Probe with optical waveguide and method of producing the same

Details Probe with optical waveguide and method of producing the same Probe with optical waveguide and method of producing the same

2000-02-16

2002-05-14

Ullah, Akm E. (Department: 2874)

Optical waveguides

Planar optical waveguide

Thin film optical waveguide

C257S184000, C385S129000, C385S130000

Reexamination Certificate

active

06389210

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a tunneling microscope utilizing spin-polarized electrons, and more particularly to a probe used in such a tunneling microscope and a method of manufacturing the probe.
BACKGROUND ART
When a conventional probe is used in spin measurement, the following problems arise.
(1) Since a conventional probe does not have an optical waveguide, external light is radiated to the tip of the probe. Therefore, light is radiated onto the probe at a certain angle relative to the probe, so that only a portion of the probe which receives light comes into an excited state. That is, since light is not radiated uniformly on the tip portion of the probe, excitation of the entire tip portion of the probe cannot be attained. Therefore, the conventional probe is poor in terms of electron excitation efficiency and efficiency in extracting spin-polarized electrons. Accordingly, strong light must be radiated onto the probe in order to obtain spin-polarized electrons which are sufficient for microscopic observation.
(2) However, when strong light is radiated on the probe, excitation light is radiated onto a sample surface in close proximity to the tip portion of the probe, and thus reflection and absorption of the excitation light occur on the side of the sample surface.
(3) Further, the probe is excited by light scattered from the sample surface. Since the scattered light is polarized disorderly, the degree of spin polarization of spin-polarized electrons decreases, resulting in a decrease an in detection efficiency in spin measurement.
(4) The conventional probe is formed of GaAs or a like material. These materials are soft and prone to cleavage fracture. Therefore, the mechanical strength of the probe is low, and during use, the probe frequently breaks upon contact with a sample. In addition, since GaAs has a low melting point, the tip end of the probe fuses when excited with strong light. Further, when the GaAs probe is heated for cleaning. As having a high vapor pressure evaporates. As a result, the structure and the state of electrons of the tip end of the probe change, so that spin-polarized electrons having a high degree of spin polarization cannot be obtained. Further, due to the same reason, the conventional probe cannot be subjected to cleaning by application of heat for reuse.
DISCLOSURE OF THE INVENTION
An object of the present invention is to solve the above-described problems and to provide a probe having an optical waveguide which (1) enables spin measurement with high efficiency even under weak excitation light, (2) has high mechanical strength and is less prone to breakage, (3) can be used under strong excitation light, (4) facilitates cleaning of the probe tip end, (5) permits excitation of the probe tip end, and (6) suppresses the influence of excitation light on a sample; i.e., a probe having an optical waveguide which is robust and highly reliable. Another object of the present invention is to provide a method of manufacturing the probe.
To achieve the above objects, the present invention provides the following.
[1] A probe having an optical waveguide which comprises an optical waveguide portion having a double hetero structure and comprising an In
1−x′−y′
Ga
x′
Al
y′
N layer, an In
1−x−y
Ga
x
Al
y
N layer, and an In
1−x″−y″
Ga
x″
Al
y″
N layer; and an Al
x
Ga
1−x
N probe portion grown in a conical shape on the In
1−x−y
Ga
x
Al
y
N layer of the optical waveguide portion.
[2] A probe having an optical waveguide which comprises an optical waveguide portion having a double hetero structure and comprising an In
1−x′−y′
Ga
x′
Al
y′
N layer, an In
1−x−y
Ga
x
Al
y
N layer, layer, and an In
1−x″y″
Ga
x″
Al
y″
N layer, where 0≦x, y, x′, y′, x″, y″, x+y, x′+y′, x″+y″≦1, and the In
1−x−y
Ga
x
Al
y
N layer has a minimum band gap energy; and an Al
x
Ga
1−x
N layer, probe portion grown in a conical shape such that the probe portion is connected to a portion of the In
1−x−y
Ga
x
Al
y
N layer,layer, wherein light propagating through an optical waveguide layer constituted by the In
1−x−y
Ga
x
Al
y
N layer,layer is led to the probe portion in order to excite electrons at the tip end of the probe portion.
[3] A probe having an optical waveguide as described in [1] or [2] above, further characterized in that the In
1−x−y
Ga
x
Al
y
N layer, is formed to have a large thickness, and a portion of the layer is maintained unremoved, so that the portion serves as an inlet for incident excitation light.
[4] A method of manufacturing a probe having an optical waveguide, the method comprising: growing on a (0001) face of a sapphire substrate a double hetero structure comprising an In
1−x′−y′
Ga
x′
Al
y′
N layer, and an In
1−x″−y″
Ga
x″
Al
y″
N layer by use of organometallic vapor phase epitaxy to thereby form an optical waveguide portion; and growing an Al
x
Ga
1−x
N probe portion in a conical shape on the In
1−x−y
Ga
x
Al
y
N layer of the optical waveguide portion such that the Al
x
Ga
1−x
N probe portion is connected to the In
1−x−y
Ga
x
Al
y
N layer of the optical waveguide portion.
[5] A method of manufacturing a probe having an optical waveguide, the method comprising: growing on a (0001) face of a sapphire substrate a double hetero structure comprising an In
1−x′−y′
Ga
x′
Al
y′
N layer, an In
1−x−y
Ga
x
Al
y
N layer and In
1−x″−y″
Ga
x″
Al
y″
N layer, to thereby form an optical waveguide, where 0≦x, y, x′, y′, x″, y″, x+y, x′+y′, x″+y″≦1 and the In
1−x−y
Ga
x
Al
y
N layer has a minimum band gap energy; exposing a portion of the In
1−x−y
Ga
x
Al
y
N layer; and growing an Al
x
Ga
1−x
N probe portion in a conical shape on the exposed portion of the In
1−x−y
Ga
x
Al
y
N layer,
[6] A method of manufacturing a probe having an optical waveguide as described in [4] or [5] above, further characterized in that the In
1−x−y
Ga
x
Al
y
N layer is formed to have a large thickness, and a portion of the layer is maintained unremoved, so that the portion serves as an inlet for incident excitation light.
As described above, in the present invention, the probe is formed of Al
x
Ga
1−x
N, which is a hard material having a high melting point; and an optical waveguide having a double hetero structure and comprising an In
1−x′−y′
Ga
x′
Al
y′
N layer, an In
1−x−y
Ga
x
Al
y
N layer, and an In
1−x″−y″
Ga
x″
Al
y″
N layer is integrated with the probe by use of organometallic vapor phase epitaxy.
The most important feature of the present invention resides in use of Al
x
Ga
1−x
N, which is a material having a small electron affinity, as a material of the probe. In contrast to the conventional technique, excitation light is led to the tip end of the probe via a waveguide provided inside the probe. Therefore, a sample surface is less likely to be affected by reflection and absorption of excitation light.
Further, since the entire tip end portion of the probe is excited, the probe has a high electron excitation efficiency, as well as a high efficiency in extracting spin-polarized electrons.
Moreover, unlike the conventional probe, the probe of the present invention is formed of a hard material, and therefore is less prone to breakage. In addition, since the melting point of the material is high, the probe can sustain electron excitation by use of a high output excitation light source, and cle

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