JPS62122190A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To form a semiconductor laser having a sufficient leakage inhibiting effect to both sides of electrons and holes and also, having structure wherein the electrons and the holes are easy to be injected into the active layer by providing a first and second barrier layers for the use of leakage prevention. CONSTITUTION:An n-type Al0.7Ga0.3As clad layer 2, a first undoped Ga0.49In0.51P barrier layer 3, an undoped GaAs active layer 4, a second undoped AlAs barrier layer 5, a p-type Al0.7Ga0.3As clad layer 6 and a p-type GaAs cap layer 7 are laminated in order on an n-type GaAs substrate 1 in a thickness of 1.0mum, 300Angstrom , 0.1mum, 300Angstrom , 1.0mum and 0.5mum respectively by a molecular beam epitaxial method. Moreover, a p-type electrode 8 and an n-type electrode 9 are each provided on the upper surface and back side of this laminated structure and a semiconductor laser is formed. Si is doped to the clad layer 2 in an impurity concentration of 5X10<17>cm<-3>, Be to the clad layer 6 in an impurity concentration of 5X10<17>cm<-3> and Be to the cap layer 7 in an impurity concentration of 1X10<19>cm<-3>. Hereby, the injection of electrons and holes into the active layer 4 is efficiently executed and also, the electrons and holes are prevented from leaking out in the clad layers 2 and 5. As a result, the laser beam is oscillated in a low threshold current, the low threshold current is not increased even at a high temperature and this laser is operated at a low current.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser whose oscillation threshold current has little temperature dependence and can be operated at high temperatures.

(Prior Art) Since the oscillation threshold current of a semiconductor laser usually increases as the temperature rises, various efforts have been made to enable operation at high temperatures, which are important for practical use. The main reason why the threshold current increases with temperature rise is considered to be that carriers injected into the active layer easily leak out across the potential barrier between the active layer and the cladding layer. To prevent this, Applied Fixtures Letters (Appl.Phys,
A semiconductor laser proposed by Lett, 38 (1981) 835) is shown in FIG.

FIG. 2(a) is a cross-sectional view showing the structure of a conventional semiconductor laser, and FIG. 2(b) is an energy band diagram near its active layer. This semiconductor laser includes an n-type AlxGa1-xAs cladding layer 2 on an n-type GaAs substrate 1, undoped Al to prevent carrier leakage, Ga1. First barrier layer 3 (0<x<y<1), undoped GaAs active layer 4
, undoped At2Ga1-, As second barrier layer 5
(0<x<z<1), p-type AlxGa1-xAs cladding layer 6, p-type Ga to improve ohmic contact of the electrode
As cap layer 7 is sequentially laminated, and p-type GaAs
It has a structure in which a p-type electrode 8 is deposited on the cap layer and an n-type electrode 9 is deposited on the back surface of the n-type GaAs substrate 1. Here, as shown in FIG. 2(b), each cladding layer is made of GaAs.
The forbidden band width is larger than that of active layer 4 (0<x
<1), the first and second barrier layers have an AlAs composition y2
It is a graded barrier in which z gradually changes within the range of x<y and z<1. p-type electrode 8, n-type electrode 9
When a current is applied in the forward direction between
Electrons from the xAs cladding layer 2 become p-type AlxGa1-
Holes are injected into the active layer 4 from the rAs cladding layer 6 . Is the second barrier layer 5 the active layer 4? This serves to prevent the electrons that have been absorbed from leaking beyond the discontinuity at the edge of the conduction band formed at the heterojunction interface between the GaAs of the active layer 4 and the p-type ALxGa1-xAs cladding layer 6.

The first barrier layer 3 also prevents holes from leaking into the n-type cladding layer 2 across the valence band discontinuity between the n-type AlxGa1-xAs cladding layer 2 and the GaAs active layer 4. do the work.

(Problems to be Solved by the Invention) As described above, in the conventional semiconductor laser, the second barrier layer 5 prevents leakage of electrons, and the first barrier layer 3 prevents leakage of holes. However, since the first barrier layer 3 forms a barrier protruding toward the conduction band side, there is a drawback that injection of electrons from the n-type cladding layer 2 to the active layer 4 is hindered. Also, focusing on hole leakage, the first barrier layer 3 and the GaAs
The discontinuity at the valence band edge with the active layer 4 is not very large and is insufficient to prevent leakage of holes.

An object of the present invention is to provide a semiconductor laser which does not have the above-mentioned drawbacks, has a sufficient leakage prevention effect for both electrons and holes, and has a structure in which electrons and holes are easily injected into the active layer 4. It is in.

(Means for Solving the Problems) FIG. 1 shows a semiconductor laser of the present invention. FIG. 1(a) is a sectional view of the semiconductor laser of the present invention, and FIG. 1(b) is an energy band diagram near the active layer 4 thereof.

The semiconductor laser of the present invention has an active layer 4, a p-type cladding layer 6 and an n-type cladding layer 2 sandwiching the active layer 4 from both sides and having a larger forbidden band width than the active layer 4, and has hole leakage. A first barrier layer is provided between the n-type cladding layer 2 and the active layer 4 for preventing electron leakage, and a first barrier layer is provided between the n-type cladding layer 2 and the active layer 4, the electron energy of which is smaller at the upper end of the valence band than that of either the active layer 4 or the n-type cladding layer. The structure includes a second barrier layer between the cladding layer 6 and the active layer 4, the electron affinity of which is smaller than the gap between the active layer 4 and the p-type cladding layer 6.

(Function) In the semiconductor laser of the present invention, an energy band diagram as shown in FIG. 1(b) can be obtained. Therefore, electrons are easily injected from the n-type cladding layer 2 to the active layer 4, and the electrons are
The barrier formed by the second barrier layer 5 prevents leakage to the p-type cladding layer 6. Furthermore, holes are easily injected from the p-type cladding layer 6 into the active layer 4 , and their leakage to the n-type cladding layer 2 is suppressed by the barrier formed by the first barrier layer 3 . As a result, the injected electrons and holes are effectively confined within the active layer 4, allowing oscillation with a low threshold current even at high temperatures, and operation with a low current.

(Example) An example of the present invention will be described below with reference to FIG. In this example, an n-type Al
, 7Gao, 3As cladding layer 2 with a thickness of 1.0 pm, undoped Gao, 49Ino, sxP barrier layer 3 with a thickness of 300, undoped GaAs active layer 4 with a thickness of 0.1 pm, undoped AlAs second barrier layer 5 with a thickness of 300, p-type Alo, 7
Gao, aAs cladding layer 6 with a thickness of 1.0 pm, p-type Ga
An As cap layer 7 is sequentially laminated by a 0.5 pm molecular beam epitaxy method, and a p-type electrode 8 and an n-type electrode 9 are further provided in this laminated structure to form a semiconductor laser.

The n-type Alo, 7Gao, 3As cladding layer 2 is doped with Si at an impurity concentration of 5 x 1017 cm, and the p-type Alo7
Gao, aAs cladding layer 6 has Be impurity concentration 5X
1017am” doped p-type GaAs cap layer 7
was doped with Be at an impurity concentration of I.times.10.sup.19 cm.sup.-3.

According to this embodiment, the discontinuities of the forbidden band width, valence electron/band edge, and conduction band width of each layer are as follows at room temperature. That is, according to the literature, n- or p-type Alo7Gao, 3As cladding layers 2, 6, GaA
The forbidden band widths at point P of the s active layer 4, Gao, 49Ino, 5tP first barrier layer 3, and AlAs second barrier layer 5 are 2.368, 1.424, 1.854, and 3°01, respectively.
It is 8eV. In addition, GaAs active layer 4 and Gao49I
The discontinuity at the valence band edge between the no5zP first barrier layer 3 is 0.43 eV, and the conduction band edge is OeV, the same < AlAs
The valence band edge discontinuity with the second barrier layer 5 is 0.239
The discontinuity at the eV conduction band edge is 1.354 eV.

Let us now compare this embodiment with the conventional semiconductor laser shown in FIG. Conventionally, the Al, Ga1-yAs first barrier layer 3 and the A12Ga,-, AS second barrier layer 5 are
Assuming that there is a graded change from = 0.7 to y = z = 1, that is, AlAs with the largest discontinuity in the valence band and conduction band, the GaAs active layer 4 and the first and second barrier layers This means that discontinuities in the conduction band and valence band occur at 1.354 eV and 0.239 eV, respectively.

Therefore, in this embodiment, there is no potential barrier for electrons, making them very easy to be injected, and for holes, the potential barrier (discontinuity of the valence band) formed by the first barrier layer 3 is The amount increases by about 80%, making it difficult to leak out from the active layer 4.

In the embodiments described above, the first and second barrier layers 2.5 are made of materials that are lattice matched to the active layer 4 and the cladding layers 2 and 6, but by making the first or second barrier layers thinner, Since the strain caused by lattice mismatch can be absorbed, the material does not necessarily have to be a lattice matching material. However, since the purpose of the first and second barrier layers is to stop the leakage of carriers, it is more effective to make them thick enough to prevent carriers from flowing due to the tunnel effect, that is, 30 Å or more.

In addition, as in the case of a conventional semiconductor laser, the first and second
The composition of the barrier layer may be gradually changed to facilitate the injection of holes into the active layer 4. Furthermore, in the example, GaAs
The thickness of the active layer 4 was set to 0.1 yen 1 m, but the thickness was 200 yen.
The spirit of the present invention can be applied even to a quantum well type laser with a quantum well volume below that of a human.

In the above-described embodiments, the layered structure was formed by molecular beam epitaxy, but this may also be by organometallic thermal decomposition, hydride or halide vapor phase growth, or liquid phase growth.

In addition, In other than GaAs, GaInP, and AlGaAs
P, InGaAs.

Other I such as InGaAsP, AlInAs, AIInP, etc.
It goes without saying that the same effects can be obtained even if a II-V or II-VI compound semiconductor material is used as long as it satisfies the requirements of the present invention. Although the stripe structure was not mentioned, it is natural to adopt a stripe structure in the field of semiconductor lasers. The present invention is characterized by its laminated structure, and can be applied to any striped structure.

(Effects of the Invention) As described above, according to the present invention, electrons and holes are efficiently injected into the active layer 4, and leakage to the cladding layers 2 and 5 is suppressed. As a result, a semiconductor laser that oscillates at a low threshold current and operates at a low current without increasing the threshold current even at high temperatures can be obtained.

[Brief explanation of drawings]

FIG. 1(a) is a cross-sectional view of a semiconductor laser of the present invention, and FIG. 1(b) is an energy band diagram near its active layer. Figure 2(a) is a cross-sectional view of a conventional semiconductor laser;
b) is an energy band diagram near the active layer. In the figure, 1... substrate, 2... n-type cladding layer, 3...
- First barrier layer, 4. ...Active layer, 5. Second barrier layer, 6. P-type cladding layer, 7. P-type cap layer, 8. P-type electrode, 9.-n-type electrode 1. a) (b)

Claims (1)

[Claims] An active layer, a p-type cladding layer and an n-type cladding layer sandwiching the active layer from both sides and having a larger forbidden band width than the active layer, and between the active layer and the n-type cladding layer, valence electrons are A first barrier layer in which the electron energy at the upper end of the band is smaller than either the active layer or the n-type cladding layer, and a first barrier layer in which the electron affinity between the active layer and the p-type cladding layer is smaller than that in the active layer and the p-type cladding layer.
A semiconductor laser comprising a second barrier layer smaller than either of the mold cladding layers.