JPS6152929B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photodetection device that utilizes the pyroelectric effect, and particularly to a photodetection device with a novel structure suitable for forming in combination with a semiconductor device.

Photodetection devices that utilize the pyroelectric effect of ferroelectric materials have the following advantages: they do not have a sensitivity distribution depending on the wavelength of light, and they do not require cooling.
It has advantages not found in conventional pn junction semiconductor photodetectors. These advantages are particularly effectively exhibited in infrared detection having a wavelength of 1 μm or more.
FIG. 1 is a schematic cross-sectional view of a conventional pyroelectric photodetector using glycine sulfate (TGS). Here, 1 is a TGS substrate with a thickness of about 100 μm, and electrodes 2 and 3 are formed by depositing gold on both sides thereof. The electrode 2 for the incident light 4 is a black electrode,
It is formed by vapor depositing gold in a low vacuum nitrogen atmosphere. The incident light 4 is absorbed by the black electrode 2 and converted into heat, thus inducing a temperature change in the TGS substrate 1. This temperature change changes the magnitude of the spontaneous polarization Ps of the TGS substrate 1, so the electrodes 2 and 3
An electric charge is generated. Therefore, this charge is taken out to the outside for photodetection. By the way, the rate of change of spontaneous polarization Ps of TGS with respect to temperature dPs/dT is 3.5
×10 ^-8 coulombs/°C·cm ² , which is larger than other ferroelectric materials, and therefore has high photodetection efficiency.

In such a conventional photodetecting device, since the voltage between the electrodes 2 and 3 is extracted, its output impedance is high, and therefore it is difficult to directly process the output electrically. Therefore, it is usual to convert the impedance of the output obtained between the electrodes 2 and 3 using a field effect transistor before use, which makes the device configuration complicated. Furthermore, it is not possible to assemble a photodetecting device by combining it with a semiconductor device.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a photodetecting device with a novel structure that eliminates such drawbacks and can obtain an output with low impedance.

In order to achieve such an object, in the present invention, a semiconductor layer is monolithically formed in a photodetection section made of a ferroelectric material, and changes in the spontaneous polarization of the ferroelectric material caused by light incidence are reflected in the electrical conductivity of the semiconductor layer. Take it out as a change.

One embodiment of the photodetector of the present invention is shown in FIGS. 2 and 3. Here, 5 is a Z-axis plate of a ferroelectric material such as IiTaO ₃ having a thickness of about 200 μm, and its spontaneous polarization Ps is oriented in a direction perpendicular to the main plane (Z direction). On this LiTaO ₃ substrate 5, a circular operating portion 6 having a thickness of approximately 100 μm is formed by sputter etching or microdot polishing. 7 is an insulating layer (thickness approximately 0.1 μm) of SiO ₂ or Si ₃ N ₄ deposited on the substrate 5; in the case of SiO ₂ , SiH ₄ and
In the case of O ₂ and Si ₃ N ₄ , they are formed by thermal decomposition of SiH ₄ and NH ₄ . Reference numeral 8 denotes an amorphous silicon layer (about 0.3 μm thick) deposited on the insulator layer 7, which is formed by plasma decomposition of SiH ₄ and is easily deposited. Reference numerals 9 and 9' designate aluminum interdigital electrodes disposed on the amorphous silicon layer 8, and the electrode width and electrode interval are both about 30 μm. Layer 7 of operating section 6
A black light-absorbing electrode 10 made of gold, platinum, etc. is deposited on the side opposite to layers 7 and 8, and an aluminum electrode 11 is deposited on the side of the substrate 5 opposite to layers 7 and 8, covering a portion thereof. This electrode 11 is grounded.

To operate the photodetector having such a configuration, a DC voltage Vo is applied between the electrodes 9 and 9' via a load resistor _RL , and an output is taken out from both ends of the resistor _RL . The incident light 4 is absorbed by the black electrode 10 and becomes heat, raising the temperature of the operating section 6. the result,
Since the spontaneous polarization Ps of LiTaO ₃ changes, a positive charge equal to the change is generated at the interface between the active part 6 of LiTaO ₃ and the insulator layer 7. This interface positive charge induces electrons in the amorphous silicon layer 8. Since the amorphous silicon layer 8 has a high resistance of 10 ⁹ to 10 ¹¹ Ω·cm, no current normally flows between the electrodes 9 and 9', so the output at both ends of the resistor R _L is zero. It is.

On the other hand, when electrons are induced in the amorphous semiconductor layer 8 by light incidence, the electrode 9 is caused by the above-mentioned interface positive charge.
A current flows between and 9' to obtain an output.

Here, the rate of change of spontaneous polarization Ps of LiTaO ₃ dPs/
The value of dT is 1.76×10 ^-8 coulombs/℃・cm ² ,
Although it is smaller than the TGS mentioned above, TGS is water-soluble and difficult to form large crystals.
LiTaO ₃ is industrially more effective. In addition,
Of course, the photodetector of the present invention can also be effectively configured by using LiNbO ₃ or the above-mentioned TGS instead of LiTaO ₃ .

As explained above, according to the present invention, by forming an amorphous silicon layer on a substrate made of ferroelectric material, it is possible to realize a photodetection device that utilizes the pyroelectric effect of ferroelectric material. According to the present invention, the photodetection output can be extracted in a low impedance state without the need for external impedance conversion, and therefore,
A photodetector can also be constructed by combining it with a semiconductor device.

Amorphous silicon is used as the semiconductor layer, and as mentioned above, amorphous silicon has high resistance and low dark current in the absence of incident light. Therefore, the present invention has a high on-off ratio. In fact, even if a large number of photodetecting elements as shown in FIG. 2 are arranged on one substrate 5, each element is electrically isolated, making it easy to fabricate a two-dimensional photodetecting element array. It also has the following advantages.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a conventional pyroelectric photodetector using TGS, FIG. 2 is a plan view showing one embodiment of the photodetector of the present invention, and FIG. 3 is a cross-sectional view taken along the line ``--''. 1...TGS substrate, 2...black electrode, 3...electrode, 4...incident light, 5...LiTaO ₃ substrate, 6...
Operating part, 7... Insulator layer, 8... Amorphous silicon layer, 9, 9'... Cross finger electrode, 10... Black electrode, 11... Aluminum electrode, R _L ... Resistor,
Vo...DC power supply.

Claims (1)

[Claims] 1 It has a substrate made of a ferroelectric material whose spontaneous polarization is oriented in a direction perpendicular to its main plane, and an amorphous silicon layer is deposited on one surface of the substrate with an insulating layer interposed therebetween, and the amorphous silicon layer is deposited on one surface of the substrate. A cross-finger electrode is disposed on the layer, a black light-absorbing electrode is attached to the other surface of the substrate, and light incident on the black light-absorbing electrode is detected as a change in electrical conductivity between the cross-finger electrodes. A photodetecting device characterized by: