JP2674382B2 - 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 semiconductor laser used as a light source for information processing equipment or optical communication equipment.

[0002]

2. Description of the Related Art Since a semiconductor laser is extremely small and highly productive, it is currently widely used as a light source for information processing equipment and optical communication equipment. The main characteristics required for a semiconductor laser as a practical light source are low oscillation threshold current, stable high-temperature operation at 40 ° C. to 60 ° C., and the like. In recent years, Katsuyama et al. Reported in Electronics Letters (Vol. 26, p. 1376, 1990) that a semiconductor laser using a so-called strained quantum well active layer made of Ga _0.43 In _0.57 P exhibits a relatively low oscillation threshold current. . In addition, Ichiji et al. Reported a low oscillation threshold current in a semiconductor laser using a strained quantum well active layer made of In _0.22 Ga _0.78 As (12th International Conference on Semiconductor Lasers, digest page 44, 1990). In these semiconductor lasers, it is considered that the lasing threshold current is reduced because the valence electron effective mass of the quantum well active layer subjected to in-plane compressive strain is reduced.

[0003]

Although the oscillation threshold current of a conventional semiconductor laser using a strained quantum well active layer is low, its high temperature operation characteristic is not necessarily good. This is because the density of injected carriers in the active layer is high and the confinement of the carriers is insufficient. In order to improve the high temperature operation characteristics, it is necessary to further reduce the oscillation threshold current.

[0004]

One of the semiconductor lasers of the present invention is a semiconductor substrate having a (0, 0, 1) plane and a (0, 0, 1) plane.
An active layer including at least a compound semiconductor layer having a 0,1) in-plane compressive strain and having an ordered state in the [-1,1,1] or [1, -1,1] direction; It has a laser resonator including at least. (0,
A semiconductor substrate having a surface slightly inclined from the (0,1) plane to any direction such as the [1,1,0] direction, the [1,0,0] direction, and the [0,1,0] direction may be used. .

Another semiconductor laser of the present invention is a semiconductor laser having a plane inclined from the (0,0,1) plane to the [-1,1,0] direction or the [1, -1,0] direction. The substrate has a (0,0,1) in-plane compressive strain, and [-1,
The present invention is characterized by having an active layer including at least a compound semiconductor layer having an ordered state in the [1,1] or [1, -1,1] direction and a laser resonator including at least the active layer. Strictly speaking, however, the compressive strain surface is a surface inclined from the (0,0,1) surface in the [-1,1,0] direction or the [1, -1,0] direction.

Further, the semiconductor laser of the present invention comprises AlGaInP or I having compressive strain and an ordered state on a GaAs substrate.
It is characterized by including a semiconductor layer having an nGaAsP layer. Alternatively, a semiconductor layer having an InGaAsP layer having a compressive strain and an ordered state is provided on the InP substrate.

[0007]

The function of the semiconductor laser of the present invention having an active layer having an ordered state and an in-plane compressive strain will be described. First, the action of the ordered state will be described. Gomei et al's group (Physical Review Letters Vol. 60, page 2645, 1988)
And other groups are GaInP layer, AlGaInP
It is reported that the epitaxial layers such as the layers, the InGaAs layer and the InGaAsP layer have an ordered state. However, whether or not these semiconductor layers have an ordered state depends on the epitaxial growth conditions. Ga _0.50 In with an ordered state
_In the case of _0.50 P, the Ga atom sublattice and the In atom sublattice are alternately and regularly arranged in the [-1,1,1] or [1, -1,1] direction. Muscarenhus et al. [-1, 1,
1] The electrical vector of light that causes radiative recombination between ground levels in a semiconductor layer having the ordered state is (-1, 1, 1)
It was reported that it was biased in the plane (Physical Review Letters, Vol. 63, page 2108, 1989). Therefore, [-1,
The electric vector of recombination light generated in the semiconductor layer having an ordered state in the [1,1] or [1, -1,1] direction is (-
Biased to the (1,1,1) plane or the (1, -1,1) plane. On the other hand, the electric vector direction of the light generated in the disordered layer is isotropic. Next, regarding the effect of compressive strain,
The electric vector of light generated by radiative recombination between the ground levels of the semiconductor layer having in-plane compressive strain on the (0,0,1) plane is (0,
It is known to be biased in the (0, 1) plane.

The active layer of the semiconductor laser of the present invention has both the function of the ordered state and the function of compressive strain described above. The electric vector orientation of the recombination light of the active layer is biased to the (-1,1,1) plane or the (1, -1,1,) plane due to the action of the ordered state. Furthermore, the electric vector orientation is biased in the (0,0,1) plane by the action of the in-plane compressive strain. As a result of these, as shown in FIG. 3A, the electric vector of the recombination light generated in the active layer of the semiconductor laser of the present invention is (-1,1,1) plane or (1, -1,1,) plane. And (0,0,1) plane are included in the only direction, that is, in the [1,1,0] direction.
The emission direction of light having an electric vector in the [1,1,0] direction is the (1,1,0) in-plane direction. Therefore, [-1,
(1,0] direction and (0,0,1] direction (1,1,
In the semiconductor laser of the present invention having the laser resonator formed in the orientation included in the (0) plane, the ratio of the recombined light that gives the gain to the oscillation mode to the total recombined light is higher than in the conventional case. As a result, the semiconductor laser exhibits a low oscillation threshold current. Since the conventional strained quantum well active layer semiconductor laser is only affected by the lattice strain, the electric vector orientation of the emitted recombination light is a free orientation in the (0,0,1) plane as shown in FIG. 3B. Take In this case, the recombined light is emitted in all directions, and the proportion of the recombined light that gives a gain to the oscillation mode is low.

According to another semiconductor laser of the present invention,
A semiconductor substrate having a surface inclined from (0,0,1) in the [-1,1,0] direction (or [1, -1,0] direction) is used. The orientation of the ordered state of the epitaxial layer on the semiconductor substrate having the (0,0,1) plane is [-1,1,
1] direction and [1, -1,1] direction are mixed equally, while (0,0,1) to [-1,1,0] direction (or [1, -1,0] It has been reported that the orientation of the ordered state is biased toward the [-1,1,1] direction ([1, -1,1] direction) on a semiconductor substrate having a plane inclined in the [] direction] (Japanese Journal). Of Applied Physics Vol. 28, L1728, 1989, and 1991
Spring Symposium on Applied Physics Lecture 32a-ZG-
5). That is, the order degree of the ordered state of the epitaxial layer on the tilted substrate is higher. Therefore, the operation of the present invention described above works more strongly. When the tilted substrate is used, the compressive strain plane direction is tilted from the (0,0,1) plane, but the radiation direction of the recombined light is still (1,1,) according to the principle of the operation of the present invention.
1, 0) In-plane orientation. The direction of the laser cavity is also [-
Although tilted from the [1,1,0] direction to the [0,0,1] direction or from the [0,0,1] direction to the [-1,1,0] direction, these laser resonator directions are still ( It is included in the (1,1,0) plane. Therefore, the geometrical relationship between the recombination light emission orientation and the laser cavity orientation when using the above-mentioned tilted substrate is kept exactly the same as that for the (0,0,1) substrate.

[0010]

FIG. 1 shows one embodiment of the semiconductor laser of the present invention. First, on a semiconductor substrate 2 made of Si-doped n-type GaAs, a 1.2 μm thick Si-doped n-type (Al
_{0. 7} Ga _{0.3) 0.5} In clad layer 3 of _0.5 P,
Active layer 4 consisting of multi-strained quantum wells, 1.2 μm thick Zn
A doped p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 5 was epitaxially grown. The multi-strained quantum well comprises three layers of 8 nm thick undoped Ga _0.40 In
_{A 0.60} P in-plane compressive strain well layer and four 4-nm thick undoped (Al _0.4 Ga _0.6 ) _0.55 In _0.45 P strain barrier layers were used. In the in-plane compressive strain well layer, (Al _x Ga _1-x ) _y In _1-y
P layer (y <0.51) and In _x Ga _1-x As layer (x>)
It is also possible to use 0). In addition, In
_{When an x} Ga _1-x As _1-y P _y layer (x> 0.49y) is used, for example, while maintaining the Ga: In ratio at 1: 1 (x =
0.5) In-plane compressive strain can be applied (y = 0.1). This is useful for coexistence of highly ordered ordered state and compressive strain. In addition, I is added to the well layer and the barrier layer.
An n _1-x Ga _x As _y P _1-y layer may be used. In this case, InP is used for the semiconductor substrate 2, the cladding layer 3, the cladding layer 5, and the like.

The plane orientation of the semiconductor substrate 2 is (0, 0, 1)
Is a surface inclined by 6 degrees in the [-1,1,0] direction. To form an ordered state with high order in the active layer, 1
A tilt angle of 0 degrees or less is suitable. The plane orientation of the semiconductor substrate 2 may be the (0,0,1) plane. Further, from the (0,0,1) plane, [1,1,0] direction, [1,0,0] direction, [0,
The semiconductor substrate 2 having a surface inclined by 1 to 3 degrees in an arbitrary direction such as the [1,0] direction may be used. As is well known, such a semiconductor substrate has an effect of improving the morphology of an epitaxial crystal.

Epitaxial growth was performed by the low pressure metal organic crystal growth method (MOVPE method). In this example, the crystal growth temperature was 660 ° C. and the group V / group III feed material ratio was 200. In order to form an ordered state with a high degree of order, the crystal growth temperature is 700 ° C. or lower, and the V / III supply flow rate ratio is 10
0 or more is suitable. Since these crystal growth conditions are conditions for forming an ordered state having the effect of the present invention in the active layer, the crystal growth conditions of other layers such as the cladding layer may be different. Growth rate is about 1.8μ
It was m / hr. The raw materials are trimethyl aluminum (TMA), triethyl gallium (TEG), trimethyl indium (TMI), dimethyl zinc (DMZ),
Phosphine (PH _3), arsine (AsH _3), was used disilane (Si ₂ H _6). It is also possible to grow using a gas source molecular beam crystal growth method (GSMBE method) or a chemical beam epitaxial method (CBE method).

After the epitaxial growth, stripes 9 were formed on the cladding layer 5 by using the photolithography method. The azimuth of the stripe 9 is approximately [-1,1,0]. The stripe 9 forms a laser resonator. Strictly speaking, when an inclined substrate is used, the laser cavity direction is [-
It is inclined from the [1,1,0] direction to the [0,0,1] direction.
After forming the stripes 9, Si-doped n-type GaAs
A block layer 6 made of p was selectively grown outside the stripe 9, and a contact layer 7 made of Zn-doped p-type GaAs was grown on the entire surface. After forming the contact layer 7, the n-side electrode 1 and the p-side electrode 8 were formed. Finally, cleavage was performed to form opposing reflecting mirrors on the (-1,1,0) plane. The reflecting mirror may be formed by using dry etching instead of cleaving. In addition, a vertical emission semiconductor laser (T. Takamori et al., Applied Physics Letters, Vol. 55, page 1053, 1989).
For example, a reflecting mirror having a surface other than (-1,1,0) such as (year) or a reflecting mirror having a curved surface may be used. The semiconductor laser is completed through the above steps. The electric vector azimuth of the laser beam 10 of the semiconductor laser is [1,1,0] direction, and the radiation direction is almost [-1,1,0] direction and [1, -1,0] direction.
0] direction.

FIG. 2 shows another embodiment of the semiconductor laser of the present invention. First, on a semiconductor substrate 2 made of Si-doped n-type GaAs, a 1.2 μm thick Si-doped n-type (Al
Clad layer 3 made of _0.7 Ga _0.3 ) _0.5 In _0.5 P,
Active layer 4 consisting of multi-strained quantum wells, 1.2 μm thick Zn
A cladding layer 5 made of doped p-type (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P was epitaxially grown. The multi-strained quantum well comprises three layers of 8 nm thick undoped Ga _0.50 In
_{A 0.50} P _0.90 As _{0.10 in-} plane compressive strain well layer and four 4-nm thick undoped (Al _0.4 Ga _0.6 ) _0.55 In _0.45 P strain barrier layers were used. For in-plane compressive strain well layer (Al _x Ga _1-x )
_y In _1-y P layer (y <0.51) and In _x Ga _1-x As
It is also possible to use layers (x> 0). In addition, In _1-x Ga _x As _y P _1-y layers may be used for the well layer and the barrier layer. In this case, InP is used for the semiconductor substrate 2, the cladding layer 3 and the cladding layer 5. The plane orientation of the semiconductor substrate 2 is from (0, 0, 1) to [-
Although the surface is inclined by 6 degrees in the direction of (1,1,0), (0,0,
1) A surface or the like may be used. Epitaxial growth is performed by the low pressure metal organic crystal growth method (MOVPE method). In order to form an ordered state in Ga _0.50 In _0.50 P _0.90 As _0.10 forming the active layer, the crystal growth temperature was 660 ° C. and the group 5/3 group supply flow rate ratio was 200. Raw materials and the like are the same as those in the previous embodiment. It is also possible to grow using a gas source molecular beam crystal growth method (GSMBE method) or a chemical beam epitaxial method (CBE method). Next, a disk-shaped SiO ₂ film having a diameter of 7 μm was formed on the clad layer 5 by photolithography.
A dielectric film was formed. The shape of the SiO ₂ dielectric film may be polygonal. Next, Zn impurities, Mg impurities, Si impurities, Fe impurities, or Au impurities were diffused into the crystal using the SiO ₂ dielectric film as a mask. You may inject these impurities by the ion implantation method. On this occasion,
Ga _0.50 In _0.50 P _0.90 included in the active layer 4 of the high-concentration impurity region 11 not covered with the circular or polygonal dielectric film
The ordered state of As _0.10 is disordered and the Ga _0.50 In
_The bandgap energy of _0.50 P _0.90 As _0.10 increases and the refractive index decreases. As a result, the carriers injected into the active layer 4 are confined in the region covered by the dielectric film (hereinafter referred to as the light emitting region), and the light generated by the active layer 4 is confined in the light emitting region. The light emitting region forms a laser resonator in the [0,0,1] direction. Strictly speaking, when an inclined substrate is used, the laser resonator direction is inclined from the [0,0,1] direction to the [-1,1,0] direction. After the diffusion, the SiO ₂ dielectric film was removed, a reflection film 12 having a reflectance of 90% made of a dielectric multilayer film was formed, and further an electrode 8 was formed. After that, circular or polygonal holes of the same shape were formed in the semiconductor substrate 2, and a reflective film 13 having a reflectance of 98% made of a dielectric multilayer film was formed in the region. Finally, the electrode 1 was formed on the semiconductor substrate 2. Through the above steps, a surface emitting semiconductor laser was completed. The electric vector direction of the laser beam 10 of the semiconductor laser is [1, 1,
The [0] direction and the radiation direction are approximately the [0,0,1] direction and the [0,0, -1] direction.

[0015]

The semiconductor laser of the present invention having the laser cavity formed in the [-1,1,0] direction exhibits a low threshold current and excellent high-temperature operating characteristics. A semiconductor laser using a semiconductor substrate tilted by 6 degrees from the (0,0,1) plane in the [-1,1,0] direction has a threshold value lower than that in the case of using the (0,0,1) semiconductor substrate. The current was shown. Also, (0,
When a semiconductor substrate tilted by 6 degrees from the (0,1) plane in the [-1,1,0] direction is used, Ga _0.50 In _0.50 P _0.90 As
A semiconductor laser using a _0.10 strained quantum well layer is Ga _0.40 In
_The threshold current was even lower than that of the semiconductor laser using the _0.60 P strained quantum well layer.

Further, the semiconductor laser of the present invention having the laser resonator formed in the [0,0,1] direction exhibits a low threshold current and excellent high temperature operation characteristics as compared with the conventional surface emitting laser. .

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of a semiconductor laser of the present invention.

FIG. 2 is a sectional view showing another embodiment of the semiconductor laser of the present invention.

FIG. 3 is a diagram illustrating an electric vector direction of recombination light in the active layer of the semiconductor laser of the present invention.

[Explanation of symbols]

 1 Electrode 2 Semiconductor Substrate 3 Cladding Layer 4 Active Layer 5 Cladding Layer 6 Block Layer 7 Contact Layer 8 Electrode 9 Stripe 10 Laser Light 11 High Concentration Impurity Region 12 Reflective Film 13 Reflective Film

Continuation of front page (56) Reference JP-A-5-67839 (JP, A) JP-A-4-273490 (JP, A) JP-A-5-41560 (JP, A) JP-A-63-120492 (JP , A) JP-A-4-237183 (JP, A) JP-A-5-29700 (JP, A)

Claims (6)

(57) [Claims] 1. A semiconductor substrate having a (0,0,1) plane,
It has (0,0,1) in-plane compressive strain and [-1,1,
1] or [1, -1,1] direction, a semiconductor laser comprising an active layer including at least a compound semiconductor layer having an ordered state, and a laser resonator including at least the active layer. 2. From the (0,0,1) plane to [-1,1,0]
A semiconductor substrate having a plane inclined in the direction or the [1, -1,0] direction, and having a (0,0,1) in-plane compressive strain, and
An active layer including at least a compound semiconductor layer having an ordered state in the [-1,1,1] or [1, -1,1] direction, and a laser resonator including at least the active layer. Semiconductor laser. 3. The laser resonator is formed in a [−1,1,0] direction.
4. The semiconductor laser according to claim 1. 4. The semiconductor laser according to claim 1, wherein the laser resonator is formed in a [0,0,1] direction. 5. The semiconductor substrate is made of GaAs and Ga
(Al _x Ga _1-x ) _y In _1-y P layer or In _x as the active layer in the semiconductor multilayer structure formed on the As substrate.
5. The semiconductor laser according to claim 1, further comprising a Ga _1-x As _1-y P _y layer. 6. The semiconductor substrate is made of InP and the In
5. The semiconductor laser according to claim 1, wherein an In _1-x Ga _x As _y P _1-y layer is provided as the active layer in a semiconductor multi-layer structure formed on a P substrate.