KR100970180B1 - Method of forming a thin film and luminescence device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film formation method and a light emitting device, and forms a p-type ZnO thin film by forming a gallium and acetonitrile-doped ZnO thin film by pulse laser deposition using a GaAs doped ZnO target. In addition, by using a ZnO thin film co-doped with gallium and acene as a transparent electrode, it is possible to improve the luminous efficiency and lifetime of the UV optical device.

GaAs, co-doped, p-type semiconductor, ZnO, PLD

Description

Method of forming a thin film and luminescence device

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a thin film, and more particularly, to a method of depositing a ZnO thin film doped with gallium (Ga) and acenic (As) using pulse laser deposition (PLD) and a light emitting device.

ZnO, a wide bandgap semiconductor, has a bandgap energy of 3.3 eV at room temperature and an exciton binding energy of 60 meV. Because of these effects, ZnO attracts considerable attention. ZnO may be variously used as a transparent conductive thin film, a solar cell window, a bulk acoustic wave device, or the like. GaN is one of very useful materials used in optical devices such as light emitting diodes and laser diodes. The band structure and optical properties of ZnO are very similar to GaN. Due to the similar properties of GaN and ZnO, ZnO is spotlighted as the most promising material for photonic devices within the ultraviolet range. ZnO has an exciton binding energy greater than GaN exciton binding energy at room temperature. That is, ZnO has an exciton binding energy of 60 meV, but GaN has an exciton binding energy of 25 meV. Thus, ZnO can be used in place of GaN in exciton-related devices.

ZnO is formed by methods such as molecular beam epitaxy (MBE), chemical vapor deposition (CVD), sputtering, pyrolysis and pulsed laser deposition (PLD). Among them, pulsed laser deposition is widely used to form metal oxide thin films and related materials. Pulsed laser deposition allows the deposition of metal oxide thin films in a very simple manner, and atomic layer control is possible by controlling the laser fluence and pulse rate. In addition, a multi-layer hetero structure may be formed in-situ by using a multi target carrousel.

In order to implement an optical device using ZnO, simultaneous growth of n-type and p-type ZnO is required. Most semiconductors, including ZnO, naturally have n-type conductivity. The n-type ZnO is easy to manufacture, and the conductivity can be controlled by the doping and doping levels of other materials. However, p-type ZnO is not easy to manufacture, and it is reported that p-type ZnO has been obtained by many research results. However, some results are only repetition of research results. In addition, the characteristics of the p-type ZnO are difficult to use in the device.

The present invention provides a thin film forming method and a light emitting device for forming a p-type ZnO thin film by doping gallium and acenic.

The present invention provides a thin film forming method and a light emitting device for forming a gallium and acetonitrile-doped ZnO thin film using a pulse laser deposition method.

According to one or more exemplary embodiments, a method of forming a thin film includes: mounting a GaAs-doped ZnO target in a pulse laser deposition chamber and then loading a substrate into the chamber; And irradiating a pulse laser to the target to form a gallium and arsenic-doped ZnO thin film on the substrate.

The gallium and arsenic are contained from 0.005 to 0.02 at.%.

The target is produced by mixing the GaAs powder and ZnO powder using a plastic container having a ball in a planetary milling system, followed by uniaxial pressurization and room temperature integral molding.

The target is sintered for 3-5 hours in a furnace at 1000-1300 ° C.

The chamber maintains a pressure of 50 to 200 mTorr and an oxygen atmosphere and a substrate temperature of 100 to 600 ° C.

The light emitting device according to another aspect of the present invention includes an anode, a light emitting layer, and a cathode sequentially formed in a predetermined region on the substrate, and the anode is formed of a ZnO thin film co-doped with gallium and acenic.

The gallium and acenic ^- doped ZnO thin film has a resistivity of 4.79 × 10 ⁻³ to 3.35 × 10 ⁻² dBm, a mobility of 18.79 to 47.98 cm ² V ⁻¹ s ⁻¹ , and -4.58 × 10 ¹⁹ to − At least one of a carrier density of 9.90 × 10 ¹⁸ cm ⁻³ and a hole coefficient of −0.63 to −0.22 m 2 C ⁻¹ .

According to the present invention, a p-type ZnO thin film is formed by forming a gallium and acetonitrile-doped ZnO thin film by pulse laser deposition using a GaAs doped ZnO target. In addition, by using a ZnO thin film co-doped with gallium and acene as a transparent electrode, it is possible to improve the luminous efficiency and lifetime of the UV optical device.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to those skilled in the art. It is provided for complete information.

1 is a schematic cross-sectional view of a pulse laser deposition apparatus used for thin film deposition according to an embodiment of the present invention.

As shown, the present invention is irradiated with a pulse laser to the target 20 installed in the chamber 10 of the pulse laser deposition apparatus, the target 20 on the substrate 30 disposed at a position opposite to the target 20 A thin film of approximately the same composition is deposited. The chamber 10 includes a target holder (not shown) for fixing the target 20 and a substrate holder (not shown) for fixing the substrate 30. The target holder (not shown) and the substrate holder (not shown) are provided. For example, four and one is provided, respectively.

A window 40 is formed at one side of the chamber 10, and the pulse laser is irradiated to the target 20 through the window 40. Here, the focal length and the degree of condensing of the pulse laser are adjusted by the lens 50 so that the pulse laser is irradiated to a predetermined position on the target 20 exactly. The laser irradiated onto the target 20 generates a strong plasma plume on the surface of the target 20, and when the plasma plume reaches the substrate 30, a thin film having a composition substantially the same as that of the target 20 is formed on the substrate ( 30).

As the pulse laser, for example, a KrF excimer laser or the like which outputs a wavelength in the ultraviolet region is used. KrF excimer laser (λ = 248 nm, τ = 25 μs) is used for ablation of the target 20 at an energy density of about 1.5 J / cm ² .

As the target 20, a ZnO target doped with gallium and an arsenic is used. The target 20 is manufactured using, for example, Aldrich Co.'s high purity ZnO powder (99.99%) and GaAs powder (99.99%). The content of GaAs is 0.005 to 0.02 at.%, Preferably 0.01 at.%. In order to dope GaAs in the desired amount, high purity GaAs powder and ZnO powder are mixed for 10 hours using a plastic container with balls, for example in a milling system.

In addition, the target 20 is produced in the shape of a disk of 1 inch diameter, for this purpose by uniaxial pressing at 700kg / ㎠ and then produced by cold iso-static press of 24000㎏ / ㎠ do. The denser the target 20 is, the higher the quality of plasma can be obtained. Therefore, in order to produce the dense target 20, the disk-shaped target 20 is sintered for 3 to 5 hours in the furnace of 1000-1300 degreeC. Preferably it is sintered for 4 hours in a furnace at 1200 ℃. The target 20 is uploaded to the chamber after being attached to the target holder (not shown). The target 20 is disposed to maintain a distance of about 35 mm from the substrate 30.

In addition, the chamber 10 should be maintained at a predetermined atmosphere, pressure and temperature while the thin film is deposited, and maintains an oxygen atmosphere of 20 to 100 mTorr, preferably 50 mTorr and a substrate temperature of 100 to 600 ° C. Then, the repetition frequency of the pulse laser is 5 kHz, and a thin film is deposited to a thickness of about 400 nm by performing a deposition process for about 40 minutes. After deposition, the thin film is naturally cooled at room temperature for various measurements.

The characteristics of the thin film deposited under the above conditions are observed by various methods. That is, the crystal structure of the thin film was observed using an X-ray diffractometer (XRD, X'pert MPD, Panalytical, 400 kV, 30 mA) with CuKα1 emission λ = 1.5405 kHz, and the surface shape of the thin film was atomic microscope It is observed with a scanning probe microscope (SPM) in atomic force microscope (AFM) mode. In addition, the electrical properties of gallium and acenic-doped ZnO thin films are measured by the van der pauw method in a hall-effect measurement system. The transmittance of the thin film is measured with a UV-Vis-IR spectrophotometer (Vary-5 Australia) at a wavelength in the range of 300 to 700 nm. The excitation source used for photoluminescent (hereinafter referred to as "PL") measurement is a He-Cd laser operated at 325 nm with an output power of 30 mW. In this case, a cutoff filter is used to suppress dispersion of the laser. The cutoff wavelength at the ultraviolet side of the cutoff filter is about 340 nm.

The characteristics of the gallium and acetonitrile-doped ZnO thin films formed by the pulse laser deposition according to the present invention measured by the above method are as follows. Hereinafter, the characteristics of the ZnO thin film doped with gallium and acetonitrile 0.01 at.% Will be described.

FIG. 2 shows an X-ray diffraction pattern of gallium and acenic co-doped ZnO thin films deposited on sapphire substrates by pulsed laser deposition at various temperatures. That is, (a) to (f) show the X-ray diffraction pattern of the ZnO thin film co-doped with gallium and acenic, increasing the temperature by 100 ° C. from 100 ° C. to 600 ° C., respectively. Here, the x axis represents an angle and the y axis represents an intensity expressed in logarithmic scale.

Referring to Figure 2, it is shown that the growth temperature plays an important role in the determination of the crystal structure. That is, as shown in (a), the thin film deposited at 100 ° C. is amorphous. In contrast, as shown in (b) to (f), thin films deposited at 200 ° C. or higher show the (002) and (004) orientations, and the (002) and (004) peak intensities increase with increasing temperature. do. In addition, as shown in (d) to (f), when the growth temperature rises above 400 ° C., one or more (100) ZnO peaks appear. This increase in peak intensity means that the film quality is improved with growth temperature. In addition, the temperature dependence of the film quality can be explained by the mobility of the particles at different growth temperatures. That is, the low mobility of particles grown at low temperatures interferes with the crystallization of the thin film. This weakens the intensity of the peak. On the other hand, no new phase associated with GaAs is observed in all thin films, which means that when the amount of impurities is small, the doping level does not change the structure of the ZnO thin film.

FIG. 3 is an image showing the surface structure of a gallium- and acenic-doped ZnO thin film deposited on a sapphire substrate by pulse laser deposition at various temperatures, and scanning probe microscope (SPM) in AFM mode. 400, Seiko Instruments). The scanning area is 2 μm × 2 μm, and the grain size, mean diameter, and root-mean-square (RMS) roughness observed by AFM are shown in [Table 1].

Growth temperature (℃) Grain size (× 10 ⁴ nm ² ) Average diameter (× 10 ² nm) RMS (nm) 100 0.15 0.44 0.43 200 0.95 1.10 5.48 300 1.13 1.20 8.28 400 1.15 1.21 9.37 500 1.19 1.23 9.15 600 2.88 1.92 16.75

As can be seen in Figure 3 and Table 1, the surface shape of the thin film is strongly dependent on the growth temperature. That is, the grain size and surface shape obviously change as the growth temperature increases. Thin films deposited at 100 ° C. have the smallest grain size and the smallest surface roughness. Therefore, it is very difficult to deposit gallium and arsenic co-doped thin films at low temperatures. This can be explained by the movement of the particles. As the growth temperature increases, the mobility of the particles increases, and particles having high mobility tend to form grains of large size. That is, as can be seen in [Table 1], the RMS value of the thin film grown at 100 ° C. and 600 ° C., respectively, increases from 0.43 nm to 16.75 nm.

Hall effect measurement is performed at room temperature to measure the electrical properties of the thin film. Table 2 shows the results measured using the Van der Pau method using four probes. However, this method does not measure the electrical properties of the thin film grown at 100 ℃.

Temperature (℃) Resistivity (Ω㎝) Mobility (㎠V ^-1 s ^-1 ) Carrier Density (cm ^-3 ) Hall Coefficient (㎡C ^-1 ) 100 - - - - 200 7.15 × 10 ^-3 30.20 -2.89 × 10 ¹⁹ -0.22 300 4.79 × 10 ^-3 28.47 -4.58 × 10 ¹⁹ -0.13 400 3.35 × 10 ^-2 18.79 -9.90 × 10 ¹⁸ -0.63 500 2.43 × 10 ^-2 24.96 -1.03 × 10 ¹⁹ -0.61 600 5.95 × 10 ^-3 47.98 -2.18 × 10 ¹⁹ -0.29

As can be seen from Table 2, all the measured thin films are n-type semiconductors. This experiment demonstrates that ZnO thin films co-doped with gallium and sodium at a doping level of 0.01 at.% Are n-type semiconductors. In addition, the thin film deposited at all temperatures is very conductive, and the resistivity of the thin film is in the range of 10 ⁻² to 10 ⁻³ [Ωcm]. And carrier density of all the thin films has a range of 10 ¹⁹ cm <^-3> , and hole mobility has a range of ^18-19 cm <^2> V <^-1> s <^-1> .

Spectrophotometers (Cary-5, UV-VIS-NIR) are used to measure the transparency of thin films at room temperature. The transparency of gallium and acenic-doped ZnO thin films is shown in FIG. 4. Transparency was measured in the UV-visible region with a wavelength of 300-700 nm. All thin films show greater than 90% light transparency in the visible region. In addition, all thin films have very sharp absorption edges and oscillations. The sharp linear edges are used for the calculation of the bandgap energy of the thin film, and the oscillating portion of the spectra is used for the calculation of the refractive index and thickness of the thin film. For example, a method of calculating the band gap energy of a thin film deposited at 500 ° C. is shown in FIG. 5. The bandgap energy of gallium and acenic-doped ZnO thin films is calculated by linear fitting of sharp absorption edges. ZnO is a direct band gap semiconductor and has an absorption coefficient α∝-lnT. Therefore, the photon energy hυ is expressed by [α × (hυ)] ² . Sharp absorption edges can be used to accurately determine high quality thin films using linear adjustments. The bandgap energy of the thin film after calculation is shown in FIG. As shown in FIG. 6, it can be seen that as the growth temperature increases, the bandgap energy decreases and saturates. The bandgap energy of co-doped thin films grown at 100 ° C. and 200 ° C. is very large compared to pure ZnO thin films of 3.27 eV. This is due to the Burstein-Moss effect due to the doping of gallium and acenic. ZnO thin films are naturally n-type materials and the Fermi level is inside the conducting band when doped with gallium and arsenic. Also, the absorbing edge moves to high energy after doping. However, the bandgap energy of thin films deposited at high temperatures is similar to pure ZnO. This is due to the different barometric pressures at different growth temperatures.

PL measurements are performed at room temperature to study the emission characteristics of gallium and arsenic co-doped ZnO thin films. The PL spectra of gallium and acenic-doped ZnO thin films grown at various temperatures using pulsed laser deposition are shown in FIG. 7. Thin films deposited at 100 ° C. were observed to show very weak emission. This is consistent with amorphous natural phenomena investigated by XRD measurements. Thin films deposited above 200 ° C. exhibit near band edge (NBE) emission and deep level (DL) emission. NBE emissions increase as the growth temperature rises above 500 ° C. However, the NBE emission of thin films deposited at 600 ° C is weaker than thin films deposited at 500 ° C. This is due to the change in thickness.

NBE emission and DL emission are always observed in undoped ZnO thin films, where doped ZnO thin films are inhibited from DL emission. This is because DL emission originates from oxygen vacancy, but impurities doped in the ZnO thin film inhibit DL emission. However, ZnO thin films doped with gallium and arsenic according to the present invention at 0.01 at.% Show a clear DL emission. Therefore, a ZnO target having GaAs introduced at a doping level higher than the doping level proposed in the present invention, and a ZnO thin film co-doped with a doping level of 0.1 at% gallium and acenic were prepared under the same conditions. Then, the PL stack of the ZnO thin film co-doped with a doping level of 0.1 at.% Was measured. A PL spectra having a doping level of 0.1 at.% Deposited at 500 ° C. and 600 ° C. is shown in FIG. 8, and FIG. 8 for comparison of the PL spectra of a thin film having a doping level of 0.01 at.% Deposited under the same conditions. Shown in All thin films with a doping level of 0.1 at.% Show only NBE emission and no DL emission is observed. On the other hand, the intensity of NBE emission also decreases. This means that the doping level of 0.1 at.% In the ZnO thin film sufficiently suppresses DL emission and many non-emitting recombination centers are formed.

9 is a cross-sectional view of a light emitting device manufactured by using a gallium and acetonitrile-doped ZnO thin film according to the present invention.

Referring to FIG. 9, a light emitting device according to an embodiment of the present invention includes an anode 110, a light emitting layer 120, and a cathode 130 on the substrate 100. The emission layer 120 may include a hole injection layer 121, a hole transport layer 122, an organic emission layer 123, and an electron injection layer 124. .

The substrate 100 may use an insulating substrate, a semiconductor substrate, or a conductive substrate, that is, a plastic substrate (PE, PES, PET, PEN, etc.), a glass substrate, an Al ₂ O ₃ substrate, a SiC substrate, a ZnO substrate, Si At least one of a substrate, a GaAs substrate, a GaP substrate, a LiAl ₂ O ₃ substrate, a BN substrate, an AlN substrate, an SOI substrate, and a GaN substrate may be used.

The anode 110 is an electrode for hole injection, and is formed by using a ZnO thin film doped with gallium and anaceans according to the present invention. The gallium and acenic-doped ZnO thin film is formed by pulsed laser deposition using a gallium and acenic-doped ZnO target and maintains an oxygen atmosphere of 50 to 200 mTorr and a substrate temperature of 100 to 600 ° C. To form a thickness of about 150 nm.

The hole injection layer 121 constituting the light emitting layer 120 may be formed to a thickness of about 20 nm using copper phthaloyanine (CuPc) or the like, and the hole transport layer 122 may include α-NPD. Can be formed to a thickness of about 40 nm. In addition, the organic light emitting layer 123 may be formed to a thickness of about 60 nm using 8-hydroxyquinoline aluminum (Alq ₃ ) or the like, and the electron injection layer 124 may be formed of lithium fluorine (LiF). Or the like to form a thickness of about 0.5 nm.

The cathode 130 is used as the electron injection electrode, any material having electrical conductivity may be used, and the cathode 130 may be formed to a thickness of 20 to 150 nm. The cathode 130 is preferably made of metals such as Al, Ag, Au, Pt, Cu, which have low electrical resistance and excellent interface properties with conductive organic materials. However, it is more preferable to use a metal having a low work function in order to obtain a high current density in electron injection by lowering a barrier formed between the organic layer 120 and Al, which is a material that is relatively stable to air. It is most preferable to use.

1 is a schematic cross-sectional view of a pulse laser deposition equipment for thin film deposition according to an embodiment of the present invention.

2 is an XRD pattern of gallium and acenic co-doped ZnO thin films deposited on sapphire substrates by pulse laser deposition at various temperatures.

3 is an AFM photograph of gallium and acenic co-doped ZnO thin films deposited on sapphire substrates by pulse laser deposition at various temperatures.

4 is a graph of transparency of gallium and acenic co-doped ZnO thin films deposited on sapphire substrates by pulsed laser deposition at various temperatures.

5 is a graph for explaining a bandgap energy calculation method by the linear adjustment of the absorption edge.

FIG. 6 is a graph for explaining the temperature dependence of the bandgap energy of gallium and acenic-doped ZnO thin films deposited on sapphire substrates by pulse laser deposition at various temperatures.

7 is a PL spectrum of gallium and acenic co-doped ZnO thin films deposited on sapphire substrates by pulse laser deposition at various temperatures.

8 is a graph illustrating NBE emission and DL emission characteristics according to the doping concentrations of gallium and acenic co-doped ZnO thin film.

9 is a cross-sectional view of a light emitting device manufactured by using a gallium and acetonitrile-doped ZnO thin film according to an embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

10 chamber 20 target

30: substrate 40: window

50: Lens

100: substrate 110: anode

120 emitting layer 130 cathode

121: hole injection layer 122: hole transport layer

123: organic light emitting layer 124: electron injection layer

Claims (7)

Mounting a GaAs doped ZnO target in a pulsed laser deposition chamber and then loading a substrate into the chamber; Irradiating a pulsed laser to the target to form a gallium and arsenic co-doped ZnO thin film on the substrate. The method of claim 1, wherein the gallium and the arsenic are present in an amount of 0.005 to 0.02 at.%. The method of claim 1, wherein the target is made by mixing GaAs powder and ZnO powder using a plastic container having balls in a planetary milling system, followed by uniaxial pressurization and normal temperature integral molding. The method of claim 3, wherein the target is sintered in a furnace at 1000 to 1300 ° C. for 3 to 5 hours. The method of claim 1, wherein the chamber maintains a pressure of 50 to 200 mTorr, an oxygen atmosphere, and a substrate temperature of 100 to 600 ° C. 6. It includes an anode, a light emitting layer and a cathode sequentially formed in a predetermined region on the substrate, The anode is a light emitting device formed of a ZnO thin film co-doped with gallium and arsenic. The method of claim 6, wherein the gallium and the acenic ^- doped ZnO thin film has a resistivity of 4.79 × 10 ^-3 to 3.35 × 10 ^-2 dBm, mobility of 18.79 to 47.98 cm ² V ^-1 s ^-1 , A light emitting element having a carrier density of 4.58 × 10 ¹⁹ to -9.90 × 10 ¹⁸ cm ^-3 and a hole coefficient of -0.63 to -0.22 m 2 C ^-1 .

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