Wide Bandgap Semiconductors What is a wide bandgap

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 (Al. N, Ga. N and In. N), Si. C have recently become feasible. Other materials (like diamond) are being investigated. What are they good for?

WBG nitride for photonics Band Gap Energy (e. V) 7 6. 2 e. V Al. N 6 5 4 3 UV 3. 4 e. V Ga. N Visible light 2 1. 95 ev In. N IR 1 2. 6 2. 8 3. 0 3. 2 3. 4 3. 6 o Lattice Constant a (A) 3. 8 4. 0

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

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

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

Violet Laser Diode Nichia announced commercial release of VIOLET LASER DIODE (Model No. NLHV 500 A) on October 1, 1999 Costs $2000 apiece.

Possible new applications • • • Si. C and Ga. Nbased switches Smart power controls Smart cars Smart manufacturing Si. C and Ga. NSmart transportation based sensors Smart house (energy management) Si. C and Ga. NInformation technology non-volatile memories Displays Ga. N-based light emitters Solid state lighting Medicine Ga. N-solar blind Defense detectors

Solid State Lighting • Ga. N-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.

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, Si. C Transistors, in "Si. C Materials and Devices", ed. Y. S. Park, (1998), Academic Press; see also http: //nina. ecse. rpi. edu/shur/Ga. N. htm

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, Ga. N and Al. Ga. N Ultraviolet Photodetectors, Academic Press, T. Moustakos and J. Pankove, Editors (1998) see also http: //nina. ecse. rpi. edu/shur/Ga. N. htm

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

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).

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

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

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

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

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 10 x longer.

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. Lumi. Leds‘ 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 longlasting, energy-efficient products will also improve the planet, by reducing waste and power consumption.

How does a semiconductor laser work?

Absorption and Emission E 1 photon in photon out Eo

Stimulated vs. Spontaneous Emission Spontaneous Stimulated E 1 photon in photon out Eo

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.

Population Inversion by Photopumping

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

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

Violet Laser Diode

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

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

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

Quantum Wells

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

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