JPH098399A - Surface optical switching element - Google Patents

Abstract

PURPOSE: To obtain a surface optical switching element being modulated directly by external light in which the absorptivity of light impinging on an active layer is enhanced and the available wavelength band is enlarged while facilitating the mounting. CONSTITUTION: The surface optical switching element comprises a first mirror 14 formed on a semiconductor substrate 11, semiconductor layers 15-17 formed on the first mirror 14 each having an active layer 16, a second mirror 20 formed on the semiconductor layers 15-17 while having a protrusion 20a surrounded by a thinned or removed light incident region, a first electrode 21 formed on the second mirror 20 or the semiconductor layer 17, and a second electrode 23 formed on the bottom face of semiconductor substrate 11 with a light radiation window 24 being provided under the protrusion 20a.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface type optical switching element, and more particularly to a surface type optical switching element which is directly modulated by external light.

[0002]

2. Description of the Related Art A surface emitting semiconductor laser is shown in FIG.
It has a structure as shown in FIG. In FIG. 4 (a), the first DBR mirror 2,
n-type AlGaAs cladding layer 3, undoped active layer 4, p-type
The AlGaAs cladding layer 5 and the second DBR mirror 6 are formed in order. The active layer 4 is, for example, GaAs and InGaAs.
It has a quantum well structure in which is formed alternately.

The first DBR mirror 2 contains n-type impurities, and the second DBR mirror 6 contains p-type impurities. A p-side electrode 7 is formed on the second DBR mirror 6, while an n-side electrode 9 having a window 8 in the light output portion is formed below the n-type GaAs substrate 1. When such a surface-emitting type semiconductor laser is used as an optical switching element, a current slightly smaller than the threshold is applied to the active layer 4.
It is conceivable that the semiconductor laser is oscillated by irradiating the active layer 4 with signal light through the window 8 while maintaining the state of flowing into the laser.

[0004]

The signal light is transmitted to the active layer 4
In order to irradiate the first DBR mirror 2, it is necessary to transmit the signal light to the first DBR mirror 2. However, the DBR mirror
As shown in Fig. 4 (b), the reflectance is high and the Q value (resonance sharpness) of the resonator is very large, so there are restrictions such as increasing the intensity of the signal light and selecting a wavelength with a narrow band. is there.
In addition, there is a mounting limitation because the region for irradiating the signal light is the window 8 of the n-side electrode 9.

The present invention has been made in view of the above problems, and improves the absorptance of the light with which the active layer is irradiated,
It is an object of the present invention to provide a surface-type optical switching element that broadens the usable wavelength band of the light and is easy to mount.

[0006]

Means for Solving the Problems The above-mentioned problems are shown in FIG.
2, a first mirror 14 formed on the semiconductor substrate 11, semiconductor layers 15 to 17 formed on the first mirror 14 and having an active layer 16, and the semiconductor layer A second mirror 20 having a projection 20a formed on the light incident region to be thinned or removed and formed on the second mirror 20 or the semiconductor layers 15 to 17; And a second electrode 23 formed on the bottom surface of the semiconductor substrate 11 and having a light emission window 24 below the protrusion 20a. Solve.

In the surface type optical switching element, the second mirror 20 constituting the protrusion 20a is thinly formed around the protrusion 20a. In the planar optical switching element, at least one of the first mirror 14 and the second mirror 20 is composed of a semiconductor multilayer film in which high refractive index layers and low refractive index layers are alternately laminated. And

In the surface-type optical switching element, the second mirror 20 is formed of a dielectric multilayer film in which high refractive index layers and low refractive index layers are alternately laminated. In the planar optical switching element, the semiconductor layer 15
The optical path length of ˜17 is an integral multiple of ½ of the emission wavelength. In the surface type optical switching element,
The active layer 16 has a quantum well structure.

[0009]

[Operation] According to the present invention, the first and second mirrors are formed above and below the semiconductor layer having the active layer, and a part of the second mirror around the resonator is thinned or removed. To be a light incident area and to radiate light through the first mirror. Further, the first electrode is formed on or around the protrusion of the second mirror adjacent to the light incident region, and the second electrode having the light emission window is formed under the semiconductor substrate.

When the active layer is irradiated with signal light from the outside through the light incident region while maintaining a state in which a current slightly smaller than the threshold value is applied between the first and second electrodes,
In the semiconductor layer, recombination of electrons and holes is promoted, and the light generated by this is emitted from the light emission window below the semiconductor substrate. According to this structure, the second mirror is thin or completely removed in the light incident region, and the reflectance in the light incident region becomes relatively low, so that the Q value of the resonator becomes small. It is possible to use signal light of a wide wavelength band. Further, the wavelength band can be changed by adjusting the thickness of the thinned second mirror in the light incident region.

Further, since the light input / output directions are the same, the present invention can be applied to a multi-stage connection system in which it is difficult to completely match the wavelengths. By the way, when the first mirror and the second mirror are formed of a semiconductor multilayer film, it is possible to contain impurities to impart conductivity, and to allow a current to flow through the resonator through the first and second mirrors. Therefore, electrodes can be connected to the surfaces of the first and second mirrors.

When the first mirror and the second mirror are formed of a dielectric multilayer film, the degree of freedom of high refractive index and low refractive index is increased, and the reflection efficiency can be increased with a small number of layers. Further, when the optical path length of the semiconductor layer sandwiched between the first mirror and the second mirror is an integral multiple of 1/2 of the emission wavelength, oscillation occurs. Furthermore, if the active layer has a quantum well structure, it is easy to obtain an integral multiple of 1/2 of the emission wavelength.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. 1 (a) and 1 (b) are cross-sectional views showing a manufacturing process of the surface-type optical switching element of one embodiment of the present invention, and FIG.
(a), (b) is the top view and bottom view. First, FIG.
As shown in (a), Si content 2 × 10 ¹⁸ cm ^-3 , thickness 300
3 × 1 silicon (Si) on the μm n-GaAs substrate 11
The low refractive index n-AlAs layers 12 and the high refractive index n-GaAs layers 13 respectively contained at a concentration of 0 ¹⁸ cm ^-3 are alternately laminated for 22.5 pairs, and the first DBR mirror 14 is formed by these layers. Make up. The film thickness t of each of the n-AlAs layer 12 and the n-GaAs layer 13 is t = λ / 4n ₁ . Here, λ is the oscillation wavelength of the switching element, and n ₁ is the refractive index of AlAs or GaAs. n-
The number of pairs of AlAs layer 12 and n-GaAs layer 13 has a decimal point in the uppermost layer and the lowermost layer of the first DBR mirror 14.
This is because the n-AlAs layer 12 is arranged.

Then, on the first DBR mirror 14,
N-Al _0.2 Ga _0.8 As layer 15 with Si content of 5 × 10 ¹⁷ cm ⁻³ , non-doped active layer 16, zinc (Zn) content of 5 × 10 ¹⁷ cm ⁻³
Then, the p-Al _0.2 Ga _0.8 As layer 17 is sequentially formed. The total film thickness (total optical path length) of these layers is set to a thickness equal to an integral multiple of 1/2 of the emission wavelength. The active layer 16 has a quantum well, and for example, InGaAs having a thickness of 8 nm is formed between three GaAs layers having a thickness of 10 nm.
It has an MQW structure in which two layers are sandwiched.

Further, on the p-Al _0.2 Ga _0.8 As layer 17, Si
Containing ^{3 at} a concentration of 3 × 10 ¹⁸ cm ^-3
Twenty-two pairs of n-AlAs layers 18 and n-GaAs layers 19 having a high refractive index are alternately laminated, and these layers constitute the second DBR mirror 20. The film thickness t of each of the n-AlAs layer 18 and the n-GaAs layer 19 is t = λ / 4n ₁ . The layers from the first DBR mirror 14 to the second DBR mirror 20 described above are grown by, for example, a metal organic chemical vapor deposition (MOVPE) method.

Next, steps required until a sectional shape as shown in FIG. First, the second DBR mirror 20 around the resonance region is partially thinned or removed by a lithography technique using wet etching or dry etching and a mask to form a light incident region. The island-shaped mesa portion (projection portion) 20a is formed.

Then, on the island-shaped mesa portion 20a of the second DBR mirror 20, Ti having a three-layer structure as shown in FIG. 2 (a) is formed.
The p-side electrode 21 made of / Pt / Au is formed by the lift-off method. Further, as shown in FIG. 2B, an n-side electrode 23 made of AuGe / Au having a window 24 is formed on the bottom surface of the GaAs substrate 11 below the island-shaped mesa portion 20a. The n-Al _0.2 Ga _0.8 As layer 15, the active layer 16, and the p-Al _0.2 Ga _0.8 As layer 17 below the island-shaped mesa portion 20 a form a resonator.

In order to drive the optical switching element as described above, a current slightly smaller than the threshold is passed from the p-side electrode 21 to the n-side electrode 23, and this state is maintained. Then, when light is applied to the surface of the second DBR mirror 20 from vertically above or obliquely above and the active layer 16 is irradiated with the light, the light is reflected inside the resonator and reflected by the active layer 16.
Is guided to promote recombination in the active layer 16. As a result, oscillation occurs in the resonator and light is emitted from the window 24 of the n-side electrode 23.

When the irradiation of light from above the second DBR mirror 20 is stopped, the emission of light is stopped at the same time.
By the way, as shown in FIG. 1B, when the second DBR mirror 20 is irradiated with signal light from the outside, the relationship between the incident rate of light and the wavelength can be schematically represented as shown in FIG. Island mesa 20
Even if light is irradiated from above a, the light incident on the second DBR mirror 20 is blocked by the p-side electrode 21. p-side electrode 2
Even when there is no 1, the reflectance of the second DBR mirror 20 is high as shown by the one-dot chain line in FIG. 3, so that the Q value of the resonator is extremely high and only light with a wavelength in an extremely narrow band can be incident.

On the other hand, at least a part of the second DBR mirror 20 around the island-shaped mesa portion 20a is removed in the depth direction, so that the reflectance thereof is relatively low,
Since the Q value of the resonator is reduced as shown by the solid line in FIG. 3, the active layer 16 can be irradiated with light in a wide wavelength band. In addition, this wavelength band can be controlled by the depth of removal of the second DBR mirror 20, and the thinner the wavelength band, the wider the wavelength band. Moreover, since the light transmittance increases as the thickness decreases, it becomes unnecessary to increase the light intensity.

Further, in this surface type optical switching element,
Since the light is emitted from the second DBR mirror 20 side,
It is suitable for a multi-stage connection system in which the directions of light input and output are the same and it is difficult to completely match the wavelengths. In the above operation, the oscillation wavelength is set to 980 nm and the material and thickness of the substrate and each layer are shown, but other compound semiconductors may be used.

The second DBR mirror 20 is formed of a high refractive index semiconductor and a low refractive index semiconductor.
When removing the second DBR mirror 20 around the island mesa portion 20a entirety, a second DBR mirror 20 SiO ₂
The p-side electrode may be formed on the p-Al _0.2 Ga _0.8 As layer 17 around the DBR mirror 20 while the p-side electrode is formed in a ring shape while being composed of a dielectric multilayer film of Si and Si. In this case, the light from the outside is incident from the periphery of the annular p-side electrode.

[0023]

As described above, according to the present invention, two mirrors are formed above and below a semiconductor layer having an active layer, and one of the mirrors is partially thinned or removed to form a light incident region. Since the light is radiated through the other mirror, the reflectance of the mirror is relatively low in the light incident region of the one mirror, and the Q value of the resonator is small. Signal light can be used.
Further, the wavelength band can be changed by adjusting the thickness of the mirror on the light incident region side.

Further, since the input and output directions of light are the same, it can be applied to a multi-stage connection system in which it is difficult to make the wavelengths completely coincide with each other. Furthermore, when the first mirror and the second mirror are formed of a semiconductor multilayer film, impurities can be contained to impart conductivity, and a current can be passed through the resonator through the first and second mirrors. Because you can
Electrodes can be connected to the surfaces of the first and second mirrors.

If the first mirror and the second mirror are formed of a dielectric multilayer film, the degree of freedom of high refractive index and low refractive index is increased, and the reflection efficiency can be increased with a small number of layers. Further, when the optical path length of the semiconductor layer sandwiched between the first mirror and the second mirror is an integral multiple of 1/2 of the emission wavelength, oscillation occurs. Furthermore, if the active layer has a quantum well structure, it is easy to obtain an integral multiple of 1/2 of the emission wavelength.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a manufacturing process of a planar optical switching element according to an embodiment of the present invention.

FIG. 2 is a top view and a bottom view of a surface-type optical switching element according to an embodiment of the present invention.

FIG. 3 is a characteristic diagram showing the relationship between the light emission wavelength and the light incidence rate of the surface-type optical switching element of one embodiment of the present invention.

FIG. 4 is a reflectance characteristic diagram of a conventional surface-emitting type semiconductor laser and a mirror used in the semiconductor laser.

[Explanation of symbols]

11 GaAs Substrate 14 First DBR Mirror 15 n-Al _0.2 Ga _0.8 As Layer 16 Active Layer 17 p-Al _0.2 Ga _0.8 As Layer 20 Second DBR Mirror 20 a Island Mesa (Protrusion) 21 P-side Electrode 23 n-side electrode 24 window

Claims (6)

[Claims] 1. A first mirror formed on a semiconductor substrate, a semiconductor layer formed on the first mirror and having an active layer, and a protrusion shape formed on the semiconductor layer. A second mirror, a first electrode formed on the second mirror or the semiconductor layer, and a second electrode formed on the bottom surface of the semiconductor substrate and having a light emission window below the protrusion. A surface-type optical switching element comprising: 2. The surface type optical switching element according to claim 1, wherein the second mirror forming the protrusion is also thinly formed around the protrusion. 3. A semiconductor multilayer film in which at least one of the first mirror and the second mirror is formed by alternately stacking high refractive index layers and low refractive index layers. Alternatively, the surface-type optical switching element described in 2. 4. The surface-type optical switching element according to claim 1, wherein the second mirror is composed of a dielectric multilayer film in which high refractive index layers and low refractive index layers are alternately laminated. 5. The optical path length of the semiconductor layer is 1/2 of the emission wavelength.
2. The surface-type optical switching element according to claim 1, which is an integral multiple of. 6. The planar optical switching element according to claim 1, wherein the active layer has a quantum well structure.