JPH05110193A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a semiconductor laser of low threshold current by reducing the recombination current in the photoconfinement layer of a semiconductor laser used as a light source for optical communication or optical interconnection. CONSTITUTION:The title semiconductor laser is a laser having an n-type clad layer 12, an n-side photoconfinement layer 14, an active layer 16, a p-side photoconfinement layer 18, and a p-type clad layer 20 formed on an n-type semiconductor substrate 10 in the order. And it is so constituted that the amount of discontinuity DELTAEcp between the p-side photoconfinement layer 18 and the lower end of the conduction band of the active layer 16 may be larger than the amount of discontinuity DELTAEcn between the n-side photoconfinement l-ayer 14 and the lower end of the conduction band of the active layer 16, and that the amount of discontinuity DELTAEvn between the n-side photoconfinement layer 14 and the upper end of the valence band of the active layer 16 may be larger than the amount of discontinuity DELTAEvp between the p-side photoconfinement layer 18 and the upper end of the valence band of the active layer 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to a semiconductor laser used as a light source for optical communication and optical interconnection.

[0002]

2. Description of the Related Art Semi-improved light confining effect on the active layer
Conventionally, as a conductor laser, SCH (Separate Confinem)
ent Heterostructure) semiconductor lasers are known.
It FIG. 4 shows the basic structure of a conventional SCH structure semiconductor laser.
Shown in. As shown in FIG. 4A, the n-type InP substrate 70
An n-type clad layer 72 made of n-type InP is formed on top.
On the n-type cladding layer 72, GaInAsP (λg =
An n-side light confinement layer 74 of 1.3 μm) is formed,
Ga on the n-side light confinement layer 74 _0.47In_0.53Consists of As
The active layer 76 is formed, and GaInAsP is formed on the active layer 76.
The p-side light confinement layer 78 made of (λg = 1.3 μm) is formed.
Formed of p-type InP on the p-side light confinement layer 78.
The mold cladding layer 80 is formed.

This SCH semiconductor laser is shown in FIG.
It has a band structure as shown in (b). In this semiconductor laser, the n-side light confinement layer 74, the active layer 76, and the p-side light confinement layer 78 have a double heterostructure and are active layers 76 of carriers.
N-type clad layer 72 and n-side light confinement layer 74, p-type clad layer 80 and p-side light confinement layer 7
By confining light in the regions of the n-side light confinement layer 74, the active layer 76, and the p-side light confinement layer 78 due to the difference in the refractive index from that of No. 8, the light confinement effect on the active layer 76 is improved. ..

[0004]

However, in the conventional semiconductor laser having the SCH structure, the n-side light confining layer 74 and the p-side light confining layer 78 are formed of the same semiconductor material. ), The lower end of the conductor and the upper end of the valence band of the n-side light confinement layer 74 and the p-side light confinement layer 78 have the same energy level. Therefore, electrons in the conduction band of the n-side light confinement layer 74 cross the active layer 76, enter the p-side light confinement layer 78, and recombine with holes in the valence band of the p-side light confinement layer 78. Recombination current flows. Similarly, holes in the valence band of the p-side light confinement layer 76 cross over the active layer 76 and enter the n-side light confinement layer 74, so that the n-side light confinement layer 74.
Recombine with electrons in the conduction band of and the recombination current flows. Therefore, there is a problem in that this recombination current causes an increase in the threshold current of laser oscillation.

An object of the present invention is to provide a semiconductor laser having a low threshold current by reducing the recombination current in the optical confinement layer.

[0006]

The principle of the present invention will be described with reference to FIG. FIG. 1A shows the basic structure of the semiconductor laser according to the present invention, and FIG. 1B shows the band structure. As shown in FIG. 1A, the n-type cladding layer 12 is formed on the n-type semiconductor substrate 10, the n-side light confinement layer 14 is formed on the n-type cladding layer 12, and the n-side light confinement layer is formed. The active layer 16 is formed on the active layer 16 and the p-side optical confinement layer 1 is formed on the active layer 16.
8 is formed, and the p-type cladding layer 20 is formed on the p-side light confinement layer 18.

The semiconductor laser according to the present invention is shown in FIG.
As shown in, the discontinuity amount ΔEcp at the bottom of the conduction band of the p-side light confinement layer 18 and the active layer 16 is larger than the discontinuity amount ΔEcn at the bottom of the conduction band of the n-side light confinement layer 14 and the active layer 16,
A material such that the discontinuity amount ΔEvn at the upper end of the valence band between the n-side light confinement layer 14 and the active layer 16 is larger than the discontinuity amount ΔEvp at the upper end of the valence band between the p-side light confinement layer 18 and the active layer 16. It is formed by.

[0008]

According to the present invention, the discontinuity amount ΔEcp at the bottom of the conduction band of the p-side light confinement layer 18 and the active layer 16 is the discontinuity amount at the bottom of the conduction band of the n-side light confinement layer 14 and the active layer 16. Since it is formed so as to be larger than ΔEcn, the p-side light confinement layer 18 serves as a barrier for electrons, and the n-side light confinement layer 1 is formed.
Electrons in the conduction band of 4 do not cross the active layer 16 and enter the p-side optical confinement layer 18. In addition, the discontinuity ΔEvn at the upper end of the valence band of the n-side light confinement layer 14 and the active layer 16
Is formed so as to be larger than the discontinuity amount ΔEvp at the upper end of the valence band of the p-side light confinement layer 18 and the active layer 16, the n-side light confinement layer 16 becomes a barrier against holes, and p Holes in the valence band of the side light confinement layer 16 do not cross the active layer 16 and enter the n side light confinement layer 14. Therefore, a recombination current does not occur in the n-side light confinement layer 14 and the p-side light confinement layer 18, and a semiconductor laser having a low threshold current can be realized.

[0009]

FIG. 2 shows a semiconductor laser according to an embodiment of the present invention.
Will be explained. The present embodiment is an InP semiconductor laser. About 2 made of n-type InP on the n-type InP substrate 30
An n-type cladding layer 32 having a thickness of μm is formed, and n-type Ga _0.29 In _0.71 As _0.62 P _0.38 (λg
= 1.3 μm) and an n-side light confinement layer 34 having a thickness of about 0.1 μm is formed, and i-type Ga is formed on the n-side light confinement layer 34.
An active layer 36 of _0.42 In _0.58 As _0.9 P _0.1 (λg = 1.55 μm) having a thickness of about 0.05 μm is formed, and p-type Al _0.22 Ga _0.26 In _0.52 As (λg =
1.2 μm) is formed on the p-side light confinement layer 38 having a thickness of about 0.1 μm, and a p-type cladding layer 40 made of p-type InP is formed on the p-side light confinement layer 38 with a thickness of about 2 μm. There is.

On the p-type cladding layer 40, p + -type GaIn is formed.
Contact layer 42 made of AsP (λg = 1.3 μm)
Are formed. The upper portion of the p-type cladding layer 40 and the contact layer 42 has a ridge structure.
SiO ₂ layer 44 on 2 is opened in a stripe shape is formed, TiP is on the contact layer 42 and the SiO ₂ layer 44
A p-side electrode 46 made of t / Au is formed. An n-side electrode 48 made of AuGeNi / Au is formed on the lower surface of the n-type InP substrate 30.

The semiconductor laser of this embodiment has an n-side optical confinement.
Layer 34 is n-type Ga_0.29In_0.71As _0.62P_0.38(Λg =
1.3 μm), and the p-side light confinement layer 38 is p
Type Al_0.22Ga_0.26In_0.52As (λg = 1.2 μm)
Since it is formed of, as shown in FIG.
Discontinuity at the bottom of the conduction band of the p-side light confinement layer 38 and the active layer 36
The amount ΔEcp is the conduction of the n-side light confinement layer 34 and the active layer 36.
It becomes larger than the discontinuity amount ΔEcn at the bottom of the band, and p-side light confinement
Layer 38 functions as a barrier against electrons, and n-side light confinement
Amount of discontinuity ΔEv at the upper end of the valence band between the first layer 34 and the active layer 36
n is the upper end of the valence band of the p-side light confinement layer 38 and the active layer 36.
Is larger than the discontinuity ΔEvp of the n-side optical confinement layer 3
6 functions as a barrier against holes. Therefore, n
Reconnection in the side light confinement layer 34 and the p side light confinement layer 38
Combined current can be suppressed and the semiconductivity of the conventional SCH structure
Threshold current is about 20% smaller than body laser
be able to.

When lattice matching is achieved with InP, p
Type Al_0.22Ga_0.26In_0.52As (λg = 1.2 μm)
Of the p-side light confinement layer 38 of n-type Ga_0.29In_0.71As
_0.62P _0.38(Λg = 1.3 μm) n-side light confinement layer 34
Compared to, the refractive index is the same, but the bandgap energy is
Is large, it enters the p-side light confinement layer 34 and recombines.
To form an effective barrier to electrons that easily cause current
Wear.

In the above embodiment, the active layer 36 is formed of Ga _{1 -x} In _x As having a thickness of about 10 nm or less at which the quantum effect can be obtained.
It may be formed by (0.3 ≦ x ≦ 0.7). By making the active layer a quantum well structure, the threshold current can be reduced compared to a semiconductor laser with a thick active layer due to the effect of improving the gain and thinning the active layer. As a result, since electrons or holes easily enter the light confinement layer, the recombination current in the light confinement layer tends to increase. Therefore, in the structure of the conventional semiconductor laser, the effect of forming the quantum well structure in the active layer is reduced. However, if the recombination current in the optical confinement layer is suppressed by using the structure of this embodiment,
The effect of the active layer having the quantum well structure can be effectively utilized, and a semiconductor laser having a lower threshold can be realized.

A semiconductor laser according to another embodiment of the present invention will be described with reference to FIG. This embodiment is a GaAs semiconductor laser. n-type Al _0.45 G on n-type GaAs substrate 50
An n-type clad layer 52 made of a _0.55 As and having a thickness of about 1 μm is formed, and n-type Ga _0.73 In is formed on the n-type clad layer 52.
An n-side optical confinement layer 54 of _0.27 As _0.45 P _{0.55 with a} thickness of about 0.08 μm is formed, and an active layer 56 of i-type GaAs with a thickness of about 0.05 μm is formed on the n-side optical confinement layer 54. A p-side light confinement layer 58 of p-type Al _0.2 Ga _0.8 As having a thickness of about 0.08 μm is formed on the active layer 56.
A p-type cladding layer 60 of p-type Al _0.45 Ga _0.55 As having a thickness of about 1 μm is formed on the p-side light confinement layer 58.

On the p-type cladding layer 60, p + -type GaAs
And a contact layer 62 of about 0.2 μm thick is formed. The upper portion of the p-type clad layer 60 and the contact layer 62 has a ridge structure, and a SiO ₂ layer 64 having a stripe-shaped opening on the contact layer 62 is formed. AuZn / Au is formed on the contact layer 62 and the SiO ₂ layer 64. The p-side electrode 66 is formed. In addition, n-type Ga
An n-side electrode 68 made of AuGe / Au is formed on the lower surface of the As substrate 50.

The semiconductor laser of this embodiment has an n-side optical confinement.
Layer 54 is n-type Ga_0.73In_0.27As _0.45P_0.55Shaped by
And the p-side light confinement layer 58 is made of p-type Al._0.2Ga_0.8A
Since it is formed of s, as shown in FIG.
At the bottom of the conduction band of the p-side light confinement layer 58 and the active layer 56,
The continuous amount ΔEcp of the n-side light confinement layer 54 and the active layer 56 is
It becomes larger than the discontinuity ΔEcn at the bottom of the conduction band, and the p-side light
The confinement layer 58 functions as a barrier against electrons,
Discontinuity Δ at the upper end of the valence band of the confinement layer 54 and the active layer 56
Evn is the valence band of the p-side light confinement layer 58 and the active layer 56.
It becomes larger than the discontinuity amount ΔEvp at the upper end, and n-side light confinement
Layer 56 acts as a barrier to holes. others
Therefore, in the n-side light confinement layer 54 and the p-side light confinement layer 58,
Therefore, the recombination current can be suppressed.

In the above embodiment, the active layer 56 is formed of Ga _{1 -x} In _x As having a thickness of about 10 nm or less at which the quantum effect can be obtained.
It may be formed by (0 ≦ x ≦ 0.2). Since the threshold carrier density is much higher than that of a semiconductor laser having a thick active layer, the quantum well structure can further prevent electrons or holes from entering the optical confinement layer.

The present invention is not limited to the above embodiment, but various modifications can be made. For example, the amount of discontinuity at the bottom of the conduction band between the p-side light confinement layer and the active layer is larger than the amount of discontinuity at the bottom of the conduction band between the n-side light confinement layer and the active layer, If the discontinuity amount at the upper end of the valence band of is larger than the discontinuity amount at the upper end of the valence band of the p-side light confinement layer and the active layer, a semiconductor material other than the above-mentioned examples may be used.

If the amount of discontinuity at the bottom of the conduction band between the p-side light confinement layer and the active layer is larger than the amount of discontinuity at the bottom of the conduction band between the n-side light confinement layer and the active layer, the n-side light confinement is achieved. A semiconductor material may be used in which the discontinuity amount at the upper end of the valence band between the layer and the active layer is substantially equal to the discontinuity amount at the upper end of the valence band between the p-side light confinement layer and the active layer. This is because holes are less likely to enter the optical confinement layer than electrons.

Further, although the semiconductor laser is formed on the n-type semiconductor substrate in the above embodiment, it may be formed on the p-type semiconductor substrate with the p-type and the n-type being reversed. Further, in the above embodiment, the n-side light confining layer is formed of an n-type semiconductor material, and p
Although the side light confinement layer is formed of the p-type semiconductor material, both the n-side light confinement layer and the p-side light confinement layer may be formed of the i-type semiconductor material.

[0021]

As described above, according to the present invention, the discontinuity amount at the bottom of the conduction band between the p-side light confinement layer and the active layer is determined by the discontinuity at the bottom of the conduction band between the n-side light confinement layer and the active layer. Since the p-side light confinement layer serves as a barrier against electrons, the electrons in the conduction band of the n-side light confinement layer pass through the active layer to the p-side light confinement layer. Intrusion can be suppressed, recombination current does not occur in the p-side optical confinement layer, and a semiconductor laser having a low threshold current can be realized.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a sectional view showing a semiconductor laser according to an embodiment of the present invention.

FIG. 3 is a sectional view showing a semiconductor laser according to another embodiment of the present invention.

FIG. 4 is a diagram showing a basic structure of a conventional semiconductor laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... n-type semiconductor substrate 12 ... n-type clad layer 14 ... n side optical confinement layer 16 ... active layer 18 ... p side optical confinement layer 20 ... p type clad layer 30 ... n type InP substrate 32 ... n type clad layer (N-type InP) 34 ... n-side optical confinement layer (n-type Ga _0.29 In _0.71 As _0.62
P _0.38 ) 36 ... Active layer (i-type Ga _0.42 In _0.58 As _0.9 P _0.1 ) 38 ... P-side optical confinement layer (p-type Al _0.22 Ga _0.26 In _0.52)
As) 40 ... p-type clad layer (p-type InP) 42 ... contact layer (p + -type GaInAsP) 44 ... SiO ₂ layer 46 ... p-side electrode (TiPt / Au) 48 ... n-side electrode (AuGeNi / Au) 50 ... n-type GaAs substrate 52 ... n-type cladding layer (n-type Al _0.45 Ga _0.55 As) 54 ... n-side optical confinement layer (n-type Ga _0.73 In _0.27 As _0.45
P _0.55 ) 56 ... Active layer (i-type GaAs) 58 ... P-side optical confinement layer (p-type Al _0.2 Ga _0.8 As) 60 ... P-type clad layer (p-type Al _0.45 Ga _0.55 As) 62 ... Contact layer (p + Type GaAs) 64 ... SiO ₂ layer 66 ... p-side electrode (AuZn / Au) 68 ... n-side electrode (AuGe / Au) 70 ... n-type InP substrate 72 ... n-type clad layer (n-type InP) 74 ... n-side Light confinement layer (GaInAsP) 76 ... Active layer (Ga _0.47 In _0.53 As) 78 ... P-side light confinement layer (GaInAsP) 80 ... P-type cladding layer (p-type InP)

Claims (3)

[Claims] 1. An n-type cladding layer, an n-side light confinement layer provided on the n-type cladding layer, an active layer formed on the n-side light confinement layer, and an active layer on the active layer. P formed
A side light confinement layer and a p formed on the p side light confinement layer
In a semiconductor laser having a type clad layer, a discontinuity amount at a conduction band lower end of the p-side light confinement layer and the active layer is a discontinuity amount at a conduction band lower end of the n-side light confinement layer and the active layer. A semiconductor laser characterized by being larger. 2. The semiconductor laser according to claim 1, wherein the amount of discontinuity at the upper end of the valence band between the n-side light confinement layer and the active layer is a valence electron between the p-side light confinement layer and the active layer. A semiconductor laser characterized by being larger than the discontinuity amount at the upper end of the band. 3. The semiconductor laser according to claim 1, wherein the active layer has a quantum well structure.