The one-dimensional metal grating and the method for designing thereof that are used for the Terahertz quantum well detector
Technical field
The present invention relates to a kind of optical coupler and method for designing thereof, particularly a kind of one-dimensional metal grating and method for designing thereof that is used for the Terahertz quantum well detector.Belong to the semiconductor photoelectric device applied technical field.
Background technology
Terahertz (THz) ripple is meant electromagnetic spectrum medium frequency (1THz=10 from 100GHz to 30THz
12Hz), respective wavelength is from 3 millimeters to 10 microns, and the electromagnetic spectrum between millimeter wave and infrared light is regional.Because have high using value at aspects such as national defense safety, anti-terrorism, imaging of medical, material discriminating and environmental monitorings, THz science and technology has progressively received the many concerns of People more and more.
THz quantum well detector (THzQWP) is based on the semiconductor photo detector of GaAs/AlGaAs mqw material system.Intersubband transitions in the GaAs/AlGaAs MQW observed early than 1985 experimentally, was applied to subsequently in the infrared quantum well detector (QWIP).THzQWP is the natural expansion of QWIP at the THz wave band, and THzQWP is the earliest proposed in 2004 by people such as Canadian professors Liu Huichun.
See that from operation principle THzQWP is a kind of intersubband transitions type (ISBT) detector, during unglazed the photograph; Electronics is in the bound state of SQW; Under the effect of THz light field, the Electron absorption light field energy in the SQW transits to continuous state or accurate continuous state by bound state; Biased outside effect forms photoelectric current down, thereby realizes the detection to the THz ripple.According to quantum mechanics, the selection rule of ISBT has determined the electromagnetic field polarized component not response of such detector to being parallel to multiple quantum well layer.In other words, if incident light shines (front of device or the back side, promptly usually said normal incidence and back of the body incident) along the direction of growth of device, ISBT can not take place, and can not produce photoelectric current yet.Therefore; In experimental study; Common way is to be mapped in the device light is oblique, makes incident field comprise to be parallel to the polarization component of quantum trap growth direction, such as the Brewster angular direction incident along the QWP surface; Or the end face of QWP worn into miter angle, again along this surface feeding sputtering.Yet in many application of THz, an important application relevant with national defense safety and medical diagnosis is the THz real time imagery.This just need become focal plane array with combinations of detectors, and incident light must be perpendicular to the focal plane.So for the THzQWP focal plane array; The oblique incidence scheme of more than mentioning is no longer suitable; And must make optical coupler on the surface of device, will partly be converted into polarization perpendicular to the polarization electric field of quantum trap growth direction, to realize the ISBT under the normal incidence situation along parallel direction.
Grating is one of the most frequently used optical coupler, like reflective gratings, one-dimensional metal grating, V-shape grating, metal grill grating and the unordered grating etc. of standard.Wherein the one-dimensional metal grating is simple and practical relatively, prepares easily and has a considerable coupling efficiency.The design of common one-dimensional metal grating is based on simple grating equation, and in the GaAs/AlGaAs material system, grating material generally adopts Ti/Pt/Au.Fig. 1 has provided the structural representation of one-dimensional metal grating coupling THzQWP.
Given this, the present invention involves the design feature of THzQWP according to THz, proposes a kind of grating of THzQWP efficiently method for designing, and to the THzQWP of development high-performance normal incidence work, and the research of THz real time imagery and realization have great importance.
Summary of the invention
The technical problem that the present invention will solve is to provide a kind of one-dimensional metal grating and method for designing thereof that is used for the Terahertz quantum well detector.
In order to solve the problems of the technologies described above, the present invention adopts following technical scheme:
A kind of one-dimensional metal grating that is used for the Terahertz quantum well detector is characterized in that:
The cycle d of this one-dimensional metal grating equals the wavelength X of peak response frequency in the device material of said Terahertz quantum well detector of corresponding Terahertz quantum well detector
Peak
As preferred version of the present invention, the material of said one-dimensional metal grating is golden Au.
As preferred version of the present invention, the thickness of said one-dimensional metal grating is less than 1 μ m.When material was golden Au, the thickness of said one-dimensional metal grating was preferably 0.4 μ m.
The above-mentioned method for designing that is used for the one-dimensional metal grating of Terahertz quantum well detector comprises the steps:
1) according to the wavelength X of peak response frequency in the device material of this Terahertz quantum well detector of Terahertz quantum well detector
PeakThe cycle d of design one-dimensional metal grating makes d=λ
Peak
2) calculate one-dimensional metal grating and device material at the interface the size of electromagnetic field loss choose the material of the little metal of electromagnetic field loss as the one-dimensional metal grating;
3) thickness of design one-dimensional metal grating.
As preferred version of the present invention; In the step 1); Utilize the infrared Fourier transform spectrometer to measure the optogalvanic spectra of said Terahertz quantum well detector under the miter angle surface feeding sputtering situation; Obtain the intrinsic response zone and the peak response frequency f of device, calculate the corresponding wavelength X of THz wave in device material of peak response frequency f then
Peak, make the cycle d=λ of one-dimensional metal grating
Peak
As preferred version of the present invention, step 2) in, according to the more little relation of the high more electromagnetic field loss of conductivity of metal, choose the material of the high metal of conductivity as said one-dimensional metal grating.Further, the material of choosing said one-dimensional metal grating is golden Au.
As preferred version of the present invention, in the step 3), the thickness of choosing the one-dimensional metal grating is below the 1 μ m, and when material selection gold Au, the thickness of said one-dimensional metal grating is preferably 0.4 μ m.
Beneficial effect of the present invention is: this method can be the Terahertz quantum well detector a kind of grating of one-dimensional metal efficiently is provided; Realize the THzQWP that works under the high-performance normal incidence situation, to based on the research of the THz real time imagery of focal plane array with use significant.
Description of drawings
It below is elaboration to each sketch map that the present invention relates to.
Fig. 1 is the structural representation of one-dimensional metal grating coupling THzQWP device;
Fig. 2 is a miter angle surface feeding sputtering experimental configuration sketch map among the embodiment;
Fig. 3 is the graph of a relation that average intensity changed with the grating cycle in the device active region among the embodiment;
Fig. 4 is the graph of a relation that average intensity changes with grating thickness in the device active region among the embodiment.
Embodiment
Below in conjunction with accompanying drawing, be example with the THzQWP device of a reality, further specify embodiment of the present invention.
THzQWP device number: TQWPA.
The peak response frequency of TQWPA :~3.0THz.
The first step, the design grating cycle:
Adopt infrared Fourier to change the optogalvanic spectra that spectrometer has recorded TQWPA under miter angle surface feeding sputtering (Fig. 2) situation, the zone that meets with a response is about 1.0-5.0THz, and peak value of response is about 3.0THz.
If according to common one-dimensional metal grating method for designing, according to grating equation
mλ=nd(sinα+sinβ)
Wherein m is a diffraction progression, and λ is an incident wavelength, and n is the medium dielectric function, and d is the grating cycle, and α and β are respectively the incidence angle and the angle of diffraction.
For guaranteeing at the diffraction mould of response device region memory more than at least 1 grade (containing 1 grade), so the grating cycle should for
d≈λ
max/n
λ wherein
MaxFor the pairing wavelength of the main response region low-limit frequency of device, get λ
Max=200 μ m, n=3.2, then the grating cycle is d=62.5 μ m.
Inventor of the present invention simulates the Electric Field Distribution in the device active region (multiple quantum well layer) according to the concrete structure of device, and calculated the variation relation of average intensity with the grating cycle.The result finds that when the grating cycle wavelength corresponding with the peak response frequency (in device material) equated, the grating coupling efficiency is maximum, and was as shown in Figure 4.So in design of the present invention, confirm the cut-off frequency of grating according to the peak value of response frequency of device, and then design the cycle of grating, the cycle d that gets grating is the wavelength X of its peak value peak response frequency in device material
PeakFor TQWPA, the peak response frequency is about 3.0THz, and corresponding wavelength is 27.5 μ m, is 27.5 μ m so get the grating cycle of TQWPA.
Second step: choose grating material
At metal grating and semi-conducting material at the interface, there is loss in electromagnetic field, and the dielectric function of metal can be expressed as
Wherein ω is an electromagnetic field frequency, ω
MBe metal plasma body frequency, δ
MBe attenuation rate, determined the size of electromagnetic field loss.The metal δ that conductivity is higher
MLower, the conductivity of gold is higher, stable in properties, and semiconductor technology is ripe, so grating material can be chosen gold.
In the semiconductor technology; Common growth titanium and two thin layers of platinum earlier before GaAs superficial growth gold; Form Ti/Pt/Au, perhaps growth palladium, germanium, palladium, four thin layers of indium form Pd/Ge/Pd/In/Au earlier, and purpose is the adhesive force that forms good electrical contact and increase Au.Yet the conductivity of Ti and Pd is far below Au, can introduce very big metal to electromagnetic field and dissipate, so but when the growing metal grating direct growth Au reduce loss.
The 3rd step: design grating thickness
In the semiconductor technology, adopt electron beam evaporation at GaAs superficial growth gold usually, growth thickness is generally the hundreds of nanometer, the thickest 2.5 μ m that are no more than.Present embodiment has been simulated the relation of the light intensity in the device with the thickness of gold, and is as shown in Figure 5.In simulation context, light intensity increases with the thickness of gold, but the increase amplitude is no more than 10%.Consider the use amount of High Purity Gold and the growth thickness in the common semiconductor technology, preferably grating thickness is 0.4 μ m.
The 4th step: preparation of devices
On the table top of TQWPA device, coat photoresist, the use duty ratio is 50% grating mask board to explosure, on part table, forms the pattern of grating.Have the thick gold of the growth about 0.4 μ m of one deck on the table top of grating pattern through electron beam evaporation, adopting lift-off technology to wash photoresist off subsequently and also together remove, thereby form final one-dimensional metal grating attached to the gold on the photoresist.The grating device responsiveness of processing is 0.2A/W, and this numerical value is far above the responsiveness that has the grating THzQWP of report at present.
The grating method for designing of metal grating coupling Terahertz quantum well detector of the present invention is through grating cycle, thickness reasonable in design and choose suitable grating material; Can realize high performance grating coupling THzQWP, for the exploitation and the imaging applications of THzQWP array provides research means.
The other technologies that relate among the present invention belong to the category that those skilled in the art are familiar with, and repeat no more at this.The foregoing description is the unrestricted technical scheme of the present invention in order to explanation only.Any technical scheme that does not break away from spirit and scope of the invention all should be encompassed in the middle of the patent claim of the present invention.