JP3230576B2 - Semiconductor light emitting device - 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 light emitting device in which a multilayer structure and an active layer are formed as a composite structure on a semiconductor substrate and emits light in a direction perpendicular to the laminated surface. The present invention relates to a uniquely determined semiconductor light emitting device.

[0002]

2. Description of the Related Art As a semiconductor light emitting device of this kind, for example, a semiconductor light emitting device having a distributed Bragg reflector formed of a semiconductor multilayer film and a semiconductor active layer formed on a GaAs substrate, the polarization of oscillating light is uniquely determined. To decide
Several approaches have been taken. One is a method of fabricating a structure on a plane orientation such as (311) having different optical transition probabilities in a plane. In addition, there is a method of making the element structure anisotropic and giving anisotropy to gain and loss for an optical mode.

[0003] Further, in a commonly used semiconductor surface emitting laser having a (100) plane orientation having no in-plane optical anisotropy and having a symmetric shape in the plane, the polarization of oscillation light is determined. The use of quantum dots having an anisotropic structure in the plane for the active layer has also been proposed and proven. This is described by Saito et al. In Applied Physics Letters, Vol. 71, No. 5 (19
1997), pp. 590-592. In this report, 10 layers of InGaAs quantum dots are used as the active layer, and a surface-emitting laser on a GaAs substrate realizes oscillation in the [01 ^* 1] direction (* means a bar) at a wavelength of 985 nm. are doing.

[0004]

Considering each of the above-mentioned prior arts for determining the polarization of the oscillation light of the surface emitting laser, it is found that the structure in the plane orientation other than the (100) plane is In some cases, the manufacturing process becomes complicated, and when the element structure is asymmetric, the light emission pattern becomes asymmetric, and there is a problem in that loss occurs when the device is coupled to a symmetric waveguide structure. . In the case where an active layer is formed of a quantum dot having an asymmetric structure, which does not have these problems, the current manufacturing technology is compared with a conventional surface emitting laser using a quantum well as an active layer due to variation in the size of the quantum dot. In addition, there is a problem that characteristics such as an oscillation threshold value are deteriorated.

On the other hand, in a semiconductor light emitting device in which a surface emitting laser or the like is formed on a (100) substrate, the above-described problem is rarely caused and good characteristics are obtained. As a layer, a symmetrical light emission pattern is realized, and when an element is manufactured by a simple process technique, it is difficult to uniquely control the polarization of light emission, which causes noise when performing intensity modulation. And the laser characteristics were degraded.

SUMMARY OF THE INVENTION An object of the present invention is to overcome such disadvantages of the prior art, to provide a quantum well having good characteristics but indeterminate polarization in a plane, a quantum wire having anisotropic in-plane emission, Or to provide a semiconductor light-emitting element that realizes the required characteristics by combining quantum dots, has a symmetrical light-emitting pattern, and the polarization is uniquely determined, and emits light in a direction perpendicular to the stacked surface. is there.

[0007]

A semiconductor light emitting device according to the present invention has a composite structure of a multilayer film structure and an active layer emitting light by current injection on a semiconductor substrate, and is defined by the multilayer film structure. The active layer emits light having a wavelength in a direction perpendicular to the stacking surface, and the active layer has at least one or more quantum wells having a film thickness of about the electron de Broglie wavelength or less, and
At least one of a layer composed of quantum wires in which the carrier is two-dimensionally confined and a layer composed of semiconductor quantum dots three-dimensionally confined, whose dimension is about 100 nm or less in the lamination direction and in the lamination direction. It has one or more layers, and the resonance wavelength is set to a wavelength common to the gain band of the quantum well and the gain band of the quantum wire or quantum dot.

In the semiconductor light emitting device according to the present invention, the dimension in the lamination plane and in the lamination direction is about 100 nm or less,
It is known theoretically and experimentally that a layer made of quantum wires in which carriers are confined two-dimensionally has a large gain for polarized light parallel to the direction of the wires when light emission occurs by current injection. Similarly, in a layer made of semiconductor quantum dots that are confined three-dimensionally and have a dimension of about 100 nm or less in the lamination plane and lamination direction,
It is experimentally known that the gain for polarized light parallel to the direction in which the size of the quantum dot structure increases is large.
Moreover, the quantum dots are usually asymmetric in shape regardless of the manufacturing method due to the asymmetry of the crystal axis in the semiconductor plane.

Therefore, if the quantum well structure is combined with the above-described quantum wires, quantum dots, and the like, and the resonance wavelength is set to a wavelength common to the gain band of the quantum well and the gain band of the quantum wires or quantum dots, When light emission is generated by current injection, as a whole, the gain for polarized light in a specific direction, that is, the direction of the quantum wire or the direction in which the size of the quantum dot is large, is large. The injected current is
If most is consumed by radiative recombination in the quantum well and the rest is consumed by quantum wires or quantum dots, characteristics such as the oscillation threshold are comparable to those of semiconductor light-emitting devices using a conventional quantum well for the active layer. In addition, because of the anisotropy of the gain as a whole, the gain of polarized light in a specific direction increases, and oscillation with the polarized light is realized.

Here, the quantum wires or quantum dots are made of a semiconductor having a lattice constant different from that of a substrate. If the quantum wires or quantum dots are made of a semiconductor with a lattice constant different from that of the substrate, the effect of distortion enhances the anisotropy of light emission and increases the anisotropy of gain, enabling more stable polarization control. Becomes

Further, said multi-layer laminated structure is a multilayer structure of a semiconductor, for example, _{Al x Ga 1-X As /} Al y
It is made of Ga _1-y As, wherein x is 0 or more and less than 1, and y is more than 0 and 1 or less. This eliminates the problem of lattice mismatch, so that a multilayer film structure can be easily formed.

Further, the semiconductor substrate is made of GaAs, and the quantum well has a thickness of In _z G in which z is 0 or more and 1 or less.
a _1-z As, wherein the quantum wires or quantum dots are made of In _a Ga _1-a As in which a is 0 or more and 1 or less. In this way, it is possible to realize a semiconductor light emitting device that oscillates at a wavelength of 0.85 mm or 0.98 mm, which is important for application.

Further, the semiconductor substrate is made of GaAs, and the quantum well has a G value of z being greater than 0 and equal to or less than 1.
aAs _1-Z Sb _Z , wherein the quantum wires or quantum dots are made of In _a Ga _1-a As in which a is 0 or more and 1 or less. By doing so, the wavelength 1.3
It is possible to realize a semiconductor light emitting device having a wavelength of about 0.5 mm in a low loss and low dispersion wavelength range of a quartz fiber.

Further, the fact that the lattice constant of the semiconductor forming the quantum dot structure is different from the lattice constant of the layer forming the surface on which the quantum dot structure is laminated, makes it possible for the quantum dot structure to grow in a self-forming manner. This makes it possible to easily realize a semiconductor light emitting device with good device characteristics only by growth when producing a layer structure.

[Detailed Description of the Invention] Next, an embodiment of the present invention will be described with reference to the drawings.

(First Embodiment) FIG. 1A shows GaAs.
FIG. 4 is a schematic cross-sectional view of an example in which the present invention is applied to a surface emitting laser on a substrate 1. FIG. 4B shows an active layer portion near the surface before the regrowth after forming the quantum wires. It is a perspective view which represents typically. First, a distributed Bragg reflector 2 having a multilayer structure of Si-doped n-type GaAs / AlAs is grown on an n-type GaAs substrate 1 having a (100) plane orientation by MBE, and a GaAs cladding layer is formed thereon. After growing 3, three cycles of a 6 nm thick In _0.2 Ga _0.8 As quantum well 4 and a 6 nm thick GaAs barrier layer 5 are grown, and then an about 8 nm thick In _0.2 Ga _0.8 As layer 6 is formed. The outermost surface is covered with a 2 nm GaAs layer 7. After the growth up to this point, the above-mentioned In near the surface is formed by the method described below.
_The quantum wire layer 8 is formed by patterning the _0.2 Ga _0.8 As layer 6.

First, a resist is applied to the surface of the GaAs layer 7 and is exposed to an electron beam to have a width of 20 nm.
m linear resist patterns at intervals of 20 nm [0
11]. Thereafter, the GaAs layer 7 and In _0.2 Ga _{0.8 are formed} by reactive ion beam etching.
A portion of the As layer 6 without a resist pattern is reduced to about 10 nm.
Etch. MBE growth is again performed on the surface formed of the quantum wire layer 8 thus formed. Here, a cladding layer 3 and a distributed Bragg reflector 9 having a multilayer structure of Be-doped p-type GaAs / AlAs are grown, and a GaAs layer 10 for ohmic junction is grown on the surface. Thereafter, a circular mesa structure having a diameter of about 10 mm is formed by ordinary photolithography and wet etching, and an electrode 11 for current injection is formed on the upper surface and a portion close to the mesa. Here, the resonance wavelength of the distributed Bragg reflector is designed to be 980 nm.

Here, the 6 nm thick In _0.2 Ga _0.8
The As quantum well 4 has a peak wavelength of 980 n due to current injection.
m has a gain. The quantum wire layer 8 is
The gain wavelength slightly changes depending on the amount of current injection.
It has a large gain in the [011] direction from about nm to 960 nm. Therefore, the gain due to current injection is 98
With the peak at 0 nm, the total becomes larger in the [011] direction. FIG. 2 shows the light output characteristics of the surface emitting laser. Oscillation occurred at an injection current of about 10 mA, and the oscillation light was polarized in the [011] direction.
This characteristic was the same in 20 or more devices whose device characteristics were tested.

(Second Embodiment) In the second embodiment, quantum dots are used instead of the quantum wires having the structure shown in the first embodiment. The quantum dot structure obtained by the technique is used. FIG. 3A is a schematic sectional view of the surface emitting laser according to the second embodiment, and FIG. 3B is a schematic sectional view of a region near an active layer immediately after forming a quantum dot. It is a perspective view. The basic structure is the same as that of the first embodiment, but here, the quantum dot structure is formed only by a growth method without using an etching technique.

First, the plane orientation (100) is determined by the MBE method.
Si-doped n-type GaAs /
A distributed Bragg reflector 2 having a multilayer structure of AlAs is grown, and after growing a GaAs cladding layer 3, three periods of 6n are formed.
An In _0.2 Ga _0.8 As quantum well 4 having a thickness of m and a GaAs barrier layer 5 having a thickness of 6 nm are grown, and then InAs and GaAs are alternately formed to form quantum dots.
Laminate 6 nm each. And the total film thickness is 1.4 nm.
When this is reached, the growth of this layer is terminated. in this case,
The average composition of InAs and GaAs is In _0.5 Ga
_The thickness becomes _0.5 As, and the quantum dot structure 21 is formed in a self-forming manner by the lamination of the above total film thickness. Subsequently, a clad layer 3 is grown, and Be-doped p-type GaAs / AlAs
Growing a distributed Bragg reflector 9 having a multilayer structure of
A GaAs layer 10 for ohmic junction is grown on the surface. Thus, a semiconductor multilayer film and a quantum dot structure are continuously formed only by crystal growth. Thereafter, a circular mesa structure having a diameter of about 10 mm is formed by ordinary photolithography and wet etching, and an electrode 11 for current injection is formed on the upper surface and a portion close to the mesa. Here, the resonance wavelength of the distributed Bragg reflector is 98
It is designed to be 0 nm.

As described in the first embodiment, the In _0.2 Ga _0.8 As quantum well 4 having a thickness of 6 nm is formed by current injection.
It has a gain at a peak wavelength of 980 nm. The quantum dot structure 21 has a gain peak due to transition between ground levels of 10%.
00 nm, and the gain peak due to the transition between higher levels is 9
It is on the short wave side near 60 nm. Here, the gain due to the transition between ground levels is in the longitudinal direction of the quantum dot [01
^* 1] It is reported that the size is large in the direction. In addition, the quantum dot obtained by this method has a large gain width due to size variation, and the gain at 980 nm is also [0101].
^* 1] Large in the direction. Therefore, the gain due to the current injection has a peak at 980 nm and is [011] as a whole.
^* 1) It becomes larger in the direction. As for the device characteristics, oscillation occurs at an injection current of about 8 mA, and the oscillation light is [01
^* 1] It was polarized in the direction. This characteristic was the same in 20 or more devices whose device characteristics were tested.

(Third Embodiment) Next, the surface emitting laser shown in the second embodiment, which is a combination of a quantum well and a quantum dot, has an oscillation wavelength of 1.3 m instead of 980 nm.
A third embodiment, m, will be described. FIG. 4 (a)
FIG. 4 is a schematic cross-sectional view of a surface emitting laser according to a third embodiment, and FIG. 4B is a schematic perspective view of a region near an active layer immediately after quantum dots are formed.

First, the plane orientation (100) is determined by the MBE method.
Si-doped n-type GaAs /
A distributed Bragg reflector 2 having a multilayer structure of AlAs is grown, and after the GaAs cladding layer 3 is grown, two cycles of 8
GaAs _0.65 Sb _0.35 quantum well 31 nm thick and 20 nm
A thick GaAs barrier layer 32 is grown. Then, InA
An InAs quantum dot layer 33 is formed in a self-forming manner by supplying an amount for growing s by 0.72 nm. On the self-formed quantum dot layer, a 5 nm-thick In _0.2 Ga _0.8 As strain relaxation layer 34 for continuously reducing the strain of the quantum dots is continuously grown. Subsequently, the cladding layer 3 is grown,
A distributed Bragg reflector 9 having a multilayer structure of Be-doped p-type GaAs / AlAs is grown, and a GaAs layer 10 for ohmic junction is grown on the surface. Thus, a semiconductor multilayer film and a quantum dot structure are continuously formed only by crystal growth. Thereafter, a circular mesa structure having a diameter of about 10 mm is formed by ordinary photolithography and wet etching, and an electrode 11 for current injection is formed on the upper surface and a portion close to the mesa. Here, the resonance wavelength of the distributed Bragg reflector is designed to be 1.28 mm.

In the third embodiment, an 8 nm-thick Ga
The As _0.65 Sb _0z35 quantum well 31 has a gain at a peak wavelength of 1.28 mm due to current injection. Further, when the InAs quantum dot layer 33 is covered with the In _0.2 Ga _0.8 As strain relaxation layer 34, the gain also has a peak wavelength of 1.28 mm. This is because the internal strain of the InAs quantum dots is alleviated to some extent, and the shortening of the band gap wavelength is reduced. Also, the gain from quantum dots is
As in the second embodiment, it is large in the [01 ^* 1] direction, which is the longitudinal direction of the quantum dot. Therefore, the gain due to the current injection is large in the [01 ^* 1] direction as a whole, with a peak at 1.28 mm. In the surface emitting laser according to the third embodiment, an injection current of about 15 mA and a wavelength of 1.2
Oscillation occurred at 8 mm, and the oscillation light was polarized in the [01 ^* 1] direction.

As described above, in the first to third embodiments, (1
00) A surface emitting semiconductor laser in which a semiconductor multilayer film and a quantum well formed on a GaAs substrate are combined with a quantum wire by processing and a quantum dot structure by a self-forming method by growing a strained structure has been described. However, a similar effect can be obtained even when a dielectric multilayer film is used instead of the semiconductor multilayer film.

The semiconductor substrate may have a plane orientation (10
For example, an InP substrate may be used instead of GaAs of 0). Of course, the process for fabricating the element becomes complicated, but even if a plane orientation such as (311) B is used,
The effect according to the present invention appears.

Further, as for the method of forming the quantum wire or the quantum dot structure, in addition to the combination of the growth and the etching of the quantum well structure and the self-forming method, semiconductor fine particles or local strain is effectively used. It may be one that realizes confinement of dimensions. The growth method is M
Metal organic chemical vapor deposition (MOVPE) as well as BE
Or a combination thereof.

Further, in the respective embodiments have been described distributed Bragg reflector comprising a multilayer structure of GaAs / AlAs as the semiconductor multilayer film as an example, In addition to this an In _x G
a _1-x As / InP and _{GaAs 1-xy P x Sb y} / Al
As _1-ab P _a Sb may be used material system such as _b.

[0029]

As described above, according to the present invention, in a semiconductor light emitting device having a multi-layer structure and an active layer, the structure of the active layer is the same as the quantum well and the gain wavelength of the quantum well. By combining quantum wires or quantum dots that have gain in the wavelength range of 素 子, the polarization of the surface emitting laser can be obtained even if the device structure and the plane orientation do not have anisotropic optical characteristics in the plane. Can be controlled, and a semiconductor light emitting device that can uniquely control the polarization of the oscillation light can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a first embodiment of the present invention,
FIG. 9 is a perspective view schematically showing an active layer portion near the surface before regrowth.

FIG. 2 is a graph showing light output characteristics of the surface emitting laser according to the first embodiment.

FIG. 3 is a schematic sectional view of a second embodiment of the present invention,
FIG. 3 is a schematic perspective view of a region near an active layer immediately after forming quantum dots.

FIG. 4 is a schematic cross-sectional view of a third embodiment of the present invention,
FIG. 3 is a schematic perspective view of a region near an active layer immediately after forming quantum dots.

[Explanation of symbols]

Reference Signs List 1 n-type GaAs substrate 2 Si-doped n-type GaAs / AlAs distributed Bragg reflector 3 GaAs cladding layer 4 6 nm thick In _0.2 Ga _0.8 As quantum well 5 6 nm thick GaAs barrier layer 6 About 8 nm thick In _0.2 Ga _0.8 As Layer 7 2 nm GaAs layer 8 Quantum wire layer 9 Be-doped p-type GaAs / AlAs distributed Bragg reflector 10 GaAs contact layer 11 Electrode 21 Self-formed InGaAs quantum dot structure 31 8 nm thick GaAs _0.65 Sb _0.35 quantum well 32 20 nm Thick GaAs barrier layer 33 Self-forming InAs quantum dot layer 34 In _0.2 Ga _0.8 As strain relaxation layer

────────────────────────────────────────────────── ─── Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 JICST file (JOIS)

Claims (7)

(57) [Claims] 1. A multilayer structure having a multilayer structure and an active layer that emits light by current injection formed as a composite structure on a semiconductor substrate, and emits light having a wavelength defined by the multilayer structure in a direction perpendicular to the stacking surface. In the emitting semiconductor light emitting element,
The active layer has at least one or more quantum wells having a film thickness of about the electron de Broglie wavelength or less, and has a dimension of about 100 nm or less in the lamination plane and in the lamination direction.
A carrier comprising two or more layers of quantum wires confined two-dimensionally or a layer of semiconductor quantum dots three-dimensionally confined; A semiconductor light emitting device, wherein a resonance wavelength is set to a wavelength common to gain bands of the quantum wires or quantum dots. 2. The semiconductor light emitting device according to claim 1, wherein said quantum wires or quantum dots are made of a semiconductor having a lattice constant different from that of said semiconductor substrate. 3. The semiconductor light emitting device according to claim 1, wherein said multilayer structure is composed of a semiconductor multilayer film. 4. The method according to claim 1, wherein the semiconductor multilayer film is made of Al _x Ga _{1 -x} A.
s / Al _y Ga consists _1-y As, x is 0 to less than 1,
4. The semiconductor light emitting device according to claim 3, wherein y is greater than 0 and equal to or less than 1. 5. The semiconductor substrate is made of GaAs, and the quantum well has an In _z Ga ₁ -z in which z is 0 or more and 1 or less.
As, the quantum wire or the quantum dot is such that a is 0
2. The semiconductor light-emitting device according to claim 1, wherein the semiconductor light-emitting device is made of In _a Ga _1-a As that is at least 1. 6. The GaAs in which the semiconductor substrate is made of GaAs, and the quantum well has a z of more than 0 and 1 or less.
_2. The semiconductor light emitting device according to claim 1, wherein the semiconductor is made of _1-Z Sb _Z , and the quantum wires or quantum dots are made of In _a Ga _1-a As in which a is 0 or more and 1 or less. 7. The quantum dot structure is grown in a self-forming manner because a lattice constant of a semiconductor forming the quantum dot structure is different from a lattice constant of a layer forming a surface on which the quantum dot structure is stacked. The semiconductor light emitting device according to claim 2, wherein: