JP3333476B2 - Method of forming ohmic electrode in n-type ZnO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an ohmic electrode in n-type ZnO.

[0002]

BACKGROUND OF THE INVENTION Conventionally, ZnO, ZnS, ZnSe,
II-VI group n-type compound semiconductor such as ZnTe or CdS, GaP, GaAs, GaSb, InP, I
Various types of n-type compound semiconductors, such as a group III-V n-type compound semiconductor such as nAs or InSb, are known.

[0003] In recent years, ZnO-based crystals, which are II-VI group n-type compound semiconductors, have attracted attention as new short-wavelength light emitting device materials.

[0004] In addition, bulk crystals of Wz-ZnO (ZnO having a wurtzite type crystal structure) have become commercially available and can be used as a substrate for growing a ZnO-based optical device structure. I have.

Further, the lattice constant of Wz-ZnO is
-GaN (GaN (gallium nitride) having a wurtzite crystal structure) has a small difference from the lattice constant, so that Wz-ZnO
It has been studied to use as a substrate of a GaN-based optical device structure.

However, since ZnO is an n-type compound semiconductor as described above, the surface of the ZnO substrate (in addition to the surface of the ZnO substrate to be used as a substrate for growing a ZnO-based optical device structure or a substrate for a GaN-based optical device structure). In this specification, the term “surface” means a surface of an arbitrary portion such as a front side or a back side of a substrate.
It is necessary to form an electrode having a linear voltage characteristic.

However, up to now, no effective method has been proposed for forming an ohmic electrode on the surface of various n-type compound semiconductors such as the above-mentioned ZnO, and the proposal of such a method is strongly desired. Was what it was.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above demands for the prior art, and has as its object to form an ohmic electrode on the surface of n-type ZnO. It is an object of the present invention to provide a method for forming an ohmic electrode in n-type ZnO, which enables the above.

[0009]

In order to achieve the above-mentioned object, the present invention according to claim 1 of the present invention provides an n-type ZnO
In the method for forming an ohmic electrode in n-type ZnO for forming an ohmic electrode on the surface of the substrate, the surface of the n-type ZnO is irradiated with pulsed laser light at a fluence of 0.3 to 0.4 J / cm ² , A first step of cutting a bond between Zn and O to form a low-resistance layer which is a Zn-rich non-stoichiometric layer; and forming an ohmic property on the low-resistance layer formed in the first step. A second step of forming a conductor as an electrode.

Further, the invention according to claim 2 of the present invention is characterized in that the n-type ZnO is formed by n-type ZnO (000
1) (ρ = 2000 Ωcm).

[0011] In the invention according to claim 3 of the present invention, one pulse of the pulse laser light is irradiated.

In the invention according to claim 4 of the present invention, the pulse laser beam is a KrF excimer pulse laser beam.

[0013]

[0014]

[0015]

[0016]

[0017]

[0018]

[0019]

[0020]

[0021]

[0022]

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a method for forming an ohmic electrode in n-type ZnO according to the present invention will be described in detail with reference to the accompanying drawings.

In one embodiment of the method for forming an ohmic electrode in n-type ZnO according to the present invention, an n-type
The surface of nO is irradiated with pulsed laser light at a fluence of 0.3 to 0.4 J / cm ² to cut the bond between Zn and O and to be a Zn-rich non-stoichiometric layer having a low stoichiometry. And a conductor forming process as a second step of forming a conductor as an ohmic electrode on the low resistance layer formed in the first step. An ohmic electrode is formed on n-type ZnO.

The conductor formed by the above-described conductor forming process is to be an ohmic electrode, and the user can use this conductor as an ohmic electrode.

In the present invention, the conductor formed on the surface of the n-type ZnO may be In (indium) or Al.
Various metals such as (aluminum) can be used. In the embodiment described below, a case where indium is used as a conductor formed on the surface of n-type ZnO will be described.

First, FIG. 1 shows an n-type ZnO according to the present invention.
FIG. 1 is a conceptual explanatory diagram of an example of an apparatus configuration for realizing a laser irradiation process in a method of forming an ohmic electrode in FIG.

The apparatus shown in FIG. 1 is a laser irradiation apparatus for performing a laser irradiation process, that is, a process of irradiating laser light to n-type ZnO in a nitrogen gas atmosphere at normal pressure (760 Torr). A KrF excimer laser oscillation device 10 for generating light, a laser energy adjustment mirror 12 for adjusting the laser energy of the pulsed laser light emitted from the KrF excimer laser oscillation device 10, and a laser energy adjustment mirror 12 emitted from the laser energy adjustment mirror 12. A mirror 14 for causing the pulsed laser light to enter a projection system 16 described below, and a projection system 16 for equalizing the laser energy density of the pulsed laser light incident via the mirror 14 and setting an irradiation area thereof,
Projection system 16 with synthetic quartz window 18
And a vacuum chamber 24 in which n-type ZnO is mounted as a sample 22 on a sample stage 20 disposed inside the pulse laser beam emitted from the laser.

Then, the sample table 2 in the vacuum chamber 24
The position of each of the samples 22 mounted on the laser beam 0 is set such that the sample 22 is irradiated with the pulse laser light emitted from the projection system 16 through the synthetic quartz window 18.

In the vacuum chamber 24, a turbo molecular pump 26, a rotary pump 28, valves 30, 3
2. A known vacuum system including a pressure gauge 34 and the like is connected, and the inside of the vacuum chamber 24 can be set to a vacuum state as needed.

Further, the vacuum chamber 24 contains N
₂ A pipeline 36 for introducing nitrogen gas into the vacuum chamber 24 from a gas cylinder (not shown) filled with (nitrogen gas) is connected to the vacuum chamber 24. It has been made possible to introduce.

The projection system 16 includes a mirror 16a for bending the optical path of the pulsed laser beam incident via the mirror 14, and a mirror 1a.
6a, a fly's-eye type laser energy density equalizing element 16b for equalizing the laser energy density of the pulse laser light whose optical path is bent, and an optical path of the pulse laser light emitted from the fly's eye type laser energy density equalizing element 16b. Mirror 1 for bending
6c, 16d, and the pulse laser beam whose optical path is bent by the mirror 16d is passed through to irradiate the pulse laser beam irradiation area (in this embodiment,
It is 2.2 mm × 2.2 mm (when laser irradiation is performed on the n-type compound semiconductor) or 4 mm × 4 mm (when electric measurement is performed after the laser irradiation). )
Aperture 16e with an opening for setting
And a condenser lens 16f for condensing the pulsed laser light whose irradiation area has been set through the opening of the aperture 16e, and the pulsed laser light condensed by the condenser lens 16f to the synthetic quartz window 18 of the chamber 24. And a projection lens 16g for emitting light toward the light source.

Reference numeral 40 denotes a pressure gauge for measuring the pressure in the vacuum chamber 24.

FIG. 2 shows an n-type ZnO according to the present invention.
1 is a conceptual configuration explanatory diagram of an example of an apparatus configuration for realizing a conductor forming process of a method for forming an ohmic electrode in FIG.

The apparatus shown in FIG. 2 is a so-called vapor deposition apparatus which can perform a metal film forming process for forming a metal thin film as a conductor on the surface of n-type ZnO.
1 shows an example in which a thin film of indium, which is a metal, is formed as a conductor on the surface of a ZnO substrate that has been subjected to laser irradiation by the laser irradiation apparatus shown in FIG.

That is, the vapor deposition apparatus shown in FIG. 2 has a vacuum chamber 54 in which a ZnO substrate 52 is mounted on a substrate holder 50 provided inside.

Further, inside the vacuum chamber 54,
A tungsten (W) heater 58 is provided which is energized and heated by a power supply 56, and the indium 60 is evaporated by the heating of the tungsten heater 58.

In the vacuum chamber 54, a liquid nitrogen trap 62, an oil diffusion pump 64, a rotary pump 6
6 is connected.

[0039] Then, the vacuum chamber 54, these vacuum system ^- is maintained at "3 × ¹⁰ 6 Torr" vacuum degree of about.

An example of the embodiment of the method for forming an ohmic electrode in n-type ZnO according to the present invention will be described with reference to the process steps shown in FIG. 3 together with FIGS. I do.

[0041]

First, an n-type ZnO substrate 100 (FIG. 3A)
(See FIG. 1), a shadow mask 10 is used as a mask for shielding a region other than a region where an ohmic electrode is to be formed.
2 (see FIG. 3B), and the n-type ZnO substrate 100 thus covered with the shadow mask 102 is mounted as a sample 22 on a sample stage 20 in a vacuum chamber 24 of the laser irradiation apparatus shown in FIG. Place.

Then, the laser irradiator shown in FIG. 1 is operated to irradiate pulse laser light emitted from the KrF excimer laser oscillating device 10.

Then, the surface of the n-type ZnO substrate 100 irradiated with the pulse laser beam has a low resistance, and a low resistance layer 104 having a thickness of, for example, about 1 μm or less is formed (FIG. 3C). )reference).

Next, as described above, the resistance lowering layer 104 is formed.
The n-type ZnO substrate 100 on which is formed
4 and attached to a substrate holder 50 in a vacuum chamber 54 of the vapor deposition apparatus shown in FIG. In particular,
It is arranged at the position of a zinc oxide (ZnO) substrate indicated by reference numeral 54 in FIG.

The vacuum chamber 54 is evacuated by the above-described vacuum system, and the inside of the vacuum chamber 54 is maintained at a degree of vacuum of about 3 × 10 ⁻⁶ Torr.

In such a vacuum chamber 54,
The tungsten heater 58 is energized and heated to evaporate the indium 60. Then, the evaporated indium is deposited on the surface of the n-type ZnO substrate 100 attached to the position facing the indium 60 to be evaporated on the substrate holder 50, and the indium is evaporated, whereby the surface of the low resistance layer 104 is formed. Indium thin film 1
06 is formed (see FIG. 3D). As described above, the indium thin film 106 formed on the surface of the low-resistance layer 104 becomes an ohmic electrode.

That is, when an energization measurement as shown in FIG. 3E was performed using the indium thin film 106 formed as described above, the current-voltage characteristic became linear, and the indium thin film 106 became an ohmic electrode. It was functioning as.

The shadow mask 102 may be removed from the surface of the n-type ZnO substrate 100 after forming the indium thin film 106 on the surface of the low resistance layer 104.

Here, the experimental results by the present inventor will be described in detail. As the n-type ZnO, n-type ZnO (0001) (ρ = 2000 Ωcm) grown by the hydrothermal method was used.

In the laser irradiation apparatus shown in FIG. 1, one pulse of the pulsed laser light is "0.2 to 0.2.
The n-type ZnO substrate 100 was irradiated with a fluence of 4 J / cm ² .

At this time, at a fluence of 0.3 J / cm ² or more, the irradiation region of the n-type ZnO substrate 100 with the pulse laser beam is off-stoichiometric of Zn-rich.
Ometric (stoichiometric) layers, ie, Zn and O
A bond was broken to form a Zn-rich layer having a non-stoichiometric composition, and a low-resistance layer 104 was obtained.

By the low resistance layer 104, n-type ZnO
When a conductor is formed on the surface of the substrate 100, the contact resistance is reduced.

Here, in measuring the current-voltage characteristics of the n-type ZnO substrate 100 before irradiating the pulse laser beam, the indium thin film 10
6, the indium thin film 10 is formed on the surface of the n-type ZnO substrate 100 by the vapor deposition apparatus shown in FIG.
Even when the sample No. 6 was formed, almost no current flowed (see FIG. 4A).

On the other hand, immediately after irradiating the n-type ZnO substrate 100 with the pulse laser beam, if conduction occurs from the low-resistance layer 104 formed by the irradiation of the pulse laser beam, the ohmic current is not measured in the current-voltage characteristic measurement. As a result, characteristics as an active electrode were obtained (see FIG. 4B).

However, after annealing in a nitrogen atmosphere at 300 ° C. for 5 minutes, the current decreased to 25%.

The low-resistance layer 10 on the surface of the n-type ZnO substrate 100 formed by the laser irradiation apparatus shown in FIG.
4, the indium thin film 106 was deposited by the evaporation apparatus shown in FIG.
Has a thickness of 50 nm.
m, the current increased in comparison with FIG. 4B in the current-voltage characteristic measurement, and the characteristic as an ohmic electrode was obtained (FIG. 4C). )reference).

Further, the decrease in current after annealing in a nitrogen atmosphere at 300 ° C. for 5 minutes could be suppressed to 82%.

[0059]

Incidentally, any crystal structure can be used as the n-type ZnO.

As a technique for forming a metal as a conductor on the surface of n-type ZnO, various techniques such as sputtering can be used without being limited to the above-described vapor deposition.

[0062]

As described above, the present invention provides a method for forming an ohmic electrode in n-type ZnO, which makes it possible to form an ohmic electrode on the surface of n-type ZnO. The effect is excellent.

[Brief description of the drawings]

FIG. 1 is a conceptual configuration explanatory view of an example of an apparatus configuration for realizing a laser irradiation process in a method for forming an ohmic electrode in n-type ZnO according to the present invention.

FIG. 2 is a conceptual configuration explanatory view of an example of an apparatus configuration for realizing a conductor forming process in a method for forming an ohmic electrode in n-type ZnO according to the present invention.

FIG. 3 is an explanatory diagram of a process showing an example of an embodiment of a method for forming an ohmic electrode in n-type ZnO according to the present invention.

FIG. 4 is a measurement graph of current-voltage characteristics showing experimental results according to the present invention.

[Explanation of symbols]

 Reference Signs List 100 ZnO substrate 102 Shadow mask 104 Low resistance layer 106 Indium thin film

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-57-143825 (JP, A) JP-A-59-98528 (JP, A) JP-A-11-74199 (JP, A) JP-A-5-98 343737 (JP, A) JP-A-4-302173 (JP, A) JP-A-4-199752 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/28 H01L 29 / 48 H01L 33/00 H01S 3/18

Claims (4)

(57) [Claims] 1. A method of forming an ohmic electrode in n-type ZnO for forming an ohmic electrode on the surface of n-type ZnO, comprising the steps of: forming a surface of n-type ZnO with a fluence of 0.3 to 0.4 J / cm ² ; A first step of irradiating a pulsed laser beam to cut a bond between Zn and O to form a Zn-rich layer having a low stoichiometric composition and a low-resistance layer; Forming a conductor as an ohmic electrode on the reduced resistance layer thus formed. 2. The method for forming an ohmic electrode in n-type ZnO according to claim 1, wherein the n-type ZnO is n-type ZnO grown by a hydrothermal method.
1) A method for forming an ohmic electrode in n-type ZnO with (ρ = 2000 Ωcm). 3. The method for forming an ohmic electrode in n-type ZnO according to claim 1, wherein the ohmic electrode is formed in n-type ZnO irradiated with one pulse of the pulsed laser light. Method. 4. The method of forming an ohmic electrode in n-type ZnO according to claim 1, wherein the pulsed laser beam is a KrF excimer pulsed laser beam. A method for forming an ohmic electrode in ZnO.