1. A photodetector comprising:
at least two optically sensitive layers, a first optically sensitive layer and a second optically sensitive layer, the first optically sensitive layer over at least a portion of an integrated circuit and the second optically sensitive layer over the first optically sensitive layer;
wherein the first optically sensitive layer comprises a first absorption band including at least one first set of colors and is devoid of a local absorption maximum, and the second optically sensitive layer comprises a second absorption band including at least one second set of colors and is devoid of a local absorption maximum, wherein the second absorption band includes the first set of colors;
wherein each optically sensitive layer is interposed between a respective first electrode and a respective second electrode; and
wherein the integrated circuit selectively applies a bias to the electrodes and reads signals from the optically sensitive layers.
2. The photodetector of claim 1, wherein the second optically sensitive layer is relatively completely absorbent of light in a first wavelength interval and relatively completely transmissive of light outside the first wavelength interval.
3. The photodetector of claim 2, wherein the first optically sensitive layer is relatively completely absorbent of the light outside the at least one first wavelength interval.
4. The photodetector of claim 3, wherein the first optically sensitive layer is relatively completely absorbent of light in the first wavelength interval.
5. The photodetector of claim 1, wherein each of the optically sensitive layers comprises nanocrystals of a material having a bulk bandgap of less than approximately 0.5 eV.
6. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 490 nm wavelength.
7. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap of approximately 2.5 eV.
8. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 560 nm wavelength.
9. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap of approximately 2.2 eV.
10. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap of approximately 1.8 eV.
11. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap of approximately 1.2 eV.
12. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap of approximately 0.9 eV.
13. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap of approximately 0.7 eV.
14. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 630 nm wavelength.
15. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 650 nm wavelength.
16. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 670 nm wavelength.
17. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 700 nm wavelength.
18. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 800 nm wavelength.
19. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 900 nm wavelength.
20. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 1000 nm wavelength.
21. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 1300 nm wavelength.
22. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 1650 nm wavelength.
23. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 3 um wavelength.
24. The photodetector of claim 5, wherein the nanocrystals of at least one optically sensitive layer are quantum confined to a bandgap corresponding to 5 um wavelength.
25. The photodetector of claim 1, wherein an optical sensitivity of at least one optically sensitive layer is at an intensity of light less than approximately 1 lux is more than twice the optical sensitivity of the optically sensitive material at an intensity of light of at least 100 lux.
26. The photodetector of claim 1, wherein the optical sensitivity of at least one optically sensitive layer at an intensity of light less than approximately 1 lux is more than ten times the optical sensitivity of the optically sensitive material at an intensity of light of at least 100 lux.
27. The photodetector of claim 1, wherein the optical sensitivity of at least one optically sensitive layer is more than 1000 mVlux-s at relatively low light levels and less than 500 mVlux-s at relatively high light levels.
28. The photodetector of claim 1, wherein the optical sensitivity of at least one optically sensitive layer is more than 2000 mVlux-s at relatively low light levels and less than 400 mVlux-s at relatively high light levels.
29. The photodetector of claim 1, wherein the optical sensitivity of at least one optically sensitive layer is more than 3000 mVlux-s at relatively low light levels and less than 300 mVlux-s at relatively high light levels.
30. The photodetector of claim 1, wherein the first optically sensitive layer comprises a first material having a first thickness, and the combination of the first material and the first thickness provides a first responsivity to light of a first wavelength, wherein the second optically sensitive layer comprises a second material having a second thickness, and the combination of the second material and the second thickness provides a second responsivity to light of a second wavelength, wherein the first responsivity and the second responsivity are approximately equal.
31. The photodetector of claim 1, wherein the first optically sensitive layer comprises a first material having a first thickness, and the combination of the first material and the first thickness provides a first photoconductive gain to light of a first wavelength, wherein the second optically sensitive layer comprises a second material having a second thickness, and the combination of the second material and the second thickness provides a second photoconductive gain to light of a second wavelength.
32. The photodetector of claim 31, wherein the first photoconductive gain and the second photoconductive gain are approximately equal.
33. The photodetector of claim 1, wherein the first optically sensitive layer comprises a first material having a first thickness, and the combination of the first material and the first thickness provides a first absorbance to light of a first wavelength, wherein the second optically sensitive layer comprises a second material having a second thickness, and the combination of the second material and the second thickness provides a second absorbance to light of a second wavelength, wherein the first absorbance and the second absorbance are approximately equal.
34. The photodetector of claim 1, wherein persistence of each of the optically sensitive layers is approximately equal.
35. The photodetector of claim 1, wherein persistence of each of the optically sensitive layers is approximately in a range of 1 ms to 200 ms.
36. The photodetector of claim 1, wherein the first optically sensitive layer comprises a nanocrystal material having first photoconductive gain and the second optically sensitive layer comprises a nanocrystal material having a second photoconductive gain.
37. The photodetector of claim 1, wherein at least one of the optically sensitive layers comprises a nanocrystal material having photoconductive gain and a responsivity of at least approximately 0.4 ampsvolt (AV).
38. The photodetector of claim 37, wherein the responsivity is achieved when a bias is applied across the at least one of the optically sensitive layers, wherein the bias is approximately in a range of 1 volt to 5 volts.
39. The photodetector of claim 37, wherein the first optically sensitive layer comprises a nanocrystal material having first photoconductive gain and a first responsivity approximately in a range of 0.4 AV to 100 AV.
40. The photodetector of claim 39, wherein the second optically sensitive layer comprises a nanocrystal material having a second photoconductive gain and a second responsivity approximately in a range of 0.4 AV to 100 AV.
41. The photodetector of claim 40, wherein the second photoconductive gain is greater than the first photoconductive gain.
42. The photodetector of claim 1, wherein at least one of the optically sensitive layers includes nanocrystals comprising nanoparticles.
43. The photodetector of claim 42, wherein the nanocrystals are quantum confined to have an effective bandgap more than twice the bulk bandgap.
44. he photodetector of claim 42, wherein a nanoparticle diameter of the nanoparticles is less than a Bohr exciton radius of bound electron-hole pairs within the nanoparticle.
45. The photodetector of claim 42, wherein a first diameter of nanocrystals of the first optically sensitive layer is greater than a second diameter of nanocrystals of the second optically sensitive layer.
46. The photodetector of claim 42, wherein a first diameter of nanocrystals of the first optically sensitive layer is less than a second diameter of nanocrystals of the second optically sensitive layer.
47. The photodetector of claim 42, wherein at least one of the optically sensitive layers comprises nanocrystals of a material having a bulk bandgap of less than approximately 0.5 electronvolts (eV), and wherein the nanocrytals are quantum confined to have a bandgap more than 1.0 eV.
48. The photodetector of claim 1, wherein the first optically sensitive layer comprises a first composition including one of lead sulfide (PbS), lead selenide (PbSe), lead tellurium sulfide (PbTe), indium phosphide (InP), indium arsenide (InAs), and germanium (Ge).
49. The photodetector of claim 1, wherein the second optically sensitive layer comprises a second composition including one of indium sulfide (In2S3), indium selenide (In2Se3), indium tellurium (In2Te3), bismuth sulfide (Bi2S3), bismuth selenide (Bi2Se3), bismuth tellurium (Bi2Te3), indium phosphide (InP), gallium arsenide (GaAs), silicon (Si), and germanium (Ge).
50. The photodetector of claim 1, wherein each of the optically sensitive layers comprises different compound semiconductor nanocrystals, wherein the first optically sensitive layer comprises a composition including lead and the second optically sensitive layer comprises a composition including one of indium and bismuth.
51. The photodetector of claim 1, wherein at least one of the optically sensitive layers comprises monodisperse nanocrystals.
52. The photodetector of claim 1, wherein each of the optically sensitive layers comprises nanocrystals of different materials.
53. The photodetector of claim 1, wherein the first optically sensitive layer includes a first material having a first bulk bandgap and the second optically sensitive layer includes a second material having a second bulk bandgap.
54. The photodetector of claim 1, wherein at least one of the optically sensitive layers comprises nanocrystals comprising colloidal quantum dots.
55. The photodetector of claim 54, wherein the quantum dots include a first carrier type and a second carrier type, wherein the first carrier type is a flowing carrier and the second carrier type is one of a substantially blocked carrier and a trapped carrier.
56. The photodetector of claim 55, wherein the colloidal quantum dots include organic ligands, wherein a flow of at least one of the first carrier type and the second carrier type is related to the organic ligands.
57. The photodetector of claim 1, wherein at least one optically sensitive layers comprises a continuous film of interconnected nanocrystal particles in contact with the respective first electrode and the respective second electrode.
58. The photodetector of claim 57, wherein the nanocrystal particles comprise a plurality of nanocrystal cores and a shell over the plurality of nanocrystal cores.
59. The photodetector of claim 58, wherein the plurality of nanocrystal cores are fused.
60. The photodetector of claim 58, wherein a physical proximity of the nanocrystal cores of adjacent nanocrystal particles provides electrical communication between the adjacent nanocrystal particles.
61. The photodetector of claim 60, wherein the physical proximity includes a separation distance of less than approximately 0.5 nm.
62. The photodetector of claim 60, wherein the electrical communication includes a hole mobility of at least approximately 1E-5 square centimeter per volt-second across the nanocrystal particles.
63. The photodetector of claim 58, wherein the plurality of nanocrystal cores are electrically interconnected with linker molecules.
64. The photodetector of claim 1, wherein at least one of the optically sensitive layers comprises a unipolar photoconductive layer including a first carrier type and a second carrier type, wherein a first mobility of the first carrier type is higher than a second mobility of the second carrier type.
65. A photodetector comprising:
an integrated circuit; and
at least two optically sensitive layers, a first optically sensitive layer and a second optically sensitive layer, the first optically sensitive layer over at least a portion of the integrated circuit and the second optically sensitive layer over the first optically sensitive layer;
wherein each optically sensitive layer is interposed between two electrodes, the electrodes including a respective first electrode and a respective second electrode;
wherein the integrated circuit selectively applies a bias to the electrodes and reads signals from the optically sensitive layers, wherein the signal is related to the number of photons received by the respective optically sensitive layer; and
wherein the first optically sensitive layer comprises a nanocrystal material having an absorption onset at a first wavelength and the second optically sensitive layer comprises a nanocrystal material having an absorption onset at a second wavelength, wherein the first wavelength is shorter than the second wavelength, and a local absorption maximum is absent from an absorption spectrum of at least one of the first optically sensitive layer and the second optically sensitive layer.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. An RF tag reader and writer comprising:
a communication unit that performs a communication process with an RF tag using a slot aloha method of performing the communication process with the RF tag as an information acquisition target at each of a plurality of time slots of a round, transmits a response request command to the RF tag at each time slot, acquires a response transmitted from the RF tag with an acquisition of the response request command, transmits a tag information request command for requesting for transmitting tag information, which is information stored in the RF tag, to the RF tag having transmitted the acquired response, and acquires the tag information transmitted from the RF tag with an acquisition of the tag information request command; and
a communication success rate calculator that calculates a communication success rate aID=nIDnACK with the RF tag on the basis of the number of times nACK by which the tag information request command for requesting for transmitting the tag information, which is information stored in the RF tag, in the communication process of the communication unit with the RF tag in a calculation period including one or more rounds and the number of times nID by which the tag information is received from the RF tag as a return to the tag information request command in the calculation period including one or more rounds;
a signal level information acquiring section that acquires received signal level information which is information indicating the magnitude of a signal transmitted from the RF tag;
a signal level determining section that acquires signal level reference information, which is a reference for the magnitude of the received signal, stored in a predetermined memory area, determines whether the magnitude of the received signal transmitted from the RF tag is greater than the reference on the basis of a comparison result of the signal level reference information with the received signal level information acquired by the signal level information acquiring section for every time slot, and determines that a response is transmitted from the RF tag with the acquisition of the response request command transmitted from the communication unit at the time slot at which the magnitude of the received signal is greater than the reference;
a response rate calculator that calculates a response rate aRN16=nRN16nSL0 indicating a rate of the number of time slots at which the response is transmitted from the RF tag in the calculation period on the basis of the number of time slots nRN16 at which it is determined by the signal level determining section that the response is transmitted in the calculation period and the number of time slots nSL0 in the calculation period; and
a communication stability determining unit that performs a communication state determining process of determining whether a communication state with the RF tag is good on the basis of a comparison result of communication success rate reference information, which is a reference for the communication success rate and is acquired from a predetermined memory area, with the communication success rate aID calculated by the communication success rate calculator, and does not perform the communication state determining process in the calculation period in which the response rate calculated by the response rate calculator is 0.
2. The RF tag reader and writer according to claim 1, wherein the communication stability determining unit performs the communication state determining process in the calculation period in which the response rate calculated by the response rate calculator is greater than 0.
3. The RF tag reader and writer according to claim 1, wherein the communication process in the communication unit is performed on the basis of a protocol of ISO 18000-6 type C, and
wherein the communication unit transmits a Query command at the first time slot in a round in the slot aloha method.
4. The RF tag reader and writer according to claim 1, wherein the communication process in the communication unit is performed in a plurality of the calculation periods set on the basis of a protocol of ISO 18000-6 type C, and
wherein when there exists the calculation period in which the communication stability determining unit determines that the communication state is good, the communication unit communicates with the RF tag by transmitting a Query-adjust command as the response request command in the calculation period subsequent to the calculation period in which it is determined that the communication state is good.
5. The RF tag reader and writer according to claim 1, wherein the communication process in the communication unit is performed in a plurality of the calculation periods, and
wherein the RF tag reader and writer further comprises a position determining unit that determines that a position of an antenna of the RF tag reader and writer is shifted when a determination result by the communication stability determining unit varies between the successive rounds.
6. The RF tag reader and writer according to claim 5, further comprising a grouping unit that groups the tag information acquired by the communication unit before the determination by the position determining unit and stores the grouped tag information in a predetermined memory area when the position determining unit determines that the position of the antenna of the RF tag reader and writer is shifted.
7. The RF tag reader and writer according to claim 6, wherein the grouping unit stores the grouped tag information in the predetermined memory area in correlation with information on the order of grouping and storage.
8. A tag information acquiring method comprising:
performing a communication process with an RF tag using a slot aloha method of performing the communication process with the RF tag as an information acquisition target at each of a plurality of time slots of a round, transmitting a response request command to the RF tag at each time slot, acquiring a response transmitted from the RF tag with an acquisition of the response request command, transmitting a tag information request command for requesting for transmitting tag information, which is information stored in the RF tag, to the RF tag having transmitted the acquired response, and acquiring the tag information transmitted from the RF tag with an acquisition of the tag information request command; and
calculating a communication success rate aID=nIDnACK with the RF tag on the basis of the number of times nACK by which the tag information request command for requesting for transmitting the tag information, which is information stored in the RF tag, in the communication process of the communication unit with the RF tag in a calculation period including one or more rounds and the number of times nID by which the tag information is received from the RF tag as a return to the tag information request command in the calculation period including one or more rounds;
acquiring received signal level information which is information indicating the magnitude of a signal transmitted from the RF tag;
acquiring signal level reference information, which is a reference for the magnitude of the received signal, stored in a predetermined memory area, determining whether the magnitude of the received signal transmitted from the RF tag is greater than the reference on the basis of a comparison result of the signal level reference information with the received signal level information for every time slot, and determining that a response is transmitted from the RF tag with the acquisition of the response request command transmitted from the communication unit at the time slot at which the magnitude of the received signal is greater than the reference;
calculating a response rate aRN16=nRN16nSL0 indicating a rate of the number of time slots at which the response is transmitted from the RF tag in the calculation period on the basis of the number of time slots nRN16 at which it is determined that the response is transmitted in the calculation period and the number of time slots nSL0 in the calculation period;
performing a communication state determining process of determining whether a communication state with the RF tag is good on the basis of a comparison result of communication success rate reference information, which is a reference for the communication success rate and is acquired from a predetermined memory area, with the communication success rate aID; and
not performing the communication state determining process in the calculation period in which the response rate is 0.