KR100509748B1 - Method for growing N-doped P-type ZnO thin film - Google Patents

Abstract

A method of growing a p-type zinc oxide (ZnO) thin film in which a zinc (Zn) source, an oxygen and a dopant source are separated from each other and flow on a substrate, thereby suppressing homogeneous nuclei before the source reaches the substrate and allowing a reaction to occur only on the substrate. This is disclosed. Charging a predetermined substrate into the chamber, introducing nitrogen gas into the chamber, supplying a carrier gas and an oxygen and dopant source of the zinc precursor, and introducing the zinc source into the chamber. . The zinc precursor uses diethyl zinc (DEZn) or dimethyl zinc (DMZn), and the carrier gas of the zinc precursor uses argon (Ar). In addition, the oxygen and dopant sources are nitrogen monoxide (N ₂ O) or nitrogen dioxide (NO ₂ ) is used, the zinc source and oxygen source is separated from each other to flow over the substrate.

Description

Method of growing a zinc oxide thin film formed by nitrogen doping {Method for growing N-doped P-type ZnO thin film}

The present invention relates to a method for growing a zinc oxide (ZnO) thin film, and in particular, diethylzinc (DEZn) or dimethylzinc (DMZn) and oxygen gas are separated from each other to flow on the substrate to form a uniform nucleation before the source reaches the substrate. The present invention relates to a zinc oxide thin film growth method that suppresses the reaction and causes the reaction to occur only on the substrate.

In particular, the present invention relates to a method of growing a p-type zinc oxide thin film doped with nitrogen using nitrogen monoxide (N ₂ O) or nitrogen dioxide (NO ₂ ) as an oxygen and dopant source.

Zinc Oxide (ZnO) is a material that has been studied for decades due to its excellent electrical, optical, and piezoelectric properties. It is highly applicable to surface acoustic devices, transparent electrodes, and optical devices.

In particular, zinc oxide has a wide band gap of 3.37 eV, and the band gap can be changed to 4 eV by the addition of Mg, so that the next generation photon capable of oscillating a laser in the ultraviolet region. It is attracting attention as a magnetic material.

In addition, the development of quantum well structures (quantum wells, wires, dots) through miniaturization in nanometer (nm) units can significantly improve optical characteristics.

Although research on the photonic device of GaN-based III-nitride has been actively conducted and reaches the application stage, most GaN-based nitride films are required to have a high temperature of 1000 ° C or higher in growth, thus limiting substrate selection. However, it is difficult to grow a good quality epi thin film on Si substrate which is most used in actual process.

Zinc oxide has the advantage that the exciton binding energy is 60 meV at room temperature, which is considerably greater than that of GaN 28 meV, and thus the efficiency of an optical device capable of operating at room temperature and high temperature can be maximized. Since epitaxial thin film growth at high temperature is possible, epitaxial growth is easier than that of GaN even on a Si substrate, which is an advantageous position for practical use.

Due to these material advantages, many studies have been conducted to obtain high quality zinc oxide epi thin films since the 1990s. Most of the initial researches on zinc oxide thin films have been conducted for application to transparent electrode devices that can replace indium-tin-oxide (ITO), and most of the deposition processes are sputtering processes. The quality was not very good. Since then, with the activation of GaN-based optical device research and development, research to obtain high quality epi thin film has begun in earnest from the late 90s.

The leading research groups to date are the Tokyo Institute of Technology and Tohoku University in Japan. Researchers at the Tokyo University of Technology have already successfully launched UV laser oscillations at room temperature in 1998 using the Laser Molecular Beam Epitaxy (LMBE). Also Ohotomo the like of this group are ZnO / Zn1-xMgxO from superlattice (superlattice) structure produced at the time of PL (photoluminescence) analysis were examined for blue shift due to the quantum effect, S _c ALMGO a lattice constant difference of about 0.09% ₄ substrate A high quality epitaxial film synthesis with high electron mobility (100 cm 2 / V) and low residual charge concentration (10 ¹⁵ / cm 3) is reported. Recently, Zn1-xMnxO epi thin film production by Mn addition has announced the possibility of band gap control.

Ko, et al., Of Tohoku University, has optical properties using a CaF ₂ substrate that has a smaller lattice constant mismatch than conventional sapphire substrates and can efficiently compensate for compressive stress caused by differences in thermal expansion coefficients with tensile stress caused by lattice mismatch. This excellent zinc oxide epi thin film synthesis was reported. In addition, they introduced a MgO buffer layer to grow a thin film from the initial growth stage to the surface shape to the atomic stage. In addition, Vispute et al. Introduced GaN as a buffer layer in zinc oxide optical device fabrication using similar lattice constants of zinc oxide and GaN. Iwata et al. Reported that p-type thin films were prepared by adding nitrogen when zinc oxide thin films were grown, but the effect was not observed. P-type doping of zinc oxide is difficult.

Compared to such advanced foreign studies, there are few studies in Korea except for some groups. Recently, the magnetron sputtering method has been reported to grow a thin film having a half width of 0.13 ° of the x-ray rocking curve, but other research results are not very good crystal quality. Therefore, much research and development is urgently needed to grow zinc oxide epitaxial thin films for domestic optical devices.

High-quality single crystals are required for application to optical devices such as lasers, but zinc oxide has to be heterogeneously epitaxially grown since it is not easy to manufacture bulk single crystals. However, due to the large difference in lattice constant from most substrate materials (sapphire (Al ₂ O ₃ ), Si), the grown thin film has many defects, and these have a great adverse effect on mineral properties and should be minimized.

In addition, since zinc oxide thin films generally exhibit n-type electrical conductivity due to invasive atoms of zinc or oxygen vacancies, doping into p-types is a serious problem. There are few studies on point defects, interfacial defects caused by lattice mismatches, and oxygen ion effects in plasmas.

Ultraviolet detectors are used for military purposes, including missiles and rocket guidance systems, for industrial purposes such as ultraviolet detection in flames, for atmospheric environment investigation and engine monitoring, for research purposes such as plasma diagnostics, and for astronomy. In addition, since it is used for signal detection of optical communication using ultraviolet rays, and signal detection for communication between the earth and satellites and communication between the satellites, as an optical detection element of a high-speed communication network in the future, with the arrival of the aerospace era, It is expected that the demand for communication detection elements in space will increase greatly. Currently, an optical amplifier or a silicon photodiode is used as an ultraviolet detection element, but an optical amplifier requires a high voltage, has low efficiency, and a silicon photodiode is sensitive to visible light and infrared rays so that a band-control filtration device is attached. The volume is large, and its configuration is complicated.

In addition, since silicon has a small band gap, there is a problem in thermal stability, and there is a disadvantage in that it is not chemically stable in a harsh environment. In order to solve this disadvantage, it is necessary to use a semiconductor that is thermally and chemically stable and has low reactivity to visible and infrared regions. Zinc oxide is a direct-transition maximal bandgap semiconductor, which has many advantages in application as an ultraviolet detection device such as chemical thermal stability, high mobility, high quantum efficiency, and selectivity of specific wavelength according to the mole fraction of Mg added. Many research and development is required as a material that can effectively replace the device.

Despite the above advantages, according to the prior art, it is difficult to reproducibly form a zinc oxide film having a hole concentration of 10 ¹⁹ / cm 3 or more.

In addition, zinc oxide thin films used as optical materials require high quality crystallinity and uniformity. To meet such demands, metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy and pulsed laser deposition methods have recently been used.

Moreover, the MOCVD method is suggested as the most suitable alternative for mass production of zinc oxide thin films.

Therefore, the present invention separates the zinc source and the oxygen source and flows onto the substrate, thereby suppressing uniform nucleation before the source reaches the substrate and allowing the reaction to occur only on the substrate, thereby growing a zinc oxide thin film having excellent characteristics. The purpose is to provide a way.

Another object of the present invention is to provide a p-type zinc oxide thin film growth method doped with nitrogen using nitrogen monoxide (N ₂ O) or nitrogen dioxide (NO ₂ ) as the oxygen and dopant source.

Other objects and features of the present invention will be more clearly understood through the preferred embodiments described below.

Zinc oxide thin film growth method according to an embodiment of the present invention comprises the steps of charging a predetermined substrate into the chamber; Introducing N ₂ gas into the chamber; Supplying a carrier gas and an oxygen and dopant source of the zinc precursor; Introducing a zinc source into the chamber.

Preferably, charging the substrate into the chamber comprises washing the substrate in the order of trichroloethylene (TCE), acetone, methanol, ultrapure water; And drying the cleaned substrate with nitrogen gas.

Preferably, diethylzinc (DEZn) or dimethylzinc (DMZn) is used as the zinc precursor, and the carrier gas of the zinc precursor is Ar. In addition, the oxygen and dopant sources are nitrogen monoxide (N ₂ O) or nitrogen dioxide (NO ₂ ) is used, the zinc source and oxygen source is separated from each other to flow over the substrate.

The chamber is composed of a reaction chamber and a specimen loading chamber, and the reaction chamber and the specimen loading chamber are separately installed so that the reaction chamber maintains a high vacuum of 10 ^-6 torr when the specimen is loaded. The reaction chamber maintains a constant growth pressure of 10 torr through an automatic pressure controller (APC), and the reaction chamber uses a corrosion resistive rotary pump to prevent corrosion by organic compounds.

The carrier gas, oxygen and dopant source of the zinc precursor are supplied through a mass flow controller (MFC), and a bubbler is placed in a thermostat to maintain a constant vapor pressure of the zinc precursor at 50 to 100 μmol. The bubbler temperature is maintained at 5 ° C. to −10 ° C. when the zinc precursor is diethyl zinc (DEZn) during thin film growth, and at 10 ° C. to −30 ° C. when dimethyl zinc (DMZn) is used. The pressure is maintained at 350 torr to 900 torr using an electronic pressure conotroller (EPC).

Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.

1 is a view schematically showing a MOCVD apparatus used for growing a zinc oxide thin film according to the present invention. The MOCVD apparatus was evacuated up to 1 × 10 ⁻⁶ torr or less using a turbo molecular pump for initial vacuum prior to growing the thin film. Referring to FIG. 1, the MOCVD apparatus is composed of a reaction chamber 110 and a load-lock chamber 120. Here, the reaction chamber and the specimen loading chamber are installed separately so that the high vacuum of the reactor can be maintained during loading of the specimen.

During thin film growth, the reaction chamber 110 was able to maintain a constant pressure through an automatic pressure controller (APC), and a vacuum using a corrosion resistive rotary pump to prevent corrosion by organometallic compounds. Exhausted.

The nozzle is configured such that the zinc source and the oxygen source are separated from each other and flow over the substrate 130, thereby suppressing homogeneous nuclei before reaching the substrate 130 and reacting only on the substrate. As a precursor of zinc, diethylzinc (DEZn) (optical grade) or dimethylzinc (DMZn) is used. In order to maintain a constant inflow of diethyl zinc (DEZn) by placing a bubbler (bubbler) in a thermostat to maintain a constant vapor pressure (vapor pressure) of diethyl zinc (DEZn). In addition, the pressure of the bubbler is kept constant, and the Ar gas, which is a carrier gas, flows into the reaction chamber 110.

Nitrogen monoxide (N ₂ O) gas or nitrogen dioxide (NO ₂ ) is used as the oxygen source and the nitrogen dopant source. In addition, a pushing flow is formed in the upper portion of the reaction chamber 110 using nitrogen gas to prevent the gas from rising inside the reaction chamber 110.

After growing the nitrogen-doped p-type zinc oxide thin film, the Al-doped zinc oxide thin film was deposited on the p-type zinc oxide thin film using a high-frequency magnetron sputter through a masking process, and then a current-voltage characteristic was observed. Make a measurement.

Hereinafter, a method of growing a zinc oxide thin film according to the present invention will be described.

First, before growing the zinc oxide thin film, the GaAs (001) substrate is preferably washed for about 5 minutes using an ultrasonic cleaner in the order of trichroloethylene (TCE), acetone, methanol, and ultrapure water, and then dried with nitrogen gas. Let's do it. The dried GaAs substrate is then loaded into the specimen loading chamber 120 of the MOCVD apparatus.

Then, after making the reaction chamber 110 in a vacuum state at about 1 × 10 ⁻⁶ torr, the temperature to be grown is maintained while maintaining the vacuum state. When the growth temperature is reached, nitrogen (N ₂ ) gas is first flowed using a needle valve to form a desired deposition atmosphere, followed by transport of diethyl zinc (DEZn) through a mass flow controller (MFC). Ar, a gas, and nitrogen monoxide (N ₂ O), an oxygen and dopant source, are supplied. At this time, in order to make the pressure in the reaction chamber 110 constant, the growth pressure is automatically maintained using APC.

Then, after adjusting the valve to pass the Ar gas through the bubbler in the bypass line, the zinc oxide thin film growth starts while introducing a diethylzinc (DEZn) source into the reaction chamber 110.

The bubbler temperature is maintained at 5 ° C. and −10 ° C., respectively, during thin film growth, to maintain a constant diethylzinc (DEZn) vapor pressure. For reference, when using a dimethylzinc (DMZn) source can be extended to 10 ℃ to -30 ℃. The internal pressure of the bubbler is maintained at a constant pressure of 350 to 900 torr, preferably 500 torr, using an electronic pressure controller (EPC) to maintain a constant ratio of diethyl zinc (DEZn) and Ar introduced into the chamber. By doing so, the inflow of zinc is kept constant. Table 1 below shows the growth conditions of the nitrogen doped zinc oxide thin film using the MOCVD apparatus.

Sample number Growth temperature (℃) Working pressure (torr) Ar (sccm) Bubbler temperature (℃) EPC (torr) N ₂ O (sccm) Street Growth time Thin film thickness (μm) One 450 10 80 5 500 40 1.5 60 2 2 450 10 80 -10 500 30 1.5 60 0.6

Table 2 below shows the results of the energy dispersive X-ray spectrometer (EDS) composition analysis of the nitrogen-doped zinc oxide thin film.

Sample number Zn Ka (%) O Ka (%) N Ka (%) C Ka (%) Ga Ka (%) As Ka (%) One 23.50 39.16 19.06 6.99 6.03 5.26 2 18.48 29.71 15.89 0 18.34 17.61

Referring to [Table 2], it is found that at least 15% of high nitrogen is detected in all the thin films, through which nitrogen is doped into the thin film when the zinc oxide thin film is grown using nitrogen monoxide (N ₂ O) gas. have.

Figure 2 is a field emission scanning electron microscopy (FESEM) photograph showing the surface shape and cross section of the nitrogen-doped zinc oxide thin film according to the present invention. Referring to FIG. 2, in the case of the thin film 1, when the cross-sectional shape is observed, a dense cross section may be observed, and the surface shape may show a rough surface shape. However, in the case of the thin film 2, when the flow of nitrogen monoxide (N ₂ O) is lowered to reduce the amount of oxygen source introduced, it can be seen that a thin thin film is formed.

3 is a view showing a photoluminescence measurement result at room temperature of the nitrogen-doped zinc oxide thin film according to the present invention. Referring to FIG. 3, a broad peak is observed in the range of about 425 nm, and it is determined as a peak due to a transition of a donor pair (DAP) due to the formation of an acceptor level by nitrogen doping.

4 is a view showing an XDR measurement result of the nitrogen-doped zinc oxide thin film according to the present invention. Referring to FIG. 4, a peak corresponding to zinc oxide 002 is strongly observed around 34.5 °, and a peak corresponding to zinc oxide 101 is weakly observed at 36.2 °. At 31.7 ° and 66.7 °, peaks due to GaAs substrates are observed. In the case of nitrogen-doped zinc oxide thin film, it grows in the direction of zinc oxide (002), which is the first growth direction, because it has the lowest surface energy.

[Table 3] below shows the Hall measurement results by Van der Pauw method of the nitrogen-doped zinc oxide thin film.

division Sample 1 Sample 2 Carrier type P type P type Mobility (cm ² / Vsec) 13.23 5.03 Concentration (cm ^-3 ) 2.80E18 2.75E18

Referring to [Table 3], both thin films exhibit a p-type conductivity, and the hole concentrations are 2.80E18 (cm ⁻³ ) and 2.75E18 (cm ⁻³ ), respectively. The hole mobility is 13.2 (cm ² / Vsec) and 5.0 (cm ² / Vsec). In the case of the thin film 2, the thin film has a lower hole mobility than the thin film 1 by inducing residual stress and defects caused by the thin film.

5 is a view showing the current-voltage characteristics of the n-type zinc oxide and Al-doped zinc oxide thin film doped with nitrogen according to the present invention. FIG. 5 shows the results obtained by measuring the current-voltage characteristics between n-type zinc oxide and p-type zinc oxide after fabricating an n-type ZnO / p-type ZnO / GaAs structure using a MOCVD apparatus. When the reverse bias is applied, the leakage current value is as low as about 4.5V, and break-down phenomenon starts to occur above 4.5V. Also, when forward bias is applied, a turn-on voltage appears at about 1.5V. The low turn-on voltage as described above is caused by a defect between the p-type zinc oxide thin film and the n-type zinc oxide thin film interface.

As described above, the present invention separates the zinc source and the oxygen source and flows them onto the substrate, thereby suppressing homogeneous nucleus before the source reaches the substrate and allowing the reaction to occur only on the substrate, thereby providing excellent zinc oxide properties. It is effective to obtain a thin film.

1 is a view schematically showing a MOCVD apparatus used for growing a zinc oxide thin film according to the present invention.

Figure 2 is a field emission scanning electron microscope (FESEM) photograph showing the surface shape and cross section of the nitrogen-doped zinc oxide thin film according to the present invention.

3 is a view showing a photoluminescence measurement result of the nitrogen-doped zinc oxide thin film according to the present invention.

4 is a view showing the results of X-ray diffraction (XDR) measurement of the nitrogen-doped zinc oxide thin film according to the present invention.

5 is a view showing the current-voltage characteristics of the n-type zinc oxide and Al-doped zinc oxide thin film doped with nitrogen according to the present invention.

Claims (14)

Charging the substrate into the chamber; Introducing nitrogen gas into the chamber; Supplying a zinc precursor comprising diethylzinc (DEZn) or dimethylzinc (DMZn), a zinc source comprising a carrier gas, an oxygen and a dopant source, the zinc source and oxygen being separated from each other and flowing over the substrate step; And A method of growing a zinc oxide thin film formed by nitrogen doping, comprising growing a zinc oxide thin film on the substrate by a MOCVD (Metalorganic Chemical Vapor Deposition) method. delete delete The method of claim 1, wherein the carrier gas comprises argon (Ar). The method of claim 4, wherein the dopant source is nitrogen monoxide (N ₂ O) or nitrogen dioxide (NO ₂ ). delete delete delete delete The method of claim 1, wherein the carrier gas, the oxygen, and the dopant source are supplied through an MFC (mass flow controller) to form a zinc oxide thin film. delete The method according to claim 1, wherein a bubbler is placed in a thermostat in order to maintain a constant flow rate of the zinc precursor, and the temperature of the bubbler is 5 ° C. to 5 ° C. when the zinc precursor is diethyl zinc (DEZn) during thin film growth. A method of growing a zinc oxide thin film formed by nitrogen doping, which is maintained at -10 ° C. The method according to claim 1, wherein a bubbler is placed in a thermostat to maintain a constant flow rate of the zinc precursor, and the temperature of the bubbler is 10 ° C. to − when the zinc precursor is dimethylzinc (DMZn) during thin film growth. A method of growing a zinc oxide thin film formed by nitrogen doping, which is maintained at 30 ° C. The method of claim 12, wherein the bubbler internal pressure is maintained at a pressure of 350 torr to 900 torr using an electronic pressure conotroller (EPC).