CN101539519B - Method and device for generating electriferous excitors in quantum well by undoped photo excitation - Google Patents
Method and device for generating electriferous excitors in quantum well by undoped photo excitation Download PDFInfo
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- CN101539519B CN101539519B CN2009100207190A CN200910020719A CN101539519B CN 101539519 B CN101539519 B CN 101539519B CN 2009100207190 A CN2009100207190 A CN 2009100207190A CN 200910020719 A CN200910020719 A CN 200910020719A CN 101539519 B CN101539519 B CN 101539519B
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Abstract
The invention relates to a method and a device for generating electriferous excitors in a quantum well by undoped photo excitation, in particular to a method and a device for generating electriferous excitors. Laser with the energy higher than the forbidden band width of a ZnSe quantum well is used for exciting a zinc selenide well layer in a hetero-structure of zinc selenide/beryllium telluride so as to generate electrons and cavities. The device comprises a low-temperature thermostat, a laser, a spectrometer, and the like, and an optical path which consists of a reflective mirror, a lens and a prism is put in front of the laser, wherein the low-temperature thermostat is put in front of the prism, and the laser turned by the prism can be irradiated into the low-temperature thermostat; the other lens is put in the rear of the prism and can converge radiant light (namely fluorescence PL) of a zinc selenide/beryllium telluride sample in the low-temperature thermostat; and optical fibersand the spectrometer are put at the rear of the lens, wherein the spectrometer is provided with a CCD detector, and both the spectrometer and the CCD detector are connected to a computer so as to automatically complete spectrum detecting duties. The device has simple method, loose experiment condition and no influence on the structural quality of crystals.
Description
Technical field
The present invention relates to a kind of generation method and device of charged exciton, particularly a kind of method and device that in non-doped quantum well, produces charged exciton with photoexcitation.
Background technology
Zinc selenide (ZnSe) and tellurium beryllium (BeTe) all are important wide bandgap compound semiconductors, have stronger ionic and big binding energy.By the two zinc selenide of forming (ZnSe/BeTe) heterojunction structure good architecture quality is arranged, low dislocation desity and point defect are arranged, its lattice mismatch at the interface is less than 0.5%.ZnSe/BeTe has an II type band structure, makes the electronics and the hole of being excited to produce in the ZnSe layer that apart take place, thereby and can form the appearance that two-dimensional electron gas causes charged exciton in ZnSe layer.These characteristics make ZnSe/BeTe II type quantum well (or superlattice) structure become the good candidate material of research condensed state phenomenon.
Charged exciton is one of important morphological of coacervation, is to understand the important topic of having a mind to doping or being not intended to relate in the doped structure many two-phonon process of spin state.Mainly contain in I type quantum well according to the generation method of disclosed charged exciton and to mix, to be not intended to impurity and defective and the injection of tunnelling particle etc. in the doped structure by structure.U.S.'s academic journal magazine " PhysicalReview B " (2002, the 65th volume, the 115310th page, " Optical method for the determination of carrierdensity in modulation-doped quantum wells ") preparation method (G.V.Astakhov that the structure doping method generates charged exciton disclosed, et al., 65 (2002) 115310), also will cause the distortion of band structure even quantum well will be impacted but these foreign ions not only influence the architecture quality of crystal, and also make growth technique complicated simultaneously because of doping; U.S.'s academic journal magazine " Physical Review B " is (1996 in addition, the 54th volume, the 10609th page, " Exciton and trion spectral lineshape in the presence of an electron gas in GaAs/AlAs quantum wells ") preparation method (A.Manassen that tunnelling particle method for implanting generates charged exciton disclosed, et al., 54 (1996) 10609), but because the tunnelling particle injects reflection and the various defect influence of barrier layer that are subjected to barrier layer, the formation efficient of charged exciton is affected, and must uses two excitation sources simultaneously.
Summary of the invention
For defective and the deficiency that overcomes prior art, the present invention proposes a kind of method and device that in non-doped quantum well, produces charged exciton with photoexcitation.
A kind of method of using photoexcitation in non-doped quantum well, to produce charged exciton, step is as follows:
1. zinc selenide (ZnSe/BeTe) sample is cut into rectangular bimorph, after its surface is dried up with acetone soln decontamination, ultra-pure water flushing, high pure nitrogen, sample is sticked on the circular copper sheet again;
2. the copper sheet that will be pasted with zinc selenide is fixed on the sample holder, is positioned over then in the light cryostat that fills cryogenic liquid helium (He); The light cryostat links to each other with air pump, other heater strip and the temperature detection device of being equipped with of sample; By the pumping speed of independent bleeding regulating machine or the electric current in the heater strip, the temperature of sample is controlled between about 1～150K;
3. be that 2.8～4.0eV, excitation density are 0.001～200W/cm with energy
2The laser beam perpendicular projection on the upper surface of sample;
4. can export spectrometer to via optical fiber after the fluorescence planoconvex lens convergence that sample produces;
5. after the spectrometer beam split, obtain the fluorescence spectrum of charged exciton by the CCD detecting device.
Zinc selenide in the described step 1 (ZnSe/BeTe) sample structure can be a single quantum well, also can be Multiple Quantum Well or superlattice structure.
The thickness of ZnSe quantum well is about 10～80ML in zinc selenide in the described step 1 (ZnSe/BeTe) sample.
ML is the abbreviation of English words monolayer, i.e. molecular layer.For BeTe or ZnSe, 1ML is about 0.28nm.
Filling in the said method when temperature in the light cryostat of liquid helium wants to reach under the 4.2K needs regulate by pumping with exhaust blower; Temperature needs on 4.2K the time control temperature by the electric current of regulating in the heater strip.
Specimen in use ZnSe/BeTe of the present invention adopts GaAs substrate, and growing with the method for molecular beam epitaxy (MBE) forms, and is the preparation method of this sample below.
A kind ofly prepare the method for II type quantum well with molecular beam epitaxial process, step is as follows:
1, gallium arsenide (GaAs) substrate with (001) orientation is fixed in the holder of molybdenum (Mo) sample with indium (In);
2, logical cooled with liquid nitrogen growth room, confirm III-V family growth room's vacuum tightness be below 1 * 10-10Torr after, by the magnetic force driven rod sample is sent in the III-V family growth room; With the sample holder, the K-cell container of As solid source is housed and the K-cell container heat temperature raising of Ga solid source is housed, the temperature that makes it to reach setting is respectively 300 ℃, 100 ℃ and 750 ℃;
3, adjust the temperature of As source K-cell container, after making it to begin to warm to 295 ℃ by 100 ℃, temperature with sample holder and Ga source K-cell container is set at 550 ℃ and 915 ℃ respectively again, and begin to heat up, open the baffle plate of As source K-cell container simultaneously, the As molecular beam is radiated on the substrate, the evaporation of the substrate surface As cause because of underlayer temperature raises with compensation, and make the evaporation of As on the substrate surface reach balance with adhering to;
4, treat that Ga source K-cell container rises to 915 ℃ after, again the sample holder is warming up to 620 ℃, can on [1 ī 0] direction, observe by reflected high energy electron diffraction (RHEED instrument) instrument between temperature raising period, striped occurs if can observe clearly, the oxide of having removed substrate surface under this temperature then is described and obtains the orderly substrate surface of cleaning;
5, the generation of GaAs cushion: open the baffle plate that temperature has risen to 915 ℃ Ga source K-cell container, the Ga molecular beam is radiated on the substrate; This moment, the molecular beam of Ga and As was radiated at substrate surface simultaneously, the growth of GaAs cushion begins, growth time is 24 ~ 120 minutes, the thickness of GaAs cushion can reach 200 ~ 1000nm, turn off the Ga source this moment, and the temperature of Ga source K-cell container reduced to 750 ℃ by 915 ℃, reduce to 300 ℃ afterwards again, and a cleaning, smooth and orderly surface are arranged by the substrate that the RHEED instrument can be observed this moment;
6, stablize 5 minutes after, underlayer temperature is reduced to 580 ℃ gradually by 620 ℃, cool-down method is a staged, promptly each cooling is set at falls 5 ℃, sets next time when reaching design temperature again, divides and finishes cooling 8 times; After the cooling beginning, when observing image and do not have what ANOMALOUS VARIATIONS, the As source is turned off, and the As source temperature is transferred to 100 ℃ by 295 ℃ by the RHEED instrument; Underlayer temperature is reduced to 500 ℃ gradually by 580 ℃, and cool-down method is a staged, falls 10 ℃ at every turn; Afterwards, again underlayer temperature is reduced to 300 ℃ gradually by 500 ℃, whole temperature-fall period divides and carries out for 10 times, and each cooling is spaced apart 20 ℃;
7, observe RHEED instrument image and do not have what ANOMALOUS VARIATIONS, can turn off the RHEED instrument this moment, after the vacuum tightness of determining III-V family growth room becomes below 7.5 * 10-9Torr, turn off being used for the power supply of heated substrate, and prepare substrate is passed to II-VI family growth room by the high vacuum transmission pipeline;
8, be below 1 * 10-10Torr and the temperature in the Zn in the II-VI family growth room, Be, Te, Se and Mg source is heated to respectively after 150,820,150,50 and 200 ℃ in the vacuum tightness of determining II-VI family growth room, again substrate be sent to II-VI family growth room by III-V family growth room by ultra-high vacuum transmission pipeline; Substrate is warming up to 300 ℃ ~ 350 ℃, and the temperature in Zn, Be, Te, Se and Mg source is warming up to 307,1065,320,202 and 322.5 ℃ more respectively;
9, the generation of BeTe cushion: after the temperature in Be, Te source reaches 1065 and 320 ℃ respectively, stablized 30 minutes, open the baffle plate in Be, Te source, Be molecular beam and Te molecular beam are radiated at the surface of substrate, and the BeTe cushion begins to grow this moment; Monitor in real time with the RHEED instrument and (perhaps, to set, to control with computing machine according to the growth rate of each solid source of recording in advance before the growth.Down together), when the growth thickness of BeTe cushion was about 5ML, growth ending was turned off the Be source then earlier, turned off the Te source subsequently again, made surperficial rich Te;
10, the growth of Zn0.77Mg0.15Be0.08Se separation layer: the baffle plate of opening the Zn source earlier, the baffle plate of opening Se, Be and Mg source again carries out the growth of Zn0.77Mg0.15Be0.08Se separation layer, have Zn molecular beam, Se molecular beam, Be molecular beam and Mg molecular beam to be radiated at the surface of substrate simultaneously this moment respectively, when the separation layer growth thickness is 200 ~ 1000nm, finish growth, close Se, Be, Mg source earlier, close the Zn source again after about 5 ~ 10 seconds;
11, the growth of ZnSe potential well layer: open Zn, Se source, make the two be radiated on the substrate surface simultaneously, the temperature of Zn, Se solid source remains on 307 and 202 ℃ respectively, when the thickness of ZnSe layer growth is 10 ~ 80ML, growth ending, close the Se source earlier, after about 5 ~ 10 seconds, close the Zn source again, so that form rich Zn superficial layer;
12, the temperature in the growth of BeTe barrier layer: Be, Te source remains on 1065 and 320 ℃ respectively, open the Te source, through opening the Be source BeTe barrier layer that begins to grow after 5 ~ 10 seconds again, when the thickness of BeTe layer growth is about 10ML, growth ending is closed the Be source earlier, closes the Te source again after about 5 ~ 10 seconds, so that form rich Te superficial layer, can reduce to 150 ℃ this moment with the temperature in Te source; Above-mentioned growth course can be between ZnSe and BeTe the chemical bond that obtains the Zn-Te form at the interface
13, the growth of ZnSe potential well layer: open the Zn source, opened Se source growing ZnSe potential well layer again after 5 ~ 10 seconds, the temperature of Zn, Se solid source remains on 307 and 202 ℃ respectively, when the thickness of ZnSe layer growth is 10 ~ 80ML, growth ending is successively closed Se source and Zn source; Above-mentioned growth course can be between BeTe and ZnSe the chemical bond that obtains the Te-Zn form at the interface;
14, the growth course of the separation layer of repeating step 11 can obtain the thick Zn0.77Mg0.15Be0.08Se separation layer of 200 ~ 1000nm; To close Se, Be, Mg source earlier during growth ending, close the Zn source again after about 10 seconds, can not corroded with the protection sample at grown on top one deck Zn of sample as overlayer like this; Behind the growth ending, underlayer temperature is made as 150 ℃ and make it cooling, also the temperature in Zn, Se, Be and Mg source is set at simultaneously 100,50,820 and 150 ℃ and make it cooling respectively; Reduce to after 150 ℃ and the temperature of confirming the Se source reduce to below 100 ℃ when underlayer temperature, sample is taken out from the growth room, can obtain the quantum-well materials of complete ZnSe/BeTe/ZnSe form.
By above-mentioned growth course, we can obtain the quantum well structure (that is, two potential well layers and a barrier layer being arranged) of ZnSe/BeTe/ZnSe form.
Above-mentioned ML is the abbreviation of English words monolayer, i.e. molecular layer.For BeTe or ZnSe, 1ML is about 0.28nm.
Above-mentioned employed RHEED instrument is the refletcion high-energy electron diffraction instrument.
The thickness size of ZnSe quantum well has a significant impact the formation efficient of charged exciton among the present invention, and its thickness is about 10 ~ 80ML.Laser instrument can be cw type or impulse type.Incoming laser beam can be vertical with sample surfaces also can be at an angle.In addition, the fluorescence intensity of charged exciton is along with the enhancing of the reduction of temperature, excitation intensity and strengthen.
The principle of work of the inventive method is as follows:
Adopt energy the ZnSe trap layer among the heterojunction structure ZnSe/BeTe to be excited at low temperatures and produce electronics and hole greater than the laser of ZnSe quantum well energy gap, (promptly work as electronics and be in ZnSe layer because the minimum energy value in electronics and hole is in respectively in the different quantum well layers, and the hole when being in the BeTe layer their energy minimum), thereby the apart of generation electric charge, thereby make the electronics in the ZnSe layer higher concentration be arranged and generate electronegative charged exciton (promptly by two electronics and the exciton complex that the hole is formed) with respect to the hole.
Employed device in a kind of said method is made up of laser instrument, catoptron, two convex lens, prism, light cryostat, zinc selenide, optical fiber, spectrometer, CCD detecting device and computing machines.It is characterized in that catoptron, convex lens, prism are formed light path and be placed on before the laser instrument, can reflect the shoot laser of laser instrument, focus on and turn to; The light cryostat is placed in the prism front, can incide in the light cryostat through the laser of prism vergence; Another convex lens are placed on the back of prism, can receive fluorescence (PL) spectrum of zinc selenide in the light cryostat; Optical fiber and spectrometer are placed in the convex lens back, and spectrometer has the CCD detecting device, and both connections can be finished the spectral detection task on computers automatically.Described prism is the half-reflection and half-transmission prism.
The inventive method need not mixed in crystal prototype, also need not by tunneling effect sample to be carried out particle injects, this method is simple, can produce charged exciton as long as satisfy some loose experiment conditions (energy and shot densities as temperature, laser all allow very big variation range).Simultaneously because the present invention used be non-doped samples, so needn't consider influences the architecture quality problem of crystal and because of doping causes the complicacy of growth technique because of doping, also needn't as the tunnelling method, need two excitation sources and must consider that factors such as barrier width are to generating the influence of charged exciton.
Charged exciton is a fermion, also is one of important morphological of coacervation.Studying various spectral characteristics and the electrology characteristic of charged exciton under different experimental conditions, is the important topic of understanding the many physical processes that comprise spin state and high density attitude.It also has important use at aspects such as optical communication, quantum computer (comprising quantum information storage and processing), photoelectric devices simultaneously.
Description of drawings
Fig. 1 is the synoptic diagram of apparatus of the present invention.
Wherein: 1, laser instrument, 2, catoptron, 3, convex lens, 4, prism, 5, the light cryostat, 6, zinc selenide, 7, convex lens, 8, optical fiber, 9, spectrometer, 10, the CCD detecting device, 11, computing machine.
Fig. 2 is the crystal structure of zinc selenide of the present invention and can be with synoptic diagram.
Wherein the left side is the sectional view of ZnSe/BeTe structure (sample), and the right side is its corresponding band structure.C.B and V.B represent conduction band and valence band respectively, and DT represents the direct transition in the space in the ZnSe layer (being the transition of I type).
Embodiment
The present invention will be further described below in conjunction with drawings and Examples, but be not limited thereto.
Embodiment 1:(method embodiment)
A kind of method of using photoexcitation in non-doped quantum well, to produce charged exciton, step is as follows:
1. zinc selenide (ZnSe/BeTe) sample is cut into rectangular bimorph, after its surface is dried up with acetone soln decontamination, ultra-pure water flushing, high pure nitrogen, sample is sticked on the circular copper sheet again;
2. the copper sheet that will be pasted with zinc selenide is fixed on the sample holder, is positioned over then in the light cryostat that fills cryogenic liquid helium; The light cryostat links to each other with air pump, other heater strip and the temperature detection device of being equipped with of sample; Pumping speed by the bleeding regulating machine is controlled at the temperature of sample about 1.4K;
3. be that 2.85eV, excitation density are 0.1W/cm with energy
2The laser beam perpendicular projection on the upper surface of sample;
4. can export spectrometer to via optical fiber after the fluorescence planoconvex lens convergence that sample produces;
5. after the spectrometer beam split, obtain the fluorescence spectrum of charged exciton by the CCD detecting device.
Zinc selenide in the described step 1 (ZnSe/BeTe) sample structure is a single quantum well; The thickness of ZnSe quantum well is 20ML in the sample.
Embodiment 2:(method embodiment)
The inventive method embodiment 2 is identical with embodiment 1, and just the temperature of zinc selenide is by regulating Current Control in the heater strip about 20K; The energy of laser beam is that 3.06eV, excitation density are 5W/cm
2Zinc selenide (ZnSe/BeTe) sample structure is a Multiple Quantum Well, and the thickness of ZnSe quantum well is 28ML in the sample.
Embodiment 3:(method embodiment)
The inventive method embodiment 3 is identical with embodiment 1, and just the temperature of zinc selenide is by regulating Current Control in the heater strip about 70K; The energy of laser beam is that 3.35eV, excitation density are 90W/cm
2Zinc selenide (ZnSe/BeTe) sample structure is a superlattice structure, and the thickness of ZnSe quantum well is 40ML in the sample.
Embodiment 4:(method embodiment)
The inventive method embodiment 4 is identical with embodiment 1, and just the temperature of zinc selenide is by regulating Current Control in the heater strip about 140K; The energy of laser beam is that 3.8eV, excitation density are 180W/cm
2Zinc selenide (ZnSe/BeTe) sample structure is a superlattice structure, and the thickness of ZnSe quantum well is 55ML in the sample.
Embodiment 5:(device embodiment)
The embodiment of the invention 2 as shown in Figure 1, form by laser instrument 1, catoptron 2, two convex lens 3 and 7, prism 4, light cryostat 5, zinc selenide 6, optical fiber 8, spectrometer 9, CCD detecting device 10 and computing machines 11, it is characterized in that, catoptron 2, convex lens 3, prism 4 are formed light path and are placed on before the laser instrument 1, can reflect the shoot laser of laser instrument 1, focus on and turn to; Light cryostat 5 is placed in prism 4 fronts, can incide in the light cryostat 5 through the laser that prism 4 turns to; Another convex lens 7 are placed on the back of prism 4, can receive fluorescence (PL) spectrum of zinc selenide 6 in the light cryostat 5; Optical fiber 8 and spectrometer 9 are placed in convex lens 7 back, and spectrometer 9 has CCD detecting device 10, and both are connected on the computing machine 11, can finish the spectral detection task automatically.Described prism 4 is half-reflection and half-transmission prisms.
Claims (3)
1. one kind produces the method for charged exciton with photoexcitation in non-doped quantum well, and wherein charged exciton is electronegative exciton, and it is by two electronics and the exciton complex that the hole is formed, and this method step is as follows:
1) zinc selenide is cut into rectangular bimorph, after its surface is dried up with acetone soln decontamination, ultra-pure water flushing, high pure nitrogen, sample is sticked on the circular copper sheet again;
2) copper sheet that will be pasted with zinc selenide is fixed on the sample holder, is positioned over then in the light cryostat that fills cryogenic liquid helium; The light cryostat links to each other with air pump, other heater strip and the temperature detection device of being equipped with of sample; By the pumping speed of independent bleeding regulating machine or the electric current in the heater strip, the temperature of sample is controlled between 1～150K;
3) be that 2.8～4.0eV, excitation density are 0.001～200W/cm with energy
2The laser beam perpendicular projection on the upper surface of sample;
4) the fluorescence planoconvex lens of sample generation is assembled after export spectrometer to by optical fiber;
5) after the spectrometer beam split, obtain the fluorescence spectrum of charged exciton by the CCD detecting device.
2. a kind of method of using photoexcitation to produce charged exciton in non-doped quantum well as claimed in claim 1 is characterized in that the zinc selenide structure in the step 1) can be a single quantum well, also can be Multiple Quantum Well or superlattice structure.
3. a kind of method of using photoexcitation to produce charged exciton in non-doped quantum well as claimed in claim 1, the thickness that it is characterized in that ZnSe quantum well in the zinc selenide in the step 1) is 10～80ML.
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