Stacking faults are local zinc-blende (cubic close-packed lattice) modifications in a wurtzite matrix (hexagonal close-packed lattice) and can be considered as quantum wells due to a difference in the energy gaps of the two phases and a band-offset between the two phases. Cathodoluminescence spectroscopy and imaging in a scanning electron microscope is used to assess the optical emission of such quantum wells of different thickness, i.e. different stacking fault types, on the cross-sections of GaN microcrystals.
The spontaneous polarization of the zinc-blende phase vanishes as a result of the higher symmetry of this phase, and the misfit strain at the wurtzite/zinc-blende interface is negligible. Therefore, stacking faults are an ideal system to study the spontaneous polarization of the wurtzite phase. Using Poisson-Schrödinger calculations and density functional theory, it is shown that the change in the emission energy as a function of thickness is governed by the spontaneous polarization, thereby allowing for a deduction of an experimental value for the spontaneous polarization of GaN by treating the stacking faults as plate capacitors. Our obtained value for the spontaneous polarization of GaN is (-0.022+/-0.007) C/m². This approach should be applicable also to other important wurtzite materials such as SiC and ZnO.
|1||Author||J. Lähnemann , O. Brandt , U. Jahn , C. Pfüller , C. Roder , P. Dogan , F. Grosse , A. Belabbes , F. Bechstedt , A. Trampert , L. Geelhaar|
Direct experimental determination of the spontaneous polarization of GaN
|Source||Phys. Rev. B , 86 , 081302(R) ( 2012 )|
: 10.1103/PhysRevB.86.081302 |
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