Strain Relaxation in Metamorphic Buffer Layers, Millunchick, DMR-0092602

• Metamorphic buffer layers have a range of lattice constants that relax the stress due to lattice mismatch in semiconductor heterostructures without degrading the crystalline quality of the active region.

• We investigate the strain relaxation in GaAs0.5Sb0.5/GaAs films and show that dislocation interactions play an important role. As a result of this insight, we are able to predict the linear dislocation density nondestructively.

• Also, we show that the glide velocity has a weak temperature dependence, contrary to conventional wisdom, indicating that other mechanisms, such as roughening, contribute to the strain relaxation.

GaAs0.5Sb0.5/GaAsT=470C

Figure 1: Strain relaxation for a GaAs0.5Sb0.5/GaAs film grown at T=470C (black points) and a fit (red line) using the Dodson Tsao model taking dislocation interaction into account.

Thickness (A)

Str

ain

Re

laxa

tion

Figure 2: Arrhenius plot of the fitting parameters for the stress evolution model of GaAs0.5Sb0.5/GaAs films grown 440<T<505C.

Self Assembled Templates in Strained Semiconductor Films, Millunchick, DMR 0104509

• The morphology of strained semiconductor layers plays an important role in the development of the final microstructure of a multilayer film and may act as a template for subsequent growth.

• We examine the morphology of these very thin intermediately strained layers in order to understand how their morphology develops. For example, GaAs surfaces are rougher, more anisotropic, and correlated along the [110] direction compared to AlAs, despite their having the same lattice mismatch. We are modeling this behavior in collaboration with groups at UCLA and University of Michigan in order to understand its origin.

• The ultimate goal of this research is to engineer these templates to direct the self assembly of nanostructures.

a)

b)

c)

Sa= 1.3 Å

Sa= 0.9 Å

In situ Scanning Tunneling Micrographs of 2 monolayer thick films of GaAs (top) and AlAs (bottom) grown on In0.53Ga0.47As/InP under similar growth conditions. Also shown to the left of the images are the autocorrelation maps (top), angular spectra (bottom), and average roughness, Sa, of the films.

Girls In Science and Engineering (GISE):Outreach to middle-school-aged girls

Campers measure out ingredients of nail polish

Grad student Jenny Lee assists a camper with beadmaking

Finished beads

MIllunchickDMR 0092602DMR 0104509

Campers assemble and test their lava lamps

Scientific and Technical concepts :•Adhesion and wear•Phase transitions•Glass transition temperature•Viscosity•Microstructure•Microscopy•Miscibility•Thermal conductivity•Thermal stress•Electricity

Activities:•Designed and Tested microfluidic chips with different liquids•Made glass beads•Made nail polish•Built lava lamps

•Top Row, left to right: Jessica Bickel (grad), Lee (Trey) Sears (grad), Darius Dixon (grad), Hugh McKay (post doc), Associate Professor Chris Pearson (UM Flint) •Bottom row, left to right: Benny Perez (grad), Jenny Lee (grad), Associate Professor Joanna Mirecki Millunchick

Diversity in the Mirecki Millunchick Research Group

MIllunchickDMR 0092602DMR 0104509