1. Gallium Nitride Research & Development Rakesh Sohal
Presented by
Rakesh Sohal
Supervision
Prof. Dieter Schmeißer

2. Outline GaN - Research & Development Introduction GaN - Physics
Crystal Growth
MOVPE
MBE
Substrates & Buffer layers
Recent Advances
Applications

3. Why GaN ? GaN - Research & Development
Semiconductor with Direct and Wide Bandgap
Optoelectronics Devices
Blue & Blue/green light emitters
Transistors withstand extreme heat and
High frequencies and power levels
More efficient amplifiers at base stations
Si-only 10% power used and 90% wasted as heat

4. GaN Physics GaN - Research & Development Crystal Structure a
Zince Blende
Wurtzite

5. GaN - Research & Development
GaN Physics
Energy band Structure

6. GaN comparison GaN - Research & Development
Silicon cannot provide the power-bandwidth product for military applications

7. GaN-Crystal Growth GaN - Research & Development MOVPE Approach
First epilayer by vapour transport - Murusk and Tietjen (1969)
Growth rate - 0.5µm/min.
High background n-type carrier concentrations ~1019 cm-3
Modern Technique - MOVPE by Nakamura
Key aspect : downward subflow of He and N2
Claim - Improves the interaction of the reactant gases with the substrate
Shortcomings
High Substrate temperature
Thermal mismatch  strain & defects

8. GaN-Crystal Growth GaN - Research & Development MBE Approach
N - supplied by µ-wave plasma excitation provided by compact ECR
Limited N-flux  lower growth rate(GR) ~ 500Å/hr.
GR can be increased by higher power
Degraded Material Quality

9. The most Stringent Issue/Barrier
GaN - Research & Development
GaN-Crystal Growth
Substrates for Epigrowth
Baule Growth efforts are ongoing
Till date - not possible
The only Option - Heteroepitaxy
The most Stringent Issue/Barrier

10. Thermal & lattice mismatch - Strain and Defects
GaN - Research & Development
GaN-Crystal Growth
Substrates for Epigrowth
650nm
AlN BN
MgO
3C-SiC
6H-SiC
GaN
InN
Sapphire
Lattice Constant / Å
Band gap / eV
4.5
5.5
3.5
2.5
1.5
6.5 2 3 4 5
ZnO
Hexagonal
Cubic
Thermal & lattice mismatch - Strain and Defects

11. Thermal & lattice mismatch - Strain and Defects
GaN - Research & Development
GaN-Crystal Growth
Substrates for Epigrowth
Thermal & lattice mismatch - Strain and Defects

12. GaN-Crystal Growth GaN - Research & Development
Interfacial buffer layer
Large lattice and thermal mismatch
Strained and sometime cracked layers
AlN
GaN
- Akashaki
- Nakamura

13. GaN-Advances GaN - Research & Development
Three major hurdles has been cleared
Heteroepitaxy - via buffer layer
Control of n (Si) & p(Mg)-type doping
Reduction in dislocation density
Residual e-concentrations -
--- due to N-vacancies(earlier)
Van de Walle showed - energy required for Nv too high
--- due to O incorporation

14. GaN-Advances GaN - Research & Development Use for patterned SiO2
Robert F. Davis, Proceedings of the IEEE, Vol. 90, No. 6, 2002

15. Comparison - bulbs & LEDs
GaN - Research & Development
Comparison - bulbs & LEDs

16. GaN - Research & Development
New two flow MOCVD
Nakamura‘s Method

17. Pioneer of Nakamura GaN - Research & Development
1989-Started III-V nitride research.
1990-Develops new ‘two-flow’ MOCVD equipment for growth of high quality single crystal GaN layers.
1992-begins to grow InGaN single crystal layers for the production of double heterostructures.
1993-Succeeded in developing a blue LED with a luminous intensity as high as 2cd using III-V nitride materials.
1995-Developed high-brightness SQW structure blue/green LEDs with a luminous intensity of 2 cd and 10 cd, and developed a violet laser diode using III-V nitride materials for the first time.
1996-The first current infection III-V nitride based LDs were fabricated.
1996-Announces the first CW blue GaN based injection laser at room temperature.

18. Steps to grow crystalline GaN
GaN - Research & Development
Steps to grow crystalline GaN
Nakamura‘s Method
The substrate was heated to 1050oC in a stream of hydrogen
The thickness of the GaN buffer layer was varied between 100Å and 1200Å
The substrate temperature was lowered to between 450oC and 600oC to grow the GaN buffer layer.
The substrate temperature was elevated to between 1000oC and 1030oC to grow the GaN film.
The total thickness of the GaN film was about 4 mm,and the growth time was 60 min.

19. Buffer layer thickness
GaN - Research & Development
Buffer layer thickness
The value of the FWHM is almost constant between 200Å and 1200Å thickness.The optimum thickness of the GaN buffer layer was around 200Å

20. GaN - Research & Development
GAN - Potential

21. Applications GaN - Research & Development
Large scale displays (large outdoor television screens)
Smaller full-color flat panel display screens
(inside trains or subway stations)
Full-color scanners
Full-color photocopying machines
Full-color FAX machines
Traffic lights
LED white lamps

22. Applications GaN - Research & Development
2 inch dia blue LED wafer on GaN-on-sapphire

23. Thanks for your attention!
GaN - Research & Development
Thanks
for
your attention!