Abstracts Book - IMRC 2018

• SD4-O005 Invited Talk
STRUCTURE VARIATIONS AND DEFECT IDENTIFICATION IN GaN-
BASED HETEROSTRUCTURES
Petra Specht 1
1 University of California, Berkeley, MSE, United States.
GaN-based devices are utilized for a variety of electronic applications: in
transistor technology, as power switches, in light emitting diodes, photodiodes
or sensors. The growth and device process of such hetero-structured materials,
however, is still quite challenging as strain accumulation due to lattice
mismatched systems and the influence of residual dislocations among other
defects affect interface abruptness, dopant homogeneity and the incorporation
of native point defects. Any of those material changes will also change the
devices’ performance, resulting in distinct device reliability issues. Device
optimization for any such device structure requires imaging techniques which
maintain original, often highly defective device areas, at heterostructure
interfaces, in the vicinity of metal contacts or otherwise locally strained, selected
material areas. We report on TEM investigations of specific areas in GaN-based
device structures, covering AlGaN/AlN multi quantum well structures, Mgimplanted
GaN quasi-substrates as well as metal contact / epilayer interfaces. A
focus area of this research is to understand the underlying basic physical
phenomena which result in device reliability issues, and to counter-act them if
possible. For these, often highly complex material systems TEM sample
preparation which maintains the areas of interest in their pristine condition is
demanding. The technique of choice is usually a focused ion beam cross section
followed by a low voltage Ar ion mill (Nanomill, Fischione), to carefully thin and
clean the FIB-induced damaged surface areas. Here, imaging is performed in low
dose HR-TEM, utilizing a Nelsonian illumination scheme [1], in an aberrationcorrected
microscope with monochromated electron beam (TEAM, FEI). HR-TEM
is complemented by chemical analysis (EDS) in aberration-corrected STEM mode
as well as low loss EELS in a monochromated TEM. Damaged areas the latter
techniques are either removed by additional thinning prior to performing HR-
TEM, or such techniques are used as a last investigation step, after HR-TEM is
completed. Observations include the in-situ formation of MgO clusters in Mgimplanted
GaN at higher electron doses (around 300e - /Å 2 ), simultaneous
identification of nitrogen bubbles in annealed GaN:Mg, inter-diffusion in
AlGaN/AlN multi quantum wells, evidence of native point defects accumulated
along specific interfaces in proton-irradiated AlGaN/GaN:Si HEMTs and the