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

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

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

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

GaN - Research & Development GaN Physics Energy band Structure

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

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

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

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

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

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

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

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

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

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

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

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.

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.

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

GaN - Research & Development GAN - Potential

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

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

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