Raman spectroscopy for dopant optimization in GaN nanowire light-emitting diodes
Kristine A. Bertness, Bryan T. Spann, Matthew D. Brubaker, Todd E. Harvey, Paul T. Blanchard
We apply Raman spectroscopy to optimize both n-type and p-type doping in GaN nanowire light- emitting diodes (LEDs) grown with selective epitaxy on Si(111) with molecular beam epitaxy. N-type doping with Si is characterized using the peak shift in the LO phonon peak due to coupling with carrier plasmon modes. As doping increases beyond concentrations of mid- 1017 cm 3, we find that the assumption of negligible plasmon line width1 begins to fail and estimates based on peak shift alone will underestimate the carrier concentration. We also observe that densely packed nanowires have systematically lower carrier concentration than nanowires grown far apart. The most likely explanation is that Si continues to incorporate from the sidewalls in the absence of shadowing by nearest neighbors. Mg doping for p-type conductivity has been studied with the peak intensity of the local vibrational mode at 655 cm 1 associated with active Mg in thin films.2 We have shown that the high N:Ga flux ratios favored for GaN nanowire growth also enhance the incorporation of Mg (see Fig. 1). Lower growth temperature also enhances Mg incorporation. A convenient nanowire LED geometry is therefore a nanowire with an n-type core surrounded by a p-type shell grown at lower temperature. Electrical measurements on core-sleeve nanowires with semi-insulating cores confirm that the Mg Raman signal, normalized to other GaN peaks and appropriate volume fraction, is a good indicator of electrical conductivity. Nanowire LEDs grown with optimized dopants continue to function down to cryogenic temperatures, another strong indicator of effective doping.
, Spann, B.
, Brubaker, M.
, Harvey, T.
and Blanchard, P.
Raman spectroscopy for dopant optimization in GaN nanowire light-emitting diodes, Nanowire Week Abstract Book, Hamilton, -1
(Accessed September 30, 2023)