Group Meeting Reporter: Welson T.H. Sung Date: 2008/3/5 Topic: Raman and cathodoluminescence study of dislocation in GaN

JOURNAL OF APPLIED PHYSICS [VOLUME 92, NUMBER 11] (2002) H. Leia) and H. S. Leipner Center of Materials Science, Hoher Weg 8, Martin Luther University Halle-Wittenberg, D Halle, Germany J. Schreiber Department of Physics, Friedemann-Bach-Platz 6, Martin Luther University Halle-Wittenberg, D Halle, Germany J. L. Weyher Experimental Solid Physics III, RIM, University of Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands T. Wosin´ ski Institute of Physics, Polish Academy of Sciences, aleja Lotniko´w 32/46, PL Warsaw, Poland I. Grzegory High Pressure Research Center, Polish Academy of Sciences, ulica Sokolowska 29/37, PL Warsaw, Poland

Outline  Motivation  Background info of Sample: GaN  Growth & Etching  Equipment & Method:  Microindenter  Raman&CL  Analyze Spectrum  Conclusion

Motivation  The cause of YL Band (550nm)  Intrinsic defects V Ga, dislocation  Impurity( Oxygen, Carbon)  For my further work of analyzing pillar’s spectrum

Background info of Sample: GaN  Growth: N-polar(0001), Wurtzite structure, 250~350 o C  Compress: Vickers, 2N, 1~20mins ( Stress induce fresh dislocation )  Etching: 200~250 o C, KOH-NaOH ( Intrinsic dislocation )

Equipment & Method  Micro-Raman:  Laser source: 632.8nm( green), 1um spot, 0.1cm -1  CL:  10K (For increase radiation free electron, decrease thermal radiation)  SEM-JSM6400 ( 20kV)

Phonon-Plasmon mode  C 6v space group(#183 P6mm)  8 phonon modes:  E 2 X2 (Stress free 567cm -1 )  A 1 (TO) (518cm -1 ) LOPP -1  E 1 (TO) (740cm -1 ) matrix  B 1 X2  A 1 (LO)  E 1 (LO)  Energy transmit between Raman and Lattice vibration

Analyze Spectrum

 Intensity decrease from 1 to 4

Comparision (Near center)  Curves 1 (intensity X1 ) & 2(intensity X2.3 )  C1:LPP combine with A1(TO)  C2: Split: Free electron concentration  ( close to center), A1(TO) broad.  Curves 1-3 EF peak  Curves3 & 4 EF blue shifting:  Free electron concentration  X wrong  Compress stress induce

Comparision (Near center)  Curve 4: Broad,weak of peak E 2 (poor order)  Other:  Peak P1 P2: might be phase transformation  (wurtzite => rock-salt structure)  Raman Mapping : (E2 mode peak) compress 1.5GPa Max

Dislocation nonradiative recombination  Intrinsic dislocation etching pit 15um -> larger  -20% compare with Matrix

CL result  Source: 400~1100nm  YL: 550nm  V Ga : N-type native acceptor

CL spectrum Curve 1: intrinsic vacancy Curves 2~6: compress induce dislocations and vacancies(blue shift)

Conclusion  GaN brittle to ductile  V Ga induce edge dislocation jogging  Intensity of radiation:  recombinative recombination at vacancy  nonradiative recombination at dislocations.  Other possibility

Thank You for Your Attention