KR100967628B1 - Enhanced structural, electrical and optical characteristics with lithium - zinc oxide thin film and Dorf the manufacturing methods - Google Patents

Abstract

The present invention is a promising broadband semiconductor useful for the fabrication of optical devices capable of meeting various demands in the optoelectronic field by improving the structural, electrical and optical properties by appropriately doping lithium (Li) in zinc oxide (ZnO) thin films. The present invention relates to a high quality Li-doped ZnO thin film and a method for manufacturing the same, wherein the method for preparing a Li-doped ZnO thin film having the improved structural, electrical and optical properties of the present invention is pulsed laser deposition (PLD). The doping effect of Li ions on the structural, electrical and optical properties of ZnO thin films obtained by producing high quality ZnO thin films by doping Li ions into ZnO under specific conditions using the .

The present invention constructed as described above makes it possible to easily and repeatedly produce high quality ZnO thin films having improved structural, electrical and optical properties by doping Li ions into ZnO under constant conditions using pulsed laser deposition techniques.

Lithium, thin film, dopant, zinc oxide, optoelectronics, properties.

Description

Improved structural, electrical and optical characteristics with lithium-zinc oxide thin film and Dorf the manufacturing methods

The present invention relates to a Li-doped ZnO thin film having improved structural, electrical and optical properties, and a method of manufacturing the same, and more particularly, to improving structural, electrical and optical properties by appropriately doping lithium in a ZnO thin film as a promising broadband semiconductor. The present invention relates to a high quality Li-doped ZnO thin film having improved structural, electrical and optical properties, which can be usefully used in the manufacture of an optical device capable of meeting various needs in the optoelectronic field.

In general, ZnO thin films having various dopants as promising broadband semiconductors can be presented as important materials in manufacturing optical devices for meeting various demands in the optical field.

Specifically, ZnO is a broadband semiconductor material, that there is known a DC broadband of 3.3 eV at 300K and has a large exciton of 60 meV binding energy (WY Liang and AD Yoffe, Phys . Rev. Lett. 20 (1968) 59 This interest in ZnO is mainly related to the application of ZnO in the optoelectronic field with the above characteristics. The band structure and optical properties of ZnO are very similar to those of GaN.

As is known, GaN is widely used in the production of green, blue-ultraviolet, and white light emitting diodes. However, ZnO has several advantages in addition to GaN, which is conventionally used in the optoelectronic field as described above, and these advantages include the availability of high quality ZnO substrates and a very large exciton bonding energy. In addition, ZnO crystals are grown by several methods, which are simpler crystal growth techniques.

This may also result in the advantage of being able to produce ZnO based devices at lower cost. Moreover, the large exciton binding energy of this ZnO's 60 meV makes strong near-band-edge (NBE) exciton emission at room temperature and high temperature. This is because this value is 2.4 times larger than that of room temperature (RT) thermal energy ( K _b T = 25 meV).

Moreover, in addition to the above-mentioned advantages, ZnO also has the advantage of being resistant to high energy radiation. This high resistance to energy radiation offers the possibility that ZnO can be used even in narrow spaces without compromising its efficiency, making it more useful for the manufacture of optoelectronic devices. At the same time, as a transparent conductive oxide, ZnO is a useful material that can be used as a transparent conductive film, solar window and bulk sonic device (U. Ozgur, YI Alivov, C. Liu, A. Teke, MA Reshchikov, S. Dogan, V. Avrutin, SJ Cho, and H. Morkov, J. Appl. Phys. 98 (2005) 041301; B. Sang, A. Yamada, and M. Konagai, Jpn. J. Appl. Phys . 37 (Part 2) (1998) L206; P. Verardi, N. Nastase, C. Gherasim, C. Ghica, M. Dinescu, R. Dinu, and C. Flueraru, J. Crystal Growth 197 (1999) 523 JF Cordaro, Y. Shim, and JE May, J. Appl. Phys . 60 (1986) 4186.), ZnO-related materials have attracted considerable attention (YR Ryu, S. Zhu, JD Budai, HR). Chandrasekhar, PF Miceli, and HW White, J. Appl. Phys . 88 (2000) 201; DC Look, Mater.Sci. And Eng.B 80 (2001) 383; FK Shan, BC Shin, SC Kim, and YS Yu , J. Eur. Ceram. Soc . 24 (2004) 1861; FK Shan and YS Yu, J. Eur. Ceram. Soc . 24 (2004) 1869; HT Ng, B. Chen, J. Li, J. Han, and M. Meyyappan, Appl. Phys. Lett . 82 (2003) 2023; XT Zhang, YC Liu, LG Zhang, JY Zhang, YM Lu, DZ Shen, W. Xu, GZ Zhong, XW Fan, and XG Kong, J. Appl. Phys . 92 (2002) 3293; FK Shan, ZF Liu, GX Liu, WJ Lee, GH Lee, IS Kim, BC Shin, and YS Yu, J. Electroceram . 13 (2004) 195; FK Shan, BC Shin, SW Jang, and YS Yu, J. Eur . Ceram . Soc . 24 (2004) 1015).

On the other hand, in order to realize ZnO having the above excellent characteristics in an optical device based thereon, growth of both n-type and p-type ZnO is required. By the way, most semiconductors including ZnO have the property of naturally exhibiting n-type conductivity. Thus, n-type ZnO thin films are very easy to manufacture and their conductivity can be easily controlled by doping with different materials and different doping levels. However, p-type ZnO is considered very difficult to obtain. Among broadband semiconductors, the addition of certain impurities causes sometimes very unpredictable changes in their electrical and optical properties, and some literature suggests that p-type ZnO is achieved by other doping methods such as the addition of certain impurities. Is described. However, the method according to the above-mentioned documents has little problem that the properties of the obtained p-type ZnO are difficult to be used in the manufacture of optoelectronic devices, even if few results can be repeated or are achieved. there was.

Therefore, there is a need to achieve ZnO and a method of manufacturing the same, which can be easily and repeatedly produced and have satisfactory properties and can be used in the manufacture of optoelectronic devices.

As a related art related to a ZnO manufacturing method having the above characteristics, a "Zinc oxide oxide semiconductor thin film manufacturing method" of Korean Patent Application No. 2000-0024465 is disclosed. The present invention relates to a method of manufacturing a zinc oxide oxide semiconductor thin film using a post-heat treatment process under a high purity oxygen atmosphere to reduce oxygen vacancy, by depositing zinc oxide doped with aluminum on an aluminum oxide substrate. A first step of growing a zinc oxide sample and a post-heat treatment of the zinc oxide sample for a predetermined time within a predetermined temperature to produce a zinc oxide oxide semiconductor thin film, the zinc oxide oxide semiconductor thin film is a high purity oxygen atmosphere quartz Zinc oxide oxide semiconductor thin film manufacturing method comprising the second step of manufacturing in a high temperature furnace having a tube, but the high quality with easy repeatability and satisfactory characteristics In terms of providing a ZnO thin film, it still does not solve the problem. I can't.

Accordingly, the present inventors, as described above, have made intensive studies to solve the above-mentioned problems in consideration of the situation in the technical field, and have a satisfactory characteristic that can be repeatedly produced by using a specific technology under certain conditions. The ZnO thin film can be obtained to complete the present invention.

Accordingly, it is an object of the present invention to provide a high quality ZnO thin film that can be repeatedly produced while having improved structural, electrical and optical properties.

Another object of the present invention is to provide a method for more easily manufacturing a ZnO thin film having the above characteristics.

In order to achieve the above object of the present invention, the present inventors have fabricated a high quality ZnO thin film by doping lithium (Li) ions into ZnO under various conditions using pulsed laser deposition (PLD) technology. The purpose of the present invention was to examine the doping effect of Li ions on the structural, electrical and optical properties of the resulting ZnO thin film using various analytical instruments, and to select the ZnO thin film which can achieve the object of the present invention. Could be achieved.

Method for producing a lithium-doped ZnO thin film having improved structural, electrical and optical properties of the present invention for achieving the above object;

A method of fabricating a ZnO thin film by doping lithium (Li) ions into ZnO using pulsed laser deposition (PLD) technology, the method comprising

Mixing a high purity lithium oxide powder with the ZnO powder and a homogeneous agent to obtain a desired amount of lithium dopant in the high purity ZnO powder;

Uniaxially pressing the mixture into a specific shape to obtain a target;

Sintering a target of a specific shape obtained above at a constant temperature in a furnace; And

The energy density of the excimer laser is set constant. The ablated material is then characterized in that it consists of depositing under a specific condition onto a substrate on a target.

According to another configuration of the invention, the amount of the lithium dopant is 0.001 to 0.1 at. Characterized by a percentage.

According to another configuration of the present invention, the substrate temperature to be deposited is characterized in that 100 to 600 ℃, more preferably 200 to 500 ℃.

According to another configuration of the invention, the specific deposition conditions are characterized in that the repetition frequency of the laser is 4 to 6 Hz, the background O ₂ pressure is 90 to 110 mTorr.

According to another configuration of the invention, the deposition time is characterized in that 1 hour.

Lithium-doped ZnO thin film having improved structural, electrical and optical properties of the present invention for achieving the above another object is characterized in that obtained by the above-described manufacturing method.

The lithium-doped ZnO thin film having the improved structural, electrical and optical properties of the present invention and the method of manufacturing the same as described above are manufactured by high-quality ZnO thin film by doping Li ions into ZnO under constant conditions using a pulse laser deposition technique. By fabricating the ZnO thin film, the doping effect of Li ions on the structural, electrical and optical properties of the obtained ZnO thin film can be observed using various analytical instruments, thereby providing a high quality ZnO thin film having improved structural, electrical and optical properties. In addition, the method according to the invention makes it possible to easily and repeatedly produce high quality ZnO thin films with improved structural, electrical and optical properties.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail with reference to preferable embodiment and attached drawing. However, the embodiments described below are merely for illustrating the present invention in more detail, and the scope of the present invention is not limited thereto.

In order to measure the structural, morphological and optical properties of the thin film obtained according to the present invention, an X-ray diffractometer, atomic force microscope, spectrophotometer and spectrometer were used, and hole measurement was also performed to identify electrical properties of the thin film. Was performed.

The PLD system used according to the configuration of the present invention has already been disclosed by the inventors (FK Shan, BI Kim, GX Liu, ZF Liu, JY Sohn, WJ Lee, BC Shin, and YS Yu, J. Appl. Phys 95 (2004) 4772; FK Shan, and YS Yu, Thin Solid Films 435 (2003) ® FK Shan, GX Liu, WJ Lee, and BC Shin, J. Appl. Phys . 101 (2007) 053106; FK Shan , GX Liu, WJ Lee, GH Lee, IS Kim, and BC Shin, Appl. Phys. Lett . 86 (2005) 221910). The energy density of the excimer laser is set at ˜1.5 J / cm 2. The ablated material is then deposited on a substrate held 53 mm above the target. To prepare the target, a high purity ZnO powder (99.99%) purchased from Adrich Co. was used. To obtain the desired amount of lithium dopant (0.01 at.%) In the target, high purity lithium oxide powder was uniformly mixed with the ZnO powder for 20 hours in a milling system using a plastic container with balls. Disc shaped targets of 1 inch diameter and 0.2 inch thickness were obtained by uniaxial pressing at 700 kg / cm 2. The disk-shaped target was then sintered at 1200 ° C. in a furnace for 4 hours.

During the deposition, the conditions are as follows: the repetition frequency of the laser is 5 Hz; Background O ₂ pressure is 100 mTorr; And the substrate temperature was varied to 100 to 600 ℃. The deposition time is 1 hour.

Under the above conditions, the thickness of the thin film was prepared to about 400 nm, and after the deposition was completed, the thin film was cooled to room temperature in a natural state and its properties were measured as follows.

The crystal structure of the prepared thin film was measured by X-ray diffraction (XRD, X'pert MPD, Panalytical, 40 kV, 30 mA) measurement using CuKα1 emission having λ = 1.5406 Hz. The surface morphology of the thin film was examined by scanning probe microscope in AFM mode (SPA-400, Seiko Instruments). In addition, the electrical parameters of the thin films were measured by the van der pauw method at room temperature using a Hall-effect measurement system, and the transmittance of the thin films was UV-Vis-IR spectrophotometer in the wavelength range of 300-600 nm. (Vary-5, Australia). The excitation source used for the photoluminescence (PL) measurement is a He-Cd laser operated at 325 nm with an output voltage of 30 mW. The light emitted from the sample is focused into the inlet slit of the monochromator with a spectrum rated at 1200 grooves / mm, which is taken by the photomultiplier tube. Cutoff filters were used to suppress scattered laser radiation. On the ultraviolet side, the cutoff wavelength of this filter is about 340 nm.

1 shows an XRD pattern of a Li-doped ZnO thin film (0.01 at.%) Deposited at different temperatures on a sapphire (001) substrate using PLD. The Y axis was plotted on a log scale. It can be seen from FIG. 1 that the growth temperature, which is the temperature of the substrate, is important for determining the structure of the crystal. (002) orientation was observed in all Li-doped ZnO thin films except sapphire (006) peak. However, it can be clearly seen that the (002) peak intensity is enhanced as the growth temperature is increased. An increase in this (002) peak intensity means that the quality of the film increases with increasing growth temperature. As can be seen from Figure 1, the ZnO (004) peak appeared in the thin film was grown at a temperature of more than 300 ℃ and its intensity increased with increasing the growth temperature. The crystal structure at different temperatures can be explained by the mobility of the particles at different growth temperatures. Particles at low temperatures have low surface mobility, and low particle mobility prevents crystallization of the thin film. This weakens the (002) peak and the (004) peak.

The surface morphology of the thin film was examined by scanning probe Microsco (SPA-400, Seiko Instruments) in AFM mode and is shown in FIG. 2. 2 (a), (b), (c), (d), (e), and (f) were deposited on sapphire (0001) substrates at 100, 200, 300, 400, 500, and 600 ° C., respectively. An AFM image of a Li-doped ZnO thin film is shown. The scanning range is 2 μm × 2 μm. The AFM image of the thin film does not have a noticeable change in visual observation. The values of particle size, particle average diameter and roughness (RMS) irradiated by AFM are shown in Table 1 below.

Particle Size, Average Grain Diameter, and Roughness of Li-doped ZnO (0.01 at.%) Thin Films Deposited at Various Temperatures on Sapphire (001) Substrates Using PLD Sample
(℃) Particle size
(ㅧ 10 ⁴ nm ² ) Average diameter
(nm) RMS
(nm) 100 2.89 192 2.90 200 3.19 202 3.52 300 1.99 159 4.14 400 2.12 164 3.01 500 3.49 211 3.00 600 4.40 238 7.18

From Table 1, it can be seen that the particle size, particle average diameter, and surface roughness of the thin film grown at a temperature of 500 ° C. or less do not have an obvious change. However, when the growth temperature was increased up to 600 ° C., the particle size, particle average diameter and surface roughness of the thin film were improved. Surface roughness increased from 3.00 nm to 7.18 nm.

The electrical parameters of the Li-doped ZnO thin films were measured by a Hall-effect measuring device at room temperature, and the electrical parameters are shown in Table 2 below.

Electrical Parameters of Li-doped ZnO (0.01 at.%) Thin Films Deposited at Various Temperatures on Sapphire (001) Substrates Using PLD Sample
(℃) resistance
(Cm) Mobility
(Cm2 / Vs) Carrier density
(/ Cm 3) Hall constant
(㎡ / C) 100 - - - - 200 4.36 ㅧ 10 ^-2 8.29 -1.72 ㅧ 10 ¹⁹ -0.36 300 3.26 ㅧ 10 ^-2 20.97 -9.12 ㅧ 10 ¹⁸ -0.68 400 6.77 ㅧ 10 ^-1 12.79 -6.87 ㅧ 10 ¹⁸ -0.94 500 0.14 9.23 -4.95 ㅧ 10 ¹⁸ -1.25 600 - - - -

The electrical parameters could not be measured using this instrument for thin films grown at 100 ° C. and 600 ° C. and thus were not described. These two thin films are because the value of the electrical variable is beyond the measurement range. As the growth temperature increases from 200 ° C to 500 ° C, the carrier concentration decreases from 1.71 1.10 ¹⁹ cm ^-3 to 4.95 ㅧ 10 ¹⁸ cm ^-3 and the resistance increases from 4.36 ㅧ 10 ^-2 to 0.14 Ωcm . The hole mobility for all thin films is in the range of 10-20 cm / Vs.

Spectrophotometer (Cary-5, Australia) was used to measure the transmittance of the thin film in the wavelength range of 300 ~ 600 nm, the transmission spectrum is shown in FIG. All thin films deposited at various temperatures show an optical transmission as high as 95% in the visible region. Steep absorbance edges (risings) were observed in all films. This means that the deposited thin film is of high quality. The vibration of the transmission spectrum is derived from the interference of light reflected from the surface and interface of the thin film. The spectral oscillator can be used to calculate the refractive index and thickness of the thin film (FK Shan, and YS Yu, Thin Solid Films 435 (2003) 174).

Since ZnO is a direct current band semiconductor, in the present invention, [α ㅧ ( hυ )] ² graphs for photon energy hυ were prepared. The insert in the graph of FIG. 3 shows the relative absorption coefficients of Li-doped ZnO thin films deposited at 600 ° C. The steep absorption edge is accurately determined for high quality thin films by straight fit. The band energy of Li-doped ZnO thin films deposited at various temperatures was calculated and shown in FIG. 4. As the growth temperature was increased from 100 ° C. to 300 ° C., the band energy of the Li-doped ZnO thin film decreased from 3.283 eV to 3.261. However, as the growth temperature increases from 300 ° C. to 600 ° C., the band energy increases from 3.261 eV to 3.284 eV. The band energy of Li-doped ZnO thin films does not have a significant change compared to the band energy of non-doped ZnO thin films (FK Shan, GX Liu, WJ Lee, and BC Shin, J. Appl. Phys . 101 (2007) 053106 ).

PL measurements were performed at room temperature to study the luminescence properties of Li-doped ZnO thin films (0.01 at.%). 5 shows the PL spectra of thin films grown at various temperatures using PLD. It can be seen that all thin films exhibit low NBE emission, and the intensity of NBE emission increases with increasing growth temperature. However, the intensity of NBE emission of Li-doped ZnO thin films is much weaker than that of pure ZnO thin films deposited under the same conditions. Although the dope level of Li ions in the ZnO thin film is 0.01 at. Although as small as%, the NBE emission of Li-doped ZnO thin films was greatly suppressed. This is due to the generation of non-radiative recombination centers in Li-doped ZnO thin films. Deep-level (DL) luminescence was also observed in all Li-doped ZnO thin films. According to previous results, dope ZnO generally exhibits suppressed DL luminescence. However, DL light emission in the Li-doped ZnO thin film was not suppressed. It is reported that DL luminescence in ZnO thin films deposited by PLD is derived from oxygen deprivation. This therefore means that doping Li ⁺ and O ^2- in the ZnO thin film does not reduce oxygen deficiency.

As above, according to the present invention, a Li-doped ZnO (0.01 at.%) Thin film was deposited on a sapphire (001) substrate at different temperatures of 100 to 600 ° C. using PLD technology, and thus XRD measurement for the thin film It can be seen that all thin films have a preferred (002) orientation, and also the peak intensity of the (002) orientation increased with temperature. A new orientation of (004) was observed in Li-doped ZnO thin films deposited at temperatures above 300 ° C. The particle size and surface roughness of the thin film grown at a temperature lower than 500 ° C. did not change, but the particle size and surface roughness of the thin film grown at 600 ° C. were significantly increased. In addition, the thin film prepared according to the present invention showed a very high transmittance in the visible region and a steep absorption edge was observed, and the PL measurement showed that the NBE emission intensity was greatly reduced compared to the pure ZnO thin film, and that DL emission had no obvious change. This can be attributed to the formation of non-radiative recombination centers that inhibit NBE luminescence in Li-doped ZnO thin films.

1 is an XRD pattern of a Li-doped ZnO (0.01 at.%) Thin film grown at various temperatures on a sapphire (001) substrate using PLD,

2 shows a Li-doped ZnO (0.01 at.%) Thin film grown at various temperatures on a sapphire (0001) substrate using PLD. AFM image,

FIG. 3 shows Li-doped ZnO (0.01 at.%) Thin films grown at various temperatures on sapphire (001) substrate using PLD Transmittance,

4 shows a Li-doped ZnO (0.01 at.%) Thin film grown at various temperatures on a sapphire (001) substrate using PLD. Band energy,

5 is a PL spectrum of a Li-doped ZnO (0.01 at.%) Thin film grown at various temperatures on a sapphire (001) substrate using PLD.

Claims (7)

A method of fabricating a ZnO thin film by doping lithium (Li) ions into ZnO using pulsed laser deposition (PLD) technology, the method comprising 0.001 to 0.1 at. In high purity ZnO powder. Mixing the ZnO powder with a homogeneous agent in a milling system using a plastic container with balls of high purity lithium oxide powder to obtain a lithium dopant of%; Uniaxially pressing the mixture into a specific shape to obtain a target; Sintering a target of a specific shape obtained above at a constant temperature in a furnace; And The energy density of the excimer laser is set constant. The ablated material is then deposited onto the substrate under specific conditions on the target, Improved structural, electrical and optical properties, characterized in that the deposited substrate temperature is between 200 and 500 ° C., wherein the specific deposition conditions are 4 to 6 Hz repetition frequency of the laser and 90 to 110 mTorr background O ₂ pressure. Method for producing a lithium-doped ZnO thin film having a. delete delete delete delete The method of claim 1, wherein the deposition time is 1 hour. 3. The method of claim 1, wherein the lithium doped ZnO thin film has improved structural, electrical, and optical properties. A lithium-doped ZnO thin film having improved structural, electrical and optical properties, characterized in that it is prepared by the method of any one of claims 1 or 6.

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