JPH0480713A - Superlattice optical switch - Google Patents

Abstract

PURPOSE:To make the function of the optical switch sufficiently fast by providing a 1st and a 2nd electrode in a 1st and a 2nd semiconductor area at both-side positions opposed to a superlattice layer. CONSTITUTION:At both-side positions opposed to the superlattice layer 2, the p-type semiconductor area 6P and n-type semiconductor area 6N are arranged in contact with flanks 2c and 2d opposed to the superlattice layer 2, and the electrodes 7P and 7N are added in the semiconductor areas 6P and 6N respectively. In this case, the speed where a pair of an electrode and a positive hole which are coupled with each other with the coulomb force of a high electric field becomes a pair of an electron and a positive hole which are not coupled with the coulomb force is extremely fast and the rising time from the point of time when a resetting voltage is applied to the point of time when the high electric field is obtained can be made sufficiently short. Consequently, the function of the optical switch can be obtained sufficiently fast.

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a superlattice optical switch using a superlattice layer in which well layers made of a compound semiconductor and barrier layers made of another compound semiconductor are sequentially and alternately stacked and have a sufficiently low carrier concentration.

[Conventional technology]

Conventionally, a superlattice optical switch described below with reference to FIG. 3 has been proposed. That is, on a semiconductor substrate 1 made of, for example, GaAs, a well layer 3a made of, for example, GaAs and having a thickness of, for example, 10 nm and a well layer 3a made of, for example, AlGaAs system and having a thickness of, for example,
Barriers 113b having a thickness of 0 nm are sequentially and alternately stacked by epitaxial growth so that the logarithm thereof is, for example, 50 to 200, and has a sufficiently low carrier concentration, for example, 10 cm or less. A superlattice 1g2 is formed. Further, a window 4 that allows the superlattice N2 to be exposed to the outside is formed in the semiconductor substrate 1, and a metal or dielectric material is formed on the main surface 2a of the superlattice layer 2 on the semiconductor substrate 1 side at a position facing the window 4. Anti-tlJlli made of film or multilayer dielectric film! 5
A is arranged on the main surface 2 on the opposite side to the semiconductor substrate 1 side.
On b, another reflection opposite reflection 114! ! ! 5B is placed. The above is the configuration of the conventionally proposed superlattice optical switch. According to the superlattice optical switch having such a configuration, the exciton level of the well 113a of the superlattice layer 2 is entered into the superlattice layer 2 from, for example, from the outside on the semiconductor substrate 1 side via the reflective film 5A. The input light L1 having the corresponding wavelength is shown in FIG.
As shown in FIG. 2, the intensity of the input light L1 is changed from the state in which it is input as bias light at the scheduled intensity IB until time t1 to the setting light for the scheduled intensity I between times t and 12. P, the state in which excitons, which are electron-hole pairs that are bonded to each other by Coulomb force, in the superlattice Wj2 remains approximately constant until time t1. Therefore, the absorption coefficient of the superlattice Ji2 for the input light L1 decreases greatly, and the intensity of light based on the input light L1 in the superlattice layer 2 increases accordingly. At the same time, the refractive index of the superlattice layer 2 changes greatly to a high value accordingly. Therefore, the distance between the reflective films 5A and 5B and the superlattice layer 2
The resonance condition determined by the refractive index at this time is satisfied, and as shown in FIG. 4, until now the expected intensity of zero or the sufficiently low intensity r! IIo
Then, the intensity of the output light L2 that was emitted to the outside from the superlattice layer 2 via the anti-11g15B becomes the planned large intensity 1.
6 minutes, so that from time t1 a switched-on state is obtained. Furthermore, from the state where the switch is on as described above, the intensity of the input light L1 is changed between time points t3 and t4 (v# between points t3 and t4) as shown in FIG. 4A. f[(t4-t3) is usually the time from the switch-on state to the switch-off state, which will be described later, or a slightly longer time], from the planned intensity IB to the planned intensity 1. Only the reset light P,
If the number of excitons is reduced as
Therefore, the absorption coefficient of the superlattice 112 for the input light L1 increases greatly, and the intensity of the input light L1 in the superlattice layer 2 decreases greatly, and The refractive index of layer 2 changes significantly to a lower value.For this reason, the above-mentioned resonance condition in the switch-on state is not satisfied, and the intensity of the output light L2 changes to the point at time t4 or as shown in FIG. 4B. As such, from time 13', which is slightly before time t4, the intensity returns to the time tl @ at which the above-mentioned switched-on state is obtained, and therefore, from time t or t', the switched-off state is obtained. From the above, the conventional superlattice optical switch shown in FIG. 3 functions as an optical switch.

[Problems to be Solved by the Invention] In the case of the conventional superlattice optical switch shown in FIG. The time point t when an intensity higher than the planned intensity IH is obtained from the sufficiently low intensity ■,
The rise time (t'-t1) to 1' is relatively short, such as about 1 p second. However, when the switch is turned off, the falling time (t' -t3) is
The rise time (1
It is very long compared to 1t1). In the superlattice layer 2, excitons are naturally annihilated based on the reset light Pr, and the number of excitons is greatly reduced. , because it can be determined. Therefore, in the case of the conventional superlattice optical switch shown in FIG.
It has the disadvantage that it cannot function as an optical switch at a sufficiently high speed. Therefore, the present invention seeks to propose a novel superlattice optical switch that does not have the above-mentioned drawbacks. [Means for Solving the Problems] The superlattice optical switch according to the present invention, as in the case of the conventional superlattice optical switch described above in FIG. A superlattice layer in which barrier layers are sequentially and alternately stacked and has a sufficiently low carrier concentration, and first and second reflective films disposed on opposing main surfaces of the superlattice layer, and , ■ Input light from the outside through the first anti-1) film into the superlattice layer, and input light from the superlattice layer to the outside through the second reflective film. It has a configuration that allows output light to be obtained. However, in the superlattice optical switch according to the present invention, in the superlattice optical switch having such a configuration:
a semiconductor region and a second semiconductor region having n-type are arranged in contact with opposing side surfaces of the superlattice layer, respectively,
and (2) first and second electrodes are attached to the first and second semiconductor regions, respectively.

[Action/effect]

According to the superlattice optical switch according to the present invention, a state in which an input voltage is applied from a power source to the first electrode with a value of zero, for example with the second electrode as a reference; With the voltage between the
From a state in which input light having a wavelength corresponding to the exciton unit of the well layer of the superlattice layer is incident as bias light at a predetermined intensity through the reflective film of the superlattice layer, the intensity of the input light is If the light is increased for a predetermined amount of time for a predetermined intensity valve setting, the light will be coupled to a large extent within the superlattice layer by the Coulomb force, as in the case of the conventional superlattice optical switch described above in Fig. 3. The number of excitons, which are made up of electron-hole pairs, increases significantly from a state where it was kept at a constant amount, and as a result, the absorption coefficient of the superlattice layer for input light decreases greatly, and accordingly, the superlattice The intensity of light based on the input light within the layer increases significantly, and the refractive index of the superlattice layer changes significantly to a high value accordingly. Therefore, as in the case of the conventional superlattice optical switch described above in FIG. 3, the resonance condition determined by the distance between the first and second reflection legs and the refractive index of the superlattice layer at this time is satisfied. This means that the intensity of the output light that has been emitted from the superlattice layer to the outside through the second reflective film at the planned zero intensity or sufficiently low intensity has changed to the planned large intensity valve. 3, and thus a switched-on state is obtained, as in the case of the conventional superlattice optical switch described above in FIG. However, in the case of the superlattice optical switch according to the present invention,
From the state where the switch-on state has been obtained as described above, the input voltage applied to the first electrode from the above-mentioned power supply with the second electrode as a reference is applied for a scheduled time for reset purposes. If the voltage is set to a negative value, the superlattice layer becomes a depletion layer, and the excitons therein, and therefore the electron-hole pairs that are bonded to each other by the Coulomb force, are depleted by the Coulomb force. A high electric field is generated that forces the electron-hole pairs that are not bonded to each other, thereby resetting the intensity of the input light for a predetermined time, as in the case of the conventional superlattice optical switch described above in Figure 3. Even if the amount of excitons in the superlattice layer is not reduced, the amount of excitons in the superlattice layer changes from the previous large amount to the amount described above, as in the case of the conventional superlattice optical switch described above in FIG. As a result, the absorption coefficient of the superlattice layer for the input light increases greatly, and the light absorption coefficient of the input light in the superlattice layer increases accordingly. The intensity of the superlattice layer decreases significantly, and the refractive index of the superlattice layer changes significantly to a lower value accordingly. Therefore, as in the case of the conventional superlattice optical switch described above in FIG. 3, the resonance condition in the switch-on state described above is not satisfied, and the output light is The intensity returns to that before it was obtained, and thus a switch-off condition is obtained. From the above, the superlattice optical switch according to the present invention also functions as an optical switch in the same way as the conventional superlattice optical switch described above in FIG. In addition, in the case of the superlattice optical switch according to the present invention, the switch-on state can be obtained even for the setting light, as in the case of the conventional superlattice optical switch described above in FIG. The rise time from the time when light is obtained to the time when output light is obtained at a predetermined high intensity is relatively short, as in the case of the conventional superlattice optical switch shown in FIG. However, in the case of the superlattice optical switch according to the present invention,
The switch-off state is obtained from the switch-on state in the conventional method described above in Figure 3, in which the excitons in the superlattice layer are greatly reduced by spontaneous annihilation based on the reset light. Unlike in the case of a superlattice optical switch, excitons and therefore electron-hole pairs that are coupled to each other by Coulomb forces are activated by the negative side of the input voltage applied to the second electrode with the first electrode as the tj quasi. Due to the high electric field in the superlattice layer based on the reset voltage, which is a predetermined value, the excitons in the superlattice layer are greatly reduced by forming electron-hole pairs that are not bonded to each other by Coulomb force. In this case, the speed at which electron-hole pairs that are bonded to each other by the Coulomb force due to the high electric field become electron-hole pairs that are not bonded to each other by the Coulomb force is extremely fast, and the reset The rise time from the time when the application voltage is applied to the time when a high electric field is obtained can be made sufficiently short. For this reason, the fall time for the output light to reach the expected intensity from the switch-on state when the switch-off state is obtained to the intensity before the switch-on state is obtained is shown in Figure 3. The length can be significantly shorter than that of the conventional superlattice optical switch described above. Therefore, according to the superlattice optical switch according to the present invention, the function as an optical switch can be obtained sufficiently faster than in the case of the conventional superlattice optical switch described above in FIG. Embodiment 11 Next, an embodiment of the superlattice optical switch according to the present invention will be described with reference to FIG. In FIG. 1, parts corresponding to those in FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. The superlattice optical switch according to the present invention shown in FIG. 1 has p-type semiconductor regions 6P on opposite sides of the superlattice layer 2 in the configuration of the conventional superlattice optical switch described above in FIG. , n-type semiconductor regions [6N are arranged in contact with opposing side surfaces 2C and 2d of the superlattice layer 2, respectively, and electrodes 7P and 7N are attached to the semiconductor regions 6P and 6N, respectively. . Note that the semiconductor regions 6P and 6N are formed on the semiconductor substrate 1,
forming a superlattice layer similar to superlattice layer 2 which is longer than superlattice layer 2;
Next, after or before introducing an n-type impurity such as Zn and an n-type impurity such as Si or S into both sides of the superlattice layer, the superlattice layer itself is It can be formed by performing a known mixed crystal treatment between a well layer and a barrier layer. The above is the configuration of the embodiment of the superlattice optical switch according to the present invention. According to the superlattice optical switch according to the present invention having such a configuration, an input voltage V is applied from a power source to the electrode 7P, for example, with the electrode 7N as a reference, as shown before time t3 in FIG. 2B, through the resistor. is applied at a value of zero, and therefore the voltage between electrodes 7N and 7P is zero,
In the superlattice layer 2, as in the case of the conventional superlattice optical switch described above in FIG. The input light L1 having a wavelength corresponding to the exciton unit is shown in FIG.
Correspondingly, as shown in FIG. 2A, from a state in which the input light L1 is input as bias light at a scheduled intensity I8 up to time t1, the intensity of the input light L1 is changed between time t1 and time 12 as follows. If the setting light P is increased by the planned intensity, electron-hole pairs will be coupled by Coulomb force within the superlattice layer, as in the case of the conventional superlattice optical switch described above in Fig. 3. The excitons in the state of , which had been kept at a constant amount up to time t1, greatly increase from time t1, and therefore the absorption coefficient of the superlattice layer 2 for the input light L1 decreases significantly. Accordingly, the intensity of the input light L1 in the superlattice layer 2 increases greatly, and the refractive index of the superlattice layer 2 changes to a high value accordingly. Therefore, as in the case of the conventional superlattice optical switch described above in FIG. 3, the resonance condition determined by the distance between the reflective films 5A and 5B and the refractive index of the superlattice layer 2 at this time is satisfied. Therefore, as shown in Fig. 2C, until now, the radiation has been emitted from the superlattice layer 2 to the outside via reflection 1!5B at the planned zero intensity or at a sufficiently low intensity as shown in the figure. The intensity of the output light L2, which had been in use, increases by a predetermined large amount of intensity, and therefore, as in the case of the conventional superlattice optical switch described above in FIG. 3, a switch-on state is obtained from time t1. However, in the case of the superlattice optical switch according to the present invention shown in FIG.
The input voltage ■ applied to the electrode 7P with N as a reference,
As shown in FIG. 2B, between time points t3 and t4,
Although it depends on the carrier concentration of the negative superlattice layer 2 as the reset voltage Pv', if it is set to a predetermined value of 1 to 5V, for example, the superlattice layer 2 is A pin junction with ``1'' is configured, and the pin junction is reverse biased, so
The superlattice layer 2 is made into a depletion layer, and the excitons therein are coupled to each other by the Coulomb force (the energy depends on the width of the superlattice layer 2, for example, 15 m).
eV) A high electric field that transforms electron-hole pairs into electron-hole pairs that are not bonded to each other by Coulomb force (depending on the energy of electron-hole pairs that are bonded to others by Coulomb force) However, for example, about 1 x 103 V/cm), the voltage U is generated.For this reason, as in the case of the conventional superlattice optical switch described above in Fig. 3, the input light is inputted and the intensity of 1 is used as the reset light Pr for a scheduled time. Even without reducing the number of excitons in the superlattice layer 2, as in the case of the conventional superlattice optical switch described above in FIG. Contrary to the case where the on state is obtained, the absorption coefficient of the superlattice layer 2 for input light increases greatly, and accordingly, the absorption coefficient of the superlattice layer 2 increases.
The intensity of the input light L1 within the superlattice layer 2 decreases greatly, and the refractive index of the superlattice layer 2 changes significantly to a lower value accordingly. Therefore, as in the case of the conventional superlattice optical switch described above in FIG. As shown in C, from time t3', which is slightly before time t4, the intensity returns to the level before time t1 at which the above-mentioned switch-on state is obtained, and therefore,
From the instant t or t', the switch F state is obtained. From the above, the superlattice optical switch according to the present invention also functions as an optical switch in the same way as the conventional superlattice optical switch described above in FIG. In addition, in the case of the superlattice optical switch according to the present invention shown in FIG. 1, the switch-on state is variable based on the setting light, as in the case of the conventional superlattice optical switch described above in FIG. Therefore, the time t1 when the setting light P is obtained
The rise time (t'-11) from the time t' at which the output destination L2 is obtained from the planned sufficiently low intensity to the planned intensity I higher than the conventional superlattice light described above in FIG. Relatively short as in the case of switches. However, in the case of the superlattice optical switch according to the present invention shown in FIG. 1, the switch-off state is obtained from the switch-on state due to the spontaneous annihilation of excitons based on the reset light Pr. Unlike the case of the conventional superlattice optical switch described above in FIG. A reset voltage P is a predetermined negative value of the input voltage V to be applied to the electrode 7P with reference to 7N. Due to the high electric field in the superlattice layer 2 based on this, the excitons in the superlattice layer 2 are greatly reduced by forming electron-hole pairs that are not bonded to each other by Coulomb force. In this case, the speed at which electron-hole pairs that are bonded to each other by the Coulomb force caused by the electric field becomes an electron-hole pair that is not bonded to each other by the Coulomb force is extremely high. Furthermore, the rise time from the time point t3 when the reset voltage P,' is applied to the time point when a high electric field is obtained is determined by the above-mentioned pin
Semiconductor region 6 of superlattice layer 2 constituting junction "1"
By appropriately shortening the length between P and 6N, p
Since the capacitance of 1n junction can be made sufficiently small, 0.017D
It can be made sufficiently short so that it is about the size of a person's body. Therefore, the fall time from the switch-on state to the switch-off state is obtained (t4t) or (t
'-t3) can be significantly shorter than that of the conventional superlattice optical switch described above in FIG. 3, which is about 10 psec. Therefore, according to the superlattice optical switch according to the present invention shown in FIG. 1, the function as an optical switch can be obtained sufficiently faster than in the case of the conventional superlattice optical switch described above in FIG. In the above description, the input light L1 is input into the superlattice layer 2 from the outside on the semiconductor substrate 1 side via the reflective film 5A, and the output light L2 is inputted from the superlattice layer 2 via the reflection WA5B. , the input light L1 is reflected from the outside on the side opposite to the semiconductor substrate 1. 5B, and the output light L2 can also be emitted from the superlattice layer 2 to the semiconductor substrate 1 side via the reflective film 5A. Furthermore, in the above description, the well layer 3a of the superlattice layer 2 is made of Ga.
When the barrier layer 3b is made of AIGaAS, the semiconductor substrate 1 is made of GaAs, and therefore the semiconductor substrate 1 itself does not act as a window for the input light L1. and reflective film 5A.
A window 4 is formed on the main surface 2a of the superlattice layer 2 on the semiconductor substrate 1 side.
In the above case, the superlattice layer 2 is formed of an InGaAs-based layer and an InAlAs-based layer, or an InP layer and an InGaA layer.
If the semiconductor substrate 1 is made of InP that acts as a window for the superlattice layer 2, then the semiconductor substrate 1 is provided with a window. First, the reflective film 5A may be provided on the side of the semiconductor substrate 1 opposite to the superlattice layer 2 side. Furthermore, when the semiconductor substrate 1 is made of GaAs, and the superlattice layer 2 is a well-known strained superlattice layer consisting of a layer made of GaAS and a layer made of InGaAs, the semiconductor substrate 1 It is also possible to have a configuration in which the reflective film 5A is provided on the side opposite to the superlattice layer side of the semiconductor substrate 1 without providing a window, and various other modifications and changes can be made without departing from the spirit of the present invention. will be able to do it.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a superlattice optical switch according to the present invention. FIG. 2 is a diagram for explaining the operation. FIG. 3 is a sectional view showing a conventional superlattice optical switch. FIG. 4 is a diagram for explaining the operation. 1... Semiconductor substrate 2...
......Superlattice layers 2a, 2b...Main surface 2C12d of superlattice layer 2...Side surface 3b of superlattice layer 2...・Barrier layer 4...
...... Window 5A, 5B... Reflective film 6P, 6N... Semiconductor region 7P, 7N... Electrode Ll... ......Input light L2...
・・・・・・・・・Output light Figure 1 Figure 3

Claims (1)

[Claims] 1. A superlattice layer in which a well layer made of a compound semiconductor and a barrier layer made of another compound semiconductor are sequentially and alternately stacked and have a sufficiently low carrier concentration, and a superlattice layer on opposing main surfaces of the superlattice layer. and a first and second reflective film arranged in the superlattice layer, based on input light from the outside through the first reflective film into the superlattice layer. In the superlattice optical switch in which output light to the outside is obtained through the second reflective film, at opposing positions of the superlattice layer,
A first semiconductor region having p-type and a second semiconductor region having n-type are disposed in contact with opposing side surfaces of the superlattice layer, and a first semiconductor region is provided in the first and second semiconductor regions. and a second electrode, respectively.