Phototransistor-based photoelectric detection method

Abstract

The invention discloses a phototransistor-based photoelectric detection method and relates to a photoelectric detection technology. The method comprises the following steps: a, applying a turn-on voltage to a grid electrode of a photo-transistor, turning on the photo-transistor, monitoring an output current of the photo-transistor, and if the output current indicates that an optical signal is detected, entering a step b; and b, applying a turn-off voltage to the grid electrode of the photo-transistor, turning off the photo-transistor, and then returning to the step a. According to the invention, the dynamic photoelectric response characteristic of the phototransistor can be regulated and controlled, and the dynamic photoelectric response characteristic of the phototransistor is remarkably improved, so that the photoelectric response speed of the phototransistor is remarkably improved; and a new choice is provided for development of a photoelectric detector with large responsivity, high detection rate and quick response and imaging equipment thereof.

Description

Technical Field

[0001] The invention relates to photoelectric detection technology. Background Art

[0002] In life, optical imaging is the most direct way for humans to observe and record the external environment; in modern information technology, light has long become an important carrier of information transmission; in science, optical imaging is also the most important technical means relied on by scientific research work in various disciplines and various scientific activities of mankind by utilizing the interaction between matter and light; at present, although people are working hard to explore all-optical information processing solutions, overall, at least at the current technical stage, information processing based on electrical signals is still the most mature and widely used, and the main function of photoelectric detection devices is to complete the conversion of optical signals into electrical information, which lays the foundation for the technical value of photoelectric detection devices in the modern information society.

[0003] As the cornerstone of modern information society, photodetectors based on semiconductor photoelectric effect occupy the largest market share in the field of photodetectors. In order to better meet social needs, people have invented photodetectors of various structures. However, similar to other semiconductor devices, their basic devices are no more than three types: photoresistors, photodiodes, and phototransistors. Almost all photodetector device structural designs can be considered as a combination or improvement of these basic devices. For example, the common MSM (metal-semiconductor-metal) structure photodetector can be equivalent to a combination of "Schottky photodiode" and "photoresistor". The performance of this combined photodetector is often determined by the performance characteristics of its basic devices. As one of the three basic photoelectric detection devices, "photoresistor" is also often called "photoconductive device". Since it directly utilizes the change of semiconductor resistivity under light, it must work under a certain DC bias. Although this ensures that its photoelectric gain is large, it has high responsiveness technical indicators and is sensitive to changes in light intensity, but because of this, its dark current is relatively large, the detection rate is usually low, and it is restricted by the "sustainable photoconductivity effect", so its response speed is usually slow. Of course, it has a simple structure, uncomplicated manufacturing process, and low price, and is widely used in cost-sensitive scenarios; as the photoelectric detection device with the most active research, the most application scenarios, and the richest application solutions, people have invented many "photodiodes" with different structures. Although their performances vary, they have one common feature, that is, their response speed is fast; as the only three-terminal structure photoelectric detection device, the performance advantages and disadvantages of the "phototransistor" are basically the same as those of the "photoresistor", but its manufacturing process is relatively complex, and its cost disadvantages have led to relatively less research on it.

[0004] Due to different focuses, various application scenarios have very different requirements for the performance indicators of photoelectric detection devices. As the two largest application fields of photoelectric detection devices, optical communications and optical imaging have the most representative performance requirements for photoelectric detectors. In the field of optical communications, people hope that photoelectric detectors have the fastest possible response speed, and a response time constant of the order of picoseconds has become a routine requirement. In most imaging observation application scenarios, although people do not have strict requirements on the response speed of photoelectric detectors, in order to better distinguish the differences in local details in photos, people often use photoelectric detectors with higher responsiveness technical indicators. In order to achieve imaging observation of extremely weak light signals, people tend to prefer photoelectric detectors with higher detection rate technical indicators.

[0005] Although people can always choose suitable photoelectric detection devices according to their needs, with the wider penetration of photoelectric detection technology in the modern information society, people are constantly putting forward higher requirements on the performance indicators of photoelectric detection devices. Among them, the most typical development is "single photon detection".

[0006] Simply put, single photon detection is to count the photons incident on the detector. Assume that the number of photons incident on the surface of the photodetector within the time interval t is n, and the incident light power is P, then:

[0007]

[0008] Where λ is the wavelength of the incident light in nanometers, the time interval is in seconds, and the optical power is in watts.

[0009] Taking 1μm infrared photon detection as an example, assuming that the effective photosensitive area of ​​the photodetector is 10 -4 cm 2 , if the time interval t is 1 μs, the light power density incident on the detector surface is 2 nW / cm 2 , the intensity of the incident light is very weak, but when the time interval t is taken as 1 nanosecond, the light power density incident on the detector surface is 2μW / cm 2 , which is about the same intensity as the light source commonly used in laboratories. Although "single-photon detection" is not completely equivalent to weak-light detection, the "single-photon" mode can detect extremely weak light signals, and "single-photon" imaging will have a significant impact on national security.

[0010] Since it is necessary to count the incident photons, the detector must have the fastest possible response speed, which should usually reach the nanosecond level. Among semiconductor-based photodetection devices, there is currently only one option that can achieve this response speed technical indicator, namely: photodiode; In addition, when an incident photon is absorbed by a semiconductor photodiode, it can only generate a pair of photogenerated carriers in theory. In order to obtain an electrical signal sufficient for counting, a gain mechanism must be introduced in the photodiode. Therefore, the photodiode must work in avalanche mode. Single photon incidence induces avalanche discharge, thereby obtaining extremely high photoelectric gain. Of course, after obtaining a pulse electrical signal sufficient for counting, in order to avoid missing counts as much as possible, a feedback circuit must be used to control the bias voltage of the photodiode, so as to achieve photocurrent quenching as soon as possible, restore the normal working state of the photodiode, and prepare for the next photon counting. Of course, due to the high operating voltage of the avalanche photodiode single-photon detector, its dark current and dark state noise are relatively large, which inevitably has an adverse effect on the detection of extremely weak light signals. Summary of the invention

[0011] The technical problem to be solved by the present invention is to provide a fast-response photoelectric detection method based on a photosensitive transistor.

[0012] The technical solution adopted by the present invention to solve the technical problem is a photoelectric detection method based on a photosensitive transistor, characterized in that it includes the following steps:

[0013] a. Applying a turn-on voltage to the gate of the phototransistor, turning on the phototransistor, and monitoring its output current. If the output current indicates that a light signal is detected, proceeding to step b.

[0014] b. Apply a turn-off voltage to the gate of the phototransistor to turn off the phototransistor, and then return to step a.

[0015] Furthermore, the photosensitive transistor is an NMOS, and the turn-off voltage is a negative level.

[0016] The turn-on voltage is the threshold voltage of the phototransistor.

[0017] Further, the step a comprises:

[0018] (a1) applying a threshold voltage to the gate of the phototransistor;

[0019] (a2) While the light signal is being generated, a pulse higher than the threshold voltage is applied to the gate of the phototransistor and its output current is monitored.

[0020] The present invention can regulate the dynamic photoelectric response characteristics of the phototransistor, significantly improve the dynamic photoelectric response characteristics of the phototransistor, and thus significantly improve the photoelectric response speed of the phototransistor; it provides a new option for the development of photoelectric detection devices with large responsiveness, high detection rate, and fast response and their imaging equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 (a) is a transfer characteristic curve of a phototransistor;

[0022] Figure 1 (b) is a schematic diagram of the pulse gate voltage loading control process of the present invention;

[0023] Figure 2 A system block diagram for designing an experimental verification platform architecture for controlling the dynamic photoelectric response characteristics of a phototransistor by pulse gate voltage loading according to the present invention;

[0024] Figure 3 A schematic diagram of the gate voltage regulation principle of a phototransistor implemented in the present invention;

[0025] Figure 4 This is a schematic diagram of the verification platform device structure for improving the photoelectric response speed of a phototransistor by pulse gate voltage loading proposed by the present invention;

[0026] Figure 5 A schematic diagram of the verification platform chassis device proposed by the present invention;

[0027] Figure 6 This is a schematic diagram of the synchronous control principle of the gate and deep ultraviolet LED in the transistor driving power module proposed by the present invention;

[0028] Figure 7 This is a schematic diagram of the working principle of the transistor output signal detection module proposed in the present invention;

[0029] Figure 8 This is a test result diagram of the pulse gate voltage loading scheme proposed in the present invention for improving the response speed of an actual device, wherein: Figure 8 (a) is a schematic diagram of the structure of an amorphous indium gallium zinc oxide (a-IGZO) thin film transistor. Figure 8 (b) is a transmission electron microscope image of a cross section of an amorphous indium gallium zinc oxide (a-IGZO) thin film transistor. Figure 8 (c) is a device response curve diagram when the gate voltage loading scheme proposed by the present invention is not used, Figure 8 (d) is a device response curve diagram when the gate voltage loading scheme proposed by the present invention is used, Figure 8 (e) is the detailed characteristic diagram of the rising and falling edges. DETAILED DESCRIPTION

[0030] As a three-terminal device, the output characteristics of the phototransistor are related to the source-drain bias voltage and are also regulated by the gate voltage. Therefore, the most convenient way to regulate the dynamic response characteristics of the phototransistor is to load the pulse gate voltage. To this end, the basic idea of ​​realizing the fast response of the phototransistor proposed in the present invention is as follows:

[0031] in accordance with Figure 1 The transfer characteristic curve shown in (a) is the same as the common transistor working mode. The source is grounded, a certain DC working voltage VDS is applied between the source and the drain, and a certain DC gate voltage VGS is applied to the gate, so that the phototransistor is in a critical state of being turned on in the absence of light; when photons are incident on the phototransistor, a positive gate voltage pulse of a certain amplitude is superimposed on the original DC gate voltage, so that the phototransistor is fully turned on and reaches a saturated current state, thereby obtaining the largest possible photocurrent; after the photocurrent pulse signal is successfully recorded, the pulse gate voltage load is switched to a negative gate voltage pulse, so that the phototransistor quickly switches from a fully turned-on state to a fully turned-off state. After a certain time interval, the pulse gate voltage power supply is completely cut off, so that the gate voltage returns to V GS The DC gate voltage is loaded, and the phototransistor is in the critical state of being turned on again, ready for the next photon counting. The control process designed by the present invention and its expected control effect are as follows: Figure 1 (b) as shown.

[0032] In order to verify the technical solution proposed by the present invention to realize the rapid response of the photosensitive transistor by pulse gate voltage loading, the present invention provides a set of experimental verification platform, which includes: a light source module and its control circuit, a transistor drive power supply module, a synchronization signal control module, a transistor output signal processing module, an optical microscope observation module, a digital oscilloscope and system structural parts, such as Figure 2 shown.

[0033] The optical module and its control circuit include: a high-frequency flash deep ultraviolet semiconductor light-emitting diode, an anti-ultraviolet dual-core optical fiber, a fast-response ultraviolet light detector, a light output lens, and a start-stop circuit of the deep ultraviolet light-emitting diode; the optical module and its control circuit are used to realize the periodic opening and closing of the pulse light source, and the light is divided into two paths, one of which is loaded onto the photosensitive transistor to be tested to meet the needs of the photosensitive transistor dynamic photoelectric response characteristic test for rapid changes in light intensity; the other path is loaded onto the fast-response ultraviolet detector in the module, and the output signal of the ultraviolet detector is connected to an oscilloscope after being processed by an amplifier, so as to intuitively observe and record the periodic opening and closing characteristics of the high-frequency flash deep ultraviolet semiconductor light-emitting diode in the module.

[0034] It should be noted that if this experimental platform uses an infrared laser or an infrared light-emitting diode as a light source, it cannot meet the test requirements of the dynamic photoelectric response characteristics of the phototransistor visible light detector and the phototransistor ultraviolet light detector. The reason why the present invention uses a deep ultraviolet light-emitting diode as a light source is to expand the scope of application of this experimental verification platform and meet the test requirements of ultraviolet-visible light-infrared phototransistors.

[0035] The transistor driving power supply module comprises: a transistor gate driving voltage source and a transistor drain-source loading voltage source; the external test conditions required for the phototransistor test are realized by this module, wherein a certain DC working voltage V is applied between the source and drain of the phototransistor to be tested by the transistor drain-source loading voltage source. DS ; Through the transistor gate drive voltage source, a certain DC gate voltage V is applied to the gate of the photosensitive transistor to be tested GS In addition, it is also necessary to implement the following according to the output characteristics of the light source: Figure 3 Designed pulse gate voltage loading.

[0036] The synchronization signal control module mainly realizes the synchronization of the light source control voltage and the transistor driving voltage, thereby realizing the attached Figure 3 The light source shown is loaded synchronously with a pulsed grid voltage.

[0037] The transistor output signal processing and display module includes: a signal amplification and processing circuit module, and a digital oscilloscope. Through this module, in addition to obtaining the output characteristics of the photosensitive transistor to be tested, in order to more intuitively observe the dynamic photoelectric response characteristics of the photosensitive transistor to be tested under the simultaneous loading of an alternating light source and a pulsed gate voltage, this module also needs to amplify the output signal of the photosensitive transistor to be tested and connect it to the oscilloscope for display.

[0038] The optical microscopic observation module comprises: a microscopic support, a microscope lens, an imaging CCD, and a display; the module is mainly used to fix the photosensitive transistor to be tested and observe the contact between its source, drain, gate and the probe.

[0039] The system structural parts include: an all-aluminum chassis, support parts, and cable anti-interference magnetic rings. This component mainly shields interference from external environmental light sources and space electromagnetic signals.

[0040] Figure 3 The figure is a schematic diagram of the effect of gate voltage regulation on the dynamic photoelectric response characteristics of a phototransistor. The present invention synchronously loads a +10V voltage on the gate of the phototransistor and maintains it when the deep ultraviolet light source is turned on, and synchronously loads a -10V voltage on the gate of the phototransistor and maintains it when the ultraviolet light source is turned off, thereby helping the phototransistor to recover quickly after the light is removed.

[0041] Figure 4The overall structure diagram of the verification platform for the dynamic photoelectric response characteristics of the phototransistor based on gate voltage regulation proposed in the present invention. It mainly includes (1) a verification platform chassis device, (2) a function generator, (3) a digital oscilloscope, and all the cables connecting the components. (1) The verification platform chassis device is connected to (2) the function generator and (3) the digital oscilloscope respectively.

[0042] Figure 5 The (1) verification platform chassis equipment mainly includes (11) a deep ultraviolet light source (12) an ultraviolet light detector (13) a probe station (14) a driving power module. The (11) deep ultraviolet light source is driven by a control signal synchronized with the gate voltage of the photosensitive transistor. The (11) deep ultraviolet light source is divided into two beams by an anti-ultraviolet double-core optical fiber, one beam is output as an irradiation light source to the transistor to be tested, and the other beam is output to the ultraviolet light detector for real-time detection and then output to the (3) digital oscilloscope to monitor the on state of the (11) deep ultraviolet light source. The transistor to be tested is placed on the (15) vacuum adsorption chuck of the (13) probe station, and voltages are applied to the drain, source, and gate ends of the transistor to be tested using the corresponding probe pins in turn. The image is amplified and collected by the (16) microscope system and the (17) CCD camera and transmitted to the (18) screen for real-time display, so that the operator can observe the test process more clearly.

[0043] Figure 6 The schematic diagram of the gate voltage source control principle in the transistor drive power module proposed in the present invention. In order to achieve a high degree of synchronization between the opening and closing of the deep ultraviolet light source and the positive gate voltage loading and negative gate voltage loading of the gate drive voltage of the transistor to be tested, the same signal source is used to control the gate voltage source of the deep ultraviolet light source and the transistor to be tested. The same square wave signal source is divided into two paths, one path is amplitude controlled to obtain the required positive and negative gate drive voltages, and the other path is shaped to remove the negative half-cycle pulses before driving the deep ultraviolet light source.

[0044] Figure 7 The figure is a schematic diagram of the working principle of the transistor output signal detection module proposed in the present invention. In order to achieve a large dynamic range detection from nA level current to mA level current, a dual-channel micro-current detection circuit is designed. The circuit consists of two channels, each with a different transimpedance coefficient, and can detect micro-currents of different magnitudes through switch switching. When the photosensitive transistor to be tested generates a micro-current, the current is converted into an output voltage V by a transimpedance amplifier. O The output is then sent to (3) a digital oscilloscope for display.

[0045] Figure 8 The figure is a test result of the pulse gate voltage loading scheme proposed in the present invention on the response speed improvement of the actual device. The device used in the test is an amorphous indium gallium zinc oxide (a-IGZO) thin film transistor, and its structure is as follows: Figure 8(a) shows a cross-sectional transmission electron microscope image. Figure 8 (b) is shown. The device response when the gate voltage loading scheme proposed by the present invention is not used is shown in Figure 8 As shown in (c), its response speed is very low, the rise time and decay time are about 12 seconds and more than 1800 seconds respectively. Then, when the gate voltage loading scheme proposed by the present invention is used, as shown in Figure 8 (d) shows that the response time is greatly shortened to less than 25μs. UV The amplitude of the signal is related to the incident deep ultraviolet light power density, V UV The high level of the signal represents that the deep ultraviolet light source LED is turned on, and the low level represents that the deep ultraviolet light source LED is turned off. output It is the voltage value output after the transistor output current is processed by the output circuit, which represents the size of the output current. Figure 8 (e) shows more detailed rising and falling edge characteristics. After gate voltage loading, the rising time is about 2 μs, and the falling decay time is about 22 μs. It is verified that the gate voltage loading scheme proposed by the present invention to improve the response speed of the phototransistor is feasible and effective.

[0046] Example 1

[0047] This embodiment provides a photoelectric detection method based on a photosensitive transistor, comprising the following steps:

[0048] a. Applying a turn-on voltage to the gate of the phototransistor, turning on the phototransistor, and monitoring its output current. If the output current indicates that a light signal is detected, proceeding to step b.

[0049] b. Apply a turn-off voltage to the gate of the phototransistor to turn off the phototransistor, and then return to step a.

[0050] This embodiment uses an NMOS type photosensitive transistor as NMOS, and the turn-off voltage is a negative level. The same is true for PMOS.

[0051] In this embodiment, a negative level is applied to the gate of the NMOS phototransistor, so as to quickly "reset" the phototransistor and greatly improve the response speed of the phototransistor.

[0052] Example 2: See Figure 1 (b).

[0053] Step a of this embodiment includes the following steps:

[0054] (a1) applying a threshold voltage Vth to the gate of the phototransistor;

[0055] (a2) While the light signal is being generated, a pulse higher than the threshold voltage is applied to the gate of the phototransistor and its output current is monitored.

[0056] b. Apply a turn-off voltage to the gate of the phototransistor to turn off the phototransistor, and then return to step a.

[0057] Figure 1 In (b), V GS The pulse width can be set according to device parameters and requirements, which is easy to understand for ordinary technicians and does not require special limitations.

[0058] This embodiment requires a control signal generated synchronously with the light signal. Taking the NMOS phototransistor as an example, when the threshold voltage is applied to the gate, the phototransistor is in a critical state. When a light signal is generated, a positive pulse is superimposed on the gate on the basis of the threshold voltage, and the phototransistor quickly enters the saturation region. After the photoelectric characteristics in the output current of the phototransistor are detected, a negative pulse is applied to the gate to reset the phototransistor.

Claims

1. A photoelectric detection method based on a phototransistor, characterized in that: The steps include: a. Applying a turn-on voltage to the gate of the phototransistor, turning on the phototransistor, and monitoring its output current. If the output current indicates that a light signal is detected, proceeding to step b. b. Apply a turn-off voltage to the gate of the phototransistor to turn off the phototransistor, and then return to step a.

2. The photoelectric detection method based on a phototransistor as claimed in claim 1, characterized in that: The photosensitive transistor is an NMOS, and the turn-off voltage is a negative level.

3. The photoelectric detection method based on a phototransistor as claimed in claim 1, characterized in that: The turn-on voltage is the threshold voltage of the phototransistor.

4. The photoelectric detection method based on a phototransistor as claimed in claim 1, characterized in that: The step a comprises: (a1) applying a threshold voltage to the gate of the phototransistor; (a2) While the light signal is being generated, a pulse higher than the threshold voltage is applied to the gate of the phototransistor and its output current is monitored.

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