Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2000-07-18
2001-08-21
Picardat, Kevin M. (Department: 2822)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S029000, C438S514000, C438S522000
Reexamination Certificate
active
06277664
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to rare earth (RE) doped gallium nitride (GaN), and more particularly, to the luminescence of gallium nitride doped with RE ions. In recent years, RE doped semiconductors have been of considerable interest for possible application in light emitting devices and for their unique optical and electrical properties. The RE luminescence depends very little on the nature of the host and the ambient temperature. The GaN and AlN semiconductors doped with Er and co-doped with O have been the most extensively studied. However, the doping of GaN and AlN with Er and O by molecular beam epitaxy (MBE) and metal organic chemical vapor deposition (MOCVD) both during epitaxial growth and post growth by ion implantation exhibits only infrared emissions at 1.54 &mgr;m. In addition, only infrared photoluminescence (PL) spectra have been achieved from GaN implanted with Nd and Er without oxygen co-doping.
Recently, two green emission lines at 537 nm and 558 nm were obtained from Er doped GaN grown by solid source MBE on a sapphire substrate. In addition, that experiment achieved a broad peak of low intensity blue emission between 480 nm and 510 nm. However, the blue emission has little practical utility due to its low intensity. Moreover, the experiment was unable to achieve luminescence spectra over the range from about 380 nm to about 1000 nm.
In light of the shortcomings of known technology relating to RE doped GaN, a need exists for an improved RE doped GaN structure that has increased industrial applicability. In particular, a need exists for a RE doped GaN structure that is suitable as a material for visible optoelectronic devices. A need also exists for a method of manufacturing a RE doped GaN structure that is suitable as a material for visible optoelectronic devices.
SUMMARY OF THE INVENTION
The present invention satisfies one or more of the aforementioned needs. A preferred embodiment of the structure of the present invention includes a GaN semiconductor crystal that is doped with at least one RE ion, wherein the structure has been annealed at a temperature of at least about 1,000 degrees Celsius, and more preferably at about or above 1,100 degrees Celsius. As a result, the structure is preferably adapted to provide a luminescence spectra over the range from about 350-380 nanometers to about 900-1000 nanometers when excited by a suitable excitation.
The GaN may be grown by MBE, MOCVD, or by any other conventional technique. For example, the GaN may be grown on a sapphire substrate. The GaN may be n-type undoped prior to being doped with the RE ion(s). In an alternative embodiment of the present invention, the GaN may be doped with silicon as well as RE ion(s).
In one embodiment of the structure, the GaN is doped with the RE ion(s) during its growth process. Alternatively, the RE ion(s) may be implanted in the GaN using ion implantation techniques that are well known to those of ordinary skill in the art. For one example of doping, the GaN semiconductor crystal is doped with a beam of RE ions that are inclined at about 10 degrees to the normal of the epilayers of the GaN semiconductor crystal.
The annealing of the GaN semiconductor crystal is preferably performed under a flow of N
2
or NH
3
. The annealing of the GaN semiconductor crystal preferably repairs any damage which may have been caused by the doping of RE ion(s). For example, the annealing preferably repairs damage to the GaN semiconductor crystal that is caused by the implantation of the RE ion(s). In addition, the annealing preferably incorporates the RE ion(s) as an optically active center.
Utilizing a preferred method and structure of the present invention, the Applicant has observed visible cathodoluminescence of the rare earth Dy, Er and Tm implanted in GaN. The implanted samples were given isochronal thermal annealing treatments at a temperature of 1100° C. in N
2
or NH
3
, at atmospheric pressure to recover implantation damages and activated the rare earth ions. The sharp characteristic emission lines corresponding to Dy
3+
, Er
3+
, and Tm
3+
intra-4f
n
-shell transitions, are resolved in the spectral range from 380 nm to 1000 nm, and are observed over the temperature range of 8.5 K-411 K. The cathodoluminescence emission is only weakly temperature dependent. The results indicate that rare earth-doped GaN epilayers of the present invention are suitable as a material for visible optoelectronic devices.
The present invention also includes apparatus and methods for producing cathodoluminesence and electroluminesence that may be suitable for use in any of a wide variety of optoelectronic devices.
In general terms, the method of producing cathodoluminesence comprises: (a) obtaining a gallium nitride crystal, the gallium nitride crystal having a dopant of at least one rare earth ion; wherein the structure has been annealed at a temperature of at least about 1,000 degrees Celsius; and (b) exciting the gallium nitride crystal with an electron beam so as to cause the crystal to produce cathodoluminesence.
In general terms the method of producing electroluminesence comprises: (a) obtaining a gallium nitride semiconductor crystal, the gallium nitride semiconductor crystal having a dopant of at least one rare earth ion; wherein the structure has been annealed at a temperature of at least about 1,000 degrees Celsius; and (b) placing the gallium nitride semiconductor crystal in an electric field of sufficient strength so as to cause the gallium nitride semiconductor crystal to produce electroluminesence.
The present invention also includes devices, such as optoelectronic devices (e.g., lasers and light-emitting diodes), for producing cathodoluminesence and electroluminesence using the structures and methods disclosed herein.
The devices and methods of the present invention may be produced using manufacturing techniques, mechanical and electronic arrangements and application protocols, otherwise known and used in the art.
The Applicants have also observed visible cathodoluminescence of the rare earth Sm and Ho implanted in GaN utilized a preferred method and structure of the present invention. The implanted samples were given isochronal thermal annealing treatments at a temperature of 1100° C. in N
2
or NH
3
, at atmospheric pressure to recover implantation damages and activated the rare earth ions. The sharp characteristic emission lines corresponding to Sm
3+
and Ho
3+
intra-4f
n
-shell transitions are resolved in the spectral range from 400 nm to 1000 nm, and observed over the temperature range of 11 K-411 K. The cathodoluminescent emission is only weakly temperature dependent. The results again indicate that rare earth doped GaN epilayers of the present invention are suitable as a material for visible optoelectronic devices.
The Applicant has also observed similar results with Nd doped GaN of the present invention. Furthermore, it should be recognized that all other rare earth ions might be utilized in the present invention. In addition to the novel features and advantages mentioned above, other objects and advantages of the present invention might become apparent from the following descriptions of the drawings and preferred embodiments.
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Jadwisienczak W. M.
Lozykowski Henryk J.
Ohio University
Picardat Kevin M.
Standley & Gilcrest LLP
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