Background technology
Terahertz (THz) ripple typically refers to frequency at 0.1~10THz (1THz=10
12Hz) electromagnetic wave, its wavelength is between microwave and near-infrared.On frequency domain, THz wave is in macroscopic view to the microcosmic transitional region, and on radiation mechanism, THz wave is in classical electromagnetic radiation to the quantum leap transitional region.For a long time, owing to lack effective THz wave generation, modulation, detection method, people are very limited for the electromagnetic application of this frequency range, so that this wave band is called as the Terahertz space in the electromagnetic spectrum.Yet because the peculiar property of THz wave, it has a wide range of applications in fields such as communication, spectrum analysis, safety inspections.In order to produce effective Terahertz wave modulation apparatus, people such as J.G ó mez Rivas are converted to the Terahertz surface plasma wave to THz wave, by temp control switch the Terahertz surface plasma wave are carried out switch modulation.If temp control switch is closed, then there is not signal to pass through; If temp control switch is open-minded, again the Terahertz surface plasma wave is coupled as THz wave, or directly transmits, thereby realized switch modulation the Terahertz frequency range with the Terahertz surface plasma wave.
Yet existing Terahertz surface plasma wave temp control switch need use grating, and is therefore still imperfect on performance.At first, and since the use of grating, the energy of grating meeting scattering Terahertz surface plasma wave itself, thus make signal energy incur loss.Secondly, need produce the grating that can reflect characteristic frequency Terahertz surface plasma wave, this has also increased difficulty and the cost made.The more important thing is that existing Terahertz surface plasma wave temp control switch can only be realized switch control to the characteristic frequency of very narrow wave band, can not regulate and control the Terahertz surface plasma wave of wide range.If there are all multi-wavelength signals far away of being separated by in the THz wave of incident the inside, just can't be simultaneously the signal of several wavelength be carried out switch modulation with conventional device.Therefore, we are necessary to design the Terahertz surface plasma wave temp control switch of a kind of low cost, low-loss, wide spectrum.
The background technology file:
1.J.Gómez?Rivas,M.Kuttge,H.Kurz,P.Haring?Bolivar,and?J.A.Sánchez-Gil,“Low-frequency?active?surface?plasmon?optics?on?semiconductors”Appl.Phys.Lett.88,082106(2006).
2.J.Gómez?Rivas,M.Kuttge,P.Haring?Bolivar,H.Kurz,and?J.A.Sánchez-Gil,“Propagation?of?surface?plasmon?polaritons?on?semiconductor?gratings”Phys.Rev.Lett.93,256804(2004).
3.JoséA.Sánchez-Gil,and?Jaime?Gómez?Rivas,“ Thermal?switching?of?the?scattering?coefficients?of?terahertz?surface?plasmon?polaritons?impinging
Summary of the invention
Technical problem: the object of the present invention is to provide a kind of Terahertz surface plasma wave temp control switch, solve technical problems such as cost of manufacture is higher in the background technology, energy loss is bigger, tuning frequency bandwidth is narrower.
Technical scheme: the present invention is a kind of Terahertz surface plasma wave temp control switch and control method thereof.Terahertz surface plasma wave temp control switch of the present invention comprises that a plasma frequency is in blade and a temperature control equipment of the intrinsic semiconductor wafer of terahertz wave band, two parallel placements at normal temperatures.Two blades are perpendicular to the intrinsic semiconductor wafer, the edge of a knife of two blades is from the distance of the intrinsic semiconductor upper wafer surface aerial decay distance of Terahertz surface plasma wave less than peak frequency, the distance between two blades less than the Terahertz surface plasma wave of peak frequency in the semiconductor surface propagation distance.The thickness of intrinsic semiconductor wafer is greater than the decay distance of Terahertz surface plasma wave in semiconductor of minimum frequency.Temperature controller is close to the lower surface of intrinsic semiconductor wafer.The temperature regulating range of temperature controller should make semiconductor wafer plasma frequency can along with variations in temperature greater than with less than the surface plasma wave frequency of being propagated.
The present invention proposes a kind of Terahertz surface plasma wave temperature-controlled process.Control the intrinsic semiconductor chip temperature by temperature controller, thereby change the carrier concentration of this intrinsic semiconductor.When semi-conductive carrier concentration changed, its plasma frequency also changed, thereby its dielectric constant will change.In general, when the frequency of Terahertz surface plasma wave during greater than the plasma frequency of intrinsic semiconductor wafer, this semiconductor shows as dielectric property, and its real part of permittivity is for just; When the frequency of Terahertz surface plasma wave during less than the plasma frequency of intrinsic semiconductor wafer, this semiconductor shows as metallic character, and its real part of permittivity is for negative.Because the Terahertz surface plasma wave can only be propagated at the opposite two media interface of dielectric constant, so the Terahertz surface plasma wave can be propagated at semiconductor surface when semiconductor shows as metallic character, and the Terahertz surface plasma wave can not be propagated at semiconductor surface when semiconductor shows as dielectric property, thereby has realized the function of switch.Blade is to be used for THz wave is converted into the Terahertz surface plasma wave and the Terahertz surface plasma wave of conducting is converted into THz wave.The knife-edge part that THz wave need be incided at a certain angle one of them blade when THz wave is converted into the Terahertz surface plasma wave could be realized maximum coupling efficiency.Equally, the THz wave of sending in the edge of a knife place of another blade also is the strongest on certain orientation.
Device can place general air, but influence the switch effect for the globule (when reducing temperature with temperature controller) that prevents airborne steam and condense in the intrinsic semiconductor surface absorbs THz wave, device is placed in the environment of vacuum or inflated with nitrogen can reach better effect.
In order to realize the switch control in the broad spectrum scope, need the temperature range of control to increase.Kong Zhi temperature and normal temperature differ bigger if desired, can adopt multistage temperature controller to realize.
Beneficial effect: the present invention has the following advantages:
1, cost of manufacture is low.Need not make grating, so the cost of whole device is lower in the intrinsic semiconductor wafer surface.
2, energy loss is little.Do not have structural scattering energy such as grating, so the energy loss of Terahertz surface plasma wave is less, signal to noise ratio is improved.
3, modulation range is wide.Can carry out switch modulation to the terahertz wave band of broad, improve the performance and the range of application of device.
Embodiment
The structure of Terahertz surface plasma wave temp control switch of the present invention is: two blades of parallel placement above the intrinsic semiconductor wafer, a temperature control equipment is close in intrinsic semiconductor wafer below.The edge of a knife of two blades of top is from the distance of the intrinsic semiconductor upper wafer surface aerial decay distance of Terahertz surface plasma wave less than peak frequency, distance between two blades is less than the Terahertz surface plasma wave of the peak frequency propagation distance at semiconductor surface, and the thickness of intrinsic semiconductor wafer is greater than the decay distance of Terahertz surface plasma wave in intrinsic semiconductor of minimum frequency.
The intrinsic semiconductor wafer be characterized as at normal temperatures or during near normal temperature its plasma frequency at terahertz wave band.When at a certain temperature, the plasma frequency of intrinsic semiconductor wafer is greater than the THz wave frequency of being transmitted.At this moment, the THz wave that a part incides the blade knife-edge part is coupled as the Terahertz surface plasma wave earlier, the Terahertz surface plasma wave can be propagated along the surface of intrinsic semiconductor then, when the Terahertz surface plasma wave arrived the knife-edge part of second blade, some Terahertz surface plasma wave was coupled into THz wave at last.Under this temperature, just realize like this to all conductings, as shown in Figure 1 less than the THz wave of the Terahertz frequency range of intrinsic semiconductor plasma frequency.Yet, by reducing temperature, the intrinsic carrier concentration of intrinsic semiconductor reduces, the plasma frequency of intrinsic semiconductor is along with reducing, at this moment the intrinsic semiconductor plasma frequency is less than the THz wave frequency of being transmitted, at this moment the Terahertz surface plasma wave of this frequency range can not be propagated on the intrinsic semiconductor surface, thereby has realized the blocking-up to the THz wave of this frequency range.On the contrary, by improving temperature, can realize conducting again to the THz wave of this frequency range.
The propagation distance of Terahertz surface plasma wave and externally the decay distance in gas (or vacuum) and the intrinsic semiconductor can try to achieve according to the dispersion equation of surface plasma, the dispersion equation of Terahertz surface plasma is:
K in the above formula
xIt is propagation constant along the Terahertz surface plasma wave of intrinsic semiconductor surface direction (+x direction).k
Z1And k
Z2Be perpendicular to respectively the intrinsic semiconductor surface upward to the propagation constant of (+z direction) and downward direction (z direction).C is the light velocity in the vacuum.ω is the pairing angular frequency of peak frequency in the THz wave.
Be the complex dielectric permittivity (ε of extraneous gas or vacuum
1Be the real part of extraneous gas complex dielectric permittivity, ε
1' be the imaginary part of extraneous gas complex dielectric permittivity).
Be the complex dielectric permittivity (ε of intrinsic semiconductor wafer
2Be the real part of intrinsic semiconductor complex dielectric permittivity, ε
2' be the imaginary part of intrinsic semiconductor complex dielectric permittivity).A, C and E be respectively this frequency Terahertz surface plasma wave edge+x direction ,+the z direction ,-phase constant of z direction, B, D and F be respectively this frequency Terahertz surface plasma wave edge+x direction ,+the z direction ,-attenuation constant of z direction.
The Terahertz surface plasma wave of this frequency is propagated on the interface of air and intrinsic semiconductor, when its intensity is reduced to original 1/e the Terahertz surface plasma wave the distance of process be propagation distance.Propagation distance δ
SpThe attenuation constant B of (+x direction) calculates and to try to achieve along the direction of propagation for expression, available Terahertz surface plasma wave:
Referring to Fig. 2, the Terahertz surface plasma wave is along the electric field strength perpendicular to the intrinsic semiconductor surface direction | E
z| be exponential damping in this direction (± z direction).Vertical range to the intrinsic semiconductor surface when electric field strength is reduced to the 1/e of intrinsic semiconductor surface field intensity is respectively the decay distance of this frequency Terahertz surface plasma wave in air and intrinsic semiconductor medium, uses δ respectively
dAnd δ
mExpression.Available Terahertz surface plasma wave is along trying to achieve perpendicular to the attenuation constant D and the F calculating of intrinsic semiconductor surface direction in air and intrinsic semiconductor:
Can this Terahertz temp control switch use, and selects for use suitable intrinsic semiconductor most important.In order to make this Terahertz temp control switch not need very low or very high temperature to regulate, the plasma frequency of this intrinsic semiconductor must be near terahertz wave band.This conclusion can be derived by the Drude model, according to the Drude model
In the above-mentioned formula,
Be the complex dielectric permittivity of intrinsic semiconductor, ε
2Be the real part of intrinsic semiconductor complex dielectric permittivity, ε
2' be the imaginary part of intrinsic semiconductor complex dielectric permittivity, ε
StaticBe the static dielectric of intrinsic semiconductor, ω
pBe the plasma angular frequency of intrinsic semiconductor, ω is the THz wave angular frequency that is transmitted, and is the momentum relaxation time, and it can be calculated by the carrier mobility of intrinsic semiconductor
In the above-mentioned formula, m
*Be the effective mass of charge carrier, μ is a carrier mobility, and e is a charge carrier institute carried charge.
According to the Drude model, by changing the plasma angular frequency of intrinsic semiconductor
pCan change intrinsic semiconductor complex dielectric permittivity real part ε
2Sign.If the plasma angular frequency of intrinsic semiconductor at normal temperatures
pMore approaching with the THz wave angular frequency of being transmitted, ω so
pNeed the amount of change just smaller.The plasma angular frequency of intrinsic semiconductor
pPlasma frequency f with intrinsic semiconductor
pRelation be:
The plasma angular frequency of intrinsic semiconductor
pCan calculate by following formula
In the above-mentioned formula, n is the free carrier concentration of intrinsic semiconductor, ε
0Be absolute dielectric constant, ε
StaticBe the static dielectric of intrinsic semiconductor, m
*It is the effective mass of charge carrier.Because the free carrier concentration of intrinsic semiconductor can change along with variations in temperature, so change the plasma angular frequency that temperature just can change intrinsic semiconductor
pThereby, the sign of change intrinsic semiconductor real part of permittivity.At normal temperatures, the plasma frequency f of intrinsic semiconductor
pNear (ω 1THz
pBe about 2 π * 10
12Rad/s) pairing carrier concentration can be calculated by following formula
Or 10
16Cm
-3
Because different semiconductors has different static dielectric and charge carrier effective mass, so as long as the free carrier concentration of this intrinsic semiconductor is near 10 at normal temperatures
15Cm
-3Or 10
16Cm
-3, its plasma frequency is all near 1THz.And the intrinsic semiconductor that meets such condition has indium arsenide and indium antimonide.Indium arsenide intrinsic carrier concentration under the temperature of 300K is about 7 * 10
14Cm
-3, indium antimonide intrinsic carrier concentration under the temperature of 300K is about 1 * 10
16Cm
-3
And other a lot of intrinsic semiconductors do not meet such requirement.Be about 2.1 * 10 such as GaAs intrinsic carrier concentration under the temperature of 300K
6Cm
-3If make the intrinsic carrier concentration of gallium arsenide wafer reach 1THz, the amplitude that needs to change temperature at normal temperatures will be greater than 650K, and obviously this is unpractical.Germanium intrinsic carrier concentration under the temperature of 300K is about 2 * 10 for another example
13Cm
-3If make the intrinsic carrier concentration of germanium wafer reach 1THz, need to change temperature amplitude at normal temperatures and be approximately 480K, this does not meet actual yet.And other semiconductors are about 1 * 10 as silicon intrinsic carrier concentration under the temperature of 300K
10Cm
-3, intrinsic carrier concentration is from 10
15Cm
-3Or 10
16Cm
-3All fall far short.So these intrinsic semiconductors all are not suitable for the Terahertz surface plasma wave temp control switch among the present invention.
Comparatively speaking, it is all very little to make that the intrinsic carrier concentration of indium arsenide and indium antimonide reaches the required temperature change of 1THz.Reach 1THz such as indium arsenide intrinsic carrier concentration under the temperature of about 250K, indium antimonide intrinsic carrier concentration under the temperature of about 333K reaches 1THz.These temperature all hardly differ with normal temperature 300K, so still be that the angle of cost considers that indium arsenide and indium antimonide all are more suitable for making near the Terahertz surface plasma wave temp control switch of modulation wave band 1THz than some other semiconductor from performance no matter.
If as intrinsic semiconductor, change to 30 ℃ from-30 ℃ when temperature with indium antimonide so, the plasma frequency of indium arsenide changes to 2.0THz from 0.8THz.If the THz surface plasma wave frequency of being transmitted is between 0.8THz and 2.0THz, such as the wideband THz surface plasma wave that is distributed in 0.9THz to 1.9THz, change to 30 ℃ from-30 ℃ when temperature so, the wideband THz surface plasma wave that is transmitted just becomes logical by breaking.On the contrary, if temperature changes to-30 ℃ from 30 ℃, the wideband THz surface plasma wave that is transmitted just by logical become disconnected.
If as intrinsic semiconductor, change to 127 ℃ from 30 ℃ when temperature with indium arsenide so, the plasma frequency of indium arsenide changes to 1.4THz from 0.4THz.If the THz surface plasma wave frequency of being transmitted is between 0.4THz and 1.4THz, such as the THz surface plasma wave that is positioned at 0.5THz and two frequencies of 1.3THz, change to 127 ℃ from 30 ℃ when temperature so, just can make the THz surface plasma wave of these two frequencies of being transmitted just become logical simultaneously by breaking.On the contrary, if the temperature of semiconductor wafer changes to 30 ℃ from 127 ℃, just can make simultaneously these two frequencies of being transmitted just by disconnected become logical.
So select suitable intrinsic semiconductor, just can carry out switch control to certain wave band THz surface plasma wave.In order to carry out switch control to the THz surface plasma wave of broad, variations in temperature is the bigger the better.But our semiconductor surface uniformity of temperature profile of needing the Terahertz surface plasma wave to flow through simultaneously, temperature controller is just very important preferably to select performance so for use.General current-modulation temperature controller has two surfaces, and when positive current was passed through temperature controller, heat can be transferred to another surface from a surface; If negative current passes through, the heat delivered direction is opposite.The electric current that temperature controller flows through is big more, and the temperature difference on two surfaces is big more, but a limit is arranged.
Suppose that we need the temperature of intrinsic semiconductor to change in-40 ℃ to 50 ℃ scope, because-40 ℃ temperature differs bigger with the room temperature ratio, we can adopt structure as shown in Figure 3, adopt multistage temperature controller and water cooling plant to realize.Topmost the upper surface of one-level temperature controller is close to an intrinsic semiconductor wafer, and its lower surface is close to a copper sheet.Below copper sheet, be close to two temperature controllers again, then at the lower surface filled with water device for cooling of these two temperature controllers.So just can be so that heat can transfer out from semiconductor quickly.If make conductor temperature than room temperature height, as long as we just can reach the pyrogenicity effect opposite the direction of the current delivery of top all temperature controllers.In order to make semi-conductive variations in temperature even, we can adopt the bigger temperature controller of area, are the temperature controller of 5cm * 5cm such as surface area.The area of copper sheet will make it greater than the area of two temperature controllers, such as adopt thickness be 2cm, area is the copper sheet of 5cm * 15cm.
The said temperature controller has adopted the two-stage temperature controller, if still can not reach the lower temperature of expection, we can also adopt three grades: i.e. temperature controller of ground floor, two temperature controllers of the second layer, the 3rd layer of three temperature controller.Each layer centre is separated by with copper sheet, and the temperature controller of basecoat contacts water cooling plant respectively.