JPH03296280A - Infrared sensor - Google Patents

Abstract

PURPOSE:To allow a cut-off wavelength to be kept unchanged during the storage of electric charge by installing efficient hot holes or the supply mechanism of hot electrons obtained by utilizing energy band structure that is formed by contact between a metal having high absorptivity of an infrared ray and a p-type or an n-type degenerated semiconductor. CONSTITUTION:A 1st photoelectric conversion region 4 that is formed into a thin film shape by using silicide as a metal material is provided on the surface of a substrate. A de-generated p-type 2nd photoelectric conversion region 5 that is in the state of ohmic contact with silicide is formed directly below silicide and further, a potential barrier region 6 is formed between the above region 6 and a carrier-injection region 7. An nA<+> type guard ring 8 for relieving electric field concentration is prepared around the 2nd photoelectric conversion region 5 and the potential barrier region 6. Metal wiring 9 consisting of aluminum or the like is formed into a shape surrounding the 2nd photoelectric conversion region 5 so that its wiring is in ohmic contact with the above 2nd region 5 and guard ring 8. Then carriers 18 are not stored at a part of a photodetector 1 and the fluctuations of bias potential is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an infrared sensor that converts optical signals in the infrared region into electrical signals.

[Conventional technology]

As a conventional technique, an infrared sensor proposed in Japanese Patent Application Laid-Open No. 63-237583 will be described.

This infrared sensor includes a photoelectric conversion region made of a degenerate semiconductor of the first conductivity type, a carrier injection region made of a non-degenerate semiconductor of the first conductivity type, and a carrier injection region that exists between the photoelectric conversion region and the carrier injection region. A device with a homojunction structure consisting of a potential barrier region made of a first conductivity type semiconductor whose concentration is lower than that of the carrier injection region, an intrinsic semiconductor, or a second conductivity type semiconductor that is fully depleted at least under operating conditions. It is.

The third section explains the operating principle of photoelectric conversion in this sensor.
This will be explained using Figures (a) and (b).

Figure 3 (a) shows the case where the first conductivity type is p type and the second conductivity type is n type, and the same figure (b) conversely shows the case where the first conductivity type is n type and the second conductivity type is p type. The energy band structure and photoelectric conversion mechanism are shown in FIG. 3. Although infrared light is incident from the carrier injection region side, it may also be incident from the insulator 48, 60 side.

First, a case will be described in which the first conductivity type in FIG. 3(a) is p type and the second conductivity type is n type.

Since the photoelectric conversion region 45 is made of a p-type degenerate semiconductor, the acceptor impurity level, which was localized near the valence band edge Ev in the non-degenerate state, loses its locality and spreads, and the valence band 4 There is some overlap. In this state, the Fermi level Er enters into the four valence bands, so in this region, a vacant level 53 exists between the Fermi level Et and the valence band edge Ev. Carrier injection region 4
Reference numeral 7 is made of a p-type non-degenerate semiconductor, and the potential barrier region 46 existing between the photoelectric conversion region 45 and the carrier injection region 47 is a p-type semiconductor whose acceptor impurity concentration is lower than that of the carrier injection region 47, or an intrinsic semiconductor. Alternatively, at least under operating conditions, an n-type semiconductor having a donor impurity concentration and thickness that is completely depleted by a depletion layer extending from the junction interface with the photoelectric conversion region 45 and a depletion layer extending from the junction interface with the carrier injection region 47. Therefore, in the carrier injection region 47, the Fermi level Ef exists near the valence band edge Ev, and in the potential barrier region 46, the Fermi level Ef exists near the conduction band edge Ev among the three regions made of semiconductor. exists near. Therefore, a potential barrier is formed in the vicinity of the junction interface between the potential barrier region 46 and the other region 45, 47 with the potential barrier region 46, which becomes an obstacle to the holes in the four valence bands.

In particular, the potential barrier for holes in the four valence bands in the photoelectric conversion region 45 is φ().

When light enters from the carrier injection region 47 side, the forbidden band width E
Light with energy greater than g is mostly absorbed near the incident surface in the semiconductor, but the forbidden band width Eg
Light with lower energy (such light is usually infrared light) is transmitted through the carrier injection region 47 and the potential barrier region 46 without being absorbed, and enters the photoelectric conversion region 45 .

In the photoelectric conversion region 45, the electrons below the Fermi level in the valence band 49 absorb the energy hv of the incident infrared light 52, and the energy hν of the incident infrared light 52 is absorbed from below the Fermi level to between the Fermi level Ef and the valence band edge Ev. transitions to a vacant level 53, forming hot electrons 54 and hot holes 55. These hot electrons 54 and hot holes 55 move in any direction with almost equal probability of occurrence until recombining within the photoelectric conversion region 45, or the hot holes 55 reach the potential barrier region 46 while in motion. If it has a larger energy than the potential barrier φH, there is a probability that it will pass through the potential barrier region 46 and be injected into the carrier injection region 47. When the hot holes 55 are injected into the carrier injection region 47, the hot electrons 54 left behind in the photoelectric conversion region 45 and the hot holes 55 injected into the carrier injection region 47 become signal charges.

Even when the first conductivity type is n type and the second conductivity type is p type in FIG. 3(b), the operating principle of photoelectric conversion is as follows: the first conductivity type is p type and the second conductivity type is p type. is almost the same as in the case of n-type.

Since the photoelectric conversion region 57 is made of an n-type degenerate semiconductor, it is at the conduction band edge E in a non-degenerate state. The donor impurity level, which was localized in
There is an overlap. In this state, the Fermi level Er
enters the inside of the conduction band 63, so in this region, the space between the Fermi level Er and the conduction band edge E0 is occupied by electrons 65. The five carrier injection regions are made of an n-type non-degenerate semiconductor, and include a photoelectric conversion region 57 and a carrier injection region 59.
The potential barrier region 58 existing between the two is either an n-type semiconductor whose donor impurity concentration is lower than that of the carrier injection region 59, an intrinsic semiconductor, or at least a depletion layer extending from the junction interface with the photoelectric conversion region 57 under operating conditions. Since it is composed of a p-type semiconductor having an acceptor impurity concentration and thickness that is fully depleted by the depletion layer extending from the junction interface with the five carrier injection regions, the Fermi level E is Conduction band edge E.

In the potential barrier region 58, it exists closest to the valence band edge Ev among the three regions made of semiconductor. Therefore, a potential barrier that becomes an obstacle to electrons in the conduction band 63 is formed near the junction interface between the potential barrier region 58 and the other three regions 57 and 59 with the potential barrier region 58. In particular, the photoelectric conversion region 57
The potential barrier for electrons in the conduction band 63 at is φ. It is.

Infrared light 64 (1) incident from the carrier injection region 59 side
ν E8) is the carrier injection region 5 as in the above case.
The light is transmitted through the potential barrier region 58 without being absorbed, and enters the photoelectric conversion region 57 .

The photoelectric conversion region 57 has a Fermi level E in the conduction band 63.
r and the conduction band edge E. The electron 65 absorbs the energy l]v of the incident infrared light 64 and transits from below the Fermi level to an empty level above the Fermi level, forming hot electrons 66 and hot holes 67. As in the case described above, these hot potentials 66 and hot holes 67 move in the direction of recombination within the photoelectric conversion region 57 with almost equal probability of occurrence, or the hot electrons 66 are in motion. reaches the potential barrier region 58, or the potential barrier φ. If the carrier has a larger energy, there is a probability that the carrier passes through the potential barrier region 58 and is injected into the carrier injection region 59. When hot electrons 66 are injected into the five carrier injection regions, the photoelectric conversion region 57
Hot hole 67 and carrier injection region 5 left behind
The hot electrons 66 injected into the cell 9 become signal charges.

Because of the operating principle described above, the cutoff wavelength of the infrared sensor is the potential barrier φ1. Or φ. These potential barriers are determined by the conductivity type of the potential barrier region.

By controlling the thickness of the potential barrier region, the balance of impurity concentrations in the three semiconductor regions, and the bias conditions, it is possible to set the potential barrier to any value between zero and the energy equivalent to the diffusion potential of the pn junction. can. Therefore, the infrared sensor has an extremely large degree of freedom in setting the cutoff wavelength.

Furthermore, due to the low potential barrier, at room temperature,
When there are many carriers that can cross the potential barrier region due to thermal excitation and the dark current is accordingly large, the infrared sensor is used while being cooled.

[Problem to be solved by the invention]

In general, one of the major challenges for sensors, including the above-mentioned infrared sensors, is to increase their sensitivity.

Furthermore, optical sensors are often driven in an accumulation mode that allows for high sensitivity. In this mode, the optical sensor is set to a certain bias state and then floated, and the optical signal charge generated for a certain period of time is stored and then output. During charge accumulation, the bias state of the optical sensor changes moment by moment. The conventional infrared sensor described above has a bias voltage dependence on the cutoff wavelength, so when operated in this accumulation mode, the cutoff wavelength changes during charge accumulation, which is a drawback.

Similar to the infrared sensor described above, the purpose of the present invention is to be able to set the cutoff wavelength arbitrarily, and to have higher sensitivity.
Despite the bias voltage dependence of the cutoff wavelength,
The object of the present invention is to provide an infrared ray sensor whose cutoff wavelength does not change during charge accumulation even when the storage mode operation described above is performed.

[Means to solve the problem]

In order to solve the above-mentioned problems, the infrared sensor of the present invention includes a first photoelectric conversion region made of metal, and a second photoelectric conversion region made of a degenerate semiconductor of a first conductivity type and in ohmic contact with the first photoelectric conversion region. , a carrier injection region made of a first conductivity type semiconductor having a lower impurity concentration than the second photoelectric conversion region;
Carrier injection 0 The second photoelectric conversion region and carrier injection are made of a first conductivity type semiconductor with a lower impurity concentration than the region, an intrinsic semiconductor, or a second conductivity type semiconductor that is fully depleted under at least operating conditions. and a potential barrier region existing between the first photoelectric conversion region/second photoelectric conversion region/
A light-receiving element that has a stacked structure of a potential barrier region/carrier injection region, and also constitutes a homojunction structure such as a second photoelectric conversion region, a potential barrier region, and a carrier injection region, and a charge storage that stores optical signal charges generated in this light-receiving element. It is equipped with an element.

[Effect]

The operating principle of photoelectric conversion in the light receiving element included in the infrared sensor of the present invention will be explained using FIGS. 2(a> and 2(b)).

Figure 2 (a) shows a case where the first conductivity type is p type and the second conductivity type or n type, and conversely, in figure (1)), the first conductivity type is n type and the second conductivity type is p type. The energy band structure and photoelectric conversion mechanism in this case are shown. Although infrared light is incident from the semiconductor side, it may also be incident from the insulator 23, 36 side.

First, a case will be described in which the first conductivity type is p type and the second conductivity type is n type in FIG. 2(a, ).

Like the photoelectric conversion region 45 in FIG. 3(a), the second photoelectric conversion region 20 is made of a p-type degenerate semiconductor, so that in a non-degenerate state, acceptor impurities localized near the valence band edge EV The level loses its locality and spreads out,
It overlaps with the valence band 24. In this state, the Fermi level Er enters the valence band 24, so in the region 20, an empty level 28 exists between the Fermi level Ef and the valence band edge EV. At the contact interface with the first photoelectric conversion region made of metal] 9, bending of the energy band occurs due to the difference between the work function of the metal and the work function of the semiconductor, but the second photoelectric conversion region 20 degenerates. Therefore, even if a metal and a semiconductor are combined to form a potential barrier, the curved region of the energy band is extremely thin and the barrier's center point is lowered, making it virtually impossible for the ball, which is the majority carrier, to It becomes an existence that can be ignored. Therefore, there is one first photoelectric conversion area and one second photoelectric conversion area.
Ohmic contact is always formed with the photoelectric conversion region 20. Note that one first photoelectric conversion area and one second photoelectric conversion area 20
The bending of the energy band at the contact interface can be ignored, regardless of whether the bending is toward the higher potential side or the lower potential side. It is omitted.

The carrier injection region 22 and the potential barrier region 21 existing between the second photoelectric conversion region 20 and the carrier injection region 22 are also similar to the carrier injection region 47 and the potential barrier region 46 in FIG. 3(a), respectively. A potential barrier that becomes an obstacle to holes in the valence band 24 is formed near the junction interface between the potential barrier region 21 and the other three regions 20 and 22 made of semiconductor. In particular, the potential barrier for holes in the valence band 24 in the second photoelectric conversion region 20 is φ□.

When light is incident from the carrier injection region 22 side, as in the case of conventional infrared sensors, light with energy greater than the forbidden band width Eg is mostly absorbed near the incident surface within the semiconductor. However, light with an energy smaller than the forbidden band width Eg (such light is usually infrared light) is transmitted through the carrier injection region 22 and the potential barrier region 21 without being absorbed, and is not absorbed in the second photoelectric conversion. The light is incident on the region 20.

In the second photoelectric conversion region 20, the electrons below the Fermi level in the valence band 24 absorb the energy hv of the incident infrared light 27, and from below the Fermi level to the Fermi level Er and the valence band edge Ev. The hot electron 2 transitions to the vacant level 28 between
9a and hot pole 30a are formed. In addition, in the second photoelectric conversion region 20, the infrared light 27 that could not be completely absorbed is
is incident on the first photoelectric conversion region 19.

In one first photoelectric conversion region, electrons filling below the Fermi level Ef absorb the energy q-hν of the incident infrared light 27 and transition from below the Fermi level to an empty level above the Fermi 3 4 level. hot electrons 29b and hot holes 30b are formed.

Since there is no obstacle to hot holes at the contact interface between one first photoelectric conversion region and the second photoelectric conversion region 20, the hot holes generated in the first photoelectric conversion region ]9 and the second photoelectric conversion region 20 are 19.20, and these regions 1.9 until recombined with Hola 1 and electrons.
．． Since the transition probability of one electron in the first photoelectric conversion region 20 is higher than that in the second photoelectric conversion region 20,
From the first photoelectric conversion region 19 to the second There is a strong tendency to move to the photoelectric conversion region 20. On the other hand, regarding hot electrons, the second photoelectric conversion region 20
What occurs in the empty level 28 of the second photoelectric conversion region 20
and the first photoelectric conversion region 19, but the first
The situation is different if the problem occurs in one photoelectric conversion region. In the first photoelectric conversion region] 9, hot electrons at a level less excited than the valence band edge Ev in the second photoelectric conversion region 20 or at a lower level are similar to those generated in the second photoelectric conversion region 20,
Regarding hot electrons whose excited level is higher than the valence band edge Ev, whether they can go back and forth between the first photoelectric conversion region] and the vacant level 28 of the second photoelectric conversion region 20, the forbidden band 25 or an obstacle. Therefore, it is impossible to move to the second photoelectric conversion area 20. Therefore, even though the first photoelectric conversion region 19 has a higher electron concentration in the hole 1 than the second photoelectric conversion region 20, the electrons in the hole 1 tend to be trapped in the first photoelectric conversion region 19. That is, the first
One photoelectric conversion region becomes a good source of hot holes by forming a junction with the second photoelectric conversion region 20 made of an n-type degenerate semiconductor.

The hot pole generated in the first photoelectric conversion region] 9 and the second photoelectric conversion region 20, or the potential barrier region 2 during movement.
1 and has a larger energy than the potential barrier φ11, there is a probability that the carrier will pass through the potential barrier region 21 and be injected into the carrier injection region 22. When hot holes are injected into the carrier injection region 22, the hot electrons left behind in the first photoelectric conversion region 19 and the second photoelectric conversion region 20 and the carrier injection region 2
The hot poles injected into 2 become signal charges.

Even in the case where the first conductivity type is n type and the second conductivity type or p type in Figure 2(b), the operating principle of photoelectric conversion is as follows: the first conductivity type is p type and the second conductivity type is p type. is almost the same as in the case of n-type.

Like the photoelectric conversion region 57 in FIG. 3(1), the second photoelectric conversion region 33 is made of an n-type degenerate semiconductor, so it is at the conduction band edge E in a non-degenerate state.

The donor impurity level, which was localized nearby, loses its locality and spreads out, overlapping with the three conduction bands. In this state, the Fermi level E enters into the conduction band 39, so in the region 33, the space between the Fermi level Er and the conduction band edge Ec is occupied by electrons 41. Due to the difference between the work function of a metal and the work function of a semiconductor, a region with a curved energy band that occurs at the contact interface with the first photoelectric conversion region 32 made of metal has a first conductivity type of p type and a second conductivity type.
For the same reason as when the conductivity type is n-type, the majority carrier
It becomes a virtually negligible existence for electrons. Therefore, the first photoelectric conversion region 2 and the second photoelectric conversion region 33 form ohmic contact. Note that, similar to FIG. 2(a), also in FIG. 2(l), the bending of the energy band at the contact interface between the first photoelectric conversion region 32 and the second photoelectric conversion region 33 is omitted.

The carrier injection region 35 and the potential barrier region 34 existing between the second photoelectric conversion region 33 and the carrier injection region 35 are also similar to the carrier injection region 59 and the potential barrier region 58 in FIG. 3(b), respectively. In the vicinity of the junction interface between the potential barrier region 34 and the other three regions 33 and 35 made of semiconductor, a potential barrier is formed that becomes an obstacle to electrons in the three conduction bands. In particular, the second photoelectric conversion region 3
The potential barrier for electrons in the conduction band 39 at 7 8 at 3 is φ.

Infrared light 40 (hν
<Eg) is the carrier injection region 35 as in the above case.
The light is transmitted through the potential barrier region 34 with almost no absorption, and enters the second photoelectric conversion region 33 .

The second photoelectric conversion region 33 includes the Fermi level Ef and the conduction band edge E among the three conduction bands. The electron 41 between the
a and a hot hole 43a is formed. Further, the infrared light 40 that has not been completely absorbed in the second photoelectric conversion region 33 enters the first photoelectric conversion region 32 .

As described above, in the first photoelectric conversion region 32, electrons satisfying the Fermi level Er or the energy 1 of the incident infrared light 40
] ν and transitions from below the Fermi level to an empty level above the Fermi level, forming a hot electron 42b and a pothole 43b.
form.

Since there is no obstacle to hot electrons at the contact interface between the first photoelectric conversion region 32 and the second photoelectric conversion region 33, the hot electrons generated in the first photoelectric conversion region 32 and the second photoelectric conversion region 33 pass between these regions 3233. They can freely come and go and move in these regions 32 and 33 until recombining with hot holes, but since the transition probability of electrons in the first photoelectric conversion region 32 is higher than that in the second photoelectric conversion region 33, From the first photoelectric conversion region 32 to the second photoelectric conversion region 32, the hot electron concentration is higher in the conversion region 32, and the hot electron concentrations in the first photoelectric conversion region 32 and the second photoelectric conversion region 33 are approximately the same.
There is a strong tendency to move to the photoelectric conversion region 33. On the other hand, regarding the pot poles, those generated in the second photoelectric conversion region 33 are located between the Fermi level Ef and the conduction band edge E occupied by the electrons 41 in the second photoelectric conversion region 33. Although the particles go back and forth between the area between them and the first photoelectric conversion area 32, the situation is different for those generated in the first photoelectric conversion area 32. ] conduction band edge E in the second photoelectric conversion region 33 in the photoelectric conversion region 32; Hot holes generated by the excitation of electrons at a higher level occupy the electrons 41 in the first photoelectric conversion region 32 and the second photoelectric conversion region 33, similar to those generated in the second photoelectric conversion region 33. The Fermi level Ef~
Conduction band edge E. However, since the forbidden band 38 becomes an obstacle for hot poles generated by excitation of electrons at a level lower than the conduction band edge Ec, the second photoelectric conversion region 33 cannot move to. Therefore, the first photoelectric conversion area 32 is smaller than the second photoelectric conversion area 33.
Even though the hot hole concentration is higher in the first photoelectric conversion region 32, the hot holes tend to be confined in the first photoelectric conversion region 32. That is, the first photoelectric conversion region 32 made of metal
forms a junction with the second photoelectric conversion region 33 made of an n-type degenerate semiconductor, thereby becoming a good source of hot electrons.

The hot electrons generated in the first photoelectric conversion region 32 and the second photoelectric conversion region 33 or the potential barrier region 34 during movement
reaches and has an energy greater than the potential barrier φ6, the potential barrier region 34
There is a probability that the carrier will pass through the carrier injection region 35 and be injected into the carrier injection region 35. When the pot electrons are injected into the carrier injection region 35, the hot holes left behind in the first photoelectric conversion region 32 and the second photoelectric conversion region 33 and the carrier injection region 35
The injected electrons become signal charges.

As described above, the light-receiving element of this external wire sensor, like the conventional sensor, controls the conductivity type of the potential barrier region, the thickness of the potential barrier region, the balance of impurity concentration in the three regions made of semiconductor, and the bias conditions. As a result, the cutoff wavelength is determined by the potential barrier φ□ or φ0, which can be set to any size between zero and the energy equivalent to the diffusion potential of the pn junction, and the degree of freedom in setting it is extremely large. At the same time, it is equipped with an efficient hot hole or hot electron supply mechanism that utilizes the energy band structure formed by contact between a metal with high infrared absorption rate and a p-type or n-type degenerate semiconductor. It is possible to provide higher infrared detection sensitivity than conventional sensors.

Furthermore, in the infrared sensor of the present invention, the above-mentioned light receiving element and the charge storage element that stores the generated optical signal charge are independent, so even if it is operated in the accumulation mode for high sensitivity, the light receiving element is Keep the bias state constant,
It is possible to make the cutoff wavelength unchanged.

Note that, like the conventional infrared sensor, the infrared sensor of the present invention is used after being cooled if the dark current is large at room temperature, perhaps due to the small potential barrier.

〔Example〕

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which (a) is a vertical cross-sectional structural diagram thereof, and (b) is a potential distribution diagram corresponding to the vertical cross-sectional structural diagram in (a).

This will be explained using (a). In this embodiment, Si is used as a semiconductor material, the first conductivity type is p type, the second conductivity type is n type, and it is a back-illuminated type in which infrared light is incident from the carrier injection region side.

The structure of the light receiving element 1 is as follows. In the light receiving element 1 portion of the n-type single-crystal Si substrate 3, a region that remains in the same state as when the substrate was manufactured is the carrier injection region 7. A first photoelectric conversion region 4 in the form of a thin film using silicide as a metal material is provided on the surface of the substrate. As a silicide,
Examples are platinum, palladium, nickel, and cobal. Each silicide of molybdenum, tanksten, titanium, chromium, iron, magnesium, yttrium, niobium, lithium, etc. can be used. Directly below this silicide,
A potential barrier region 6 is formed between the degenerate n-type second photoelectric conversion region 5 and the carrier injection region 7 in ohmic contact. The reason why silicide is used for the first photoelectric conversion region 4 is that it has the advantage of excellent stability of characteristics, but it is not absolutely necessary to use silicide. Even if it is replaced with another metal, there is no problem in the negative direction. Examples of other metals include Mo.

W, Ti, Pt, Cr, AI, Cu, Ni, Ag, Au
Single metals such as Al-8i, Al-3i-Cu,
An alloy such as Ti-Pt-Au Au-Ge-Ni can be used. Also, the potential ltl
Wall region 6 is p-type, which has a lower impurity concentration than carrier injection region 7, or is intrinsic, or at least n-type, which is fully depleted under operating conditions.

An n+ type guard link 8 is provided around the second photoelectric conversion region 5 and the potential barrier region 6 to alleviate electric field concentration. Second photoelectric conversion region 5 and n+ type guard link 8
A metal wiring 9 made of aluminum or the like is formed to surround the second photoelectric conversion region 5 so as to make ohmic contact with both. The metal wiring 9 and the n+ type guard link 8 form a short circuit mechanism that electrically connects the first photoelectric conversion region 4, the second photoelectric conversion region 5, and the potential barrier region 6. This short circuit mechanism has the following effects.

In the photodetector, when electron-hole pairs are generated in the potential barrier generating portion of the three semiconductor regions and in the vicinity thereof, as in this example, when the first conductivity type is p type (
The energy band structure is shown in Figure 2 (a). Electrons that have transitioned to the conduction band gather at the minimum potential part of the conduction band in the potential barrier region, and holes in the valence band that are generated in pairs with them form a second photoelectron. captured in the conversion region or carrier injection region. On the other hand, in the case of the first conductivity type or n-type (the energy band structure is shown in Figure 2(b)), conversely, the pole generated in the valence band due to electron transition is the maximum potential part of the potential barrier region ( For holes, electrons are collected at the minimum potential portion) and transferred to the conduction band, where they are captured in the second photoelectric conversion region or carrier injection region.

The cause of the generation of electron-hole pairs is that light with energy greater than the forbidden band width of the semiconductor material reaches the region.
In this region, thermal excitation of electrons in the valence band occurs. When free carriers accumulate in the potential barrier region, a potential change in the potential barrier region, that is, a fluctuation in the potential barrier height occurs. The first photoelectric conversion region and the second
The short circuit mechanism that electrically connects the photoelectric conversion 5 6 region and the potential barrier region serves to immediately remove free carriers that collect in the potential barrier region, thereby making the operation of the light receiving element more stable. Note that even if the present light-receiving element is not equipped with a short-circuiting mechanism, it does not essentially become inoperable for infrared detection, so it is also possible to construct one without such a mechanism. However, the performance will be degraded.

The element surface is covered with a 5i02 film]0, and its Si
A metal reflective film 11 made of aluminum or the like is provided on a portion of the 02 film 10 facing the first photoelectric conversion region 4 . Due to the presence of the metal reflective film 11, infrared light that has passed through even the first photoelectric conversion region 4 is reused.

If an anti-reflection film is provided on the incident surface of the infrared light [7] in the light-receiving element 1, that is, on the back surface, the light-receiving element 1 will have even higher sensitivity. Further, the present invention may be applied even if the light-receiving element 1 is a front-illuminated type that does not have the metal reflective film 11.

The charge storage element 2 is located opposite to the n+ type card link 8.
An n-type storage well 12 is formed across the part of the type single crystal Si substrate 3 that is the same as when the substrate was manufactured, and an accumulation well is formed from the part of the 13 type single crystal Si substrate 3 that is the same as when the substrate is manufactured, with Si02M10 in between. N stacking diameter 1 formed to cover 12
It is made up of 3.

Furthermore, an n+ type train region 4 for finally extracting signal charges is provided separating the part of the p-type tunic crystal S1 substrate 3 which is the same as when the substrate was fabricated, and connects the storage well 12 and the drain region 14. A transfer electrode 15 is provided for switching between the two. A metal wiring ] 6 is connected to the train region 14 .

The ticket outside line sensor operates as follows. In the water field external radiation sensor, the storage electrode 13 has a certain positive bias so that an appropriate bias is applied between the first photoelectric conversion region 4 and the second photoelectric conversion region 5 of the light receiving element 1 and the carrier injection region 7. It is set to potential VB. With this, the light receiving element 1 is as shown in Fig. 2 (
It is set as in a). A pulse signal Φ1 is applied to the transfer electrode 15 so that the area between the storage well 12 and the drain region 14 is in the OFF state when photoelectric conversion is performed in the storage mode, and the pulse signal Φ1 is in the ON state when the signal charge is read out. The potential distribution within the present infrared sensor at the stage of photoelectric conversion in the accumulation mode is as shown by the solid line in FIG. 1(b). By photoelectric conversion, the first
When carriers (electrons) 18, which are signal charges, are generated in the photoelectric conversion region 4 and the second photoelectric conversion region 5, the potentials of the first photoelectric conversion region 4 and the second photoelectric conversion region 5 increase as a result. Then, the carriers 18 flow into the storage well 2 through the metal wiring 9 with a lower potential, the n4 type guard link 8, and the inversion region of the n type single crystal Si substrate 3 under the storage electrode 13. Therefore, carriers 18 are not accumulated in the light receiving element 1 portion, and fluctuations in the bias potential can be avoided. After continuing this operation for a certain period of time, the storage well 12-drain region 1 is transferred to the transfer electrode]5.
A voltage is applied that turns on the voltage between 4 and 4. Then, the potential of the n-type single crystal Si substrate 3 under the transfer electrode 15 becomes as shown by the broken line, and the signal charges stored in the storage well 12 are read out to the outside.

With the above structure and operation, in the infrared sensor of the present invention, even in the accumulation mode, the bias state of the light receiving element is constant during charge accumulation, and the cutoff wavelength remains unchanged.

It should be noted that the infrared sensor of the present invention can of course be constructed by replacing p and n of the first conductivity type and second conductivity type in the above-mentioned embodiments, and in principle, it is possible to use a semiconductor material other than Si. is also possible. Furthermore, a monolithic or hybrid image sensor that combines the infrared sensor array of the present invention with an electronic scanning circuit can also be realized.

〔Effect of the invention〕

As explained above, according to the present invention, efficient hot hole or The two-power supply mechanism allows for higher infrared detection sensitivity than conventional infrared sensors, and also reduces the cutoff wavelength during charge accumulation when operating in the accumulation mode, which was the case with conventional infrared sensors. It is possible to provide an infrared sensor having an arbitrary cut-off wavelength longer than the wavelength corresponding to the forbidden band width of the semiconductor material, which eliminates the problem of change in the bandgap.

[Brief explanation of drawings]

FIG. 1(a) is a longitudinal cross-sectional structure diagram of an embodiment of the present invention, and FIG. 1(1) is a potential distribution diagram corresponding to the longitudinal cross-sectional structure diagram of FIG. 1(a). FIGS. 2(a) and 2(b) are explanatory diagrams of the energy band structure and photoelectric conversion mechanism of the light receiving element in the infrared sensor of the present invention, in which (a) the first conductivity type is p type and the second conductivity type is Diagram for n-type, (b) is the first
It is a figure when a conductivity type is an n type and a 2nd conductivity type is a p type. Figure 3 is an explanatory diagram of the energy structure and photoelectric conversion mechanism in a conventional infrared sensor. conductivity type is n
FIG. ]... Light receiving element, 2... Charge storage element, 3... P-type wheel crystal Si substrate, 4, 19.32... First photoelectric conversion region, 5, 20.33... Second photoelectric conversion Area, 621.3
4, 46.58 Potential barrier region, 7... Carrier injection region (p-type wheel crystal Si substrate), 8... Card link (n+ type), 91.6... Metal wiring, 10... 5i
02 film, 11...Metal reflective film, 12...Storage well (n type), ]3...Storage electrode, 14...Train region (n+ type), ]5...Transfer electrode, 1.7 ,27.40,
52.64...Infrared light, 18...Carrier (electron)
, 22. :35 4.759...Carrier injection region,
2B, 36, 4.860...Insulator, 24. /1.9
...Valence band, 2538...Forbidden band, 26,39.6
3. Conduction band, 28.53-empty level, 29a, 29b, 4
2a. 4, 2 b, 54, 66・Hot electron, 30
a, 30b, 43a, 43b, 55
, 67-Hot Ball, 4. ],,65...electron,
45.57...Photoelectric conversion area. 3

Claims (1)

[Claims] A first photoelectric conversion region made of a metal, a second photoelectric conversion region made of a degenerate semiconductor of a first conductivity type and in ohmic contact with the first photoelectric conversion region, and a first conductivity type semiconductor having a lower impurity concentration than the second photoelectric conversion region. a carrier injection region consisting of;
Between the second photoelectric conversion region and the carrier injection region, it is made of a first conductivity type semiconductor having a lower impurity concentration than the carrier injection region, an intrinsic semiconductor, or a second conductivity type semiconductor that is fully depleted under at least operating conditions. It has a layered structure of a first photoelectric conversion region/second photoelectric conversion region/potential barrier region/carrier injection region, and further includes a potential barrier region existing in the second photoelectric conversion region, a potential barrier region, and a carrier injection region. 1. An infrared sensor comprising: a light receiving element having a homojunction structure; and a charge storage element storing optical signal charges generated in the light receiving element.