1. Intelligent Epitaxy Technology, Inc.
Presentation: SMU EE 5312/7312 Class
Band Gap Engineering
for
Heterostructure Devices
Grown by
Molecular Beam Epitaxy (MBE)
18 October 2006

2. Outline Band Gap Engineering & Molecular Beam Epitaxy (MBE)
Company profile & product mix
Company technology
Selected Applications of compound semiconductor
HBT for high speed electronics
BandProf* demonstration/open discussion
*BandProf is a Java based device simulation software developed by Prof. Frensley at UT Dallas.

3. Compound Semiconductor Band Gap Engineering
Band Gap vs. Lattice Constant
Example of
Epi structure
VCSEL
Band Gap Engineering: Altering properties of layered epitaxy materials while maintaining crystalline lattice registration
Band gap
Band alignment
Dielectric constant
Thermal conductivity
3rd degree of freedom for device design based Heterojunction concept!

4. IntelliEPI : MBE Technology for III-V Compound Semiconductor
MBE System
Substrate
Platen
Materials Capability
Substrate: GaAs, & InP
Group III: Al, Ga, & In
Group V: As, P, Sb, & N
N-type Dopant: Si
P-type Dopant: Be, & C (from CBr4)
Molecular
Beam Fluxes
Deposition
Source Materials
UHV Growth Chamber
Molecular Beam Epitaxy (MBE)
Impinging molecular/atomic beam fluxes are the precursors for the epitaxy growth process
Epitaxy growth process maintain lattice registration along the growth direction
MBE process grows each atomic monolayer at a time
Ultra high vacuum growth chamber: Torr base pressure
Growth of customized active device/structure on top of crystalline substrate
Peanut butter and Jelly analogy.

5. IntelliEPI: Thickness Uniformity Across Platen for 7x6” MBE
Riber 7000 thickness uniformity
measured by white light reflection
Center wafer
Outside wafer
7X6” platen
2,500Å GaAs
2,000Å AlAs
GaAs substrate
Thickness variation across platen < 1% across 7X6” platen configuration
Si doping GaAs layer uniformity by contactless resistivity mapping:
6” wafer doping variation < 1%
Difference from center wafer to outside wafer < 0.5%

6. Overview of IntelliEPI in-situ Sensor Technologies
Substrate temperature
Pyrometry
Absorption Band-Edge Spectroscopy (ABES): band-gap dependence on temp
Materials composition
Optical-based Flux Monitor (OFM): atomic absorption of group III fluxes
Growth rate
Optical Reflectometry
Pyrometric Interferometry
ABES light source:
Light pipe, or
Heater filament
Optical Pyrometer
OFM
Optical Reflectometry
OFM setup
Absorption Band-Edge Spectroscopy,
Pyrometer, and
Laser Reflection.

7. PHEMT In-situ Composition Monitoring with OFM
PHEMT Structure
OFM Profile During PHEMT Growth
InGaP
Etch
Stop
InGaAs
Channel
Si - delta
AlGaAs
Gate
GaAs/AlGaAs SL
Direct composition monitoring for each critical layer
In-situ composition monitoring for key layers:
InGaAs Channel: Accurate x-ray measurement
AlGaAs Gate: X-ray represents average of SL and Gate
InGaP Etch Stop: Very thin layer limits x-ray accuracy

8. Absorption Band-Edge Spectroscopy (ABES)
Light from heater
or light source
Transmitted light
Through substrate
Substrate
~500 um
EPI
~1 UM c
Transmitted light has photon energy smaller than substrate band gap
Input light at different photon energies v
ABES measures transmission of light through the substrate
EPI material not the dominate effect when:
EPI material is not too thick
EPI material has larger band-gap than substrate
Substrate semiconductor band-gap shrinks with increase substrate temperature

9. IntelliEPI: ABES Temperature Measurement
InP Band-edge transmission spectra
Band-edge wavelength vs. temperature
Determine substrate temperature by monitoring shift in substrate band gap as a function of temperature.
Measurement range extends to substrate temperature well below the operating range of optical pyrometer.

10. C-doped InP-DHBT: Temperature and Group III flux control
In-situ flux profile and substrate temperature during growth
InP Collector
InP Emitter
InGaAs Base
Data from Riber6000
Control of temperature & composition profile critical for HBT device parameters such as beta, Vbe, Rbs
Substrate temperature: measured by ABES
Group III fluxes: measured by OFM

11. IntelliEPI: InP HBT Large Area Device Processing
InP/InGaAs SHBTs & DHBTs
InP/GaAsSb/InP DHBTs
Be or Carbon-doped base
2E19 to 1E20 cm-3 base doping

12. Communications Technology Evolution
III-V semiconductors
from elements of group III and group V columns of Periodic Table
InP and GaAs are key enabling technology for all communications systems
Wireless, telecomm, satellite, fiber optics, and other high frequency systems such as collision warning radar system all require faster semiconductors like GaAs and InP
InP outperforms all existing RF/telecomm technology in terms of speed
Wireless from 2GHz to 300 GHz with 2x breakdown voltage vs. SiGe, high gain, better efficiency
Current fasted flip-flop speed at 150 GHz (from IntelliEPI/Vitesse) vs. 96GHz of SiGe

13. Competing Building Blocks - Fiber optic network example
Internet is the main driving force
data, speed, bandwidth, wireless
Both long-haul and local networks shift to fiber optic networks
Current 2.5Gbps networks will be replaced by 10Gbps (OC192) GaAs is the major semicon building block
40Gbps network will be the 2nd largest in 2005 and will be dominated by InP
Silicon will be dominant for market adoption in the “late majority” and “laggard” phases
Fiber optics industry major recovery expected in

14. High Speed Technology Race
InP Heterojunction
Bi-Polar Transistor (HBT)
W. Hafez, et al, IEEE Elect. Dev. Lett., Vol 24, #7, pg 346, July 2003.
*Partial slide Source: N. Pan, UCLA.

15. Divide by Two Circuit operating at 152 GHz!
IntelliEPI supplied materials.
Static digital flip-flop circuit fabricated by Vitesse using VIP-2 process (InP DHBT)
*Data courtesy of Vitesse Semiconductor for DARPA-TFAST program.

16. Summary of Key Concepts
Band gap engineering enable the additional degree of freedom along the growth direction
MBE: ultra high vacuum deposition/crystal growth process
Compound semiconductor suited for high speed applications due to fast intrinsic electron mobility
PHEMT analogous to FET
HBT analogous to Si Bi-Polar Junction Transistor (BJT)