Nitrides Seminar - Dr. Micha Fireman, Postdoctoral Researcher

2/16/2017 12PM ESB 1001

 

III-Nitride materials for optoelectronic devices have been largely driven by the large range of bandgap afforded.  However, the lattice mismatch which exists between the binary endpoints of the system, 2.4% of AlN on GaN and 11.0% InN on GaN, place limits on the attainable compositions and layer thicknesses of fully strained heterostructure designs.  The onset of strain induced defects, primarily misfit dislocations (MDs), detrimentally traps charge carriers and presents a large obstacle to device design.  In this talk, I present the results of strained and strain compensated superlattices (SLs), on m-plane (10-10) non-polar GaN substrates by Ammonia Molecular Beam Epitaxy (NH3-MBE).  A low temperature, N-rich growth regime is achieved on this orientation that affords a step-flow growth mode for both InGaN and AlGaN.  High Resolution Xray Diffraction (HRXRD) and Cathodoluminscence (CL) clearly show the formation of coherent SLs, with MDs to relieve the increasing strain in AlN/GaN, AlGaN/GaN and InGaN/GaN superlattices.  To avoid the formation of MDs, a third SL system is investigated using alternating layers of tensile strained AlGaN and compressive strained InGaN.  At the correct strain compensated compositions, SL structures of 3.6 nm Al0.2Ga0.8N and 3.6 nm In0.06Ga0.94N, of 20 periods show no MD by CL.  Further characterization by Atom Probe Tomography (APT) confirms the interfacial abruptness and homogeneous alloy composition of all SL structures investigated regardless of MDs.   Strain compensated SLs have interesting potential device applications which will be further discussed, a result of the ability to grow thick SL regions while minimizing the risk of strain induced defects.

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