Semiconductor photodetector

• US 20050104064A1
• Filed: 03/03/2003
• Published: 05/19/2005
• Est. Priority Date: 03/01/2002
• Status: Active Grant

• Current Assignee: The Provost Fellows and Scholars of the College of the Holy and Undivided Trinity of Queen Elizabeth, near Dublin
• Original Assignee: The Provost Fellows and Scholars of the College of the Holy and Undivided Trinity of Queen Elizabeth, near Dublin
• Inventors: Hegarty, John, Barry, Liam Paul, O'Gorman, James Christopher, Folliot, Herve Armel Francois
• Granted Patent: US 7,557,368 B2
• Time in Patent Office: Days
• US Class Current: 257/53
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: H01L 31/035236 Superlattices; Multiple quantum well structures
• CPC Class Codes: H01L 31/105 the potential barrier being of the PIN type
• CPC Class Codes: H01L 31/108 the potential barrier being of the Schottky type
• CPC Class Codes: H01L 31/1085 the devices being of the Metal-Semiconductor-Metal [MSM] Schottky barrier type

Abstract

A semiconductor photodetector (1) for detecting short duration laser light pulses of predetermined wavelength in a light signal (2) comprises a micro-resonator (3) of vertical Fabry-Perot construction having a Bragg mirror pair, namely, a front mirror (5) and a rear mirror (6) with an active region (8) located between the front and rear mirrors (5,6). An N-type substrate (11) supports the rear mirror (6). The light signal (2) is directed into the active region (8) through the front mirror (5) while a pump beam (17) is directed into the active region (8) at an end (18) thereof. The spacing between the front and rear mirrors (5,6) is such as to cause light of the predetermined wavelength to resonate between the mirrors (5,6). The semiconductor material of the active region (8) is selected so that one photon from each of the light signal (2) and the pump beam (17) are required to transfer one electron from a valence band (21) of the active region (8) across a bandgap (22) to a conduction band (20) so that the active region operates on the principle of Two-Photon Absorption. On the active region (8) being simultaneously subjected to the pump beam and light of the predetermined wavelength in the light signal (2) electrons are transferred by Two-Photon Absorption from the valence band (21) to the conduction band (20), thus causing a change in the voltage developed across the active region (8). The change in voltage is detected between an electrode (15) on the substrate (11) and electrodes (8) on the front mirror (5) thereby indicating the presence of light of the predetermined wavelength in the light signal (2).

Claims

1-55. -55. (canceled)

56. A semiconductor photodetector for detecting light of a predetermined wavelength, the photodetector comprising an active semiconductor region for receiving a light signal of the predetermined wavelength, and a pump light beam, the active region defining a conduction band and at least one valence band, the conduction band defining with the valence band closest to the conduction band an energy bandgap, the width of the energy bandgap being such as to require absorption of more than one photon to effect transition of one electron from the valence band to the conduction band so that when a light signal of the predetermined wavelength is received by the active region simultaneously with the pump beam, a photon is required from each of the light signal and the pump beam for transferring an electron across the energy bandgap from the valence band to the conduction band, the photon from one of the light signal and the pump beam transferring the electron from the valence band to a virtual state between the valence band and the conduction band, and the photon from the other of the light signal and the pump beam transferring the electron from the virtual state to the conduction band for providing a detectable voltage change across the active region for indicating the presence of light of the predetermined wavelength in the light signal, characterised in that the active region is located in a resonator, the resonant frequency of which is selected for causing the light of the predetermined wavelength to resonate within the resonator for enhancing absorption of the light of the predetermined frequency in the active region.

57. A semiconductor photodetector as claimed in claim 56 characterised in that absorption of two photons is required to effect transition of one electron from the valence band to the conduction band.

58. A semiconductor photodetector as claimed in claim 56 characterised in that the material of the active region is selected to have non-linear absorbing characteristics of light in the predetermined wavelength, and preferably, the material of the active region is selected so that the active region does not exhibit linear absorbing characteristics of light in the predetermined wavelength.

59. A semiconductor photodetector as claimed in claim 56 characterised in that the material of the active region is selected so that the energy bandgap is such that the photon energy of the light of the predetermined wavelength is less than the energy gap of the bandgap, and the wavelength of the light of the pump beam is selected so that the photon energy of the light of the pump beam is not less than the energy gap of the bandgap less the photon energy of the light of the predetermined wavelength, and preferably, the material of the active region is selected so that the energy bandgap is such that the photon energy of the light of the predetermined wavelength is less than half of the energy gap of the bandgap, and advantageously, the light of the pump beam is selected so that the photon energy of the light is equal to the energy gap of the bandgap less the photon energy of the light of the predetermined wavelength, and ideally, the material of the active region is selected so that the energy bandgap is such that the photon energy of the light of the predetermined wavelength is just less than half of the energy gap of the bandgap.

60. A semiconductor photodetector as claimed in claim 56 characterised in that the material of the active region is selected so that the width of the energy bandgap is such as to minimise single photon absorption at the predetermined wavelength, and preferably, the resonator is selected for simultaneously maximising detection of light of the predetermined wavelength and for preventing detection of light of other wavelengths.

61. A semiconductor photodetector as claimed in claim 56 characterised in that a pair of electrodes are provided co-operating with the active region so that the detectable voltage change across the active region resulting from detection of the light of predetermined wavelength is established between the electrodes, and preferably, the resonator comprises a pair of spaced apart mirrors and the active region is located between the mirrors so that light of the predetermined wavelength resonates between the mirrors across the active region, and preferably, the spacing between the mirrors is selected so that the light of the predetermined wavelength resonates between the mirrors, and advantageously, the effective spacing between the mirrors is approximately half the wavelength of the light of predetermined wavelength or a harmonic thereof, and ideally, the effective spacing between the mirrors is approximately half the wavelength of the light of predetermined wavelength, and preferably, a non-active region is located between the mirrors, and the active region is located in the non-active region.

62. A semiconductor photodetector as claimed in claim 61 characterised in that the non-active region is provided by a semiconductor material, and preferably, the non-active region is substantially non-absorbing of light of the predetermined wavelength, and advantageously, a plurality of active regions are provided in the non-active region at locations substantially corresponding to anti-nodes of the electromagnetic field resonating between the mirrors, and each active region may be undoped, and alternatively, each active region may be doped.

63. A semiconductor photodetector as claimed in claim 61 characterised in that each active region is provided by a quantum well, and preferably, the material of each quantum well and their respective confinement barriers may be selected from any one or more of the following materials:

Gallium arsenide

Indium phosphide

Indium arsenide

Aluminium gallium arsenide

Gallium nitride

Aluminium nitride

Zinc selenide

Zinc sulphide

Silicon

Germanium

Gallium phosphide

Cuprous oxide.

64. A semiconductor photodetector as claimed in claim 61 characterised in that the reflectivity of the respective mirrors is chosen so that the resonator is resonant at the predetermined wavelength, and preferably, the reflectivities of the respective mirrors is selected for simultaneously maximising the detection of the light of the predetermined wavelength and for preventing detection of light of other wavelengths.

65. A semiconductor photodetector as claimed in claim 61 characterised in that one of the light signal and the pump beam is directed into the active region through one of the mirrors, and preferably, one of the light signal and the pump beam is directed perpendicularly to the mirror, and advantageously, the light signal and the pump beam are directed into the active region through the same mirror, and preferably, the light signal and the pump beam are directed at the same mirror at an angle to each other, and alternatively, one of the light signal and the pump beam is directed into the active region substantially parallel to the active region, and preferably, the pump beam is at an angle of approximately 90°

to the light signal.

66. A semiconductor photodetector as claimed in claim 65 characterised in that the reflectivity of the mirror through which the one of the light signal and the pump beam is passed is less than the reflectivity of the other mirror.

67. A semiconductor photodetector as claimed in claim 65 characterised in that the light signal is passed into the active region through one of the mirrors, and preferably, the light signal is directed into the active region substantially parallel to the active region, and preferably, the reflectivities of the mirrors is selected so that light in the light signal of wavelengths other than the predetermined wavelength passes through the detector substantially unimpeded.

68. A semiconductor photodetector as claimed in claim 56 characterised in that the photodetector is a direct bandgap semiconductor, and preferably, the material of the active region is selected from any one or more of the following materials and any one or more of their alloys:

Gallium arsenide

Indium phosphide

Indium arsenide

Aluminium gallium arsenide

Gallium nitride

Aluminium nitride

Zinc selenide

Zinc sulphide.

69. A semiconductor photodetector as claimed in claim 56 characterised in that the semiconductor photodetector is an indirect bandgap semiconductor, and preferably, the material of the active region is selected from any one or more of the following materials and any one or more of their alloys:

Silicon

Germanium

Gallium phosphide.

70. A semiconductor photodetector as claimed in claim 56 characterised in that the semiconductor photodetector is a direct one photo forbidden bandgap detector at the wavelength of the light of the predetermined wavelength, and preferably, the material of the active region is selected from any one or more of the following materials and any one or more of their alloys:

Cuprous oxide

Silicon

Germanium.

71. A semiconductor photodetector as claimed in claim 56 characterised in that the photodetector is adapted for detecting a light signal comprising pulsed light of the predetermined wavelength where the duration of each pulse is relatively short, and preferably, the duration of each pulse is of the order of picoseconds.

72. A semiconductor photodetector as claimed in claim 70 characterised in that the duration of each pulse is of the order of sub-picoseconds, and preferably, the duration of each pulse of the light is in the range of 1 femtosecond to 500 picoseconds.

73. A semiconductor photodetector as claimed in claim 56 characterised in that the photodetector is of Fabry-Perot construction, alternatively, the mirrors of the photodetector are of Bragg pair construction, alternatively, the photodetector is of Schottky construction, alternatively, the photodetector is of PIN construction.

74. A semiconductor photodetector as claimed in claim 56 characterised in that the photodetector is of metal semiconductor metal construction.

75. A semiconductor photodetector as claimed in claim 56 characterised in that the pump beam is a strobed beam, and preferably, the light signal is a pulsed light signal, and preferably, the frequency of strobing of the probe of the pump beam is substantially similar to the frequency at which the light signal is being pulsed or a harmonic thereof.

76. A semiconductor photodetector as claimed in claim 56 characterised in that the resonator is a microresonator.

77. An optical switch comprising a semiconductor photodetector as claimed in claim 56, characterised in that the photodetector is adapted for absorbing light of predetermined wavelength in a light beam comprising a plurality of co-propagating signals of respective different wavelengths, the optical switch being responsive to the light of the predetermined wavelength being absorbed for outputting an electrical signal.