Si/SiGe(C) Heterostructures

1. Si/SiGe(C) Heterostructures S. H. Huang Dept. of E. E., NTU

2. OUTLINE • Introduction • Strain Effects • Device Performance • Fabrication technologies

3. Introduction The Si/SiGe:C heterostructures add the colorful creativity in the monotonic Si world. The Si/SiGe heterojunction bipolar transistors have the cutoff frequency of 300 GHz and maximum oscillation frequency of 285GHz with carbon incorporation in the base. (IBM)

4. Table I: The recent performance of electronic and optoelectronic devices based on SiGe technology. The last column indicates the growth techniques to achieve the device quality material Device Figure of Merit Growth Technique Strained NMOSFET Peak effective electron mobility 800 cm2/Vs [6] relaxed buffer Strained PMOSFET Peak effective hole mobility 2700 cm2/Vs [5] relaxed buffer Npn-HBT fT=210GHz [1], fmax=285GHz [2] Pseudomorphic Pnp-HBT fT=59GHz at RT, fT=61GHz at 85K [12] Pseudomorphic Heterojunction Phototransistors 1.47 A/W at 850 nm, bandwidth=1.25 GHz [13] Pseudomorphic n-MODFET Gm=460ms/mm fT=76GHz fmax=107GHz at RT [14] Gm=730ms/mm fT=105GHz fmax=170GHz at 50K relaxed buffer p-MODFET Gm=300ms/mm fT=70GHz fmax=135GHz at RT[15] relaxed buffer n-RTD P/V7.6 at RT [7], 2 at 4.2K [8] relaxed buffer p-RTD P/V=1.8 at RT, 2.2 at 4.2K[9] Pseudomorphic Detector (IR) 1.3μm , 1.5μm[16] quantum dots Detector (LWIR) Schottky barrier:λc=10μm[17] Pseudomorphic LED 1.3μm , 1.5μm at RT[18,19] Pseudomorphic

5. ：SiGe virture atoms : Si atoms The strained SiGe grown on (100) Si. The misfit dislocation is the missing bond between Si and SiGe atoms.

6. strained Si or Ge relaxed SiGe Si threading dislocation misfit dislocation The misfit dislocation and threading dislocation. The misfit dislocation is at the Si/SiGe interface, and threading dislocation ends at the surface of the epilayers.

7. 20 nm (b) (a) (a) TEM photo of multi-layer Ge dots. The spacer thickness is ~20nm. The SiO2 dots are also formed above the Ge dots. (b) The strain field in Si layers.

8. Composite dots with fine structures such as Ge/Si/Ge composite dots

9. (a) (b) AFM picture of (a) composite dots and (b) conventional dots. The composite dots has larger coverage area.

10. The bandgap of strained Si1-xGex on (001) Si substrate and relaxed band gap of Si1-xGex alloys. The showdow areas indicate the optical communication bandwidth of 1.3 and 1.5 mm.

11. Theoretical values of the hole mobility in relaxed SiGe alloys at 300K and doping concentration of NA=1016cm-3 with experimental results of Gaworzewski

12. The in-plane and out-of-plane majority hole mobility of SiGe strained alloys for different doping concentration.

13. In-plane and out-of-plane minority electron mobilities of SiGe alloys at different doping level at 300K.

14. The in-plane electron and hole mobility of strained Si.

15. The calculated electron and hole mobility enhancement factor in MOS inversion layers of strained Si.

16. Electron and hole mobility in strained Ge.

17. Smart-cut and layer transfer process flow for making strained Si on SiGe-on-insulator material.

18. Cross-section TEM picture of relaxed SiGe on SOI using the smart-cut method.

19. Band diagram of typical SiGe HBT. In forward active region, the base-emitter junction is forward-biased (VBE) and the base-collector junction reverse-biased (VCB)

20. Compositionally graded Si1-xGex can build an electrical field in the base of Si/SiGe HBTs.

21. Device structures for strained Si NMOSFETs with (a) Si on the surface, (b) Si buried channel.

22. Effective low-field mobility versus effective field for different NMOSFETs. The surface channel strained-Si mobility shows a fairly constant mobility enhancement compared with that of control-Si device, while the buried strained-Si mobility peaks at low fields but decreases rapidly at higher fields.

23. NMOSFET effective mobility vs vertical effective field.

24. PMOSFET effective mobility vs vertical effective field.

25. Schematic diagram of a buried strained-SiGe PMOSFET. Most current flow is in the strained SiGe channel.

26. Typical layer sequences: (a) NMODFETs with Si-channel on relaxed-SiGe buffer, (b) PMODFET with SiGe channel and (c) PMODFET with Ge channel on relaxed-SiGe buffer.

27. Available experimental data [71-75] at 300K for effective electron and hole mobility in MODFET. “A” denotes modulation doping above strained Si channel, “B” denotes doping supply layer below strained silicon channel, x is the Ge fracion in the channel, and y is Ge fraction in the buffer layers.

28. The absorption length at 820, 1300, and 1550 nm vs Ge mole fraction. The absorption length decreases as the Ge mole fraction increases. For the large Ge fraction, the shadowed areas indicate the uncertainty of the estimation.

29. The structure of 5-layer Ge quantum dot devices prepared by UHV/CVD