JPH06103774B2 - Semiconductor optical functional light emitting device - Google Patents

Description

The present invention relates to a semiconductor optical functional light emitting device used for optical communication and optical information processing.

(Prior Art) A semiconductor light emitting element is one of key devices used for optical communication and optical information processing, and its performance and function are expected to be improved. Among them, AlGaAs / GaAs semiconductor light emitting devices are currently used as mere light source devices for compact discs, optical disc devices, etc., but due to the vast demand for optical information processing, semiconductor optical functional light emitting devices that can be controlled by light input. Is expected to be realized. Furthermore, in order to increase the capacity of these optical information processing, it is desirable that the output light has a shorter wavelength,
Further, it has been desired to realize an element having an output light on / off function by the input light and a wavelength conversion function of the input light.

On the other hand, an attempt to realize a light emitting element having an on / off function of an output light by an optical input has been performed by, for example, a journal of
Applied Physics 1986, 59, 596 (GWTaylo
r et al., J. Appl. Phys. 59 , 596 (1986)). In this example, the absorbing layer and the light emitting layer are GaAs layers, and the structure is such that light can enter the light absorbing layer.

(Problems to be Solved by the Invention) However, a light emitting layer (AlGaAs having a larger forbidden band width)
The following problems have been encountered in pursuing a shorter emission wavelength by using a layer). In other words, as is well known, mixed crystal AlGaAs, which has a larger forbidden band than GaAs, changes from direct transition type to indirect transition type when a certain forbidden band width is exceeded (when the Al composition ratio exceeds 0.45), and a light emitting device is realized. There was a problem I couldn't do. In the past, absorption was performed in the light emitting layer or the adjacent layer, but since the forbidden band width of the light emitting layer is not larger than the forbidden band width of the adjacent layer, the emission wavelength is equal to or longer than the absorption wavelength of the incident light. There was a problem that only the wavelength side could be obtained.

Therefore, an object of the present invention is to improve the above-mentioned conventional problems, to realize a short-wavelength light-emitting element in a region that was difficult with the conventional AlGaAs-based element, and to output light at a wavelength shorter than the input wavelength. A semiconductor optical functional light emitting device is provided.

(Means for Solving the Problems) The present invention has a double hetero structure in which an active layer is sandwiched between two cladding layers, and at least one of the cladding layers has a plurality of semiconductor layers. The multilayer structure is formed by stacking layers. The multilayer structure has a forbidden band width smaller than the energy of incident light of a desired wavelength and serves as a light absorption layer.
And a semiconductor layer of a second material having a forbidden band width larger than the forbidden band width of the semiconductor layer of the first material. In addition, the active layer has a superlattice structure in which at least one GaAs2 atomic layer and at least one AlAs2 atomic layer are combined and laminated.

(Operation and Principle of the Invention) FIG. 1 is a perspective view showing a schematic structure of the semiconductor optical functional light emitting device of the present invention. This light emitting device has a double hetero structure in which an active layer 14 is sandwiched between clad layers 13 and 15 on a substrate 11 like a normal light emitting device. However, the cladding layer 13 is provided with the light absorption layer 12 inside, and has a structure in which the output light 19 from the active layer 14 can be controlled when the incident light 18 is input. This structure is a feature of the present invention. FIG. 2 is a conceptual diagram showing the band structure of a conventional example, and FIG. 3 is a conceptual diagram showing the band structure of the semiconductor light emitting device of the present invention, where 20 is the upper end of the valence band and 21 is the Γ point of the conduction band. (Solid line), 22
Indicates the position of point X (broken line). As shown in Figure 2,
In the case of a conventional AlGaAs element, if the band gap of the active layer 14 is increased to reduce the emission wavelength, the AlGaAs
When the composition ratio exceeds 0.45, the Γ point 21 (solid line) of the conduction band is located higher than the X point 22 (broken line), and a direct transition light emitting device cannot be obtained.

In contrast, in the present invention, Applied Physics Letters, 1976, Vol. 29, p. 327 (AC Gassard et al., Appl.
s. Lett. 29 , 323 (1976)), the method of short-period atomic layer component modulation is further advanced, and using the recently possible atomic layer growth technique, Form an active layer. That is, an active layer is formed by alternately stacking at least one GaAs2 atomic layer and at least one AlAs2 atomic layer. In the crystal layer of this structure, as shown in FIG. 4, the conduction band Γ point position (circle) and X were compared with the average Al composition ratio.
When compared with the point position (marked with Δ), the Γ point position can be made lower than the X point position in most of the Al composition ratio region (average composition ratio of about 0.7 or less). That is, compared with the relationship between the Γ point position (solid line) and the X point position (broken line) in the case of the conventional AlGaAs mixed crystal, the average Al
Direct transition is possible in a wider range of composition ratio. In the present invention, the wavelength of the active layer is shortened by utilizing the characteristics of the crystal structure as described above.

Next, the relationship between the light input and the light emission output will be described. The conventional example described above has a pnpn thyristor layer structure, and the operating principle is an n-type that contacts the p-type AlGaAs base layer at the stage when no light is incident.
In the carrier depletion layer generated in the GaAs layer, light is absorbed and carriers are injected, and the light is output from the GaAs layer which also serves as an absorption layer and a light emitting layer.

The present invention provides a layered structure as shown in FIG. 3 which is different from the conventional pnpn structure. The principle of its operation is that, as shown in FIG. 3 (b), the potential barriers (spikes) 31 and 32 and the depletion region 33 which become remarkable as the Al composition ratio increases at the hetero interface where the composition changes sharply at the stage where no light is incident. Therefore, since the voltage applied to the region of the active layer 14 cannot be increased sufficiently, the property that the emission current hardly flows is used first. Next, when light is incident on the light absorption layer 12, carriers are injected into the depletion layer region 33, the carriers are accelerated by the electric field of the depletion layer region 33, and a minute current instantaneously flows, as shown in FIG. As the potential barrier decreases, the active layer current increases and light is emitted at the active layer 14 portion, and finally laser oscillation is reached.

Here, even when an indirect transition type AlGaAs mixed crystal layer is used as the light absorption layer and the forbidden band width of the light absorption layer is set smaller than the forbidden band width of the active layer, the above mechanism causes It can contribute to carrier injection into the active layer without emitting light. That is, it is also possible to pump light with a wavelength longer than the emission wavelength to emit laser light. That is, the element of the present invention is also suitable for a wavelength conversion element including a shorter wavelength side, an optical amplification element, a switch, and a modulation element.

Hereinafter, examples of the present invention will be described in more detail.

(Embodiment 1) FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG. 3 is a conceptual view showing a band structure of this embodiment. As shown in FIG. 1, in the present embodiment, an n-type AlGaAs clad layer 13, an active layer 14 and a p-type AlGaAs clad layer in which an n-type AlGaAs clad layer 13, AlAs2 atomic layers and GaAs2 atomic layers are alternately laminated. 15, the current blocking layer 16, the electrodes 10 and 17, and the AlGaAs light absorption layer 12 having a narrower bandgap is included inside the n-type cladding layer 13 on the substrate side. As a crystal growth method for the active layer 14, a metal organic vapor phase epitaxy (MOVPE) method, which is one method of monoatomic layer crystal growth, was used. In this embodiment, as an example, [(G
aAs) ₂ (AlAs) ₂ (AlAs) ₂ ] active layer with a structure in which 50 periodic structural elements are repeated (average Al composition ratio 0.66)
Grew up. It was confirmed by photoluminescence measurement that this grown layer exhibits direct transition type light emission. The forbidden band width is about 2eV, which is sufficiently larger than 1.4eV of GaAs.

For the clad layers 13 and 15 adjacent to the active layer, an AlGaAs mixed crystal layer having an Al composition ratio of 0.8 having a forbidden band width larger than 2 eV was used, and n-type and p-type doping was performed as in a normal laser device. As shown in Fig. 3, the light absorption layer region 12 has a width of 200 at a cycle of about 300Å.
Å, AlGaAs mixed crystal layer with Al composition ratio of 0.5 was provided for 10 cycles. After the above layer growth, a semi-insulating current blocking layer 16 was formed on both sides of the mesa structure including the active layer for current confinement by a normal laser manufacturing process as shown in FIG.

Applying a voltage of about 1.6 V to such a device,
When light of μm was incident, the device current drastically flowed, and laser emission of wavelength of about 0.60 μm was observed from the active layer.

(Example 2) By changing the initial applied voltage of the device of Example 1, the absorption edge wavelength of the input light could be changed. The principle is that the absorption edge of the light absorption layer (quantum well) is shifted by the Franz-Keldish type, that is, by shifting to the long wavelength side by the electric field. Therefore, the present embodiment can be applied to a light emitting switch element that processes multi-wavelength input light, a wavelength conversion element including a shortened wavelength, and an optical amplification element.

(Example 3) [(GaAs) ₂ (AlAs) ₂ (AlAs) ₂ ] in Example 1
Instead of the active layer of the structure, [(GaAs) ₂ (AlAs) ₂ ] (average Al composition ratio 0.5) and [(AlAs) ₂ (GaAs) ₂ (AlA
Even when an active layer having a s) ₂ (GaAs) ₂ (AlAs) ₂ ] (average Al composition ratio 0.6) structure was used, short-wavelength light emission that was not obtained by the conventional AlGaAs mixed crystal was obtained.

Example 4 In the above example, a diffraction grating was provided in the layer adjacent to the active layer, and further laser emission with a narrow line width was obtained. Further, by using the second-order diffraction, not only the planar input in-plane output light concept of the above-described embodiment but also a planar input planar output optical element can be functioned.

Although the n-type GaAs substrate is used in the above embodiment, the entire device is turned upside down and the uppermost layer is the n-type cap layer and the lowermost layer is p.
Type GaAs substrate.

(Effects of the Invention) As described above, the semiconductor light emitting device of the present invention is capable of short-wavelength light emission in a region, which was difficult with the conventional AlGaAs light emitting device, and further absorbs input light to emit light. It is controllable and is suitable for various optical information processing elements such as an optical switch light emitting element, multi-wavelength input control, wavelength conversion element including shortening of wavelength, and optical amplification element.

[Brief description of drawings]

FIG. 1 is a perspective view showing a schematic structure of one embodiment of the present invention,
2 is a conceptual diagram showing the band structure of a conventional semiconductor light emitting device, FIG. 3 is a conceptual diagram showing the band structure of the embodiment of FIG. 1,
FIG. 4 is a diagram showing the characteristics of the active layer material of the present invention. 10 ... Electrode, 11 ... Substrate, 12 ... Light absorption layer, 13 ... Clad layer, 14 ... Active layer, 15 ... Clad layer, 16 ... Current blocking layer, 17 ... Electrode, 18 ... Input light, 19 ... output light, 20 ... valence band, 21 ... conduction band Γ point, 22 ... conduction band X point, 31,32 ... potential barrier, 33 ... depletion layer region.

Claims (1)

[Claims] 1. A double hetero structure in which an active layer is sandwiched between two clad layers, and at least one of the clad layers has a multi-layer structure in which a plurality of semiconductor layers are laminated, This multi-layered structure has a forbidden band width smaller than the energy of incident light having a desired wavelength and is a semiconductor layer made of a first material that serves as a light absorption layer and a layer that sandwiches the semiconductor layer made of the first material from both sides. A semiconductor layer of a second material having a band width larger than the forbidden band width of the semiconductor layer of the first material, wherein the active layer is a combination of at least one GaAs2 atomic layer and at least one AlAs2 atomic layer. A semiconductor optical functional light emitting device having a superlattice structure described above.