JP2020178048A - Photodetector and photodetection device - Google Patents

Abstract

To provide a photodetector or the like having two wavelengths and one element capable of simultaneous reading, which is easy to be manufactured when applied to an imaging element and does not require arithmetic processing for subtracting a current value.SOLUTION: A photodetector 903 includes a first light receiving layer 13 in which the cutoff wavelength which is the upper limit of a detectable light wavelength is a first wavelength, a second light receiving layer 14 in which the cutoff wavelength is a second wavelength, and an electron barrier layer 15 that significantly hinders the movement of electrons between the first light receiving layer 13 and the second light receiving layer 14 compared to the movement of holes between the first light receiving layer 13 and the second light receiving layer 14.SELECTED DRAWING: Figure 3

Description

The present invention relates to a device that detects light.

A type 2 superlattice (T2SL, Type 2 Superlattice) has a structure in which, for example, several hundred pairs of first semiconductor layers and second semiconductor layers, which are thin film layers of two semiconductors having different compositions, are laminated. Here, in T2SL, the band arrangement of the two semiconductor layers is a staggered arrangement. In the staggered arrangement, the energy at the lower end of the conduction band of the second semiconductor layer is higher than the upper end of the valence band of the first semiconductor layer and lower than the lower end of the conduction band of the first semiconductor layer. Further, in the staggered arrangement, the energy at the upper end of the valence band of the second semiconductor layer is lower than that of the upper end of the valence band of the first semiconductor layer. Here, the first semiconductor layer is a semiconductor layer farther from the semiconductor substrate.

Thereby, the difference in energy level between the electron miniband and the hole miniband can be made smaller than the band gaps of the first semiconductor layer and the second semiconductor layer constituting the superlattice. Hereinafter, the "energy level" is referred to as "EL". Here, the electron miniband is the EL of the electron in the superlattice. Hereinafter, the "energy level" is referred to as "EL". The hole mini-band is the EL of holes in the superlattice. The T2SL infrared detector detects infrared rays by utilizing the photoexcitation of electron-hole pairs between the electron mini-band and the hole mini-band. The T2SL infrared detector can detect infrared rays having a wavelength smaller than the band gaps of the first semiconductor layer and the second semiconductor layer, respectively. The cutoff wavelength of the T2SL photodetector is determined by the EL difference between the mini bands. Here, the cutoff wavelength is the upper limit of the wavelength of light that can be converted into a detection current by the photodetector. The cutoff wavelength can be freely adjusted from the wavelength of short wavelength infrared rays to the wavelength of long wavelength infrared rays depending on the composition and film thickness of the first semiconductor layer and the second semiconductor layer.

Considering the application of the infrared detector to an imager, it is desirable to be able to acquire not only a single wavelength image but also a multi-wavelength image. For example, assume the use of a night-vision camera. When an infrared detector that detects short-wavelength infrared rays is used, visibility can be ensured without being blocked by rain or fog. On the other hand, when an infrared detector that detects long-wavelength infrared rays is used, the heat of humans and animals can be captured without a light source. As a result, if the infrared detector can detect both short-wavelength infrared rays and long-wavelength infrared rays, the image information of the detected light of each wavelength is fused to obtain an image that cannot be obtained by only one of the wavelengths. can do.

Non-Patent Documents 1 to 3 are detectors that detect light in two or more wavelength bands with one element by stacking two or more T2SL light receiving layers capable of detecting light in different wavelength bands (hereinafter, "two wavelengths"). One element detector ”) is disclosed.

FIG. 1 is a conceptual cross-sectional view showing the configuration of a photodetector 901, which is an example of a general two-wavelength one-element detector disclosed in Non-Patent Documents 1 and 2. The photodetector 901 includes contact layers 11 and 12, an electron barrier layer 21, and light receiving layers 13 and 14. Each of the light receiving layers 13 and 14 is a T2SL light receiving layer having different cutoff wavelengths from each other.

The photodetector 901 sequentially reads out which of the light receiving layers 13 and 14 reads out the light detection signal by switching the direction of the bias voltage applied between the contact layer 11 and the contact layer 12. It is a type. Therefore, the photodetector 901 cannot simultaneously read the light detection signal by the light receiving layer 13 and the light detection signal by the light receiving layer 14. Therefore, the photodetector 901 has a problem that the frame rate when generating image information is less than half that of the case where the photodetector capable of detecting only light in one wavelength band is used.

FIG. 2 is a conceptual cross-sectional view showing the configuration of a photodetector 902, which is an example of a simultaneous readout type two-wavelength one-element detector disclosed in Non-Patent Document 3. The photodetector 902 includes contact layers 11 and 12, light receiving layers 13 and 14, contact layers 23, and electrodes 16 to 18. Each of the light receiving layer 13 and the light receiving layer 14 is a light receiving layer of T2SL having different cutoff wavelengths from each other.

As a method of forming one pixel of a two-wavelength one-element detector by a photodetector signal by a photodetector 902, first, one electrode 16 to 18 is independently provided for each pixel. In this method, the light detection current from the light receiving layer 13 is taken out by the electrode 16, and the light detection current from the light receiving layer 14 is taken out by the electrode 17, so that the optical signals in the two wavelength bands are simultaneously read out. In that case, the holes generated by the light receiving layer 13 and the light receiving layer 14 are taken out from the electrode 18.

However, in the first method, three electrodes 16 to 17 are required for each pixel, and it is necessary to prevent the wiring provided between each electrode and the readout circuit from electrically contacting other electrodes or wiring. There is. Therefore, in this method, the difficulty of the element manufacturing process becomes high, and the area of pixels increases due to the increase in the area of electrodes and wiring. Further, in the first method, it is necessary to join the readout circuit via electrodes 16 to 18 having different heights for each pixel. Therefore, the joining technique is also difficult as compared with the one-wavelength one-element detector.

Therefore, the following method can be considered as a second method of forming one pixel of the two-wavelength one-element detector by the light detection signal by the photodetector 902. The second method is a method in which the electrodes 16 and 18 are independently provided for each pixel, but the electrodes 17 are common to all pixels. The photoelectrons generated in the light receiving layer 13 are acquired as a current at the electrode 16 as in the first method. Further, the photoelectrons generated in the light receiving layer 14 are recovered as an electric current in the electrode 17. However, since the electrode 17 is common to all pixels, the value of the photocurrent generated by one pixel cannot be detected from the current value. On the other hand, the holes generated by the light receiving layer 13 and the light receiving layer 14 are both acquired from the electrode 18.

In the T2SL light receiving layer, electron-hole pairs are generated by receiving infrared rays. That is, in the T2SL light receiving layer, one electron and one hole are generated for each photon. Therefore, from the current value obtained from the electrode 18 representing the number of holes generated in the light receiving layers 13 and 14 per unit time, from the electrode 16 representing the number of electrons generated in the light receiving layer 13 per unit time. Subtract the acquired current value. As a result, the current value due to the electrons generated in the light receiving layer 14 can be estimated.

In this way, in the second method, first, the detection current by the light receiving layer 13 and the detection current by the light receiving layer 14 can be measured at the same time. On top of that, the second method is easier to manufacture when applied to an imaging device than the first method.

A. M. Hoang et al. , Apple. Phys. Lett. , 102, 011108 (2013). A. Haddi et al. , Apple. Phys. Lett. , 106, 011104 (2015). M. Munzberg et al. , Proc. SPIE 6206, 62060Y (2006). H. S. Kim et al. , Applied Phys. Lett. , 92, 183502 (2008).

However, in the second method described in the background art section, the number of holes per unit time obtained from the electrode 18 is twice the number of electrons per unit time obtained from the electrode 16. Here, for the sake of clarity, it is assumed that the number of photons in the wavelength band of the light receiving layer 13 and the number of photons in the wavelength band of the light receiving layer 14 that are incident per unit time are substantially equal. As a result, the capacitance of the capacitor of the readout circuit connected to the electrode 18 required to stock the holes acquired within a certain time is the capacitor of the readout circuit connected to the electrode 16 in the case of one element and one pixel. It requires about twice the capacity. Therefore, the technical difficulty of manufacturing the read circuit increases. Further, in the second method, it is necessary to implement the arithmetic processing for subtracting the current value in the reading circuit or the circuit in the subsequent stage as described above.

An object of the present invention is to provide a photodetector having two wavelengths and one element, which has a simple manufacturing process when applied to an imaging element and can be simultaneously read out without the need for arithmetic processing for subtracting a current value.

The photodetector of the present invention includes a first light receiving layer having a cutoff wavelength of the first wavelength, which is the upper limit of the wavelength of light that can be detected, a second light receiving layer having the cutoff wavelength of the second wavelength, and the above. The first light receiving layer and the second light receiving layer of electrons are compared with the movement of holes between the first light receiving layer and the second light receiving layer. It comprises an electron barrier layer, which significantly hinders movement to and from the light receiving layer.

The photodetector or the like of the present invention is a two-wavelength one-element device capable of simultaneous reading, and when applied to an imaging element, the manufacturing process is easy and no arithmetic processing for subtracting the current value is required.

It is sectional drawing which shows the structural example (the 1) of the general two-wavelength one-element detector. It is sectional drawing which shows the structural example (the 2) of the general 2 wavelength 1 element detector. It is a conceptual diagram which shows the structural example of the photodetector of this embodiment. It is a conceptual diagram which shows the composition example of each layer provided with the photodetector of this embodiment, and the electron | hole mini-band thereof. It is a conceptual diagram which shows the change in the film thickness direction of EL of each layer of a photodetector. It is a conceptual diagram (the 1) which shows the example of the generation process of the layer structure of a photodetector. It is a conceptual diagram (No. 2) which shows the example of the generation process of the layer structure of a photodetector. It is a conceptual diagram which shows the structural example of the photodetector of this embodiment. It is a conceptual diagram which shows the minimum structure of the photodetector of embodiment.

The structure and manufacturing method of the two-wavelength one-element detector of the present embodiment will be described with reference to the drawings. In each of the drawings below, the same elements shall be represented in common by the same reference numerals, and duplicate description will be omitted unless otherwise specified.
[Configuration and operation]
FIG. 3 is a conceptual diagram showing the configuration of a photodetector 903, which is an example of the photodetector of the present embodiment. The photodetector 903 is a simultaneous readout type (simultaneous readout possible) two-wavelength one-element detector described in the background art section. The light detected by the photodetector 903 is, for example, infrared rays.

The photodetector 903 includes contact layers 11, 12 and 22, light receiving layers 13 and 14, an electron barrier layer 15, and electrodes 16, 17 and 19.

Each of the light receiving layer 13 and the light receiving layer 14 is a light receiving layer of T2SL having different cutoff wavelengths from each other. TSSL is described in the Background Techniques section. Configuration examples of the light receiving layers 13 and 14 are shown in FIG.

The electron barrier layer 15 is a layer that significantly hinders the movement of electrons from the light receiving layer 13 to the light receiving layer 14. The electron barrier layer 15 either does not hinder the movement of holes between the light receiving layer 13 and the light receiving layer 14, or does not hinder the movement of holes to a lesser extent. A configuration example of the electron barrier layer 15 is shown in FIG.

The contact layers 11 and 22 are n-type semiconductor layers. The contact layer 12 is a p-type semiconductor layer.

Each of the electrodes 16, 17 and 19 is ohmically connected to the contact layer in contact.

FIG. 4 is a conceptual diagram showing a configuration example of each layer included in the photodetector 903 shown in FIG. 3 and a mini band which is an EL of electrons and holes thereof. FIG. 4A shows the configuration of each layer of the photodetector 903. Further, FIG. 4B shows a mini-band of electrons and holes in each layer.

The upper side of each rectangle shown in FIG. 4B represents the EL at the lower end of the conduction band when each layer is a single layer, and the lower side represents the EL at the upper end of the valence band.

The photodetector 903 is a two-wavelength, one-element detector described in the background art section. The light receiving layers 13 and 14, the electron barrier layer 15, and the contact layers 11 and 12 are provided. The EL for the contact layers 11 and 12 is not shown in FIG. 4 (b).

Each of the light receiving layers 13 and 14 is a T2SL described in the background art section, both having different wavelength bands of detectable light.

The light receiving layer 13 has a superlattice structure in which the semiconductor layer 131 and the semiconductor layer 132 are sequentially stacked. The EL (electron mini-band) of the conduction band in the single layer when the semiconductor layer 131 is not superlattice as shown in FIG. 4A is EL941, and the EL of the valence band is EL951. Further, the EL of the conduction band in the single layer when the semiconductor layer 132 is not formed into a superlattice as shown in FIG. 4A is EL942, and the EL (hole miniband) of the valence band is EL952. As described above, the electron EL of the superlattice light receiving layer 13 as shown in FIG. 4A is EL94, and the hole EL is EL95.

The electron barrier layer 15 has a superlattice structure in which a semiconductor layer 151 and a semiconductor layer 152 are sequentially stacked. The electron barrier layer 15 is a type 1 superlattice (T1SL). The T1SL has a structure in which hundreds of pairs of a first semiconductor layer and a second semiconductor layer, which are thin film layers of two semiconductors having different compositions, are laminated. In T1SL, the band arrangement of the two semiconductor layers has a lower EL at the lower end of the conduction band of the second semiconductor layer than the lower end of the conduction band of the first semiconductor layer, and the second semiconductor is lower than the upper end of the valence band of the first semiconductor layer. It is a superlattice with a high EL at the lower end of the conduction band of the layer. Here, the first semiconductor layer is a semiconductor layer farther from the substrate.

The EL of the conduction band is EL981 and the EL of the valence band is EL991 in the single layer of the semiconductor layer 151 when the superlattice is not formed as shown in FIG. 4A. Further, in the semiconductor layer 152, the EL of the conduction band is EL982, and the EL of the valence band is EL992. As described above, when the superlattice is formed as shown in FIG. 4A, the EL of the electron is EL98 and the EL of the hole is EL99.

The light receiving layer 14 has a superlattice structure in which the semiconductor layer 141 and the semiconductor layer 142 are sequentially stacked. The EL (electron mini-band) of the conduction band in the single layer in the case of not forming a superlattice as shown in FIG. 4A of the semiconductor layer 141 is EL961, and the EL of the valence band is EL971. Further, the EL of the conduction band in the single layer when the semiconductor layer 142 is not formed into a superlattice as shown in FIG. 4A is EL962, and the EL (hole miniband) of the valence band is EL972. As described above, the electron EL of the superlattice light receiving layer 14 as shown in FIG. 4A is EL96, and the hole EL is EL97.

The characteristic feature of the configuration shown in FIG. 4 is that the EL95 of the holes in the light receiving layer 13 is equal to the EL99 of the holes in the electron barrier layer 15.

Next, the operation when the configuration shown in FIG. 4A is applied to the photodetector 903 shown in FIG. 3 and the light receiving layers 13 and 14 detect the light will be described. At that time, between the electrode 19 (that is, the upper surface of the light receiving layer 14) and the electrode 16 (that is, the contact layer 11) and between the electrode 19 (that is, the upper surface of the light receiving layer 14) and the electrode 17, that is, the contact layer. A bias voltage is applied to each of 11). The bias voltage is such that the electrode 16 has a positive voltage with respect to the electrode 19 and the electrode 19 has a positive voltage with respect to the electrode 17.

FIG. 5 is a conceptual diagram showing a change in the EL film thickness direction of each layer of the photodetector 903 when the bias voltage is applied. In FIG. 5, for each of the contact layers 11, 12 and 22, the EL at the lower end of the conduction band (upper line in FIG. 5) and the EL at the upper end of the valence band (lower line in FIG. 5) are shown. Represent. On the other hand, for the light receiving layers 13 and 14 and the electron barrier layer 15, the EL of the electron mini band (upper line in FIG. 5) and the EL of the hole mini band (lower line in FIG. 5) are used as if they were the lower end of the conduction band. It is expressed as if it is the EL at the upper end of the valence band.

When the light receiving layer 13 absorbs light having a wavelength shorter than the cutoff wavelength, electrons 81 and holes 71 are generated in the respective mini bands in the light receiving layer 13. Further, when the light receiving layer 14 absorbs light having a wavelength shorter than the cutoff wavelength, electrons 82 and holes 72 are generated in the respective mini bands in the light receiving layer 14.

The electrons 81 generated in the light receiving layer 13 flow to the left due to the bias voltage described above, and flow into the contact layer 11. The electron 81 further moves in the contact layer 11 which is an n-type semiconductor layer.

On the other hand, there is a large difference between the EL of the electron mini band of the light receiving layer 14 and the EL of the electron mini band of the electron barrier layer 15. Therefore, this difference becomes a barrier, and the electrons 82 generated in the light receiving layer 14 do not flow from the light receiving layer 14 to the light receiving layer 13 (the probability of flowing is very small). Therefore, the current detected through the contact layer 11 and the electrode 16 shown in FIG. 2 is limited to the current caused by the electrons 81 generated in the light receiving layer 13. The current generated at this time to the current i _1.

On the other hand, the holes 71 generated in the light receiving layer 13 flow to the right and reach the electron barrier layer 15. Here, as described in the description of FIG. 4, the EL of the hole mini-band of the light receiving layer 13 and the EL of the hole mini-band of the electron barrier layer 15 are the same. Therefore, the holes 71 pass through the electron barrier layer 15 and reach the light receiving layer 14 without being hindered from moving at the interface between the light receiving layer 13 and the electron barrier layer 15.

Here, if the EL of the holes in the electron barrier layer 15 is lower than that in the light receiving layer 13 at the interface between the light receiving layer 13 and the electron barrier layer 15, the movement of the holes 71 to the right is relevant. It is hindered at the interface. On the other hand, if the electron barrier layer 15 has a higher hole EL than the light receiving layer 13 at the interface between the light receiving layer 13 and the electron barrier layer 15, the phonons when the holes 71 pass through the interface. Is released, and the release becomes a scattering factor for holes 71. Therefore, the movement of the holes 71 to the right is also hindered.

The hole mini-band (and the electron mini-band) in the electron barrier layer 15 rises toward the right due to the bias voltage described above. Therefore, the holes 71 move to the right in the electron barrier layer 15.

At the interface between the electron barrier layer 15 and the contact layer 22, the upper end of the valence band of the contact layer 22 is higher than the hole mini band. Therefore, the holes 71 flow into the contact layer 22. At this time, the holes 71 release phonons. The release becomes a scattering factor for holes 71. The scattering becomes an obstacle to the movement of the holes 71 to the right. However, since the hole mini-band in the electron barrier layer 15 rises toward the right due to the bias voltage described above, it is considered that the probability that the hole 71 returns to the light receiving layer 13 is small.

The EL of the hole miniband of the light receiving layer 14 is higher than the EL of the hole miniband of the contact layer 22. Therefore, the holes 71 flow into the light receiving layer 14.

Further, the EL at the valence band end of the contact layer 12 is larger than the EL of the hole mini band of the light receiving layer 14. Therefore, the holes 71 flow from the light receiving layer 14 into the contact layer 12. Then, it flows to the outside through the electrode 17 shown in FIG.

On the other hand, the electrons 82 generated in the light receiving layer 14 do not flow into the light receiving layer 13 due to the electron barrier layer 15. The electrons 82 flow from the electrode 19 shown in FIG. 3 to the outside through the contact layer 22 due to the bias voltage. The current generated at this time is defined as the current i ₂ . The current i ₂ is all the current caused by the electron 82.

On the other hand, the holes 72 generated in the light receiving layer 14 flow to the right and flow to the outside through the contact layer 12 and the electrode 17 in FIG.

According to the above, the current i _{1 of} FIG. 5 flowing from the electrode 16 of FIG. 3 to the outside is a current caused only by the electrons 81 generated in the light receiving layer 13, and the current i _{2 of} FIG. 5 flowing to the outside from the electrode 19 of FIG. Is a current caused only by the electrons 82 generated in the light receiving layer 14. Therefore, in the photodetector 903 of FIG. 3, the difference derivation process for deriving the current caused by the electrons generated only in each light receiving layer, which is necessary for the photodetector 902 shown in FIG. 2, is not required.

Next, a method of generating the photodetector 903 shown in FIGS. 3 and 4 will be described. As described above, the photodetector 903 is a photodetector in which the EL at the upper end of the hole mini-band becomes equal at the interface between the light receiving layer 13 and the electron barrier layer 15.

6 and 7 are conceptual diagrams showing an example of a layer structure generation process constituting the photodetector 903. Each layer constituting the photodetector 903 is formed by an organic metal vapor phase growth method, a molecular beam epitaxy (MBE) method, or a method similar thereto.

First, as shown in FIG. 6A, a substrate 41, which is a substrate for generating a photodetector 903, is prepared. The substrate 41 is an InP substrate.

Next, as shown in FIG. 6B, an InP buffer layer 42 is formed on the substrate 41. The thickness of the buffer layer 42 is, for example, about 500 nm.

Next, as shown in FIG. 6C, the contact layer 12 is formed on the buffer layer 42. The contact layer 12 is shown in FIGS. 3 to 5. The contact layer 12 is a P-type semiconductor layer in which a P-type dopant is added to InP. As the P-type dopant, for example, Zn or the like can be used. The thickness of the contact layer 12 is, for example, about 500 to 1000 nm.

Next, the light receiving layer 14 is formed on the contact layer 12 as shown in FIG. 6 (d). The light receiving layer 14 is the light receiving layer 14 shown in FIGS. 3 to 5. As shown in FIG. 4, the light receiving layer 14 is a T2SL semiconductor layer in which semiconductor layers 142 and semiconductor layers 141 are alternately superposed. As shown in FIG. 4, the semiconductor layer 142 is formed directly above the contact layer 12. The uppermost layer of the light receiving layer 14 is the semiconductor layer 142.

The number of times the set of the semiconductor layer 141 and the semiconductor layer 142 is laminated is about several hundred times. The film thickness of the light receiving layer 14 is, for example, 1 to 3 μm.

The semiconductor layer 141 is, for example, In _0.52 GaAs, but other materials may be added as long as the semiconductor layer 141 is lattice-matched with the upper layer and the lower layer thereof. Such a composition is described, for example, as In _(a) Ga _(1-a) As _(b) P _(1-b) . Here, a and b are the In ratio and the As ratio, respectively, and 0 ≦ a ≦ 1 and 0 ≦ b ≦ 1. In _(a) Ga _(1-a) As _(b) P _(1-b) includes the above-mentioned In _0.52 GaAs / GaAs _0.55 Sb.

The semiconductor layer 142 is, for example, GaAs _0.55 Sb, but other elements may be added as long as it is lattice-matched with the upper layer and the lower layer thereof. Such a composition is described, for example, as GaAs _(c) Sb _(d) P _(1-cd) . Here, c and d are the As ratio and the Sb ratio, respectively, and 0 ≦ c ≦ 1 and 0 ≦ d ≦ 1. GaAs _(c) Sb _(d) P _(1-c-d) includes the above-mentioned GaAs _0.55 Sb.

The uppermost layer of the light receiving layer 14 is the semiconductor layer 142 as described above.

Next, as shown in FIG. 6E, the contact layer 22 is formed on the light receiving layer 14. The contact layer 22 is shown in FIGS. 3 and 5. The contact layer 22 is, for example, an n-type semiconductor layer in which a dopant such as Si is added to GaAsSb. The film thickness of the contact layer 22 is, for example, about several hundred nm.

Next, as shown in FIG. 6 (f), the electron barrier layer 15 is formed on the contact layer 22. As shown in FIG. 4, the electron barrier layer 15 is a superlattice semiconductor layer in which semiconductor layers 151 and semiconductor layers 152 are alternately laminated. The semiconductor layer 152 is formed directly above the contact layer 22. The uppermost layer of the electron barrier layer 15 is a semiconductor layer 151 as shown in FIG.

The number of times the set of the semiconductor layers 151 and 152 is laminated in the electron barrier layer 15 is, for example, about 100 times. Also. The film thickness of the electron barrier layer 15 is, for example, about several hundred nm.

The semiconductor layer 151 is, for example, GaAs _0.55 Sb, but other elements may be mixed within the range of lattice matching with the InP substrate. Such a composition is described, for example, as In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) . Here, s, t, and u are In ratio, As ratio, and Sb ratio, respectively, and satisfy 0 ≦ s ≦ 1, 0 ≦ t ≦ 1, and 0 ≦ u ≦ 1. In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) comprises GaAsSb. In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) further comprises InP, InGaAs, InAsP, InSbP, GaSbP, InGaP. In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) further comprises InGaAsP, InGaSbP, InGaAsSb, InGaAsP, InGaAsSbP.

The semiconductor layer 152 is, for example, AlAs 0.55Sb, but other elements may be mixed within the range of lattice matching with the InP substrate. Such materials are described, for example, as Al _(v) In _(w) Ga _(1-v-w) As _(x) Sb _(y) P _(1-xy) . Here, v, w, x, and y are Al ratio, In ratio, As ratio, and Sb ratio, respectively, and 0 ≦ v ≦ 1, 0 ≦ w ≦ 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1. Fulfill. Al _(v) In _(w) Ga _(1-v-w) As _(x) Sb _(y) P _(1-xy) includes the above-mentioned AlAsSb.

Here, In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer and Al _(v) In _(w) Ga _(1-v-w) As _{(x ) )} The ratio of Group V elements does not necessarily have to be the same for the Sb _(y) P _(1-xy) layer. Here, the In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer is the semiconductor layer 151 of FIG. Further, the Al _(v) In _(w) Ga _(1-v-w) As _(x) Sb _(y) P _(1-xy) layer is the semiconductor layer 152.

However, it is more preferable to make them equal, that is, t: u = x: y. The reason is as explained below. When the ratios of Group V elements are equal, Al _(v) In _(w) Ga _{(1 )} after the In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer growth. _−V−w) As _(x) Sb _(y) P _(1-xy) layer is grown. Alternatively, after the Al _(v) In _(w) Ga _(1-v-w) As _(x) Sb _(y) P _(1-xy) layer growth, the In _(s) Ga _(1-s) As _{(t ) )} Sb _(u) P _(1-t-u) layer is grown. The above reason is that it is not necessary to change the flux of the group V elements (As, Sb, and P) in these cases. Here, the flux is the amount of deposit of the target material per unit time. For example, when these layers are grown by the MBE method, it is necessary to change the temperature of the raw material cell in order to change the flux. Then, in order to change the temperature of the raw material cell, it takes a considerable amount of time to reach the target temperature. Therefore, in the generation of a superlattice having a large number of laminations, a particularly large amount of time is required to change the temperature of the raw material cell. If the ratio of the group V elements is the same, it is not necessary to change the temperature of the cell, so that the time required for lamination can be shortened.

Here, the description will be continued by returning to the example of the electron barrier layer 15 in which the semiconductor layer 151 of FIG. 4 is GaAsSb and the semiconductor layer 152 is AlAsSb. The As ratio of GaAsSb of the electron barrier layer 15 may be any value as long as it is lattice-matched with the InP substrate, but the case where the As ratio of GaAsSb of the light receiving layer is 0.55 will be described below. To do.

The optimum value of the As ratio of AlAsSb is around 0.56, which is 5.8686 Å by linearly interpolating the lattice constant of AlAs (5.6605 Å) and the lattice constant of AlSb (6.1355 Å). In the following example, the case where the As ratio is also 0.55 will be described, but this is also not bound by this as long as the condition of lattice matching with the InP substrate is satisfied. The difference in the lattice constant of AlAs _0.55 Sb from the InP substrate is estimated to be about 0.1%, and it is considered that the most preferable condition among the lattice matching conditions is satisfied. Here, the condition for lattice matching in the present specification is that the difference between the lattice constant of the light receiving layer and the lattice constant of the INP substrate is 1% or less, more preferably 0.5% or less, and most preferably 0.2%. It shall be as follows.

Next, as shown in FIG. 7 (g), the light receiving layer 13 is formed on the electron barrier layer 15.
The light receiving layer 13 is the light receiving layer 13 shown in FIGS. 3 to 5. As shown in FIG. 4, the light receiving layer 13 is a superlattice semiconductor layer in which semiconductor layers 131 and semiconductor layers 132 are alternately superposed. As shown in FIG. 4, the semiconductor layer 131 is formed directly above the electron barrier layer 15. The uppermost layer of the light receiving layer 13 is the semiconductor layer 131. Further, the number of times the set of the semiconductor layer 131 and the semiconductor layer 132 is laminated is about several hundred times. The thickness of the light receiving layer 13 is about 1 to 3 μm.

The semiconductor layer 131 is, for example, In _(a) Ga _(1-a) As _(b) P _(1-b) . Here, a and b are the In ratio and the As ratio, respectively, and 0 ≦ a ≦ 1 and 0 ≦ b ≦ 1. In _(a) Ga _(1-a) As _(b) P _(1-b) includes In _0.52 GaAs / GaAs _0.55 Sb.

The semiconductor layer 132 is, for example, GaAs _(c) Sb _(d) P _(1-cd) . Here, c and d are the As ratio and the Sb ratio, respectively, and 0 ≦ c ≦ 1 and 0 ≦ d ≦ 1. GaAs _(c) Sb _(d) P _(1-cd) contains GaAs _0.55 Sb.

In the photodetector 101, as described above, the energy of the hole miniband of the light receiving layer 13 and the energy of the hole miniband of the electron barrier layer 15 are matched. An example of the method will be described below. Here, it is assumed that the semiconductor layer 131 shown in FIG. 4A of the light receiving layer 13 is InGaAs, and the semiconductor layer 132 is GaAsSb. Further, it is assumed that the semiconductor layer 151 of the electron barrier layer 15 is GaAsSb and the semiconductor layer 152 is AlAsSb.

As shown in FIG. 4B, the electron barrier layer 15 made of the AlAsSb / GaAsSb superlattice has an EL at the lower end of the electron miniband and an EL at the upper end of the hole miniband than the light receiving layer 13 made of the InGaAs / GaAsSb superlattice. There is a big difference with.

Here, it is assumed that the film thickness of the AlAsSb layer of the electron barrier layer 15 composed of the AlAsSb / GaAsSb superlattice is equal to the film thickness of the InGaAs layer of the light receiving layer 13 composed of the InGaAs / GaAsSb superlattice. Then, it is assumed that the film thickness of the GaAsSb layer of the electron barrier layer 15 is made equal to the film thickness of the GaAsSb layer of the light receiving layer 13. In that case, the EL of the hole mini-band of the electron barrier layer 15 is lower than the EL of the hole mini-band of the light receiving layer 13.

Therefore, among the AlAsSb / GaAsSb superlattices constituting the electron barrier layer 15, the film thickness of the AlAsSb layer is made equal to the film thickness of the InGaAs layer of the light receiving layer 13. Then, the thickness of the GaAsSb layer constituting the electron barrier layer 15 is made thicker than the film thickness of the GaAsSb layer of the light receiving layer 13.

When the film thickness of InGaAs of the light receiving layer 13 is 5 nm and the film thickness of GaAsSb is 5 nm, the film thickness of AlAsSb of the electron barrier layer 15 is 5 nm and the film thickness of GaAsSb is 5.284 nm. In that case, the simulation showed that the EL of the hole miniband of the light receiving layer 13 coincided with the EL of the hole miniband of the electron barrier layer 15.

Next, as shown in FIG. 7 (h), the contact layer 11 is formed on the light receiving layer 13. The contact layer 11 may be InP or another semiconductor (InGaAs or the like) that lattice-matches with InP. The film thickness of the contact layer 11 is, for example, about 500 nm to 1 μm.

The photodetector 903 shown in FIG. 3 undergoes a microfabrication process such as fabrication of a mesa structure by photolithography or wet etching and fabrication of an electrode structure by metal deposition and annealing on the semiconductor laminated structure in which the crystal is grown in this way. Is produced. To describe the fabrication of the electrode structure in a little more detail, the electrode 17 is formed on the contact layer 12, the electrode 19 is formed on the contact layer 22, and the electrode 16 is formed on the contact layer 11 so as to be ohmic contact.

Although not shown, when the configuration shown in FIG. 3 is applied to the sensor array, the electrodes 16 and 19 shown in FIG. 2 are manufactured for each pixel. On the other hand, the electrode 17 may be common to all the pixels of the sensor array. The reason is that the electrode 17 is for allowing holes to flow to the outside and is not related to the current detected by the first light receiving layer and the second light receiving layer.

Next, the manufactured photodetector 903 is flip-chip bonded to a readout circuit made of a silicon semiconductor to fabricate a photodetector array.

The above-mentioned process for manufacturing a photodetector array is a general process well known to those engaged in the art, and is disclosed in, for example, Non-Patent Document 4.

FIG. 8 is a conceptual diagram showing the configuration of a photodetector 500, which is an example of the photodetector of the present embodiment.

The photodetector 500 includes a photodetector 903, a voltage application device 501, and current detectors 511 and 512.

The photodetector 903 is shown in FIG. The light incident on the photodetector 903 enters the light receiving layer 13, passes through the light receiving layer 13, and also enters the light receiving layer 14.

The light receiving layer 13 generates electron-hole pairs according to the intensity of the incident light having a wavelength equal to or lower than the cutoff wavelength of the light receiving layer 13. Of these electrons, through the current detector 511 from the electrode 16 as a current _{i 1,} it flows to the ground. Current detecting device 511 measures the level of the current _{i 1.}

The light receiving layer 14 generates electron-hole pairs according to the intensity of light having a wavelength equal to or lower than the cutoff wavelength of the light receiving layer 14 and incident through the light receiving layer 13. Among them, the electrons flow from the electrode 19 to the ground via the current detection device 512 as the current i ₂ . The current detector 512 measures the level of the current i ₂ .
[effect]
In the photodetector of the present embodiment, an electron barrier layer is provided between the first light receiving layer and the second light receiving layer to suppress the conduction of electrons between them and to conduct holes. As a result, the current caused by the electrons generated in the first light receiving layer and the current caused by the electrons generated in the second light receiving layer are separately taken out so as not to be mixed, and their current values are obtained.

Therefore, the photodetector first makes it possible to simultaneously acquire the intensity of light detected by each light receiving layer. At the same time, the photodetector does not require a difference derivation process for deriving the current caused by the electrons generated in the first light receiving layer and the current value caused by the electrons generated only in each light receiving layer. The difference derivation process is necessary when the photodetector described in Patent Document 2 is used in which the current caused by the holes generated in the second light receiving layer is mixed with the current caused by the holes generated in the first light receiving layer. It will be.

Further, in the photodetector, the electrode in the lowermost layer (corresponding to the electrode 17 in FIG. 3) is for allowing holes to flow to the outside and is not related to the detection current by the first light receiving layer and the second light receiving layer. Therefore, in the photodetector, when applied to an image sensor, the electrodes of the lowermost layer can be shared. Therefore, the photodetector provides the same level of ease of manufacturing process as the second method of the background art.

That is, the photodetector has a simple manufacturing process when applied to an imaging element, and is a simultaneous readout type (simultaneous readout possible) two-wavelength, one-element light that does not require arithmetic processing to subtract the current value. It is a detector.

FIG. 9 is a conceptual diagram showing the configuration of the photodetector 903x, which is the minimum configuration of the photodetector of the embodiment.

The photodetector 903x includes a first light receiving layer 13x, a second light receiving layer 14x, and an electron barrier layer 15x.

The first light receiving layer 13x has a cutoff wavelength which is an upper limit of the wavelength of light that can be detected.

The cutoff wavelength of the second light receiving layer 14x is the second wavelength.

The electron barrier layer 15x is located between the first light receiving layer 13x and the second light receiving layer 14x, and the electron th-order is compared with the movement of holes between the first light receiving layer 13x and the second light receiving layer 14x. It significantly hinders the movement between the first light receiving layer 13x and the second light receiving layer 14x.

The electron barrier layer 15x has a significant movement of electrons between the first light receiving layer 13x and the second light receiving layer 14x as compared with the movement of holes between the first light receiving layer 13x and the second light receiving layer 14x. To hinder. Therefore, when a predetermined voltage is applied between the surface 851 and the surface 854, all the currents caused by the electrons generated by the first light receiving layer 13x are acquired from the surface 851 and generated by the second light receiving layer 14x. All currents due to the generated electrons are taken from surface 853.

Therefore, the photodetector 903x first makes it possible to simultaneously acquire the intensity of light detected by each light receiving layer. At the same time, the photodetector 903x does not require a difference derivation process for deriving the current caused by the electrons generated in the first light receiving layer 13x and the current value caused by the electrons generated only in the second light receiving layer 14x.

Therefore, the photodetector 903x is a part of the configuration of a simultaneous readout type (simultaneous readout possible) two-wavelength, one-element photodetector that does not require arithmetic processing to subtract the current value.

Further, assuming that the photodetector 903 is applied to an imaging element, the electrodes connected to the surface 854 can be shared by a plurality of pixels. The reason is that the electrode is not related to the detection of the current generated by the first light receiving layer 13x and the second light receiving layer 14x. Therefore, the photodetector 903 can be easily manufactured when applied to an imaging element.

Therefore, the photodetector 903x exhibits the effects described in the section [Effects of the Invention] according to the above configuration.

The photodetector 903x is, for example, the photodetector 903 shown in FIGS. 3 and 8. The first light receiving layer 13x is, for example, the light receiving layer 13 shown in FIGS. 3, 4, 5, and 7. The second light receiving layer 14x is, for example, the light receiving layer 14 shown in FIGS. 3, 4, 5, 6, and 7. The second light receiving layer 14x is, for example, the light receiving layer 14 shown in FIGS. 3, 4, 5, 6, and 7. The electron barrier layer 15x is, for example, the electron barrier layer 15 shown in FIGS. 3, 4, 5, 6, and 7.

Although each embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and further modifications, substitutions, and adjustments can be made without departing from the basic technical idea of the present invention. Can be added. For example, the composition of the elements shown in each drawing is an example for assisting the understanding of the present invention, and is not limited to the composition shown in these drawings.

In addition, a part or all of the above-described embodiment may be described as in the following appendix, but is not limited to the following.
(Appendix 1)
The first light receiving layer whose cutoff wavelength, which is the upper limit of the detectable light wavelength, is the first wavelength,
A second light receiving layer having a cutoff wavelength of the second wavelength,
The first light receiving layer and the first light receiving layer of electrons are compared with the movement of holes between the first light receiving layer and the second light receiving layer. (Ii) An electron barrier layer that significantly hinders movement between the light receiving layer and
A photodetector equipped with.
(Appendix 2)
Appendix 1 The electron barrier layer includes a barrier superlattice, which is a superlattice in which a set of a plurality of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated multiple times. The photodetector described in.
(Appendix 3)
The photodetector according to Appendix 2, wherein the barrier superlattice is a type 1 superlattice.
(Appendix 4)
The first light receiving layer includes a first superlattice in which a set of a plurality of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated a plurality of times, and the second light receiving layer is provided. It is described in Appendix 1 or Appendix 2, wherein the layer comprises a second superlattice in which a set of a plurality of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated multiple times. Light detector.
(Appendix 5)
The first light receiving layer includes a first superlattice in which a set of a plurality of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated a plurality of times. The photodetector according to 3.
(Appendix 6)
The photodetector according to Appendix 5, wherein the first superlattice is a type 2 superlattice.
(Appendix 7)
The second light receiving layer includes a second superlattice in which a set of a plurality of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated a plurality of times. The photodetector according to 6.
(Appendix 8)
The photodetector according to Appendix 7, wherein the second superlattice is a type 2 superlattice.
(Appendix 9)
The photodetector according to Appendix 7 or Appendix 8, wherein the second superlattice is formed on a semiconductor substrate.
(Appendix 10)
The second superlattice is formed on the InP substrate.
The barrier superlattice is an In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer and an Al _(v) In _(w) Ga _(1-v-w). As _(x) Sb _(y) P _(1-xy) superlattice consisting of layers (each of s, t, u, v, w, x, y is 0 or more and 1 or less), Appendix 7 or The photodetector according to Appendix 8.
(Appendix 11)
The In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer and the Al _(v) In _(w) Ga _(1-v-w) As _(x) Sb _{(y) The} photodetector according to Appendix 10, wherein at least one of the In ratio, the Ga ratio, the As ratio and the Sb ratio in the P _(1-xy) layer is equal.
(Appendix 12)
The photodetector according to Appendix 11, wherein the lattice constant mismatch between the barrier superlattice and the InP substrate is less than 1%.
(Appendix 13)
Each of the first superlattice and the second superlattice is an In _(a) Ga _(1-a) As _(b) P _(1-b) layer and a GaAs _(c) Sb _(d) P _{(1-c ). -D) The} photodetector according to any one of Supplementary notes 10 to 12, which is a superlattice composed of layers (each of a, b, c, and d is 0 or more and 1 or less).
(Appendix 14)
The composition of the In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer and the GaAs _(c) Sb _(d) P _(1-cd) layer The photodetector according to Appendix 13, which is the same.
(Appendix 15)
The photodetector according to any one of Appendix 10 to Appendix 14, wherein the first superlattice has a lower energy level of the hole miniband than the second superlattice.
(Appendix 16)
The photodetector according to Appendix 15, wherein the energy level of the hole miniband of the first superlattice is substantially the same as the energy level of the hole miniband of the electron barrier layer.
(Appendix 17)
The photodetector according to any one of Supplementary note 10 to Supplementary note 16, wherein the mismatch of the lattice constant between at least one of the first superlattice and the second superlattice and the InP substrate is less than 1%.
(Appendix 18)
A first semiconductor layer is formed in the first superlattice, and a second semiconductor layer is formed between the electron barrier layer and the second superlattice, respectively, in any one of Appendix 10 to Appendix 17. The photodetector described.
(Appendix 19)
The photodetector according to Appendix 18, wherein both the first semiconductor layer and the second semiconductor layer are n-type.
(Appendix 20)
The electron miniband of the first light receiving layer has a higher energy level than the lower end of the conduction band of the first semiconductor layer, and the hole miniband of the first light receiving layer has energy higher than the lower end of the valence band of the first semiconductor layer. The photodetector according to Appendix 18 or Appendix 19, which has a higher level.
(Appendix 21)
The electron miniband of the second light receiving layer has a higher energy level than the lower end of the conduction band of the second semiconductor layer, and the hole miniband of the second light receiving layer has energy higher than the lower end of the valence band of the second semiconductor layer. The photodetector according to any one of Supplementary note 18 to Supplementary note 20, which has a high level.
(Appendix 22)
The photodetector according to Appendix 21, wherein a first electrode is formed on the first semiconductor layer and a second electrode is formed on the second semiconductor layer.
(Appendix 23)
The photodetector according to any one of Supplementary note 18 to Supplementary note 22, wherein a third semiconductor layer is formed between the second light receiving layer and the InP substrate.
(Appendix 24)
The photodetector according to Appendix 23, wherein the third semiconductor layer is p-type.
(Appendix 25)
The lower end of the conduction band of the third semiconductor layer has a higher energy level than the electron miniband of the second light receiving layer, and the lower end of the valence band of the third semiconductor layer has higher energy than the hole miniband of the second light receiving layer. The photodetector according to Appendix 23 or Appendix 24, which has a higher level.
(Appendix 26)
The photodetector according to any one of Supplementary note 23 to Supplementary note 25, wherein a third electrode is formed on the third semiconductor layer.
(Appendix 27)
The photodetector according to any one of Supplementary note 23 to Supplementary note 26, wherein the potential of the first semiconductor layer is higher than the potential of the third semiconductor layer.
(Appendix 28)
The photodetector according to any one of Supplementary note 23 to Supplementary note 27,
A voltage application unit that applies a positive voltage to the third semiconductor layer with respect to the first semiconductor layer.
A photodetector including a current measuring unit that measures the level of the first current acquired from the first semiconductor layer and the level of the second current acquired from the second semiconductor layer.
(Appendix 29)
The photodetector according to any one of Supplementary note 1 to Supplementary note 27,
The second end surface of the first light receiving layer, which is the end surface opposite to the direction in which the electron barrier layer is located, is the end surface of the second light receiving layer opposite to the direction in which the electron barrier layer is located. A voltage application part that applies a positive voltage to
A photodetector comprising a current measuring unit for measuring the level of the first current acquired from the first end surface and the level of the second current acquired from the second end surface.

11, 12, 22, 23 Contact layer 13, 14 Light receiving layer 131, 132, 141, 142, 151, 152 Semiconductor layer 15 Electronic barrier layer 16, 17, 18, 19 Electrodes 41 Substrate 42 Buffer layer 500 Photodetector 501 Voltage Applying device 511, 512 Current detector 71, 72 Hole 81, 82 Electron 901 Photodetector 94, 941, 942, 95, 951, 952, 96, 961, 962, 97, 971, 972, 98, 981, 982 , 99, 991, 992 Energy level

Claims (10)

The first light receiving layer whose cutoff wavelength, which is the upper limit of the detectable light wavelength, is the first wavelength,
A second light receiving layer having a cutoff wavelength of the second wavelength,
The first light receiving layer and the first light receiving layer of electrons are compared with the movement of holes between the first light receiving layer and the second light receiving layer. (Ii) An electron barrier layer that significantly hinders movement between the light receiving layer and
A photodetector equipped with. A claim that the electron barrier layer includes a barrier superlattice, which is a superlattice in which a plurality of sets of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated a plurality of times. The photodetector according to 1. The first light receiving layer includes a first superlattice in which a set of a plurality of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated a plurality of times. The light according to claim 2, wherein the layer comprises a second superlattice in which a set of a plurality of semiconductor layers having different combinations of an energy level at the lower end of the conduction band and an energy level at the upper end of the valence band are laminated a plurality of times. Detector. The second superlattice is formed on the InP substrate.
The barrier superlattice is an In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer and an Al _(v) In _(w) Ga _(1-v-w). 3. A superlattice composed of As _(x) Sb _(y) P _(1-xy) layers (each of s, t, u, v, w, x, and y is 0 or more and 1 or less). The photodetector described in. The In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer and the Al _(v) In _(w) Ga _(1-v-w) As _(x) The photodetector according to claim 4, wherein at least one of the In ratio, the Ga ratio, the As ratio and the Sb ratio in the Sb _(y) P _(1-xy) layer is equal. Each of the first superlattice and the second superlattice is an In _(a) Ga _(1-a) As _(b) P _(1-b) layer and a GaAs _(c) Sb _(d) P _{(1-c ). -D) The} photodetector according to claim 4 or 5, wherein each of the layers is a superlattice (each of a, b, c, and d is 0 or more and 1 or less). The composition of the In _(s) Ga _(1-s) As _(t) Sb _(u) P _(1-t-u) layer and the GaAs _(c) Sb _(d) P _(1-cd) layer The photodetector according to claim 6, which is the same. The photodetector according to any one of claims 3 to 7, wherein the first superlattice has a lower energy level of the hole miniband than the second superlattice. The energy level of the hole miniband of the first superlattice is substantially the same as the energy level of the hole miniband of the electron barrier layer, according to any one of claims 3 to 8. Photodetector. The photodetector according to any one of claims 1 to 9.
The second end surface of the first light receiving layer, which is the end surface opposite to the direction in which the electron barrier layer is located, is the end surface of the second light receiving layer opposite to the direction in which the electron barrier layer is located. A voltage application part that applies a positive voltage to
A photodetector comprising a current measuring unit for measuring the level of the first current acquired from the first end surface and the level of the second current acquired from the second end surface.

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