JPH01265225A - Photosemiconductor element - Google Patents

Abstract

PURPOSE:To uniform the quantity of variation in the wavelength of an absorption peak among plural quantum wells by increasing the thickness of well layers gradually from the side of a p type semiconductor layer to an n type semiconductor layer. CONSTITUTION:The superlattice 6 between the p type semiconductor layer 1 and n type semiconductor layer 2 is formed by laminating a barrier layer and a well layer alternately and the number of cycles is 50. Then the thickness of 50 well layers shown by 8#1-8#50 is increased gradually from 80Angstrom to 110Angstrom from the side of the p type semiconductor layer 1 to the 8#40, and the barrier layers are also increased in thickness toward 7#50. Thus, the quantum wells are increased gradually in thickness, so the quantity of variation in the wave length of the absorption peak is uniformed among the quantum wells and the characteristics of an external optical modulator are improved.

Description

[Detailed Description of the Invention] [Summary] A superlattice in which barrier layers and well layers are alternately stacked between n-type semiconductor layers to form a quantum well structure is provided. Regarding optical semiconductor devices in which the wavelength of the absorption peak of light absorbed by a superlattice changes due to reverse bias, the purpose of this method is to make the amount of change in the wavelength uniform among multiple quantum wells, and to In between, the thickness is configured to gradually increase from the side of the n-type semiconductor layer toward the side of the n-type semiconductor layer.

[Industrial application field]

The present invention has a superlattice in which barrier layers and well layers are alternately laminated to form a quantum well structure between n-type semiconductor layers, and the superlattice absorbs light. The present invention relates to an optical semiconductor device whose absorption peak wavelength changes due to reverse bias.

With the demand for faster optical communication systems, there is a need for an external optical modulator that modulates laser light continuously emitted from a semiconductor laser with an electrical signal at high speed.

The above-mentioned optical semiconductor element can perform the above-mentioned modulation by matching or removing the wavelength of the absorption peak with respect to the wavelength of the laser beam, and has a characteristic that it can greatly change the optical absorption coefficient for the wavelength to be modulated. have.

[Conventional technology]

FIG. 5 is a side view of a main part of a conventional example of the above-mentioned optical semiconductor device.

In the same figure, 1 is p”-1nP (carrier concentration-I
P-type semiconductor layer of X 10"/co, 2 is n"-
1nP (carrier concentration≠lXto''/c%)
3 is a p-type semiconductor layer l and an n-type semiconductor layer 2.
It is a superlattice between.

The superlattice 3 has barrier layers 4 and well layers 5 stacked alternately,
A quantum well structure as shown in (a) of the energy hunt structure diagram in FIG. 6 is formed. In the figure, Ec is the conduction band bottom and Ev is the valence electron matter. The barrier layer 4 has a thickness of 100 people n-1nP (Carian seismic intensity -1×10”/cffl
), the well layer 5 is made of n-1nGaAs with a thickness of 100 nm.
(carrier concentration #2×10 15 /Cbo), and the number of periods of lamination is about 50 to 100. Here, the period refers to a combination of one barrier layer and one well layer in contact with the barrier layer, and in this case, the period is 200 people.

In this quantum well structure, since the thickness of the well layer 5 is approximately 100 mm thick, the movement of the electrons and poles in the quantum well in the stacking direction is restricted and the energy level is quantized. The excitons existing in the quantum well are compressed and subjected to strong Coulomb attraction, so their binding energy increases and they remain stable even at room temperature.

Therefore, the absorption spectrum of light absorbed by the superlattice 3 is as shown by the solid line in FIG. 7, for example. Clear absorption peaks P1, P2, and P3 are observed in this spectrum, and the wavelengths of the absorption peaks are identified.

When a reverse bias is applied to this element, the energy band structure diagram changes from (al to (b) in figure ÷ figure) due to the electric field.Then, due to the triangular potential formed at the bottom of the quantum well, the energy band structure diagram changes from (al to (b)). The energy level decreases.The electric field E acts in the direction of separating the excitons, but both electrons and holes are confined within the quantum well by the potential barrier, and excitons exist even in a high electric field.

From this, the energies of the absorption peaks P1 to P3 in the light absorption spectrum are shifted to the lower energy side by the application of the electric field E, and the light absorption spectrum changes from the solid line to the broken line in FIG. The wavelengths of the absorption peaks P1 to P3 change toward longer wavelengths.

As can be seen from FIG. 7, when the absorption peak P3 in the state shown by the broken line is matched to the wavelength of the modulation target described above, the optical absorption coefficient changes greatly between the state shown by the solid line and the state shown by the broken line. This is why this device can be used as an external optical modulator.

[Problem to be solved by the invention] By the way, in the light absorption spectrum described in FIG.
Since this spectrum is a composite of the individual effects of multiple quantum wells existing in the quantum well structure, the optical absorption coefficient of the absorption peak P3 in the state indicated by the broken line is increased so that it exhibits good characteristics as an external light modulator. In order to achieve this, it is desirable that the amount of change in the wavelength of the absorption peak P3 when changing from the state shown by the solid line to the state shown by the broken line is the same among the plurality of quantum wells.

In order to achieve this in the conventional example described above, it is necessary that the electric field strengths in the individual well layers 5 are equal. However, the barrier layer 4 and the well layer 5 have the carrier concentration described above. Therefore, the electric field strength E in the superlattice 3
is distributed, for example, as shown in the electric field intensity distribution diagram in FIG. Figure 8 shows the case where the number of cycles of the stacked layers mentioned earlier is 100, and in the figure, Z is a p-type half-four.
The distance in the stacking direction of the superlattice 3 with the interface between the body layer l and the superlattice 3 as the origin, and U is the reverse bias voltage applied to the element.

Therefore, the amount of change in the wavelength of the absorption peak P3 is large in the quantum wells on the p-type semiconductor layer I side and small in the quantum wells in the two n-type semiconductor layers, and becomes uneven among the plurality of quantum wells. As a result, the light absorption coefficient of the absorption peak P3 in the state indicated by the broken line decreases.

Therefore, the present invention includes a superlattice in which barrier layers and well layers are alternately stacked to form a quantum well structure between an n-type semiconductor layer and an n-type semiconductor R-j, and the superlattice has a quantum well structure. It is an object of the present invention to provide an optical semiconductor device in which the absorption peak wavelength of light changes due to reverse bias, so that the amount of change in the wavelength is the same among a plurality of quantum wells.

[Means to solve the problem]

The above object is achieved by the optical semiconductor device of the present invention, in which the thickness between the plurality of well layers gradually increases from the n-type semiconductor layer side to the n-type semiconductor layer side.

[For production]

The amount of change in the wavelength of the absorption peak in each quantum well increases as the electric field strength therein increases, and also increases as the width of the quantum well (ie, the thickness of the well layer) increases.

Therefore, by setting the thickness of the well layer as above,
It becomes possible to equalize the amount of change in wavelength among a plurality of quantum wells.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 4. Fig. 1 is a side view of the main part of the embodiment (al and partially enlarged view (b)), Fig. 2 is an energy band structure diagram of the embodiment,
FIG. 3 is an electric field intensity distribution diagram of the example, and FIG. 4 is a quantum unit characteristic diagram in a quantum well, and the same reference numerals indicate the same objects throughout the figures.

In the embodiment shown in FIG. 1, the conventional superlattice 3 described in FIG. 5 is replaced with a superlattice 6.

Similar to the conventional superlattice 3, the superlattice 6 is made of n-InP (
A barrier layer with a carrier concentration of −I
5/cJ) are alternately laminated, and the number of lamination cycles is 50. And as shown in Figure 1(b),
5 indicated by 8#1 to 8#50 from the side of the p-type semiconductor layer l
The thickness of the 0 well layer is gradually increased from 80 to 110 from 8#1 to 8#50, and the 50 wells indicated by 7#1 to 7#50 are The thickness of the barrier layers is varied so that each period is 200 people, and the last barrier layer 7#51 has a thickness of 100 people.

From this, the energy hand structure diagram of this element is as shown in FIG. 2, and the width of the quantum well changes according to the change in the thickness of the well layers 8#1 to 8#50.

Here, the thickness of the well layers 8111 to 8#50 is determined as follows using FIGS. 3 and 4.

That is, if the reverse bias voltage U applied to the element is 20V, the electric field strength E in the superlattice 6 will be as shown in FIG. 3 due to the circumstances explained in FIG. 8. According to FIG. 3, the electric field strength E in the well layer is maximum at well layer 8#l, Emax = 2 Xl05V/cm, and minimum at well layer 8#50, Emin = l Xl05V.
/■, is.

Figure 4 also shows the dependence of the electric field strength E on the quantum level E of excited electrons in the quantum well (the energy difference with the conduction band bottom Ec), and the dependence of the electric field strength E on the quantum well width (well layer thickness). This quantum level E1 where L) is a parameter
corresponds to the amount of change in the wavelength of the absorption peak in question, and by aligning the quantum levels E1 in the individual quantum wells, the amount of change in wavelength can be made equal among the quantum wells. The characteristics shown in FIG. 4 are determined by the material of the well layer, and the material is n In
This is the case for GaAs.

In FIG. 4, if the thickness of the well layer 8#1 is 80 people as mentioned above, the electric field strength in the well layer 8#1 is E.
Since =Emax = 2Xl05V/c+n, the quantum level in the quantum well to which the well layer 8111 corresponds is E + = 18meν. Therefore, the well layer 8
The quantum level in the quantum well to which #50 corresponds is E+=1
If we try to set it to 8 meV, the electric field strength in the well layer 81150 is E=Emin=l xios V/am
Therefore, the thickness of the well layer 8#50 is determined to be 110 as described above.

Regarding the well layers 8#2 to 8#49, since the electric field strength E in each can be determined from FIG. 3, the well layer 8115
In the same way as finding the thickness of 0, the quantum level is E+=1
It is possible to find each thickness of 8meν.

The thickness is within the range of 80 to 110 people and gradually increases from the well layer 8#1 to the well layer 8#50.

In this way, in the embodiment, the amount of change in the wavelength of interest is made uniform among the plurality of quantum wells. As a result, the optical absorption coefficient of the absorption peak P3 indicated by the broken line in the optical absorption spectrum described in FIG. .

Note that the embodiment shows an example of the optical semiconductor device according to the present invention, and the present invention is directed to a method in which the thickness between the plurality of well layers in the superlattice is as shown in FIGS. 3 and 4 described above. If the thickness is gradually increased from the p-type semiconductor layer side to the n-type semiconductor layer side, details such as the material used, the period and number of periods of the superlattice, etc. are limited to the examples. It is not something that will be done.

〔Effect of the invention〕

As explained above, according to the configuration of the present invention, a superlattice in which barrier layers and well layers are alternately stacked to form a quantum well structure is provided between a p-type semiconductor layer and an n-type semiconductor layer. In an optical semiconductor device in which the wavelength of the absorption peak of light absorbed by the superlattice changes due to reverse bias, it is possible to make the amount of change in the wavelength uniform among a plurality of quantum wells. This has the effect of making it possible to improve the characteristics as a modulator.

[Brief explanation of the drawing]

Figure 1 is a side view and partially enlarged view of the main parts of the example, Figure 2 is the energy band structure diagram of the example, Figure 3 is the electric field strength distribution diagram of the example, and Figure 4 is the quantum standard in the quantum well. Fig. 5 is a side view of the main part of the conventional example, Fig. 6 is an energy band structure diagram of the conventional example, Fig. 7 is a spectrum diagram of optical absorption, and Fig. 8 is an electric field intensity distribution diagram of the conventional example. , is. In the figure, l is a p-type semiconductor layer, 2 is an n-type semiconductor layer, 3.6 is a superlattice, 4.7#1 to 7#50 are barrier layers, 5.8111 to 8#50 are well layers, and E is Electric field or electric field strength, El is quantum level, L is thickness of well layer, P1 to P3 are optical absorption peaks, U is reverse bias voltage, ZI! The distance in the stacking direction of the superlattice is . Actual home example of 尰舒詬, 1st page drawing and report p. -11 Sword 2nd figure award example n spirit world evening U costume figure 3''
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Claims (1)

[Claims] It has a superlattice in which barrier layers and well layers are alternately stacked to form a quantum well structure between a p-type semiconductor layer and an n-type semiconductor layer, and the wavelength of the absorption peak of light absorbed by the superlattice is An optical semiconductor device in which the current changes due to reverse bias, wherein the thickness of the well layers between the plurality of well layers gradually increases from the p-type semiconductor layer side to the n-type semiconductor layer side. semiconductor element.