Active solid-state devices (e.g. – transistors – solid-state diode – Responsive to non-electrical signal – Electromagnetic or particle radiation
Reexamination Certificate
2001-05-14
2002-12-17
Chaudhari, Chandra (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Responsive to non-electrical signal
Electromagnetic or particle radiation
C257S101000, C257S103000, C257S428000
Reexamination Certificate
active
06495894
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention:
This invention relates to a photonic device such as a light-emitting device and a photodetector, and a substrate for fabricating such a photonic device, in which multilayered thin films made of III-V nitride semiconductor are epitaxially grown.
(2) Background of the Invention
A III-V nitride semiconductor material is commercially used for a photonic device such as a light-emitting device and a photodetector. As the above III-V nitride semiconductor material, an AlxGayInzN (x+y+z=1, x, y, z≧0) material is widely available, that is, each layer of the photonic device is composed of the AlxGayInzN film that is epitaxially grown by a MOCVD method. In this basic case, TMA (trimethyl aluminum) is employed as the Al raw material and TMG (trimethyl gallium) is employed as the Ga law material, and TMI (trimethyl indium) is employed as the In law material. Moreover, NH
3
is employed as the nitrogen raw material. N
2
gas and/or H
2
gas is used as a carrier gas.
Then, various control of the above raw materials in flow rate can change the composition of the AlxGayInzN film. An AlN film has its bandgap Eg of 6.2 eV, and a GaN film has its bandgap Eg of 3.4 eV. Therefore, in the case of forming an AlxGal-xN film using TMA and TMG, the AlxGal-xN film has substantially its bandgap of 6.2x+3.4(1−x)eV, and has substantially its emission wavelength &lgr;=1240/{6.2x+3.4(1−x)} from an equation &lgr;=1240/Eg. Given x=0.3, the emission wavelength &lgr; is 292 nm. In this case, the detection wavelength is below 292 nm.
In the case of fabricating a light-emitting diode from the AlxGayInzN (x+y+z=1, x, y, z≧0) multilayered thin films, when the AlxGayInzN film is epitaxially grown on a C-faced sapphire substrate by a MOCVD method, it includes large amount of defect, resulting in the deterioration of its crystallinity and thus the deterioration of its light-emitting efficiency.
From this point of view, it is proposed that the AlxGayInzN (x+y+z=1, x, y, z≧0) multilayered thin films is formed on the sapphire substrate via a buffer layer made of a GaN film which is epitaxially grown by a CVD at low temperature. The GaN buffer layer supplements the lattice constant of 10% and over between the sapphire substrate and the multilayered thin films, and provides a favorable crystallinity to the multilayered thin films. Instead of the GaN buffer layer, an AlN buffer layer may be employed.
A conventional light-emitting device as mentioned above can emit a light having only 400 nm or over. Therefore, the AlxGayInzN multilayered thin films are required to have a relatively large amount of the Al component in order to emit a short wavelength blue light or a short wavelength ultraviolet light. Moreover, for emitting a green to blue light, all the AlxGayInzN films except a light-emitting layer are required to have a relatively large amount of the Al components, respectively, in order to confine energy in the light-emitting layer effectively. However, if the Al-rich AlxGayInzN tin film is formed on the buffer layer, made of e.g. the GaN film or the AlN film, epitaxially grown by the CVD at low temperature, it may bring about cracks in the Al-rich AlxGayInzN thin film and deteriorate the crystallinity thereof.
The reason is that since the Al-rich AlxGayInzN thin film has a smaller lattice constant, a large tensile stress may be brought about in the thin film due to the large difference in the lattice constants between the thin film and the buffer layer if the thin film is formed on the buffer layer. Moreover, the lateral growth speed of the Al-rich AlxGayInzN thin film is very small, and thus, the enhancement of the crystallinity of the thin film is hindered by the poor crystalline buffer layer due to the low temperature epitaxial growth. Moreover, in a photodetector such as a UV photodetector, its detecting sensitivity is degraded due to the poor crystallinity of the buffer layer.
In order to iron out the above matters, such a light-emitting device having a Al-rich AlxGayInzN multilayered thin films on a buffer layer made of an AlxGal-xN (1≧x>0) film is disclosed and proposed in the publication of unexamined patent application, Tokukai Hei 9-64477 (JP A 9-64477).
Moreover, such a light-emitting device is disclosed in the publication of unexamined patent application, Tokukai Hei 5-291628 that plural Gal-x-yInxAlyN (1≧x≧0, 1≧x≧0) thin films having their various x- and/or y-components are formed on a sapphire substrate to obtain a predetermined Gal-a-bInaAlbN (1≧a≧0, 1≧b≧0) buffer layer, and then, the Gal-a-bInaAlbN (1≧a≧0, 1≧b≧0) multilayered thin films are formed on the buffer layer.
In Tokukai Hei 9-64477, since the AlGaN buffer layer is formed at a relatively high temperature, the Al-rich AlxGayInzN multilayered thin films epitaxially grown on the buffer layer can have relatively favorable crystallinity and does not have cracks therein.
However, the AlGaN buffer layer requires to be formed at a high temperature of 1300° C. or over, and annealed at a high temperature of about 1500° C. after the formation of the buffer layer. Such a high temperature treatment overloads a heater in a MOCVD apparatus, resulting in the complication of the maintenance and the increase of the manufacturing cost.
Particularly, in realizing a photonic device to emit or detect an above-mentioned short wavelength light, since the required Al-rich AlxGayInzN multilayered thin films has its respective small vertical and lateral growth speed, its high film-forming temperature must be held for a long time, thus overloading a heater and so on of a MOCVD apparatus.
When the above AlGaN buffer layer having a thickness of 0.3 &mgr;m is formed at about 1200° C., many cracks come into being in the buffer layer and the crystallinity of the buffer layer is deteriorated. As a result, the entire crystallinity of the Al-rich AlxGayInzN multilayered thin films is deteriorated.
In Tokukai Hei 5-291618, since the Gal-a-bInaAlbN (1≧a≧0, 1≧b≧0) multilayered thin films is formed on the Gal-a-bInaAlbN (1≧a≧0, 1≧b≧0) buffer layer composed of the laminated plural Gal -x-yInxAlyN (1≧x≧0, 1≧x≧0) thin films having their various x- and/or y-components, it can have its favorable crystallinity and almost never have cracks therein. Moreover, since the buffer layer is formed at a low temperature of about 700° C., a heater in a MOCVD apparatus is not overloaded.
However, in the above conventional fabricating method, the multilayered thin films and the buffer layer have the same component and composition, so that they are continued though their boundaries. In this case, a leak current is flown to the buffer layer from the multilayered thin films, resulting in the reduction of the light-emitting efficiency of the light-emitting device having the multilayered thin films due to the resistance loss.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a photonic device having an AlaGabIncN (a+b+c=1, a, b, c≧0) buffer layer and an AlxGayInzN (x+y+z=1, x, y, z≧0) multilayered thin films without cracks epitaxially grown on the buffer layer which have their favorable crystallinities, and a substrate for fabricating the photonic device.
It is another object of the present invention to provide a method for fabricating the photonic device and a method for manufacturing the photonic device-fabricating substrate.
For achieving the above objects, this invention relates to a photonic device comprising a substrate, a buffer layer with a composition of AlaGabIncN a+b+c=1, a, b, c≧0) formed on the substrate and a multilayered thin films with a composition of AlxGaylnzN (x+y+z=1, x, y, z≧0) epitaxially grown on the buffer layer, the Al component of the Al component-minimum portion of the buffer layer being set to be larger than that of at least the thick
Asai Keiichiro
Nagai Teruyo
Shibata Tomohiko
Tanaka Mitsuhiro
Burr & Brown
Chaudhari Chandra
Hogans David L.
NGK Insulators Ltd.
LandOfFree
Photonic device, a substrate for fabricating a photonic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Photonic device, a substrate for fabricating a photonic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Photonic device, a substrate for fabricating a photonic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2994985