Stacking Faults Reveal Spontaneous Polarization of Wurtzite Semiconductors

The spontaneous polarization is a fundamental property of wurtzite semiconductors or any other pyroelectric crystal. It results in electric fields in semiconductor heterostructures affecting the design of devices for solid-state lighting or power electronics. However, this quantity is difficult to directly assess experimentally as it manifests itself only at interfaces and, to complicate things, is usually superimposed by the piezoelectric polarization due to misfit-related strain at the interface.

Figure 1 False-color monochromatic cathodoluminescence maps superimposed on the corresponding cross-sectional scanning electron micrograph of a GaN microcrystal. The detected energies are color coded. The cathodoluminescence intensity related to stacking faults shows a characteristic elongation along the basal plane, while the upper part of the crystal exhibits luminescence at the energy known for strain-free bulk material.

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.

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1	Author	J. Lähnemann , O. Brandt , U. Jahn , C. Pfüller , C. Roder , P. Dogan , F. Grosse , A. Belabbes , F. Bechstedt , A. Trampert , L. Geelhaar
	Title	Direct experimental determination of the spontaneous polarization of GaN
	Source	Phys. Rev. B , 86 , 081302(R) ( 2012 )
DOI : 10.1103/PhysRevB.86.081302 \| Download: PDF \| 2267 Cite : Bibtex RIS @article{ author = { J. Lähnemann and O. Brandt and U. Jahn and C. Pfüller and C. Roder and P. Dogan and F. Grosse and A. Belabbes and F. Bechstedt and A. Trampert and L. Geelhaar }, title = { Direct experimental determination of the spontaneous polarization of GaN }, journal = { Physical Review B: Solid State }, volume = { 86 }, year = { 2012 }, pages = { 081302(R) } } J. Lähnemann, O. Brandt, U. Jahn, C. Pfüller, C. Roder, P. Dogan, F. Grosse, A. Belabbes, F. Bechstedt, A. Trampert, and L. Geelhaar TY - JOUR AU - J. Lähnemann AU - O. Brandt AU - U. Jahn AU - C. Pfüller AU - C. Roder AU - P. Dogan AU - F. Grosse AU - A. Belabbes AU - F. Bechstedt AU - A. Trampert AU - L. Geelhaar TI - Direct experimental determination of the spontaneous polarization of GaN JF - Physical Review B: Solid State JA - Phys. Rev. B J1 - VL - 86 SP - 081302(R) PY - 2012/08/09

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Stacking Faults Reveal Spontaneous Polarization of Wurtzite Semiconductors

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