Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group GaN based Blue Laser diode ECE 355 presentation Seiyon Kim Dept of ECE and Microelectronics Lab Advanced Processing and Circuits Group Electrical and Computer Engineering University of Illinois at Urbana Champaign Outline Motivation Why we need BLUE lasers Material property GaN vs other wide bandgap materials Growth Techniques Dislocations Blue LD InGaN multi quantum well structure Future research Conclusion Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group Why BLUE Laser laser printing smaller optics larger depth of field high density optical storage 630 650nm 4 7GB 400 430nm 20 50GB projection display replace halide lamp spectroscopy sensing Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group Why GaN devices SiC GaP indirect bandgap II VI short lifetime 1 100hrs GaN high efficiency in spite of much more dislocations than II VI 1010 103cm 2 Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group How to grow GaN No GaN substrate large lattice mismatch bad quality Substrate Sapphire 13 SiC 3 5 Spinel Mg2Al4O 9 5 Si GaAs ZnO Equipment MOVPE TMGa NH3 MBE HVPE Method two step growth buffer growth epitaxial layer ELOG epitaxially laterally overgrown GaN PE pendeoepitaxy Electrical and Computer Engineering University of Illinois at Urbana Champaign ELOG Growth fewer dislocation 107 cm 2 LD lifetime enhanced 2500hrs Advanced Processing and Circuits Group Advanced Processing and Circuits Group Electrical and Computer Engineering University of Illinois at Urbana Champaign Bulk GaN TDI October 2001 First bulk GaN How to make they never tell us 1 5 inch diameter Lower dislocation density than conventionally grown GaN 3 4 inch commercial wafer expected in 6 months Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group Dislocation One two dimensional structural defect High density in GaN related materials 107 1010 cm 2 Non radiative recombination center Sugahara et al CL TEM Electrically active path of current generate heat cause to fail LD Characterization is not easy generally studied by TEM AFM STM Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group InGaN MQW Laser Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group Future research prolong life time present blue violet 10000hrs blue 500hrs high power LD for DVD 30 40mW and projector 1W reduce cost 5000 now reduce defect density develop better p type ohmic contact growth GaN or AlN bulk p type doping various substrates other than sapphire and SiC Advanced Processing and Circuits Group Electrical and Computer Engineering University of Illinois at Urbana Champaign Conclusion GaN InGaN AlGaN system makes highly efficient blue UV emitting laser diodes There are several growth techniques to grow GaN layer with low defect density to overcome short lifetime of current LDs ELOG Dislocations act as non radiative centers to degrade device performance Advanced Processing and Circuits Group Electrical and Computer Engineering University of Illinois at Urbana Champaign Questions Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group Characterization by Selective Etching Crystalline region removed left dislocations New easy way to count and characterize dislocations high resolution spectroscopy CL NSOM Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group Dislocation as nonradiative center a SEM image bright spot whisker b CL image dark spots nonradiative centers Electrical and Computer Engineering University of Illinois at Urbana Champaign Advanced Processing and Circuits Group Cross sectional CL Smaller bandgap emission larger YL in whisker region