KR101965368B1 - Preparation Method for Zinc Tin Nitrogen Single Crystal Thin Film - Google Patents

Abstract

The present invention relates to a method for manufacturing a zinc tin nitrogen single crystal thin film capable of manufacturing a single crystal thin film having a regular crystal lattice structure on various kinds of substrates and easily adjusting a band gap only by simple adjustment of conditions. More particularly, the present invention relates to a method for manufacturing a ZnSnN_2 single crystal thin film, comprising the steps of: (A) forming a ZnO single crystal thin film buffer layer of a wurtzite structure on a substrate; and (B) epitaxially growing a ZnSnN_2 single crystal thin film on the ZnO buffer layer.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a zinc-tin nitrogen single crystal thin film,

The present invention relates to a method of manufacturing a zinc-tin nitrogen single crystal thin film capable of easily fabricating a single crystal thin film having a regular crystal lattice structure on various kinds of substrates and easily adjusting a band gap only by a simple adjustment of conditions.

Semiconductors are an integral part of the electronics industry and are used in almost every area from smart phones to solar panels. However, rare metals such as Te, Ga and In are used in these semiconductors. Since rare elements can not predict the supply and price of raw materials, it is necessary to develop semiconductor materials using rich and cheap elements.

Zn-IV-N2 (IV = Si, Ge or Sn) is abundant in nature, environmentally friendly, and has no toxicity. Therefore, it is a substitute for semiconductor materials such as InGaN and solar cell light absorbing layers such as CdTe and CuOnGaSe2 It is getting attention. Therefore, the synthesis methods and properties of ZnSiN2 and ZnGeN2 have been actively studied. ZnSnN2 has not been studied much in comparison with ZnSiN2 or ZnGeN2, and since its synthesis was first reported in 2013, it is still in the early stage of research. ZnSnN2 is less theoretically calculated than ZnSiN2 or ZnGeN2 because of its low bandgap energy, making it suitable for the application of semiconductor devices such as solar cells. TD Veal et al (Adv. Energy Mater. 2015, 5, 1501462) can adjust the band gap energy in the range of 1.33 ~ 2.21 eV by changing the growth condition of the thin film on yttria-stabilized cubic zirconia It has been recognized for potential application potential as a promising material to replace semiconductor materials containing rare metals. Both zinc and tin are readily available through existing recycling facilities.

In 2013, Paul C. Quayle et al. (MRS Communications 2013, 19, 135-138) fabricated ZnSnN2 polycrystalline thin films with a bandgap energy of about 1.7 eV by the plasma assisted gas-liquid-solid method at 400 ℃. Feldberg et al. (Applied Physics Letters 2013, 103, 042109) reported that a high purity ZnSnN2 polycrystalline thin film with a band gap energy of 2.1 eV can be fabricated using the molecular beam epitaxy method. In the same year, L. Lahourcade et al. (Adv. Mater. 2013, 25, 2562-2566) also reported that a polycrystalline ZnSnN2 thin film with a band gap energy of 2.0 eV on sapphire and GaN was produced at 250 ° C by magnetron sputtering. Chinese Patent Publication No. 104195514 also reported a method of manufacturing a ZnSnN2 polycrystalline thin film at low temperature by magnetron sputtering.

All of the above methods relate to a ZnSnN2 polycrystalline thin film. However, since the quality of a semiconductor device largely depends on defects such as dislocation and dislocation of the atomic arrangement existing in the grain boundaries and grain boundaries, Growth of high-quality ZnSnN2 single crystal thin films is required. ZnSnN2 single crystal thin films were only grown on (111) YSZ and (001) LiGaO2 substrates. However, since (111) YSZ and (001) LiGaO2 substrates contain rare metals, they still have problems in supply and demand. Because commercial substrates are small and expensive, they are applied to industrial applications by large area production or mass production of ZnSnN2 single crystal thin films. it's difficult.

Chinese Patent Publication No. 104195514

Adv. Energy Mater. 2015, 5, 1501462. MRS Communications 2013, 19, 135-138. Applied Physics Letters 2013, 103, 042109. Adv. Mater. 2013, 25, 2562-2566.

It is an object of the present invention to provide a method for manufacturing a high quality ZnSnN2 single crystal thin film on various kinds of substrates.

It is another object of the present invention to provide a method of manufacturing a ZnSnN2 single crystal thin film which can easily control the band gap energy of a ZnSnN2 single crystal thin film to be manufactured.

According to an aspect of the present invention, there is provided a method of manufacturing a thin film transistor, including: (A) forming a ZnO single crystal thin film buffer layer of a Wurtzite structure on a substrate; And (B) epitaxially growing a ZnSnN2 single crystal thin film on the ZnO buffer layer. The present invention also relates to a method for manufacturing a ZnSnN2 single crystal thin film.

Conventional ZnSnN2 single crystal thin films have been grown on (111) YSZ and (001) LiGaO2 substrates, but they are difficult to fabricate large-area substrates and are in need of replacing themselves with rare earth- But also the price is too expensive and there is a problem in actual application. The present invention relates to a method for manufacturing a high-quality ZnSnN2 single crystal thin film using a buffer layer of a Wurtzite structure ZnO thin film, on which a method of forming a single crystal thin film on various substrates is known.

The present invention is characterized in that a ZnSnN2 single crystal thin film is epitaxially grown by using a ZnS thin film of a Wurtzite structure as a buffer layer. Since the ZnS thin film is not characterized by the growth method of the ZnO thin film of step (A) A detailed description of the method of forming the thin film is omitted. As a method for growing a ZnO thin film having a Wurtzite structure on a variety of substrates, many prior studies have already been made in the prior art, so that those skilled in the art will be able to select a suitable method according to the type of substrate on which a thin film is to be formed, will be. When the thickness of the buffer layer is too thin, it is difficult to form a buffer layer having a uniform thickness, which adversely affects the growth of the ZnSnN2 thin film. If the thickness of the buffer layer is too thick, it may affect the thickness of the device. Respectively.

In the step (B), the ZnSnN2 single crystal thin film is epitaxially grown along the crystal lattice of the ZnO buffer layer. In the case where the crystal lattice mismatch between the crystal lattice of the substrate and the grown crystal lattice mismatch is large at the time of epitaxial growth, a combination of misfit dislocation, threading dislocation, lamination bonding and inversion domain boundary (IDB) And such defects shorten the lifetime of the device and deteriorate the performance. The ZnO thin film of the Wurtzite structure has a lattice mismatch of 4.2% with the ZnSnN2 single crystal thin film, which is considered to be very useful for the growth of the ZnSnN2 single crystal thin film. As a result of the actual epitaxial growth of the ZnSnN2 single crystal thin film, a high quality Pseudo-Wurtzite ZnSnN2 single crystal thin film Was grown. Therefore, according to the present invention, a ZnSnN2 single crystal thin film can be manufactured on various substrates without being limited to the substrate material without using expensive substrates such as YSZ and LiGaO2. In the following examples, Al2O3 used as a substrate had a lattice mismatch with ZnSnN2 of 29%, and an amorphous ZnSnN2 thin film was formed on an Al2O3 substrate not using a ZnO buffer layer.

The epitaxial growth method of the ZnSnN2 single crystal thin film may be any method as long as it is a method for epitaxial growth of a conventional thin film. For example, molecular beam epitaxy, sputtering, chemical vapor deposition (CVD), atomic layer deposition (ALD), and pulsed laser deposition (PLD) But is not limited thereto.

The specific epitaxial growth conditions of the ZnSnN2 single crystal thin film can be optimized by controlling the growth method of the thin film, the kind of the used equipment, the size, the degree of vacuum, the flow rate of the working gas, the growth temperature of the thin film, Of course. The thickness of the thin film to be grown can also be easily controlled by the thin film formation time. Therefore, it is meaningless to finely define the epitaxial growth conditions of the ZnSnN2 single crystal thin film.

In the case of using the molecular beam epitaxy method as in the following examples, for example, the supply ratio of Zn and Sn is preferably from 10: 1 to 40: 1. However, the actual thin film formation The contribution is also affected, so it does not exclude temperatures outside the above range. At this time, the growth temperature of the ZnSnN 2 single crystal thin film was preferably 350 to 550 ° C. When the temperature is too low or the temperature is too high, crystallinity is lowered and it is difficult to grow into a single crystal thin film. However, since temperatures may also be affected by changes in detailed conditions, temperatures outside the above ranges are not excluded.

Tunable band gaps are one of the most important characteristics when applied to optoelectronic devices such as solid-state lighting or solar cells. The bandgap energy of the ZnSnN2 single crystal thin film prepared by the molecular beam epitaxy method was 1.8 ~ 2.2ev and can be easily controlled only by changing the ZnSnN2 thin film growth temperature in step (B).

The present invention also relates to a semiconductor device comprising a ZnSnN2 single crystal thin film produced by the above method. The semiconductor device is preferably a photoelectric device such as solid lighting or a solar cell.

As described above, the method of manufacturing the ZnSnN2 single crystal thin film of the present invention can produce a high quality ZnSnN2 single crystal thin film regardless of the kind of the substrate by utilizing the well known ZnO buffer layer on the various substrates, The present invention can be effectively used for manufacturing a semiconductor device including a ZnSnN2 thin film made of elements rich in deposits.

In addition, since the band gap energy can be easily controlled by adjusting only the growth temperature of the thin film, the ZnSnN2 single crystal thin film of the present invention can be widely applied to an optoelectronic device such as a solid-state lighting or a solar cell.

FIG. 1 is a half-dead energy electron diffraction image of a ZnSnN2 thin film prepared according to an embodiment of the present invention.
2 is an XRD spectrum of a ZnSnN2 thin film produced according to an embodiment of the present invention.
3 is a TEM image of a ZnSnN2 thin film section fabricated according to an embodiment of the present invention.
4 is a HRTEM image of the ZnO / ZnSnN2 interface and the upper ZnSnN2 region of a ZnSnN2 thin film fabricated according to an embodiment of the present invention.
5 is a reflection high-speed electron beam diffraction image at the initial stage of the production of a ZnSnN2 thin film produced by an embodiment of the present invention.
6 is an AFM image of a ZnSnN2 thin film produced according to an embodiment of the present invention.
7 is an absorption spectrum of a ZnSnN2 thin film produced according to an embodiment of the present invention.

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, these embodiments are merely examples for explaining the content and scope of the technical idea of the present invention, and thus the technical scope of the present invention is not limited or changed. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the technical idea of the present invention based on these examples.

[Example]

Example 1: Preparation of ZnSnN2 thin film

(0001) Al ₂ O ₃ substrate of 1 × 1 inch size was sequentially ultrasonicated in acetone and methanol, and then immersed in an etching solution of H ₂ SO ₄ : H ₃ PO ₄ = 3: 1 (v / v) And treated for a minute to remove grease. Then washed with DI water and dried using nitrogen gas.

ZnO buffer layer and ZnSnN2 thin film layer were successively grown on Al ₂ O ₃ substrate using plasma assisted molecular beam epitaxy (PAMBE) equipment. The metal zinc (Zn) and tin (Sn) sources of 6N purity were supplied using a standard effusion cell and the flux was measured using a quartz crystal microbalance. Oxygen or nitrogen radicals were supplied using an RF plasma source.

Before forming the ZnO buffer layer, the substrate was treated with oxygen plasma at 800 ° C for 30 minutes. Thereafter, a ZnO buffer layer having a thickness of 100 nm was formed at 700 ° C. under a plasma power of 300 W, an oxygen flow rate of 2 sccm, and a Zn flow rate of 2 Å / s for 30 minutes. After growing the ZnO buffer layer, the main shutter was closed and the oxygen plasma was turned off.

A nitrogen plasma was generated for 5 minutes while the main shutter was closed to remove oxygen remaining in the plasma cell. Then, the ZnSnN2 thin film was grown to a thickness of 40 nm for 2 hours by adjusting the plasma power to 300 W and the nitrogen flow rate to 0.2 sccm while maintaining the Zn flow rate at 2 Å / s and increasing the temperature of the Sn cell to a flow rate of 0.1 Å / . The growth temperature was adjusted to 350, 450, 550 or 650 ° C.

Example 2 Evaluation of Structural Characteristics of ZnSnN2 Thin Films

The ZnSnN2 thin film grown at each temperature was monitored in real time by reflection high-energy electron diffraction (RHEED) and the results are shown in Fig. Figure 1 is a image showing a RHEED pattern according to the sapphire substrate [1100] and [1200] azimuth, (a) is Al ₂ O ₃ substrate, (b) is a ZnO buffer layer (c) ~ (f) are respectively 350, 450, 550, and 650 ° C of the ZnSnN2 thin film. (g) is a schematic diagram showing an epitaxial relation between ZnO and ZnSnN ₂ , and (h) shows a diffraction pattern for a ZnSnN 2 thin film formed directly on an Al ₂ O ₃ substrate without a ZnO buffer layer.

Figures 1 (a) and 1 (b) show RHEED of a typical single crystal ZnO rotated at 30 degrees relative to the crystal orientation of sapphire. The ZnO lattice is aligned along the oxygen sublattice of Al ₂ O ₃ so that the [1100] direction of ZnO is aligned along the [1120] direction of the sapphire. The RHEED pattern shows a line of bright stripes characterized by a very flat surface.

The ZnSnN2 thin film grown at 350 캜 on the ZnO buffer layer shows a blurred and spreading stripe pattern as shown in Fig. 1 (c), suggesting that the surface is irregular. The ZnSnN2 thin films grown at 450 ° C and 550 ° C (Fig. 1 (d) and (e)) show a clear and clean stripe pattern, which indicates that a flat, highly crystalline thin film is grown. As the growth temperature of the thin film was increased to 650 ° C (FIG. 1 (f)), the RHEED pattern was again blurred and changed into a spread dotted line to show that the crystallinity was lowered.

ZnSnN2 is known to have mainly orthorhombic and pseudo-wurtzite monoclinic structures. As a result of observing the growth process of ZnSnN2 thin film by RHEED in real time, no doubling streaks characteristic of the orthorhombic ZnSnN2 structure were observed, and azimuth angle, which is the same characteristic as the RHEED pattern of the ZnO buffer layer of the Wurtzite structure Only 60 ° rotational symmetry is shown. The orthorhombic ZnSnN2 has a 180 ° rotational symmetry property. Therefore, it can be confirmed that the ZnSnN2 thin film grown by the above Example 1 has a pseudo-urushian structure.

[1120] and [1110] of the ZnSnN2 thin film are obtained from the (0001) Pseudo-Wurtzite ZnSnN2 and (0001) Wurtzite ZnO having the same symmetry property and the degree of mismatching is as small as 4% Direction were determined to be parallel to the [1120] and [1110] directions of ZnO, respectively. The epitaxial relationship between ZnSnN2 and ZnO is shown in Fig. 1 (g). Pseudo-Ur lattice mismatching of the structure of cheugwang ZnSnN2 and c-Al ₂ O ₃ is too large to grow a high-quality thin film ZnSnN2 to 29%. Thin film growth temperature in order to determine the growth characteristics of the thin film of ZnSnN2 in the absence of the buffer layer ZnO ZnO state exists when grown directly on thin ZnSnN2 c-Al ₂ O ₃ substrate under the conditions of 450 ℃ who is the crystalline solid. Fig. 1 (h) shows the RHEED pattern of the grown ZnSnN2, and no pattern was observed. This means that the grown ZnSnN2 is amorphous or very irregular.

High resolution X-ray diffraction (XRD) analysis was performed using a Bruker AXS D8 DISCOVER diffractometer to further confirm the crystallinity of the ZnSnN2 thin film formed on the ZnO buffer layer.

FIG. 2 shows spectra of the results. FIG. 2 (a) shows XRD θ-2 θ measurement results of the thin films grown at 450 and 550 ° C., and FIG. 2 shows peaks due to the sapphire substrate.

Both samples showed the same peak at 68.35 ° at a 2θ position of 32.65 ° for ZnSnN 2, which is attributed to (0002) and (0004) ZnSnN 2 diffraction of the pseudo-wurtzite structure. No peaks of zinc oxide (ZnN) or tin oxide (SnN) were observed. Thin films grown at 450 ℃ showed narrower and sharp peaks compared to the films grown at 550 ℃, showing better crystallinity. The positions of the (0002) and (0004) ZnSnN2 peaks indicate that the c-axis lattice parameters averaged 5.480 Å, corresponding to 5.416-5.567 Å reported by N. Feldberg et al. (0002) and (0004) peaks of ZnO are observed at 34.44 ° and 72.370 ° near the (0002) and (0004) peaks of ZnSnN 2, respectively, and the c-axis lattice parameters of the calculated wurtzite ZnO are averaged 5.201 Å, which is known as 5.207 Å. No other peaks were observed except for the diffraction peaks of ZnSnN2 and ZnO, indicating that the c-axis growth of the thin film predominated.

FIG. 2 (b) shows the results of phi stanting for the (1011) ZnSnN 2 and (1011) ZnO diffraction measured from the ZnSnN 2 thin film grown at 450 ° C., and the ZnSnN 2dl in-plane alignment ). The XRD phi scan conditions for ZnSnN2 were tailored to the crystal structure based on the Pseudo-Wurtzite structure reported by N. Feldberg et al. The Pseudo-Wurtzite ZnSnN2 phi scan diffraction peak was observed at the correct position predicted from 2θ 34.68 ° of (1011) ZnSnN 2 and χ value 62.15 ° representing the angle (1011) and (0001) of ZnSnN 2. (1011) ZnSnN2 and (1011) ZnO, the pits were separated at intervals of 60 degrees of phi, and 60 ° rotational symmetry, which is characteristic of the Wurtzite crystal structure, was confirmed. The fact that only ZnSnN2 and ZnOdml [000L] peaks are observed in the XRD θ-2θ measurement and that the ZnSnN2 thin film is a single crystal thin film together with the ZnO buffer layer in the fact that the ZnOnN2 and ZnOdml [000L] peaks are observed from (0011) ZnSnN2 and (0011) ZnO.

Crystallinity of the ZnO buffer layer and the ZnSnN2 thin film can be seen from the omega rocking curves shown in Fig. 2 (c). The full width at half maximum (FWHM) of the (0002) reflection of the omega rocking curve generally represents the tilt mosaic structure of the epitaxial film. The FWHM of ZnSnN2 indicates that a thin film prepared at 450 ° C has a crystallinity of 0.50 or 550 ° C and a thin film made at 450 ° C has a crystallinity of 0.71 °.

In order to confirm the microstructure of the ZnSnN2 thin film, a cross section was observed with a TEM (JEOL JEM-ARM200F), and the results are shown in Fig. TEM samples were prepared using the focus ion beam process (FEI Nova 200).

FIG. 2 (a) is a bright-field TEM image of a ZnSnN 2 thin film sample grown at 450 ° C., and FIG. 2 (b) is an EDS element mapping showing that the sample has a ZnSnN ₂ / ZnO / Al ₂ O ₃ structure It clearly shows. In FIG. 3 (a), the boundary between the ZnO buffer layer and the ZnSnN2 layer is indicated by a dotted line. (C) and (d) of FIG. 3 are the diffraction patterns (SAD patterns) of the regions of the ZnO / Al ₂ O ₃ and ZnSnN ₂ / ZnO interfaces, respectively, circled in (a). From FIG. 3 (c), the [1010] Al ₂ O ₃ single-stage diffraction pattern and the [1120] single crystal diffraction pattern of ZnO can be confirmed. 3 (d) shows a ZnO [1120] single crystal diffraction pattern and a ZnSnN2 [1120] diffraction pattern. The SAD pattern of ZnSnN2 corresponds to the pattern of Pseudo-Wurtzite structure like the above-mentioned result. Therefore, [1010] ZnSnN2 // [1010] ZnO // [1120] Al 2 O 3, [1120] ZnSnN2 // [1120] ZnO // [10100] Al 2 O 3 , and [0001] ZnSnN2 // [0001] ZnO // [0001] Al ₂ O ₃ was determined for an epitaxial relationship, which is consistent with the results of RHEED and XRD. According to quantitative EDS analysis of the ZnSnN2 thin film, the atomic ratio of Zn / Sn was 1.3: 1.

4 is an image obtained by observing the crystal structure of the (a) ZnO / ZnSnN2 interface and (b) the upper ZnSnN2 region by HRTEM. Fig. 4 (a) clearly shows that ZnO has a wurtzite structure, and the d-spacing of (10O10) and (0001) planes is shown in the figure. The lattice image of the ZnSnN2 region at the interface was not clearer than that of ZnO or the top surface, but the d-spacings of the (0001) and (1010) planes were 5.47 and 2.90 Å, respectively. The somewhat unclear lattice structure at the interface suggests that there is some transient at the beginning of ZnSnN2 growth on the ZnO buffer layer. According to Fig. 4 (a), the transition period is estimated to be about 2 nm in the thin film growth period. FIG. 5 is a RHEED pattern after 5 minutes of ZnSnN2 thin film growth corresponding to 2 nm. FIGS. 5A to 5D show thin films grown at 340, 450, 550 and 650 ° C., respectively. Although the pattern sharpness is somewhat lower than the RHEED pattern after 2 hours of thin film growth, it can be confirmed that a ZnSnN2 thin film having a Pseudo-Wurtz structure is still produced.

The ZnSnN2 thin films prepared at all temperatures showed a pale brown color when viewed from the eye, and no excess metal liquid droplets produced on the growth surface in micrometer size were observed in general. In order to observe it more closely, the surface structure was confirmed and the surface roughness was measured using an atomic force microscope (AFM, Asylum Research MFP-3D model). FIG. 6 shows AFM images of the thin films grown at 450 ° C. (a, c) and 550 ° C. (b, d), and no metal droplets were observed and the RMS surface roughnesses were 1.12 and 1.02, respectively.

Example 3 Evaluation of Optical Properties of ZnSnN2 Thin Films

The optical band gap of the ZnSnN2 thin film was calculated from the absorption spectrum measured at room temperature using a Shimadzu UV-2600 spectrometer. FIG. 7 shows (? Hν) 2 vs photon energy (h?) From the absorption spectrum to measure the band gap of the ZnSnN2 thin film grown at each temperature. For band gap calculation, it is assumed that ZnSnN2 has a direct bandgap, and the direct bandgap (Eg) is calculated from the following equation.

(? h?) ² = A (h? n-Eg)

α: Measurement of extinction coefficient and transmittance

A: constant

hν: energy of incident light

For the ZnSnN2 thin films prepared at 350 ° C, 450 ° C, 550 ° C and 650 ° C, the band gap energies calculated from Fig. 6 were 1.85, 2.0, 2.05 and 2.15 eV, respectively, . From this, it can be seen that the band gap energy can be controlled by simply changing the temperature.

Claims (8)

(A) forming a ZnO single crystal thin film buffer layer of a Wurtzite structure on a substrate; And
(B) epitaxially growing a ZnSnN2 single crystal thin film on a ZnO buffer layer;
Wherein the ZnSnN2 single crystal thin film has a thickness of 10 nm or less.
The method according to claim 1,
Wherein the ZnSnN2 single crystal thin film has a Pseudo-Wurtzite structure.
3. The method according to claim 1 or 2,
Wherein the step (B) is performed by a molecular beam epitaxy method, sputtering, chemical vapor deposition, atomic layer deposition or pulse laser deposition.
The method of claim 3,
The step (B) is performed by a molecular beam epitaxy method,
Wherein the supply ratio of Zn and Sn in the growth of the ZnSnN2 single crystal thin film is in the range of 10: 1 to 40: 1 atomic ratio.
5. The method of claim 4,
Wherein the growth temperature of the ZnSnN2 single crystal thin film in the step (B) is 350 to 550 ° C.
6. The method of claim 5,
Wherein the band gap energy of the ZnSnN2 single crystal thin film is 1.8 to 2.2 eV.
The method according to claim 6,
Wherein the band gap energy of the ZnSnN2 single crystal thin film is controlled by the growth temperature of the ZnSnN2 single crystal thin film.
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