Abstract:
A method and associated structure for forming a free-standing electrostatically-doped carbon nanotube device is described. The method includes providing a carbon nanotube on a substrate in such a way as to have a free-standing portion. One way of forming a free-standing portion of the carbon nanotube is to remove a portion of the substrate. Another described way of forming a free-standing portion of the carbon nanotube is to dispose a pair of metal electrodes on a first substrate portion, removing portions of the first substrate portion adjacent to the metal electrodes, and conformally disposing a second substrate portion on the first substrate portion to form a trench.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation-in-part, and claims the benefit, of U.S. patent application Ser. No. 10/683,895, filed Oct. 10, 2003, the entire contents of which is incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     The present invention relates generally to the field of nanotechnology. More specifically, the present invention relates to a method and associated structure for forming a free-standing electrostatically-doped carbon nanotube device.  
         [0003]     Carbon nanotubes have attracted a great deal of attention in recent years due to their possibilities for use as nanoscale electronic devices, such as diodes, transistors and semiconductor circuits. Structurally, a carbon nanotube resembles a hexagonal lattice of carbon rolled into a cylinder and may belong to one of two varieties, a single-walled variety and a multi-walled variety. Either of these varieties may, in whole or in part, exhibit the behavior of a metal or a semiconductor material, depending upon their chirality (i.e., conformational geometry).  
         [0004]     Carbon nanotubes that exhibit the behavior of a semiconductor material are typically doped using various chemical methods. In other words, different chemicals are used to create p-type (hole majority carrier) regions and n-type (electron majority carrier) regions in the carbon nanotube. This results in a P—N junction that, when an appropriate voltage is applied, emits light (in the case of a light-emitting diode (“LED”)). The chemical methods for doping a carbon nanotube, however, suffer from the problem that the p-type regions and the n-type regions are typically not well characterized, resulting in nanoscale electronic devices with reduced performance characteristics.  
         [0005]     Thus, what is needed are a method and associated structure for forming an electrostatically-doped carbon nanotube device having well characterized p-type regions and n-type regions, allowing for the creation of nanoscale electronic devices, such as, for example, photodiodes, photo detectors, photovoltaic devices, sensors, and power devices with enhanced performance characteristics.  
       SUMMARY  
       [0006]     Embodiments of the invention provide an electrostatically-doped carbon nanotube device that includes a carbon nanotube disposed on a substrate such that at least a portion of the carbon nanotube is free-standing.  
         [0007]     Embodiments of the invention provide a photovoltaic device that includes an electrostatically-doped carbon nanotube device.  
         [0008]     Embodiments of the invention provide a method for forming a free-standing electrostatically-doped carbon nanotube device. The method includes providing a carbon nanotube on a substrate. The carbon nanotube has a first end, a second end, and a free-standing portion therebetween.  
         [0009]     These and other advantages and features will be more readily understood from the following detailed description of preferred embodiments of the invention that is provided in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a cross-sectional view of an electrostatically-doped carbon nanotube device constructed in accordance with an embodiment of the invention.  
         [0011]      FIG. 2  is a circuit diagram representing the electrostatically-doped carbon nanotube device of  FIG. 1 .  
         [0012]      FIGS. 3-7  are cross-sectional views illustrating a method for forming an electrostatically-doped carbon nanotube device in accordance with an embodiment of the invention.  
         [0013]      FIG. 8  is a cross-sectional view of a free-standing electrostatically-doped carbon nanotube device constructed in accordance with an embodiment of the invention.  
         [0014]      FIG. 9  is a circuit diagram representing the free-standing electrostatically-doped carbon nanotube device of  FIG. 8 .  
         [0015]      FIG. 10  is a graph illustrating photovoltaic results from the free-standing electrostatically-doped carbon nanotube device of  FIG. 8 .  
         [0016]      FIGS. 11-16  are cross-sectional views illustrating a method for forming a free-standing electrostatically-doped carbon nanotube device in accordance with an embodiment of the invention.  
         [0017]      FIGS. 17-21  are cross-sectional views illustrating a method for forming a free-standing electrostatically-doped carbon nanotube device in accordance with an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0018]     Described embodiments of the invention provide a method and associated structure for forming an electrostatically-doped carbon nanotube device having well characterized p-type regions and n-type regions, allowing for the creation of nanoscale electronic devices, such as photovoltaic diodes, power devices, photodiodes, photo detectors, light-emitting diodes (“LEDs”), and the like, with enhanced performance characteristics. One specific form of electrostatically-doped carbon nanotube device is a free-standing electrostatically-doped carbon nanotube device. More specifically, embodiments of the invention provide for the use of a plurality of doping electrodes that are decoupled from a plurality of bias electrodes. Thus, the doping of a carbon nanotube may be finely tuned by varying the bias of each of the plurality of bias electrodes. Advantageously, the described method and associated structure are capable of providing a carbon nanotube having a P—N junction, a P—I—P junction, a P—I—N junction, an N—I—P junction, an N—I—N junction, a P—N—P junction or an N—P—N junction.  
         [0019]     Referring to  FIG. 1 , an electrostatically-doped carbon nanotube device  10  is illustrated including a carbon nanotube  12  having a first end  14  and a second end  16 . The carbon nanotube  12  may be either a single-walled carbon nanotube (“SWCNT”) or a multi-walled carbon nanotube (“MWCNT”). The carbon nanotube  12  has a length of between about 0.1 microns and about 10 microns and a diameter of between about 0.4 nm and about 20 nm, however other suitable dimensions may be used. In general, a carbon nanotube may act as a metal or a semiconductor material, depending upon its chirality (i.e., conformational geometry). Preferably, the carbon nanotube  12  of the present invention acts as a semiconductor material. The first end  14  of the carbon nanotube  12  is disposed adjacent to and in direct electrical contact with a first metal contact  18 . Likewise, the second end  16  of the carbon nanotube  12  is disposed adjacent to and in direct electrical contact with a second metal contact  20 . The first metal contact  18  and the second metal contact  20  are each made of Ti, Mo, Au, Cr or the like, and each has an area or size of between about 0.1 microns by about 10 microns and about 1 micron by about 10 microns. In general, any dimensions that provide adequate electrical contact with the first end  14  of the carbon nanotube  12  and the second end  16  of the carbon nanotube  12  may be used. The first metal contact  18  and the second metal contact  20  may be disposed either above or below the first end  14  of the carbon nanotube  12  and the second end  16  of the carbon nanotube  12 , respectively.  
         [0020]     The first metal contact  18  and the second metal contact  20  are disposed on the surface of a dielectric material  22 . The dielectric material  22  includes SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2  or the like. A first metal electrode  24  and a second metal electrode  26  are disposed within the dielectric material  22 , adjacent to and at a distance from the first metal contact  18  and the second metal contact  20 , respectively. Because of this separation, the first metal electrode  24  is capacitively coupled to the first end  14  of the carbon nanotube  12  and the second metal electrode  26  is capacitively coupled to the second end  16  of the carbon nanotube  12 . Preferably, the distance between the first metal electrode  24  and the first end  14  of the carbon nanotube  12  and the second metal electrode  26  and the second end  16  of the carbon nanotube  12  is between about 2 nm and about 100 nm, respectively. The first metal electrode  24  and the second metal electrode  26  are each made of Mo, Ti, Pt, Au, Cr or the like, and each has an area or size of between about 0.1 microns by about 10 microns and about 1 micron by about 10 microns. Advantageously, the area or size of the first metal electrode  24  and the second metal electrode  26  may be selected to achieve a desired spacing between the first metal electrode  24  and the second metal electrode  26 . The significance of this spacing is described in detail below. Preferably, the first metal electrode  24  is separated from the second metal electrode by a distance of between about 100 nm and about 1 micron.  
         [0021]     The dielectric material  22  is disposed on the surface of a semiconductor material  28 , such as Si, SiC or the like. Alternatively, the dielectric material  22  is disposed on the surface of a metal layer  28 , such as Al, Cr, Mo, Ti, Pt or the like. As described above, the carbon nanotube  12  has a first end  14  and a second end  16 . Accordingly, a center section  30  is disposed between the first end  14  of the carbon nanotube  12  and the second end  16  of the carbon nanotube  12 . In one embodiment of the present invention, a portion of the semiconductor material  28  is disposed adjacent to and at a distance from the center section  30  of the carbon nanotube  12 , with the dielectric material  22 , a portion of the first metal electrode  24  and a portion of the second metal electrode  26  disposed between the semiconductor material  28  and the center section  30  of the carbon nanotube  12 . In an alternative embodiment of the present invention, a portion of the semiconductor material  28  is disposed adjacent to and at a distance from the center section  30  of the carbon nanotube  12 , with only the dielectric material  22  disposed between the semiconductor material  28  and the center section  30  of the carbon nanotube  12 . Again, this difference relates to the spacing between the first metal electrode  24  and the second metal electrode  26  and its significance is described in detail below.  
         [0022]     Referring to  FIG. 2 , the structure for forming an electrostatically-doped carbon nanotube device  10  ( FIG. 1 ) is represented by a circuit diagram. The first metal contact (“M 1 ”)  18  is electrically coupled to the first end  14  of the carbon nanotube  12  and the second metal contact (“M 2 ”)  20  is electrically coupled to the second end  16  of the carbon nanotube  12 . Similarly, the first metal electrode (“VC 1 ”)  24  is capacitively coupled to the first end  14  of the carbon nanotube  12  and the second metal electrode (“VC 2 ”)  26  is capacitively coupled to the second end  16  of the carbon nanotube  12 . In this respect, VC 1   24  and VC 2   26  form a first gate and a second gate, respectively. In the alternative embodiment of the present invention described above, with only the dielectric material  22  ( FIG. 1 ) disposed between the semiconductor material  28  and the center section  30  of the carbon nanotube  12 , the semiconductor material (“SI”)  28  is capacitively coupled to the center section  30  of the carbon nanotube  12  and forms a third gate, which otherwise does not exist.  
         [0023]     In operation, a first bias is applied to VC 1   24 , resulting in the electrostatic doping of the first end  14  of the carbon nanotube  12 . Likewise, a second bias is applied to VC 2   26 , resulting in the electrostatic doping of the second end  16  of the carbon nanotube  12 . Depending upon the bias applied, the first end  14  of the carbon nanotube  12  and the second end  16  of the carbon nanotube  12  may each be made a p-type semiconductor (hole majority carrier) or an n-type semiconductor (electron majority carrier). If the first end  14  of the carbon nanotube  12  is made a p-type semiconductor and the second end  16  of the carbon nanotube  12  is made an n-type semiconductor, or vice versa, the result is a P—N junction. A P—N junction may be used to form a light-emitting diode (“LED”), as is well known to those of ordinary skill in the art. The preferred voltage range of the structure for forming an electrostatically-doped carbon nanotube device  10  is between about +/−1 V and about +/−30 V for VC 1   24  and VC 2   26 .  
         [0024]     In the alternative embodiment of the invention described above, with only the dielectric material  22  disposed between SI  28  and the center section  30  of the carbon nanotube  12 , SI  28  is used to modulate the doping of the center section  30  of the carbon nanotube  12 . Thus, the center section  30  of the carbon nanotube  12  may be made a p-type semiconductor, an I-type (intrinsic) semiconductor or an n-type semiconductor. This results in a number of possible configurations, summarized in Table 1 below, and a number of possible devices, well known to those of ordinary skill in the art.  
                                               TABLE 1                           Electrostatically-Doped Carbon Nanotube Junctions and Devices            Bias Modes                VC1   SI   VC2   Junction   Device(s)               Low   —   Low   P-I-P   Back-to-Back Junctions       Low   —   High   P-I-N   Light-Emitting Diode (“LED”)       High   —   Low   N-I-P   Light-Emitting Diode (“LED”)       High   —   High   N-I-N   Back-to-Back Junctions       Low   High   Low   P-N-P   Bipolar Junctions       High   Low   High   N-P-N   Bipolar Junctions                  
 
         [0025]     Referring to  FIGS. 3 and 4 , in another embodiment of the invention, a method for forming an electrostatically-doped carbon nanotube device includes first providing the semiconductor layer  28  described above. Again, the semiconductor layer  28  includes Si, SiC or the like. Alternatively, a metal layer  28  may be provided, such as Al, Cr, Mo, Ti, Pt or the like. Preferably, the semiconductor layer  28  has a thickness of between about 1 micron and about 550 microns. A first insulating layer  40  is deposited or grown on the surface of the semiconductor layer  28  using a thermal oxide, a chemical vapor deposition dielectric, a plasma-enhanced chemical vapor deposition dielectric, a low-pressure chemical vapor deposition dielectric or the like. The first insulating layer  40  includes SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2  or the like. Preferably, the first insulating layer  40  has a thickness of between about 2 nm and about 100 nm. Following the deposition or growth of the first insulating layer  40 , a metal electrode material is patterned and deposited on the surface of the first insulating layer  40  to form the first metal electrode  24  and the second metal electrode  26  described above. The metal electrode material includes Mo, Ti, Pt, Au, Cr or the like. Preferably, the first metal electrode  24  and the second metal electrode  26  each have a thickness of between about 10 nm and about 100 nm.  
         [0026]     Referring to  FIG. 5 , a second insulating layer  42  is then deposited or grown on the surface of the first insulating layer  40 , substantially surrounding the first metal electrode  24  and the second metal electrode  26 , using a chemical vapor deposition dielectric, a plasma-enhanced chemical vapor deposition dielectric, a low-pressure chemical vapor deposition dielectric or the like. The second insulating layer  42  includes SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2  or the like. Preferably, the second insulating layer  42  has a thickness of between about 2 nm and about 100 nm. Collectively, the first insulating layer  40  and the second insulating layer  42  form the dielectric layer  22  described above. Following the deposition or growth of the second insulating layer  42 , a metal contact material is patterned and deposited on the surface of the second insulating layer  42  to form the first metal contact  18  and the second metal contact  20  described above. The metal contact material includes Ti, Mo, Au, Cr or the like. Preferably, the first metal contact  18  and the second metal contact  20  each have a thickness of between about 10 nm and about 100 nm.  
         [0027]     Referring to  FIG. 6 , a catalyst material  44  suitable for growing a carbon nanotube is then patterned and deposited on the surfaces of the first metal contact  18  and the second metal contact  20  using, for example, a lift-off technique, well known to those of ordinary skill in the art. The catalyst material  44  may take the form of a thin film or a nanoparticle and includes Ni, Fe, Co, Mo, Al 2 O 3  in Fe nitrate or the like. Preferably, the catalyst material  44  has a thickness of between about 0.1 nm and about 1 nm. Prior to depositing the catalyst material  44  on the surfaces of the first metal contact  18  and the second metal contact  20 , the surfaces of the first metal contact  18  and the second metal contact  20 , as well as the dielectric layer  22 , may be selectively coated with photo-resist. This photo-resist forms the appropriate pattern for the deposition of the catalyst material  44  and is subsequently removed. It should be noted that the catalyst material may be selectively deposited on the surface of only one of the first metal contact  18  and the second metal contact  20 . Following the deposition of the catalyst material  44 , the carbon nanotube  12  described above is grown, as illustrated in  FIG. 7 . Preferably, the carbon nanotube  12  is aligned substantially parallel to the surface of the dielectric layer  22 . In general, the carbon nanotube  12  is grown in a chemical vapor deposition (CVD) tube coupled to a flowing carbon (hydrocarbon) source, such as a methane source or an acetylene source, at between about 700 degrees C. and about 1000 degrees C. The catalyst material  44  forms a plurality of “islands” at these temperatures and becomes supersaturated with carbon. Eventually, the carbon nanotube  12  grows from these catalyst islands. This process is well known to those of ordinary skill in the art.  
         [0028]     Referring to  FIG. 8 , a free-standing electrostatically-doped carbon nanotube device  110  having a carbon nanotube  112  is shown. The free-standing electrostatically-doped carbon nanotube device  110  may be useful in photovoltaic devices, sensors, and/or power devices. When the carbon nanotube  112  is suspended as shown, the resulting diode exhibits a more ideal behavior, and such a configuration is better suited for electronic devices in general and more specifically for photovolataics. The carbon nanotube  112  has a first end  114  and a second end  116 . The carbon nanotube  112  extends between and contacts a first metal contact  18 , through the first end  114 , and a second metal contact  20 , through the second end  116 . The carbon nanotube  112  may be either a single-walled carbon nanotube (“SWCNT”) or a multi-walled carbon nanotube (“MWCNT”). The carbon nanotube  112  is similar in physical appearance, configuration, and size to the carbon nanotube  12  ( FIG. 1 ). The first metal contact  18  and the second metal contact  20  may comprise Ti, Mo, Au, Cr, or the like, and each may comprise an area or size of between about 0.1 microns by about 10 microns and about 1 micron by about 10 microns. In general, however, it should be appreciated that any dimensions providing adequate electrical contact with the ends of the carbon nanotube  112  may be used. The first metal contact  18  and the second metal contact  20  may be disposed either above or below the ends  114 ,  116  of the carbon nanotube  112 .  
         [0029]     The first metal contact  18  and the second metal contact  20  are disposed on the surface of a substrate  22 , such as, for example, a dielectric material. The dielectric material  22  may be formed of SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2 , or the like. A first metal electrode  24  and a second metal electrode  26  are disposed within the dielectric material  22 , adjacent to and at a distance from the first metal contact  18  and the second metal contact  20 , respectively. Because of this separation, the first metal electrode  24  is capacitively coupled to the first end  114  of the carbon nanotube  112  and the second metal electrode  26  is capacitively coupled to the second end  116  of the carbon nanotube  112 . In certain embodiments, the distance between the first metal electrode  24  and the first end  114  of the carbon nanotube  112  and the second metal electrode  26  and the second end  116  of the carbon nanotube  112  is between about 2 nm and about 100 nm, respectively. The first metal electrode  24  and the second metal electrode  26  are each made of Mo, Ti, Pt, Au, Cr or the like, and each has an area or size of between about 0.1 microns by about 10 microns and about 1 micron by about 10 microns. Advantageously, the area or size of the first metal electrode  24  and the second metal electrode  26  may be selected to achieve a desired spacing between the first metal electrode  24  and the second metal electrode  26 . The significance of this spacing has been described in detail.  
         [0030]     The dielectric material  22  is disposed on the surface of a base material  28 . The base material  28  may be a semiconductor material formed of Si, SiC, or the like. Alternatively, the base material  28  may be a metal layer  28 , such as a layer comprising Al, Cr, Mo, Ti, Pt, or the like. A trench  128  is formed in the dielectric material  22 , thus allowing the carbon nanotube  112  to be free-standing in that location. Enabling the carbon nanotube  112  to be free-standing from the dielectric material  22  allows for enhanced light emission when the carbon nanotube  112  is biased as a P—N junction diode.  
         [0031]     With specific reference to  FIG. 9 , the free-standing electrostatically-doped carbon nanotube device  110  is represented by a circuit diagram. The first metal contact (“M 1 ”)  18  is electrically coupled to the first end  114  of the carbon nanotube  112  and the second metal contact (“M 2 ”)  20  is electrically coupled to the second end  116  of the carbon nanotube  112 . Similarly, the first metal electrode (“VC 1 ”)  24  is capacitively coupled to the first end  114  of the carbon nanotube  112  and the second metal electrode (“VC 2 ”)  26  is capacitively coupled to the second end  116  of the carbon nanotube  112 . In this respect, VC 1   24  and VC 2   26  form a first gate and a second gate, respectively.  
         [0032]     In operation, a first bias is applied to VC 1   24 , resulting in the electrostatic doping of the first end  114  of the carbon nanotube  112 . Likewise, a second bias is applied to VC 2   26 , resulting in the electrostatic doping of the second end  116  of the carbon nanotube  112 . Depending upon the bias applied, the first end  114  of the carbon nanotube  112  and the second end  116  of the carbon nanotube  112  may each be made a p-type semiconductor (hole majority carrier) or an n-type semiconductor (electron majority carrier). If the first end  114  of the carbon nanotube  112  is made a p-type semiconductor and the second end  116  of the carbon nanotube  112  is made an n-type semiconductor, or vice versa, the result is a P—N junction. A P—N junction may be used to form a light-emitting diode (“LED”), a photovoltaic diode, a power device, a photo diode, a photo detector, or the like. The preferred voltage range of the structure for forming an electrostatically-doped carbon nanotube device  10  is between about +/−1 V and about +/−30 V for VC 1   24  and VC 2   26 .  
         [0033]     Single-walled carbon nanotubes are direct bandgap semiconductors and thus one or more of the free-standing electrostatically-doped carbon nanotube devices  110  may be utilized in a photovoltaic device, sensor, and/or a power device.  FIG. 10  illustrates the photovoltaic responses of a single free-standing electrostatically-doped carbon nanotube device  110 . The graph shows a shift in the current voltage characteristics of the free-standing electrostatically-doped carbon nanotube device  110  under progressively higher illumination intensity. The progressive shift to the fourth quadrant means greater power is being generated by the diode.  
         [0034]     Referring now to  FIGS. 11-16 , there is shown process steps for forming a free-standing electrostatically-doped carbon nanotube device  110 . As an initial step ( FIGS. 11 and 12 ), an insulating layer  40  is deposited or grown on the surface of the semiconductor layer  28 . The first insulating layer  40  may be formed using a thermal oxide, a chemical vapor deposition dielectric, a plasma-enhanced chemical vapor deposition dielectric, a low-pressure chemical vapor deposition dielectric, or the like. The first insulating layer  40  may comprise SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2 , or the like. Preferably, the first insulating layer  40  has a thickness of between about 2 nm and about 1000 nm. Following the deposition or growth of the first insulating layer  40 , a metal electrode material is patterned and deposited on the surface of the first insulating layer  40  to form the first metal electrode  24  and the second metal electrode  26  described above. The metal electrode material may be formed of Mo, Ti, Pt, Au, Cr, or the like. Preferably, the first metal electrode  24  and the second metal electrode  26  each have a thickness of between about 10 nm and about 100 nm.  
         [0035]     Referring to  FIG. 13 , a second insulating layer  42  is then deposited or grown on the surface of the first insulating layer  40 , substantially surrounding the first metal electrode  24  and the second metal electrode  26 . The second insulating layer  42  may be formed using a chemical vapor deposition dielectric, a plasma-enhanced chemical vapor deposition dielectric, a low-pressure chemical vapor deposition dielectric or the like. The second insulating layer  42  includes SiO 2 , Si 3 N 4 , Al 2 O 3 , ZrO 2  or the like. Preferably, the second insulating layer  42  has a thickness of between about 2 nm and about 100 nm. Collectively, the first insulating layer  40  and the second insulating layer  42  form the dielectric layer  22  described above. Following the deposition or growth of the second insulating layer  42 , a metal contact material is patterned and deposited on the surface of the second insulating layer  42  to form the first metal contact  18  and the second metal contact  20  described above ( FIG. 15 ). The metal contact material may comprise Ti, Mo, Au, Cr or the like. Preferably, the first metal contact  18  and the second metal contact  20  each have a thickness of between about 10 nm and about 100 nm.  
         [0036]     Referring to  FIG. 14 , a catalyst material  44  suitable for growing a carbon nanotube is then patterned and deposited on the surfaces of the first metal contact  18  and the second metal contact  20  using, for example, a lift-off technique, which is well known to those of ordinary skill in the art. The catalyst material  44  may take the form of a thin film or a nanoparticle and may include elements such as Ni, Fe, Co, or Mo, or mixtures such as Al 2 O 3  in Fe nitrate, or the like. In some embodiments, the catalyst material  44  has a thickness of between about 0.1 nm and about 1 nm. Prior to depositing the catalyst material  44  on the surfaces of the first metal contact  18  and the second metal contact  20 , the surfaces of the first metal contact  18  and the second metal contact  20 , as well as the dielectric layer  22 , may be selectively coated with photo-resist. The photo-resist serves to form the appropriate pattern for the deposition of the catalyst material  44  and is subsequently removed. It should be noted that the catalyst material  44  may be selectively deposited on the surface of only one of the first metal contact  18  and the second metal contact  20 .  
         [0037]     Following the deposition of the catalyst material  44 , the carbon nanotube  112  described above is grown, as illustrated in  FIG. 15 . Preferably, the carbon nanotube  112  is aligned substantially parallel to the surface of the dielectric layer  22 . In general, the carbon nanotube  112  is grown in a chemical vapor deposition (CVD) tube coupled to a flowing carbon (hydrocarbon) source, such as a methane source or an acetylene source, at between about 700 degrees C. and about 1000 degrees C. The catalyst material  44  forms a plurality of “islands” at these temperatures and becomes supersaturated with carbon. Eventually, the carbon nanotube  112  grows from these catalyst islands. This process is well known to those of ordinary skill in the art. Finally, as shown in  FIG. 16 , a trench  128  is etched in the dielectric layer  22  to enable the carbon nanotube  112  to be free-standing.  
         [0038]     Referring now to  FIGS. 17-21 , there is shown an alternative method for forming a free-standing electrostatically-doped carbon nanotube device  110 . As an initial step ( FIG. 17 ), an insulating layer  40  is deposited or grown on the surface of the semiconductor layer  28 . The first insulating layer  40  may be formed using a thermal oxide, a chemical vapor deposition dielectric, a plasma-enhanced chemical vapor deposition dielectric, a low-pressure chemical vapor deposition dielectric, or the like. Following the deposition or growth of the first insulating layer  40 , a metal electrode material is patterned and deposited on the surface of the first insulating layer  40  to form the first metal electrode  24  and the second metal electrode  26  described above.  
         [0039]     Referring to  FIG. 18 , a portion of the first insulating layer  40  is removed to form an altered first insulating layer  40   a . Suitable removal processes include etching and lithographic techniques. The first and second metal electrodes  24 ,  26  may be used as masks during an etching or lithography process. Suitable etchant material for etching the first insulating layer  40   a  includes wet etchants such as buffered oxide etch for SiO 2  or plasma dry etchants. An open area  127  is formed between the first and second metal electrodes  24 ,  26  through the etching process. With reference to  FIG. 21 , a second insulating layer  42   a  is then deposited or grown on the surface of the etched first insulating layer  40   a , substantially surrounding the first metal electrode  24  and the second metal electrode  26 . The second insulating layer  42   a  conforms to the etched first insulating layer  40   a . The conformance of the second insulating layer  42   a  at the open area  127  allows for the formation of a trench  128  between the first and second metal electrodes  24 ,  26 . Following the deposition or growth of the second insulating layer  42   a , a metal contact material is patterned and deposited on the surface of the second insulating layer  42  to form the first metal contact  18  and the second metal contact  20 .  
         [0040]     Referring to  FIG. 20 , a catalyst material  44  suitable for growing a carbon nanotube is then patterned and deposited on the surfaces of the first metal contact  18  and the second metal contact  20  using, for example, a lift-off technique, which is well known to those of ordinary skill in the art. Prior to depositing the catalyst material  44  on the surfaces of the first metal contact  18  and the second metal contact  20 , the surfaces of the first metal contact  18  and the second metal contact  20 , as well as the dielectric layer  22 , may be selectively coated with photo-resist. The photo-resist serves to form the appropriate pattern for the deposition of the catalyst material  44  and is subsequently removed. It should be noted that the catalyst material  44  may be selectively deposited on the surface of only one of the first metal contact  18  and the second metal contact  20 . Following the deposition of the catalyst material  44 , the carbon nanotube  112  described above is grown, as illustrated in  FIG. 21 .  
         [0041]     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, while embodiments of the invention have been described in terms of a single electrostatically-doped carbon nanotube, it should be appreciated that an array, or suite, of electrostatically-doped carbon nanotubes  12 ,  112  may be arranged to form numerous power devices. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.