JP2897052B2 - Surface emission type optical threshold device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention has been developed to improve a surface-emitting light threshold device in which an operation state is changed by turning on / off an external input light. A barrier film made of the first substance and having a thickness capable of tunneling carriers, and a barrier film sandwiched between the barrier films. A quantum well comprising a first well film made of a second material having a narrow bandgap compared to the first material and having a thickness in which a two-dimensional exciton can exist; and The quantum well is made of a material and is thickened so that there is at least one energy quantum level for electrons lower than the lowest energy quantum level for electrons generated in the first well film; Contact the outside of the barrier membrane at A saturable light-absorbing layer having a second well film formed separately from the first well as a material of the second well film. The method is configured to use a third substance that is selected such that there is at least one energy quantum level for electrons that is lower than the lowest energy quantum level for electrons generated in the film.

[Industrial applications]

1. Field of the Invention The present invention relates to an improvement of a surface-emitting type light threshold device in which an operation state is changed by turning on / off external input light.

At present, for example, in the field of optical information processing such as optical communication and optical control, the use of an optical threshold device is indispensable, and there are great expectations for speeding up the device.

[Conventional technology]

FIG. 3 is a cutaway side view of a main part of a conventional basic optical threshold device.

In the figure, 1 is a substrate also serving as a cladding layer, 2 is an active layer, 2A is a light emitting region set in a part of the active layer 2, and 2B is a saturable light absorption set in a part of the active layer 2. The region 3 is an electrode contact layer also serving as a cladding layer, and 4 and 5 are electrodes, respectively.

As is clear from the figure, the electrodes 4 and 5 correspond to the light emitting area 2A.
And a saturable light absorbing region 2B
Is not present in the portion opposite to the light emitting element, and therefore light can be incident on the part from outside.

By the way, usually, the light absorptivity in the saturable light absorbing region 2B is large, and the laser light generated in the light emitting region 2A is absorbed to suppress radiation to the outside. When light is incident, the light absorptivity decreases and the laser light is emitted to the outside.

Therefore, by controlling external light irradiation on the saturable light absorbing region 2B, it is possible to turn on / off the laser light from the light emitting region 2A.

[Problems to be Solved by the Invention] In the conventional example shown in FIG. 3, it is difficult for the saturable light absorbing region 2B, which is irradiated with light from the outside and has a reduced light absorption rate, to recover the light absorbing ability. In addition, it is necessary for the excited electrons to have a time to return to the valence band after the lifetime of the electrons that have been knocked up from the valence band to the conduction band.

Therefore, although the time until the control light is externally incident on the saturable light absorbing region 2B and the laser light is output from the light emitting region 2A is short, the time until the control light is shut off and the laser light output is stopped is stopped. The present invention has a unique configuration of the surface emitting light threshold device in which the active layer and the saturable light absorbing layer are separated and independent from each other. Try to speed up using.

[Means for solving the problem]

FIG. 1 is a cutaway side view of a main part of an optical threshold device for explaining the principle of the present invention.

In the figure, 11 is a substrate, 11A is a recess formed in the substrate 11, 12 is an etching stop layer, and 13 is a quantum well.
II: QW), saturable light absorbing layer, 14 is a buffer layer, 15 is an active layer, 16 is a buffer layer, 17 is an electrode contact layer, and 18 and 19 are mirrors made of a semiconductor multilayer film or a dielectric multilayer film. A surface film, 20 indicates an n-side electrode, and 21 indicates a p-side electrode.

By the way, in the saturable light absorbing layer 13 of the surface emitting light threshold device, it is indispensable to add a certain configuration to the QW having a normal configuration.

FIG. 2 shows an energy band diagram near a multi quantum well (MQW) in the optical threshold device described with reference to FIG. Note that MQW is not essential in the present invention.

In the figure, E _V is the top of the valence band, E _C is the bottom of the conduction band, 13
B is a barrier film for forming a quantum well, 13W is a well film for forming a quantum well, and 13W 'is a well film outside the barrier film 13B. Incidentally, for example, “barrier film 13B” shown in FIG.
This means a portion corresponding to the barrier film 13B on the diagram, and the same applies to other portions.

As is clear from the figure, in the well film 13W 'located outside the barrier film 13B, the energy quantum level generated there is lower than that generated in the well film 13. . The thickness of the barrier film 12 is selected so that electrons can be tunneled.

In order to maintain the relationship between the energy quantum levels, if the constituent materials are the same, the thickness of the well film 13W 'should be larger than that of the well film 13W, and if the thickness is the same. For example, it can be easily realized by changing the constituent materials.

Now, the operation of the saturable light absorbing layer 13 in the optical threshold device shown in FIG. 1 will be described.

Now, it is assumed that a standard bias voltage is applied to the optical threshold device, and when control light is incident on the saturable light absorbing layer 13, for example, the valence band E in the well film 13W _The electrons and holes present in _V are excited and the electrons and excitons are driven up into the conduction band. In such a state, the laser light generated in the active layer 15 is radiated to the outside, and this is performed at a high speed similarly to the optical threshold value semiconductor device according to the conventional technology. In the figure, the struck-up electrons are indicated by a symbol e.

Next, when the control light incident on the saturable light absorbing layer 13 is cut off, the electrons e are tunneled from the well film 13W to the barrier film 13B, and fall into a low energy quantum level in the adjacent well film 13W '. Saturable light absorbing layer
The light-absorbing ability released to 13 quickly recovers, and the emission of laser light is immediately stopped. This operation is extremely fast,
This is absolutely impossible with a light threshold semiconductor device according to the prior art.

For this reason, in the optical threshold value semiconductor device according to the present invention, the barrier film made of the first material (for example, AlGaAs) having a wide band gap and having such a thickness that the carrier can be tunneled. (E.g., barrier film 13B) and a second material (e.g., GaAs) sandwiched between the barrier films and having a narrower forbidden band width than the first material. A quantum well composed of a first well film (for example, a well film 13W) having the same energy quantum level as that of the second material and generated in the first well film. Then, a second well film (for example, a well film 13W ') formed so as to have at least one energy quantum level for a lower electron and formed in contact with the outside of the barrier film in the quantum well is formed. Bored with A barrier layer that is provided separately and independently in the vicinity of the active layer in the vicinity of the active layer, or is made of a first material having a wide band gap and has a thickness enough to allow a carrier to be tunneled; A quantum well comprising a first well film sandwiched between the second material and having a narrow band gap compared to the first material and having a thickness in which a two-dimensional exciton can exist; A third material whose composition is selected such that there is at least one energy quantum level for an even lower electron compared to the lowest energy quantum level for an electron generated in the first well film (eg, When the first well film 13W is made of AlGaAs, the saturable light absorbing layer is made of GaAs) and has a second well film formed in contact with the outside of the barrier film in the quantum well. Separate and independent near the layer Have been.

[Action]

By adopting the above means, the operation of injecting control light to excite excitons in the quantum well in the saturable light absorbing layer or exciting free electrons to change the light absorptivity depends on the prior art. It is as fast as the optical threshold device, and when the control light is cut off, the excited free electrons or free electrons generated by the exciton ionizing pass through the barrier film in the quantum well. The light absorption recovers rapidly because it escapes immediately after tunneling. In addition, the recovery time of the light absorptance is determined by the time required for free electrons to tunnel through the barrier film, and can be controlled by changing the thickness of the barrier film or the thickness or material of the well film. .

〔Example〕

Examples of data for the optical threshold device shown in FIG. 1 are as follows: (1) Substrate 11 Material: n-type GaAs (2) Etching Stop Layer 12 Material: n-type AlGaAs Thickness: 0.3 [μm] (3 ) Saturable light absorbing layer 13 Barrier film 13B material; AlGaAs thickness: 40 [40] Well film 13W material; GaAs thickness: 40 [Å] Well film 13W 'Material; GaAs thickness: 90 [Å] Here, a single quantum well (SQW) is formed by sandwiching the well film 13W between the barrier films 13B.
Was used in 20 layers. In this case, a well film 13W 'is provided between each SQW.
Is of course interposed.

(4) Buffer layer 14 Material: n-type AlGaAs Thickness: 2 [μm] (5) Active layer 15 When quantum well (semiconductor superlattice) is used Barrier film Material: AlGaAs Thickness: 90 [Å] Well About film Material: GaAs Thickness: 40 [Å] Number of layers: 20 (6) About buffer layer 16 Material: p-type AlGaAs Thickness: 1 [μm] (7) About electrode contact layer 17 Material: p-type AlGaAs thickness : 0.5 [μm] (8) Mirror films 18 and 19 Semiconductor multilayer film Material: GaAs / AlGaAs Dielectric multilayer film Material: SiO ₂ / TiO ₂ (9) n-side electrode 20 Material: Au / Sn (10) About the p-side electrode 21 Material: Au / Cr The barrier film 12 in the above embodiment has a thickness of 40/40.
Although [Å] is used, the thickness may be selected within a range where electrons and excitons can be tunneled, that is, 200 [範 囲] or less.

The well film 13W in the above embodiment has a thickness of 40
Although [Å] was used, the thickness may be appropriately selected within the range where the two-dimensional exciton can exist, that is, 280 [Å] or less.

The energy quantum level in the well film 13W 'is changed to the well film 1
As a means of lowering the thickness compared to that of 3W, when increasing the film thickness, it is appropriately selected so as to be thicker than the film thickness of the well film 13W in consideration of the difference in the energy quantum level. Just do it.

If the thickness of the well film 13W 'is equal to or smaller than that of the well film 13W, the well film 13W'
It is preferable to appropriately select the materials of W ′ and the well film 13. For example, the well film 13W 'is made of GaAs, and the well film 13W'
May be made into AlGaAs by adding a little Al. still,
In such a case, the energy in the well film 13W is
It is essential that the band gap be narrower than that of the barrier film 12.

The active layer 15 released in the above-described embodiment is formed of a semiconductor superlattice, for example, an n-type AlGaAs buffer layer 14 and a p-type
AlGaAs buffer layer 16 is a non-doped AlGa with a changed composition.
A double hetero structure may be used by using As or the like.

In the above embodiment, the GaAs / Al _X Ga _1-X As system was described. However, in addition to this system, for example, an InGaAs or InAlAs system can also be implemented.

〔The invention's effect〕

In the surface emitting light threshold device according to the present invention, a barrier film made of the first material and having a thickness capable of tunneling the carrier, and a forbidden band narrower than the first material sandwiched between the barrier films. A quantum well composed of a first well film made of a second material having a width and having a thickness in which a two-dimensional exciton can exist; and a quantum well made of a second material and formed in the first well film. A second well film formed so as to have one energy quantum level for electrons lower than the lowest energy quantum level for electrons, and formed in contact with the outside of the barrier film. Having a saturable light-absorbing layer or a lower energy quantum level compared to the lowest energy quantum level for electrons generated in the first well film as a material of the second well film. There is one level Using a third material selected so.

By adopting the above configuration, the operation of injecting control light to excite excitons in the quantum well in the saturable light absorbing layer or exciting free electrons to change the light absorption rate depends on the conventional technology. It is as fast as the optical threshold device, and when the control light is cut off, the excited free electrons or free electrons generated by the exciton ionizing pass through the barrier film in the quantum well. The light absorption recovers rapidly because it escapes immediately after tunneling. Also, the recovery time of the light absorptance is determined by the time during which free electrons tunnel through the barrier film, and thus can be controlled by changing the thickness of the barrier film or the thickness or material of the well film.

[Brief description of the drawings]

FIG. 1 is a cutaway side view of a main part of an optical threshold device for explaining the principle of the present invention, and FIG. 2 is an energy band near MQW in the optical threshold device described with reference to FIG. FIG. 3 is a cutaway side view of a main part of a conventional basic optical threshold device. In the figure, 11 is a substrate, 11A is a recess formed in the substrate 11, 12 is an etching stop layer, 13 is a saturable light absorbing layer composed of QW, 14 is a buffer layer, 15 is an active layer, and 16 is a buffer. layer, 17 electrode contact layer, 18 and 19 specular film composed of a semiconductor multilayer film or a dielectric multilayer film, 20 is n-side electrode, 21 is a p-side electrode, E _V is the valence band top of, E _C is conducted The bottom of the band, 13B is a barrier film for forming a quantum well, 13W is a well film for forming a quantum well, and 13W 'is a well film outside the barrier film 12.

Claims (2)

(57) [Claims] 1. A barrier film comprising a first material having a wide band gap and having a thickness such that a carrier can be tunneled, and a narrow band gap sandwiched between the barrier films as compared with the first material. A quantum well composed of a first well film made of a second material having the following thickness, and having a thickness in which a two-dimensional exciton can exist; and a quantum well made of the second material and contained in the first well film. The energy quantum level for the lower electrons is made thicker so that there is at least one energy quantum level compared to the lowest energy quantum level for the generated electrons, and is formed in contact with the outside of the barrier film in the quantum well. A saturable light-absorbing layer comprising: a second well film; and a saturable light-absorbing layer provided separately and in the vicinity of the active layer. 2. A barrier film comprising a first material having a wide band gap and having a thickness such that a carrier can be tunneled, and a narrow band gap sandwiched between the barrier films as compared with the first material. And a quantum well comprising a first well film having a thickness in which a two-dimensional exciton can exist, comprising a second material having the following formula: A third material whose composition is selected such that there is at least one energy quantum level for electrons lower than the energy quantum level and formed in contact with the outside of the barrier film in the quantum well And a saturable light-absorbing layer having a second well film provided separately and independently in the vicinity of the active layer.