JP2018181918A - Photodetector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GePD (Germanium Photodetector) which can withstand high power input (about 100 mW).SOLUTION: The photodetector includes: a lower cladding layer on a silicon (Si) substrate; a silicon slab layer 121 including a Si region 111 including a first conductive type impurity on the lower cladding layer; a silicon waveguide layer 120 connected to the silicon slab layer 121; a Ge layer 114 including a germanium (Ge) region 115 including a second conductivity type impurity on the silicon slab layer 121; an upper cladding layer on the silicon slab layer 121 and the Ge layer 114; and electrodes 112, 113, 116, 117, and 118 each connected to the silicon region 111 or the Ge region 114. In the photodetector, voltage drop means 130 is connected in series to the electrode 117.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a photodetector, and more particularly to a structure for providing a photodetector used in an optical communication system or an optical information processing system.

  With the spread of optical communication in recent years, cost reduction of the optical communication device is required. As one of the solutions, there is a method of forming an optical circuit constituting an optical communication device on a large-diameter wafer such as a silicon wafer using a minute optical circuit technology such as silicon photonics. Thereby, the material cost per chip can be dramatically reduced, and the cost reduction of the optical communication device can be achieved.

  As a typical photodetector formed on a silicon (Si) substrate using such a technology, there is a germanium photodetector (hereinafter referred to as GePD) which can be monolithically integrated. FIG. 1 schematically shows the structure of a conventional waveguide-coupled vertical GePD. FIG. 2 shows a cross-sectional view of dotted line I-I 'in the structure of the waveguide-coupled vertical GePD of FIG. In order to make the structure intelligible, in FIG. 1, the cladding layer 103 shown in FIG. 2 is omitted, and only the positions where the electrodes 116 to 118 are in contact with the p ++ Si electrode portion 112, p ++ Si 113 and the n-type There is.

Patent No. 5370857 gazette

  GePD is formed on a silicon-on-insulator (SOI) substrate composed of a Si substrate, a Si oxide film, and a surface Si layer using a lithography technique or the like. The GePD 100 shown in FIG. 2 includes a Si substrate 101, a lower cladding layer 102 made of Si oxide film on the Si substrate, a silicon core layer 110, and a Ge layer 114 absorbing light formed on the silicon core layer 110. And an upper cladding layer 103 made of an insulator formed on the silicon core layer 110 and the Ge layer 114.

  As shown in the top view of FIG. 1, the silicon core layer 110 is divided into a silicon waveguide layer 120 through which light is guided and a silicon slab layer 121 underlying the Ge layer 114 and the like.

  The silicon slab layer 121 is provided with a p-type Si region 111 doped with p-type impurity ions, and p ++ silicon electrode portions 112 and 113 which are doped with p-type impurities at high concentration and function as electrodes. The Ge layer 114 is stacked by epitaxial growth, and an n-type Ge region 115 doped with an n-type impurity is formed thereon. Then, electrodes 116 to 118 are provided on the p ++ silicon electrode portion 112, the p ++ silicon electrode portion 113, and the n-type Ge region 115 so as to be in contact with them via the contact holes in the upper cladding layer 103.

  When light is made incident from the silicon waveguide layer 120 to the silicon slab layer 121 and the light is absorbed by the Ge layer 114, the GePD 100 of FIG. 1 is disposed between the electrode 117 and the electrode 116 and between the electrode 117 and the electrode 118, respectively. , Photocurrent flows. Then, light can be detected by detecting the current.

  GePD 100 is shown in FIG. The GePD 100 has a problem that it can not withstand high-power light input. A graph 200 of FIG. 3 is a graph in which the temperature of the Ge layer 114 is plotted at the time of thermal analysis in which the power is changed using the bottom of the Ge layer 114 of the GePD 100 as a heat source. It can be said that the power given to GePD by the light input is the power of the heat source of the graph 200 of FIG. It is known from experiments that germanium grown on silicon melts at about 600 to 800 ° C. (about 600 to 800 ° C.) and loses its function as a photodiode. In particular, in the waveguide-type GePD as shown in FIGS. 1 and 2, the portion close to the waveguide in the Ge layer 114 intensively absorbs light, so the vicinity of the region 119 in FIG. 1 is melted. In the graph 200 of FIG. 3, when a power of about 75 to 100 (75 to 100) mW is applied to GePD, the Ge layer 114 reaches the melting temperature. On the other hand, in a receiver of a metro network, power in the above range may be given to GePD.

The power directly given to GePD by the optical input is strictly calculated by the following equation 1 using the current (the input optical power multiplied by the sensitivity) flowing in GePD by light absorption and the voltage applied to GePD. Ru.
W ₀ = PV _g r (Equation 1)
W ₀ : Power given to GePD, P: Input optical power, r: GePD sensitivity, V _g : Voltage applied to GePD

  Therefore, as the voltage applied to GePD increases, even when a weaker input light power is given, the power applied to GePD reaches a value such as 75 to 100 (75 or more and 100 or less) mW, and germanium melts as a photodiode. Lose the functionality of For this reason, in GePDs that can be given high optical input power, it is common to operate with the applied voltage suppressed.

  On the other hand, since preparing a plurality of power supplies leads to an increase in circuit scale, in a small integrated optical device, the voltage applied to the PD may be shared with the power supply voltage of another electronic device. At this time, the voltage applied to PD deviates from the value designed in consideration of the value of the maximum input optical power, so the power given to GePD reaches a value of 75 to 100 (75 to 100 or less) mW depending on the operation. Germanium may melt and lose its function.

  The present invention has been made in view of such problems, and the object of the present invention is to eliminate the need for additional components such as an attenuator and a switch, and to use whatever voltage the voltage applied to GePD is. An object of the present invention is to provide GePD which can withstand high power input up to about mW.

  The present invention is characterized by having the following configuration in order to achieve such an object. As shown in FIG. 4, the electrode 117 of the GePD 100 is provided with a voltage drop means 130. The voltage drop means 130 may be connected to the electrode 116 or the electrode 118 because it may be connected to either the anode or the cathode of GePD.

  Further, as the voltage drop means, any means may be used as long as the voltage drops as a result, and it is not limited to a single resistance or the like. The voltage drop means may have any function.

  One aspect of the photodetector of the present invention is a silicon substrate, a lower cladding layer on the silicon substrate, a silicon slab layer including a silicon region containing a first conductivity type impurity on the lower cladding layer, and the silicon A silicon waveguide layer connected to the slab layer; a germanium layer including a germanium region containing a second conductivity type impurity on the silicon slab layer; the upper cladding layer on the silicon slab layer and the germanium layer; In a photodetector having a silicon region or an electrode connected to the germanium region through a contact hole in the upper cladding layer, any one of the electrodes connected to the silicon region or the germanium region On the other hand, it is a photodetector characterized in that voltage drop means is connected in series.

  The voltage drop means may be a resistor.

  The resistor may contain a metal, a metal compound or an impurity.

  A transimpedance amplifier may be connected to the other of the electrodes electrically connected to the silicon region or the germanium region.

  Furthermore, a capacitor may be electrically connected between the voltage drop means and the electrode, and the voltage drop means may be grounded.

  Compared to the conventional vertical GePD, it can provide GePD that can withstand high power input (about 100 mW).

It is a top view of conventional vertical GePD. It is sectional drawing of GePD in dotted line I-I 'of FIG.1, FIG4 and FIG.5. It is a thermal calculation model and analysis result of general vertical GePD shown in FIG.1 and FIG.2. It is a top view of the photodetector of this invention. It is a top view of the photodetector of Example 1 of this invention. It is sectional drawing in the II-II 'surface when a resistor is produced by impurity doping in the photodetector of Example 1 of this invention. It is sectional drawing in the II-II 'surface when a resistor is produced with a metal or a metal oxide in the photodetector of Example 1 of this invention. It is a top view which shows the structure of the photodetector of Example 2 of this invention. It is a top view which shows the structure of the photodetector of Example 3 of this invention. It is a circuit diagram of the photodetector of Example 3 of this invention.

  Hereinafter, the form of the light modulator of the present invention will be described in detail with reference to the drawings. However, it is obvious for those skilled in the art that the present invention is not limited to the description contents of the embodiments shown below, and that various modifications can be made in the form and details without departing from the spirit of the invention disclosed in the present specification. is there. Further, configurations according to different embodiments can be implemented in combination as appropriate. Note that in the structures of the invention described below, the same portions or portions having similar functions are denoted by the same reference numerals, and description thereof will not be repeated.

Example 1
In this embodiment, FIG. 5 shows an example in which a resistor 132 formed on a silicon slab layer 121 is used as the voltage drop means 130 of the present invention. The resistor 132 is a resistor produced by doping the silicon slab layer 121 with an impurity, or a metal resistor produced by applying a metal. The resistance value is determined with respect to the target maximum input optical power P ₁ = W / r (V _go −V _g1 ). P ₁ : Target maximum optical input power, such as the value of maximum optical input rating. W: Maximum input power. (75 to 100 (75 or more and 100 or less) mW in this case). V _go : Bias applied to GePD. r: GePD sensitivity. V _g1 : R r P ₀ . R: resistance value of resistance 132. P ₀ : Input light power. However, the resistance value is smaller than the bias voltage V _{th at} which the sensitivity r can maintain linearity with respect to the optical power, as the voltage drop value V _g1 = RrP _{0 and} the value of V _go when the optical power P ₀ is input. (V _go -V _g1 > V _th ). Generally, in GePD, V _th is about 1 to 1.5 V for inputs up to about 0 dBm. Therefore, the resistance value of the resistor 132 needs to satisfy the design condition indicated by the bias voltage V _{th at} which the maximum input optical power P ₁ and the sensitivity r can maintain linearity.

  FIG. 6 is a cross-sectional view taken along the line II-II 'of FIG. 5 when the resistor 132 is a resistor formed by doping the silicon slab layer 121 with an impurity. FIG. 7 is a cross-sectional view taken along the line II-II 'of FIG. 5 when the resistor 132 is formed by applying a metal resistor to the silicon slab layer 121.

In the present embodiment, when light is input to the photodetector of the present invention provided with the voltage drop means 130, current flows between the electrode 116, the electrode 118 and the electrode 131. At the same time, current flows through the voltage drop means 130, so that a voltage drop occurs in the voltage drop means 130. When a voltage drop occurs, the voltage V _g applied to the GePD 100 also decreases, so the power W applied to the GePD decreases.

For example, when a certain voltage V _go is applied between the electrode 131 and the electrode 116, the electrode 118, an input optical power P ₀ (= W / r V _go ) for reaching a power at which germanium melts according to Equation 1. Is decided. However, when actually input optical power approaches P _0, a photoelectric current is increased, (defined as _{V g1 .V g1 = R r P} 0) the voltage drop by the voltage drop means 130 along with this happens.

The input light power P ₁ (= W / r (V _go −V _g1 )) for melting germanium determined from the equation 1 in the state after the voltage drop occurs is larger than P ₀ .

Experience a similar phenomenon when the optical input power approaches P _1, an input light power with germanium melt is greater than P _1. That is, regardless of how much the input optical power increases, the voltage applied to the GePD is lowered due to the voltage drop by the voltage drop means 130, so the input optical power to which germanium melts is not reached. This phenomenon (V _go -V _g1 = 0) until the voltage becomes 0 applied to GePD by the voltage drop of the voltage drop means 130 continues. Therefore, the photodetector of the present invention can extend the input optical power tolerance to the value when the voltage applied to GePD is zero, regardless of the voltage applied to GePD. If the voltage applied to the GePD is 0, the formula 1; W = PV _g r from (W: power given to GePD, P: input optical power, r:: sensitivity GePD, V _g the voltage that applied to GePD) Since the power given to GePD becomes extremely small, GePD has very high tolerance to the input light power.

  This embodiment can be used to provide GePD that can withstand high power input (about 100 mW).

(Example 2)
In this embodiment, FIG. 8 shows an example in which the resistor 132 of the present invention is integrated in the circuit 136. The circuit 136 is formed of a transimpedance amplifier 133 and a resistor 135 for signal amplification. The power supply 134 is for supplying power to the transimpedance amplifier 133 and for biasing the GePD 100. By arranging the resistor 135 between the power source 134 and the wiring connecting the electrode 117, the same effect as the voltage drop means 130 of the present invention can be expected. The resistor 135 may be formed by the internal resistance of the circuit or may be integrated like a chip capacitor. In order to maintain the high speed characteristics of GePD, when the transimpedance amplifier 133 is connected to the electrodes 116 and 118, the resistor 135 is connected to the electrode 117, and when the transimpedance amplifier 133 is connected to the electrode 117, the resistor 135 is It needs to be connected to 116 and electrode 118. Further, the resistance value of the resistor 135 needs to satisfy the same condition as that of the first embodiment.

  This embodiment can be used to provide GePD that can withstand high power input (about 100 mW).

(Example 3)
In this embodiment, FIG. 9 shows an example in which a capacitor 137 is inserted between the voltage drop means 130 (resistor 132) of the GePD provided with the resistor of the embodiment 1 and the electrode 117 in a schematic manner. The capacitor 137 is grounded through the electrode 138. A capacitor 137 shown in the drawing indicates a capacitor having one of the electrodes on the upper surface in the vertical direction of the drawing and the other of the electrodes on the surface perpendicular to the drawing. The electrode 117 and the capacitor 137 are connected via the connection electrode 139. FIG. 10 is an example in which FIG. 9 is shown in a circuit diagram. The GePD 100 includes a capacitor 137 between the resistor 132 and the capacitor 137, and the capacitor 137 is grounded. Since the resistance 132 is not necessarily smaller than the internal resistance of the GePD 100 or the input resistance value of the transimpedance in the latter stage, in Example 1, the high speed characteristics of the GePD 100 are degraded by inserting the resistance 132 due to the relationship of the CR time constant. There is a case.

  The present embodiment is characterized in that the high speed signal received by the GePD is coupled to the ground through the capacitor 137. Therefore, the resistance viewed from the high-speed signal becomes the internal resistance of GePD or the input resistance value of the transimpedance amplifier, so that the high-speed characteristics of GePD are not deteriorated. The capacitor 137 may be a chip capacitor, or may be a capacitor formed by impurity doping on the silicon slab layer 121.

  This embodiment can be used to provide GePD that can withstand high power input (about 100 mW).

(Example 4)
The photodetectors described in the first to third embodiments can be applied to display portions provided in electronic devices such as telephones.

  The present invention can be applied to a technology for producing a photodiode that can withstand high power input up to about 100 mW regardless of the voltage applied to the photodiode.

100 GePD
101 Si substrate
102 lower cladding layer 103 upper cladding layer 110 silicon core layer 111 p-type Si region 112 p ++ Si silicon electrode portion 113 p ++ Si silicon electrode portion 114 Ge layer 115 which absorbs light n-type Ge region 116 to 118 electrode 119 region 120 silicon waveguide layer 121 silicon slab layer 130 voltage drop means 131 electrode 132 resistance 133 transimpedance amplifier 137 capacitance 138 electrode 139 connection electrode 200 graph

Claims (6)

Silicon substrate,
A lower cladding layer on the silicon substrate,
A silicon slab layer including a silicon region containing a first conductivity type impurity on the lower cladding layer;
A silicon waveguide layer connected to the silicon slab layer;
A germanium layer comprising a germanium region comprising a second conductivity type impurity on the silicon slab layer,
An upper cladding layer on the silicon slab layer and the germanium layer;
An electrode connected to the silicon region or the germanium region through a contact hole in the upper cladding layer, respectively;
In the light detector having
A voltage drop means is connected in series to any one of the electrodes connected to the silicon region or the germanium region.
A photodetector characterized by that. The photodetector according to claim 1, wherein
The light detector characterized in that the voltage drop means is a resistor. The photodetector according to claim 2, wherein
The photodetector is characterized in that the resistor contains a metal, a metal compound or an impurity. The photodetector according to any one of claims 1 to 3, wherein
And a transimpedance amplifier is connected to the other of the electrodes respectively connected to the silicon region or the germanium region. The photodetector according to any one of claims 1 to 4, wherein
A capacitance is connected between the voltage drop means and the electrode,
Said capacitance is grounded,
A photodetector characterized by The photodetector according to any one of claims 1 to 5, wherein
The first conductivity type impurity is a p-type impurity,
The second conductivity type impurity is an n-type impurity,
A photodetector characterized by

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