JPH07307525A - Surface emission semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a surface emission semiconductor laser having a strained quantum well active layer of low element resistance and excellent crystallizability. CONSTITUTION:A multilayer structure, in which an active layer 4 is pinched by an n-type semiconductor multilayer film reflecting mirror 2 whereon an n-type InGaP layer and an n-type GaAs layer are alternately formed and a p-type semiconductor multilayer film reflecting mirror 6, whereon a p-type InGaP layer and a p-type GaAs layer are alternately formed, is arranged on an n-type GaAs substrate 1, and an InGaAsP layer having an inhibit band width, which is an intermediate on of an InGaP forbidden band width and GaAs inhibit band width, is provided in the surface emission semiconductor laser. A dielectric multilayer film reflecting mirror may be used as one of the semiconductor multilayer reflecting mirrors.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface emitting semiconductor laser.

[0002]

2. Description of the Related Art In a conventional 0.98 μm band-emission semiconductor laser having an InGaAs quantum well active layer, its semiconductor multilayer mirror is formed of a combination of AlAs and GaAs. However, AlAs may impair the reliability of the device due to oxidation and deliquescent phenomena. On the other hand, a surface emitting semiconductor laser fabricated on a GaAs substrate by using a semiconductor multi-layered film reflection mirror in which Al-free InGaP and GaAs are combined is described in Electronics Letters, Vol. 29, pp. 1854 to 1855 (1993).
(Electronics Letters, vol.
29, pp. 1854-1855, 1993).

[0003]

[Problems to be Solved by the Invention] The above-mentioned conventional InGaP
The 0.98 μm band surface emitting semiconductor laser using the semiconductor multilayer film reflecting mirror in which GaAs and GaAs are combined has the following two problems. First, as shown in FIG. 2A, the hetero barrier between InGaP and GaAs forming the semiconductor multilayer film reflection mirror is large, and the difference in the refractive index between InGaP and GaAs is 0.3. And that of GaAs are lower than those of 0.6, and in order to obtain a high reflectance, the number of cycles of the semiconductor multilayer film is 40, which increases the element resistance. And high temperature continuous operation is hindered.

Another problem is that when a semiconductor multi-layer film in which an InGaP layer and a GaAs layer are combined is grown by a metal organic chemical vapor deposition method, a chemical beam epitaxy method, etc., the group V elements of both layers are different, so that the growth As and P on the surface
Is replaced, a strained layer having a non-uniform composition is formed. Along with this, lattice defects are generated, and the crystallinity of the InGaAs strained quantum well layer is deteriorated.

An object of the present invention is to provide a 0.98 μm band surface emitting semiconductor laser having a strained quantum well active layer having a small element resistance and good crystallinity.

[0006]

In order to achieve the above object, in a surface emitting semiconductor laser of the present invention, an active layer for generating light has an n-type InGaP layer and an n-type GaAs layer alternately laminated. First semiconductor multilayer film reflecting mirror and p-type InGa
A laminated structure sandwiched by a second semiconductor multilayer film reflecting mirror in which P layers and p-type GaAs layers are alternately laminated is arranged on a semiconductor substrate, and each of the first and second semiconductor multilayer film reflecting mirrors is arranged. The InGaAsP layer having an intermediate band gap between the band gap of InGaP and the band gap of GaAs is provided in at least one of the InGaP layer and the GaAs layer.

Further, in order to achieve the above object, the surface emitting semiconductor laser of the present invention has an active layer for generating light
A laminated structure sandwiched between a semiconductor multilayer film reflecting mirror in which GaP layers and GaAs layers are alternately laminated and a dielectric multilayer film reflecting mirror is arranged on a semiconductor substrate, and InG of the semiconductor multilayer film reflecting mirror is arranged.
InG is formed on at least one of the aP layer and the GaAs layer.
An InGaAsP layer having a bandgap intermediate between the bandgap of aP and the bandgap of GaAs is provided.

This semiconductor multilayer film reflecting mirror is constructed by laminating at least two semiconductor layers having different refractive indexes, for example, 30 to 50 cycles. In addition, InGaP layer and In
The composition of the GaAsP layer is preferably such that its lattice constant is within ± 0.2% of the lattice constant of the semiconductor substrate. For example, when the semiconductor substrate is GaAs, the lattice constant of the compound in the composition range of In _0.45 Ga _0.552 P to In _0.52 Ga _0.48 P is within ± 0.2% of the lattice constant of the GaAs substrate. It is preferable that

[0009]

The operation of the present invention will be described below with reference to FIG. Forming an n-type semiconductor multilayer film reflector I
When an n-type InGaAsP layer having a forbidden band width intermediate between the forbidden band widths of the both layers is formed between the nGaP layer and the GaAs layer, the band edge discontinuity energy value on the conduction band side becomes small, as shown in FIG. As in the case of b), the height of the hetero barrier against electrons is reduced, and as a result, the resistance in the n-type semiconductor multilayer film reflection mirror section can be significantly reduced. On the other hand, between the InGaP layer and the GaAs layer forming the p-type semiconductor multilayer film reflection mirror, a p-type InGa having a forbidden band width intermediate between the forbidden band widths of both layers is formed.
When the AsP layer is formed, the band edge discontinuity energy value on the valence band side is reduced for the same reason as above, and the resistance in the p-type semiconductor multilayer film reflection mirror portion can be significantly reduced.

Further, by interposing an InGaAsP layer containing both V group elements between an InGaP layer in which the V group element is P and a GaAs layer in which the V group element is As, the metal organic chemical vapor deposition method is used. It is possible to reduce the formation of a strained layer due to the substitution of As and P on the growth surface during crystal growth.

However, even when sandwiching the InGaAsP layer, if the growth temperature is 650 ° C. and the composition wavelength of the InGaAsP layer is less than 760 nm, it is difficult to obtain a homogeneous crystal due to the influence of immiscibility. . Also, In
When the composition wavelength of the GaAsP layer exceeds 790 nm,
The effect of reducing the height of the hetero barrier is weakened. Therefore,
When the composition wavelength of the InGaAsP layer is 760 to 790 nm, a high-quality semiconductor multilayer film reflecting mirror with low series resistance can be realized. This corresponds to x = 0.79 to 0.92 when this layer is represented by In _1-x Ga _x As _y P _1-y .

Further, the sum of the optical thickness n ₁ d _{1 of the} InGaP layer and the optical thickness n ₂ d ₂ of the InGaAsP layer and GaAs
The sum of the optical thickness n ₃ d ₃ of the layer and the optical thickness n ₂ d ₂ of the InGaAsP layer is L / 4 (L: oscillation wavelength, n ₁ ~
By forming a periodic structure in which n _{3 is} the refractive index of each layer and d _{1 to} d _{3 is} the thickness of each layer), the reflectance of the semiconductor multilayer film reflecting mirror can be set high, and it is effective as a resonator for laser oscillation. Can be operated.

[0013]

Embodiments of the present invention will be described below with reference to FIGS. Example 1 FIG. 1 is a schematic cross-sectional view of a 0.98 μm band surface emitting semiconductor laser having an InGaAs strained single quantum well active layer of the present invention. GaA on the n-type GaAs substrate 1
n-In _0.48 Ga _0.52 with a layer thickness of 56 nm lattice-matched to s
P and n-InGaAsP with a layer thickness of 20 nm (composition wavelength: 76
0 nm), a layer thickness of 50 nm n-GaAs and a layer thickness of 20 nm n-InGaAsP (composition wavelength 760 n
m) n-type semiconductor multilayer film reflecting mirror 2 having a periodic structure (40 periods) in which combinations of layers are alternately laminated, n-InGaAsP
Spacer layer 3, In _0.2 Ga _0.8 As active layer 4, p-In
The GaAsP spacer layer 5, p-In _0.48 Ga _0.52 P having a layer thickness of 56 nm lattice-matched to GaAs and the p layer having a layer thickness of 20 nm.
-InGaAsP (composition wavelength 760 nm) combination,
P-GaAs with a layer thickness of 50 nm and p-In with a layer thickness of 20 nm
A p-type semiconductor multilayer film reflecting mirror 6 having a periodic structure (30 periods) in which a combination of GaAsP (composition wavelength 760 nm) is alternately laminated is sequentially formed by a metal organic chemical vapor deposition method. The composition of InGaAsP having a composition wavelength of 760 nm is I
n _0.18 Ga _0.82 As _0.64 P _0.36, which is ±
Lattice matching is performed in the range of 0.2%.

Next, the p-side electrode 7 is formed, the periphery is etched by using a mask to limit the area to a diameter of 10 μm, and then the mask is used as a mask to irradiate 300 keV of protons, and the high-resistance current confinement layer 8 is formed. To form. Furthermore, p
After forming the side electrode 9 and limiting the region to a diameter of 30 μm in the same manner as described above, 50, 10 is used as a mask.
The current confinement layer 10 of high resistance is formed by irradiation with protons of 0,200 keV. Finally, the laser light 28
An n-side electrode 11 having a window region for taking out was formed.

The prototype device has a device resistance of about 20 ohms due to the introduction of a low resistance structure into the n-type semiconductor multilayer film reflecting mirror, and a 0.98 μm band surface emission without using the conventional InGaAsP layer. The device resistance of the semiconductor laser could be reduced to about 1/30. As a result, it oscillates with a threshold current of 0.5 mA in continuous operation at room temperature and
The continuous operation at 00 ° C or higher was confirmed, and the maximum optical output of 2 mW was obtained at 90 ° C. The InGaAsP layer is Ga
Although it is provided in all between As and InGaP, if it is provided in at least one, some effect is recognized.

Example 2 FIG. 3 is a schematic sectional view of a 0.98 μm band surface emitting semiconductor laser having a matching gain structure of the present invention. On the n-type GaAs substrate 12, n-In _0.48 Ga _0.52 P having a layer thickness of 60 nm lattice-matched to GaAs and a layer thickness of 1 are formed.
Combination of 6 nm n-InGaAsP (composition wavelength 780 nm), n-GaAs layer thickness 60 nm and layer thickness 16 nm
N-InGaAsP (composition wavelength of 780 nm) is alternately laminated to form an n-type semiconductor multilayer film reflecting mirror 13 having a periodic structure (35 periods).
The active layer 14 consisting of three periods of In _0.2 Ga _0.8 As separated by the sP layer by a thickness of ½ the oscillation wavelength in the medium is sequentially formed by the gas source MBE method (molecular beam growth method). . InGa with a composition wavelength of 780 nm
The composition of AsP is In _0.14 Ga _0.86 As _0.72 P _0.28, which is lattice-matched with GaAs within a range of ± 0.2%.

Next, using a mask, the n-type semiconductor multilayer film reflecting mirror 13 is partially etched by reactive ion beam etching to form a convex light emitting region (diameter 5 μm). Then, after forming the polyimide embedding layer 15, the ring-shaped p-side electrode 16 was formed. Then Si
A dielectric multilayer film reflection mirror 17 having a periodic structure (5 periods) in which an O ₂ film and an a-Si film are alternately laminated with a thickness of ¼ times the oscillation wavelength in each medium is formed. An n-side electrode 18 was formed on the bottom. The laser light 28 is extracted from the dielectric multilayer film reflection mirror 17 side.

The prototype device is
It oscillated with a threshold current of 0.2 mA, and a maximum optical output of 10 mW was obtained. Furthermore, by introducing a low resistance structure into the n-type semiconductor multilayer film reflecting mirror, the device resistance is about 30 ohms, which is 0.98 μm without using the conventional InGaAsP layer.
The device resistance of the surface emitting semiconductor laser can be reduced to about 1/30.

Example 3 FIG. 4 is a schematic sectional view of a 0.98 μm band surface emitting semiconductor laser of the present invention formed on a p-type substrate. GaAs on the p-type GaAs substrate 19
P-In _0.48 Ga _0.52 P with a layer thickness of 65 nm lattice-matched to
And p-InGaAsP with a layer thickness of 11 nm (composition wavelength 790
nm) and p-GaAs with a layer thickness of 65 nm and p-InGaAsP with a layer thickness of 11 nm (composition wavelength 790 nm)
P-type semiconductor multilayer film reflecting mirror 20 having a periodic structure (45 periods) in which the above combinations are alternately laminated, a p-InGaAsP spacer layer 21, an In _0.2 Ga _0.8 As strained quantum well active layer 22, and an n-InGaAsP spacer layer 23. Are sequentially formed by a chemical beam epitaxy method. The composition of InGaAsP having a composition wavelength of 790 nm is In _0.12 Ga.
_0.88 As _0.76 P _0.24, which is lattice-matched with GaAs within a range of ± 0.2%.

Then, in the same manner as in the above-mentioned embodiment, the p-type semiconductor multilayer film reflecting mirror 20 was etched to the middle of the p-type semiconductor multilayer film reflecting mirror 20 by reactive ion beam etching to form a convex light emitting region (7 μm).
Forming a corner). After that, the SiO ₂ burying layer 24 was formed, and then the ring-shaped n-side electrode 25 was formed. After that, a dielectric multilayer film reflecting mirror 26 having a periodic structure (10 cycles) in which SiO ₂ films and SiN films are alternately laminated with a thickness of ¼ times the oscillation wavelength in each medium is formed. The p-side electrode 27 was formed on the lower part. Laser light 2
8 is taken out from the side of the dielectric multilayer film reflecting mirror.

The prototype device was tested at room temperature for continuous operation.
It oscillated with a threshold current of 1 mA. Furthermore, by introducing a low resistance structure into the n-type semiconductor multilayer film reflecting mirror, the device resistance is about 30 ohms, which is the same as that of the conventional 0.98 μm band surface emitting semiconductor laser without using the InGaAsP layer. It could be reduced to about 1/50.

[0022] In the above embodiments 2 and 3, a dielectric multilayer film reflective mirror has been described for the case of using a combination of SiN and when SiO ₂ is used in combination with a-Si and SiO _2, TiO ₂ And SiO ₂ or CaF ₂ and SiO ₂
Almost the same characteristics were obtained with the laser device using the combination of No. ₂ and the combination of MgO ₂ and SiO ₂ . Also,
In the above embodiments, application to a single surface emitting semiconductor laser has been described, but it is obvious that the present invention can also be applied to a two-dimensional laser array used for an optical interconnect or the like.

[0023]

As described above, between the InGaP layer and the GaAs layer forming the semiconductor multi-layer film reflective mirror, the forbidden band width which is intermediate between the forbidden band widths of the respective layers is provided. By forming the InGaAsP layer containing both the constituent V group elements, the formation of a strained layer due to the substitution of As and P on the growth surface during the formation of the semiconductor multilayer film is reduced, and the element resistance is small and the Al-free The surface emitting semiconductor laser of was obtained. This surface emitting semiconductor laser has a low threshold value, high output, and can be continuously operated at high temperature.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a surface emitting semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a principle diagram for explaining the operation of a conventional example and the present invention.

FIG. 3 is a schematic sectional view of a surface emitting semiconductor laser according to a second embodiment of the present invention.

FIG. 4 is a schematic sectional view of a surface emitting semiconductor laser according to a third embodiment of the present invention.

[Explanation of symbols]

1, 12 ... N-type GaAs substrate 2, 13 ... N-type semiconductor multilayer film reflecting mirror 3, 23 ... N-InGaAsP spacer layer 4, 14, 22 ... Active layer 5, 21 ... P-InGaAsP spacer layer 6, 20 ... P Type semiconductor multilayer film reflecting mirror 7, 9, 16, 27 ... P-side electrode 8, 10 ... Current constricting layer 11, 18, 25 ... N-side electrode 15 ... Polyimide burying layer 17, 26 ... Dielectric multilayer film reflecting mirror 19 ... p-type GaAs substrate 24 ... SiO ₂ burying layer 28 ... laser light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Misuzu Sagawa 1-280, Higashi Koikeku, Kokubunji, Tokyo (Inside Central Research Laboratory, Hitachi, Ltd.) Central Research Laboratory

Claims (8)

[Claims] 1. An active layer for generating light is formed on a semiconductor substrate.
-Type InGaP layers and n-type GaAs layers are alternately laminated to form a first semiconductor multilayer-film reflective mirror, and p-type InGaP layers and p-type GaAs layers are alternately laminated to form a second semiconductor multilayer-film reflective mirror In a surface emitting semiconductor laser in which a laminated structure sandwiched between mirrors is formed, an InGaP bandgap is formed in at least one of the InGaP layer and the GaAs layer of each of the first and second semiconductor multilayer film reflecting mirrors. 2. A surface emitting semiconductor laser having an InGaAsP layer having a bandgap intermediate between the bandgap of GaAs and that of GaAs. 2. An active layer for generating light is provided on a semiconductor substrate.
In a surface emitting semiconductor laser in which a laminated structure sandwiched between a semiconductor multilayer film reflecting mirror in which InGaP layers and GaAs layers are alternately laminated and a dielectric multilayer film reflecting mirror are formed, an InGaP layer of the semiconductor multilayer film reflecting mirror is formed. A surface emitting semiconductor laser, wherein an InGaAsP layer having a bandgap intermediate between the bandgap of InGaP and the bandgap of GaAs is provided in at least one of the GaAs layers. 3. The surface emitting semiconductor laser according to claim 1, wherein the semiconductor substrate is GaAs, and the active layer is composed of at least one InGaAs strained quantum well layer. Light emitting semiconductor laser. 4. The surface emitting semiconductor laser according to claim 1, 2 or 3, wherein the lattice constant of the InGaP layer is a value within ± 0.2% of the lattice constant of the semiconductor substrate. Surface emitting semiconductor laser. 5. The surface emitting semiconductor laser according to claim 1, wherein the lattice constant of the InGaAsP layer is a value within ± 0.2% of the lattice constant of the semiconductor substrate. A characteristic surface emitting semiconductor laser. 6. The surface emitting semiconductor laser according to claim 1, wherein the composition wavelength of the InGaAsP layer is in the range of 760 to 790 nm at room temperature. 7. The surface emitting semiconductor laser according to claim 1, wherein the composition of the InGaAsP layer is In _1-x Ga _x As _y P _1-y , where x = 0. 79
To a surface-emitting semiconductor laser having a composition in the range of 0.92. 8. The surface emitting semiconductor laser according to claim 2, wherein the dielectric multilayer film reflecting mirror comprises a SiO ₂ film and an amorphous S film.
a multilayer film in which i films are alternately stacked, a multilayer film in which SiO ₂ films and SiN films are alternately stacked, a multilayer film in which TiO ₂ films and SiO ₂ films are alternately stacked, and a CaF ₂ film and SiO ₂ film. 1. A surface emitting semiconductor laser, comprising a multilayer film which is alternately stacked or a multilayer film which is a stack of MgO ₂ films and SiO ₂ films.