U.S. patent application number 14/963533 was filed with the patent office on 2016-03-31 for electromagnetic wave generation device and detection device.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Toshihiko Ouchi, Ryota Sekiguchi.
Application Number | 20160094183 14/963533 |
Document ID | / |
Family ID | 51164702 |
Filed Date | 2016-03-31 |
United States Patent
Application |
20160094183 |
Kind Code |
A1 |
Ouchi; Toshihiko ; et
al. |
March 31, 2016 |
ELECTROMAGNETIC WAVE GENERATION DEVICE AND DETECTION DEVICE
Abstract
The invention provides an electromagnetic wave generation
device. The device includes a substrate provided with a terahertz
wave oscillation section including a resonant tunneling diode
structure, a two-dimensional electron layer having a semiconductor
heterojunction structure, and a transistor section including a
source electrode and a drain electrode provided at end portions of
the two-dimensional electron layer and a gate electrode provided
above the two-dimensional electron layer. The terahertz wave output
of the terahertz wave oscillation section changes distribution of
electrons in the two-dimensional electron layer.
Inventors: |
Ouchi; Toshihiko;
(Machida-shi, JP) ; Sekiguchi; Ryota;
(Hiratsuka-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
51164702 |
Appl. No.: |
14/963533 |
Filed: |
December 9, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
14155033 |
Jan 14, 2014 |
9236833 |
|
|
14963533 |
|
|
|
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Current U.S.
Class: |
250/338.4 |
Current CPC
Class: |
H03B 7/00 20130101; G01J
1/44 20130101; H03B 17/00 20130101; H03B 7/08 20130101; H03C 7/025
20130101; H03C 7/00 20130101; H01S 1/02 20130101; H03B 2200/0084
20130101 |
International
Class: |
H03B 7/00 20060101
H03B007/00; G01J 1/44 20060101 G01J001/44; H01S 1/02 20060101
H01S001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 16, 2013 |
JP |
2013-005056 |
Nov 13, 2013 |
JP |
2013-234730 |
Claims
1. An electromagnetic wave detection device for detecting an
electromagnetic wave, the device comprising: a terahertz wave
oscillation section including a resonant tunneling diode structure;
a two-dimensional electron layer including a semiconductor
heterojunction structure; and a transistor section including a
source electrode and a drain electrode provided at end portions of
the two-dimensional electron layer and a gate electrode provided
above the two-dimensional electron layer, wherein, in the case
where the electromagnetic wave detection device is irradiated with
the electromagnetic wave, the transistor section outputs a signal
corresponding to an intensity of the electromagnetic wave, and
wherein the signal is a mixing signal produced by mixing the
electromagnetic wave and a terahertz wave from the terahertz wave
oscillation section.
2. The device according to claim 1, wherein the terahertz wave
oscillation section and the transistor section are arranged on the
same side of a substrate.
3. The device according to claim 1, wherein the terahertz wave
oscillation section and the transistor section are arranged on
different sides of a substrate.
4. An apparatus comprising the electromagnetic wave detection
device according to claim 1 and a power source configured to drive
the electromagnetic wave detection device, the apparatus being
configured to transmit a terahertz wave signal.
Description
[0001] This application is a continuation of application Ser. No.
14/155,033, filed on Jan. 14, 2014, which claims the benefit of
Japanese Patent Application No. 2013-005056, filed Jan. 16, 2013,
and Japanese Patent Application No. 2013-234730, Nov. 13, 2013,
which are hereby incorporated by reference herein in their
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an oscillation device, a
detection device, and the like, of a semiconductor, for a terahertz
waveband.
[0004] 2. Description of the Related Art
[0005] In recent years, non-destructive sensing techniques using
electromagnetic waves in a terahertz (THz) waveband (at frequencies
of approximately 30 GHz to 30 THz) have been developed.
Electromagnetic waves in such a frequency band allow applications
in imaging techniques developed in the form of safe imaging and
examining apparatuses without the use of X-rays. Other techniques
that have been developed include spectroscopic techniques for
obtaining the absorption spectrum and the complex permittivity of a
substance to determine its properties such as molecular bonding,
measurement techniques for determining properties such as carrier
density and mobility, conductivity, and the like, and analytic
techniques for biomolecules. Additionally, the IEEE802.15 THz
Interest Group has been active in the development of wide-band
wireless communications using THz waves as carrier waves.
[0006] Light sources for such THz waves have been developed using
nonlinear phenomena through laser excitation or using
photoconductivity of semiconductors. Microwave-band oscillators
that multiply waves are also used. However, they all suffer
difficulty in improving the efficiency of generating THz waves and
have complex configurations, and thus there is demand for
semiconductor chips that can be driven electrically. One such
oscillator is a resonant tunneling diode (RTD) device (see IEEE
Microwave and Guided wave letters, vol. 5, p. 219, 1995.). This
device, through electromagnetic wave gain due to the negative
resistance of the RTD and the integration of a resonator that also
works as an electromagnetic wave emitter, provides oscillation
output in a terahertz waveband with voltage application at room
temperatures.
[0007] Other attempts include integrating such a device having the
negative resistance with a transistor device for amplification and
mixing of the oscillation output to thereby improve the performance
of space transmission by high frequency electromagnetic waves
(Japanese Patent Application Laid-Open No. 2005-142476).
[0008] An HEMT (high electron mobility transistor) device provided
with grating electrode gates has been disclosed as one type of high
speed transistor (see Japanese Patent Application Laid-Open No.
2009-224467). In this device, the frequency of a plasmon occurred
in a two-dimensional electron gas region is adjusted through the
grating electrode gates. External rays of light with two
wavelengths are allowed to enter the device, and the beat frequency
is tuned in the resonance frequency of the plasmon to generate THz
waves.
[0009] An RTD oscillator necessitates the integration of a shunt
resistor and a MIM capacitor in proximity to an RTD device to
oscillate at a desired oscillation frequency. Depending on the
structure of a resonator required for the oscillator, there may be
problems as described below. That is, the structural size may be
limited for obtaining a resistance value required for the
integrated-type shunt resistor, and the application of a modulation
signal from an external power source may impose an upper limit of
approximately 10 GHz by the MIM capacitor required to prevent
parasitic oscillation. Note that this calculation assumes a
modulation bandwidth of 3 db down, MIM capacitance of 10 pF, and
wiring resistance slightly less than 1.OMEGA..
[0010] By integrating this type of oscillator with a transistor as
described in Japanese Patent Application Laid-Open No. 2005-142476
to obtain an amplifying function, the transistor may provide a
modulating function to alleviate the problems described above.
Fabricating such an integrated circuit for a terahertz region,
however, may require highly accurate shape control, making it
difficult to obtain a high yield.
SUMMARY OF THE INVENTION
[0011] An aspect of the invention is an electromagnetic wave
generation device, the device including a substrate, the substrate
being provided with a terahertz wave oscillation section including
a resonant tunneling diode structure, a two-dimensional electron
layer having a semiconductor heterojunction structure, and a
transistor section including a source electrode and a drain
electrode provided at end portions of the two-dimensional electron
layer and a gate electrode provided above the two-dimensional
electron layer, wherein a terahertz wave output of the terahertz
wave oscillation section changes distribution of electrons in the
two-dimensional electron layer.
[0012] Further features of the present invention will become
apparent from the following description of exemplary embodiments
with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A is a block diagram of an electromagnetic wave
generation device according to a first embodiment of the present
invention;
[0014] FIG. 1B is a block diagram of the electromagnetic wave
generation device according to the first embodiment of the
invention;
[0015] FIG. 1C is a block diagram of the electromagnetic wave
generation device according to the first embodiment of the
invention;
[0016] FIG. 2A is a block diagram of an electromagnetic wave
generation device according to a second embodiment of the
invention;
[0017] FIG. 2B is a block diagram of the electromagnetic wave
generation device according to the second embodiment of the
invention;
[0018] FIG. 2C is a block diagram of the electromagnetic wave
generation device according to the second embodiment of the
invention;
[0019] FIG. 3 is a block diagram of an electromagnetic wave
generation device according to a third embodiment of the invention;
and
[0020] FIG. 4 is a diagram for describing signal transmission using
the electromagnetic wave generation device according to the
invention.
DESCRIPTION OF THE EMBODIMENTS
[0021] In some embodiments described herein, an interaction between
the output of an oscillator oscillating stably and an oscillator
capable of high speed modulation achieves high-speed signal
modulation and the like. Specifically, in an electromagnetic wave
generation device, a certain voltage corresponding to a negative
resistance region is applied to a resonant tunneling diode
oscillator to obtain oscillation, and this output is allowed to
enter a two-dimensional electron layer of an HEMT device, and the
presence of the oscillation of the HEMT device is controlled by
voltage applied to the HEMT device. This allows high speed
modulation with a relatively simple configuration using the HEMT
device, which is capable of the high speed modulation. To enable
this operation and the like, the device according to some
embodiments includes a substrate provided with a terahertz wave
oscillation section including a resonant tunneling diode structure,
a two-dimensional electron layer having a semiconductor
heterojunction structure to configure the HEMT device, and a
transistor section including a source electrode, a drain electrode,
and a gate electrode. In the electromagnetic wave generation
device, the terahertz wave output of the terahertz wave oscillation
section changes the distribution of electrons in the
two-dimensional electron layer. The distribution of electrons in
the two-dimensional electron layer can be changed by positioning
the terahertz wave oscillation section such that its terahertz wave
output enters the two-dimensional electron layer.
First Embodiment
[0022] A first embodiment of the present invention provides an
electromagnetic wave generation device or an oscillation device 1,
which is provided with an RTD oscillator (FIG. 1C) and an HEMT
device (FIG. 1A) on one substrate on its different surfaces as
illustrated in FIGS. 1A to 1C. In other words, structures
illustrated in FIGS. 1A and 1C in plan views are integrated on an
identical substrate 3 with a cross-sectional structure illustrated
in FIG. 1B in a sectional view taken along long dashed short dashed
lines in the figures. The HEMT device includes grating gate
electrodes 6 and 7 to be able to adjust the frequency of a plasmon
occurred at a two-dimensional electron layer 2 having a
semiconductor heterojunction structure. The RTD oscillator, which
is a terahertz wave oscillation section including a resonant
tunneling diode structure, is configured to be able to oscillate at
a frequency determined by a length L of an antenna 15 provided as a
resonator and an emitter. An output of the RTD oscillator
propagates in the substrate 3 as marked with reference numeral 16
and enters the two-dimensional electron layer of the HEMT device at
a region beneath the gate electrodes to allow an interaction with
the plasmon occurring there. When a frequency of the plasmon and an
oscillation frequency of the RTD oscillator are able to be tuned in
a lock range, the HEMT device oscillates at the oscillation
frequency of the RTD oscillator by the same principle described in
Japanese Patent Application Laid-Open No. 2009-224467, which allows
the HEMT device to radiate the oscillation output to an external
space as marked with reference numeral 17. The electromagnetic
waves emitted into the substrate from the RTD oscillator in this
manner are allowed to interact with the HEMT device directly,
thereby alleviating the difficulty of accurate integration
alignment.
[0023] The devices will now be described. The RTD oscillator
includes two electrodes 11 and 12 and an RTD section 14. In this
device, the two electrodes 11 and 12 are isolated from each other
with regard to direct current by an insulation film 13 and the
like, provided at an overlapping portion of the electrodes, but are
in conduction at the oscillation frequency of the oscillator to
function as a slot antenna having a rectangular non-electrode
portion as marked with reference numeral 15 in FIG. 1C. A part of
the electrode 12 extends into the non-electrode portion like a
protrusion to be in electrical contact with a surface of the RTD
section 14. A layer of the RTD section at the side of the substrate
3 is in electrical contact with the electrode 11 through a heavily
doped layer (not shown). The RTD section has a double-barrier or
triple-barrier configuration including an InGaAs well layer and an
InAlAs tunnel barrier layer (or possibly InAs) in the case in which
the substrate 3 is of, for example, InP (semi-insulating). The
length L of a long side of the slot antenna primarily determines
the oscillation frequency, but the oscillation frequency also
varies with a cross-sectional area of a mesa of the RTD section 14
and the position of the protrusion of the electrode 12 in relation
to the long side of the slot antenna (the position being a position
between the center of the long side and a short side of the slot
antenna, and this position is at the center of the long side in
FIG. 1C). This type of configuration for an RTD oscillator, which
is described in an IEEE Microwave and Guided wave letters, vol. 5,
p. 219, 1995, "Applied Physics Express, vol. 4, p. 064101," is well
known to those skilled in the art.
[0024] Applying a DC voltage to the electrodes 11 and 12 results in
oscillation in a terahertz region, and this oscillation output is
emitted mainly toward the substrate 3 with high permittivity. As a
result, the output enters the two-dimensional electron layer 2 of
the HEMT device to cause the interaction described above. Here, it
is important that electric field E generated at the slot antenna in
a direction of its short side as illustrated in FIG. 1B makes an
entry in a direction orthogonal to a longitudinal direction of a
grating of the grating gate electrodes of the HEMT device.
[0025] The HEMT device will now be described. An InAlAs buffer
layer 19, an InGaAs channel layer 60, and an InAlAs carrier supply
layer 18 are arranged on the semi-insulating InP substrate 3 that
is provided with the RTD section, and the grating gate electrodes 6
and 7 are formed on a surface of the InAlAs carrier supply layer
18. These heteroepitaxial layers are non-doped layers in principle,
but delta doping with Si near an interface of the carrier supply
layer 18 with the channel layer 60 results in the two-dimensional
electron layer 2 formed near the interface of the two layers. A
source electrode 4 and a drain electrode 5 are formed at end
portions of the two-dimensional electron layer outside a region
corresponding to the gate electrodes, with heavily doped n+InGaAs
layers or ion-implanted layers 8 and 9 provided beneath the source
electrode 4 and the drain electrode 5 to obtain ohmic contact. To
obtain electrode contact with the n+InGaAs layers, an n+InGaAs
layer is further formed through epitaxial growth on a semiconductor
layer structure identical to that of the gate region, and this
layer alone is selectively etched to be removed in the gate region.
Suitable electrode materials include Ti/Pt/Au and Ti/Pd/Au, or Mo,
TiW, and polysilicon having the lower plasma frequencies. An
arrangement of a typical HEMT device has been described.
Additionally, in this embodiment, the gate electrodes 6 and 7 have
interdigital structures, so that a potential difference between the
adjacent grating electrodes can be adjusted. The transistor section
is arranged in this manner to include the source electrode and the
drain electrode provided at the end portions of the two-dimensional
electron layer and the gate electrodes provided above the
two-dimensional electron layer. With the arrangement described
above, the terahertz wave output of the terahertz wave oscillation
section propagates inside the substrate to be able to change the
distribution of electrons in the two-dimensional electron
layer.
[0026] These two devices can be integrated on the identical InP
substrate 3 through the epitaxial growth and alignment patterning
with a double sided aligner to achieve the interaction by the
terahertz electromagnetic waves. While the terahertz wave
oscillation section and the transistor section are arranged on two
different surfaces of the substrate 3 at opposite positions in the
arrangement described above, an alternative may be viable. That is,
the RTD oscillator and the HEMT device may be fabricated on
separate substrates, which then may be hybrid integrated by joining
the substrates with an adhesive having electromagnetic wave
permeability, by joining the substrates directly, or by joining
metals, such as Au, shaped to avoid the region of the
electromagnetic wave interaction. In any manners described above,
the transistor section is arranged so as to achieve the interaction
with the output of the terahertz wave oscillation section.
[0027] An operation of the device of the invention will now be
described. The emission of a terahertz wave from the HEMT device is
basically by an emission principle similar to that described in
Japanese Patent Application Laid-Open No. 2009-224467. That is, the
application of voltage between the source and the drain causes
drift current due to two-dimensional electrons at the
two-dimensional electron layer. When the frequency of the plasmon
oscillation that can be caused by periodic density modulation of
the two-dimensional electrons by the grating gate electrodes
achieves a predetermined relationship with the widths (gate
lengths) of the gate gratings, amplification gain is obtained. With
a typical carrier density of 10.sup.11 to 10.sup.12 cm.sup.-2 in
the two-dimensional electron layer, the two-dimensional electrons
can induce the plasmon as coherent polarization oscillations by
photons in a terahertz band. The voltage between the source and the
drain and a gate voltage are used to adjust the carrier density of
the two-dimensional electrons, the electron concentration of the
grating region, the drift velocity of electrons, and the like to
provide the amplification gain at the frequency of terahertz
electromagnetic waves from the RTD oscillator. In this manner, the
electromagnetic waves, with the oscillation frequency fixed by the
RTD oscillator, can be emitted with the amplified output.
[0028] Here, the carrier density can be changed by changing the
gate voltage for detuning from the amplifiable frequency to achieve
a transition so that the electromagnetic waves are not emitted to
the outside. Hence, the application of a modulation signal to the
gate electrodes of the HEMT device allows on/off-modulated
terahertz electromagnetic waves to radiate to the outside. The
roll-off frequency to the application of the modulation signal due
to parasitic impedance of the device can be made several hundred
GHz or greater, depending to some extent on the gate lengths as
with a common HEMT device. In this manner, modulation with a
significantly wider band is viable in contrast to an approach with
the application of a modulation signal to an RTD oscillator alone.
For InP, applying 0.3 V to the electrode 6 and 1 V to the electrode
typically induces carriers with densities of approximately
10.sup.12 cm.sup.-2 and 10.sup.14 cm.sup.-2 beneath the respective
electrodes. For example, adjustment to the 10.sup.12 cm.sup.-2
region to obtain agreement between the oscillation frequency of the
RTD oscillator and the plasma frequency induces plasma resonance in
a portion of the electrode 6 alone at a period of grating pitch of
the grating electrodes. This plasma resonance is emitted as
electromagnetic waves from the entire grating gate electrodes to
the outside.
[0029] Applying 0 V to the electrode 7 reduces the carrier density
thereof to lower than that of the region of the electrode 6 and
thus reduces a concentration difference of the plasma resonance (a
magnitude width), thereby preventing the electromagnetic waves from
being emitted. Hence, applying a square wave modulation signal of,
for example, 0 to 1 V, to the electrode 7 enables intensity
modulation of the terahertz electromagnetic waves. For an
oscillation frequency of, for example, 1 THz, the gate lengths
(grating widths) of the electrodes for inducing the plasma
resonance are on the submicron order. As an example, an arrangement
below may provide an exemplary embodiment. Here, one electrode has
a gate length of 100 nm, and the other electrode has a gate length
of 1800 nm, with 40 periods of a structure having a pitch of 2
.mu.m per period. The distance from the source to the drain is
approximately 80 .mu.m.
[0030] Note that these specific values are provided as a design
example, and the oscillation frequency, driving conditions, and the
like can be set in accordance with materials, carrier densities,
and grating electrode sizes (gate lengths, the ratio of the two
gate lengths, and a pitch). Guidelines for such designing can be
found in, for example, "Physical Review B, vol. 58, p. 1517," which
is an IEEE Microwave and Guided wave letters, vol. 5, p. 219, 1995.
Additionally, as described in Japanese Patent Application Laid-Open
No. 2009-224467, changing the gate lengths in stages from the
source to the drain may bring about further efficient emission.
[0031] The description above assumes the use of only the
amplification of the plasmon resonance between the source and the
drain for the emission of electromagnetic waves from the HEMT
device. Here, the emitted terahertz electromagnetic waves can be
confined in a substrate resonator to improve Q-value, thereby
further enhancing frequency stability and intensifying the
oscillation output. In other words, in the case of the
semi-insulating substrate 3, the attenuation of the terahertz wave
is extremely small. Such a substrate 3 having a thickness of, for
example, an integral multiple of .lamda./2 of the oscillation
wavelength can be a vertical resonator with reflecting mirrors of
electrodes 11 and 12 of the RTD oscillator and the electrodes 4 to
7 of the HEMT device. The refractive index of InP is approximately
3.5 for 1 THz oscillation, and thus the substrate 3 having a
thickness of 510 .mu.m for an effective wavelength 85 .mu.m for 1
THz can function as a 6.lamda. resonator. To change the oscillation
wavelength, a different substrate thickness may be selected or the
substrate may be polished to adjust the structure.
[0032] The specific examples in the embodiment described above have
been provided as examples. For example, the semiconductor to be
used may be GaAs based (AlGaAs, InGaAs, InGaP) or GaN based (InGaN,
AlGaN), instead of InP based. Additionally, in the case in which an
RTD oscillator and an HEMT device are hybrid integrated, different
crystals of, for example, InP based and GaAs based may be combined
for each device.
[0033] FIG. 4 is a diagram of an example of transmission of a
terahertz wave signal by the oscillator according to the present
embodiment. An electromagnetic wave generator including the
electromagnetic wave generation device according to this embodiment
is connected to a direct current power source 67 for driving the
RTD oscillator and to a power source 62 for driving the HEMT
device. A modulation power source 63 superimposes a modulation
signal on the gate electrodes of the HEMT device. As an example,
0.8 V is applied to the RTD oscillator, 2.8 V is applied between
the source and the drain of the HEMT device, and 0.3 V and 1 V are
applied between the source and the two gates, respectively, to
achieve oscillation at 0.8 THz. A modulation signal of 0 to 1 V is
then supplied to the latter gate electrode to obtain approximately
30 GHz in the form of a modulation bandwidth of 3 dB down. For a
detection section 65, for example, a schottky-barrier diode and a
low noise amplifier 66 may be used. With the arrangement as
described above, high speed wireless transmission can be performed
using the 8B10B code at 10 Gbps. Furtherance of high frequency can
be achieved by a different design, for example, for the gate
lengths of the HEMT device.
Second Embodiment
[0034] In the first embodiment, two surfaces of a substrate are
used for the interaction of the RTD oscillator and the HEMT device,
whereas this embodiment provides a device with the two devices
integrated on an identical surface of a substrate 20. FIG. 2A is a
plan view of this device, FIG. 2B is a sectional view along A-A',
and FIG. 2C is a sectional view along B-B'.
[0035] A typical arrangement of an RTD oscillator is illustrated in
FIG. 2B in a sectional view. An RTD section 25 having a mesa
structure as in the first embodiment and an insulator 29 are
interposed between two electrodes 21 and 24. In this embodiment, an
antenna provided as a resonator and an emitter is a patch antenna,
and the RTD oscillator oscillates at an oscillation frequency
determined by an antenna length with a bias supply line 23 as a
null point. Applying a DC voltage from a power source through a pad
22 to the electrodes 21 and 24 allows the RTD oscillator to
oscillate at the predetermined frequency. A standing wave from the
oscillation has antinodes at a left end and a right end of the
electrode 24 in FIG. 2A. The terahertz wave electric field of the
standing wave is applied to a source electrode 30 and a drain
electrode 31 of an HEMT device illustrated in FIG. 2C in a
sectional view. The patch antenna electrode 24 of the RTD
oscillator is insulated from the source and drain electrodes 30 and
31 by an insulation film 32 connected to the insulator 29, and only
an AC component, which is a terahertz wave from the oscillation, is
applied to the electrodes 30 and 31 of the HEMT device. The
electrode 21, which is a ground electrode, is arranged such that it
is absent beneath a semiconductor region 33 of the source and the
drain as illustrated in FIG. 2C. Consequently, reduced efficiency
of signal coupling between the RTD oscillator and the HEMT device
can be set, in contrast to an arrangement with a connection with
regard to direct current, increasing flexibility in design.
Additionally, the HEMT device is in part of the antenna of the
oscillator in this arrangement, precluding high frequency wiring
such as a microstrip line, which in turn precludes a problem of a
propagation loss or a yield reduction due to wiring.
[0036] An arrangement of the HEMT device (the layer configuration
of the semiconductor region 33, and an arrangement of electrodes,
such as a gate electrode 28, the source electrode 30, and the drain
electrode 31) is similar to that in the first embodiment. A gate
voltage set so as to obtain the plasmon resonance allows the
amplification of electromagnetic waves emitted from the patch
antenna to be greater than the output of the RTD oscillator alone.
This can be used to perform intensity modulation of the terahertz
electromagnetic waves. Alternatively, to achieve separation from
the output of the RTD oscillator, the terahertz wave output from
the HEMT device may be radiated from a surface of the substrate 20
opposite to the surface with the devices formed thereon, as marked
with reference numeral 34. In this case, an anti-reflection
coating, a hemispherical lens, and the like (not shown) may be
formed as appropriate on the surface of the substrate 20 with no
devices formed thereon.
[0037] Additionally, while the gate electrode 28 has a single
electrode arrangement to adjust the carrier density, grating gate
electrodes may be used as in the first embodiment. Furthermore, to
achieve the single electrode 28, a quantum wire structure having an
array of alternate submicron regions with different carrier
densities as described in the first embodiment may be provided at a
carrier supply layer beneath the gate electrode in place of the
grating electrodes.
[0038] As described above, in this embodiment, electrical wiring
(an antenna in this embodiment) to propagate the terahertz wave
output from a terahertz wave oscillation section is connected with
regard to alternating current to a transistor section. In other
words, the connection from the terahertz wave oscillation section
to the transistor section is in conduction at a frequency band of
the terahertz waves from the oscillation and is isolated with
regard to direct current. This embodiment offers an advantage of
alleviating difficulty in processing and alignment of two surfaces
of a substrate.
Third Embodiment
[0039] FIG. 3 is a plan view of an oscillation device 40 according
to a third embodiment, which is a modification of a structure with
two devices integrated on an identical plane as with the second
embodiment. In the second embodiment, which combines the RTD
oscillator and the HEMT device, the oscillation output of the RTD
oscillator is separated from the output of the HEMT device with
difficulty. As illustrated in FIG. 3, the present embodiment is not
designed to allow the output of an RTD oscillator to be emitted
from an antenna to the outside, but is designed to apply the
oscillation output to electrodes 49 and 50 of an HEMT device
through a transmission line 44.
[0040] In an RTD oscillator with an electrode 43 serving as a
resonator, an RTD section 45, as in the first and second
embodiments, and an insulation film, not shown, are interposed
between an electrode 42 and the electrode 43. The electrode 43
constitutes the resonator of the RTD oscillator and may be provided
with a circular dielectric section 53 in proximity to further
increase the Q-value of the resonator. The height of the dielectric
section 53 is approximately up to the height of the electrode 43
and the transmission line 44.
[0041] The oscillation output of the RTD oscillator is transmitted
through transmission lines formed by reference numerals 44 and 42
to electrodes 48 and 47, and AC electric fields of the oscillation
output transmitted to the electrodes 48 and 47 are applied to the
source electrode 49 and the drain electrode 50 of the HEMT device.
In this arrangement, a short circuit with regard to direct current
is prevented between the electrode 48 and the electrode 49 and
between the electrode 47 and the electrode 50, as with the
cross-sectional structure (FIG. 2C) described in the second
embodiment. Grating gate electrodes 51 and 52 are similar to those
in the first embodiment. Reference numeral 41 represents a pad, and
reference numeral 46 represents a bias supply line to the RTD
oscillator.
[0042] In this embodiment, in the oscillator with two devices
integrated on an identical plane, a modulated terahertz wave from
the HEMT device can be radiated efficiently.
Fourth Embodiment
[0043] While the devices according to the embodiments described
above operate as an oscillator, the devices may be used as
detection devices. In such a detection device, a detection signal
of an external terahertz wave the device is irradiated with can be
obtained in the form of drain voltage and drain current. The drain
voltage and the drain current increase when a gate voltage is
before proximity to a threshold voltage (in a case with the
voltage) or after the proximity to the threshold voltage (in a case
with the current). Thus, the gate electrode voltage, at which the
frequency of a terahertz electromagnetic wave to be detected agrees
with the frequency of the plasmon induced at the two-dimensional
electron layer of the HEMT device, is to be in proximity to the
threshold voltage. To achieve it, the carrier density of the
two-dimensional electron layer may be adjusted in advance through
modulation doping or the like. When a terahertz wave from the
integrated RTD oscillator is further applied, a mixing signal with
the oscillation frequency can be detected, allowing the detection
with excellent SN ratio.
[0044] As described above, this embodiment, which is formed as an
electromagnetic wave detection device, also includes a substrate
provided with a terahertz wave oscillation section including a
resonant tunneling diode structure, a two-dimensional electron
layer having a semiconductor heterojunction structure, and a
transistor section. The transistor section includes a source
electrode and a drain electrode provided at end portions of the
two-dimensional electron layer and a gate electrode provided above
the two-dimensional electron layer. When this transistor section is
irradiated with external terahertz waves, an output corresponding
to the intensity of the electromagnetic waves is obtained from the
transistor section. A terahertz wave output from the terahertz wave
oscillation section is allowed to enter the two-dimensional
electron layer to obtain the output of the transistor section as a
mixing signal with the oscillation frequency of the terahertz wave
from the terahertz wave oscillation section. An electromagnetic
wave detector including this electromagnetic wave detection device
may be used as a detector 65 illustrated in FIG. 4.
[0045] As described above, in the present embodiments, the
oscillator including the electromagnetic wave generation device in
a terahertz region enables high speed modulation through direct
modulation from an external power source. This allows an increase
in a transmission capacity for a use as a communication light
source, for example. The oscillator may also be formed as, for
example, an electromagnetic wave detection device, which is capable
of detecting a terahertz wave. Additionally, the present
embodiments can provide a device configuration with, for example,
high manufacturing yield.
[0046] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
* * * * *