1. Wide Bandgap Semiconductors What is a wide bandgap semiconductor? Larger energy gap allows higher power and temperature operation and the generation of more energetic (i.e. blue) photons The III-nitrides (AlN, GaN and InN), SiC have recently become feasible. Other materials (like diamond) are being investigated. What are they good for?

2. WBG nitride for photonics 2.62.83.03.23.43.63.84.0 1 2 3 4 5 6 7 o InN GaN AlN Band Gap Energy (eV) Lattice Constant a (A) Visible light UV IR 1.95ev 3.4eV 6.2eV

3. Market for III-Nitride Devices  Blue / UV solid state diodes and lasers  UV optical detectors  High power microwave devices  High power switches  High temperature devices  High density data storage devices Additional Specialty Applications:  Surface acoustic wave (SAW) devices (for wireless communication)  High thermal conductivity substrates

4. Impact Automotive industry Avionics and defense Traffic lights Solid state lighting Electric power industry Health care Information technology (data storage) Wireless communications Displays

5. The Market for GaN Devices From Strategies Unlimited (1997) Nichia estimates that the LD market alone will be worth $10B.

6. Violet Laser Diode Nichia announced commercial release of VIOLET LASER DIODE (Model No.NLHV500A) on October 1, 1999 Costs $2000 apiece.

7. Possible new applications Smart power controls Smart cars Smart manufacturing Smart transportation Smart house (energy management) Information technology Displays Solid state lighting Medicine Defense SiC and GaN- based switches SiC and GaN- based sensors SiC and GaN- non-volatile memories GaN-based light emitters GaN-solar blind detectors

8. Solid State Lighting GaN-based solid state display lighting is nearly an order of magnitude more efficient than incandescent lamps and twice as efficient for general lighting. Practically does not require replacement. Will affect the energy industry, construction, automotive, and avionics applications.

9. Compact power switches Compact efficient power switches for power distribution, automotive, avionics, and industrial applications. These switches should allow energy savings up to 10%. This may allow us to avoid the deployment of new power plants, cut our dependence on imported oil, and improve reliability of power distribution in order to minimize blackouts during natural disasters. Example of research by WBS faculty: M. S. Shur, SiC Transistors, in "SiC Materials and Devices", ed. Y. S. Park, (1998), Academic Press; see also http://nina.ecse.rpi.edu/shur/GaN.htm

10. UV detectors and sources UV sources and sensitive and fast UV detectors for applications in medicine, biology, chemical industry, and defense. Example of research by WBS scientists: M. S. Shur and M. A. Khan, GaN and AlGaN Ultraviolet Photodetectors, Academic Press, T. Moustakos and J. Pankove, Editors (1998) see also http://nina.ecse.rpi.edu/shur/GaN.htm

11. Flat panel, high-resolution low power displays for computer and medical applications. Example of research by WBS scientists: M. S. Shur, M. D. Jacunski, H. Slade, and M. Hack, Analytical Models for Amorphous-Silicon and Polysilicon Thin-Film Transistors for High Definition Display Technology, in Journ. Society for Information Display, vol. 3, No. 4, pp. 223-236, Dec. (1995) 8 mm Prototypes: Toshiba displays for billboards Sharp displays for Pachinko

12. Non-volatile solid state memories These memories will make hard drives obsolete and revolutionize banking, medical record-keeping, and information storage. After W. Xie, J. A. Cooper, Jr., M. R. Melloch, J. W. Palmour, and C. H. Carter, Jr., " IEEE Electron Device Lett., 15, 212 (1994).

13. Flat panel, high-resolution low power displays for computer and medical applications. 8 mm Prototypes: Toshiba displays for billboards Sharp displays for Pachinko

14. Wireless Applications AlN attractive for surface acoustic wave devices due to large piezoelectric effect. Sound velocity 10x materials currently used.

15. Laser Diode for Mass Data Storage Optical Data Storage Market will use over 300M LDs in 1999 (Compound Semicond., March 1999) HD-DVD will use GaN or SHG laser; will dominate future market with 15GB capacity or greater Market expects laser cost to be approx. $10 but current cost ~$2000.

16. Light-emitting Diode (LED) First visible LED Blue LED

17. Traffic Lights One of the first applications of the new nitride semiconductor technology. The Green light uses 10% of the power and last more than 10x longer.

18. a Philips Lighting and Agilent Technologies joint venture that's changing the future of light. In the next century, LED-based lighting will quickly replace conventional lighting in a wealth of commercial, industrial and consumer applications. LumiLeds‘ LED-based solutions will bring irresistible value to lighting solutions of all kinds, earning us a leadership position in a fast-growing and lucrative marketplace. Our long- lasting, energy-efficient products will also improve the planet, by reducing waste and power consumption.

19. How does a semiconductor laser work?

20. Absorption and Emission E o E 1 photon out photon in

21. Stimulated vs. Spontaneous Emission E o E 1 photon in Spontaneous photon out Stimulated

22. Stimulated vs. Spontaneous Emission (Cont.) Derived in 1917 by Einstein. (Required for thermal equilibrium was it was recognized that photons were quantized.) However, a “real” understanding of this was not achieved until the 1950’s.

23. Population Inversion by Photopumping

24. Biased junction n-type p-type depleted region (electric field) Negative bias photon out

25. History of Lasers  First operating Laser in 1960 (Maser in 1958)  Simulated emission concept from Einstein in 1905  Townes (1964) and Schawlow (1981)  First solid-state injection Laser in 1962  First was Robert Hall but many competing groups  Year before he had argued it was impossible

26. Violet Laser Diode

27. Nichia Laser Diode Epitaxial Lateral Overgrowth material 10,000 hours operation!

28. Other Applications for Wide band gaps  High Power devices  Large band gap allows semiconductor to be used at high voltages  Generally larger band gap means stronger bonds so material can withstand higher currents and temperatures  High Temperature devices  Much smaller effect of thermal excitation of carriers  Tougher material

29. What are the hot research topics?  How can the lifetime of the lasers be improved?  improved growth  improved substrates  improved devices  What is the role of defects?  Very high field transport  Quantum Confinement

30. Quantum Wells

31. Quantum Mechanics Probability density given by Schroedinger’s Equation: where

32. Quantum Mechanics (cont.) Main point is that energy levels are Quantized! Well defined energy level even at room temperature.