1. University of California, Santa Barbara
InAlAs/InGaAs/InP DHBTs with Polycrystalline InAs Extrinsic Emitter Regrowth
D. Scott, H. Xing, S. Krishnan, M. Urteaga, N. Parthasarathy and M. Rodwell
University of California, Santa Barbara
, fax

2. Advantages of InP vs. SiGe HBTs
InP HBT Material Properties:
Available lattice-matched materials allows for emitter bandgap wider than base, allowing for higher base doping and lower base sheet resistance
Electron velocities reported as high as 4107 cm/s
InP HBT Processing Technology :
High topography mesa structure allows for small-scale integration
Base-emitter junctions defined by etching and depositing a self-aligned base metal results in low yield and limits emitter scaling
Si/SiGe HBT Material Properties:
Allowable lattice mismatch limits Ge:Si alloy ratio resulting in smaller emitter-base bandgap difference and higher base sheet resistance
4:1 lower electron velocity is seen in silicon
Si/SiGe Processing Technology :
Planar process using silicon CMOS technology allows for VLSI
Self-aligned base-emitter junctions are diffused, extrinsic base and emitter wider than the active junction allows for high degree of scaling

3. Evolution Cbc Reduction in III-V HBTs
Emitter
Emitter
Collector
Collector
Base
Base
Subcollector
Subcollector
S.I. Substrate
S.I. Substrate
Mesa HBT
Cbc Reduction HBT
Emitter
Emitter
Collector
Base
Subcollector
Collector
S.I. Substrate
Transferred Substrate HBT
Highly Scaled HBT

4. UCSB Highly Scaled HBT UCSB has demonstrated laterally
scaled HBTs with emitters written
by e-beam lithography.
These HBTs show problems with:
High emitter resistance, Rex
Low yield
These devices demonstrated lower than predicted values of f despite aggressive thinning of the epitaxial layers.

5. Si/SiGe HBT Process Advantages
Highly scaled
very narrow active junction areas
very low device parasitics
high speed
Low emitter resistance using wide n+ polysilicon contact
Low base resistance using large extrinsic polysilicon contact
High-yield, planar processing
high levels of integration
LSI and VLSI capabilities
Published Si/SiGe HBT f as high as 210 GHz
InP-based HBT f as high as 341 GHz

6. Polycrystalline n+ InAs
Polycrystalline InAs grown on SiNx Hall measurements as high as:
Doping = 1.3 1019 cm-3, Mobility = 620 cm2/V•s
Results in doping-mobility product of 81021 (V •s •cm)-1
Compare these numbers to InGaAs lattice matched to InP:
Doping = 1.0 1019 cm-3, Mobility = 2200 cm2/V•s
Results in doping-mobility product of 221021 (V •s •cm)-1
Polycrystalline InAs has potential as an extrinsic emitter contact!

7. Base-Collector Template for Regrown Emitter HBT
prior to regrowth
Base-collector template
as-grown

8. Regrown Emitter Fabrication Process
Regrowth
Emitter/cap
etch
Base/collector
etch
Metalization

9. Large-area Small-emitter HBTs

10. First Attempt Results Regrown area very rough Transistor action!!
SiNx
Regrown area very rough
Transistor action!!

11. Growth and Process Improvements
Regrown area
Regrown area
SiNx
SiNx
First attempt at the base-
emitter junction without
RHEED or pyrometer
Second attempt with improved
pre-regrowth processing and
RHEED/pyrometer features
added to the wafer

12. Growth and Process Improvements
First attempt at the base-
emitter junction without
RHEED or pyrometer
Second attempt with improved
pre-regrowth processing and
RHEED/pyrometer features
added to the wafer

13. Base-emitter Regrowth SEM Detail

14. Base-emitter Regrowth SEM
2 μm emitter regrowth
30K magnification
1 μm emitter regrowth
55K magnification

15. Second Attempt DC Results
Unintended InAlAs Layer (>50Å)
wide-bandgap layer acts as a current block from emitter to base
reduces common-emitter gain
may account for the dip in common-emitter curves
Common-emitter gain, β > 15

16. Base-emitter Current Leakage
Evidence of resistance seen in the base-emitter diode
Evidence of base-emitter leakage seen in Gummel

17. Third Attempt DC Results
Common-emitter gain, β > 20

18. Base-collector Grade Design Error
InP collector
InP collector
InGaAs
base
InGaAs
base
Base-collector band diagram with
the incorrect base-collector grade.
This mistake may account for the
oscillations seen in the HBT I-V curve.
Base-collector band diagram with
the corrected base-collector grade.
A thin, heavily-doped layer was
inserted between the grade and
collector to pull the conduction band
down at the grade-collector junction.

19. Regrowth with Buried Base Contact

20. InP HBTs with polycrystalline InAs extrinsic emitter regrowth
Objective:
Emulate high-yield 0.2 um SiGe emitter process
Polycrystalline extrinsic emitter  wide contact for low resistance
Future Work:
RF devices need to be designed and demonstrated
GaAsSb based DHBTs should be demonstrated
Higher scaling in the regrown emitters needs to be examined
Growth Related Work:
A low-resistance p-type polycrystalline contact needs to be verified
Regrowth of the base will need to be explored to obtain a fully planar HBT completely analogous to the Si/SiGe HBT

21. InP HBTs with polycrystalline InAs extrinsic emitter regrowth
Objective: Emulate high-yield 0.2 um SiGe emitter process Polycrystalline extrinsic emitter  wide contact for low resistance
Future Work (short-term): Improve DC characteristics Improve base capping layer to lower extrinsic base resistance GaAsSb base layers for higher carbon incorporation Deep submicron scaling of regrown emitter RF device demonstration
Future work (long-term): full SiGe-like process flow for submicron InP HBT regrown emitter, regrown extrinsic base over buried dielectric spacer for Ccb reduction

22. Future Work DC Device Work:
DC characteristics should be demonstrated without the design errors
Improvements will be made to the base capping layer to lower extrinsic base resistance
GaAsSb based DHBTs should be demonstrated
Higher scaling in the regrown emitters needs to be examined
RF Device Work:
RF devices need to be designed and demonstrated
Growth Related Work:
A low-resistance p-type polycrystalline contact needs to be verified
Regrowth of the base will need to be explored to obtain a fully planar HBT completely analogous to the Si/SiGe HBT