JP2008098576A - Photoconductive switch - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the use efficiency of incident light to improve performance and miniaturize the size. <P>SOLUTION: A photoconductive switch is provided with a terminal electrode 113 and a terminal electrode 101, and is further provided with an upper containing layer 108 formed of a broad band gap material on which the incident light is given and through which the incident light passes, a photoconductive layer 106 formed of a narrow band gap material where a carrier is excited by the incident light which has passed through the material, a lower containing layer 106 formed of a broad band gap material, and a semiconductor substrate 102 in order from the terminal electrode 113 side between the terminal electrode 113 and a terminal electrode 123. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a photoconductive switch.

  2. Description of the Related Art Conventionally, a photoconductive switch that switches an electric signal by the incidence of light using a photoconductive element whose resistance value changes depending on the amount of incident light has been implemented (see, for example, Patent Documents 1 and 2). When the photoconductive switch is irradiated with light, the resistance value of the photoconductive element between the electrodes is lowered and turned on. When the light is not irradiated, the resistance value of the photoconductive element between the electrodes is increased and turned off.

  A conventional photoconductive switch 700 will be described with reference to FIG. FIG. 8A shows the top surface of a conventional photoconductive switch 700. FIG. 8B shows a cross section of the B7-B7 'portion of the photoconductive switch 700 in FIG.

As shown in FIG. 8, a photoconductive switch 700 includes a semi-insulating semiconductor substrate 702 and a lower confinement layer 704 of a semiconductor material having a wide energy band gap (hereinafter referred to as WB) and doped in an n-type. A p ^- type doped semiconductor material photoconductive layer 706 with a narrow energy band gap (hereinafter referred to as NB), an n-type doped WB material upper confinement layer 708, and a bonding pad Terminal electrodes 713 and 723 coupled to 730 and 740.

  A photoconductive layer 706 is sandwiched between the lower confinement layer 704 and the upper confinement layer 708. Terminal electrodes 713 and 723 separated by a narrow gap are disposed on the exposed surface of the upper confinement layer 708. Lower confinement layer 704 is shown as a layer of WB material grown or deposited on semi-insulating semiconductor substrate 702. The lower confinement layer 704 and the upper confinement layer 708 are thinner than the photoconductive layer 706, and the thicknesses are selected so that they are completely depleted when no incident light L7 is present.

The WB material of the upper confinement layer 708 is assumed to be highly transparent at the wavelength of the incident light L7 in order to maximize the transmission of the incident light L7 reaching the photoconductive layer 706. The NB material of the photoconductive layer 706 is assumed to have as high absorptivity as possible at the wavelength of the incident light L7. Due to these characteristics, when the incident light L7 is present, the photoconductive layer 706 absorbs the energy of the incident light L7, generates a large number of electrons and hole carriers, and becomes a conductive property from the p ⁻ type semiconductor material.

  Here, since the band gap of the photoconductive layer 706 is narrower than the upper and lower confinement layers 708 and 704, the hole carriers are confined in the region of the photoconductive layer 706, and the number of electron carriers corresponding thereto is maintained. . Accordingly, electron carriers having a high running speed are uniformly present in the photoconductive layer 706 with small doping and little influence of surface order and little scattering, and the terminal electrodes 713 and 723 are in a low resistance state, that is, turned on.

On the other hand, when there is no incident light L7, depletion occurs on the upper side or the whole including the junction between the entire n-type upper confinement layer 708 and the p ⁻ -type photoconductive layer 706. 723 is in a high resistance state, that is, off.

Thus, the on / off of the terminal electrodes 713 and 723 is controlled by the presence or absence of the incident light L7. The on-state resistance can be low. As a result, the photoconductive switch 700 can be reduced in size so that the parasitic capacitance at the time of off can be reduced, and switch characteristics from DC to high frequency can be realized.
JP 2001-36101 A Japanese Patent Laid-Open No. 10-163461

  However, in the conventional photoconductive switch 700, since both the terminal electrodes 713 and 723 are on the exposed surface of the upper confinement layer 708, the incident light L7 where the terminal electrodes 713 and 723 exist is reflected, and the incident light L7 Usage efficiency is not good. Therefore, a large light output is required for the incident light L7. As a result, the power consumption of the light emitting unit is increased, the lifetime is limited by the heat generated in the light emitting unit, and the light emitting unit has a high efficiency. Therefore, there is a problem that the switch becomes expensive. The width of the terminal electrodes 713 and 723 is also related to the conductor loss of the electrodes and the ohmic junction resistance between the upper confinement layer 708 and cannot be excessively thinned.

  Reference 1 also mentions that the terminal electrodes 713 and 723 are made of a conductive translucent material, for example, a thin layer of indium tin oxide (ITO) and silver, to improve the incident light utilization efficiency. However, there are electrode conductor losses and ohmic junction resistance deterioration, and the characteristics are not necessarily improved.

  Reference 1 discloses a method of irradiating incident light from the back surface to increase the utilization efficiency of incident light to about 100%. In this case, wiring processing for providing a light emitting element on the back side, a substrate, Since processing is required, the manufacturing process has become extremely difficult.

  In addition, the photoconductive switch 700 is illustrated in order to realize a practical conduction resistance with a light emission output of a realistic light emitting element, and that the photoconductive layer 706 spreads in the horizontal direction (horizontal direction in FIG. 8B). As shown in FIG. 8 (a), some need to be arranged and connected in parallel. As a result, the photoconductive switch area and the light emitting area of the corresponding light emitting element are also problematic.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a photoconductive switch that increases the utilization efficiency of incident light, improves the performance, and is miniaturized.

In order to solve the above-mentioned problem, a photoconductive switch according to claim 1 is provided.
A first terminal electrode;
A second terminal electrode,
Between the first terminal electrode and the second terminal electrode, in order from the first terminal electrode side,
A first confinement layer of wide bandgap material through which incident light is incident and passed;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the transmitted incident light;
A second confinement layer of wide bandgap material;
And a semiconductor substrate.

The photoconductive switch of the invention according to claim 2 is
A first terminal electrode;
A second terminal electrode;
A current spreading layer connected to the second terminal electrode;
A semiconductor substrate,
Between the first terminal electrode and the current diffusion layer, in order from the first terminal electrode side,
A first confinement layer of wide bandgap material through which incident light is passed;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the transmitted incident light;
A second confinement layer of wide bandgap material;
The first terminal electrode and the second terminal electrode are provided on a surface on the incident side of the incident light.

The photoconductive switch according to claim 3 is provided.
A first terminal electrode;
A second terminal electrode;
A semiconductor layer through which incident light is incident and passed,
Between the first terminal electrode and the semiconductor layer, in order from the first terminal electrode side,
A first confinement layer of wide bandgap material;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the incident light;
A second confinement layer of wide bandgap material through which the incident light passes;
A current diffusion layer through which the incident light passes and connected to the second terminal electrode,
The first terminal electrode and the second terminal electrode are provided on a surface opposite to the incident side of the incident light.

The photoconductive switch of the invention according to claim 4 is,
A first terminal electrode;
A second terminal electrode;
A semiconductor substrate,
Between the first terminal electrode and the semiconductor substrate, in order from the first terminal electrode side,
A first mirror layer of a wide bandgap material that reflects incident light;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the incident light;
A current spreading layer of a wide bandgap material through which the incident light is passed and connected to the second terminal electrode;
An active layer for outputting the incident light;
A second mirror layer that reflects the incident light,
The first terminal electrode and the second terminal electrode are provided on a surface opposite to the incident side of the incident light.

The photoconductive switch of the invention according to claim 5 is:
A first confinement layer of wide bandgap material through which incident light is passed;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the transmitted incident light;
A photoconductive portion comprising a second confinement layer of wide bandgap material;
A current spreading layer;
A first terminal electrode;
A second terminal electrode;
A semiconductor substrate,
The photoconductive portion is divided by a groove,
The first terminal electrode and the second terminal electrode are provided on a surface opposite to the incident side of the incident light,
The plurality of divided photoconductive portions are connected in series between the first terminal electrode and the second terminal electrode.

The photoconductive switch according to claim 6 is the photoconductive switch according to claim 5,
The photoconductive switch unit is divided by a plurality of grooves.

The invention according to claim 7 is the photoconductive switch according to any one of claims 1, 2, 3, 5 or 6.
The first confinement layer or the second confinement layer has a sub-layer that reflects incident light that has passed through the photoconductive layer.

  According to the first aspect of the present invention, since the current path has a vertical structure and the first terminal electrode is provided on the incident surface of the incident light, the efficiency of incident light is increased and the performance as a photoconductive switch is achieved. And can be downsized.

  According to the second aspect of the present invention, the current path is formed in a vertical structure, and the first terminal electrode and the second terminal electrode are provided on the same surface. The performance as a switch can be improved and the size can be reduced, and electrical connection with the outside can be easily performed.

  According to the third aspect of the present invention, since the current path is a vertical structure having a vertical direction, the first terminal electrode and the second terminal electrode are provided on the same surface opposite to the incident light incident side. Increasing the efficiency of use of incident light, improving the performance as a photoconductive switch and reducing the size, and facilitating electrical connection with the outside.

  According to invention of Claim 4, it is set as the vertical structure which makes an electric current path the vertical direction, the 1st terminal electrode and the 2nd terminal electrode are provided on the same surface on the opposite side to the incident surface of incident light, and active Since the first terminal electrode and the second terminal electrode are not provided in the path through which the incident light output from the layer is incident on the photoconductive layer, the utilization efficiency of incident light is increased and the performance as a photoconductive switch is improved. It is possible to reduce the size and facilitate electrical connection with the outside.

  According to the fifth aspect of the present invention, the current path is formed in a vertical structure, the first terminal electrode and the second terminal electrode are provided on the same surface, and a plurality of photoconductive portions are connected in series. Therefore, the utilization efficiency of incident light can be increased, the performance as a photoconductive switch can be improved and the size can be reduced, electrical connection with the outside can be facilitated, and the withstand voltage of the photoconductive switch can be improved.

  According to the sixth aspect of the present invention, since the photoconductive portions divided by the plurality of grooves are connected in series, the breakdown voltage of the photoconductive switch can be further improved.

  According to the seventh aspect of the present invention, the incident light passing through the photoconductive layer can be reflected to the photoconductive layer, and the utilization efficiency of the incident light can be further increased.

  Hereinafter, first to sixth embodiments of the present invention will be described in order with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples.

  The photoconductive switch described in each embodiment is a photoconductive switch in which on / off of a broadband signal line from DC (direct current) to microwave is controlled by light irradiation / non-irradiation. In particular, the present invention is applied to on / off control and path switching of ultrahigh-speed digital signals. Application products include measuring instruments for integrated circuits such as system LSI (Large Scale Integration) and memory, testers, antenna switching and band switching for mobile communication base stations, and line switching equipment for digital broadcasting equipment.

(First embodiment)
A first embodiment according to the present invention will be described with reference to FIG. FIG. 1A shows the top surface of the photoconductive switch 100 of the present embodiment. FIG. 1B shows a cross section of the B1-B1 ′ portion of the photoconductive switch 100 in FIG.

  As shown in FIG. 1, the photoconductive switch 100 includes a terminal electrode 101 as a second terminal electrode, an n-type semiconductor substrate 102, and a lower confinement layer as a second confinement layer made of an n-type WB semiconductor material. Layer 104, photoconductive layer 106 of p-type or i-type NB semiconductor material, upper confinement layer 108 as a first confinement layer of n-type WB semiconductor material, and part of the exposed surface of upper confinement layer 108 And the terminal electrode 113 as the second terminal electrode disposed on the upper surface and the upper left end of the photoconductive switch 100. The terminal electrode 101 is disposed on the back surface of the semiconductor substrate 102.

  Since the absorption amount of the incident light L1 in the photoconductive layer 106 decreases exponentially with the bottom being e in the thickness direction, the thickness of the photoconductive layer 106 is assumed to be thinner than the absorption length of the incident light L1. All the conductive layers 106 are caused to generate carriers due to the incident light L1. However, it is not thinned beyond the diffraction limit of the incident light L1.

  Since the upper confinement layer 108 is also operated as a current diffusion layer, it has a thickness of about 0.5 μm to 1 μm and a high doping concentration so that the sheet resistance is as small as possible.

With regard to the selection of the WB semiconductor material of the lower confinement layer 104 and the upper confinement layer 108 and the NB semiconductor material of the photoconductive layer 106, the WB semiconductor material has a transparency with respect to the wavelength of the incident light L1 as well as the lattice constant matching. For the NB semiconductor material, a material having a high absorption rate is selected. The possible material combinations are shown in Table 1 below.

For example, the lower confinement layer 104 is made of Al _0.23 Ga _0.77 As having a doping concentration of n = 1 × 10 ^{17 to} 3 × 10 ¹⁸ cm ⁻³ and a thickness of about 50 nm to 100 nm. The photoconductive layer 106 is made of GaAs having a doping concentration of p = 1 × 10 ^{16 to} 3 × 10 ¹⁶ cm ⁻³ and a thickness of 50 nm to 200 nm. The upper confinement layer 108 is made of Al _0.23 Ga _0.77 As having a doping concentration of n = 1 × 10 ^{17 to} 3 × 10 ¹⁹ cm ⁻³ and a thickness of 500 nm to 1 μm. The semiconductor substrate 102 is made of Al _0.23 Ga _0.77 As having a doping concentration of n = 1 × 10 ^{18 to} 3 × 10 ¹⁸ cm ⁻³ .

  The aluminum ratio in the lower confinement layer 104 and the upper confinement layer 108 is desirably less than 0.25. When the aluminum ratio exceeds 0.25, JPN. J. et al. APPL. PHYS. 1954 (1984). As explained by Tachikawa et al., Deep levels or DX centers increase rapidly. The DX center is detected by a compound semiconductor to which a donor (electron donor) impurity is added, and generates a deep order in the forbidden body. Is trapped in the forbidden body and exhibits a behavior in which the actual amount of free electrons is smaller than the amount of free electrons estimated from the insulating or doping amount. The DX center sharply reduces the free electron concentration in the upper confinement layer 108, and thus the ON resistance Ron is greatly increased.

  Next, the operation of the photoconductive switch 100 when the incident light L1 is turned on / off will be described. In the presence of incident light L1, the mechanism of carrier generation is that incident light L1 is transmitted through the upper confinement layer 108 made of a WB semiconductor material and made of a material having high transparency with respect to the wavelength of the incident light L1, and incident on the photoconductive layer 106. The light energy of the light L1 is absorbed and a large number of electron carriers and hole carriers are generated. Here, since the band gap of the photoconductive layer 106 is narrower than that of the upper and lower upper confinement layers 108 and 104, the hole carriers are confined in the region of the photoconductive layer 106, and the electron carriers corresponding thereto are also included in the other layers. Is prevented from being diffused to the photoconductive layer 106. As a result, the photoconductive layer 106 has a conductive property from a p-type or i-type semiconductor material. Since the lower confinement layer 104 and the upper confinement layer 108 above and below the photoconductive layer 106 have a high doping concentration, the ON resistance Ron between the terminal electrode 101 and the terminal electrode 113 becomes small in this state, and the photoconductive switch 100 turns on.

  When the incident light L1 is not present, the photoconductive layer 106 is completely depleted, and the lower confinement layer 104 and the upper confinement layer 108 are partially depleted, resulting in a high resistance state. That is, in the photoconductive switch 100, the terminal electrode 101 and the terminal electrode 113 are turned off.

  As described above, according to the photoconductive switch 100 of the present embodiment, since the current path is a vertical structure and only the terminal electrode 113 is provided on the incident surface of the incident light L1, the utilization efficiency of the incident light L1 is increased. The performance as a photoconductive switch can be improved and the size can be reduced.

  In the present embodiment, an antireflection coating may be provided on the incident light L1 incident side surface of the upper confinement layer 108.

(Second Embodiment)
A second embodiment of the present invention will be described with reference to FIGS. FIG. 2A shows the top surface of the photoconductive switch 200 of the present embodiment. FIG. 2B shows a cross section of the B2-B2 ′ portion of the photoconductive switch 200 in FIG.

  As shown in FIG. 2, the photoconductive switch 200 includes a terminal electrode 201 as a second terminal electrode, a semiconductor substrate 202, a gradually changing composition layer 203, and a lower confinement layer 204 as a second confinement layer. The graded composition layer 205, the photoconductive layer 206, the graded composition layer 207, the upper confinement layer 208 as the first confinement layer, the current diffusion layer 209, and a part of the exposed surface of the current diffusion layer 209 As the gradual composition layer 210, the cap layer 211, the ohmic contact layer 212, the terminal electrode 213 as the first terminal electrode, and the antireflection coating 250 disposed on the upper surface and the upper left end of the photoconductive switch 100, , Is composed.

  The lower confinement layer 204 is given a structure as a mirror layer with respect to the incident light L2. The mirror layer increases the absorbance of the photoconductive layer 206 by reflecting the incident light L2 passing through the photoconductive layer 206.

In the present embodiment, the lower confinement layer 204 is a distributed Bragg reflector composed of a plurality of sublayer pairs of semiconductor material. This sublayer pair consists of an Al _0.23 Ga _0.77 As sublayer with a thickness of 64 nm and a doping concentration of n = 2 × 10 ¹⁸ cm ⁻³ , and an AlAs sublayer with a thickness of 73 nm and a doping concentration of n = 1 × 10 ¹⁸ cm ⁻³ . And is composed of. The thickness tm of each sublayer is equal to an odd integer multiple of ¼ of the wavelength λ of the incident light L2 in the sublayer material, ie, the thickness tm = mλ / 4n. Here, m is an odd integer, λ is the wavelength of the incident light L2 in free space, and n is the refractive index of the material of the sublayer at the wavelength μ. This mirror layer is composed of 10 pairs of sublayers, and the reflectivity of the mirror layer is about 90%.

The photoconductive layer 206 is GaAs having a doping concentration of p = 2 × 10 ¹⁶ cm ⁻³ and a thickness of 100 nm. The upper confinement layer 208 is Al _0.23 Ga _0.77 As having a doping concentration of n = 1 × 10 ¹⁸ cm ⁻³ and a thickness of 70 nm. The current diffusion layer 209 above the upper confinement layer 208 is installed as Al _0.23 Ga _0.77 As having a doping concentration of n = 3 × 10 ¹⁸ cm ⁻³ and a thickness of 1 μm, thereby achieving a uniform current.

The gradual composition layer 207 is Al _x Ga _1-x As having a gradual increase in x = 0 to 0.23, a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ as in the upper confinement layer 208, and a thickness of 30 nm. The graded composition layer 210 is made of Al _y Ga _1-y As with a gradual decrease in y = 0.23 to 0, n = 3 × 10 ¹⁷ cm ⁻³ as in the upper confinement layer 208, and a thickness of 30 nm. Similarly, the graded composition layer 203 gradually increases from x = 0 to 0.23, the same doping concentration as the lower confinement layer 204, n = 3 × 10 ¹⁷ cm ⁻³ , and 30 nm thick Al _x Ga _1-x As. To do. The gradual composition layer 205 is made of Al _y Ga _1-y As having a gradual decrease in y = 0.23 to 0, a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ as in the lower confinement layer 204, and a thickness of 30 nm. The gradually changing composition layers 207, 210, 203, and 205 can reduce the resistance between the heterojunctions.

The cap layer 211 is made of GaAs having a doping concentration of n = 5 × 10 ¹⁸ cm ⁻³ and a thickness of 200 nm. The ohmic contact layer 212 is made of In _0.5 Ga _0.5 As having a doping concentration of n = 2 × 10 ¹⁹ cm ⁻³ and a thickness of 20 nm. The terminal electrode 213 is made of Ti / Pt / Au having a thickness of 2 μm.

The ohmic contact layer 212 and the terminal electrode 213 realize a non-alloy and low-resistance ohmic junction. This method and structure for reducing contact resistance is described in 28 ELECTRON. LETT. , 1150 (1992). This is based on the heterojunction transistor (HBT) fabrication method described by Ren et al. The semiconductor layers 203-212 are grown sequentially on an n-type GaAs semiconductor substrate 202 with a doping concentration of n = 5 × 10 ¹⁸ cm ⁻³ using molecular beam epitaxy (MBE) or another suitable epitaxial growth technique. It is done.

  The terminal electrode 201 is formed by alloying Ti / Pt / Au with an n-type GaAs semiconductor substrate 202 to form an ohmic junction.

Further, an antireflection coating 250 made of silicon nitride (Si ₃ N ₄ ) is deposited on the exposed surfaces of the semiconductor layers 203 to 212. The thickness of the antireflection coating 250 is, for example, 100 nm. The anti-reflective coating 250 prevents or reduces the reflection of the incident light L2 that occurs due to the large difference in refractive index between the AlGaAs of the upper confinement layer 208 and the surroundings such as air.

  Next, the operation of the photoconductive switch 200 when the incident light L2 is turned on / off will be described. The wavelength of the incident light L2 minimizes absorption by the confinement layer, so that the energy per photon passes through the incident light L2 and reaches the photoconductive layer 206, i.e., the upper side in this example. The wavelength that is below the band edge of the WB material of the confinement layer 208 is selected. The wavelength of the incident light L2 also maximizes the absorption of the incident light L2 by the photoconductive layer 206, so that the wavelength at which the energy per photon exceeds the band edge of the NB material of the photoconductive layer 206 is selected. Is done. In the case of the present embodiment, a beam of incident light L2 is created using a commercially available semiconductor laser having a wavelength of output light of 850 nm.

Beam characteristics of incident light L2, physical characteristics of GaAs, light absorptance αp = 7000 cm ^{−1 of} photoconductive layer 206, carrier lifetime τ = 10 ns, carrier mobility μ = 7000 cm ² / Vs, area S for receiving incident light S The semiconductor path ON resistance Rs (on) is calculated using device parameters such as = 4 × 10 ⁻⁹ m ² and the thickness of the photoconductive layer 206. The semiconductor path ON resistance is a resistance of a conductive path passing through the upper confinement layer 208 and the photoconductive layer 206 when irradiated by the incident light L2.

  FIG. 3 shows the variation of the ON resistance with respect to the laser power that generates the incident light L2. In the case of this embodiment, the thickness of the photoconductive layer 206 is 100 nm, which is sufficiently shorter than the absorption length αp = 1.1 μm. Therefore, as shown in FIG. 3, in the photoconductive layer 206 at the time of irradiation with the incident light L2, carriers are excited throughout the layer, and the photoconductive switch 200 is turned on.

  On the other hand, when there is no incident light L2, the photoconductive layer 206 forms a PN junction with the gradually changing composition layer 205 and the lower confining layer 204, and with the gradually changing composition layer 207 and the upper confining layer 208, and at least light The doping concentration at which the conductive layer 206 is depleted throughout is selected. For this reason, when there is no incident light L2, the resistance between the terminal electrode 201 and the terminal electrode 213 is high, and the photoconductive switch 200 is turned off.

The parasitic capacitance at this time is calculated using device parameters such as the thickness of the photoconductive layer 206, the area S = 4 × 10 ⁻⁹ m ² for receiving the incident light L2, and the dielectric constant of the material of the photoconductive layer 206. The The parasitic capacitance when off is about 0.5pF. Therefore, in the photoconductive switch 200, the CR product often used as a parameter for the switch performance can be made 0.05ΩpF or less. This CR product is expected to be improved by about 20% over the conventional example.

  As described above, according to the photoconductive switch 200 of the present embodiment, the same effect as that of the first embodiment is obtained, and the incident light L2 that passes through the photoconductive layer 206 is transmitted to the photoconductive layer by the lower confinement layer 204. 206 can be reflected, and the utilization efficiency of the incident light L2 can be further increased. In addition, the CR product can be reduced to improve the switch performance.

  Further, the antireflection coating 250 can prevent loss due to reflection of the incident light L2. Moreover, the resistance between heterojunctions can be lowered by the gradually changing composition layers 207, 210, 203, and 205. Further, the current diffusion layer 209 can reduce resistance and make current uniform.

(Third embodiment)
A third embodiment according to the present invention will be described with reference to FIG. FIG. 4A shows the top surface of the photoconductive switch 300 of this embodiment. FIG. 4B shows a cross-section of the B3-B3 ′ portion of the photoconductive switch 300 in FIG.

  The major difference between the photoconductive switch 300 of this embodiment and the photoconductive switch 200 of the second embodiment is that a semi-insulating substrate is used for the photoconductive switch 300, and the electrodes at both ends of the switch are formed on the upper surface of the die. Therefore, it is easy to make electrical connection with an external high-frequency integrated circuit.

  As shown in FIG. 4, the photoconductive switch 300 includes a semiconductor substrate 301, a lower current diffusion layer 302, a gradual composition layer 303, a lower confinement layer 304 as a second confinement layer, and a gradual composition. Layer 305, photoconductive layer 306, gradual composition layer 307, upper confinement layer 308 as a first confinement layer, gradual composition layer 309, upper current diffusion layer 310, and first terminal electrode Terminal electrode 313, terminal electrode 323 as a second terminal electrode, and antireflection coating 350.

The semiconductor substrate 301 is made of semi-insulating GaAs. A lower current diffusion layer 302 is provided on the semiconductor substrate 301. The lower current diffusion layer 302 is made of GaAs having a doping concentration of n = 1 × 10 ¹⁹ cm ⁻³ and a thickness of 1 μm to reduce resistance and make current uniform.

A gradual composition layer 303 is provided on the lower current diffusion layer 302. The gradual composition layer 303 is Al _x Ga _1-x As having a gradual increase in x = 0 to 0.23, a doping concentration of n = 2 × 10 ¹⁸ cm ⁻³ , and a thickness of 30 nm.

A lower confinement layer 304 is provided on the graded composition layer 303. The lower confinement layer 304 is also provided with a structure as a mirror layer, and is a distributed Bragg reflector composed of a plurality of sublayer pairs of semiconductor material, like the lower confinement layer 204 of the second embodiment. When the incident light L3 is a semiconductor laser light having a wavelength of 850 nm, a 64 nm thick Al _0.3 Ga _0.7 As sublayer having a doping concentration of n = 2 × 10 ¹⁸ cm ⁻³ and a doping concentration of n = 1 × 10 ¹⁸ cm ^-3 of 73 nm thick AlAs sublayers are used as a pair, and it is composed of 10 sublayer pairs. The thickness of each sublayer is obtained on the same principle as that of the second embodiment. The mirror layer reflects the incident light L3 that has passed through the photoconductive layer 306 without being absorbed, and returns to the photoconductive layer 306, thereby increasing the utilization efficiency of the incident light L3.

A graded composition layer 305 is provided on the lower confinement layer 304. The gradual composition layer 305 is Al _y Ga _1-y As with a gradual decrease in y = 0.23 to 0, a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ and a thickness of 30 nm. A photoconductive layer 306 is provided on the graded composition layer 305. The photoconductive layer 306 is made of GaAs having a doping concentration of p = 2 × 10 ¹⁶ cm ⁻³ and a thickness of 100 nm.

A gradual composition layer 307 is provided on the photoconductive layer 306. The graded composition layer 307 is Al _x Ga _1-x As with x = 0 to 0.23 gradually increasing, doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ , and thickness of 30 nm. An upper confinement layer 308 is provided on the graded composition layer 307. The upper confinement layer 308 is made of Al _0.23 Ga _0.77 As having a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ and a thickness of 70 nm.

On the upper confinement layer 308, a graded composition layer 309 is provided. The graded composition layer 309 is Al _y Ga _1-y As with a gradual decrease in y = 0.23 to 0, a doping concentration of n = 2 × 10 ¹⁸ cm ⁻³ , and a thickness of 30 nm. The graded composition layers 303, 305, 307, and 309 can reduce the resistance between the heterojunctions. On the gradually changing composition layer 309, an upper current diffusion layer 310 is provided. The upper current diffusion layer 310 is made of GaAs having a doping concentration of n = 1 × 10 ¹⁹ cm ⁻³ and a thickness of 1 μm to reduce resistance and make current uniform.

  A terminal electrode 313 is provided on a part of the upper current diffusion layer 310. For the terminal electrode 313, a material having a low alloy temperature for forming an ohmic junction with respect to the upper current diffusion layer 310 such as Ti / Au / Ge / Ni / Au or In / Au is selected. The thickness of the terminal electrode 313 is about 2 μm. A terminal electrode 323 is provided on a part of the lower current diffusion layer 302. The terminal electrode 323 is made of a material having a low alloy temperature for forming an ohmic junction with respect to the lower current diffusion layer 302 such as Ti / Au / Ge / Ni / Au or In / Au. The thickness of the terminal electrode 323 is about 2 μm.

  The semiconductor layers 302-310 are sequentially grown on a semi-insulating GaAs semiconductor substrate 301 using molecular beam epitaxy (MBE) or another suitable epitaxial growth technique. The terminal electrodes 313 and 323 are formed in the same process, and a material having a low alloy temperature for forming an ohmic junction is selected to suppress diffusion of the layer structure and doping material due to heat during the alloy as much as possible.

Further, an antireflection coating 350 made of silicon nitride (Si ₃ N ₄ ) is deposited on the exposed surfaces of the semiconductor layers 302 to 310. The thickness of the antireflection coating 350 film is, for example, 100 nm. The wavelength of the incident light L3 is less than the band edge of the WB material of the confinement layers 308 and 304 in order to increase the transmittance in the confinement layer and increase the absorption in the photoconductive layer 306, and The wavelength that will exceed the band edge of the NB material is selected. In the case of the example of FIG. 4, the beam of the incident light L3 is created using a commercially available semiconductor laser having a wavelength of output light of 850 nm.

  Next, the operation of the photoconductive switch 300 when the incident light L3 is turned on / off will be described. When the incident light L3 is present, the same on-resistance characteristic of FIG. 3 as that of the photoconductive switch 200 of the second embodiment can be expected, and the photoconductive switch 300 is turned on.

  When there is no incident light L3, the photoconductive switch 300 is turned off as in the photoconductive switch 200 of the second embodiment, and the parasitic capacitance at the time of off is 0.5 pF. Therefore, in the photoconductive switch 300, the CR product often used as a switch performance parameter can be made 0.05ΩpF or less. This CR product is expected to be improved by about 20% over the conventional example.

  As described above, according to the photoconductive switch 300 of this embodiment, the current path has a vertical structure, and the terminal electrode 313 and the terminal electrode 323 are provided on the incident surface of the incident light L3 as the same surface. The utilization efficiency of the light L3 can be increased, the performance as a photoconductive switch can be improved and the size can be reduced, and electrical connection with the outside can be facilitated.

  Further, the antireflection coating 350 can prevent loss due to reflection of the incident light L3. In addition, the resistance between heterojunctions can be lowered by the gradually changing composition layers 307, 309, 303, and 305. Further, the lower current diffusion layer 302 and the upper current diffusion layer 310 can reduce resistance and make the current uniform.

In this embodiment, the doping concentration of the semiconductor substrate is less than 1 × 10 ¹⁷ cm ⁻³ , and both the lower current diffusion layer and the upper current diffusion layer are provided, and the exposed surface of the lower current diffusion layer is exposed. One terminal electrode may be provided in part, and the other terminal electrode may be provided on a part of the surface of the upper current diffusion layer.

(Fourth embodiment)
A fourth embodiment according to the present invention will be described with reference to FIG. FIG. 5A shows the top surface of the photoconductive switch 400 of the present embodiment. FIG. 5B shows a cross section of the B4-B4 ′ portion of the photoconductive switch 400 in FIG.

  A significant difference between the photoconductive switch 400 of the present embodiment and the photoconductive switch 300 of the third embodiment is that a semi-insulating substrate made of a WB semiconductor material is used for the photoconductive switch 400 and the mirror layer is placed on the upper side. By providing on the confinement layer, it corresponds to the case where there is incident light L4 from the back surface of the substrate. Further, the entire structure of the photoconductive switch 400 is simplified by configuring the current diffusion layer with a WB semiconductor material and reducing the number of gradually changing composition layers. The incident light L4 is generated using a commercially available semiconductor laser whose output light wavelength is 850 nm.

  As shown in FIG. 5, the photoconductive switch 400 includes a semiconductor layer 401, a lower current diffusion layer 402, a lower confinement layer 404 as a second confinement layer, a gradually changing composition layer 405, and a photoconductive layer. 406, a graded composition layer 407, an upper confinement layer 408 as a first confinement layer, an upper current diffusion layer 410, a terminal electrode 413 as a first terminal electrode, and a terminal as a second terminal electrode An electrode 423, a protective film 450, and an antireflection coating 451 are included.

The semiconductor layer 401 is a non-doped Al _0.23 Ga _0.77 As layer. In the semiconductor layer 401, the semiconductor substrate is translucent within the wavelength range of the incident light L4. A lower current diffusion layer 402 is provided on the semiconductor layer 401. The lower current diffusion layer 402 is made of Al _0.23 Ga _0.77 As with a doping concentration of n = 3 × 10 ¹⁸ cm ⁻³ and a thickness of 1 μm to reduce resistance and make current uniform.

A lower confinement layer 404 is provided on the lower current diffusion layer 402. The lower confinement layer 404 is Al _0.23 Ga _0.77 As having a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ and a thickness of 70 nm. A graded composition layer 405 is provided on the lower confinement layer 404. The gradually changing composition layer 405 is gradually reduced from y = 0.23 to 0, Al _y Ga _1-y As having a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ , which is the same as that of the lower confinement layer 404, and a thickness of 30 nm.

A photoconductive layer 406 is provided on the graded composition layer 405. The photoconductive layer 406 is made of GaAs having a doping concentration of p = 2 × 10 ¹⁶ cm ⁻³ and a thickness of 100 nm. A gradual composition layer 407 is provided on the photoconductive layer 406. The graded composition layer 407 is Al _x Ga _1-x As with x = 0 to 0.23 gradually increasing, doping concentration n = 3 × 10 ¹⁷ cm ⁻³ , and thickness 30 nm. The resistance between the heterojunctions can be lowered by the graded composition layers 405 and 407.

An upper confinement layer 408 is provided on the graded composition layer 407. The upper confinement layer 408 is also provided with a structure as a mirror layer, and is a distributed Bragg reflector composed of a plurality of sublayer pairs of semiconductor material, like the lower confinement layer 204 of the second embodiment. When the incident light L4 is a semiconductor laser beam having a wavelength of 850 nm, the sublayer pair includes an Al _0.3 Ga _0.7 As sublayer with a doping concentration of n = 2 × 10 ¹⁸ cm ^{−3 and} a thickness of 64 nm, and a doping concentration of n = 1 × 10 ¹⁸ cm ⁻³ of 73 nm-thick AlAs sublayers and 10 sublayer pairs. The thickness of each sublayer is obtained on the same principle as that of the second embodiment. The mirror layer reflects the incident light L4 that has passed through the photoconductive layer 406 without being absorbed, and returns to the photoconductive layer 306, thereby increasing the utilization efficiency of the incident light L4.

An upper current spreading layer 410 is provided on the upper confinement layer 408. The upper current diffusion layer 410 is made of Al _0.23 Ga _0.77 As with a doping concentration of n = 1 × 10 ¹⁹ cm ⁻³ and a thickness of 1 μm to reduce resistance and make current uniform.

  A terminal electrode 413 is provided on part of the upper current diffusion layer 410. For the terminal electrode 413, a material having a low alloy temperature for forming an ohmic junction with respect to the upper current diffusion layer 410, such as Au / Sn or Au / Ge / Ni / Au, is selected. The thickness of the terminal electrode 413 is about 2 μm. A terminal electrode 423 is provided on part of the lower current diffusion layer 402. For the terminal electrode 423, a material having a low alloy temperature for forming an ohmic junction with respect to the lower current diffusion layer 402, such as Au / Sn or Au / Ge / Ni / Au, is selected. The thickness of the terminal electrode 413 is about 2 μm.

  Semiconductor layer 401 is grown on a semi-insulating GaAs semiconductor substrate using liquid phase epitaxy (LPE) or another suitable epitaxial growth technique. The semiconductor layers 402, 404 through 408 and 410 are grown sequentially using molecular beam epitaxy (MBE) or another suitable epitaxial growth technique.

The terminal electrodes 413 and 423 are formed in the same process, and a material having a low alloy temperature for forming an ohmic junction is selected to suppress diffusion of the layer structure and the doping material due to heat during the alloy as much as possible. A protective film 450 made of silicon nitride (Si ₃ N ₄ ) is provided on the exposed portions of the semiconductor layers 402, 404 to 408 and 410.

When the processing of the substrate surface is completed, the semi-insulating GaAs semiconductor substrate is shaved from the back surface to expose the non-doped semiconductor layer 401, and an antireflection coating 451 made of silicon nitride (Si ₃ N ₄ ) is provided on the back surface.

  Next, the operation of the photoconductive switch 400 when the incident light L4 is turned on / off will be described. The wavelength of the incident light L4 is less than the band edge of the WB material of the confinement layers 408 and 404 and increases the NB of the photoconductive layer 406 in order to increase the transmittance in the confinement layer and increase the absorption in the photoconductive layer. The wavelength that will exceed the band edge of the material is selected.

  When the incident light L4 is present, the on-resistance characteristic of FIG. 3 can be expected as in the photoconductive switch 200 of the second embodiment, and the photoconductive switch 400 is turned on.

  When there is no incident light L4, the photoconductive switch 400 is turned off similarly to the photoconductive switch 200 of the second embodiment, and the parasitic capacitance at the time of off is 0.5 pF. Therefore, in the photoconductive switch 400, the CR product often used as a parameter for the switch performance can be made 0.05ΩpF or less. This CR product is expected to be improved by about 20% over the conventional example.

  As described above, according to the photoconductive switch 400 of the present embodiment, the current path has a vertical structure, and the terminal electrode 413 and the terminal electrode 423 are provided on the same surface opposite to the incident side of the incident light L4. Since the terminal electrode 413 and the terminal electrode 423 are not provided in the path through which the incident light L4 is incident on the photoconductive layer 406, the use efficiency of the incident light L4 can be increased, the performance as a photoconductive switch can be improved, and the size can be reduced. It is easy to make electrical connection with.

  Further, the antireflection coating 451 can prevent loss due to reflection of the incident light L4. Further, the resistance between the heterojunctions can be lowered by the gradually changing composition layers 407 and 405, and the structure can be simplified by reducing the number of gradually changing composition layers. Further, the lower current diffusion layer 402 and the upper current diffusion layer 410 can reduce the resistance and make the current uniform.

(Fifth embodiment)
A fifth embodiment according to the present invention will be described with reference to FIG. FIG. 6A shows the top surface of the photoconductive switch 500 of the present embodiment. FIG. 6B shows a cross section of the B5-B5 ′ portion of the photoconductive switch 500 in FIG.

  In general, the photoconductive switch 500 of the present embodiment is obtained by integrating the photoconductive element (photoconductive layer or the like) of the fourth embodiment into a solid element in a surface emitting laser. The photoconductive switch 500 has a photoconductive layer sandwiched between mirror layers of a surface emitting laser. Note that, like the photoconductive switch 400 of the fourth embodiment, a mirror layer structure is added to the current diffusion layer of the photoconductive switch 500.

  As shown in FIG. 6, the photoconductive switch 500 includes a semiconductor substrate 501, a lower mirror layer 561 as a second mirror layer, an active layer 562, an upper cladding layer 563, and a first current diffusion layer 565. N layer 566, p layer 567, n layer 568, second current spreading layer 504, graded composition layer 505, photoconductive layer 506, graded composition layer 507, and first mirror. An upper mirror layer 508 as a layer, an upper current diffusion layer 510, a terminal electrode 513 as a first terminal electrode, a terminal electrode 523 as a second terminal electrode, a terminal electrode 533, a terminal electrode 534, A protective film 550. The semiconductor substrate 501 has an insulating region 564.

As shown in FIG. 6A, the photoconductive switch 500 is premised on laser emission and is preferably configured in a circular shape. The semiconductor substrate 501 is n-type GaAs with a doping concentration of n = 5 × 10 ¹⁸ cm ⁻³ . On the semiconductor substrate 501, a lower mirror layer 561 serving as a surface emitting laser lower cladding layer is provided. The lower mirror layer 561 is a distributed Bragg reflector composed of a plurality of sublayer pairs of semiconductor material. Lower mirror layer 561, and Al _0.23 Ga _0.77 As sublayer 64nm thick doping concentration ^{n = 2 × 10 18 cm -3} , AlAs of 73nm thick doping concentration n = 1 × 10 ¹⁸ cm ^-3 Vice The layer is composed of 30 sublayer pairs. Further, a gradually changing composition layer may be provided to lower the junction resistance between the heterojunctions. In this case, the thickness of each layer is selected so as to match the principle of the mirror layer configuration in the second embodiment, taking into account the gradually changing composition layer.

An active layer 562 serving as a light emitting portion is provided on the lower mirror layer 561. The active layer 562 is non-doped GaAs having a thickness of 100 nm. Alternatively, the active layer 562 may be configured with a quantum well structure including a plurality of sublayer pairs of non-doped semiconductor material. For example, 19 nm Al _0.36 Ga _0.64 As-8 nm Al _0.12 Ga _0.88 As-7 nm Al _0.36 Ga _0.64 As-8 nm Al _0.12 Ga _0.88 As-7 nm Al _0.36 Ga _0.64 As-19 nm thick Al _0.36 Ga _0.64 As may be used.

An upper cladding layer 563 is provided on the active layer 562. The upper cladding layer 563 is made of Al _0.23 Ga _0.77 As having a doping concentration of p = 2 × 10 ¹⁸ cm ⁻³ and a thickness of 256 nm. Further, a gradually changing composition layer may be provided to lower the junction resistance between the heterojunctions.

A first current diffusion layer 565 is provided on the upper cladding layer 563. The first current spreading layer 565 is Al _0.23 Ga _0.77 As having a doping concentration of p = 3 × 10 ¹⁸ cm ⁻³ and a thickness of 1.28 μm, and the resistance between the terminal electrode 534 and the upper cladding layer 563 is reduced. The current to the upper cladding layer 563 is made uniform.

On the first current spreading layer 565, an n layer 566, a p layer 567, and an n layer 568 are stacked from below. The n layer 566 is an Al _0.23 Ga _0.77 As layer having a doping concentration of n = 3 × 10 ¹⁶ cm ⁻³ and a thickness of 256 nm. The p layer 567 is an Al _0.23 Ga _0.77 As layer having a doping concentration of p = 1 × 10 ¹⁶ cm ⁻³ and a thickness of 512 nm. The n layer 568 is an Al _0.23 Ga _0.77 As layer having a doping concentration of n = 3 × 10 ¹⁶ cm ⁻³ and a thickness of 256 nm. The n layer 566, the p layer 567, and the n layer 568 electrically insulate the first current spreading layer 565 and the second current spreading layer 504 by a depleted PN junction. In place of the n layer 566, the p layer 567, and the n layer 568, a p layer, an n layer, and a p layer are provided in this order, and the first current spreading layer 565 and the second current spreading layer 504 are connected by the PN junction. It is good also as a structure electrically insulated.

A second current spreading layer 504 is provided on the n layer 568. The second current diffusion layer 504 is made of Al _0.23 Ga _0.77 As having a doping concentration of n = 3 × 10 ¹⁸ cm ⁻³ and a thickness of 1.15 μm to reduce resistance and make current uniform. A gradual composition layer 505 is provided on the second current spreading layer 504. The graded composition layer 505 is Al _y Ga _1-y As with y = 0.23 to 0 gradually reduced, a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ , and a thickness of 30 nm.

A photoconductive layer 506 is provided on the graded composition layer 505. The photoconductive layer 506 is made of GaAs having a doping concentration of p = 2 × 10 ¹⁶ cm ⁻³ and a thickness of 120 nm. A gradual composition layer 507 is provided on the photoconductive layer 506. The gradual composition layer 507 is Al _x Ga _1-x As having a gradual increase in x = 0 to 0.23, a doping concentration of n = 3 × 10 ¹⁷ cm ⁻³ , and a thickness of 30 nm.

On the gradually changing composition layer 507, an upper mirror layer 508 of a surface emitting laser is provided. Upper mirror layer 508 is a distributed Bragg reflector composed of a plurality of sublayer pairs of semiconductor material. The upper mirror layer 508 includes a 64 nm thick Al _0.23 Ga _0.77 As sublayer with a doping concentration of n = 2 × 10 ⁸ cm ⁻³ and a 73 nm thick AlAs sublayer with a doping concentration of n = 1 × 10 ¹⁸ cm ^−3. And 30 sublayer pairs. A gradually changing composition layer may be provided to lower the junction resistance between the heterojunctions. In this case, the thickness of each layer is selected so as to match the principle of the mirror layer configuration in the second embodiment, taking into account the gradually changing composition layer.

An upper current diffusion layer 510 is provided on the upper mirror layer 508. The upper current diffusion layer 510 is made of Al _0.23 Ga _0.77 As with a doping concentration of n = 1 × 10 ¹⁹ cm ⁻³ and a thickness of 1 μm to reduce resistance and make current uniform.

  Since the distance A between the upper mirror layer 508 and the lower mirror layer 561 becomes the resonance length of the oscillating laser beam L5, an integral multiple of the wavelength (the number of wavelengths in each layer determined by the refractive index of each layer is set as the upper mirror). It is necessary that the value summed between the layer 508 and the lower mirror layer 561 be an integral multiple of the wavelength in vacuum). It is necessary to adjust the layer thickness so as to satisfy this condition. Since there is no need to emit light except for the active layer 562, and in order to reduce the parasitic capacitance of the terminal electrode, an insulating region 564 is formed in the n-type GaAs semiconductor substrate 501 by proton ion implantation or the like.

  A terminal electrode 513 is provided on the whole or a part of the upper current diffusion layer 510. For the terminal electrode 513, a material having a low alloy temperature for forming an ohmic junction with respect to the upper current diffusion layer 510, such as Au / Sn or Au / Ge / Ni / Au, is selected. The thickness of the terminal electrode 513 is about 2 μm. A terminal electrode 523 is provided on part of the second current diffusion layer 504. For the terminal electrode 523, a material having a low alloy temperature for forming an ohmic junction with respect to the second current diffusion layer 504, such as Au / Sn or Au / Ge / Ni / Au, is selected. The thickness of the terminal electrode 523 is about 2 μm.

  A terminal electrode 533 is provided on part of the first current diffusion layer 565. The terminal electrode 533 is made of a material having a low alloy temperature for forming an ohmic junction with respect to the first current diffusion layer 565, such as Au / Sn or Au / Ge / Ni / Au. The thickness of the terminal electrode 533 is about 2 μm. The terminal electrodes 513, 523, and 533 may be formed in the same process.

A protective film 550 made of silicon nitride (Si ₃ N ₄ ) is provided on exposed portions of the semiconductor layers 561 to 568, 504 to 508, and 510. When the processing of the substrate surface is completed, a terminal electrode 534 is provided on the back surface of the n-type GaAs semiconductor substrate 501. The terminal electrode 534 is formed by alloying Ti / Pt / Au with the n-type GaAs semiconductor substrate 501 to form an ohmic junction. The thickness of the terminal electrode 534 is about 2 μm.

  Next, the operation of the photoconductive switch 500 when the power is turned on / off will be described. When a potential of 10 mA is applied between the terminal electrode 533 and the terminal electrode 534 so that the terminal electrode 533 has a positive potential, an optical output of about 3 mW is obtained between the semiconductor layers 561 to 563 and the resonator length A. Laser oscillation with an oscillation wavelength of 780 nm occurs, and laser light L5 is output. At this time, the photoconductive layer 506 is irradiated with the laser beam L5 and has a low resistance of 0.1Ω or less, as in the case of the incident light in the first to fourth embodiments described so far. The conductive switch 500 can be turned on between the terminal electrodes 513 and 523.

  When there is no potential between the terminal electrode 533 and the terminal electrode 534, the photoconductive switch 500 can be turned off between the terminal electrodes 513 and 523 as in the second embodiment. The parasitic capacitance during off is 0.5pF. Therefore, in the photoconductive switch 500, the CR product often used as a parameter of the switch performance can be made 0.05ΩpF or less. This CR product is expected to be improved by about 20% over the conventional example.

  As described above, according to the photoconductive switch 500 of the present embodiment, the current path has a vertical structure, and the terminal electrode 513 and the terminal electrode 523 are provided on the same surface opposite to the incident surface of the laser light L5. Since the terminal electrode 513 and the terminal electrode 523 are not provided in the path through which the laser beam L5 output from the active layer is incident on the photoconductive layer 506, the utilization efficiency of the incident light L5 is increased and the performance as a photoconductive switch is improved. It is possible to reduce the size and facilitate electrical connection with the outside.

  Further, the distance A between the upper mirror layer 508 and the lower mirror layer 561 can be set as the resonator length of the laser light L5, and the laser light L5 can be generated. In addition, the resistance between the heterojunctions can be lowered by the gradually changing composition layers 507 and 505, and the structure can be simplified by reducing the number of gradually changing composition layers. Further, the second current spreading layer 504 and the upper current spreading layer 510 can reduce the resistance and make the current uniform. In addition, the first current spreading layer 565 and the second current spreading layer 504 can be insulated by the n layer 566, the p layer 567, and the n layer 568.

(Sixth embodiment)
A sixth embodiment according to the present invention will be described with reference to FIG. FIG. 7A shows the top surface of the photoconductive switch 600 of the present embodiment. FIG. 7B shows a cross section of the B6-B6 ′ portion of the photoconductive switch 600 in FIG.

  The photoconductive switch 600 of this embodiment is a configuration example in which the photoconductive switch 300 of the third embodiment is connected in series in one element die to increase the withstand voltage.

  As shown in FIG. 7, the photoconductive switch 600 includes a semiconductor substrate 601, a lower current diffusion layer 602, a gradual composition layer 603a, a lower confinement layer 604a as a second confinement layer, and a gradual composition. A layer 605a, a photoconductive layer 606a, a gradual composition layer 607a, an upper confinement layer 608a as a first confinement layer, a gradual composition layer 609a, an upper current diffusion layer 610a, and a first terminal electrode Terminal electrode 613, gradual composition layer 603b, lower confinement layer 604b as a second confinement layer, gradual composition layer 605b, photoconductive layer 606b, gradual composition layer 607b, An upper confinement layer 608b as a confinement layer, a graded composition layer 609b, an upper current diffusion layer 610b, a terminal electrode 623 as a second terminal electrode, an antireflection coating 650, Constructed.

  Semiconductor substrate 601, lower current diffusion layer 602, gradual composition layer 603a, lower confinement layer 604a, gradual composition layer 605a, photoconductive layer 606a, gradual composition layer 607a, upper confinement layer 608a as photoconductive portions The gradual composition layer 609a and the upper current diffusion layer 610a are, in order, the semiconductor substrate 301, the lower current diffusion layer 302, the gradual composition layer 303, the lower confinement layer 304, and the gradual composition layer of the third embodiment. 305, the photoconductive layer 306, the gradual composition layer 307, the upper confinement layer 308, the gradual composition layer 309, and the upper current diffusion layer 310. Also, as the photoconductive portion, a gradually changing composition layer 603b, a lower confining layer 604b, a gradually changing composition layer 605b, a photoconductive layer 606b, a gradually changing composition layer 607b, an upper confining layer 608b, a gradually changing composition layer 609b, an upper current. The diffusion layer 610b and the antireflection coating 650 are the gradual composition layer 303, the lower confinement layer 304, the gradual composition layer 305, the photoconductive layer 306, the gradual composition layer 307, and the upper confinement layer 308 of the third embodiment. The gradual composition layer 309, the upper current diffusion layer 310, and the antireflection coating 350 have the same configuration. For this reason, a different part from 3rd Embodiment is mainly demonstrated.

  In the manufacture of the photoconductive switch 600, after forming the photoconductive switch 300 semiconductor layer structure (semiconductor layers 602 to 610) of the third embodiment, a gap 660 is formed by etching. The gap 660 roughly divides the semiconductor layers 603 to 610 into two parts to form semiconductor layers 603a to 610a and semiconductor layers 603b to 610b, respectively.

  Terminal electrodes 613 and 623 are provided on parts of the upper current diffusion layers 610a and 610b, respectively. For the terminal electrodes 613 and 623, a material having a low alloy temperature for forming an ohmic junction such as Ti / Au / Ge / Ni / Au or In / Au is selected. The terminal electrodes 613 and 623 have a thickness of about 2 μm. An anti-reflective coating 650 is deposited on the exposed surfaces of the semiconductor layers 602-610.

  Next, the operation of the photoconductive switch 500 when the power is turned on / off will be described. When the incident light L6 is present, the photoconductive layers 606a and 606b have low resistance, the on-resistance characteristics are established between the terminal electrodes 613 and 623 through the lower current diffusion layer 602, and the photoconductive switch 600 is turned on. In this case, if the size of the photoconductive switch 600 and the light output of the incident light L6 are the same as those of the photoconductive switch 300 and the incident light L3 of the third embodiment, the on-resistance of the photoconductive switch 600 is 4 times.

  When there is no incident light L4, the photoconductive switch 600 is turned off as in the third embodiment. In the photoconductive switch 600, the on-resistance is quadrupled, but the off-capacitance when there is no incident light L4 is ¼, so the CR product of the photoconductive switch 600 is the same as in the third embodiment. 0.05ΩpF or less can be achieved. Moreover, the withstand voltage at the time of OFF can be doubled.

  As described above, according to the photoconductive switch 600 of the present embodiment, the same effects as those of the third embodiment are obtained, and a plurality of semiconductor layers 603a to 610a and 603b to 610b as photoconductive portions are connected in series. Therefore, the breakdown voltage of the photoconductive switch can be doubled.

  In the present embodiment, the photoconductive switch 600 has a configuration in which two semiconductor layer configurations of the photoconductive portion are connected in series, but the present invention is not limited to this. According to the procedure of the sixth embodiment, the withstand voltage can be increased to 4 times, 6 times, etc. by making it 4 series, 6 series, etc. A plurality of photoconductive portions may be connected in series with a transmission line having a quarter-wavelength of the highest frequency of the signal band to be used interposed therebetween.

  The description in each of the above embodiments is an example of the photoconductive switch according to the present invention, and the present invention is not limited to this.

  In the second to sixth embodiments, the lower confinement layer and the upper confinement layer (in the fifth embodiment, the second current diffusion layer and the upper mirror layer) are other n-type WB materials, The photoconductive layer may be another p-type or i-type NB material, and the semiconductor substrate may be another material, or any one of the combinations shown in Table 1 above.

  In the second to fourth and sixth embodiments, the confinement layer on the side opposite to the light incident side has a mirror structure. However, the present invention is not limited to this. For example, a mirror layer that forms a distributed Bragg reflector for incident light may be provided between the confinement layer and the current diffusion layer opposite to the light incident side.

In each of the above embodiments, the WB material of the lower confinement layer and the upper confinement layer (the second current diffusion layer and the upper mirror layer in the fifth embodiment) is Al _x Ga _1-x As and x 0.02 <x <1, and the NB material of the photoconductive layer may be Al _y Ga _1-y As and x> y.

In each of the above embodiments, the combination of the WB material of the lower confinement layer and the upper confinement layer (in the fifth embodiment, the second current diffusion layer and the upper mirror layer) and the NB material of the photoconductive layer is combined. , (Al _y Ga _1-y ) _0.5 In _0.5 P (where 0.0 ≦ y ≦ 1.0) and Al _x Ga _1-x As (where 0.0 ≦ x <0.5) (Al _y Ga _1-y ) As (where 0.0 <y <1.0) and In _x Ga _1-x As (where 0.01 <x <0.3); _x Ga _1-x ) _0.5 In _0.5 As (where 0.01 <x <1.0) and In _0.5 Ga _0.5 As; (Al _x Ga _1-x ) _0.5 In _0.5 As (where 0. 01 <x <1.0) and GaAs _0.5 Sb _0.5 ; Al _x Ga _1-x N (where 0.01 <x <1.0) and GaN; Si and Ge _x Si _1-x (where in, 0.05 <x <1.0) and; Si and SiC _{and; Zn y Mg 1-y S} z Se 1-z ( where, 0 <y <1.0 and 0 <z <1 0) and ZnS _x Se _1-x (where, 0 <x <1) _{and; Al x Ga 1-x Sb} ( where, 0.01 <x <1.0) and GaSb and; Pb _x Cd ₁ It may be selected from the group consisting of _-x Te (where 0.01 <x <1.0) and PbTe.

  In each of the above embodiments, the WB material of the lower confinement layer and the upper confinement layer (in the fifth embodiment, the second current diffusion layer and the upper mirror layer) is more than the NB material of the photoconductive layer. It may be doped in a large amount.

In each of the above embodiments, the doping concentration of the NB material of the photoconductive layer may be less than 1 × 10 ¹⁷ cm ⁻³ .

Further, in the first and second embodiments, the doping concentration of the semiconductor substrate is 1 × 10 ¹⁸ cm ⁻³ or more, one terminal electrode is provided on a part or the whole of the back surface of the semiconductor substrate, and the upper side current diffusion is provided. It is good also as providing the other terminal electrode in a part of surface of a layer.

  In the first, third, and sixth embodiments, the terminal electrode formed on a part or the entire surface of the incident light incident surface may be a transparent electrode.

In each of the above embodiments, a WB material having a doping concentration of 1 × 10 ¹⁸ cm ⁻³ or more is used between the semiconductor substrate and the lower confinement layer, or the upper layer of the upper confinement layer, or both. It is good also as a structure provided with a current spreading layer.

  Moreover, it is good also as combining at least 2 of said each embodiment. For example, you may combine the structure which divides | segments the electroconductive part into 6th Embodiment with the structure of 4th Embodiment.

  Further, the configuration of the photoconductive switch of each of the above embodiments may be applied to a photocoupler (optical isolator).

  In addition, the detailed configuration and detailed operation of the photoconductive switch in each of the above embodiments can be changed as appropriate without departing from the spirit of the present invention.

FIG. 2A is a top view of the photoconductive switch 100 according to the first embodiment of the present invention. (B) is a cross-sectional view of the B1-B1 'portion of the photoconductive switch 100 in (a). (A) is a top view of the photoconductive switch 200 of the second embodiment according to the present invention. (B) is sectional drawing of the B2-B2 'part of the photoconductive switch 200 in (a). It is a figure which shows the fluctuation | variation of ON resistance with respect to the laser power which generate | occur | produces the incident light L2. (A) is a top view of the photoconductive switch 300 of the third embodiment according to the present invention. (B) is sectional drawing of the B3-B3 'part of the photoconductive switch 300 in (a). (A) is a top view of the photoconductive switch 400 of the fourth embodiment according to the present invention. (B) is sectional drawing of the B4-B4 'part of the photoconductive switch 400 in (a). (A) is a top view of the photoconductive switch 500 of the fifth embodiment according to the present invention. (B) is sectional drawing of the B5-B5 'part of the photoconductive switch 500 in (a). (A) is a top view of the photoconductive switch 600 of the sixth embodiment according to the present invention. (B) is sectional drawing of the B6-B6 'part of the photoconductive switch 600 in (a). (A) is a top view of a conventional photoconductive switch 700. FIG. (B) is sectional drawing of the B7-B7 'part of the photoconductive switch 700 in (a).

Explanation of symbols

100, 200, 300, 400, 500, 600, 700 Photoconductive switches 101, 201, 213, 313, 323, 413, 423, 513, 523, 533, 534, 613, 623, 713, 723 Terminal electrodes 102, 202 , 301, 401, 501, 601, 702 Semiconductor substrate 203, 205, 207, 210, 303, 305, 307, 309, 405, 407, 505, 507, 603a, 605a, 607a, 609a, 603b, 605b, 607b, 609b Gradual composition layer 104, 204, 304, 404, 604a, 604b, 704 Lower confinement layer 106, 206, 306, 406, 506, 606a, 606b, 706 Photoconductive layers 108, 208, 308, 408, 608a, 608b, 708 Upper confinement layer 1 13,213 Terminal electrode 209 Current diffusion layer 211 Cap layer 212 Ohmic contact layer 250, 350, 451, 650 Antireflection coating 302, 402, 602 Lower current diffusion layer 310, 410, 510, 610a, 610b Upper current diffusion layer 450 , 550 Protective film 561 Lower mirror layer 562 Active layer 563 Upper cladding layer 564 Insulating region 565 First current spreading layer 566, 568 n layer 567 p layer 504 second current spreading layer 508 upper mirror layer 730, 740 pad

Claims (7)

A first terminal electrode;
A second terminal electrode,
Between the first terminal electrode and the second terminal electrode, in order from the first terminal electrode side,
A first confinement layer of wide bandgap material through which incident light is incident and passed;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the transmitted incident light;
A second confinement layer of wide bandgap material;
A photoconductive switch comprising a semiconductor substrate. A first terminal electrode;
A second terminal electrode;
A current spreading layer connected to the second terminal electrode;
A semiconductor substrate,
Between the first terminal electrode and the current diffusion layer, in order from the first terminal electrode side,
A first confinement layer of wide bandgap material through which incident light is passed;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the transmitted incident light;
A second confinement layer of wide bandgap material;
The photoconductive switch, wherein the first terminal electrode and the second terminal electrode are provided on a surface on an incident side of the incident light. A first terminal electrode;
A second terminal electrode;
A semiconductor layer through which incident light is incident and passed,
Between the first terminal electrode and the semiconductor layer, in order from the first terminal electrode side,
A first confinement layer of wide bandgap material;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the incident light;
A second confinement layer of wide bandgap material through which the incident light passes;
A current diffusion layer through which the incident light passes and connected to the second terminal electrode,
The photoconductive switch, wherein the first terminal electrode and the second terminal electrode are provided on a surface opposite to the incident light incident side. A first terminal electrode;
A second terminal electrode;
A semiconductor substrate,
Between the first terminal electrode and the semiconductor substrate, in order from the first terminal electrode side,
A first mirror layer of a wide bandgap material that reflects incident light;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the incident light;
A current spreading layer of a wide bandgap material through which the incident light is passed and connected to the second terminal electrode;
An active layer for outputting the incident light;
A second mirror layer that reflects the incident light,
The photoconductive switch, wherein the first terminal electrode and the second terminal electrode are provided on a surface opposite to the incident light incident side. A first confinement layer of wide bandgap material through which incident light is passed;
A photoconductive layer of a narrow bandgap material in which carriers are excited by the transmitted incident light;
A photoconductive portion comprising a second confinement layer of wide bandgap material;
A current spreading layer;
A first terminal electrode;
A second terminal electrode;
A semiconductor substrate,
The photoconductive portion is divided by a groove,
The first terminal electrode and the second terminal electrode are provided on a surface opposite to the incident side of the incident light,
The photoconductive switch, wherein the plurality of divided photoconductive portions are connected in series between the first terminal electrode and the second terminal electrode.   The photoconductive switch according to claim 5, wherein the photoconductive switch unit is divided by a plurality of grooves.   The said 1st confinement layer or the said 2nd confinement layer has a sublayer which reflects the incident light which passed the said photoconductive layer, Any one of Claim 1, 2, 3, 5 or 6 characterized by the above-mentioned. The photoconductive switch according to one item.

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