Abstract:
A silicon and silicon germanium based semiconductor MODFET device design and method of manufacture. The MODFET design includes a high-mobility layer structure capable of ultra high-speed, low-noise for a variety of communication applications including RF, microwave, sub-millimeter-wave and millimeter-wave. The epitaxial field effect transistor layer structure includes critical (vertical and lateral) device scaling and layer structure design for a high mobility strained n-channel and p-channel transistor incorporating silicon and silicon germanium layers to form the optimum modulation-doped heterostructure on an ultra thin SOI or SGOI substrate capable of achieving greatly improved RF performance.

Description:
This invention was made with Government support under subcontract number N66001-00-8086 awarded by the Defense Advanced Research Projects Agency. The Government has certain rights in this invention. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates generally to silicon and silicon germanium based semiconductor transistor devices, and more specifically, to a device design including a grown epitaxial field effect transistor structure capable of ultra high-speed, low-noise for a variety of communication applications including RF, microwave, sub-millimeter-wave and millimeter-wave. Preferably, the epitaxial field effect transistor structure includes the critical device scaling and layer structure design for a high mobility strained n-channel transistor incorporating silicon and silicon germanium layers to form the optimum modulation-doped heterostructure on an ultra thin SOI or SGOI substrate in order to achieve f max  in excess of 200 GHz. 
   2. Description of the Prior Art 
   The attractiveness of substantial electron mobility enhancement (i.e. 3-5 times over bulk silicon) in modulation-doped tensile-strained Si quantum wells has inspired a long history of device development on Si/SiGe n-channel modulation doped filed-effect transistors (MODFETs). Subsequently, it has been demonstrated that SiGe MODFETs consume lower power and have lower noise characteristics compared to SiGe Heterojunction Bipolar Transistors (HBTs). Similarly, when compared to RF bulk Si CMOS device, SiGe MODFETs still have lower noise characteristics, and higher maximum oscillation frequency (f max ). Consequently, Si/SiGe MODFETs are becoming more and more attractive devices for high speed, low noise, and low power communication applications, where low cost and compatibility with CMOS logic technology are required and often essential. Recently, n-channel MODFETs with long channel lengths ranging from 0.2 μm to 0.5 μm have demonstrated encouraging device performances. 
   Typically, a Si/SiGe MODFET device have an undoped, tensile strained silicon (nFET) or a compressively strained SiGe (pFET) quantum well channels whereby the induced strain is used to increase the carrier mobility in the channel, in addition to providing carrier confinement The synergistic addition of modulation doping further improves the carrier mobility in the channel by reducing the ionized impurity scattering from the dopants and further reducing the surface roughness scattering in a buried channel. Record high room temperature mobilities of 2800 cm 2 /Vs have been achieved for electron mobilities in a tensile strained silicon channel grown on a relaxed Si 0.7 Ge 0.3  buffer. Conversely, very high hole mobility of 1750 cm 2 /V-s in a pure Ge channel grown on a Si 0.35 Ge 0.65  buffer has been achieved [R. Hammond, et al, DRC, 1991]. The highest f T  that has been achieved for a strained silicon nMODFET is 90 GHz [M. Zeuner, 2002], and the highest f max  is 190 GHz [Koester, et al to be published]. So far, neither f T  nor f max  has reached 200 GHz with Si/SiGe MODFETs. 
   As described in a simulation study conducted by the inventors, in order to achieve higher speed, the MODFET has to be scaled properly, both in the vertical dimensions and the horizontal (or lateral) dimensions. However, it turns out that the scaling of MODFETs is even more challenging than for CMOS scaling due to the following: 1) the horizontal scaling brings the source and drain closer, and, like the case in the CMOS, short-channel effects and bulk punchthrough become the major hurdles preventing the lateral scaling; and, 2) the vertical scaling of the layer structure turns out to be crucial. The lateral scaling alone cannot keep the scaling of the performance. However, the vertical scaling of the MODFET structures to reduce the depth of the quantum well (d QW ) is quite challenging, particularly due to the scaling and abruptness of the n+ supply layer, which is typically doped with Phosphorus as explained in the Annual Review of Materials Science, vol. 30, 2000, pp. 348-355.  FIG. 6  illustrates a graph  200  of the Phosphorus (P) doping profile for a G1 (generation) layer structure and the steady-state P doping  201  problem and transient P doping problems  202  associated with the Phosphorus doping in a CVD growth system. 
   It would be highly desirable to provide a scaling technique for MODFET device structures that overcomes the lateral and vertical scaling challenges in the manufacture of MODFET device structures. 
   It has been further been demonstrated in commonly-owned, co-pending U.S. patent application Ser. No. 10/389,145 entitled “Dual Strain State SiGe Layers for Microelectronics” by J. Chu, et al, filed Mar. 15, 2003, the contents and disclosure of which is incorporated by reference as if fully set forth herein, that MODFETs on a thick Silicon-Germanium-on-Insulator (SGOI) substrate will behave like MODFET on a bulk substrate. Co-pending U.S. patent application Ser. No. 10/389,145 particularly describes a generic MODFET layer structure on a SGOI substrate without specifying the critical layer structure for high performance. 
   It would be further highly desirable to provide a scaled MODFET device structure that is built on an ultra-thin SiGe-on-insulator (SGOI) substrate, wherein the MODFET device structure exhibits ultra-high speed device performance (e.g., f T , f max &gt;300 GHz) with better noise figures, acceptable voltage gain and good turn-off characteristics. 
   SUMMARY OF THE INVENTION 
   The invention is directed to a high-electron-mobility n-channel MODFET device that is properly scaled and constructed on a thin SGOI/SOI substrate that exhibits greatly improved RF performance. 
   The present invention is directed to a MODFET device and method of manufacture that addresses the prior art limitations and achieves vertical scaling of the nMODFET layer structure and the source/drain junction and lateral scaling of the device structure to unprecedented degrees, resulting in a device exhibiting ultra-high speed performance (i.e. f T , f max  &gt;300 GHz) with acceptable voltage gain and good turn-off characteristics. 
   In the method of manufacturing the MODFET device of the invention, the MODFET device is built on an ultra-thin SiGe-on-insulator (SGOI) substrate, such that the body is fully depleted. Due to the suppressed short channel effects, the output conductance (gd) may be thus be reduced. Therefore, the DC voltage gain (gm/gd), the linearity and f max  is significantly improved. In addition, the provision of ultra-thin SiGe buffer layers also reduces the self-heating due to the low thermal conductivity of SiGe, which reduces the drive current. Compared to a bulk MODFET, a fully-depleted SGOI MODFET exhibits better noise figures and lower soft error rate. Preferably, the epitaxial field effect transistor structure of the invention includes the critical device scaling and layer structure design for a high mobility strained n-channel transistor incorporating silicon and silicon germanium layers to form the optimum modulation-doped heterostructure on an ultra thin SOI or SGOI substrate in order to achieve f max  of &gt;300 GHz. 
   As studies have shown that the Phosphorus incorporation rate can be controlled by the growth rate (See aforementioned Annual Review of Materials Science, vol. 30, 2000, pp. 348-355), it is thus a further object of the present invention to provide a novel MODFET device structure method of achieving thin SiGe epitaxial layer with an abrupt P doping. In this objective, a novel low temperature growth technique is implemented for achieving abrupt phosphorous doping profiles in order to accommodate and to match the proper vertical scaling or design of the MODFET layer structure required for ultra-high speed performances. 
   In order to prevent the Phosphorus diffusion during the fabrication process, a small amount of carbon may be incorporated during the epitaxial growth of the SiGe supply layer in the manner as described in commonly-owned, co-pending U.S. patent application Ser. No. 09/838,892 entitled “Epitaxial and Polycrystalline Growth of Si 1-x-y Ge x C y  and Si 1-y C y  Alloy Layers on Si by UHV-CVD”, the contents and disclosure of which is incorporated by reference as if fully set forth herein. 
   The invention further is directed to a high-hole-mobility p-channel MODFET that is properly scaled and constructed on a thin SGOI/SOI substrate will also have very high RF performance. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Further features, aspects and advantages of the apparatus and methods of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
     FIGS.  1 ( a )- 1 ( e ) are schematic cross-sectional views showing the inventive Si/SiGe n-type MODFET structure on thin SGOI substrate (G0-G4) properly scaled in accordance with the invention; 
     FIG.  1 ( f ) illustrates a Si/SiGe p-type MODFET structure on thin SGOI substrate; 
       FIG. 2  illustrates a graph providing simulated I d -V gs  curves for the devices in FIGS.  1 ( a )- 1 ( f ) (L gs =L g =L gd =50 nm); 
       FIG. 3  depicts the simulated I d -V ds  curves for a G4 device of FIGS.  1 ( a )- 1 ( f ); 
       FIG. 4  depicts the simulated gm-V s  curves for a G4 device of FIGS.  1 ( a )- 1 ( f ); 
       FIG. 5  depicts the simulated f T  and f max  vs. V gs  curves for a G4 device of FIGS.  1 ( a )- 1 ( f ); 
       FIG. 6  depicts a SINS profile of the Phosphorus (P) doping profile for a G1 (generation) layer structure and the steady-state and transient P doping exhibited in a G1 layer structure; 
       FIG. 7  illustrates a graph  160  depicting the steady-state P concentration vs. growth UHV CVD system according to the invention; 
       FIG. 8  depicts the method for calibrating growth rate reduction  170  for a SiGe (Ge content of 30%) according to the invention; 
       FIG. 9  illustrates an example plot indicating the steady state P concentration as a function of reduced growth rate; 
       FIG. 10  is a graph illustrating the profile of transient P incorporation as a function of reduced growth rates; 
       FIG. 11  depicts a SIMS profile of the Phosphorus P doping and Ge concentration exhibited in a G2 layer structure; 
       FIG. 12  depicts a SIMS profile of the Phosphorus P doping and Ge concentration exhibited in a G3 layer structure; 
       FIG. 13  depicts a XTEM for the G1 layer structure on bulk corresponding to the SIMS profiles shown in  FIG. 6 ; 
       FIG. 14  depicts a XTEM for a G2 layer structure on bulk corresponding to the SIMS profiles shown in  FIG. 11 ; 
       FIG. 15  depicts a XTEM for a G3 layer structure on a SGOI substrate with thin re-growth; 
       FIG. 16  depicts a XTEM for a G2 layer structure on a SGOI substrate; and, 
       FIG. 17  illustrates a measured f T  vs. V gs  for a G1 device with d Qw =25 nm, L g =250 nm and a G2 device with d Qw  =15 nm, L g =70 nm. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   FIGS.  1 ( a )- 1 ( e ) are schematic cross-sectional views showing the inventive Si/SiGe n-type MODFET structures on thin SiGe-on-Insulator (SGOI) substrate (generation G1-G4 devices) properly scaled in accordance with the invention FIG.  1 ( f ) illustrates a Si/SiGe p-type MODFET structure on thin SGOI substrate properly scaled in accordance with the invention. 
   FIG.  1 ( a ) particularly depicts a MODFET device according to a first embodiment. As shown in FIG.  1 ( a ), there is depicted a top doped nMODFET device  10  comprising a Si substrate layer  5 , a buried dielectric layer  8  formed on top of the substrate  5  which may range up to 200 nm in thickness and comprise an oxide, nitride, oxynitride of silicon; and a channel region  25  formed between n+-type doped source and drain regions  11 ,  12  respectively, and a gate structure  20  including a gate dielectric layer  22  separating the gate conductor  18  from the channel  25 . As shown in the figure, the gate dielectric layer may comprise an oxide, nitride, oxynitride of silicon, and oxides and silicates of Hf, Al, Zr, La, Y, Ta, singly or in combinations. It is important to realize that according to the invention, the dimensions of the device including drain, source, gate and channel regions have been scaled. 
   The composition of the channel region  25  of device  10  in FIG.  1 ( a ) is as follows: A relaxed SiGe layer  30  having a p-type dopant is provided on a buried dielectric layer  8  having Ge content ranging between 30-50% and ranging in thickness between 20 nm-30 nm. The p-type doping concentration ranges between 1e14 cm −3 -5e17 cm −3  using one of: ion implantation or in-situ doping. The relaxed SiGe layer may be predoped to a concentration level of 1e14 cm −3 -5e17 cm −3 . Preferably, the relaxed SiGe layer and other layers comprising the channel  25  is grown according to a UHVCVD technique, however other techniques such as MBE, RTCVD, LPCVD processes may be employed. A five percent (5%) SiGe seed layer  31  (Si 0.95 Ge 0.05 ) is then epitaxially grown on top of the relaxed SiGe layer  30  and an intrinsic Si 1-x Ge x  regrown buffer layer  32  is formed on top of the formed SiGe seed layer  31 . The thickness of epitaxially grown SiGe seed layer ranges from 0 nm-5 nm and the thickness of the intrinsic SiGe regrown buffer layer  32  ranges between 20 nm-30 nm and having Ge content “x” ranging between 10%-40%. An epitaxial tensile strained Si layer  33  is then grown on top of the SiGe buffer layer  32  and ranges in thickness between 5 nm-7 nm. An epitaxial Si 1-y Ge y  spacer layer  34  is then formed on top of the strained Si layer and ranging in thickness between 3 nm-5 nm and having Ge content “y” ranging between 30-40%. Then, an epitaxial Si 1-z Ge y  supply layer  35  is grown on top of the spacer layer ranging in thickness between 2 nm-8 nm and having a n-type doping concentration ranging between 2e18 cm −3 -5e19 cm −3  and having Ge content “z” ranging between 35-50%. The Si 1-z Ge z  supply layer may be grown in a temperature range between 425° C.-550° C. and in-situ doped using phosphine gas as a dopant precursor singly or in a mixture including one or more elements including but not limited to: H2, He, Ne, Ar, Kr, Xe, N 2 . Preferably, the flow rate of the phosphine gas dopant precursor is a linear ramp or a graded profile such that said in-situ doping is performed without disrupting an epitaxial growth process. It is understood that a precursor such as AsH 3  or SbH 3  may be used as well. As mentioned herein, in order to prevent the P diffusion during the fabrication process, a small amount of carbon may be incorporated during the epitaxial growth of the SiGe supply layer  34 , e.g., a SiGeC layer, having a C content of about 0.1-2%, preferably about 1-1.5%. Finally, an epitaxial tensile strained Si cap layer  36  is grown on top of the supply layer  35  ranging in thickness between 0 nm-3 nm and having a n-type doping concentration ranging between 5e17 cm −3 -5e19 cm −3 . 
   To form the transistor device of FIG.  1 ( a ), the gate dielectric layer  22  is formed on top of the strained Si cap layer and is having an equivalent oxide thickness in a range of 0-1 nm. The gate conductor  18  may have a T-gate geometry, rectangular geometry or a multi-finger geometry formed on top of the gate dielectric layer  22  and may comprise Pt, Ir, W, Pd, Al, Au, Cu, Ti, Co either, singly or in combinations, at lengths ranging between 30 nm-100 nm. The formed drain region  12  has an n-type doping concentration greater than 5e19 cm −3 ; and the formed source region  11  has a n-type doping concentration greater than 5e19 cm −3 . The distance between the gate conductor  18  and either drain or source region ranges from about 20 nm-100 nm. Although not shown, the device may further comprise a passivation layer surrounding the gate electrode  20 , the passivation layer having a permittivity ranging between 1-4. As indicated in FIG.  1 ( a ), the depth of the quantum well, d QW  of the formed nMODFET includes the spacer layer of intrinsic SiGe  34 , the layer of n+-type doped SiGe  35  and the layer of n+-type doped Si cap layer  36  totaling approximately 10 nm in depth according to the dimensions depicted in FIG.  1 ( a ). 
   In an alternate embodiment the seed layer  31  of FIG.  1 ( a ) may be omitted. FIG.  1 ( b ) depicts a high-electron-mobility device  40  that is identical to the top-doped nMODFET of FIG.  1 ( a ), however, does not include the seed layer. 
   FIG.  1 ( c ) illustrates a second embodiment of the invention drawn to a high-electron-mobility nMODFET device  50  that is bottom doped. As shown in  FIG. 1   c ), the device  50  includes a Si substrate layer  5 , a buried dielectric layer  8  formed on top of the substrate  5  comprising an oxide, nitride, oxynitride of silicon, for example, and a channel region  55  formed between n+-type doped source and drain regions  11 ,  12  respectively, and a gate structure  20 . The channel structure  55  includes a relaxed SiGe layer  60  on insulator  8  ranging in thickness between 10 mm and 50 nm, an epitaxial Si 0.95 Ge 0.05  seed layer  61  grown on top of the SiGe layer  60  and ranging in thickness between 0 nm-5 nm; an epitaxial Si 1-z Ge z  supply layer  62  grown on top of the seed layer ranging in thickness between 2 nm-8 nm and having a n-type doping concentration ranging between 1e18 cm −3 -5e19 cm −3 ; an epitaxial Si 1-y Ge y  spacer layer  63  grown on top of the supply layer and ranging in thickness between 3 nm-5 nm; and, an epitaxial tensile strained Si channel layer  64  grown on top of the spacer layer and ranging in thickness between 3 nm-10 nm; an epitaxial Si 1-y Ge y  spacer layer  65  grown on top of the strained Si layer and ranging in thickness between 1 nm-2 nm; and, an epitaxial tensile strained Si cap layer  66  grown on top of the spacer layer ranging in thickness between 0 nm-2 nm. As in the first embodiment, a small amount of carbon may be incorporated during the epitaxial growth of the SiGe supply layer  61 , e.g., a SiGeC layer, having a C content of about 0.1-2%, preferably about 1-1.5%. Further, with respect to the second embodiment of  FIG. 1   c ) all the gate conductor geometries and distances to respective source/drain regions, the dopant concentrations of the source/drain regions, and the composition of the gate conductor metal and gate dielectric are the same as in the first embodiment (FIG.  1 ( a )). As indicated in FIG.  1 ( c ), the depth of the quantum well, d QW  of the formed nMODFET includes the layer of n+-type doped Si cap layer  66  totaling a depth of approximately 2 nm. 
   In an alternate embodiment of the structure  50  of FIG.  1 ( c ), the seed layer may be omitted. Thus a resulting structure is a high-electron-mobility device that is identical to the bottom-doped nMODFET of FIG.  1 ( c ), however, does not include the seed layer. In this alternate embodiment, an SGOI substrate comprises: a relaxed SiGe layer on insulator having Ge content ranging between 30-40% and ranging in thickness between 20 nm-30 nm; an epitaxial Si 1-z Ge z  supply layer grown on top of the relaxed SiGe layer ranging in thickness between 2.5 nm-8 nm and having a n-type doping concentration “z” ranging between 2e18 cm −3 -2e19 cm −3  and having Ge content ranging between 35-50%; an epitaxial S 1-y Ge y  spacer layer grown on top of the supply layer and ranging in thickness between 3 nm-5 nm and having Ge content “y” ranging between 30-40%; an epitaxial tensile strained Si channel layer grown on top of the spacer layer ranging in thickness between 5 nm-7 nm and having a doping concentration less than 1e16 cm −3 ; an epitaxial Si 1-y Ge y  spacer layer grown on top of the Si channel layer and ranging in thickness between 1 nm-2 nm and having Ge content ranging between 30-40%; and, an epitaxial tensile strained Si cap layer grown on top of the spacer layer ranging in thickness between 0 nm-2 nm. A transistor device is completed with the drain source and gate conductor regions as shown and explained with respect to FIG.  1 ( c ). 
   FIG.  1 ( d ) illustrates a third embodiment of the invention drawn to a high-electron-mobility nMODFET device  70  that is bottom doped and including a doped transferred layer. As shown in FIG.  1 ( d ), the device  70  includes an SGOI substrate comprising a Si 1-z Ge z  supply layer  71  ranging in thickness between 2 nm-8 nm and having a n-type doping concentration ranging between 1e18 cm −3 -5e19 cm −3 by ion implantation or in-situ doping; an epitaxial Si 1-y Ge y  spacer layer  72  grown on top of the supply layer and ranging in thickness between 3 nm-5 nm; an epitaxial tensile strained Si channel layer  73  grown on top of spacer layer  72  and ranging in thickness between 3 nm-10 nm; an epitaxial Si 1-y Ge y  spacer layer  74  grown on top of the strained Si layer  73  and ranging in thickness between 1 nm-2 nm; and, an epitaxial tensile strained Si cap layer  75  grown on top of the spacer layer ranging in thickness between 0 nm-2 nm. Preferably, the doped transferred Si 1-z Ge z  supply layer  71  has a Ge content z=x+a, where “a” ranges between about 0-30%, “x” ranges between 30-50%, and may be formed by a wafer bonding and smart-cut process. Alternatively, the Si 1-z Ge z  supply layer may be predoped to a concentration level of 1e18-5e19 atoms/cm3 before a layer transfer in forming the SGOI substrate. The doped transferred Si 1-z Ge z  supply layer may further comprise a Si 1-m-n Ge m C n  layer, where m=x+b, and “b” ranges between 0-30%, and “n” ranges between 0.1-2%. The Si 1-y Ge y  spacer layers  72 ,  74  includes a Ge content y=x+c, where “c” ranges between 0-20%. Further, with respect to the third embodiment of FIG.  1 ( d ), all the gate conductor geometries and distances to respective source/drain regions, the dopant concentrations of the source/drain regions, and the composition and thicknesses of the gate conductor metal and gate dielectric are as depicted in the first embodiment (FIG.  1 ( a )). As indicated in FIG.  1 ( d ), the depth of the quantum well, d QW  of the formed nMODFET includes the layer of n+-type doped Si cap layer  75  and spacer layer  74  having a depth of less than approximately 4 nm. 
   FIG.  1 ( e ) illustrates a fourth embodiment of the invention drawn to a high-electron-mobility nMODFET device  80  that is both bottom and top doped and including a SiGe regrown buffer layer. As shown in FIG.  1 ( e ), the nMODFET device  80  includes an SGOI substrate having: a relaxed SiGe layer  81  on insulator  8  ranging in thickness between 10 nm-50 nm, having a n-type doping concentration ranging between 1e17 cm −3 -5e19 cm −3  and a Ge content ranging between 30-50%; a Si 1-x Ge x  regrown buffer layer  82  grown on top of the SiGe layer  81  and ranging in thickness between 10 nm-50 nm and serving as a bottom spacer layer and including a Ge content “x” ranging between 10%-35%; an epitaxial tensile strained Si layer  83  grown on top of the regrown buffer layer and ranging in thickness between 3 nm-10 nm; an epitaxial Si 1-y Ge y  spacer layer  84  grown on top of the strained Si layer  83  and ranging in thickness between 3 nm-5 nm; an epitaxial Si 1-z Ge z  supply layer  85  grown on top of the spacer layer  84  ranging in thickness between 2 nm-8 nm and having a n-type doping concentration ranging between 1e18 cm −3 -5e19 cm −3 ; and, an epitaxial tensile strained Si cap layer  86  grown on top of the supply layer  85  ranging in thickness between 0 nm-3 nm and having a n-type doping concentration ranging between 5e17 cm −3 -5e19 cm −3 . The Si 1-y Ge y  spacer layer  84  includes a Ge content y=x+a, where “a” ranges between 0-20% and the Si 1-z Ge z  supply layer includes a Ge content z=x+b, where “b” ranges between 0-30%. As in the other embodiments, the Si 1-z Ge z  supply layer comprises a Si 1-m-n Ge m C n  layer, where m=x+c, and “c” ranges between 0-20%, and “n” ranges between 0.1-2%. Further, with respect to the fourth embodiment of FIG.  1 ( e ), all the gate conductor geometries and distances to respective source/drain regions, the dopant concentrations of the source/drain regions, and the composition and thicknesses of the gate conductor metal and gate dielectric are as depicted in the first embodiment (FIG.  1 ( a )). As indicated in FIG.  1 ( e ), the depth of the quantum well, d QW  of the formed nMODFET includes the layer of n+-type doped Si cap layer  86 , the epitaxial Si 1-z Ge z  supply layer  85 , and spacer layer  84  for a depth totaling less than or equal to approximately 16 nm. 
   FIG.  1 ( f ) illustrates a fifth embodiment of the invention drawn to a high-hole-mobility MODFET device  80  that is bottom doped and including a doped transferred layer. As shown in FIG.  1 ( f ), the pMODFET device  90  includes an SGOI (SiGe layer  91  on insulator  8 ) substrate having: a relaxed epitaxial Si 1-j Ge j  supply layer ranging in thickness between 5 nm-25 nm, and having ion-implanted or in-situ p-type doping of a concentration ranging between 1e18-5e19 cm −3  and serving as a supply layer. Alternately, the relaxed Si 1-j Ge j  layer may be predoped p-type to a concentration level of 1e18-5e19 boron atoms/cm3 before a layer transfer in forming the SGOI substrate; an epitaxial Si 1-k Ge k  spacer layer  92  grown on top of the supply layer  91  and ranging in thickness between 3 nm-7 nm; an epitaxial compressively strained Si 1-m Ge m  channel layer  93  grown on top of the spacer layer and ranging in thickness between 5 nm-20 nm; and, an epitaxial strained Si 1-n Ge n  cap layer  94  grown on top of the strained Si 1-m Ge m  channel layer and ranging in thickness between 2 nm-10 nm. In the high-hole-mobility layer semiconductor structure  90  the Si 1-j Ge j  supply layer  91  includes a Ge content “j” ranging between 30-70%. The Si 1-k Ge k  spacer layer  92  includes a Ge content “k” ranging between 30-70% and, the Si 1-m Ge m  channel layer  93  includes a Ge content “m” ranging between 60-100% and the strained Si 1-n Ge n  cap layer  94  includes a Ge content n ranging between 0%-30%. 
   To form the pMODFET transistor device of FIG.  1 ( f ), a gate dielectric layer  95  is formed on top of the strained SiGe cap layer  94  and is having an equivalent oxide thickness in a range of 0-1 nm. The gate conductor  18  may have a T-gate geometry, rectangular geometry or a multi-finger geometry formed on top of the gate dielectric layer  95  and may comprise Pt, Ir, W, Pd, Al, Au, Cu, Ti, Co either, singly or in combinations, at lengths ranging between 30 nm-100 nm. A formed drain region  97  has a p-type doping concentration greater than 5e19 cm −3 ; and the formed source region  96  has a p-type doping concentration greater than 5e19 cm −3 . The distance between the gate conductor  18  and either drain or source region ranges from about 20 nm-100 nm. Although not shown, the device may further comprise a passivation layer surrounding the gate electrode  20 , the passivation layer having a permittivity ranging between 1-4. As indicated in FIG.  1 ( f ), the depth of the quantum well, d QW  of the formed pMODFET  90  includes the SiGe cap layer  94  with a range from approximately between 2 nm-10 nm. 
   Completed devices comprising embodiments depicted in FIGS.  1 ( a )- 1 ( e ) having the different layer structures and design were grown by UHVCVD under growth temperature conditions ranging between 400-600° C., and preferably in a range of 500-550° C. and in a pressure ranging from 1 mTorr-20 mTorr. 
     FIG. 17  shows the performance (measured f T  vs. V gs ) curves  100  with the device scaling (i.e., for G1 and G2 devices). For example,  FIG. 17  shows the f T  curve for a G1 device with d QW =25 nm, L g =250 nm as compared to a G2 device with d QW =15 nm, L g =70 nm. As shown, in order to further improve the performance, the device has to be further scaled, both in the horizontal and vertical dimensions as in the G2 example shown in FIG.  17 . 
     FIGS. 2-5  depict simulated device characteristics for the properly scaled devices of FIGS.  1 ( a )- 1 ( f ).  FIG. 2  depicts the simulated Id-Vgs curves  105  for the G4 device of  FIG. 1  where L gs =L g =L gd =50 nm.  FIG. 3  depicts the simulated I d -V ds  curves  110  for the G4 device of FIG.  1  and  FIG. 4  depicts the simulated gm-V gs  curves  120  for the G4 device in  FIG. 1  (L gs =L g =L gd =50 nm). As shown in  FIG. 5 , there is depicted the simulated f T  and f max  vs. V gs  curves  130  for the device in  FIG. 1  where f T 230 GHz and f max =370 GHz can be achieved according to device simulations. 
   As mentioned hereinabove, experimentally it has been found that Phosphorus (P) doping can be controlled by the Ge content and its associated growth rate in a UHV CVD system.  FIG. 7  illustrates a graph  160  depicting the steady-state P concentration  161  vs. growth rate in a UHVCVD  162  system. 
   As shown in the steady-state P concentration vs. growth rate graph of  FIG. 7 , in particular, the transient incorporation for P doping depicted by curves  165  is controlled by the Ge content  167  in a SiGe film. Likewise, the steady state P concentration is controlled by the associated growth rate of the SiGe film. The key process for achieving the abruptness of P profile is to use high Ge content but at a reduced growth rate, which is difficult since it is well known that high Ge is associated with enhanced or high growth rate. 
   The growth rate calibration  170  for a SiGe (Ge content of 30%) is shown in  FIG. 8 , for example, with a Ge concentration profile exhibiting successively smaller peaks  171 ,  172  as shown in the figure. Using the same calibration with the addition of PH3, the enhanced steady-state P concentration  175  is shown in  FIG. 9  as a function of reduced SiGe growth rate depicted as curve  174 . Similarly, as shown in the graph depicting transient P incorporation vs. reduced growth rates in  FIG. 10 , for the higher Ge content  177 , the transient P incorporation rate is also increased as shown by the profile curve  178  in FIG.  10 . 
   Using a reduced flow combination of SiH4 to GeH4 of (15 sccm/17 sccm), a G1 doping profile has been obtained just like secondary ion mass spectroscopy (SIMS) profiles  201 ,  202  as shown in FIG.  6 . The corresponding cross-sectional transmission electron micrograph (XTEM) is shown in FIG.  13 . 
   Using a lower flow combination SiH4 to GeH4 of (10/17), a G2 doping profile has been achieved as shown in the SIMS profiles P doping and Ge concentration profiles shown in FIG.  11 . The corresponding XTEM is shown in FIG.  14 . 
   Using an even lower flow combination SiH4 to GeH4 of (8/10), a G3 doping profile has been achieved as shown in the SIMS profiles P doping and Ge concentration profiles shown in FIG.  12 . The corresponding XTEM is shown in FIG.  15 .  FIG. 15  particularly depicts the XTEM for a G3 layer structure on a SGOI substrate with a transferred SiGe layer of 50 mm, where the regrown SiGe on transferred SiGe is thick (e.g., about 134.1 nm) in order to minimize the effects of carbon and oxygen at the regrowth interface. However, in order to make MODFETs on thin SGOI, one task is to make the regrown SiGe layer as thin as possible. A growth process has been developed using a 5% SiGe seed layer as described in the herein incorporated co-pending U.S. patent application Ser. No. 10/389,145. 
     FIG. 16  depicts a XTEM for a G2 layer structure on a SGOI substrate with a thin regrown SiGe layer (e.g., about 19.7 nm) on a SGOI substrate with a 73 nm thick transferred SiGe layer. It is advantageous to begin with a thin SGOI substrate which can be formed by a wafer bonding and thinning process as described in co-pending U.S. patent application Ser. No. 10/389,145. 
   While the invention has been particularly shown and described with respect to illustrative and preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention that should be limited only by the scope of the appended claims.