1. The state-of-art based GaAs HBT
02/20/2015
Shin, SangHoon

2. Contents Background GaAs vs. Si Movement from GaAs to more Examples
Reliability
Conclusion

3. Device structure
Y.C. Chou and R. Ferro

4. GaAs HBT application Commercial and defence application
Wide bandwidth from low (~Hz) to high freq (GHz) (commercial – 30~60GHz)
High power
Microwave application for defense
Frequency-divider circuits

5. Advantage over Si BJT Reduce Base resistance
Collector to substrate capacitance due to semi- insulating GaAs substrate
Less lithography than other structure FETs.
Higher breakdown voltage
Broad-band impedance
Better device linearity due to higher (gain) – IC/IB
Low noise → oscillator application

6. GaAs vs. Si
Otto Berger, GaAs Mantech 1999

7. Hard to find the data after 2000
RF roadmap
GaAs
MOSFET
Otto Berger, GaAs Mantech 1999
Hard to find the data after 2000

8. Move from GaAs to GaAs1-xXx
Biryulin et al (1981)
Temperature dependence of electron Hall mobility for GaAs1-xSbx. Electron concentration no≤5·1016 cm-3. 1. x=  x=0.12.
Lecture note from Prof. Peter Ye

9. Considering lattice constant
μn = 4600 cm2/vs
μn, InGaAs = cm2/vs
μn = cm2/vs
Lattice match is very important for HBT

10. InP-InGaAs Single HBT Layer structure Epitaxial on (100) Fe-doped InP
Walid Hafez, EDL 2003’
Epitaxial on (100) Fe-doped InP
High current fT by scaling layer thickness
High power fmax by submicron lateral scaling
High emitter doping for reducing emitter RP

11. InP-InGaAs Single HBT Fabrication
mesa process for isolation by e-beam and optical contact lithography
Air bridge for air terminal for base
Etching for μ-bridge
E-beam defines emitter region
Etch for emitter
Define base meta (650A Ti-Pt-Au)
Planarization and encapsulation with BCB (bixbe..)
BCB provides structural support
Etch by RIE
Pads are formed

12. InP-InGaAs Single HBT
fmax = 230GHz
fT = 360GHz
VBD = 3.7V

13. Type-II: InP/GaInAsSb DHBT
R Fluckiger, EDL 2014’
Same abrupt blacking transition to InP collectors
Indium portion increase electron mobility p-doped GaAsSb
→ lower base transition time
Graded based GaAsSb (emitter) and GaInAsSb (Collector)
→ Improvement in RF performance

14. Type-II: InP/GaInAsSb DHBT - RF
Find appropriate mobility & doping condition

15. Type-II: InP/GaInAsSb DHBT - DC
fmax = 636 GHz & fT = 424 GHz
Emitter area 0.3 x 0.44 um2

16. Reliability for GaAs HBT
Y.C. Chou and R. Ferro
HBTs typically suffer from current-induced degradation at high-current density operation. Emitter-base and collector-base leakage currents often originate at the surface of the emitter-base and collector-base junctions, respectively.
Thermal and recombination-aided diffusion of crystalline defects from the bulk semiconductor to the hetero interface in abrupt junction HBTs has been suggested to account for increases in base current during burn-in of AlGaAs/GaAs HBTs.
implant-isolated HBTs degrade more than mesa-isolated HBTs
The degradation consisted of a shift in Vbe and a decrease in hFE , apparently resulting from the contact of the emitter-base
Junction edge to the defect-laden implant region. Passivation of the emitter junction is important in mesa-isolated HBTs. The use of depleted AlGaAs has given good results.

17. Conclusion Junction grading is very important.
More high channel material is very important.
MBE technique is very important.
Lattice match is important for grading.
Isolation is important for base and emitter.
Lithography is not very important for HBTs compared to MOSFETs.