JP2002105625A - Method for manufacturing low resistivity p-type zinc oxide thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing p-type zinc oxide thin film of which a function as a semiconductor having light transmissivity and electric conductivity can be expected. SOLUTION: In depositing the p-type zinc oxide thin film, a ZnO target and a GaN target as a dopant source are used to dope a ZnO thin film with Ga and N independently and simultaneously or with GaN. It is preferable to use a sputtering method as a thin film deposition method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a p-type zinc oxide (hereinafter referred to as a "p-type zinc oxide"), which is highly expected as a semiconductor having optical transparency and conductivity.
It is described as “ZnO” as appropriate. A) a method of producing a thin film;

[0002]

2. Description of the Related Art Zinc oxide is a semiconductive, photoconductive or piezoelectric material and is essentially transparent in the visible light region. This zinc oxide thin film is usually obtained by sputtering or chemical vapor deposition (CVD), and a method of lowering resistance by doping with n-type impurities has been devised (for example, JP-A-7-106615, JP-A-7-106615). 7-288
049, JP-A-8-50815). However, the growth of a p-type ZnO single crystal thin film with low resistance is
This was not possible due to the self-compensation effect and the small solubility of the p-type dopant.

Recently, however, p-type conductivity has been reported in a laser ablation method by a simultaneous doping method in which an acceptor and a donor are simultaneously doped into a ZnO thin film (Tetsuya Yamamoto and Hiroshi Yoshid).
a; J Appi.Phys.Vol.38 L166-L169 (1999), M.Joseph, H.Ta
bata and T. Kawai; J Appi. Phys. Vol. 38 L1205-L1207 (19
99)).

[0004]

Problems to be Solved by the Invention ZnO has attracted attention as a luminescent material according to reports of ultraviolet laser oscillation at room temperature (Masashi Kawasaki, Akira Otomo: Solid State Physics, Vol. 33, p. 59, 1998). I have. However, there is a problem that ZnO cannot be made of p-type conductivity. Conventionally, n-type Zn is used for individual doping in which a Ga source and an N source are doped from separate source materials by using a sputtering method using a high frequency.
Although an O thin film was formed, a p-type ZnO thin film was not formed.

As a solution to this problem, a method of forming a p-type ZnO film by individually doping Ga ₂ O ₃ and N ₂ O using a laser ablation method has been recently developed as described above. However, the ablation method is difficult to increase the area, increases the cost, and is not suitable for mass production. Further, there is a problem that the obtained ZnO thin film has high resistance.

[0006]

As a means for solving the above-mentioned problems, the present inventors have found a new method. That is, the present invention provides a p-type Zn
When forming an O thin film, G is used as an impurity doping substance.
This is a method for manufacturing a low-resistance p-type ZnO thin film, wherein Ga and N are separately and simultaneously doped into a ZnO thin film by using an aN target, or GaN is doped.

The ZnO thin film manufactured by the manufacturing method of the present invention is incorporated into the ZnO thin film in a form in which Ga is bonded to N by using GaN in which Ga is bonded to N as a target, and has a low-resistance p-type ZnO. A thin film is obtained. This ZnO thin film may be doped with a compound in which an element belonging to Group IIIB and an element belonging to Group VB are combined. IIIB group elements include B, Al, Ga, In and the like, and VB group elements include N, P, As, Sb and the like.

As a method of forming a ZnO thin film, a sputtering method is preferable, but molecular beam epitaxy (MB)
Any known thin film forming method such as E), ion plating, laser ablation, and chemical vapor deposition can be used. As the substrate, Si, SiC,
_{Sapphire, GaN, NdGaO 3, LiGaO 2} , Li
A crystalline substrate such as AlO ₂ or LSAT and an amorphous substrate such as glass can be used.

The GaN target can be used as a ZnO target to which GaN in which Ga is combined with N is added.
In this case, the GaN target can be manufactured, for example, by the following method. a) After the ZnO powder and the GaN powder are mixed well, they are pressed to produce a ZnO target mixed with GaN. b) The target of a) is sintered to produce a sintered target of GaN and ZnO.

A GaN target is used separately from a ZnO target. In this case, the GaN target is used, for example, as follows. a) A small GaN target is placed on the ZnO target. b) Zn
An O target and a GaN target are arranged side by side. G
As the aN target, any GaN compound such as a GaN powder, a GaN thin film, or a GaN sintered body can be applied, and the method for producing GaN is not particularly limited.

The amount of GaN to be doped is ZnO
It can be changed by the area ratio with the target.
GaN and ZnO may be evaporated or sputtered at the same time, or ZnO targets and GaN targets may be alternately used to evaporate or sputter.

When Ga and N are used independently, the binding energy between Ga and O is 68 kcal / mol, the binding energy between Zn and O is 68 kcal / mol, and the binding energy between Ga and N is 26 kcal / mol.
At 0 kcal / mol, the binding energy between Zn and N is unknown, but since the thin film obtained by sputtering a ZnO target in nitrogen is ZnO, it is considered that the binding energy is very small.

Therefore, by using GaN in which Ga as a donor and N as an acceptor are bonded,
N—Ga—N bonds are easily formed and N—
Can be captured. As described above, since the binding energy between Ga and N is very high, the method of separately co-doping Ga and N and the method of doping GaN can be controlled by changing the sputtering power. This enables high-concentration acceptor doping. Furthermore, a hole band is formed by the acceptor taken in at a high concentration, whereby a p-type can be realized. The acceptor concentration required for realizing the p-type is about 10
^It is preferably at least ¹⁸ cm ^-3, more preferably at least 10 ¹⁹ cm ^-3 .

The preparation of a ZnO thin film according to the method of the present invention
From the viewpoint of application and productivity, the sputtering method is preferable because the sputtering method can be mass-produced.
In the case of using a sputtering method, oxygen is added to a sputtering atmosphere. In general, in a ZnO thin film, the composition of Zn and O sometimes deviates from the stoichiometric composition of 1: 1. When a thin film is formed at a high temperature, oxygen vacancies are easily generated. This oxygen deficiency causes low resistance p-type Z
In order to realize nO, it is necessary to reduce the concentration of oxygen vacancies as much as possible. Oxygen deficiency can be suppressed by adding oxygen to the sputtering atmosphere. The amount of oxygen added to the atmosphere gas during sputtering must be large enough to cancel the generation of oxygen deficiency at the deposition temperature of the thin film. Therefore, it is desirable to control the amount of added oxygen according to the deposition temperature of the thin film.

The low-resistance p-type ZnO obtained by the method of the present invention
By combining the thin film with the already realized low-resistance n-type ZnO, the application to light emitting diodes and lasers as an optoelectronic material in the ultraviolet region is expanded. Further, the application thereof extends to a photoelectric conversion device (solar cell) and a thin film transistor (TFT) transparent in a visible light region.

[0016]

EXAMPLE 1 A high-purity GaN powder was cold-pressed on a ZnO sintered target having a diameter of 40 mm and a thickness of 1 mm using a Nidec Anelva SPF-210SRF high-frequency sputtering apparatus to a diameter of 2 mm.
A small GaN target 8 having a thickness of 0.1 to 0.5 mm
0 were placed one on top of the other. Corning 7059 glass was used as a substrate in a mixed gas of O ₂ and N ₂ . RF power 150W, frequency 13.56MHz, pressure 40mTorr
r, the substrate temperature was 200 ° C., the distance between the electrodes was 50 mm, and the film formation time was 120 minutes. The addition amount of GaN was adjusted by setting the area of the GaN target to 20% with respect to the area of the ZnO target. The oxygen partial pressure ratio is O ₂ / (O ₂ + N ₂ ) = 60%
And

EXAMPLE 2 Forty small GaN targets were stacked, and the area of the GaN target was 10% of the area of the ZnO target.
Sputtering was performed under the same conditions as in Example 1 except that the sputtering was performed.

Comparative Example 1 Sputtering was performed under the same conditions as in Example 1 except that a GaN target was not used.

Comparative Example 2 Sputtering was performed under the same conditions as in Example 1 except that 20 small GaN targets were stacked and the area of the GaN target was set to 5% of the area of the ZnO target.

FIG. 1 is a transmission spectrum showing the light transmittance of the ZnO thin films prepared in Examples 1 and 2 and Comparative Examples 1 and 2 by an ultraviolet-visible light spectrophotometer. It can be seen that the ZnO thin film maintains a high ultraviolet-visible light transmittance even when GaN is added. Also, even if GaN is added, there is little change in absorption edge characteristics.

FIG. 2 shows the ZnO prepared in Example 1.
4 shows an X-ray diffraction result of the thin film. 1 and 2 that a (0002) -oriented ZnO thin film having an ultraviolet-visible light transmittance of 85% or more in an infrared-visible light region was formed.

FIG. 3 shows Examples 1 and 2 and Comparative Examples 1 and 2.
Area ratio of GaN target to ZnO target and Zn
4 shows the relationship between the crystallinity of the O thin film. The left vertical axis indicates the normalized X-ray diffraction intensity, and the right vertical axis indicates the (0002) diffraction half width. FIG. 3 shows that when the GaN addition amount is excessively large, Z
It can be seen that the crystallinity of the nO thin film decreases. FIG. 4 shows the band gap of the ZnO thin film of Example 2. ZnO is a direct transition semiconductor and has a band gap of 3.35 e.
V. It can be seen that the band gap is shifted from 3.35 eV to 3.25 eV to the longer wavelength side by adding GaN. Table 1 shows the electrical characteristics of the ZnO thin films prepared in Examples 1 and 2 and Comparative Examples 1 and 2. When GaN was not added, the resistance was too high to measure.

[0023]

[Table 1]

Table 1 shows that GaN is a GaN target and Z
When the addition amount was 5% in terms of the area ratio of the nO target, n-type conductivity was exhibited. However, it can be seen that the p-type ZnO thin film was realized by adding the addition amount of 10% or more. In the case of Example 1, the Ga concentration was found to be about 5% by X-ray photoelectron spectrum (XPS) of the obtained ZnO thin film.

The van der Pa of the ZnO thin film obtained in Example 2 with the GaN addition amount of 10% shown in Table 1 was used.
In the measurement of electrical characteristics by uw, the mobility was 18.5c.
m ² / V · sec, carrier density 9.0 × 10 ¹⁵ c
It was found that a p-type ZnO thin film having m ⁻³ and a resistivity of 37.6 Ωcm was formed. This indicates that a p-type ZnO thin film can be formed by an RF sputtering method using a simultaneous doping method.

Example 3 Sputtering was performed under the same conditions as in Example 1 except that the oxygen partial pressure ratio was changed to O ₂ / (O ₂ + N ₂ ) = 50%.

Example 4 Sputtering was carried out under the same conditions as in Example 1 except that the oxygen partial pressure ratio was O ₂ / (O ₂ + N ₂ ) = 70%.

Comparative Example 3 Sputtering was performed under the same conditions as in Example 1 except that oxygen was not added.

Table 2 shows the relationship between the oxygen partial pressure ratio during the preparation of the ZnO thin film and the electrical characteristics. This indicates that a certain amount or more of oxygen is required to be added to the sputtering gas in order to realize the p-type. Therefore, in order to realize a low-resistance p-type ZnO thin film, the Ga
It can be seen that it is necessary to control the amount of added N and the amount of added oxygen in the sputtering gas as conditions.

[0030]

[Table 2]

[0031]

According to the method of the present invention, a p-type dopant can be stably doped to a high concentration, and as a result, a p-type ZnO thin film can be easily manufactured. , Can be applied to liquid crystal,
It can contribute to higher efficiency and higher performance as an optoelectronic material ranging from visible light to ultraviolet light.

[Brief description of the drawings]

FIG. 1 shows ZnO of Examples 1 and 2 and Comparative Examples 1 and 2.
It is a graph which shows the transmission spectrum by the ultraviolet visible light spectroscopy altimeter of a thin film.

FIG. 2 is a graph showing an X-ray diffraction result of the ZnO thin film of Example 1.

FIG. 3 shows GaN of Examples 1 and 2 and Comparative Examples 1 and 2.
4 is a graph showing the relationship between the area ratio of a target and a ZnO target and the crystallinity of a ZnO thin film.

FIG. 4 is a graph showing a band gap of a ZnO thin film of Example 2.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akihiro Wakahara 2-1 Hoshiura, Kitayama-cho, Toyohashi-shi, Aichi 7-302 Fushi term (reference) 4K029 AA09 BA49 BC09 CA05 DC05 DC09 DC15 DC35 5F041 AA21 CA41 CA54 CA55 CA57 CA67 5F051 AA09 CA02 CB15 CB18 GA04

Claims (2)

[Claims] When forming a p-type zinc oxide thin film, Ga and N are separately and simultaneously doped into a ZnO thin film by using a GaN target as a target and an impurity doping material, or GaN is doped. A method for producing a low-resistance p-type zinc oxide thin film. 2. The method for producing a low-resistance p-type zinc oxide thin film according to claim 1, wherein the method for forming the thin film is a sputtering method.