflow of holes from the active area to the n − type semiconductor layer, It is an object of the present invention to provide a good semiconductor laser device in which holes, electrons and light can be efficiently confined and concentrated.

[Configuration of the invention]

(Means for Solving the Problems) In the semiconductor laser device of the present invention, since the compositions of the two cladding layers are different, the conduction band discontinuity between the cladding layer having p-type conductivity and the active region and the two cladding layers are different. The valence band discontinuity between the cladding layer having n-type conductivity and the active region among the layers can be determined independently.
That is, the energy barrier for electrons due to the conduction band discontinuity between the cladding layer having p-type conductivity and the active region and the energy barrier for holes due to the valence band discontinuity can be determined independently.

The conduction band discontinuity between the active region and the cladding layer having p-type conductivity of the two cladding layers is determined by the conduction band discontinuity between the cladding layer having n-type conductivity and the active region among the two cladding layers. By making the active region larger than the continuous region, the energy barrier between the active region and the cladding layer having p-type conductivity can be made more active with the cladding layer having n-type conductivity than the cladding layer having n-type conductivity. The energy can be sufficiently large with respect to the energy of electrons injected into the active region with the energy of the conduction band discontinuity with the region.

The semiconductor substrate forming the semiconductor laser is InP, the p-type cladding layer is InAlAs or InGaAlAs, and n
If the -type cladding layer is InP, each layer can be formed so as to be substantially lattice-matched with the semiconductor of the substrate.

InP, InAlAs, InGaAlA if formed by metal organic chemical vapor deposition
Each layer of s can form a good crystal and form a steep and good heterojunction interface.

(Operation) In the semiconductor laser device of the present invention, since the energy barrier for electrons and the energy barrier for holes can be set independently large, electrons can be favorably accumulated in the active layer.

In response to the energy of electrons injected from the cladding layer having n-type conductivity into the active region, p-
If the energy barrier at the time of entering the mold cladding layer is made large, electrons can be favorably accumulated in the active layer.

For the energy of holes injected from the cladding layer having p-type conductivity into the active region, n-
By taking a large energy barrier when entering the mold cladding layer, holes can be favorably accumulated in the active layer.

InAlAs or InAlGaAs is used as the p-type cladding layer and n
If InP is used as the negative type cladding layer, crystals that are lattice-matched to the InP substrate can be formed, so that each layer of the semiconductor laser device can be formed of good crystals.

If each layer and each heterojunction interface of the semiconductor laser device are formed favorably by metal organic chemical vapor deposition, the efficiency of confining electrons and holes in the active layer is improved.

(Example) Next, an example of the present invention will be described in detail. FIG. 1 is a structural sectional view of a semiconductor laser device of the present invention. First, a semiconductor laser device of the present invention comprises an n-type (100) InP substrate 1, a Se-doped n-type InP cladding layer (2 μm thick) 2, an undoped InGaAsP active layer (0.15 μm thickness) 3, and a Zn-doped p-type substrate. A type InAlAs cladding layer (1.5 μm thick) 4 and an undoped InGaAs cap layer (0.5 μm thickness) were sequentially formed by metal organic chemical vapor deposition. Thereafter, an SiO ₂ CVD film was formed.
Next, a resist mask is formed by normal photolithography so that the stripe direction is about 2 μm so that the stripe direction is the <011> direction.
Formed in width, hydrofluoric acid (6%) + ammonium fluoride (30%
%) To form a stripe of SiO ₂ by etching with a solution. Next, the InGaAs cap layer is removed with a solution of hydrogen peroxide + sulfuric acid using SiO ₂ as a mask, and the p-InAlAs cladding layer 4 is removed by etching with hydrochloric acid.
The InGaAsP active layer 3 was removed with a sulfuric acid-based solution, and the n-InP cladding layer 2 was removed with a solution of hydrochloric acid + phosphoric acid + water 1.5 μm.
After that, Fe-doped semi-insulating In was grown by metalorganic chemical vapor deposition.
The P buried layer 5 was formed at 3 μm. (I here on the SiO ₂
nP does not grow. Next, the SiO ₂ mask was removed with a solution of hydrofluoric acid (6%) + ammonium fluoride (30%). Thereafter, a Zn-doped p-type InGaAs contact layer (0.5 μm thick) 6 was formed by metal organic chemical vapor deposition. Thereafter, an n-side ohmic electrode 7 was formed with an Au-Ge alloy. A p-side ohmic electrode 8 was formed from an Au-Zn alloy.

The semiconductor laser device thus formed is 1.55 μm
And the characteristic temperature was about twice as high as that of a semiconductor laser device in which only the p-InAlAs layer was replaced with p-InP. Also, the maximum value of the light output was increased about 1.8 times.

The present invention is not limited to the above embodiments, and for example, the semiconductor substrate may be p-type. In that case, the cladding layer on the substrate side may be a p-InAlAs layer, the cladding layer on the contact layer side may be an n-InP layer, and the conductivity type of the contact layer may be n-type. The present invention is also applicable to material systems other than the InAlAs / InGaAsP / InP system.

〔The invention's effect〕

As described above, according to the semiconductor laser device of the present invention, it is possible to prevent the electrons and holes injected into the active layer from overflowing, and to effectively convert the injected current. Therefore, the basic characteristics of the semiconductor laser such as the characteristic temperature and the maximum value of the optical output can be improved, and a semiconductor laser device suitable for high output can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing the configuration of a semiconductor laser device according to the present invention. DESCRIPTION OF SYMBOLS 1 ... InP substrate, 2 ... n-type InP cladding layer 3 ... InGaAsP active layer, 4 ... p-type InAlAs cladding layer 5 ... Fe-doped semi-insulating InP buried layer 6 ... p-type InGaAs Contact layer 7 n-side ohmic electrode 8 p-side ohmic electrode

Claims (3)

(57) [Claims] 1. An active layer that contributes to light emission and laser oscillation,
The bandgap is wider than this, one is p-type and the other is n-type.
What is claimed is: 1. A semiconductor laser device having a double heterojunction structure sandwiched between two upper and lower cladding layers having negative conductivity, wherein said two cladding layers are formed of different compound semiconductors. 2. A cladding layer having p-type conductivity and a conduction band discontinuity between an active region and a cladding layer having n-type conductivity among two cladding layers. 2. The semiconductor laser device according to claim 1, wherein said semiconductor laser device is larger than a conduction band discontinuity with said region. 3. A cladding layer having p-type conductivity, wherein the valence band discontinuity between the cladding layer having n-type conductivity and the active region is two of the two cladding layers. 2. The semiconductor laser device according to claim 1, wherein the distance is larger than a valence band discontinuity with the active region.