Abstract:
A method for forming a semi-conductor material is provided that comprises forming a donor substrate constructed of GaAs, providing a receiver substrate, implanting nitrogen into the donor substrate to form an implanted layer comprising GaAs and nitrogen. The implanted layer is bonded to the receiver substrate and annealed to form GaAsN and nitrogen micro-blisters in the implanted layer. The micro-blisters allow the implanted layer to be cleaved from the donor substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority based on U.S. Provisional Patent Application No. 60/425,388, filed Nov. 12, 2002, which is hereby incorporated by reference in full. 

   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   This invention was made with government support of grant #ACQ-1-30619-14 from National Renewable Energy Laboratory and grant #F49620-00-1-0328 from Air Force Office of Scientific Research. The government has certain rights in the invention. 

   FIELD OF THE INVENTION 
   The present invention generally relates to a gallium arsenide based semi-conductor material, and more particularly, the present invention relates to a gallium arsenide nitride semi-conductor with a narrow energy band gap. 
   BACKGROUND OF THE INVENTION 
   Gallium alloys have been shown to exhibit a reduced energy band gap that fluctuates as a function of the amount of arsenide and nitride added thereto. For example, 1% atomic nitrogen added to gallium arsenide (GaAs) to form gallium arsenide nitride (GaAsN) has been shown to reduce the energy band gap by as much as 200 meV. Likewise, the introduction of 1% arsenic into gallium nitride (GaN) to form GaAsN has been shown to reduce the band gap by as much as 700 meV. The resulting material is applicable and useful in a wide range of semi-conductor applications. Specifically, narrow energy band gap semi-conductors constructed with such alloys are useful in long wave length light emitters and detectors, high performance electronic devices, and high efficiency solar cells. 
   Many conventional methods of GaAsN formation in the semi-conductor industry involve an epitaxial or other similar growth process, molecular beam epitaxy (MBE), gas-source MBE (GS-MBE), metalorganic chemical vapor deposition (MOCVD) and sputtering. While these methods do result in the formation of GaAsN material applicable for semi-conductor usage, growth processes place a solubility limit on the amounts of nitrogen that can be contained within the resulting GaAsN material. 
   Other methods, such as that disclosed in the article entitled, “High Concentration Nitrogen Ion Doping Into GaAs For The Fabrication Of GaAsN,” reported in the publication  Nuclear Instruments And Methods In Physics Research  B 118 (1996) 743–747, discloses other methods of doping GaAs with nitrogen, which do achieve better solubility of nitrogen into the GaAs material. Specifically, nitrogen ions are implanted into a LEC formed GaAs substrate by high energy (400 keV) ion implantation. This process is then followed by an annealing process. 
   While this approach provides a means for doping GaAs with nitrogen, there is a desire to improve manufacturing methods of forming such substrates. Such desire is to conserve material and decrease the size of the GaAsN layer, as well as the underlying substrate to only the size that is needed for an application. 
   SUMMARY OF THE INVENTION 
   The present invention provides a Nitrogen implanted Gallium material with improved optical and luminescent characteristics, and an ion-cut-synthesis method to accomplish the same. 
   Other aspects of the invention will be apparent to those skilled in the art after reviewing the drawings and the detailed description below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
       FIG. 1  is a schematic view illustration of a semi-conductor material according to the present invention; 
       FIG. 2   a  is a TEM picture of semi-conductor material according to the present invention; 
       FIG. 2   b  is a TEM picture of semi-conductor material according to the present invention; 
       FIG. 2   c  is a TEM picture of semi-conductor material according to the present invention; 
       FIG. 3  is a graphical view illustration of a photoluminescence data from semi-conductor material according to the present invention; 
       FIG. 4   a  is a schematic view illustration of a manufacture of semi-conductor material according to the present invention; 
       FIG. 4   b  is a schematic view illustration of a manufacture of semi-conductor material according to the present invention; 
       FIG. 4   c  is a schematic view illustration of a manufacture of semi-conductor material according to the present invention; 
       FIG. 4   d  is a schematic view illustration of a manufacture of semi-conductor material according to the present invention; and 
       FIG. 5  is a plot of a simulation of a retained dosage of nitrogen and penetration depth of semi-conductor material according to the present invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   The present invention improves the methods for forming GaAsN substrates by providing a means for creating a GaAsN layer that includes ion implantation into a different GaAs substrate, than that which is to be used for the resulting low energy band gap application. This implantation causes a GaAsN layer to be formed to a depth in the GaAs substrate based on implanting characteristics of the implantation process. The implantation also forms microbubbles that separate the GaAsN layer from the remainder of the GaAs substrate. The GaAs substrate can then be attached to another substrate for use in a reduced energy band gap application. By this way, only a minimum needed layer can be created in the GaAs substrate, leaving the remainder of the substrate for other uses. The receiver substrate can also be specifically sized for the desired application as the exact depth of the GaAsN layer is known. 
   Referring now to  FIG. 1 , a semi-conductor material  10  is shown as having a thin film  12   b  including a GaAs matrix  16  and GaAsN nanostructures  18  positioned therein. Thin film  12   b  is disposed on substrate  14  that is composed of a base material such as GaAs, silicon or other suitable material. Thin film  12   b  is preferably initially 0.15 μm in thickness. However, it is noted that other thicknesses are possible, and that the present invention is not limited to that disclosed herein. 
     FIG. 2  shows dark-field diffraction contrast TEM images of  750  ( FIG. 2   a ),  800  ( FIG. 2   b ) and 850° C. ( FIG. 2C ) annealed samples of thin film  12   b . It should be noted that the images of thin film  12   b  as shown in  FIG. 2  are attached to substrate  15  (See  FIG. 4 ). However, for purposes of description, the structure of thin film  12   b  as described with reference to  FIG. 2 , is applicable to the thin film  12   b  of both  FIGS. 1 and 4 . The ion-cut-synthesis method used to effectuate the transfer of thin film  12   b  from substrate  15  to substrate  14 , will be described in greater detail in the following sections. 
   In  FIG. 2 , three regions are shown including a surface layer  1 , a 150-nm-thick middle layer  2 , and a near-substrate layer  3 . It is noted that although specific dimensions are shown and described, other variations to the depth and composition of the layers are possible dependent upon the nitrogen implantation and annealing characteristics as described hereinafter. For the thin film  12   b  shown in  FIGS. 2   a ,  2   b , and  2   c , the middle layers preferably contain 2–10 nm sized GaAsN nanocrystallites in an amorphous GaAs matrix. 
   Referring now to  FIG. 3 , a photoluminescence spectroscopy plot is provided depicting the intensity and wavelength optical properties of thin film  12   b  as shown and described. The intensity is in arbitrary units while the wave length is in nanometers. The un-implanted state illustrates the wavelength and photoluminescence scenario where a GaAs material is not combined with nitrogen. Here, it can be seen that the photoluminescence has a high intensity between wavelengths of about 800 to 850 nm. When nitrogen is implanted and the thin film is annealed at temperatures of 750° C., 800° C. and 850° C., respectively, it can be seen that a photoluminescence intensity increase is achieved between the wavelengths of about 900 and 1050 nm. 
   Referring now to  FIGS. 4   a – 4   d , an ion-cut-synthesis method for preparing the semi-conductor material according to the present invention is shown and described. In  FIG. 4   a , a GaAs substrate  15  is grown by VGF or other suitable methods and similar techniques. A base film  12  is then grown thereon by molecular beam epitaxy or other similar techniques such as MOCVD or GS-MBE. Preferably, the GaAs base film  12  is grown to a depth of 1.5 μm above the upper surface of the substrate  15  and formed as a uniform and stoichiometric matrix. 
   With continued reference to  FIG. 4   a , nitrogen ions are implanted into the thin film  12  by a high energy ion implantation method. In the preferred embodiment of the present invention, the nitrogen is implanted in base layer  12  by maintaining the base film  12  at a temperature of 300° C. and implanting nitrogen at a concentration of 5×10 17  cm 2  by a high energy (100 keV) ion implantation. The retained dose from this implantation is preferably about 1.7×10 22  N/cm 3  at a depth of 0.15 μm into the base film  12 . However, as will be understood by one skilled in the art from reviewing  FIG. 5 , modifications and variations of this retained dosage and implantation depth can be obtained. In the preferred embodiment of the present invention, it is desirable to obtain both a sufficient depth, as well as a high retained dosage of nitrogen in the base film  12  to form the thin film  12   b . As can be seen, the implantation depth of the nitrogen ions preferably falls far short of the depth of the grown thin film  12   b  to allow reusability of the base film  12  for forming multiple thin films  12   b . As a result, only the upper portion of the base film  12  is used for formation of thin film  12   b.    
   Referring now to  FIG. 4   b , implanted portion  12   b  is affixed to substrate  14  by wafer bonding technology. Substrate  14  can be GaAs, silicon, or other suitable material. As shown in  FIG. 4   c , substrate  14 , thin film  12   b  and substrate  15  are then annealed at a temperature between 750 and 850° C., as described in  FIG. 4 . The time for annealing is preferably 30 seconds. The annealing process results in the formation of the GaAsN nanostructures  18  (see  FIG. 1 ) to create the desired photoluminescence at longer wavelengths as described with reference to  FIG. 3 . Additionally, the annealing process causes the formation of nitrogen microbubbles  22  that causes separation of the thin film  12   b  from the remainder of base layer  12  or unimplanted portion  12   a . The microblister formation occurs at the preferred implantation depth of 0.15 μm and thereby causes cleavage of the implanted portion  12   b  from the unimplanted portion  12   a . Referring to  FIG. 4   d , the implanted portion  12   b  containing GaAsN is cleaved from unimplanted portion  12   a , thereby leaving a damaged layer  12   c . Implanted portion  12   b  is then polished, as known to one skilled in the art, to create a resulting semi-conductor material  15  that includes substrate  14  and implanted GaAsN portion  12   b . The material is then used in known semi-conductor manufacturing processes to form the desired components which include, but are not limited to, long wave length light emitters and detectors, high performance electronic devices, and high efficiency solar cells. As the implantation depth includes only a small upper portion of thin film  12 , the damage layer  12   c  can be removed by polishing to leave the remaining unimplanted portion  12   a . As only the upper layer of base film  12  is used, the remaining portion  12   a  can then be used to form additional thin films  12   b  for further applications. 
   While the present invention has been particularly shown and described with reference to the foregoing preferred and alternative embodiments, it should be understood by those skilled in the art that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention without departing from the spirit and scope of the invention as defined in the following claims. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. This description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. The foregoing embodiments are illustrative, and no single feature or element is essential to all possible combinations that may be claimed in this or a later application. Where the claims recite “a” or “a first” element of the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.