CN1293374C - Novel structure photoelectric detector capable of measuring wave length and detecting method - Google Patents

Abstract

The photodetector of the new structure of the present invention adopts double-sided polished high-resistivity semiconductor single crystal material, and is composed of two PN structures aligned and arranged vertically to the semiconductor surface and respectively located on the front and back of the semiconductor material. Utilizing the characteristic that the penetration depth of light in the semiconductor material is related to the wavelength, the invention can be used to accurately measure the intensity of light and the central wavelength of light. The photodetector of the present invention has only two electrodes, can read the photocurrent signal conveniently, can directly detect the intensity and color information of light with only one device, and is suitable for making photodetector arrays that need to measure wavelength or distinguish colors , suitable for making detection units of color imaging sensors.

Description

A New Structured Photodetector and Its Detection Method That Can Measure Wavelength Directly

technical field

The invention relates to a semiconductor photodetector and a detection method thereof, belonging to H01L 27/00 semiconductor devices

technology field.

Background technique

So far, all image sensors (including CCD, CMOS or PN junction photodiodes) cannot directly measure the wavelength of light. Their detection of color is mainly through the measurement, recording and synthesis of red, green and blue ternary color light respectively. Achieved. This method of recording color (or measuring the central wavelength of the spectrum) has the following disadvantages:

(1) Each pixel needs to contain three device elements to detect red, green, and blue three-color light respectively, which makes the image sensor and its subsequent circuits and data processing cumbersome and complicated;

(2) A pixel is composed of three device elements, and there is a certain interval between the device elements, which is unfavorable for improving the resolution;

(3) The three device elements in the pixel are arranged in the same plane and cannot overlap, causing color distortion (the ternary colors on the color photo are arranged on different layers and overlap in the direction of sight, so there is no such problem);

Pacific Silicon Sensor Inc. has developed a photodetector that can directly measure the wavelength of light [see Pacific Silicon Sensor Inc. product information, http://www.pacific-sensor.com/pages/ pro-wsd.html]. As shown in Figure 1, it consists of two back-to-back PN junction photodiodes on an ordinary silicon epitaxial wafer. When working, the two diodes are in the reverse bias state at the same time and detect optical signals at the same time. Since the penetration depth of light in silicon materials is related to the wavelength of light, the penetration depth of light with shorter wavelength is shallow, and the photocurrent of the photodiode near the surface is larger, and the penetration depth of light with longer wavelength is large, and the photodiode close to the substrate The photodiode has a larger photocurrent. By measuring the photocurrent ratio of the two photodiodes, combined with the calibration data of the detector for light of known wavelengths, the detector can detect light in the range of 450nm-950nm and its central wavelength, and the wavelength resolution can reach 0.01 nm [See Pacific Silicon Sensor Inc. Product Information, http://www.pacific-sensor.com/pages/pro-wsd.html]. The unique structure of this kind of detector and the characteristic of being able to measure the wavelength have aroused people's great attention, and the magazine "Physics Today" (Physics Today) in the United States has made a special introduction to it [see Physics Today, August 2001]. However, this detector structure is not suitable for making array detectors, especially the detection units in high-resolution imaging sensors. The reasons are: (1) each detection unit requires three electrodes, which is extremely unfavorable for making large-scale arrays (general imaging sensor detection units only need two electrodes, and even one electrode in the two is still common); (2) Since the epitaxial layer on the low-resistance silicon substrate material is used to make the device, if this structure is used to make an array detector, the signal output of each unit device close to the PN junction photodiode of the substrate is very difficult .

Contents of the invention

In view of the above problems, the object of the present invention is to provide a novel photodetector capable of directly measuring the wavelength of light, and to propose a method for measuring the wavelength of light using the detector. Not only only one device can directly detect the intensity and color information of light, but also the device only has two electrodes, which is suitable for making detection units of large-scale array detectors.

To achieve the above object, the present invention takes the following technical solutions:

A new structure photodetector capable of measuring wavelengths is characterized in that: it is made of a double-sided polished high-resistivity semiconductor single wafer, and the detector includes two PN junctions, which are respectively located on the front and back of the semiconductor material, and align and arrange in a direction perpendicular to the semiconductor surface; each PN junction has an electrode, and the detector has two electrodes in total.

When the detector is working, a bias voltage is applied to the two electrodes, so that one of the PN junctions is in a reverse biased state, and the other PN junction is in a slightly forward biased state. By changing the polarity of the bias voltage, the bias state of the PN junction can be changed, from the original forward bias to reverse bias, or from the original reverse bias to forward bias. The reverse biased PN junction is used to detect optical signals.

The semiconductor material is preferably a single crystal silicon wafer, or other semiconductor single crystal materials such as gallium arsenide, the front and back of the material are polished, the material can be N-type or P-type, and its resistivity is greater than 500 ohms cm, the crystal orientation can be <100>, <111> or <110>.

Using the detector as the basic structure, a discrete or integrated detector array on the same chip can be constructed.

The method for using the new structure photodetector of the present invention to detect light intensity and wavelength is: bias voltage is added on the two electrodes of described detector, make one of them earlier, for example the PN junction of front is in reverse bias, The bias voltage is large enough to make the depletion region extend from the front to the inside of the material, while the PN junction on the back is in a slightly forward biased state, and the photocurrent is measured (photocurrent 1). Then change the polarity of the bias voltage so that the PN junction on the back of the detector is in reverse bias, and the bias voltage is large enough to make the depletion region extend from the back to the inside of the material, while the front PN junction is in a slight In the forward bias state, measure the magnitude of the photocurrent (photocurrent 2). According to estimates, the time required for the detector to measure the optical signal can be shorter than 20 nanoseconds. If the optical signal does not change in such a short time interval, the intensity of the optical signal is proportional to the sum of the photocurrent 1 and the photocurrent 2. In direct proportion, the wavelength of the optical signal is related to the relative magnitude of photocurrent 1 and photocurrent 2. Once the detector has been calibrated, light intensity and wavelength can be measured.

The light signal to be measured is incident into the detector along a direction perpendicular or nearly perpendicular to the surface of the material.

The light signal to be measured enters the detector from the front or back of the material.

The structure of the detector and the method of measuring the wavelength of light are completely different from those of Pacific Silicon Sensors Corporation. Since the photodetector in the present invention has only two electrodes, the photocurrent signal can be read conveniently, and it is suitable for making an array detector that needs to measure wavelength or distinguish colors. Because the invention only needs one device to directly detect the intensity and color information of light, if it is used to make the detection unit of the color imaging sensor, it not only helps to improve the resolution, but also the color information of each pixel is not distorted.

The present invention is specifically described below in conjunction with examples.

Description of drawings

Fig. 2 is a structural schematic diagram of the present invention.

Detailed ways

The photodetector with the new structure of the invention is composed of two PN junctions on the same chip. FIG. 2 is a schematic diagram of a structure using n-type silicon material. Each detector includes p-type region 1 (heavily doped acceptor region), n-type region 2 (substrate material, lightly doped donor region), p-type region 3 (heavily doped acceptor region), front electrode 4 , a back electrode 5 , an anti-reflection film 6 , and an insulating dielectric film 7 .

The device is made of double-sided polished <100> crystalline silicon wafer, the resistivity of the n-type region 2 is very high, the doping concentration is very low, and the resistivity is 4000-10000 ohm cm. The thickness of the semiconductor material used in the device is 300 μm.

The method that the new structure photodetector of the present invention is used for detecting light is:

Let the light be incident on the detector perpendicular to the surface of the silicon material along the front side; apply a working voltage between the electrode 4 and the electrode 5, and the electrode 4 is negatively biased with respect to the electrode 5; make the PN junction on the front side of the detector (by p Type region 1 and substrate) is in reverse bias, and the PN junction on the back of the detector (composed of p-type region 3 and substrate) is in slight forward bias. A photocurrent signal (referred to as photocurrent 1 ) is taken out from between the electrode 4 and the electrode 5 . Change the polarity of the working voltage applied between electrode 4 and electrode 5, even if electrode 4 is positively biased relative to electrode 5, at this time the PN junction on the front of the detector is in a slightly forward biased state, and the PN junction on the back of the detector is in a slightly forward biased state. The PN junction is in a reverse bias state, and a photocurrent signal (called photocurrent 2 ) is taken out from between electrode 4 and electrode 5 . Then the intensity of the optical signal is proportional to the sum of the photocurrent 1 and the photocurrent 2, and the wavelength of the optical signal is related to the relative magnitudes of the photocurrent 1 and the photocurrent 2. After the detector is calibrated with light of known light intensity and wavelength, the detector can be used to measure the intensity and wavelength of the optical signal.

In other embodiments of the invention:

The detector can be composed of p ⁺ -n ^- -p ⁺ basic structure, or n ⁺ -p ^- -n ⁺ basic structure by the front PN junction, semiconductor substrate material and back PN junction, or it can be composed of these basic structures , to construct discrete or integrated detector arrays or other variant structures on the same chip. Among them, p ⁺ and n ⁺ respectively refer to acceptor and donor heavily doped regions, and their doping concentration is greater than 10 ¹⁸ cm ^-3 ; p ^- and n ^- respectively refer to acceptors with very low doping concentration, less than 10 ¹⁴ cm ^-3 district and donor district.

The device is preferably made of a double-sided polished single crystal silicon wafer, and gallium arsenide or other semiconductor single crystal materials can also be used. The semiconductor material may be <100>, <111> or <110> oriented. The thickness of the semiconductor material is greater than 100 μm.

The light to be detected enters the detector along a direction perpendicular or nearly perpendicular to the semiconductor surface.

The detected light enters the detector from the front or back of the semiconductor material.

It should be noted that the above-mentioned embodiments are only for illustrating the present invention but not limiting the patent scope of the present invention, and any equivalent transformation technology based on the present invention shall be within the scope of the patent protection of the present invention.

Claims (4)

1. novel structure photoelectric detector is characterized in that:

The semiconductor material of making described detector is the high resistance zone-melting monocrystalline silicon piece of twin polishing, and its resistivity is greater than 500 ohmcms;

Front and back at described semiconductor material respectively has a pn knot, and each PN junction has an extraction electrode;

Described two PN junctions and semiconductor material are formed n together ⁺-p ^--n ⁺Or p ⁺-n ^--p ⁺Basic structure.

2. novel structure photoelectric detector as claimed in claim 1 is characterized in that: described n ⁺-p ^--n ⁺Or p ⁺-n ^--p ⁺Discrete array or monolithic integrated array that basic structure is formed.

3. method of using the described novel structure photoelectric detector of claim 1 to survey monochromatic light or quasi-monochromatic light wavelength and intensity is characterized in that:

Bias voltage is added on two electrodes as claimed in claim 1 during photodetector work, makes the front PN junction be in reverse-bias state, and back side PN junction is in slight forward bias state, and the size of measuring light electric current is called photocurrent 1;

Change the polarity of bias voltage, make the front PN junction be in slight forward bias state, back side PN junction is in reverse-bias state, and the size of measuring light electric current is called photocurrent 2;

By comparing, make the intensity of light signal by photocurrent 1 and photocurrent 2 sums with the calibration data; By the ratio of photocurrent 1 and photocurrent 2, make the wavelength of light signal.

4. method of using the described novel structure photoelectric detector of claim 1 to survey monochromatic light or quasi-monochromatic light wavelength and intensity is characterized in that:

Bias voltage is added on two electrodes as claimed in claim 1 during photodetector work, makes back side PN junction be in reverse-bias state, and the front PN junction is in slight forward bias state, and the size of measuring light electric current is called photocurrent 1;

Change the polarity of bias voltage, make back side PN junction be in slight forward bias state, the front PN junction is in reverse-bias state, and the size of measuring light electric current is called photocurrent 2;

By comparing, make the intensity of light signal by photocurrent 1 and photocurrent 2 sums with the calibration data; By the ratio of photocurrent 1 and photocurrent 2, make the wavelength of light signal.

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