Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2000-10-13
2002-07-23
Nelms, David (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S103000
Reexamination Certificate
active
06423983
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optoelectronic and microelectronic devices and fabrication methods therefor, and more particularly to semiconductor devices having semiconducting oxide layers, and fabrication methods therefor.
BACKGROUND OF THE INVENTION
Optoelectronic and microelectronic devices are widely used in consumer and commercial applications. Optoelectronic devices include, but are not limited to, light-emitting diodes, laser diodes, photodetectors, optical modulators and/or broad band light sources. Microelectronic devices include, but are not limited to, transistors such as CMOS transistors, field effect transistors, and/or bipolar transistors, field emitters, high-power devices, and/or other integrated circuits. Optoelectronic devices and microelectronic devices will be referred to herein generically as “electronic devices.”
Many microelectronic devices are silicon-based. However, for high-temperature and high-power applications, other materials are being investigated and used for microelectronic devices. Similarly, other materials are being investigated for optoelectronic devices having a wider bandgap that can cover a wider range of the optical spectrum. For example, III-nitrides and their alloys having hexagonal structure are being widely investigated for microelectronic devices as well as optoelectronic devices. Mechanical, optical and electrical properties of III-nitrides are described, for example, in the publication entitled
III
-
Nitrides: Growth, Characterization, and Properties
to Jain et al., J. Appl. Phys., Vol. 87, No. 3, Feb. 1, 2000, pp. 965-1006. Hexagonal wurtzite polytypes of III-nitrides (InN, GaN, and AIN) can form continuous solid solutions with direct bandgaps ranging from 1.9 eV (InN) to 3.4 eV (GaN) to 6.2 eV (AIN). Thus, the emission wavelength can be tuned from about 653 nm (red) to about 200 nm (deep ultraviolet). The binding energy of excitons in the nitride system is about 20 meV for gallium nitride. Because the stable phase of III-nitrides and their alloys is hexagonal wurtzite, these materials only may be grown via lattice-matching epitaxy on hexagonal substrates such as 6H-silicon carbide (0001) and zinc oxide (0001).
On more practical substrates, such as hexagonal (0001) sapphire (&agr;-Al
2
O
3
), epitaxial growth only may occur via domain-matching epitaxy, where integral multiples of lattice constants on major planes of the film and substrate match across the interface, as described, for example, in U.S. Pat. No. 5,406,123 to Narayan, which discusses the epitaxial growth of titanium nitride films on silicon or gallium arsenide substrates. For example, the domain matching epitaxy on the basal plane after 30° or 90° rotation [1210]
nitride
∥[0110]
sap
involves the matching of 7 planes of the III-nitride films with 6 planes of sapphire. The epitaxial films of III-nitrides and their alloys on sapphire contain a high density of growth and misfit related dislocations which may adversely affect the lifetimes of optical devices, particularly lasers, as described in the publication entitled
The Roles of structural Imperfections in InGaN
-
Based Blue Light
-
Emitting Diodes and Laser Diodes
to Nakamura, Science, Vol. 281, No. 5379, Aug. 14, 1998, pp. 956-961. Epitaxial growth of hexagonal nitrides may be possible on (111) planes of cubic silicon, as described, for example, in he publication entitled
Epitaxial Growth of AIN Thin Films on Silicon
(111)
Substrates by Pulsed Laser Deposition
to Vispute, J. Appl. Phys., Vol. 77, No. 9, May 1, 1995, pp. 4724-4728. However, this may not be a practical plane as most silicon microelectronic devices are fabricated on (100) silicon.
As an alternative to III-nitrides, zinc oxide having an hexagonal wurtzite structure and its alloys with magnesium oxide (ZnMgO having a wurtzite structure) are being investigated. It is known to alloy zinc oxide with magnesium oxide to form high quality single crystal films having magnesium content between zero and 34 at. % while retaining the hexagonal zinc oxide lattice structure, as described, for example, in the publications entitled
Mg
x
Zn
1−x
O as a
II-VI
Wide Gap Semiconductor Alloy to Ohtomo
et al., Appl. Phys. Lett., Vol. 72, No. 19, May 11, 1998, pp. 2466-2468
; Optical and Structural Properties of Epitaxial Mg
x
Zn
1−x
O Alloys
to Sharma et al., Appl. Phys. Lett., Vol. 75, No. 21, Nov. 22, 1999, pp. 3327-3329
; Refractive Indices and Absorption Coefficients of Mg
x
Zn
1−x
O Alloys
to Teng et al., Appl. Phys. Lett., Vol. 76, No. 8, Feb. 21, 2000, pp. 979-981. The bandgap of this alloy was found to be variable with magnesium content with an upper limit around 4.19 eV. This alloy may produce a bright ultraviolet (UV) luminescence at room temperature that is excitonic in nature. Since the exciton binding energy in the ZnO system is higher (approximately 60 meV) than that in the III-nitride system (approximately 20 meV for GaN), tightly bound excitons may be responsible for higher brightness or luminescence efficiency. As with the III-nitrides and their alloys, ZnMgO alloys having an hexagonal wurtzite structure may only be grown via lattice-matching epitaxy on hexagonal substrates, such as 6 H-silicon carbide (0001) and zinc oxide (0001), and may only be grown via domain-matching epitaxy on more practical hexagonal substrates such as hexagonal (0001) sapphire (&agr;-Al
2
O
3
). Epitaxial growth of ZnMgO alloys having an hexagonal wurtzite structure may be possible on (111) planes of cubic silicon. However, as noted above, this may not be a practical plane of cubic silicon. Thus, these hexagonal zinc oxide systems as well as III-nitrides may not be epitaxially integrated with silicon (100) of cubic symmetry. This may be an important consideration as microelectronic devices and integrated circuits are fabricated almost exclusively on silicon (100) substrates.
Zinc oxide layers having hexagonal structures are described, for example, in
Optically Pumped Lasing of ZnO at Room Temperature
to Bagnall et al., Appl. Phys. Lett., Vol. 70, No. 17, Apr. 28, 1997, pp. 2230-2232
; Defects and interfaces in Epitaxial ZnO
/&agr;-
Al
2
O
3
and AlN/ZnO
/&agr;-
Al
2
O
3
Heterostructures
to Narayan et al., J. Appl. Phys., Vol. 84, No. 5, Sep. 1, 1998, pp. 2597-2601
; Room-Temperature Ultraviolet Laser Emission from Self
-
Assembled ZnO Microcrystallite Thin Films
, Appl. Phys. Lett., Vol. 72, No. 25, Jun. 22, 1998, pp. 3270-3272
; Excitonic Structure and Absorption Coefficient Measurements of ZnO Single Crystal Epitaxial Films Deposited By Pulsed Laser Deposition
, J. Appl. Phys., Vol. 85, No. 11, Jun. 1, 1999, pp. 7884-7887; and U.S. Pat. No. 6,046,464 to Schetzina. Epitaxial and polycrystalline zinc oxide films may provide lasing action. Zinc oxide films may also 10 luminesce very brightly in UV and grow 2-D on c-plane sapphire with a low density of extended defects. Zinc oxide alloys having hexagonal wurtzite structure are described, for example, in U.S. Pat. No. 5,955,178 to Orita et al.
SUMMARY OF THE INVENTION
Embodiments of the present invention provide electronic devices having a cubic alloy layer comprising magnesium oxide and at least one of zinc oxide and cadmium oxide. These cubic alloy layers can be integrated with cubic (100) silicon substrates via domain-matching epitaxy where four lattice constants of the cubic alloy can match with three lattice constants of the silicon substrate. Since the critical thickness (i.e., the minimum thickness to eliminate occurrence of misfit dislocations caused by the lattice mismatch) under this domain matching epitaxy may be less than one monolayer, many if not all of the misfit dislocations may be introduced at the beginning of the formation of the film, which may result in a film that is relaxed with many if not all of the dislocations confined to the interface. Cubic alloys according to embodiments of the present invention also may provide a cubic system having a broader bandgap than the conventional hexagonal wurtzite III-nitride system InN-GaN-AIN. More
Muth John F.
Narayan Jagdish
Sharma Ajay Kumar
Le Thao P
Myers Bigel Sibley & Sajovec P.A.
Nelms David
North Carolina State University
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