JP5067710B2 - Photoelectric conversion element and manufacturing method thereof - Google Patents

Description

The present invention relates to a photoelectric conversion element and a method for manufacturing the same, and is suitable for application to, for example, a photovoltaic element, an optical sensor, and a high-speed detection element.

Conventionally, many developments have been made on photodetecting elements, and in particular, many products for detecting elements in the visible to infrared region are already on the market.

Many of them require various structures such as semiconductor crystals such as Si and GaAs, precise doping control, pn junction and Schottky interface control, and fine structure formation. On the other hand, it was reported in the 1990s that a Schottky diode (SBD) of CoSi ₂ (polycrystal (polycrystal)) functions as a 1-2 micron band sensor (for example, non-patent literature). 1).

Further, in 2003, the band gap of CoSi ₂ of several nm to several tens of nm is distributed to around 1.2 to 2.7 eV, such as an atomic force microscope (AFM) or a scanning tunnel microscope ( It was confirmed from the verification of the measurement result of STM (Scanning Tunneling Microscope) (for example, refer nonpatent literature 2). However, other than the 1-2 micron band sensor, there has been no significant progress in application.

In recent years, application technology in the THz region has been developed and attracted attention (for example, see Non-Patent Document 3).
Roca, Elisenda, et.al., `` Electro-optical characterization of epitaxial and composite CoSi2 Schottky diodes '', Proceedings of SPIE-The International Society for Optical Engineering, 2552 (2), 456 (1995). IV Blousov, et.al., `` Self formation of Si nanostructured layer at the metal silicide / silicon interface '', Materials Science and Engineering C23, 181 (2003). M. Tonouchi, Nature Photonics 1, 97 (2007).

However, the THz electromagnetic wave utilization technology has been developed mainly depending on its generation (particularly, pulsed laser) technology. For example, the THz electromagnetic wave detection technology has been delayed for many years. The photoelectric conversion element used in the existing photodetection technology has advantages and disadvantages including a commercially available Si bolometer, and since it is composed of various complicated configurations, it is not particularly possible to realize an array.

Therefore, it is desired that the photoelectric conversion element has a simple configuration so that an array can be realized, has high reliability and durability, and can further reduce the manufacturing cost.

The present invention has been made in consideration of the above points, and an object of the present invention is to propose a photoelectric conversion element capable of reducing the manufacturing cost with a simple configuration and a method for manufacturing the photoelectric conversion element.

In order to solve such a problem, the photoelectric conversion element of claim 1 of the present invention is a photoelectric conversion element for photoelectrically converting light, a substrate made of Si, a photoelectric conversion film made of CoSi _x formed on the substrate, and an electrode provided on the photoelectric conversion layer, the light to the photoelectric conversion layer of the region within the periphery 1mm of the positive electrode of the electrode is characterized in Rukoto irradiated.

Further, in the method for manufacturing a photoelectric conversion element according to claim 2 of the present invention, a film forming step of forming a Co thin film made of Co on a substrate made of Si, and annealing treatment on the Co thin film, A step of forming a photoelectric conversion film made of CoSi _x by diffusing Si of the substrate into Co, and an electrode formation step of forming a positive electrode and a negative electrode on the photoelectric conversion film before or after the formation step. It is characterized by this.

According to the photoelectric conversion element of claim 1 and the method of manufacturing the photoelectric conversion element of claim 2 of the present invention, a photoinduced current is generated by irradiating light in the vicinity of an electrode of a photoelectric conversion film made of CoSi _x . Therefore, it is possible to omit a complicated manufacturing process for forming various configurations such as a conventional pn junction, and to reduce the manufacturing cost with a simple configuration as much as such various conventional configurations are unnecessary. A photoelectric conversion element can be provided.

Further , a photo- induced current can be generated , and the photo- induced current can be used as a photovoltaic device or a photo sensor.

Furthermore, according to the method for producing a photoelectric conversion element of claim 2 of the present invention, a positive electrode and a negative electrode can be provided on the photoelectric conversion film, and a photo-induced current can be generated by irradiating light in the vicinity of the positive electrode. A photoelectric conversion element can be provided. In addition, the carrier movement path can be limited to the device surface, scattering and transmission loss can be reduced, and high-speed carriers can be generated.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In FIG. 1, reference numeral 1 denotes a photoelectric conversion element as a whole. A photoelectric conversion film 3 made of CoSi _x is laminated on a Si substrate 2 made of n-type Si, and a positive electrode 4, a negative electrode 5, and a photoelectric conversion film 3 are formed on the photoelectric conversion film 3. Are provided at a predetermined interval (for example, 0.5 [cm]). The Si substrate 2 has a resistivity of several Ω [cm].

In this embodiment, the case where the n-type Si substrate 2 is used has been described. However, the present invention is not limited to this, and a p-type Si substrate may be used.

The positive electrode 4 and the negative electrode 5 are made of a predetermined electrode material such as Au, W, Ti, etc., are laminated on the photoelectric conversion film 3, and are electrically connected to each other by an electric wire 6.

The photoelectric conversion film 3 has a film thickness of 100 [nm] or less, and irradiates light L to a region (hereinafter referred to as an incident region) ER of about 1 [mm] or less around the positive electrode 4. Photoinduced carriers are generated, so that a photoinduced current can be generated.

In the case of this embodiment, the photoelectric conversion element 1 generates a photo-induced current when the light L is applied to the incident region ER of the photoelectric conversion film 3 by the ammeter A provided between the positive electrode 4 and the negative electrode 5. Was confirmed.

Here, the photoelectric conversion film 3 preferably has an incident region ER of about 1 [mm] or less because the value of the photo-induced current decreases when the incident region ER is larger than 1 [mm].

Next, the manufacturing method of the photoelectric conversion element 1 having such a configuration will be described below. First, a Co thin film (not shown) made of Co is formed on the Si substrate 2 by, for example, a sputtering method. Next, the positive electrode 4 and the negative electrode 5 made of an electrode material are stacked on the Co thin film with a predetermined interval.

In addition to this, the Si substrate 2 and the Co thin film are annealed under a temperature condition of 100 to 1000 [° C.], preferably about 600 [° C.], so that the Co in the Co thin film is transformed into Co. Si is diffused to form the photoelectric conversion film 3 made of CoSi _x . Then, the positive electrode 4 and the negative electrode 5 are electrically connected by the electric wire 6, and thus the photoelectric conversion element 1 can be manufactured.

In the above configuration, in the photoelectric conversion element 1, the Co thin film made of CoSi _x was formed by annealing the Co thin film under a predetermined temperature condition.

The photoelectric conversion film 3 formed by simply annealing the Co thin film under a predetermined temperature condition in this manner generates a photoinduced current by irradiating the incident region ER near the positive electrode 4 with the light L. Can be made.

Accordingly, in such a photoelectric conversion element 1, a light-induced current is generated by irradiating the incident region ER with the light L, and the photo-induced current is transmitted to various electronic devices (not shown), whereby the electronic The device can be operated. Therefore, the photoelectric conversion element 1 can be used as a photovoltaic element for operating various electronic devices.

Further, in such a photoelectric conversion element 1, by providing a detection means (not shown) for detecting whether or not a photoinduced current is generated, the light L is incident on the incident region ER via the presence or absence of the photoinduced current. It can also be determined whether or not it has been issued. Therefore, the photoelectric conversion element 1 can also be used as an optical sensor that detects whether or not the light L is emitted.

And since such a photoelectric conversion element 1 can be manufactured by a simple manufacturing method of annealing the Co thin film under a predetermined temperature condition, a conventional photovoltaic element or optical sensor such as a pn junction is provided. Such a complicated manufacturing process can be omitted.

According to the above configuration, it is possible to generate a photo-induced current by irradiating light L near the positive electrode 4 of the photoelectric conversion film 3 made of CoSi _x without providing a pn junction. A complicated manufacturing process for forming various configurations such as junctions can be omitted, and the manufacturing cost can be reduced with a simple configuration as much as conventional various configurations such as the pn junctions are unnecessary.

The present invention is not limited to the present embodiment, and various modifications can be made within the scope of the gist of the present invention. For example, CoSi _x can be various other CoSi such as CoSi and CoSi _{2. x} may be applied.

In the above-described embodiment, the case where the positive electrode 4 and the negative electrode 5 are provided in advance on the Co thin film before the photoelectric conversion film 3 made of CoSi _x is formed by the annealing process has been described. However, the positive electrode 4 and the negative electrode 5 may be provided after the photoelectric conversion film 3 made of CoSi _x is formed by annealing.

Furthermore, in the above-described embodiment, the case where the incident light ER is irradiated with the visible light L has been described. However, the present invention is not limited to this, and a photo-induced current is generated in the photoelectric conversion film made of CoSi _x. If possible, the incident region ER may be irradiated with various types of light such as infrared light.

Further, in the above-described embodiment, the case where the sputtering method is used as the film forming step for forming the Co thin film made of Co on the substrate has been described. However, the present invention is not limited thereto, and the Co thin film is formed on the substrate. As long as the film can be formed, various methods may be used.

Next, examples will be described below. In this case, a Co thin film made of Co is formed on the Si substrate 2 by a sputtering method in order to verify the temperature at which the annealing process is performed (hereinafter referred to simply as the annealing temperature). A plurality of sample substrates were prepared in which the positive electrode 4 and the negative electrode 5 to be formed were laminated on the Co thin film at a predetermined interval.

In addition to these sample substrates, a plurality of simple Si substrates were also prepared in which a Co thin film was not formed, but a positive electrode 4 and a negative electrode 5 made of Au were provided at predetermined intervals.

Next, the sample substrate was annealed at each annealing temperature of 100 [° C.], 200 [° C.], 300 [° C.], 400 [° C.], 500 [° C.], and 600 [° C.] to obtain CoSi _x. The photoelectric conversion film 3 which consists of was formed, and six types of photoelectric conversion elements from which the said photoelectric conversion film 3 differs were manufactured.

Also, a simple Si substrate was annealed at each annealing temperature of 100 [° C.] and 600 [° C.] to produce two types of Si sample substrates.

Then, an excitation laser beam having a wavelength of 635 [nm], an output of 25 [mW], and a beam diameter of 0.5 [mm] is irradiated to the incident region ER of the positive electrode 4, and at this time, zero bias is applied to the photoelectric conversion element and the Si sample substrate. The photoinduced current at the time was measured. The temperature at the time of measurement was room temperature.

In this case, a measurement result as shown in FIG. 2 was obtained. According to this measurement result, almost no photo-induced current was generated in the Si sample substrate. On the other hand, since a photo-induced current was generated in the photoelectric conversion element, it was confirmed that the photo-induced current was generated by the photoelectric conversion film 3 made of CoSi _x . Further, it was confirmed that these photoelectric conversion elements can obtain the maximum electromotive force when the annealing temperature is set to 600 degrees. Therefore, it was confirmed that when the photoelectric conversion film 3 is formed by annealing, it is preferable to set the annealing temperature to 600 degrees.

Next, the surface of the photoelectric conversion film when the annealing temperature is set to 600 degrees and the surface of the photoelectric conversion film when the annealing temperature is set to 700 degrees are used using a scanning electron microscope (SEM). Observed. In this case, as shown in FIGS. 3A and 3B, the bonding state of Si of the Si substrate and Co of the Co thin film is different, and the formation state of the photoelectric conversion film changes depending on the annealing temperature. I was able to confirm.

Next, a photoelectric conversion element manufactured by annealing at an annealing temperature of 600 [° C.] and a Si sample substrate annealed at an annealing temperature of 600 [° C.], a wavelength of 635 [nm] and an output of 25 [mW] ] And an excitation laser beam having a beam diameter of 0.5 [mm] are respectively irradiated in the vicinity of the positive electrode 4 (that is, the incident region ER), and IV measurement of the photoelectric conversion element and the Si sample substrate at this time was performed. . The temperature at the time of measurement was room temperature.

In this case, a measurement result as shown in FIG. 4 was obtained. As shown in FIG. 4, in the Si sample substrate made of only Si (the upper column simply indicated as Si in FIG. 4), the photo-induced current is below the measurement limit regardless of whether or not the induction laser beam is irradiated ( The induced current value at zero bias was 3 digits or less).

On the other hand, in the photoelectric conversion element, as shown in FIG. 4 (the lower column simply indicated as CoSi _{x in} FIG. 4), the photoinduced current could not be observed when the excitation laser beam was not irradiated. When the excitation laser was irradiated, photoinduced current could be observed. From this, in the photoelectric conversion element, it was confirmed that a photo-induced current was generated when irradiated with light. Further, as described above, it was confirmed that the generation of the photo-induced current is a characteristic phenomenon caused by CiSi.

Further, FIG. 5 shows the difference between the photo-induced current when the photoelectric conversion element is irradiated with the excitation laser beam and when the excitation laser beam is not irradiated. As shown in FIG. In the conversion element, a high potential of about 0.6 [V] was generated at room temperature, and it was confirmed that the generation efficiency was high. In FIG. 5, the photoinduced current (detection sensitivity 20 [mA / W]) of about 1 [mA] (p-type photocarrier) was detected at room temperature at zero bias potential.

Next, using a photoelectric conversion element with an annealing temperature of 600 [° C.], time response performance by pulse laser excitation was investigated. Here, the pulse laser is a ps ( ^10-12 seconds) pulse laser, and has a wavelength of 532 [nm], a repetition of 10 [Hz], a maximum power of 0.1 [mJ], and a half-value width of 20-30 ps.

The time response depends on the pulse width of the pulse laser light source, the characteristics of the peripheral circuit, and the like. Under this experimental condition, as shown in FIG. 6, a commercially available high-speed Pin photodiode (response time of about 2 [ns]) (FIG. 6, the photoelectric conversion element (lower waveform Wa1 in FIG. 6) is about four times (about 10 [ns]) compared to the upper waveform Wb1 as “Pindiode”, and at least the band frequency to GHz Met. In FIG. 6, the irradiation timing of the pulse laser is displayed as “Lasertrigger” and indicated by an arrow.

Moreover, it was found from this experiment that the time response particularly depends on the excitation position and the distance between electrodes (0.1 [cm]), and that the delay due to the transmission loss of the peripheral circuit is also greatly affected.

Here, the mobility estimated from the photoexcitation position and interelectrode distance 0.1 [cm], rise response time 10 [ns], generated electric field strength 0.14 [V], and amplifier gain 10 times is 3.6 × 10 6. It became ⁸ [cm < ² > / Vs]. This is about 10 ⁵ times the value of Si crystals, the definition of the mobility of this phenomenon was found to be not applicable.

Further, when the carrier velocity was determined only by the distance between the photoexcitation position and the electrode of 0.1 [cm] and the rising response time of 10 [ns], it was 1.0 × 10 ⁷ [cm / s]. This is almost the same as the velocity of thermoelectrons of 1.2 × 10 ⁷ [cm / s] at normal temperature (300 [K]). From this, it was found that the high-speed component of the photo-induced carrier is close to the thermionic emission characteristic. The high-speed response of thermionic emission carriers has long been used for Schottky diodes capable of THz operation at room temperature.

These features support the high-speed movement of carriers on the CoSix nanoparticle / Si device surface and are less susceptible to conduction losses such as scattering in bulk crystals. It has been found that there is a possibility that the speed can be dramatically increased from the performance of Fig. 6 (Fig. 6). Considering the similarity with thermionic emission carriers, detection band performance from GHz band to THz band can be realized.

Incidentally, in this experiment, the pulse laser was irradiated to the excitation position where the photoinduced current becomes the maximum output in the photoelectric conversion element. The excitation intensity was measured under the condition that there was no influence of photoexcited carriers from the Si substrate.

In the sample with the same structure as Si with an annealing temperature of 600 [° C.], a slow peak with a rise of about 15 [ns] was observed under the condition of high excitation intensity, confirming that it was clearly different from the above fast component (FIGS. 7 to 9). Further, the above measurement was performed under excitation conditions where the excitation intensity was weakened and this peak could be ignored.

When the pulse response waveform was observed with an oscilloscope (Tektronix TDS620B), it was found that the pulse potential was greatly influenced by the bias potential as shown in FIGS. However, these measurements are under strong excitation conditions, and the carrier component from the Si substrate is not removed.

Incidentally, FIG. 7 shows a time response waveform at a bias potential of 0 [V], Wa2 shows a time response waveform of a photoelectric conversion element with an annealing temperature of 600 [° C.], and Wb2 shows Si-Pin. The time waveform of a diode is shown.

FIG. 8 shows a time response waveform at a bias potential of +200 [mV], Wa3 shows a time response waveform of the photoelectric conversion element with an annealing temperature of 600 [° C.], and Wb3 shows the Si-Pin diode. A time waveform is shown.

FIG. 9 shows a time response waveform at a bias potential of −200 [mV]. Wa3 shows a time response waveform of the photoelectric conversion element with an annealing temperature of 600 ° C., and Wb3 shows the Si-Pin diode. A time waveform is shown.

Thus, it was confirmed that the photoelectric conversion element has a photoinduced current waveform that changes depending on the excitation intensity, the excitation position and the relative position of the electrodes, and the bias voltage.

1 is a schematic diagram illustrating an overall configuration of a photoelectric conversion element according to the present invention. It is a graph which shows the relationship between the photo-induced current at the time of zero bias, and annealing temperature. It is the photograph of the surface of a photoelectric conversion film when annealing temperature is 600 degreeC and 700 degreeC. It is a graph which shows the IV curve by light induction. It is a graph which shows the relationship between an applied bias voltage and photoinduced current. It is a graph which shows a time response waveform. It is a graph which shows a time response waveform when a bias potential is 0 [V]. It is a graph which shows a time response waveform when a bias potential is +200 [mV]. It is a graph which shows a time response waveform when a bias potential is -200 [mV].

1 Photoelectric conversion element 2 Si substrate (substrate)
3 Photoelectric conversion film 4 Positive electrode (electrode)
5 Negative electrode (electrode)

Claims (2)

In a photoelectric conversion element that photoelectrically converts light,
A substrate made of Si, a photoelectric conversion film made of CoSix laminated on the substrate, and an electrode provided on the photoelectric conversion film, the photoelectric conversion film in a region within 1 mm around the positive electrode of the electrodes the photoelectric conversion device wherein light is characterized Rukoto is irradiated to. A film forming step of forming a Co thin film made of Co on a substrate made of Si;
Forming a photoelectric conversion film made of CoSix by diffusing Si of the substrate into Co in the Co thin film by annealing the Co thin film;
An electrode forming step of forming a positive electrode and a negative electrode on the photoelectric conversion film before or after the forming step .