KR102153955B1 - Colloidal quantum dot for exhibiting mid-infrared intraband transition - Google Patents

Abstract

The present invention relates to a colloidal quantum dot exhibiting an intra-band transition in the mid-infrared region, and provides a quantum dot that satisfies the composition of Formula 1 below.
[Formula 1]
Ag _x Au _y Se _z
In Formula 1, x, y, and z are each independently 0 to 3, and x+y is greater than 2.0 and less than or equal to 2.5.

Description

Colloidal quantum dot for exhibiting mid-infrared intraband transition

The present invention relates to quantum dots, and in particular, to colloidal quantum dots exhibiting an intra-band transition in the mid-infrared region.

Semiconductor colloidal nanocrystals have received great attention due to the size-controllable bandgap transition provided by the quantum confinement effect. In addition, the confinement effect induces a size-adjustable intraband transition that occurs between electronic states in the conduction band (CB) or valence band (VB). Steady state intra-band transitions of HgS and HgSe colloidal quantum dots have been reported, and mid-IR (mid-IR) intra-band transition-based optoelectronic applications have been thoroughly studied over the past few years, the reason for this is communication, thermography. , IR photodetectors, biosensors, and other potential applications.

Steady state in-band transitions, i.e., 1S _e -1P _e transitions, are allowed when excess electrons occupy the lowest electronic state of CB, i.e. 1S _e . Due to the immediate oxidation of electrons in the CB generated by photoexcitation through oxidation reactions induced by surrounding species such as water and oxygen molecules, it has been a challenge to keep the electrons in the 1S _e state. Until now, mercury chalcogenide colloidal quantum dots have been the only material to demonstrate this intra-band transition under ambient conditions. Since due 1S _e in a sufficiently long duration of the electron occupancy, H ₂ / H ₂ O-reduction potential (-4.45 eV Vs. vacuum) than 1S _e of a low energy level, the air in the nanocrystal-induce stability.

This steady-state intra-band transition, which has led to interesting research over the past few years, is well-represented in mercury chalcogenide nanocrystals, but there are concerns about handling toxic mercury ionic compounds during synthesis. In particular, the intermediate product, organic mercury, is very toxic, making it difficult for other researchers to study this interesting intra-band transition. Therefore, there is a strong desire to replace mercury with a non-toxic element and exhibit mid-infrared optical properties.

Accordingly, an object of the present invention is to provide a quantum dot that exhibits a steady state mid-infrared in-band transition occurring in a conduction band under ambient conditions.

The present invention provides a quantum dot that satisfies the composition of Formula 1 below in order to achieve the above object.

[Formula 1]

Ag _x Au _y Se _z

In Formula 1,

x, y and z are each independently 0 to 3,

x+y is more than 2.0 and not more than 2.5.

In the present invention, the preferred formula 1 is Ag _x Se _z , x is more than 2.0 and less than or equal to 2.5, and z may be 1.

Quantum dots according to the present invention may exhibit intra-band transitions in the mid-infrared region.

In the present invention, the absorption peak of the quantum dot may exhibit a complete Gaussian line shape without overlapping with other interband transitions.

In the present invention, the absorption half width of the quantum dot may be 700 to 770 cm ^-1 , the emission half width may be 500 to 540 cm ^-1 , and the Stokes shift may be 390 to 430 cm ^-1 .

In addition, the present invention provides a photodetecting device including the above-described quantum dots.

The quantum dot according to the present invention may exhibit a transition in a steady state mid-infrared band occurring in a conduction band under ambient conditions.

Figure 1A is a transmission electron microscope image (scale bar = 10 nm), Figure 1B is Ag ₂ having different sizes _{. 3} The absorption spectrum of Se nanocrystals, Figure 1C is a schematic diagram of a spectroelectrochemical cell, Figure 1D is Ag ₂ with different electrochemical potentials _{. 3} shows the differential absorption spectrum of the Se nanocrystal, and the positive potential (green) corresponds to the reduction of the nanocrystal film.
Figure 2 is Ag _{2 . 3 shows} the X-ray diffraction (XRD) spectrum of Se nanocrystals, and the upper and lower XRD spectra correspond to the reference bulk cube Ag ₂ Se (JCPDS 01-076-0135) and tetragonal Ag _2.3 Se nanocrystals, respectively.
3 is Ag _{2 . 3} shows a TEM image and a size histogram of Se nanocrystals, Figure 3A is 4.69 ± 0.51 nm, Figure 3B is 5.10 ± 0.71 nm, Figure 3C is 5.49 ± 0.79 nm, Figure 3D is 6.03 ± 0.59 nm, Figure 3E is 6.35 ± 0.58 nm.
Figure 4 shows the 14 days after synthesis (black), 24 days (red), 30 days (blue) Ag _{2 . 3} shows the air-stability of Se nanocrystals.
Figure 5 shows Ag ₂ with a diameter of 6.03±0.59 nm _{. 3} shows the EDS composition data (Ag/Se 2.31) of the Se nanocrystal.
6 is a Gaussian (Gaussian) line fitting Ag _{2 . 3} shows the absorption spectrum of Se nanocrystals.
Figure 7 is 6.35±0.58 nm size Ag _{2 . 3} shows the differential absorption spectrum of Se nanocrystals.
8 is a Gaussian line fitting Ag _{2 . 3} shows the absorption and emission spectra of Se nanocrystals, and FIG. 8A is Sample No. 1 and FIG. 8B is Sample No. 2.
Figure 9A is Ag _{2 . 3} Se CQD in-band absorption and emission spectra, Fig. 9B is Ag _{2 .} A schematic diagram of a ₃ Se CQD/ZnO FET device, Figure 9C is Ag ₂ under mid-infrared irradiation _. Photo-response of the movement characteristics of a ₃ Se CQD/ZnO TFT device, Fig. 9D shows zoom-in at a gate voltage to which -4 V to 2 V is applied.
10 is a photoluminescence measurement Ag _{2 . 3} shows the TEM and size distribution spectrum of the Se nanocrystal sample, FIG. 10A is Sample 2, 4.93±0.53 nm, FIG. 10B is Sample 3, 5.58±0.69 nm, FIG. 10C is Sample 4, 5.69±0.65 nm, and FIG. 10D Sample 5, 5.78±0.67 nm, Figure 10E is Sample 6, 6.40±0.56 nm.
11 shows photoluminescence of Sample 6 (black), N ₂ purging sample 6 (red), and water absorption (gray).
12 is Ag ₂ under mid-infrared irradiation _{. 3} shows the transfer characteristics of a ZnO TFT device without a Se layer.
13 is Ag _{2 . 3} shows the intra-band transition of Se in the mid-infrared region.
In all figures (Figs. 1, 2, 9, 13), Ag ₂ Se is Ag _{2 . 3} means Se.

Hereinafter, the present invention will be described in detail.

The quantum dot according to the present invention may satisfy the composition of the following formula (1).

[Formula 1]

Ag _x Au _y Se _z

In Formula 1,

x, y and z are each independently 0 to 3,

x+y is more than 2.0 and not more than 2.5.

The quantum dot according to the present invention may be a colloidal quantum dot. The colloidal quantum dot may mean a low-dimensional semiconductor nanomaterial in the form of a colloid having a size of several nanometers formed by chemical synthesis.

Preferably, in the quantum dot according to the present invention, Formula 1 is Ag _x Se _z , x is greater than 2.0 and less than or equal to 2.5, and z may be 1. More preferably, the x value may be 2.2 to 2.4. According to an embodiment, Formula 1 is Ag _{2 . It is 3} Se. In the case of the existing Ag ₂ Se, the Ag/Se ratio (atomic %) was close to or less than about 2.0. However, the quantum dot of the present invention is characterized in that the x value exceeds 2 (2.5 or less).

Accordingly, while the existing Ag ₂ Se exhibits a bandgap transition, the Ag _x Se _z quantum dot according to the present invention may exhibit an intra-band transition in the mid-infrared region. At this time, the infrared region has a wavelength range of 0.75 μm to 1 mm, of which the near infrared region is 0.75 to 3 μm, the mid-IR region is 3 to 25 μm, and the far infrared region is 25 μm or more. can do. Intraband transition may mean an electron transition occurring between discontinuous energy levels occurring within the conduction band (CB) of a semiconductor nanomaterial.

In addition, in the present invention, the absorption peak of the quantum dot may exhibit a complete Gaussian line shape without overlapping with other interband transitions. In the present invention, the absorption half width of the quantum dot may be 700 to 770 cm ^-1 , the emission half width may be 500 to 540 cm ^-1 , and the Stokes shift may be 390 to 430 cm ^-1 . The half width may mean the width of a distribution corresponding to 1/2 of the maximum value in a curve representing a mountain-shaped distribution. Stokes shift may mean a difference between excitation light energy and light emission energy according to Stokes' law.

In addition, the present invention provides a photodetecting device including the above-described quantum dots. The photodetector element may mean a transducer that detects light and converts its intensity into an electric signal. Types of photodetecting devices include photovoltaic cells, photoconductive devices, photodiodes, phototransistors, photomultiplier tubes, and photoelectric tubes.

[Example]

1. Experimental section

(1) material

Oleylamine (OLAm, tech. 70%), selenium (Se, 99.99%), and trioctylphosphine (TOP, tech. 90%) were purchased from Sigma Aldrich. Silver nitrate (AgNO ₃ , 99%) and tetrachloroethylene (TCE, ultrapure) were purchased from Alfa Aesar.

(2) synthesis

34 mg of AgNO ₃ was dissolved in 3 mL oleylamine. The AgNO ₃ solution was heated to 140° C. in an Ar atmosphere. Se precursor was prepared by dissolving 7.9 mg of Se powder in 0.1 mL trioctylphosphine (1 M TOP-Se). At 140° C., the Se precursor was quickly injected into the AgNO ₃ solution, and the color of the solution immediately turned black. Growth was allowed to proceed for 1-6 minutes, and the reaction was stopped by lowering the temperature. The product was precipitated by using chloroform and ethanol. The solution was centrifuged to obtain Ag _{2 . 3} Se CQD was separated and redispersed in tetrachloroethylene (TCE).

(3) Mid-infrared spectral spectrum

The mid-infrared absorption spectrum was measured using a Thermoscientific Nicolet iS10 FT-IR having a resolution of 0.482 cm ^-1 . Ag _{2 to} TCE _{. 3} Se CQD was dispersed and the sample was loaded into a liquid cell using a ZnS window.

(4) XRD

Ag _{2 .} The crystal structure of ₃ Se CQD was obtained with a Rigku D/Max Ultima III X-ray diffractometer using graphite-monochromated CuKα (λ=1.54056 Å) of 40 kV and 30 mA with a sample width of 0.01° in the range of 25° to 55°. .

(5) TEM

Ag _{2 .} The size and elemental analysis of ₃ Se CQD was measured using a Tecnai G2 F30ST (FEI) microscope by energy-dispersive X-ray spectroscopy (EDS) at 300 kV.

(6) Spectroscopic electrochemistry

The spectroelectrochemical cell consisted of three electrodes: a Pt wire reference electrode, a Cr working electrode and a Pt counter electrode. Tetrabutylammonium perchlorate (TBAP, 0.1 M) dissolved in propylene carbonate (PC) was used as an electrolyte. Ag _2.3 Se CQD was deposited on the surface of a working electrode through a dip casting method. The original ligand of the CQD film was successfully exchanged for EDT by immersing the CQD film in a pre-made EDT 2% ethanol solution. The IR differential change absorption spectrum was obtained under a constant electrochemical potential applied to the film in the range of 0.6 V to -0.4 V. Ag ₂ using a Thermoscientific Nicolet iS10 FT-IR spectrometer with 0.482 cm ^-1 resolution _. The spectral response of the ₃ Se nanocrystalline film was monitored.

(7) Device manufacturing

Chromium metal was sputtered on a glass plate to form a gate electrode of the device. Al ₂ O ₃ and ZnO layers were deposited on the substrate using in-situ plasma enhanced atomic layer deposition (PEALD) technology. Trimethyl aluminum was released into a chamber filled with Ar gas, and trimethyl aluminum for deposition was oxidized using carbon dioxide having an RF plasma. The RF plasma power density was 0.15 W/cm 2, and the chamber temperature was fixed at 200°C. This deposition was repeated 400 times to form a 45 nm-thick Al ₂ O ₃ layer. The ZnO layer was deposited by repeating 100 cycles with the same technique. Diethyl zinc and N ₂ O gas were used as a source and an oxidizing agent for the ZnO layer, respectively. The source and drain electrodes were deposited by the sputter method, and both had a thickness of 100 nm. The width and length of the active layer of the TFT were 1500 µm and 200 µm, respectively. The prepared TFT device was placed under N ₂ atmosphere before measurement. Ag _{2 . 3} Se samples were deposited on a TFT by a drop-casting method. Ag _{2 . The 3} Se sample was also subjected to ligand exchange using 2% EDT dissolved in an ethanol solution.

(8) photocurrent

Ag ₂ on ZnO FET _. The photocurrent of the ₃ Se CQD film was measured using an HP 4156A semiconductor analyzer. The gate voltage sweeping mode was performed with -10 V to 10 V sweeping at a scanning speed of 0.1 V/s. I connected the Newport 6580 IR globar to the DC power supply for the IR source. IR light was focused on the FET active layer using an off axis gold mirror. IR light having a wavelength shorter than 2 μm was blocked using a Ge window.

(9) photoluminescence

Ag _{2 . The} photoluminescence (PL) in the mid-infrared band of the ₃ Se CQD sample was measured with a hand-made mid-infrared photoluminescence spectrometer. Nd:YAG with a 532 nm, 10 Hz, and 5 ns pulsed laser was used as an excitation source, and a HeNe laser was used as an indicator. Infrared light from the sample passed through a hand-made Michelson interferometer and measured with an MCT detector (MCT-15-1.00, InfraRed Associate, Inc.). An interferogram of IR emission was obtained using a gated integrator, boxcar integrator, and SR250 with a 50-150 ns delay and a 5-15 ns gate width setting. The voltage signal from the boxcar was converted into a spectrum using a LabVIEW coding program. Nanocrystals (NC) were re-dispersed in an octane:hexane mixed solution and an Ag _2.3 Se CQD film was deposited on an aluminum substrate using a drop cast technique.

2. Results and discussion

As the experimental results show, the transition energy in the mid-infrared band was synthesized Ag _{2 .} By relying on the size of the ₃ Se nanocrystals, it was implied that quantum confinement is still valid in these nanocrystals. Interestingly, Ag _{2 . The 3} Se nanocrystals exhibited air-stability to some extent, and were also advantageous for performing optical measurements and device fabrication.

For the synthesis of nanocrystals, a single-pot and single-step hot-injection method was used. Briefly, AgNO ₃ oleylamine solution (3 mL, 1.1 g/L) was heated to 140° C. in an Ar atmosphere. A selenium precursor (1 M TOP-Se) prepared by dissolving 7.9 mg of Se powder in 0.1 mL of trioctylphosphine was quickly injected into the AgNO ₃ solution, and the solution immediately turned black. Nanocrystal growth was allowed to proceed for 1-6 minutes, and chloroform and ethanol solutions were added to the product solution to stop growth and induce precipitation. The product solution was centrifuged to obtain Ag _{2 . 3} Se nanocrystals were separated, and the nanocrystals were redispersed in tetrachloroethylene (TCE). Spherical Ag _{2 . 3} Se colloidal nanocrystals were obtained and, as shown in Figs. 1A and 2, were consistent with other studies.

As shown in Figures 1B and 3, prepared Ag _{2 . 3} Se nanocrystals exhibited a wavelength-controllable mid-infrared transition by changing the nanocrystal size. Mid-infrared absorption spectra were observed with near-infrared (NIR) absorption characteristics. Interestingly, as shown in Figure 4, the mid-infrared features were air-stable for several weeks.

Previous studies have reported a synthesis method for Ag ₂ Se nanocrystals showing a wavelength-controllable bandgap spectrum longer than 2.5 µm in the mid-infrared region. According to the reported composition information, the Ag/Se ratio (atomic %) was close to or less than about 2.0. However, as shown in FIG. 5, as measured by energy dispersive X-ray spectroscopy (EDS) analysis, the sample of this example exhibited an average value of about 2.3 in Ag/Se ratio (atomic%). Interestingly, the excess metal part of the nanocrystals was consistent with previously reported HgS or HgSe nanocrystals.

Optical data obtained in previous studies were interpreted as bandgap transitions for Ag ₂ Se nanocrystals, but as the results of this example clearly show, the mid-infrared absorption peak of the sample of this example was distinguished from other transitions in its vicinity. As these results suggest, the observed mid-infrared transition did not appear to be a bandgap transition. In general, the bandgap transition was well-overlaid with other interband transitions with a small energy gap in the range of several hundred meV, thereby exhibiting imperfections in the complete Gaussian line-shape as shown in FIG. 6. However, the absorption peak of this example observed in FIG. 1B exhibited a complete Gaussian line-shape with a half width (fwhm) of 703 cm ^-1 without overlapping with other interband transitions.

To confirm the origin of the mid-infrared transition, Ag ₂ with 2.4 nm and 3.2 nm radii in the infrared region _{. 3} Se nanocrystals were subjected to spectroscopic electrochemical (SEC) measurements, and the results are shown in FIGS. 1D and 7 respectively. Spectral fluctuations can be directly monitored by reducing/oxidizing nanocrystals with electrochemical potential through SEC measurements. Specifically, the SEC result can confirm the origin of the electron transition by finding the correlation between the bandgap transition and the intraband transition. Since both the bandgap and the intraband transition share the 1S _e state, reduction/oxidation of the nanocrystals induces an accurate correlation of the mid-infrared potential. At the negative electrochemical potential corresponding to the reduction of the nanocrystals, the transition in the mid-infrared band at 2201 cm ^-1 became strong, while the bandgap transition at 5485 cm ^-1 was faded. Conversely, oxidation of the nanocrystals led to fading of the mid-infrared transition and enhancement of the band gap transition strength. In particular, as shown in FIG. 1D, the intensity of the mid-infrared transition was similar to that of the near-infrared transition based on the SEC results. Similarity of the intensity of the mid-infrared transition characteristic was also observed in HgSe or HgS CQD indicating intra-band transition. In addition, the fwhm (about 750 cm ^-1 , Table 1, Fig. 8) of the mid-infrared transition was similar to that of HgS CQD, and was much wider than the narrow fwhm of local surface plasmon resonance (about 300 cm ^{- 1 in} the case of conventional HgS CQD). And, as these results suggest, the mid-infrared transition is actually Ag _{2 . It was} the in-band transition of the conduction band (CB) of the ₃ Se nanocrystal, and the quantum confinement effect still dominates the carrier density effect, leading to a size-dependent mid-infrared transition. Table 1 shows Ag _{2 .} The absorption and emission peak positions, FWHM and Stokes shift of ₃ Se nanocrystals are shown.

Sample
number Absorption peak
location
[cm ^-1 ] Absorbance
FWHM
[cm ^-1 ] Luminescence peak
location
[cm ^-1 ] radiation
FWHM
[cm ^-1 ] Stokes
shift
[cm ^-1 ] One 2534 ± 8 750 ± 12 2121 ± 8 517 ± 12 413 ± 12 2 2457 ± 8 720 ± 12 2053 ± 8 525 ± 12 404 ± 12

The bandgap energy obtained by SEC is tetragonal Ag _{2 . 3 It} was much larger than the estimated bandgap transition using the parameters for Se nanocrystals (m _e * = 0.32 and m _h * = 0.54, E _{Bulk BG} = 565 cm ^-1 , E _{NC BG} = 3420 cm ^-1 , r = 2.3 nm). However, the measured bandgap energy was consistent with the bandgap energy estimated by the orthorhombic structure (m _e *=0.1 and m _h *= 0.75, E _{Bulk BG} = 1450 cm ^-1 , E _{NC BG} = 6506 cm ^-1). , r = 2.3 nm), nevertheless, the crystal structure determined by the XRD result was found to be a quasi-stable cubic (or tetragonal) structure. Ag _{2 . 3} There is controversy over the values of the effective masses of electrons and holes in various Se crystal structures. The experimental values obtained in this example are cube Ag _{2 . 3} will provide useful information for understanding the physical properties of the effective mass of the carrier of the nanocrystal. As shown in Figs. 1B and 9A, the mid-infrared absorption spectrum has been found to be still affected by quantum confinement, so the conduction band The number of electrons in is in the range of 1 or 2 electrons per nanocrystal. In this case, the k·p approximation method can be useful for understanding the electronic structure of nanocrystals, and the intra-band transition energy can be estimated by finding the correlation between the intra-band transition and the band gap transition. In order to calculate the intra-band transition energy based on spectral electrochemistry, a k·p approximation was performed to calculate the non-parabolic energy dispersion, that is, Equation 1, and at this time, the Hamiltonian of the 2-band model, that is, the following Equation 2 was used.

[Equation 1]

[Equation 2]

Ak is the matrix element of the perturbing potential. In the sphere of radius R, the values of 1S _e and 1P _e for k were π/R and 4.49/R, respectively. The in-band transition energy for 1S _e -1P _e corresponds to the difference between E1P _e and E1S _e . Valence band variance and Coulomb interactions were not considered in this model. The bulk bandgap energy used here was 565 cm ^-1 corresponding to the bulk bandgap energy of the tetragonal structure of Ag _2.3 Se. The model fits somewhat well with the experimental data. For example, the bandgap energy of 5482 cm ^-1 (0.680 eV) gave 2230 cm ^-1 (0.276 eV), which was not significantly different from the experimental value of 2201 cm ^-1 (0.272 eV). However, further theoretical studies have been conducted with advanced calculation methods of Ag _{2 . It} will be necessary to understand the microscopic electronic structure of ₃ Se CQD.

The intra-band transition necessarily produces excitons in the 1S _e -1P _e state under photoexcitation. The formation of excitons, that is, electron-hole (eh) pairs, causes radiative recombination and also affects the charge transfer characteristics of the transistor. Ag ₂ in CB _{. 3} To confirm the formation of excitons in Se nanocrystals, Ag _{2 . 3} Se nanocrystal/ZnO thin film transistor was used to measure the change in mid-infrared absorption photocurrent.

9A shows Ag ₂ with different sizes _{. 3} shows the mid-infrared absorption and photoluminescence spectra of Se nanocrystals (FIG. 10). The PL spectra in the mid-infrared band of samples (1) to (2) were found in 2053 cm ^-1 to 2021 cm ^-1 , and their fwhm was about 520 cm ^-1 . The central peaks of the other emission spectra of the (3)-(6) samples were not taken into account in calculating the fwhm, because the emission spectrum partially overlapped with the water absorption peak at about 1700 cm ^-1 . The vibration mode (asymmetric stretching) of the CO ₂ gas molecule effectively extinguished the mid-infrared PL emission at 2349 cm ^-1 shown as a sharp drop in FIG. 9A, and the extinguished spectrum was obtained by increasing the N ₂ purging time in FIG. Recovered.

The in-band PL spectrum was Ag ₂ using a 532 nm Nd:YAG SHG pulsed laser _. It was obtained by photoexcitation of a ₃ Se nanocrystalline film. The photoexcitation power and beam cross-sectional area were 30.1 mW and 0.64 cm2, respectively. A gated-integrator collected a mid-infrared light emission signal superimposed with a laser pulse with a duration of 5 ns. The heat dissipation factor was excluded by dividing the raw PL data by the heat dissipation data. The details of the mid-infrared emission spectrometer are described in the experimental methods section. Interestingly, a Stokes shift of about 404-413 cm ^- is shown in Figure 9A by Ag _{2 .} Observed from ₃ Se CQD, in contrast to the negligible Stokes shift of HgS CQD. Ag _{2 .} The only meaningful data for the Stokes shift of ₃ Se CQD will be the two data from the bottom, because the two PL spectra do not overlap with the water absorption peak. The Stokes shift, which experimentally contributed to the exchange splitting of the electronic state involved in the in-band transition, would be beneficial in increasing the in-band PL quantum yield by avoiding the self-absorption of light emission. Additional bandgap engineering will also provide more options to improve the in-band PL intensity.

Therefore, the presence of the mid-infrared PL spectrum was a direct evidence of in-band excitons, which confirmed that the observed mid-infrared absorption was not an LSPR that did not show radiative recombination, but actually an intra-band transition.

Ag ₂ with a size-controllable mid-infrared in-band transition when the in-band transition functions as an IR color filter _{. 3} Se CQD can be used in wavelength-selective photodetectors. 9B illustrates the structure of an Ag _2.3 Se/ZnO TFT device. Aluminum, aluminum oxide (Al ₂ O ₃ ) and chromium were used as source/drain electrodes, dielectrics and gates, respectively. Ag _{2 . For the} measurement of the photocurrent response of ₃ Se nanocrystals, a thin layer of ZnO is Ag _{2 . It} was used as an active layer instead of the ₃ Se nanocrystalline film, because Ag ₂ as in the HgS CQD TFT device _{. It} was a small on/off ratio of the ₃ Se TFT device. Figures 9C and 9D (zoom-in) Ag _{2 . 3} Shows the movement characteristics of the Se/ZnO TFT device. The black curve represents the IR light off state, and the red and blue curves correspond to the results under IR irradiation according to the presence or absence of a Ge filter that blocks IR light wavelengths shorter than about 2 μm (5000 cm ^{- 1} ), respectively. Globa was used as the IR light source, and apparently the property responded immediately to IR irradiation, which confirmed the occurrence of excitons in the band under photoexcitation. The negative threshold voltage (V _th ) shift is Ag _{2 . It} was shown that a positive charge was generated in the ₃ Se nanocrystal layer, which improved electron accumulation in the ZnO layer. Depending on the presence or absence of a Ge filter, V _th values were -0.61 V and -0.43 V, respectively. For reference, Ag _{2 . The} ZnO TFT device without the ₃ Se nanocrystalline layer did not respond to mid-infrared irradiation as shown in FIG. 12.

In conclusion, the metal excess of Ag _{2 .} The steady state intra-band transition of ₃ Se nanocrystals is presented. Spectroscopic electrochemical experiments confirmed the in-band absorption characteristics by finding a strong correlation between the mid-infrared transition and the NIR bandgap transition. Ag _{2 .} Photoexcitation of the ₃ Se nanocrystalline solid induces the formation of intra-band excitons, thereby revealing a new intra-band PL spectrum in the mid-infrared region. In addition, in-band excitons are Ag _{2 .} It caused a negative shift of V _th in the movement characteristics of the ₃ Se/ZnO TFT, which can be used in a wavelength selective IR TFT photodetector by using a Gaussian line-shaped intra-band transition. Non-toxic Ag ₂ showing steady state intra-band transition _{. 3} Se nanocrystals will be used as promising materials for communications, mid-infrared bio-imaging, bio-optical, photovoltaic and photo-magnetic applications.

Claims (6)

Satisfies the composition of the following formula (1),
Quantum dots showing intra-band transitions in the mid-infrared region:
[Formula 1]
Ag _x Se _z
In Formula 1,
x is from 2.2 to 2.5,
z is 1. delete delete The method of claim 1,
The absorption peak of a quantum dot is a quantum dot that shows a complete Gaussian line shape without overlapping with other interband transitions. The method of claim 1,
The absorption half width of the quantum dot is 700 to 770 cm ^-1 , the emission half width is 500 to 540 cm ^-1 , the Stokes shift is 390 to 430 cm ^-1 . A photodetecting device comprising the quantum dot according to claim 1.

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