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Si-Based Resonant Interband Tunneling Diodes

Advisor: Paul R. Berger
Students: Sean L. Rommel (Ph.D. candidate, graduates December 1999)
  Niu Jin (Ph.D. Pre-Candidate)
Collaborators: Phillip E. Thompson (Naval Research Laboratory)
  Karl D. Hobart (Naval Research Laboratory)
  Roger Lake (Raytheon Systems Company)
  Alan C. Seabaugh (Notre Dame)
  David S. Simons (NIST)
  James Kolodzey (University of Delaware, Elec. Engin.)


Importance of the Problem:

Recent demonstrations of high speed and low power resonant tunneling diode/transistor circuits1-3 have shown how the tunnel diode can boost the performance of a transistor technology. The utility of the tunnel diode has been realized since the early nineteen sixties,4 but today tunnel diodes are used only in discrete form and for niche applications, such as high speed pulse and edge generation.5 The drawback to the tunnel diode has long been the difficulty in controlling peak current6 and the lack of an integrated circuit process.4

1.
A. C. Seabaugh, B. Brar, T. Broekaert, G. Frazier, and P. van der Wagt, ``Resonant tunneling circuit technology: has it arrived?'' 1997 GaAs IC Symposium, pp. 119-122.

2.
T. P. E. Broekaert, B. Brar, J. P. A. van der Wagt, A. C. Seabaugh, T. S. Moise, F. J. Morris, E. A. Beam III, and G. A. Frazier, ``A monolithic 4-bit 2-Gsps resonant tunneling analog-to-digital converter," IEEE J. Solid State Circ., 33, 1342 (1998).

3.
J. P. A. van der Wagt, A. C. Seabaugh, and E. A. Beam, III, ``RTD/HFET low standby power SRAM gain cell,'' IEEE Electron Dev. Lett. 19, 7 (1998).

4.
R. G. Swartz, ``In perspective: the tunnel diode,'' 1986 IEEE Int. Solid-State Circ. Symp., pp. 278-280.

5.
Picosecond Pulse Labs, Boulder, CO.

6.
R. W. Keyes, ``Physics of digital devices,'' Rev. Mod. Phys., 61, 279 (1989).

Brief Description of Work and Results:

Resonant interband tunneling diodes (RITD) on silicon substrates are demonstrated using a Si/Si0.5Ge0.5/Si heterostructure grown by low temperature molecular beam epitaxy (LT-MBE) which utilized both a central intrinsic spacer and $\delta$-doped injectors. A low substrate temperature of 370$^{\circ}$C was used during growth to ensure a high level of dopant incorporation. A B $\delta$-doping spike lowered the barrier for holes to populate the quantum well at the valence band discontinuity, and an Sb $\delta$-doping spike reduces the doping requirement of the n-type bulk Si by producing a deep n+ well. Samples studied from the as-grown wafers showed no evidence of negative differential resistance (NDR). The effect of post-growth rapid thermal annealing (RTA) temperature was studied on tunnel diode properties. Samples which underwent heat treatment at 700$^{\circ}$C and 800$^{\circ}$C for 1 minute, in contrast, exhibited NDR behavior. The peak-to-valley current ratio (PVCR) and peak current density of the tunnel diodes were found to depend strongly on $\delta$-doping placement and on the annealing conditions. PVCRs ranging up to 1.54 were measured at a peak current density of 3.2 kA/cm2.

More recent results have extended this performance of Si/Si0.5Ge0.5/Si RITDs to PVCRs up to 2.05 with a peak current density of 22 kA/cm2. This high current density is sufficient for mixed-signal applications. Ultra-low current density structures are being investigated for low power T-SRAM, with the best results reported is a PVCR up to 1.2 with a peak current density of only 7.5 A/cm2.

The highest PVCR recorded to date ranged up to 2.2, with a peak current density of 6.5 kA/cm2. Through the control of the spacer thickness and annealing conditions, tremendous control of the peak current density is possible from 30 A/cm2 up to about 40 kA/cm2.


For further information contact:

Professor Paul R. Berger
University of Delaware
Department of Electrical Engineering
140 Evans Hall, Newark, DE 19716
(302) 831-4062
FAX: (302) 831-4316
Email: pberger@ee.udel.edu
URL: http://www.eecis.udel.edu/$\sim$pberger/

Supported By: Defense Advanced Research Projects Agency (DARPA)
  National Science Foundation (NSF)


Patents:

1.
Provisional patent on ``Si-Based Resonant Interband Tunneling Diodes and Method of Making Interband Tunnelling Diodes,'' Paul R. Berger, Sean L. Rommel, Phillip E. Thompson, Karl D. Hobart, and Roger Lake, (Docket No. UD99-6), submitted on August 4, 1998. Filed on May 7, 1999.

Recent Publication Activity:

1.
``Si Resonant Interband Tunnel Diodes Grown by Low Temperature Molecular Beam Epitaxy,'' Phillip E. Thompson, Karl D. Hobart, Mark Twigg, Glenn Jernigan, Thomas E. Dillon, Sean L. Rommel, Paul R. Berger, David S. Simons, Peter H. Chi, Roger Lake and Alan C. Seabaugh, Applied Physics Letters, 75, pp. 1308-1310 (August 30, 1999). PDF (46 kB)

2.
``Si-Based Interband Tunneling Devices For High-Speed Logic and Low Power Memory Applications," Sean L. Rommel, Thomas E. Dillon, Paul R. Berger, Roger Lake, Phillip E. Thompson, Karl D. Hobart, Alan C. Seabaugh, and David S. Simons, Late News in the 1998 International Electron Devices Meeting Technical Digest, pp. 1035-1037 (December 8, 1998). PDF (468 kB)

3.
``Epitaxially Grown Si Resonant Interband Tunnel Diodes Exhibiting High Current Densities,'' Sean L. Rommel, Thomas E. Dillon, Paul R. Berger, Phillip E. Thompson, Karl D. Hobart, Roger Lake, and Alan C. Seabaugh, IEEE Electron Device Letters, 20, pp. 329-331 (July 1999). PDF (75 kB)

4.
``Room Temperature Operation of Epitaxially Grown Si/Si0.5Ge0.5/Si Resonant Interband Tunneling Diodes,'' Sean L. Rommel, Thomas E. Dillon, M. W. Dashiell, H. Feng, J. Kolodzey, Paul R. Berger, Phillip E. Thompson, Karl D. Hobart, Roger Lake, Alan C. Seabaugh, Gerhard Klimeck, and Daniel K. Blanks, Applied Physics Letters, 73, pp. 2191-2193 (October 12, 1998). PDF (71 kB)

Recent Conference Activity:

1.
``Si-Based Interband Tunneling Devices For High-Speed Logic and Low Power Memory Applications," Sean L. Rommel, Thomas E. Dillon, Paul R. Berger, Roger Lake, Phillip E. Thompson, Karl D. Hobart, Alan C. Seabaugh, and David S. Simons, Late News at the International Electron Devices in San Francisco, CA, (December 6-9, 1998).

2.
``Demonstration of Room Temperature NDR in Si0.5Ge0.5/Si Heterojunction Interband Tunneling Diodes Using Delta-doped Si Injectors," Sean L. Rommel, T. E. Dillon III, M. W. Dashiell, H. Feng, J. Kolodzey, Paul R. Berger, Phillip E. Thompson, K. D. Hobart, Roger Lake, and Alan Seabaugh, Late News at 1998 IEEE Silicon Nanoelectronics Workshop in Honolulu, HI, (June 7-8, 1998).



 
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Paul R. Berger
1999-10-06