JP2757319B2 - FET structure photodetector - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an FET structure photodetector.

[Conventional technology] Conventionally, PIN photodiodes have been used as high-speed photodetectors,
Avalanche photodiodes (APD) and the like are known. In addition, an FET structure can also be used as a high-speed photodetector, and there are some reports (Umeda et al., IEICE VOL. J68-C, p. 263 (1985); CYChen et.al, Appl. .Phy
s. Lett. 41, p. 1040 (1983)).

FIG. 4 shows GaAs monolithically integrated with an optical waveguide.
-Shows an example of a photodetector with a MESFET structure (U.S. Pat.
No. 246).

In the figure, GaAs is semi-insulated.
A non-doped Al _x Ga _1-x As layer 41 is laminated on a substrate 40, a non _- doped Al _y Ga _1-y As layer 42 having a thickness of several μm is laminated thereon as a waveguide 43, and a 0.2-0.5μm n-type
A GaAs layer 44 is stacked as an active layer, and further thereon, a source electrode 47 and a drain electrode 4 for supplying and removing current.
8, the gate electrode 49 is attached. By setting the conventional example of this structure to a bias state and guiding light to the waveguide 43, a photocurrent flows between the drain electrode 48 and the source electrode 47, and light can be detected.

[Problems to be Solved by the Invention] However, among the above-described conventional photodetectors, the PIN photodiode has no photocurrent amplification function, and the APD has the amplification function, but has a large bias current when used. Is necessary, and it can be said that it is not suitable for integration.

On the other hand, a photodetector with an FET structure has a relatively low bias voltage, has a built-in amplification function, and can be used as a driver or amplifier of a semiconductor laser (LD) when integrated. However, it has not been optimized for use as a photodetector.

This will be described in detail below. FIG. 3 shows the potential when an electric field is applied as shown in FIG. 4 in the FET having the structure shown in FIG. 4 of the conventional example. It can be seen that almost no electric field is applied between the source and the gate, and a large electric field is applied between the gate and the drain.

It is also considered that the depletion layer 45 has a shape that is pulled toward the drain 48 under the gate 49 as shown in FIG.

In this state, when light is guided to the waveguide 43 immediately below the gate 49, the light also spreads to a region other than the depletion layer 45, and the carrier generated between the depletion layer 45 and the gate 49-drain 48. Drifts because a strong electric field is applied as shown in FIG. However, the carriers generated between the gate 49 and the source 47 reach the depletion layer 45 after diffusion or recombine before the diffusion because almost no electric field is applied between them as shown in FIG. As a result, there arises a problem that response characteristics are deteriorated.

Further, as shown in FIG. 4, since the waveguide 43 is provided immediately below the gate 49, it is difficult to adjust the position of this fabrication.
Some deviation may occur.

Accordingly, it is an object of the present invention to provide a photodetector having an FET structure having a configuration capable of improving the time response characteristic and facilitating the alignment of the production of the waveguide.

[Means for Solving the Problems] The FET structure photodetector of the present invention is configured as follows.

It has a source electrode, a drain electrode, a gate electrode provided on the active layer, and an optical waveguide provided under the active layer, and propagates through the optical waveguide by a current flowing between the source electrode and the drain electrode. In the FET structure photodetector for detecting the amount of light to be emitted, the distance between the gate electrode and the drain electrode is set wider than the distance between the source electrode and the gate electrode, and the optical waveguide exists between the gate electrode and the drain electrode. An FET structure photodetector characterized in that it is provided to perform

As a result, the effect of carriers generated between the source and the gate and diffused to reach the depletion layer or recombined before that to deteriorate the response characteristics can be reduced, thereby improving the light receiving rate and improving the time response characteristics. I do. In addition, the allowable range of the position where the waveguide is provided is widened, and the alignment is facilitated.

In addition, if the optical waveguide has a superlattice structure in which a first semiconductor material which is a semiconductor substrate and a second semiconductor material having a smaller refractive index than the substrate material are stacked, a relatively wide range of wavelengths can be obtained. The light possessed can be efficiently guided by the waveguide, and the detection efficiency is improved.

[Embodiment] FIG. 1 shows a first embodiment of the present invention. In FIG. 1, a non-doped GaAs layer 11 is formed on a GaAs semi-insulating substrate 10.
0.5 μm is laminated, on which Al _0.5 as a cladding layer is formed.
A Ga _{0.5 A} As layer 12 is laminated at 1 μm, and a superlattice layer 13 of Al _0.5 Ga _{0.5 As} 30 Å and GaAs 60 と し て as a waveguide layer is formed thereon.
μm stacked (that is, Al _0.5 Ga _0.5 As30Å and GaAs60Å
78 layers are stacked on top of each other)
_{A 0.5} Ga _0.5 As layer 14 is stacked 0.1 μm. Then, on this cladding layer 14, a doping concentration as an active layer
An n-type GaAs layer 15 of 1.0 × 10 ¹⁷ cm ⁻³ is stacked at a thickness of 0.2 μm. On this active layer 15, a source electrode 16, a drain electrode
AuGe / Au is attached as 17 and Al is attached as the gate electrode 18. Here, the gate length is 1 μm and the gate width is 200 μm.
m, the distance between the source 16 and the gate 18 is 1 μm, and the distance between the gate 18 and the drain 17 is 2 μm.

In the above configuration, the source electrode 16 is connected to the drain electrode 17.
The positive electric field V _D is applied against, applying a negative electric field V _G to the gate electrode 18 to the source electrode 16. The gate electrode 18
Since Schottky electrode, but depletion layer 19 is extended to the active layer 15, the depletion layer width varies with the gate voltage V _G, which channel width of the active layer 15 is changed in accordance with.
As a result, the current _ID flowing between the drain electrode 17 and the source electrode 16 changes. When the depletion layer 19 reaches the buffer layer 14, the channel is closed and the current _ID stops flowing. When light of a semiconductor laser (not shown) having a wavelength of 830 nm propagates from the waveguide 20 below the active layer 15 in a state where the flow stops, the guided light leaks into the active layer 15 and is absorbed there to generate carriers. .

The electrons generated in the depletion layer 19 and the active layer 15 between the gate 18 and the drain 17 in this manner are generated by the electric field in the drain electrode.
Reached 17 and detected. On the other hand, the holes generated together with the electrons are attracted to the depletion layer 19, and as a result, the depletion layer 19 contracts.

Thus, when light is not irradiated, no current flows because the depletion layer 19 is pinched off, but current flows because the depletion layer 19 contracts due to light irradiation. Since the amount of current flowing between the source electrode 16 and the drain electrode 17 corresponds to the change of the depletion layer 19 according to the amount of irradiation, this amount of light is detected.

On the other hand, the carriers generated between the source 16 and the gate 18 are diffused in the depletion layer because almost no electric field is applied here.
In this embodiment, the light that has propagated through the waveguide 20 is only between the depletion layer 19 and the gate 18 and the drain 17 in the strong electric field region. Therefore, the response characteristics are improved.

Also, in a short channel device aiming for high-speed response, it is difficult to align the waveguide 20 and the electrode,
In the present embodiment, the distance between the gate 18 and the drain 17 which is the waveguide installation portion is large (2 μm).
Positioning is facilitated.

FIG. 2 shows a reference example. In the figure, a GaAs layer 26 is stacked on a semi-insulating substrate 25 of GaAs by 0.5 μm, and
An Al _0.5 Ga _0.5 As layer 27 as a buffer layer is stacked at 1 μm, and a doping concentration of 1.0 × 10
An n-type GaAs layer 28 of ¹⁷ cm ^-3 is stacked at 0.2 μm.

Then, on the active layer 28, a clad layer Al
_{A 0.5} Ga _0.5 As layer 29 is laminated 0.1 μm, and a superlattice layer 30 of Al _0.5 Ga _{0.5 As} 30 Å and GaAs 60 と し て as a waveguide is formed thereon.
7 μm laminated, and further thereon a cladding layer of Al _0.5 Ga
_{The 0.5} As layer 31 is laminated by _0.5 μm. After this lamination, a 1 μm wide ridge waveguide is formed in the Al _0.5 Ga _0.5 As layer 31, the Al _0.5 Ga _0.5 As / GaAs superlattice layer 30, and the Al _0.5 Ga _0.5 As layer 29 by etching, and the etching is performed. A drain electrode is formed on the n-type GaAs active layer 28 at an interval of 2 μm with a ridge waveguide therebetween.
Wear 32 and gate electrode 33. Gate length 1 μm, gate width
200 μm.

Further, a source electrode 34 is placed 1 μm from the gate electrode 33.
Put on. AuGe / A for the source electrode 34 and the drain electrode 32
u is used, and Al is used for the gate electrode 33.

In the above configuration, similarly to the first embodiment, the positive electrode V _D is applied to the source electrode 34 to drain electrode 32, a negative electric field V _G is applied to the source electrode 34 to the gate electrode 33 Then, the depletion layer 35 reaches the buffer layer 27 to be in a pinch-off state. In this state, the wavelength 83
When light of a semiconductor laser (not shown) of 0 nm is propagated, the guided light leaks out to the active layer 28 and is absorbed there to generate carriers.

Although a current flows between the source 34 and the drain 32 in accordance with the generated carriers, the light spreads only between the depletion layer 35 and the gate 33 and the drain 32, which are the strong electric field region, as in the first embodiment. improves. Also, as in the first embodiment,
Since the distance between the gate 33 and the drain 32 is large, the alignment between the waveguide and the electrode is also easy.

[Effects of the Invention] As described above, the configuration of the present invention has the following effects.

Since the distance between the gate electrode and the drain electrode in the strong electric field region serving as the light receiving portion is made relatively wide with the same channel length, the light receiving efficiency can be improved, and the alignment of the waveguide becomes easy.

Since the optical waveguide for guiding the input signal light to the light receiving portion is provided between the relatively wide gate electrode and the drain electrode, the light can be made to enter only the strong electric field region, and the time response characteristic is improved.

Since the optical waveguide has a superlattice structure formed by laminating a first semiconductor material which is a semiconductor substrate and a second semiconductor material having a smaller curvature than the substrate material, a relatively wide range of wavelengths can be obtained. The light possessed can be guided by the waveguide.

[Brief description of the drawings]

FIG. 1 is a view showing a first embodiment of the present invention, FIG. 2 is a view showing a reference example of the present invention, FIG. 3 is a view showing a state of a potential in an FET structure, and FIG. It is a figure which shows the conventional example of a container. 15, 28 ... active layer, 16, 34 ... source electrode, 17, 32 ...
Drain electrode, 18, 33 ... Gate electrode, 19, 35 ... Depletion layer, 20, 30 ... Waveguide

Continuation of the front page (56) References JP-A-63-9162 (JP, A) JP-A-3-129780 (JP, A) JP-A-3-160764 (JP, A) JP-B-45-8520 (JP) U.S. Pat. No. 4,360,246 (US, A) IEDM Vol. 1978 p. 120−123 (1978)

Claims (2)

(57) [Claims] An electric current flowing between a source electrode and a drain electrode, comprising a source electrode, a drain electrode, and a gate electrode provided on an active layer, and an optical waveguide provided below the active layer. In the FET structure photodetector that detects the amount of light propagating through the optical waveguide, the distance between the gate electrode and the drain electrode is set to be wider than the distance between the source electrode and the gate electrode, and the optical waveguide includes the gate electrode and the drain. An FET structure photodetector, which is provided so as to be present between electrodes. 2. The photodetector with an FET structure according to claim 1, wherein said optical waveguide has a superlattice structure.