JPH09148679A - Semiconductor light emitting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light emitting device which is of composite structure composed of a multilayer film laminated structure and an active layer of quantum dot structure and capable of operating in a wide range of temperature and projecting light vertical to a laminated surface. SOLUTION: A plane emission laser is equipped with a quantum dot active layer 4 located between GaAs/AlAs distributed-type Bragg reflecting mirrors 2, wherein quantum dot structures are intentionally set irregular in in-plane size so as to enhance the plane emission laser in optical gain width when the laser is operated at temperatures of 20 to 80 deg.C. The quantum dot active layer 4 is so set as to be positive in optical gain in the resonant frequency of the distributed-type Bragg reflecting mirror 3 in the temperature range of 20 to 80 deg.C. Quantum dot structures are formed through such a manner that an In0.2 Ga0.8 As quantum well 6nm or so in thickness is patterned into structures of in-plane size 15 to 25nm in diameter. The quantum dot structures are enhanced in size and compositional irregularity corresponding to a resonant frequency change, whereby a plane emission laser of this constitution can be operated in a wider range of temperature.

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 that emits light in a direction perpendicular to a stacking surface, and more particularly to a semiconductor light emitting device that can be used in a wide temperature range.

[0002]

2. Description of the Related Art In a semiconductor surface emitting laser having a distributed Bragg reflector formed of a semiconductor multilayer and a semiconductor active layer, for example, fabricated on a GaAs substrate, a semiconductor at a resonance wavelength of the distributed Bragg reflector formed of a semiconductor multilayer is provided. Laser oscillation can be performed when the optical gain of the active layer exists. To enable this laser oscillation operation in a wide temperature range, the optical gain of the semiconductor active layer must always exist at the resonance wavelength of the distributed Bragg reflector that changes in the temperature range.

In general, the resonance wavelength of a distributed Bragg reflector made of a semiconductor multilayer film is 0.1 when the temperature changes by one degree.
The wavelength becomes longer by about nm, and the peak of the optical gain of the active layer made of a normal semiconductor layer becomes longer by about 0.3 nm by a change of 1 degree. Assuming that the range of the temperature difference when using the semiconductor surface emitting laser is 100 degrees, the resonance wavelength changes by 10 nm while the gain wavelength changes by 30 nm. Therefore, even if the laser oscillation operation is enabled by matching the two wavelengths of the resonance wavelength and the gain wavelength at a specific temperature, if the optical gain width is not wide enough, it is not possible to oscillate at all temperatures. It will be difficult.

In order to reduce the problem of temperature change at two different wavelengths, the resonance wavelength and the gain wavelength, a method of using a plurality of quantum well structures having different thicknesses in the active layer to increase the optical gain width has been proposed. Kajita et al., "I.E.E.
E. journal. of. Selected. Topics. In. Quantum. Electronics (IEEEJ
own of Selected Topics
in Quantum Electronics) "
It is described on page 654 of Vol. 1 No. 2 (1995). In this report, three types of quantum well layers with different thicknesses are positioned between two distributed Bragg reflectors composed of multiple semiconductor layers to increase the optical gain width and realize laser oscillation over a wide temperature range. Let me.

[0005]

One of the problems of an element employing a plurality of quantum well structures having different thicknesses in the active layer is that a plurality of quantum well layers having different thicknesses are stacked. That is, light emitted from is absorbed by another quantum well layer. Considering the gain / absorption spectrum determined by the density of states and carrier distribution in the quantum well layer, an absorption region is generated in the quantum well layer on the short wavelength side (high energy side) because the carrier is small.

Another problem with an element employing a plurality of quantum well structures having different thicknesses in the active layer is that the plurality of quantum well structures must be arranged at a certain distance in the stacking direction. It is in principle impossible to install all the quantum well structures in the largest part of the light intensity distribution (“film” of the light intensity distribution) generated by the distributed Bragg reflector light. Therefore, it is impossible to always keep the coupling between the optical mode determined by the resonator and the optical gain at the maximum.

Further, since the width of the optical gain of each quantum well is determined in principle by the heat distribution width of the carrier, it is impossible to artificially determine this gain width.

For the above reasons, when realizing a surface emitting laser that can operate in a wide temperature range, it is fundamentally difficult to achieve both the optimum design and the laser emission, and this is another factor that deteriorates the laser characteristics. Was.

An object of the present invention is to provide a semiconductor light emitting device which can be used in a wide temperature range without deteriorating characteristics and emits light in a direction perpendicular to a lamination surface.

[0010]

A semiconductor light emitting device according to the present invention has a composite structure of a multilayer film laminated structure and an active layer which emits light by current injection, and laminates light having a wavelength defined by the multilayer film laminated structure. In a semiconductor light emitting device that emits light in a direction perpendicular to the plane, the carrier is three-dimensionally confined in the active layer, and the emission wavelength is changed by a difference in energy shift in a portion where the carrier is confined.

Further, the semiconductor light emitting device of the present invention has a composite structure of a multilayer film laminated structure and an active layer emitting light by current injection, and emits light having a wavelength defined by the multilayer film laminated film in a direction perpendicular to the laminated surface. In the semiconductor light emitting device that emits light, the active layer has a plurality of carrier confinement means for confining carriers three-dimensionally, and the emission wavelengths of the carrier confinement means are different from each other.

Further, the semiconductor light emitting device of the present invention has a composite structure of a multilayer film laminated structure and an active layer emitting light by current injection, and emits light having a wavelength defined by the multilayer film laminated structure in a direction perpendicular to the laminated surface. In the semiconductor light emitting device that emits light, the active layer includes a plurality of quantum dot structures in which carriers are confined three-dimensionally, and the plurality of quantum dot structures have different emission wavelengths.

When carriers are confined three-dimensionally in the active layer, the wavelength of light emitted by carrier injection is determined by the energy obtained by adding the energy shift due to the quantum mechanical confinement of carriers to the band edge energy of the semiconductor material. Therefore, by changing the energy shift due to the quantum mechanical confinement of the carrier for each carrier confinement location in the active layer, the emission wavelength at each location changes.

For example, in a quantum dot structure in which carriers are three-dimensionally confined in the active layer, the wavelength of light emitted by carrier injection is the energy obtained by adding the band edge energy of the semiconductor material to the energy shift due to quantum mechanical confinement of carriers. Determined by And three
When the carrier is dimensionally confined, the density of states of the carrier becomes a delta function, and there is no absorption at a wavelength other than the wavelength corresponding to each energy level.

In order to make a semiconductor light emitting device operable in a wide temperature range, a temperature change of the resonance wavelength of the multilayer film structure for defining the emission wavelength is considered, and a gain width similar to the change due to the temperature of the wavelength is considered. What is necessary is just to form the quantum dot structure which has. This makes it possible to change the emission wavelength for each quantum dot structure by changing at least one of the size and composition of the quantum dot structure and the band gap of the surrounding material.

When the temperature changes, the band edge energy of the semiconductor material forming the quantum dot structure also changes, but in order to compensate for this change, the quantum dot structure is formed nonuniformly to compensate for this change. Therefore, it is possible to realize a sufficiently wide optical gain even with a single-layer structure.

Since only one layer is required to realize a wide optical gain, an active layer made of quantum dots having a sufficiently wide optical gain can be located at the "belly" where the light intensity distribution is maximized. it can. Therefore, the coupling between the optical mode and the optical gain determined by the resonator can always be kept to the maximum.

For example, due to a temperature change from 20 to 80 degrees Celsius, the resonance wavelength of the semiconductor multilayer film shifts by 6 nm, and the band edge of the semiconductor forming the quantum dot structure becomes 18
Suppose you move nm. In this case, if the optical gain width due to the quantum dot structure is about 12 nm or more, the optical gain at the resonance wavelength can always be obtained in the above temperature range.
At this time, the above-mentioned optical gain width can be realized by intentionally designing the growth conditions and the formation method so that the size of the semiconductor quantum dot structure becomes non-uniform.

A material having a plurality of quantum dot structures is In _z Ga
By setting _1-z As (0 ≦ z ≦ 1), it is relatively easy to change the size of each quantum dot structure and to change the composition, and further, because it does not contain Al, there is little problem due to oxidation. Thus, an optically favorable dot structure is formed.

The method of forming the quantum dot structure used in the present invention is that two-dimensional growth changes to three-dimensional growth when the lattice constant of the structure is different from the lattice constant of the layer forming the surface to be laminated. When using self-forming growth, an optically good structure is very easily formed.

When the multilayer structure for defining the emission wavelength is composed of a semiconductor multilayer film, the above structure can be formed by forming a quantum dot structure as an active layer thereon. When a semiconductor multilayer film is used as the multilayer film structure, Al _x Ga _{1 -x} As / A is used as a material.
The use of _{l y Ga 1-y As (} 0 ≦ x <1,0 <y ≦ 1), the multilayer film structure for the lattice mismatch problem is eliminated are easily formed.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In the present embodiment, a surface emitting laser using a semiconductor multilayer film as a semiconductor light emitting device is used as a semiconductor light emitting device, and a quantum dot structure is used as a carrier confinement means for confining carriers three-dimensionally in a lamination plane and in a lamination direction. An example will be described.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention. FIG. 1A is a cross-sectional view of a surface emitting laser using the present invention. Lower distributed Bragg reflector 2, clad layer 3, upper distributed Bragg reflector 2 on substrate 1
Are stacked, and the quantum dot active layer 4 is provided on the cladding layer 3. A contact layer 5 for ohmic junction is formed on the upper distributed Bragg reflector 2, and electrodes 6 are provided on the upper distributed Bragg reflector 2 and the lower distributed Bragg reflector 2.

The structure of the quantum dot active layer 4 of the first embodiment is shown in FIG. 1 (b). In the quantum dot active layer 4 according to the first embodiment, as shown in the figure, each quantum dot is formed with a different size, so that each quantum dot has a different energy shift due to in-plane confinement.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention. FIG. 3 is a sectional view of a surface emitting laser using the present invention. A lower distributed Bragg reflector 2, a cladding layer 3, and an upper distributed Bragg reflector 2 are stacked on a substrate 1, and a quantum dot active layer 4 is provided on the cladding layer 3. A contact layer 5 for ohmic junction is formed on the upper distributed Bragg reflector 2, and an electrode 6
Are provided on the upper distributed Bragg reflector 2 and the lower distributed Bragg reflector 2.

The basic structure of the quantum dot structure of the quantum dot active layer 4 of the second embodiment is the same as that of the first embodiment, but the quantum dots of the second embodiment are
It is performed only by growth without using etching. Manufactured by a self-forming method using lattice mismatched materials.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention and a method for manufacturing the same will be described in detail with reference to the drawings.

(Example 1) A specific example of the first embodiment and a method of manufacturing the same will be described below. FIG. 1 (a),
FIG. 2B shows a schematic cross-sectional view and a perspective view of an example in which the present invention is applied to a surface emitting laser on a GaAs substrate 1. FIG. 1A is a schematic sectional view of a surface emitting laser.

A manufacturing method according to the first embodiment of the present invention will be described. First, a distributed Bragg reflector 2 having a multilayer structure of GaAs / AlAs is grown on a GaAs substrate 1 having a plane orientation of (100) by MBE, and then AlGaAs or GaAs.
s is used as the cladding layer 3 and is about _0.2 nm thick In _0.2 Ga _0.8 A.
An s quantum well is formed and the surface is covered with a GaAs layer.

After the growth up to this point, the quantum dot active layer 4 is formed by patterning the substrate by the method described below. First, apply resist on the surface,
Exposure with an electron beam allows the diameter from 15 nm to 25
Patterns having a diameter of up to nm and having a diameter of 1 nm are formed on the substrate surface at intervals of about 50 nm. Thereafter, etching is performed by reactive ion beam etching so that only the lower portion of the pattern remains. For the quantum dot structures 7 thus formed having different diameters, MB
Perform E growth.

Here, a cladding layer 3 and a distributed Bragg reflector 2 having a multilayer structure of GaAs / AlAs are grown on the quantum dot active layer, and a GaAs layer 5 for ohmic junction is grown on the surface. Thereafter, the diameter is reduced to 10 by ordinary photolithography and wet etching.
A mesa structure having a circular shape of about mm is formed, and an electrode 6 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 961 nm at 20 degrees Celsius.

FIG. 1B shows a state of the quantum dot structures 7 having different diameters, so that a state immediately after the quantum dot structures are formed is schematically shown in a perspective view. The quantum dot structure is directly sandwiched between GaAs barrier layers in the stacking direction, and the confinement size in this direction is about 6 nm for all quantum dots. In the in-plane direction, the diameter is 15
Since quantum dots are distributed from nm to 25 nm, the amount of energy shift due to in-plane confinement is different in each quantum dot.

FIGS. 2A and 2B are graphs schematically showing the resonance wavelength and the optical gain spectrum of the quantum dot active layer in Example 1 at temperatures of 20 ° C. and 80 ° C.
Here, the wavelength at which the gain of the quantum dot active layer is maximized is
At 20 degrees it is about 955 nm and at 80 degrees it is about 973 nm.
The resonance wavelength is 961 nm at 20 degrees and 96 at 80 degrees.
7 nm. In this case, there is a gain due to the quantum dot active layer at this resonance wavelength at any temperature between 20 degrees and 80 degrees. Therefore, it is possible to perform an operation as a surface emitting laser in this temperature range.

(Embodiment 2) Here, a case of a structure obtained by a self-forming method using a lattice mismatched material, which is a quantum dot structure used in Embodiment 2, will be described. FIG. 3 is a schematic sectional view of the surface emitting laser according to the present embodiment. The basic structure is the same as that of the first embodiment,
When manufacturing the quantum dot structure, etching technology is not used, and only growth is performed.

A manufacturing method according to the second embodiment of the present invention will be described. First, a GaAs substrate 1 having a plane orientation (100) is formed by MBE.
A distributed Bragg reflector 2 having a multilayer structure of GaAs / AlAs is grown thereon, a cladding layer 3 of GaAs / AlGaAs is formed, and then InAs and GaAs are alternately stacked by 0.06 nm. And the total film thickness is 1.4.
When the thickness reaches about nm, the growth of this layer is completed.

In this case, the average composition of InAs and GaAs is In _0.5 Ga _0.5 As, and the quantum dot structure 21 is formed in a self-forming manner by laminating the above-described entire film thickness. In this quantum dot structure, the optical gain predicted by photoluminescence measurement is about 60 nm. After the formation of the present quantum dot structure, GaAs /
An AlGaAs cladding layer 3 is grown, and GaAs / AlA
A distributed Bragg reflector 2 having a multilayer structure of s is grown, and a GaAs layer 5 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 6 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 1000 nm at 20 degrees Celsius.

The gain width of the quantum dot structure obtained by the above-described self-forming method is about 60 nm, and the maximum gain wavelength at 20 degrees Celsius is about 990 nm. Here, when the operating temperature rises to 120 degrees Celsius, the resonance wavelength becomes 1010 nm.
And the maximum gain wavelength is about 1020 nm. here,
Since the gain width is as large as about 60 nm, optical gain at the resonance wavelength is expected at both temperatures,
Laser operation can be realized. Therefore, 2
It can be used in a very wide temperature range from 0 degrees to 120 degrees.

As described above, in Examples 1 and 2 showing specific examples of the embodiment of the present invention, a semiconductor multilayer film formed on a GaAs substrate and a semiconductor laser having a quantum dot structure have been described. A case where a dielectric multilayer film is used instead of the film may be used.

In this case, since the temperature change of the resonance wavelength becomes very small, the optical gain width of the quantum dot structure may be increased. In that case, the size and composition are intentionally made non-uniform, and the growth film thickness is increased by about 10% from the optimum value for forming the quantum dot structure by a self-forming method.
What is necessary is just to increase the size nonuniformity.

A similar effect can be obtained not only for a semiconductor laser but also for a light emitting element such as a light emitting diode.
GaAs having a plane orientation of (100) is also used as a semiconductor substrate.
In addition to s, for example, a plane orientation (311) B at which a more uniform structure is realized by a self-forming method may be used, and an InP substrate or the like may be used as a material.

Regarding the method of forming the quantum dot structure, in addition to the combination of the growth and etching of the quantum well structure and the self-forming method, semiconductor particles are used, and three-dimensional confinement is effectively realized by local distortion. It does not matter.

In the embodiment, Ga is used as the semiconductor multilayer film.
A distributed Bragg reflector having a multilayer structure of As / AlAs has been described as an example, but In _x Ga _1-x As may be used in addition to this.
/ InP and _{GaAs 1-xy P x Sb y} / AlAs 1-ab
It may be using the material system of PaSb _b, and the like.

[0044]

As described above, by using the present invention, a semiconductor light emitting device which can operate in a wide temperature range can be realized.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view schematically showing a first embodiment and Example 1 of the present invention, and FIG. 1B is a perspective view schematically showing a quantum dot structure.

FIG. 2 is a graph (a) showing the resonance wavelength at 20 ° C. and the optical gain spectrum of the quantum dot active layer when Example 1 is used, and the resonance wavelength at 80 ° C. and the quantum dot active layer; FIG. 4B is a graph (b) showing an optical gain spectrum.

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

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 GaAs substrate 2 GaAs / AlAs distributed Bragg reflector 3 GaAs / AlGaAs cladding layer 4 quantum dot active layer 5 GaAs contact layer 6 electrode 7 InGaAs quantum dot structure 21 self-forming InGaAs quantum dot structure

Claims (8)

[Claims] 1. A semiconductor light emitting device having a composite structure of a multilayer film laminated structure and an active layer which emits light by current injection, and which emits light having a wavelength defined by the multilayer film laminated structure in a direction perpendicular to a laminated surface. A semiconductor light-emitting device characterized in that carriers are three-dimensionally confined in an active layer, and an emission wavelength is changed by a difference in energy shift at a place where the carriers are confined. 2. A semiconductor light emitting device comprising a composite structure of a multilayer film laminated structure and an active layer emitting light by current injection, and emitting light of a wavelength defined by the multilayer film laminated structure in a direction perpendicular to the laminated surface. A semiconductor light emitting device, wherein the active layer has a plurality of carrier confinement means for confining carriers three-dimensionally, and the emission wavelengths of the carrier confinement means are different from each other. 3. A semiconductor light emitting device comprising a composite structure of a multilayer film laminated structure and an active layer which emits light by current injection, and emits light of a wavelength defined by the multilayer film laminated structure in a direction perpendicular to the laminated surface. A semiconductor light emitting device, wherein the active layer includes a plurality of quantum dot structures in which carriers are three-dimensionally confined, and the plurality of quantum dot structures have different emission wavelengths. 4. The semiconductor according to claim 3, wherein in the semiconductor light emitting device, at least one of a size, a composition, and a band gap of a material around the plurality of quantum dot structures is made non-uniform. Light emitting element. 5. The method according to claim 1, wherein the plurality of quantum dot structures are In _z Ga
The semiconductor light emitting device according to claim 3, wherein _1-z As (0 ≦ z ≦ 1). 6. The quantum dot structure wherein 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 laminated. 4. The semiconductor light emitting device according to claim 3, wherein: 7. The semiconductor light emitting device according to claim 3, wherein the multilayer film structure is a semiconductor multilayer film structure. 8. The semiconductor multi-layered film is made of Al _x Ga _{1 -x} As.
The semiconductor light emitting device according to claim 7, wherein / Al _y Ga _1-y As (0 ≦ x <1, 0 <y ≦ 1).