JPH01283891A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To select light emitting layers to be trapped with holes and electrons and to radiate a laser light having a plurality of wavelengths by controlling a potential to be applied to a barrier layer by utilizing the height of a barrier with respect to movements of holes or electrons on the basis of a hetero junction between the barrier layer and the light emitting layers. CONSTITUTION:A semiconductor laminated layer structure made of light emitting layers 3, 5 and a barrier layer 4 is hetero applied to the layers 3, 5 of the end of the structure, and a body of a semiconductor laser device is composed of a pair of clad layers 2, 6 formed as reverse conductivity type semiconductor layers. Means (electrode) 12 for applying a desired potential to the layer 4 is provided, and the potential to be applied to the layer 4 through the means 12 is controlled in a state that a driving voltage is applied between the layers 2 and 6 in a forward bias direction. Thus, the layers 3, 5 in which holes or electrons to be injected from the layers 2, 6 are trapped or confined can be controlled or selected, and laser lights of the wavelengths corresponding to the band gap values of the layers 3, 5 can be switched and output from the layers 3, 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor laser device capable of extracting laser light of a plurality of wavelengths.

[Conventional technology]

Recent advances in semiconductor laser technology have been remarkable.
Along with this, its applications are expanding into a wide range of fields such as optical communications and information processing, as well as laser printers and CD players.Aside from communication applications, it is extremely small and emits a relatively large amount of laser light. A double heterojunction structure is widely used as a laser device, and it is well known that the structure is shown in FIG. 3, and the principle of laser emission is shown in FIG. 4.

In FIG. 3, an n-type Al layer is placed on an n-type GaAs substrate 1.
After covering the cladding layer 2 made of GaAs,
A p-type light-emitting layer 3 is grown from AlGaAs, and then a p-type AlGaAs cladding layer 6 is placed over it. The n-type GaAs confinement layer 7 on top of the n-type confinement layer 7 is for concentrating the injected current in the center of the light emitting layer 3 in the figure. After 0M of growing the cladding layer 8 of the same p-type AlGaAs in a continuous manner, a strong p-type connection layer 9 of GaAs is provided. Next, by providing electrode films 10 and 11 on the upper and lower surfaces and applying a driving voltage V in a forward bias direction to the semiconductor laminated structure as shown in the figure, a current narrowed by the confinement layer 7 is injected into the light emitting layer 3. do.

In the center of FIG. 4, the band gap Eg of the light emitting layer 3 is shown.
is shown, and since the cladding layers 2 and 6 of opposite conductivity types are respectively heterojunctioned to the light emitting layer 3, the band structure near the light emitting layer is as shown in the figure. The conductive band is shown with hatch lugs in the figure. Holes injected into the light emitting layer 3 from the p-type cladding layer 6 side are:
Due to the barrier between the light emitting layer 3 and the cladding layer 2, the light emitting layer 3
Electrons e that are trapped inside and conversely injected into the light emitting layer 3 from the n-type cladding layer 2 side are trapped in the light emitting layer 3 by the barrier between the light emitting layer 3 and the cladding layer 6.
Laser light emission is generated by the combination of holes and electrons confined within the light emitting layer 3, and as is well known, laser light with a wavelength λ slightly corresponding to the bandgap Eg of the light emitting layer is emitted as shown in the paper of FIG. generated in a direction perpendicular to

[Problem to be solved by the invention]

The laser light obtained from the above-mentioned semiconductor laser device is monochromatic light with a wavelength λ determined by the bandgap value Eg of the light emitting layer 3, but depending on the application, laser light can be emitted by switching between light having two or more wavelengths. is required. For this reason, in recent years, several semiconductor laser devices that can obtain polychromatic light have been proposed, but as far as the applicant is aware, none of them are combinations or integrations of multiple semiconductor laser devices with the above structure. However, it is not possible to obtain laser beams of multiple wavelengths with a single semiconductor laser device, and as a result, there are more or less open issues in terms of economy, mass production, ease of use, etc.

Therefore, an object of the present invention is to provide a single semiconductor laser device capable of emitting laser light of multiple wavelengths.

[Means to solve the problem]

This purpose, according to the invention, consists of a plurality of light-emitting layers each serving as a semiconductor layer having a different bandgap value;
A barrier layer is provided as a semiconductor layer sandwiched between the light-emitting layers and forms a heterojunction with the light-emitting layers on both sides, and a semiconductor stack structure consisting of the light-emitting layer and the barrier layer is sandwiched between the barrier layers and the barrier layer is provided as a semiconductor layer between the light-emitting layers. A semiconductor laser device is constituted by a pair of cladding layers each having a heterojunction with the light-emitting layer and serving as semiconductor layers of opposite conductivity types, and means capable of applying a desired potential to the barrier layer, and a forward bias direction is applied between the cladding layers. By controlling the potential applied to the barrier layer through the potential applying means with a driving voltage applied to the barrier layer, a light emitting layer to emit laser light is selected, and a laser beam of a wavelength corresponding to the bandgap value is emitted from each light emitting layer. This is achieved by switching and taking out each.

[Effect]

As mentioned above, the wavelength of laser emission is determined by the bandgap value of the semiconductor constituting the light emitting layer, and the size of this bandgap depends on the composition of the semiconductor material, such as Al
The content of A1 in GaAs, that is, its composition, is expressed as Alx G
It can be adjusted by the value of X when expressed as a+-x As. Therefore, by creating a plurality of light emitting layers with different compositions in the stacked structure of semiconductor layers of a semiconductor laser device,
If each light-emitting layer is made to emit laser light with its own wavelength, in principle it becomes possible to emit laser light with a plurality of wavelengths.

However, as it is, it is not always determined in which light-emitting layer the holes injected from the p-type cladding layer and the electrons injected from the n-type cladding layer are trapped.
Laser light emission naturally does not occur unless holes and electrons combine within a certain light-emitting layer, so no light-emitting layer will emit light.
This may cause problems such as a plurality of light emitting layers emitting light at the same time.

Focusing on this point, the present invention includes light-emitting layers each having a different bandgap value within a semiconductor stacked structure sandwiched between a pair of p-type and n-type cladding layers that serve as hole and electron injection sources. A plurality of these light emitting layers are fabricated, and a barrier layer is incorporated between these light emitting layers to form a hetero bond with them. After making it possible to apply a desired potential to the barrier layer, it is applied to the barrier layer while utilizing the height of the barrier against the movement of holes or electrons based on the heterobond between the barrier layer and each light emitting layer. By controlling the potential, it is possible to select a light-emitting layer in which holes and electrons are trapped.

Therefore, according to the present invention, it is possible to specify the light-emitting layer to emit laser light by the potential applied to the barrier layer, thereby solving the above-mentioned problems of the present invention.

〔Example〕

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a cross-sectional view illustrating the configuration of a semiconductor laser device according to the present invention, and FIG. 2 is an explanatory diagram of its operation. In addition, in the explanation referring to FIG. 1, A11l Gap-
The composition of l1As is expressed by the χΦ value.

In FIG. 1, in this embodiment, the substrate 1 is made of n-type GaA.
For example, the thickness is about 100n, and St
The n-type impurity concentration is set to be 10I8 atoms/cd or more. Similarly, the n-type cladding layer 2 has an X of 0.4 on top of it.
AlGaAs of about 1.
It is grown to a thickness of about 5n, and its impurity concentration is, for example, 5xlOI? In this embodiment, GaAs, for example, is grown as the lower light-emitting layer 3 of the 0th order, which is around atoms/cd. AlGaAs is used for the barrier layer 4 so as to form a heterojunction with the light emitting layer 3, and its composition is such that, for example, X is 0.25.

For the upper light emitting layer 5, AlGaAs having a composition of, for example, X of 0.13 is used so that it forms a heterojunction with the barrier layer 4 and has a different bandgap value from the lower light emitting layer 3.

In this embodiment, the light-emitting layers 3 and 5 and the barrier layer 4 are all n-type, and their thicknesses are, for example, 0.
It is said to be about 1n.

The next cladding layer 6 is of an n-type conductivity type opposite to that of the lower cladding layer 2, and has a composition of, for example, AlGaA with an X value of 0.45 so as to form a heterojunction with the light emitting layer 5.
s is grown to a thickness of about o and sn, and the concentration of p-type impurities such as Zn is 5xlO, which is about the same as that of the lower cladding layer 2.
Atom/C4. As the narrowing layer 7, the cladding layer 6
For example, an n-type IQ11 atom/
GaAs with a high impurity concentration on the order of cil is used, and after growing it to a thickness of about 0.5 nm, a groove is cut in the center as described above, and while filling this groove, it is continuous with the cladding layer 6 below. The cladding layer 8 is grown with the same conductivity type and composition as the cladding layer 8.The combined thickness of the cladding layers 6 and 8 and the constriction layer 7 is about 1.5n. Finally, n-type GaAs having a high impurity concentration of about IQ11 atoms/d is grown as a connection layer 9 to a thickness of about 0.5n, thereby completing a stacked structure of semiconductor layers for a semiconductor laser device.

In the present invention, 1 shown in the figure is a door in which it is necessary to provide a scratch film 12 as a means for applying a potential to the barrier layer 4 in the laminated structure, and then photoetching or the like is performed from the upper surface of the laminated structure, for example. Recess 20 reaching barrier layer 4 by means
In Figure 0, one semiconductor laser device is shown by a solid line, but of course, at this stage, many semiconductor laser devices are connected within the wafer as shown schematically by the dashed line in the figure. . Electrode films 10 are provided on the upper and lower surfaces of the laminated structure.
and 11, respectively, and an electrode film 12 is also attached to the surface of the barrier layer 4 at the bottom of the recess 20 as a means for applying a potential thereto.Finally, the wafer is broken along the arm opening 21, and then each semiconductor laser is Separate the equipment. As is well known, the front and rear opening planes of the paper become resonant planes, and laser light is extracted from one of them. Further, as usual, a reflective film is provided on these resonant surfaces, and a protective film is provided on the left and right side surfaces in FIG. 1, respectively.

The semiconductor laser device constructed as described above is used in a forward biased state by applying a positive voltage (1) to the upper electrode film 10 in FIG. FIG. 2 illustrates the bandgap structure of the portion from the n-type cladding layer 2 having the above-mentioned composition to the p-type cladding layer 6. The operation of the laser device will be explained.

In the figure (a), the lower light emitting layer 3. The band gap values of the barrier layer 4 and the upper light emitting layer 5 are shown as Egl, 8g3 and Eg2, respectively, and in this example, the relationship Egl<Eg2<[! There is a g3 relationship. Further, the bandgap value Egl of the light emitting layer 3 is 1.43V, and the wavelength of the laser light corresponding to it is 870 nm.
The bandgap value Eg2 of the light emitting layer 5 is 1.73V, which corresponds to a wavelength of 7B0 nm. Further, in FIG. 2, conductive bands for holes and electrons e are shown with hatching.

Figures (a) and (■) show the state when no potential is applied to the barrier layer 4; in this example, the cladding layer 6
Since only one layer is p-type and the other layers 2 to 5 are all n-type, the lower band-level structure has a barrier structure based on a heterojunction between barrier layer 4 and light-emitting layers 3 and 5, as shown in the figure. appears, but the upper band-level structure has almost no barrier.

In the figure (a), a voltage (.[
4g2/e (where e is the electron charge), this corresponds to when a drive voltage of the same magnitude is applied. Holes injected from the p-type cladding layer 6 to the upper light-emitting layer 5 are reflected by the barrier based on the heterojunction between the light-emitting layer 5 and the barrier layer 4 as shown in the figure, and are absorbed into the light-emitting layer 5. Trapped. However, the electrons e injected from the n-type cladding layer 2 to the light emitting layer 3
As can be seen from the figure, the light emitting layer 3 and the barrier layer 4 are easily separated.
The light is reflected for the first time by the barrier between the light emitting layer 5 and the cladding layer 6, and is trapped within the light emitting layer 5.

Therefore, laser light emission occurs due to the combination of holes and electrons within this light emitting layer 5, and the wavelength of the laser light at this time is 87.
It becomes 0nm.

Φ) in the figure shows a state when a driving voltage larger than the voltage corresponding to the bandgap value Eg3 of the barrier layer 4 is applied between the cladding layers 2 and 6.

In this case, due to the large forward bias applied between both cladding layers, the width of the conduction band on the lower side of the figure with respect to holes becomes a barrier based on the heterojunction between the light-emitting layer 5 and the barrier layer 4, as shown in the figure. Since it spreads beyond the p-type cladding layer 6
Holes injected from the side can pass through the light emitting layer 5 and the barrier layer 4 and reach the light emitting layer 3. Of course, after reaching the light-emitting layer 3, the holes are reflected by the barrier between the holes and the cladding N2, so that they are mainly trapped within the light-emitting layer 3. Therefore, in the case of (b) in the same figure, light emission can occur simultaneously in the light emitting layers 3 and 5, but as can be easily seen, as the drive voltage is increased, the laser with the aforementioned wavelength of 78 on I11 is emitted from the light emitting layer 3. Luminescence becomes dominant.

FIG. 2(C) shows that the barrier layer 3 has a bandgap value of 8g3-Eg2 with respect to the n-type craft layer 2 by applying a potential Vc to the bridge film 12 as the potential applying means in FIG. This shows the state when a corresponding voltage is applied in the reverse bias direction. Due to this reverse bias, the barrier between the light emitting layer 5 and the barrier N4 disappears from the lower band level structure as shown in the figure, and this barrier It appears in the upper band level structure.

In this case, as shown in the figure, the p-type cladding layer 6
Holes injected from the side easily reach the light-emitting layer 3 and are reflected by the barrier between it and the cladding layer 2, and electrons e injected from the side of the n-type cladding layer 2 into the light-emitting layer 3 are reflected by the barrier. Since the light is reflected by the newly formed barrier between the light emitting layer 4 and the light emitting layer 4, both holes and electrons e are trapped within the light emitting layer 3. Therefore, in this case, laser light emission occurs exclusively within the light emitting layer 3, and from the semiconductor laser device 7
B0nm laser light is generated.

As can be seen from the above description of FIGS. 2(a) and 2(C), in the present invention, a plurality of light-emitting layers each having a unique bandgap value are incorporated in a semiconductor laser device, and a plurality of light-emitting layers each having a unique bandgap value are incorporated into the semiconductor laser device. By applying an appropriate potential to the barrier layer sandwiched between these light-emitting layers, the wavelength of the laser light obtained from the semiconductor laser device can be switched.

In addition, although it cannot necessarily be said that complete switching is performed, by selecting the drive voltage value of the semiconductor laser device without applying any particular potential to the barrier layer, it is possible to achieve the effect shown in FIG. 2(b).
As explained above, a plurality of light emitting layers can be made to emit laser light simultaneously, or a specific light emitting layer among them can be made to emit a dominant laser light.

Note that the operation of the semiconductor laser device according to the present invention explained in FIG. 2 is an embodiment in which it is configured as explained in FIG. The forward bias value given to it for selection and the value of the potential given to the barrier layer via the potential applying means are determined based on the band gap value based on the semiconductor composition given to the light-emitting layer, barrier layer and cladding layer, respectively, and the value of the potential given to the barrier layer through the potential applying means. Naturally, it should be selected appropriately depending on the value of the barrier based on the heterojunction and the conductivity type given to each of these layers. As you will see from now on,
The present invention is not limited to the illustrated embodiments, but can be implemented in various modified or applied ways within the scope of the invention.

〔Effect of the invention〕

As described above, in the present invention, a plurality of light emitting layers are formed as semiconductor layers each having a different band gap value, and a semiconductor layer is formed as a semiconductor layer sandwiched between the light emitting layers, and a heterojunction is formed with each of the light emitting layers on both sides. a barrier layer to be formed, and a pair of ground layers that are provided across a semiconductor laminated structure consisting of a light-emitting layer and a barrier layer, are in heterojunction with the light-emitting layer at the end of this laminated structure, and are semiconductor layers of opposite conductivity types. The main body of the semiconductor laser device is constituted by the above, and a means capable of applying a desired potential to the barrier layer is provided. By controlling the potential applied to the layer, it is possible to select IIn or a light-emitting layer in which holes and electrons injected from the cladding layer are trapped or confined, and this allows each light-emitting layer to have its bandgap value. Laser beams of corresponding wavelengths can be switched and extracted.

One of the interesting applications of the present invention is a semiconductor laser device capable of emitting light in three colors. For this purpose, three emissive layers emitting red, blue and green laser light can be incorporated into it, or only two emissive layers emitting red and blue light respectively can be incorporated and these emissive layers can be integrated. By emitting laser light individually or simultaneously, three colors including yellow can be switched and extracted. Furthermore, as is well known, in optical communications, there are two optimal wavelengths due to the characteristics of optical fibers: 0,9n'II and 1.55n bands, and if the present invention is used, one semiconductor It becomes possible to use the laser device by switching to any of these wavelength bands. Furthermore, since switching the wavelength of the laser beam of the semiconductor laser device according to the present invention is very simple, if a digital communication system is configured using two types of frequencies, optical communication with much higher reliability than before can be realized. It also becomes possible.

As described above, the present invention can be applied to a wide range of applications and take advantage of its features, and is expected to make a significant contribution to the advancement of optical application technology and the development of new fields in the future.

[Brief explanation of the drawing]

1 and 2 relate to the present invention; FIG. 1 is a sectional view showing an embodiment of a semiconductor laser device according to the present invention, and FIG. 2 is a bandgap configuration diagram illustrating its operation. Third
The following figures relate to the prior art: Figure 3 is a cross-sectional view of a conventional double-hetero structure semiconductor laser device that generates laser light of one wavelength, and Figure 4 is a bandgap configuration diagram showing its operation. In,

Claims (1)

[Claims] A plurality of light-emitting layers each serving as a semiconductor layer having a different bandgap value, a barrier layer serving as a semiconductor layer sandwiched between the light-emitting layers and forming a heterojunction with the light-emitting layers on both sides thereof, and the light-emitting layer and the barrier. A desired potential is applied to a pair of cladding layers which are provided sandwiching a semiconductor laminated structure consisting of layers, and which are in heterojunction with the light-emitting layer at the end of this laminated structure, and which are semiconductor layers of opposite conductivity types, and a barrier layer. selecting a light-emitting layer that emits laser light by controlling the potential applied to the barrier layer via the potential applying means with a driving voltage applied in a forward bias direction between both cladding layers; A semiconductor laser device characterized in that laser light having a wavelength corresponding to the bandgap value of each light emitting layer can be switched and extracted from each light emitting layer.