Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Ballistic transport device
Reexamination Certificate
2001-02-26
2003-09-30
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Ballistic transport device
C257S014000, C257S021000, C257S024000, C257S187000, C257S192000, C257S194000, C257S195000, C257S452000, C257S457000, C257S465000
Reexamination Certificate
active
06627914
ABSTRACT:
TECHNICAL FIELD
This invention relates to MW(Millimeter Wave)/FIR(Far Infra Red) light detectors for detecting video signals in the MW and FIR wavelength range using a MW/FIR measuring instrument, especially by controlling semiconductor quantum dots.
BACKGROUND ART
In general, detectors for electromagnetic waves include a frequency mixer that applies phase sensing wave detection and a video signal detector that adopts incoherent wave detection, of which the latter is known to provide higher sensitivity in detecting a feeble or weak light.
Of the conventional video signal detectors for such lights in an MW/FIR wavelength range, those that offer best sensitivities are a germanium composite bolometer for use at a cryogenic temperature of 0.3 K or lower for a light of a wavelength in the range of 0.1 to 1 mm, and a germanium doped photoconductive detector for use at a low temperature around 2 K for a light of a wavelength in the range of 0.06 to 0.1 mm.
These detectors provide noise equivalent powers (NEP) that reach as high as 10
−16
to 10
−18
WHZ
−½
.
This as seen in terms of energy quanta of electromagnetic waves or photons means that the sensitivity of such a detector is such that in one second of measurement, the detector cannot detect a signal as more than a noise unless photon packets of about one million or more in number are incident on the detector.
In addition, such a detector has a speed of response as very low as 100 millisecond. While slow response detectors such as a superconducting bolometer, superconducting tunnel junction and hot electrons in a semiconductor (InSb) have been utilized, their sensitivities fall below that of a germanium composite bolometer.
Apart from the detectors mentioned above, it has been known that irradiating a single-electron transistor with a microwave gives rise to a signal by photon assisted tunneling effect. However, a detector that utilizes this effect is low in sensitivity because between the electrodes no more than one electron moves by absorption of one electromagnetic-wave photon.
Thus, there has so far been no detector that is excellent in both sensitivity and speed of response. This is for the reasons that in any of the detectors, conduction electrons because of lying in a continuous energy band structure are short in the life in which they remain excited by an electromagnetic wave; that since a detector detects an electromagnetic wave in terms of a change in electrical conductance by all the electrons in the detector, an effect brought about by the excitation of a small number of electrons is weakened by the other electrons overwhelming in number; and further that as in the photon assisted tunneling, between the electrodes no more than one electron moves by absorbing one electromagnetic-wave photon.
It is accordingly an object of the present invention to circumvent resolving the problems encountered by the conventional detectors and to provide MW/FIR light detectors predicated on principles or mechanisms totally different from those mentioned above, which detectors have an extraordinary degree of sensitivity and are quick in response.
DISCLOSURE OF THE INVENTION
In order to achieve the object, mentioned above, there is provided in accordance with the present invention in one form of embodiment thereof an MW(millimeter wave)/FIR(infra red) light detector that comprises an electromagnetic-wave coupling means for concentrating an electromagnetic wave in a small special region of a submicron size a quantum dot for absorbing the concentrated electromagnetic wave to bring about an excited state between electron levels, and a single-electron semiconductor.
In addition to the make-up mentioned above an MW/FIR detector according to the present invention preferably retains a state in which an electrical conductance of the said single-electron semiconductor is varied according to the said excited state of the quantum dot.
In an MW/FIR detector as mentioned above, the said quantum dot preferably has a life in a range of 10 nanoseconds to 1000 seconds in which it remains in the said excited state before returning to a ground state thereof.
According to one specific feature of the present invention, the said electron levels have a difference in energy that is controllable variably according to any one or a combination of a change in size of the said quantum dot, an external magnetic field and a biasing voltage.
According to another specific feature of the present invention, the said excited state is established by any one or a combination of a resonance excitation of electrons according to a size effect of the said quantum dot, a resonance excitation of electrons between Landau levels by application of a magnetic field and an excitation between spin states separated by a magnetic field.
For the said electromagnetic-wave coupling means use may be made of a standard or regular BOTAI antenna for electrically coupling the said quantum dot and the said electromagnetic wave together.
For the said electromagnetic-wave coupling means, use may also be made of an anomalous or irregular BOTAI antenna having an node thereof short-circuited for magnetically coupling the said quantum dot and the said electromagnetic wave together.
Preferably, the presence or absence of short circuit through a node of the said electromagnetic-wave coupling means and the size of the said quantum dot are determined according to the wavelength of the said electromagnetic wave.
The said electromagnetic-wave coupling means may be used also to provide a gate electrode for the said single-electron transistor.
The present invention provides in a second form of embodiment, thereof an MW/FIR light detector, characterized in that the detector comprises: an electromagnetic-wave coupling means for concentrating an electromagnetic wave in a small special region of a sub-micron size; a first quantum dot for absorbing the electromagnetic wave concentrated by the said electromagnetic-wave coupling means to bring about an ionization thereof; and a single-electron transistor including a second quantum dot electrostatically coupled to the said first quantum dot, whereby the said electromagnetic wave is detected on the basis of the fact that electric conductivity of the said single-electron transistor varies with a change in electrostatic state of the said second quantum dot consequent upon an ionization of the said first quantum dot.
The above mentioned ionization of the said first quantum dot may be brought about by excitation of an electron in a quantized bound state of the said first quantum dot to a free electron state of an electron system outside of the said first quantum dot.
The ionization energy of the said first quantum dot may be controllable variably by changing the magnitude of a bias voltage applied to a gate of the said first quantum dot.
The said first quantum dot may have a life in a range between 1 microsecond and 1000 seconds in which it remains in the ionization state before returning to a neutral state.
The said first and second quantum dots preferably lie in an identical semiconductor structure and are isolated from each other electrostatically by bias voltages applied to respective gates thereof, respectively.
The said first and second quantum dots may be formed adjacent to each other across a gap in a semiconductor.
Preferably, the said second quantum dot comprises a metal dot formed on the said first quantum dot and forms the said single-electron transistor by having a tunnel junction with a metal lead wire formed on the said metal dot.
Then, the said second quantum dot preferably an aluminum metal dot and has a portion of a said tunnel junction formed from aluminum oxide.
The said electromagnetic-wave coupling means may be a standard dipole antenna for electrically coupling the said first quantum dot and the said electromagnetic wave together.
The said electromagnetic-wave coupling means may be used also to serve as a bias voltage applying gate that forms the said first and second quantum dots.
The said electromagnetic-wave coupling means p
Hirai Hiroshi
Komiyama Susumu
Kutsuwa Takeshi
Oleg Astafiev
Vladimir Antonov
Flynn Nathan J.
Japan Science and Technology Corporation
Sefer Ahmed N.
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