KR100550011B1 - Method for manufacturing photo diode detector capable of decreasing dark currents - Google Patents

Abstract

A method of manufacturing a mesa type photodetecting device that can reduce dark current is disclosed. The disclosed invention sequentially grows an N-type cladding layer, a light absorption layer, and a P-type cladding layer on a compound substrate, and then pins the P-type cladding layer, the light absorption layer, and the N-type cladding layer by predetermined patterning. Define the layer. Thereafter, a polyimide film is formed on the sidewall exposed surface of the p-i-n layer, and the polyimide film is cured. Next, an ohmic electrode is formed on each of the compound substrate and the p-i-n layer.

Photodetector, dark current, polyimide, heat treatment.

Description

Method for manufacturing photodiode detector capable of reducing dark currents

1A and 1B are perspective views of a general mesa type photodetecting device.

2 is a perspective view illustrating a method of manufacturing a mesa type photodetecting device according to the present invention.

3A is a graph showing a voltage-current curve of the photodetecting device after heat-treating the photodetecting device at a temperature of 200 ° C. for 300 hours.

3B is a graph showing a voltage-current curve of the photodetecting device after heat-treating the photodetecting device at a temperature of 250 ° C. for about 80 hours.

4A is a graph showing the dark current and the breakdown voltage when the photodetecting device is heat treated (heated) at a temperature of 200 ° C.

4B is a graph showing the dark current and the breakdown voltage when the photodetecting device is heat treated (heated) at a temperature of 250 ° C.

5 is a graph showing the degree of dark current reduction with heat treatment temperature and time.

(Explanation of symbols for the main parts of the drawing)

DESCRIPTION OF SYMBOLS 100 Compound substrate 110 N type compound layer 120 N type cladding layer

130: light absorption layer 140: P-type cladding layer 150: p-i-n layer

160: polyimide 170: N + ohmic electrode 180: P + ohmic electrode

The present invention relates to an ultra-high speed optical communication system, and more particularly, to a method for manufacturing a photodetecting device, which is applied to a receiver of an ultra-high speed optical communication system and is composed of a III-V compound semiconductor material capable of generating a dark current.

As the information communication environment develops, the use of optical communication is spreading. Accordingly, optical detection modules used for optical signal reception in ultra-high speed optical communication systems have been widely developed. Photodetector modules (photodetectors) can be broadly divided into planar and mesa types according to their structure, and planar types are known to have relatively small dark currents compared to mesa types.

However, current photodetecting devices require a small capacitance, i.e., a small area, for high speed operation. That is, when the photodetecting device occupies a large area, when light is absorbed in a region where no electric field is formed, electrons and holes generated by the absorbed light are moved by diffusion, and thus the response speed of the photodetecting device Can be limited. Accordingly, the photodetecting device requiring high speed operation adopts a mesa type in both compositions, such as vertical incidence (surface incidence) or horizontal incidence (side incidence) of light.

1A and 1B, a general mesa type photodetecting device will be described. FIG. 1A is a mesa type photodetector designed to inject light vertically, and FIG. 1B is a mesa type photodetector designed to enter light horizontally (side).

1A and 1B, an N-type cladding layer 13 doped with a high concentration N-type impurity on the compound substrate 11, a light absorption layer 15, and a P-type cladding layer 17 doped with a high concentration P-type impurity. ) Are stacked sequentially.

Subsequently, in the case of the vertical incidence type, as shown in FIG. 1A, the P-type compound layer 17, the light absorption layer 16, and the N-type compound layer 13 having a predetermined thickness are etched in a cylindrical pattern to form a pin layer 20. do.

Meanwhile, in the case of the horizontal incidence type, as shown in FIG. 1B, the P-type cladding layer 17, the light absorption layer 16, and the N-type cladding layer 13 having a predetermined thickness are etched in a line form to form a pin layer ( 20a). Here, reference numeral 13a denotes the N-type cladding layer 13 etched by a predetermined thickness, and reference numeral 25 denotes incident light.

In the mesa type photodetector as described above, the p-i-n layers 20 and 20a may be exposed to the air by an etching process, and thus a large dark current may be generated. The dark current of the photodetecting device lowers the reliability of the photodetecting device and causes noise to lower the sensitivity.

Therefore, the technical problem to be achieved by the present invention is to provide a method for manufacturing a mesa type photodetecting device that can reduce the dark current.

In order to achieve the above technical problem of the present invention, the present invention, by growing the N-type cladding layer, the light absorption layer and the P-type cladding layer sequentially on the compound substrate, the P-type cladding layer, the light absorption layer And a predetermined portion of the N-type cladding layer to define the pin layer. Thereafter, a polyimide film is formed on the sidewall exposed surface of the p-i-n layer, and the polyimide film is cured. Next, an ohmic electrode is formed on each of the compound substrate and the p-i-n layer.

In the curing of the polyimide film, the compound substrate product on which the polyimide film is formed is heat-treated at a temperature of 350 to 400 ° C. for 30 minutes to 1 hour.

The curing of the polyimide film may be performed in an inert gas, nitrogen gas, group III gas, group V gas, or a mixed gas atmosphere thereof.

Before forming the N-type cladding layer on the compound substrate, an N-type compound layer in which the device is to be formed may be formed.

 The forming of the ohmic electrode may include forming a P-type ohmic electrode on the p-i-n layer and forming an N-type ohmic electrode on the n-type compound layer on both sides of the pi-n layer.

After the forming of the ohmic electrode, further comprising the step of performing a further heat treatment at a temperature of the compound substrate product 200 ~ 1000 ℃.

The p-i-n layer is preferably patterned in the form of a ridge.

(Example)

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. However, embodiments of the present invention may be modified in many different forms, and the scope of the present invention should not be construed as being limited by the embodiments described below. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art. Accordingly, the shape and the like of the elements in the drawings are exaggerated to emphasize a more clear description, and the elements denoted by the same reference numerals in the drawings means the same elements.

2 is a perspective view of a mesa type photodetecting device according to the present invention.

As shown in FIG. 2, in the mesa type photodetecting device of the present invention, an N type compound layer 110, which is an element formation region, is formed on a compound substrate 100 in a pattern form, and an N type compound layer ( The pin layer 150 in the form of a line or ridge is disposed on an upper portion of the upper portion 110. The p-i-n layer 150 includes an N-type cladding layer 120, a light absorption layer 130, and a P-type cladding layer 140 sequentially stacked. Here, the N-type cladding layer 120 may be, for example, an InP layer doped with an N-type high concentration impurity, and the light absorption layer 130 may be a compound layer not doped with impurities, such as InGaAs or InGaAsP, and may be P-type. The cladding layer 140 may be an InP layer not doped with a P-type high concentration impurity. In addition, an N-type compound layer 110 may be present at a bottom of the N-type cladding layer 120 at a predetermined thickness. A side of the p-i-n layer 150 is covered with a protective layer, such as the polyimide layer 160, to facilitate light confinement. The N + ohmic electrode 170 is formed on the surfaces of the N-type compound layer 110 on both sides of the p-i-n layer 150, and the P + ohmic electrode 180 is formed on the p-i-n layer 150.

The photodetecting device having such a configuration is formed by the following method.

The N-type compound layer 110, for example, the InP layer, doped with a high concentration of N-type impurities is grown on the compound substrate 100, for example, a non-conductive InP substrate having low microwave loss for high speed operation. On the N-type compound layer 110, in order to confine the light, the N-type cladding layer 120 doped with a high concentration of N-type impurities, the light absorption layer 130 of InGaAs or InGaAsP, and the high-concentration P-type impurities are doped. P-type cladding layer 140 is grown sequentially. In this case, the N-type cladding layer 120 and the P-type cladding layer 140 may be obtained by introducing impurities at the same time as the growth of the compound layer or by doping the impurities after growing the compound layer.

 Next, the P-type cladding layer 140, the light absorption layer 130, the N-type cladding layer 120, and the N-type compound layer 110 having a predetermined thickness are patterned in the form of a ridge or line to form a pin layer 150. do. In this case, the p-i-n layer 150 may be patterned by, for example, a mesa etching method. As the p-i-n layer 150 has a ridge or line shape, its sidewall (outer wall) is exposed to the outside. Here, reference numeral 110a denotes an N-type compound layer etched by a predetermined thickness.

The polyimide 160 is coated on the compound substrate 100 on which the pin layer 150 is formed, and the polyimide 160 is anisotropically removed so as to exist only on the sidewalls of the pin layer 150. The polyimide 160 is left in the form of a spacer on the side wall of the spacer. At this time, the surface of the p-i-n layer 150, that is, the P-type cladding layer 150 is preferably exposed from the polyimide (160).

Next, to cure the polyimide 160, the compound substrate 100 is heat-treated for about 1 hour at a temperature of 300 to 400 ℃, preferably 365 ℃. At this time, the heat treatment is preferably carried out in any one of an atmosphere of inert gas such as argon, nitrogen gas, gas of group III, gas of group V and a mixed gas atmosphere thereof. By the heat treatment process, the polyimide 160 is cured and the dark current characteristic is greatly improved. The mechanism for reducing the dark current will be described later in detail through a graph.

In addition, as described above, the p-i-n layer 150 is formed in the form of a ridge, and the polyimide layer 160 is formed on the sidewall portion thereof, thereby increasing light constraining efficiency of the sidewall portion of the p-i-n layer 150.

Thereafter, an N + ohmic electrode 170 is formed on the exposed N-type compound layer 110 on both sides of the p-i-n layer 150 and used as a ground line. Meanwhile, the P + ohmic electrode 180 is formed on the P-type cladding layer 140 on the p-i-n layer 150 and used as a signal line. At this time, the N + ohmic electrode 170 and the P + ohmic electrode 180 form a planar waveguide to act to stably propagate the microwave mode.

The reliability of such a photodetecting device is a very important factor in applying to an actual optical communication system, and this reliability is affected by the dark current of the photodetecting device. Many studies have been reported in the academic field regarding the correlation between device reliability and dark current. First of all, when the pin photodetector is wrapped with polyimide, the change of the dark current through the reliability test has been submitted to the IEEE by Kuhara et al. (Y. Kuhara, H.Terauchi, and H). Nishizawa, "Reliability of InGaAs / InP long-wavelength pin photodiodes passivated with polyimide thin film", IEEE J. Lighywave Tech., Vol. LT-4, No. 7, pp933-937, July 1986). Also, Nakamura et al. Proposed a charge accumulation model for the reliability of InGasAlAs optical waveguide photodetectors (Hitoshi Nakamura, Masato Shishikura, Shigehisa Tanaka, Yasunobu Matsuoka, Tsunao Ono, and Shinji Tsuji, "Highly reliable". operation of InGaAlAs waveguide photodiodes for optical access network system "Jpn. J. Appl. Phys., Vol. 37, Park 1, No. 3B, pp. 1427-1431, March 1998), Mawatari, et al. We have analyzed the dark current of planar waveguide photodetectors for subscriber systems (Hiroyasu Mawatari, Mitsuo Fukuda, Kasutoshi Kato, Tatsuya Takeshita, Masahiro Yuda, Atsuo Kozen, and Hiromu Toba, "Reliability of planar waveguide photodiodes for optical subcarrier systems" IEEE J. Lightwave Tech., Vol. 16, No. 12, pp. 2428-2434, December 1998).

In general, when the p-i-n layer is fabricated through mesa etching, when the sidewall (or exposed surface) is covered with polyimide, the dark current is known to have several tens of mA under normal driving voltage.

Here, Figure 3a is a voltage-current curve of the photodetecting device after the heat treatment for 300 hours at a temperature of 200 ℃ immediately after fabrication of the photodetecting device, Figure 3b is at a temperature of 250 ℃ after the fabrication of the device is completed The voltage-current curve of the photodetecting device after the heat treatment for about 80 hours.

When the heat treatment was performed for 300 hours at a temperature of 200 ℃, as shown in Figure 3a, the difference between the dark current before or after the heat treatment was not very large.

On the other hand, when the heat treatment was performed for about 80 hours at a temperature of 250 ℃, as shown in Figure 3b, it can be seen that the dark current is significantly reduced after performing the heat treatment, than the dark current before heat treatment under the normal driving voltage 3V A low dark current of 0.2 nA, which was reduced by several orders of magnitude. As such, it can be seen that the dark current decreases as the heat treatment temperature increases.

4A and 4B are graphs showing dark current and breakdown voltage data with time at two temperatures, and FIG. 4A shows dark current and breakdown voltage data when the photodetector is heat-treated (heated) at a temperature of 200 ° C. 4B shows dark current and breakdown voltage data when the photodetecting device is heat treated (heated) at a temperature of 250 ° C. Here, the breakdown voltage is defined as the reverse voltage when the dark current reaches 100 mA.

According to FIG. 4A, when the photodetecting device was heat-treated at 200 ° C., the dark current and the breakdown voltage maintained almost constant values. On the other hand, when heat-treating the photodetecting device at 250 ° C as shown in Figure 4b, it can be seen that it takes about 80 hours to reduce the dark current to 1nA. In addition, the breakdown voltage increases little by little over time. From the graph, it can be seen that the dark current and the breakdown voltage are affected by the heat treatment temperature and time. In addition, although not shown in the graph, according to the experiments of the present inventors, the dark current was reduced to 1 nA when the heat treatment was performed for 39 hours when the heat treatment was performed at a temperature of 300 ° C.

In addition, Figure 5 is a graph showing the degree of dark current decrease with heat treatment temperature and time, this graph shows the heat treatment time data when the heat treatment is performed at a temperature of 250 ℃ and 300 ℃, by Arhenius (Arrhenius) relationship This is the result of the connection. Theoretically, the dark current should be 1nA when the heat treatment is performed at 200 ° C. for 200 hours, but in practice, the dark current does not decrease even when the heat treatment is performed at the temperature for 300 hours. As such, it can be seen that there is a minimum threshold heat treatment temperature to reduce the dark current, and the temperature is expected to be between 200 and 250 ° C. In FIG. 5, the part marked with "*" shows the 365 degreeC / 1 hour point which is the curing condition of the conventional polyimide. The condition of the * point is a high heat treatment temperature, but it can be seen that the heat treatment time was short to see the effect of dark current reduction. Here, the X-axis of the graph represents the relative temperature in absolute temperature.

As described in detail above, according to the present invention, a p-i-n layer is formed on the compound substrate and polyimide is formed on the sidewalls thereof. After the heat treatment process for curing the polyimide, an additional heat treatment is applied at a temperature of 200 ° C. or higher for a suitable time to reduce the dark current.

As described above, the dark current can be greatly reduced by the heat treatment step of the polyimide, and the reliability of the photodetecting device can be improved.

Although the present invention has been described in detail with reference to preferred embodiments, the present invention is not limited to the above embodiments, and various modifications may be made by those skilled in the art within the scope of the technical idea of the present invention. Do.

Claims (7)

Providing a compound substrate; Sequentially growing an N-type cladding layer, a light absorption layer, and a P-type cladding layer on the compound substrate; Defining a p-i-n layer by partially patterning the P-type cladding layer, the light absorption layer, and the N-type cladding layer; Forming a polyimide film on the exposed sidewall of the p-i-n layer; Curing the polyimide film; Forming an ohmic electrode on each of the compound substrate and the p-i-n layer; And Method of manufacturing a photodetecting device comprising the step of heat-treating the compound substrate resultant for a long time of 39 hours to 300 hours at 200 to 1000 ℃ temperature The method of claim 1, wherein the curing of the polyimide film comprises: The method of manufacturing a photodetecting device, characterized in that the resultant compound substrate formed with the polyimide film is heat-treated at a temperature of 350 to 400 ℃ for 30 minutes to 1 hour. The method of claim 2, wherein curing the polyimide film A process for producing a photodetecting device, characterized by advancing in an inert gas, nitrogen gas, group III gas, group V gas, or a mixed gas atmosphere thereof. The method of claim 1, further comprising forming an N-type compound layer on which the device is to be formed before forming the N-type cladding layer on the compound substrate. The method of claim 4, wherein forming the ohmic electrode comprises: Forming a P-type ohmic electrode on the p-i-n layer, And forming an N-type ohmic electrode on the n-type compound layer on both sides of the p-i-n layer. delete The method of claim 1, wherein the p-i-n layer is patterned in a ridge form.

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