JPH09298337A - Semiconductor distribution bragg reflecting mirror and surface light emitting type semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor distribution Bragg reflecting mirror which has high reflectivity with a small number of layers, a surface light emitting semiconductor laser using the semiconductor distribution Bragg reflecting mirror as a reflecting mirror, and an application system such as an optical interconnection using the surface light emitting semiconductor laser as a light source. SOLUTION: A periodical structure (13 periods) wherein In0.42 Ga0.58 P layers 12 having a film thickness of 104nm and tensile strain of 0.3% and In0.05 Ga0.95 As layers 13 having a film thickness of 90nm, compression strain of 0.35% are alternately laminated is formed on a GaAs substrate 1 by using an organic metal vapor growth method. Therefore, a thin semiconductor distribution Bragg reflecting mirror having high reflectivity can be provided, and the performance of a surface light emitting type semiconductor laser, a surface light emitting type light emitting diode, a light receiving element, etc., can be improved. The light emitting type semiconductor laser can be used in an application system such as an optical interconnection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of optical devices and optical application systems, and a reflecting mirror made of a semiconductor suitable for them, a semiconductor laser device using the same (in particular, a surface emitting laser), Further, the present invention relates to an optical application device such as an optical interconnection system using these.

[0002]

2. Description of the Related Art A semiconductor distributed Bragg reflector, which is formed by alternately stacking two types of semiconductors having different refractive indexes and having lattice matching, and which reflects incident light by light wave interference known as Bragg reflection, is a surface emitting semiconductor laser. It is used for etc.
For example, InGaP layer and G that are lattice-matched to a GaAs substrate
The reflection characteristics of a surface-emitting laser reflecting mirror in which aAs layers are alternately laminated are described in Japanese Journal of Applied Physics Part.
1 Vol. 34 No. 2B (1995) pp. 1253-1256.

[0003]

The semiconductor distributed Bragg reflector reflects light in a specific wavelength range based on the periodic refractive index distribution of the semiconductor. Usually, a structure in which the refractive index of the semiconductor laminated structure is periodically changed by the optical length of ½ wavelength of the light to be reflected is used. In particular, a structure in which two types of semiconductor layers having different refractive indexes are alternately laminated with an optical thickness of ¼ wavelength is often used. However, since the above-mentioned conventional technique uses a combination of two types of materials that are lattice-matched, there is a limit to the difference in refractive index that can be taken. For this reason, the number of layers must be increased to obtain high reflectance. As the number of stacked layers increases, the difficulty of manufacturing the semiconductor distributed Bragg reflector increases exponentially, and the yield of the device deteriorates. Further, the series resistance of the semiconductor distributed Bragg reflector increases in proportion to the number of stacked layers, and the increase of the series resistance increases the power consumption of the device. Furthermore, when the difference in refractive index is small, the number of layers required to obtain the same reflectance is large, and the penetration length of light is long, so that light is absorbed by free carriers and is lost due to scattering at the laminated interface. In some cases, the required reflectance may not be obtained no matter how many layers are stacked. Thus, in the semiconductor distributed Bragg reflector formed by the conventional technique,
There are many drawbacks because the difference in the refractive index of the material system to be composed is small and the number of layers must be large.

It is an object of the present invention to provide a semiconductor distributed Bragg reflector which can obtain a high reflectance with a small number of layers, and a surface emitting semiconductor laser having excellent characteristics using the semiconductor distributed Bragg reflector. And an optical application device such as an optical interconnection system using the surface-emitting type semiconductor laser as a light source.

[0005]

The above object is to provide a reflecting mirror constituted by a plurality of semiconductor layers so as to reflect incident light by light wave interference, in which the refractive index changes periodically, that is, a so-called semiconductor distributed Bragg reflecting mirror. In, the high refractive index region (first semiconductor layer) has a compressive strain, and the low refractive index region (second semiconductor layer) has a tensile strain. Further, in a semiconductor distributed Bragg reflector, which is formed on a semiconductor substrate and reflects incident light by light wave interference, in which the refractive index periodically changes, at least a part of the semiconductor forming the high refractive index portion is the semiconductor substrate. This is achieved by using a semiconductor having a lattice constant larger than the lattice constant, and at least a part of the semiconductor forming the low refractive index portion being formed of a semiconductor having a lattice constant smaller than the lattice constant of the semiconductor substrate.

The semiconductor distributed Bragg reflector of the present invention can be used as a reflector of a semiconductor laser, particularly a surface emitting semiconductor laser. That is, according to the present invention, an active layer that emits light is provided above the semiconductor substrate (above the main surface of the substrate), and a reflector is provided above and below the active layer to obtain laser light from the light generated from the active layer. A surface-emitting type semiconductor laser that has a resonator structure and emits light in a direction substantially perpendicular to a semiconductor substrate (to be precise, the main surface of the substrate) is provided. The semiconductor distributed Bragg reflector including a semiconductor distributed Bragg reflector that changes and reflects incident light by light wave interference (that is, formed by alternately stacking two kinds of semiconductor layers having different refractive indices), and includes a high refractive index portion of the semiconductor distributed Bragg reflector. At least part of the semiconductor to be formed has compressive strain, and at least part of the semiconductor forming one of the low refractive index portions has tensile strain. Regarding the specifications of this semiconductor distributed Bragg reflector, if specified from another point of view, at least one of the high-refractive-index semiconductor layers is a semiconductor having a lattice constant larger than that of a substrate made of a semiconductor single crystal, and has a low refractive index. At least one of the semiconductor layers is made of a semiconductor having a lattice constant smaller than that of the semiconductor substrate.

Further, the above-mentioned surface-emitting type semiconductor laser utilizing the semiconductor distributed Bragg reflector of the present invention can be used in application systems such as optical interconnection and optical fiber communication. In that case, the surface-emitting type semiconductor laser can be used as a laser light transmission module in which it is packaged together with an IC (integrated circuit) for driving it and optical fiber components.

Hereinafter, the operation of the present invention will be described. For simplification, a semiconductor distributed Bragg reflector having a periodic structure in which two types of semiconductor layers having different refractive indexes are alternately laminated with an optical thickness of ¼ wavelength on a semiconductor substrate will be described as an example.
When these two layers are alternately laminated using a material having a lattice constant larger than that of the substrate material for the high refractive index layer and a material having a lattice constant smaller than that of the substrate material for the low refractive index layer, the high refractive index layer Has a compressive strain, and the low refractive index layer has a tensile strain. In this case, the refractive index of the high refractive index layer becomes larger than that when using a material that lattice-matches the substrate material,
The refractive index of the low refractive index layer is smaller than that when a material that lattice-matches the substrate material is used. Therefore, a large difference in refractive index can be obtained, and thus a high reflectance can be obtained with a smaller number of layers than in the case of using a material that lattice-matches. Further, since the high refractive index layer and the low refractive index layer are respectively distorted in opposite directions, the average distortion amount in the entire reflecting mirror is small (stress compensation structure).
Therefore, defects such as lattice mismatch transition do not occur, and a good quality crystal can be obtained.

As an example, FIG. 6 shows a prior art GaAs.
A semiconductor distributed Bragg reflector made of In _0.5 Ga _0.5 P and GaAs that lattice-matches the substrate, and In _0.42 Ga _0.58 P with a tensile strain of 0.3% and I with a compressive strain of 0.35% according to the present invention.
The relationship between the number of layers and the reflectance in a semiconductor distributed Bragg reflector made of n _0.05 Ga _0.95 As is shown. The solid line shows the case where there is no loss in the semiconductor distributed Bragg reflector, and the loss is 40
The case of cm to ¹ is indicated by a broken line. First, the case where there is no loss will be described. Conventional lattice matching type In _0.5 Ga _0.5 P
In the / GaAs distributed Bragg reflector, 32 pairs of stacked layers (that is, a structure in which 32 semiconductor layers having different compositions are alternately stacked) are required to obtain a reflectance of 99.5%. On the other hand, the stress-compensated In _0.42 Ga _0.58 P / In _{0.05 of} the present invention
The Ga _0.95 As distributed Bragg reflector may have 13 pairs of laminated layers, and the required number of laminated layers can be reduced to about 1/3. Then the loss is 4
The case of 0 cm to ¹ will be described. The stress-compensated In _0.42 Ga _0.58 P / In _0.05 Ga _0.95 As distributed Bragg reflector of the present invention can obtain a reflectance of 99.5% with 15 pairs.
With the conventional lattice-matched In _0.5 Ga _0.5 P / GaAs distributed Bragg reflector, the reflectivity is 9 no matter how many layers are stacked.
It saturates at 9.3% and does not reach 99.5%. It is considered that there is a loss between the case where there is no loss in the actual multilayer film reflecting mirror and the case where the loss is 40 cm to ¹ , and the stress compensation type In of the present invention is
_It can be seen that the _0.42 Ga _0.58 P / In _0.05 Ga _0.95 As distributed Bragg reflector is very effective in reducing the number of layers and obtaining a high reflectance.

In the above description, the structure in which two types of semiconductor layers are alternately laminated is described, but even when the refractive index in the semiconductor film changes continuously or stepwise with a periodicity of ½ wavelength, By using a material having compressive strain in the high refractive index portion and a material having tensile strain in the low refractive index portion, the same effect as described above can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described below with reference to Examples 1 to 3 and FIGS. 1 to 5.

<Embodiment 1> FIG. 1 is a structural diagram showing an embodiment of a semiconductor distributed Bragg reflector of the present invention. GaAs
N-type strain of 0.3% tensile in thickness 104nm by organometallic vapor phase epitaxy on the substrate 1 In _0.42 Ga _0.58 P layer 12 and the film thickness 90nm with a compressive strain 0.35% n-type an In _0.05 Ga
Periodic structure in which _0.95 As layers 13 are alternately laminated (13 periods)
Was formed. The film thickness of both layers is 1.
The thickness is 3 μm (μm), and the thickness is set to an optical quarter wavelength. Since both layers have strains in opposite directions, the average amount of strain in the entire reflecting mirror was small, defects such as lattice mismatch transition did not occur, and good quality crystals could be obtained.
Figure 2 shows the reflection spectrum of the prototype reflector. The reflectance of the light to be reflected at a wavelength of 1.3 microns is 99.5.
%Met. As a result, it was possible to obtain a high reflectance of 99.5% with about 1/3 the number of layers as compared with the conventional semiconductor distributed Bragg reflector.

<Embodiment 2> This is one embodiment of the present invention.
3 micron surface emitting semiconductor laser (oscillation wavelength 1.3
FIG. 3 shows a configuration in which a (μm semiconductor laser) is coupled to an optical fiber. This device has the following semiconductor multilayer structure on the n-GaAs substrate 1. Film thickness 106 nm, tensile strain 0.
35% n-type In _0.3 Ga _0.7 As _0.1 P _0.9 and film thickness 90n
m, a semiconductor distributed Bragg reflector 2 having a periodic structure (16 periods) in which a combination of n-type In _0.06 Ga _0.94 As having a compressive strain of 0.4% is alternately laminated, and an n-type InP having a film thickness of 500 nm.
Clad layer 3, p-type InGaAsP active layer (composition wavelength: 1.3 μm) 4 having a thickness of 300 nm, p-type InP clad layer 5 having a thickness of 580 nm, p-type InG having a thickness of 300 nm
aAsP contact layer 6. Among these layers, the semiconductor distributed Bragg reflector 2 is made of GaA by metalorganic vapor phase epitaxy.
s on a substrate. Further, each layer from the n-type InP clad layer 3 to the p-type InGaAsP contact layer 6 is I
After growing on an nP substrate (not shown in FIG. 3 for removal in a subsequent step) by a metal organic chemical vapor deposition method, it was bonded on the semiconductor distributed Bragg reflector 2 by a direct bonding method. The InP substrate was removed by wet etching after joining. Diameter 10 by CVD process and photoresist process
A circular micron SiO ₂ film is formed, and this is used as a mask to wet-etch the p-type InP clad layer 5 halfway to form a convex shape. After that, the polyimide 7 is applied and cured while leaving the SiO ₂ mask. Next, RIE
In the (reactive ion etching) step, the polyimide 7 is etched until the SiO ₂ mask is exposed, and the SiO ₂ mask on the upper part of the mesa is removed as shown in the figure to obtain a flat surface. Then, the ring-shaped p-side electrode 8 is formed by the lift-off method, and the SiO ₂ film and the a-Si film (amorphous silicon film) are further formed by the sputter deposition method.
A dielectric multi-layered film reflecting mirror 10 having a periodic structure (4 periods) in which each of the above materials was alternately laminated with a thickness of 1/4 times the oscillation wavelength was formed, and the n-side electrode 9 was formed. The laser light 11 is extracted from the dielectric multilayer film reflecting mirror side and coupled to the optical fiber 14.

The 1.3 μm surface-emitting type semiconductor laser according to this embodiment has a threshold current of 3 mA at room temperature and a threshold voltage of 1. 1V, slope efficiency 0.5mW /
Device characteristics of mA and maximum output of 10 mW were obtained, and a surface-emitting type semiconductor laser having a low threshold current and a low threshold voltage was obtained. Since the oscillation wavelength of this laser is 1.3 microns, which matches the wavelength band used for optical fiber communication,
It could be used as a light source for optical fiber communication with a single element.

<Embodiment 3> In this embodiment, light is emitted using a 4 × 4 two-dimensional laser array module of a polyimide-embedded 0.98 micron surface emitting semiconductor laser diode (that is, an oscillation wavelength of 0.98 μm). An interconnection system was created. FIG. 4 shows an overall configuration diagram.
Two computers equipped with a transmitting board and a receiving board are connected by an optical fiber array to form an optical interconnection system. Eight laser light transmitting modules and eight laser light receiving modules are mounted on the transmitting board and the receiving board, respectively. The laser light transmission module is composed of a 4 × 4 surface-emitting type semiconductor laser two-dimensional array, components for driving them, such as an IC and an optical fiber array. Laser light receiving module is 4 × 4
Two-dimensional array of photodiodes and their driving I
It is composed of components such as C and an optical fiber array. In this system, signals of 8 × 4 × 4 = 128 channels can be transmitted in parallel. Each surface emitting semiconductor laser has 200
Since a signal of Mb / sec (Mb is a unit of megabit) can be transmitted, a large capacity signal of 25.6 Gb / sec (Gb is a unit of gigabit) can be transmitted in the entire optical interconnection system.

In the production of this optical interconnection system, parts other than the surface-emitting type semiconductor laser can be easily produced by the conventional technique. Therefore, the production of the surface-emitting type semiconductor laser will be described in detail below. FIG. 5 shows a cross sectional structure of the device. 1 is an n-GaAs substrate (n-type dopant concentration:
n = 1 × 10 ¹⁸ cm ³ ), 2 an n-type semiconductor distributed Bragg reflector (n = 1 × 10 ¹⁸ cm ³ ), 15 a GaAs spacer layer, 16 an InGaAs / GaAs strained quantum well active layer, 17 Is p-InGaP lattice-matched to a GaAs substrate
Cladding layer (p-type dopant concentration: p = 1 × 10 ¹⁸ cm
~ ³ ) and 18 are p-GaAs contact layers (p = 1 × 10
^{It is 19} cm ~ ³ ). The active layer 16 has three layers of 7 nm thickness I.
A strained quantum well layer having a band gap of 1.27 eV (wavelength: 0.98 micron) was used by separating the nGaAs well layer with a GaAs barrier layer having a thickness of 10 nm. The semiconductor distributed Bragg reflector 2 has a high refractive index tensile strain InGa.
P layers and low-refractive-index compressive-strained InGaAsP layers were alternately laminated with an optical thickness of ¼ wavelength. The number of stacked layers was set to 25 in order to make the reflectance 99.9% or more. Crystals of each semiconductor layer were continuously grown in a high vacuum of 1 × 10 to ⁵ Torr using an actinic ray epitaxy apparatus. Organic metal arsine, triethylgallium and trimethylindium were used as the group III raw materials, and phosphine and arsine were used as the group V raw materials. Si and Be were used as raw materials for the n-type dopant and the p-type dopant, respectively. Growth temperature is 500 ℃
I went in. Next, a circular SiO ₂ film having a diameter of 3 μm (not shown in FIG. 5 to be removed in a later step, not shown in FIG. 5) is formed by a chemical vapor deposition step and a photoresist step, and the n-type semiconductor distribution is used as a mask. The Bragg reflector 2 is wet-etched halfway to form a mesa shape. After that, SiO ₂
The SiO ₂ protective layer 19 is formed by a chemical vapor deposition process while leaving the mask, and the polyimide 7 is applied and cured.
Next, the polyimide 7 is etched by reactive ion beam etching until the SiO ₂ mask is exposed, and the SiO ₂ mask on the top of the mesa is removed as shown in the figure to obtain a flat surface. After that, the ring-shaped p-side electrode 8 was formed by the lift-off method, the dielectric multilayer reflecting mirror 10 was further formed by the sputter deposition method, and the n-side electrode 9 was formed. The dielectric multilayer film reflecting mirror 10 has
A high-refractive-index amorphous Si layer having a thickness of 4 wavelengths and a low-refractive-index SiO ₂ layer having a thickness of ¼ wavelength were alternately laminated in the dielectric. The number of stacked layers was set to 6 in order to make the reflectance 99.9% or more.

In the surface emitting semiconductor laser of this embodiment, a semiconductor distributed Bragg reflector having an extremely high reflectance (99.9%) was obtained, so that the threshold current at room temperature was 10 microamps and the threshold voltage was 1. 3V was obtained and low power consumption operation was realized. Further, since the semiconductor distributed Bragg reflector having a high reflectance was obtained with a small number of layers, the device yield was high and the device could be provided at low cost. Therefore, this optical interconnection system could be supplied as an inexpensive and low power consumption system.

In this embodiment, the dielectric multilayer film is used for the p-side reflecting mirror of the surface emitting laser, but of course, other reflecting mirrors such as a semiconductor distributed Bragg reflecting mirror may be used. Further, in the present embodiment, the material system of the amorphous Si layer and the SiO ₂ layer was used for the dielectric multilayer mirror of the surface emitting laser, but the dielectric multilayer mirror has a high refractive index layer and a low refractive index layer alternately. Therefore, other material systems such as SiN and SiO ₂ , amorphous Si and SiN, or TiO ₂ and SiO ₂ may be used. Further, it goes without saying that the surface emitting laser shown in this embodiment can also operate as a single element.

[0019]

According to the present invention, since it is possible to provide a semiconductor distributed Bragg reflector having a high reflectance with a small number of layers, a surface emitting semiconductor laser, a laser light transmission module or an optical interconnection, an optical fiber communication, etc. Can be used in the application system of.

[Brief description of drawings]

FIG. 1 is a structural diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing the reflection characteristics of the semiconductor distributed Bragg reflector of the present invention.

FIG. 3 is a structural diagram of a surface emitting semiconductor laser having a semiconductor distributed Bragg reflector which is an embodiment of the present invention.

FIG. 4 is a configuration diagram of an optical interconnection system according to a third embodiment of the present invention.

FIG. 5 is a sectional view of a surface emitting laser according to a third embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between the number of stacked layers and the reflectance in the conventional semiconductor distributed Bragg reflector and the semiconductor distributed Bragg reflector of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... GaAs substrate, 2 ... n-type semiconductor distributed Bragg reflector, 3 ... n-InP clad layer, 4 ... p-InGaAs
P active layer, 5 ... p-InP clad layer, 6 ... p-InG
aAsP contact layer, 7 ... Polyimide embedded layer, 8
... n electrode, 9 ... n electrode, 10 ... dielectric multilayer mirror, 1
1 ... Laser light, 12 ... In _0.35 Ga _0.65 P layer, 13 ... I
n _0.14 Ga _0.86 As layer, 14 ... Optical fiber, 15 ... Ga
As spacer layer, 16 ... InGaAs / GaAs strained quantum well active layer, 17 ... p-InGaP clad layer, 18 ...
p-GaAs contact layer, 19 ... SiO ₂ film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Kondo 1-280, Higashi Koikeku, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor, Kazuhisa Uomi 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Center

Claims (5)

[Claims] 1. A semiconductor distributed Bragg reflector which changes its refractive index periodically and reflects incident light by light wave interference,
A semiconductor distributed Bragg reflector, wherein at least a part of a semiconductor forming a high refractive index portion has a compressive strain, and at least a part of a semiconductor forming a low refractive index portion has a tensile strain. 2. A semiconductor distributed Bragg reflector formed on a semiconductor substrate and having a refractive index that periodically changes and reflects incident light by light wave interference, wherein at least a part of a semiconductor forming a high refractive index portion is the above-mentioned. A semiconductor having a lattice constant larger than that of the semiconductor substrate, and at least a part of the semiconductor forming the low refractive index portion is formed of a semiconductor having a lattice constant smaller than that of the semiconductor substrate. Semiconductor distributed Bragg reflector. 3. A substrate structure comprising a semiconductor substrate having an active layer for generating light and a resonator structure in which a reflector is sandwiched between upper and lower sides of the active layer to obtain laser light from the light generated by the active layer. And a surface-emitting type semiconductor laser that emits light in a substantially vertical direction, at least one of the reflecting mirrors includes a semiconductor distributed Bragg reflecting mirror that reflects the incident light by light wave interference, the refractive index changing periodically, and the semiconductor At least part of the semiconductor forming the high refractive index portion of the distributed Bragg reflector has compressive strain, and at least part of the semiconductor forming the low refractive index portion of the semiconductor distributed Bragg reflector has tensile strain. A surface-emitting type semiconductor laser characterized by: 4. A semiconductor substrate having an active layer that emits light and a resonator structure in which a reflector is sandwiched between the upper and lower sides of the active layer to obtain laser light from the light generated from the active layer. And a surface-emitting type semiconductor laser that emits light in a substantially vertical direction, at least one of the reflecting mirrors includes a semiconductor distributed Bragg reflecting mirror that reflects the incident light by light wave interference, the refractive index changing periodically, and the semiconductor At least a part of the semiconductor forming the high refractive index portion of the distributed Bragg reflector is made of a semiconductor having a lattice constant larger than that of the semiconductor substrate, and forms the low refractive index portion of the semiconductor distributed Bragg reflector. A surface-emitting type semiconductor laser, wherein at least a part of the semiconductor is composed of a semiconductor having a lattice constant smaller than that of the semiconductor substrate. 5. An optical interconnection system, wherein the surface emitting semiconductor laser according to claim 3 or 4 is used as a light source.