Direct experimental determination of the spontaneous polarization of GaN

Abstract

We present a universal approach for determining the spontaneous polarization Psp of a wurtzite semiconductor from the emission energies of excitons bound to the different types of stacking faults in these crystals. Employing micro-photoluminescence and cathodoluminescence spectroscopy, we observe emission lines from the intrinsic and extrinsic stacking faults in strain-free GaN micro-crystals. By treating the polarization sheet charges associated with these stacking faults as a plate capacitor, Psp can be obtained from the observed transition energies with no additional assumptions. Self-consistent Poisson-Schroedinger calculations, aided by the microscopic electrostatic potential computed using density-functional theory, lead to nearly identical values for Psp. Our recommended value for Psp of GaN is -0.022+/-0.007 C/m^{2}.Comment: 5 pages, 5 figure

Unit cell structure of the wurtzite phase of GaP nanowires: X-ray diffraction studies and density functional theory calculations

“…Apart from its sign, this value is only smaller by a factor 2 than that measured for WZ-GaN. 17 As a consequence, a significant internal electric field is expected for quantum well structures, when zinc blende GaP is embedded in wurtzite GaP.…”

“…The influence of the deviations from the ideal bonding tetrahedrons, in particular of u, on the electronic properties of wurtzite materials is hardly understood. Accompanying the symmetry reduction from ZB to the WZ structure it is possible that a spontaneous polarization field 15,16 in the presence of surfaces or interfaces 17 occurs. The strength of the corresponding internal electric field depends on the bond ionicity and the hexagonal crystal field.…”

Correlation between Si doping and stacking fault related luminescence in homoepitaxial m-plane GaN

“…An additional feature at $3.3 eV (PD) known as being related to partial dislocation terminating BSFs 7 was recently assigned to extrinsic BSFs. 18 The intensity of the SF related lines (SF2 and PD) is significantly smaller for point 3, where no visible defects have been observed in SEM.…”

UV Photosensing Characteristics of Nanowire-Based GaN/AlN Superlattices

“…Finally, a variable number of stacking faults at the base of the nanowires could also introduce a dispersion in the transport properties. However, the structural width and conduction band offsets associated to stacking faults, about 0.5-1.5 nm and 0.15-0.27 eV respectively, 35 are negligible in comparison to GaN/AlN heterostructures. In summary, though variations in the diameter, doping density or stacking fault density probably play a certain role, they are neither sufficient to explain the drastic (five orders) variations in dark current levels that we observe, nor could they account for the significant increase in photosensitivity at low dark current levels.…”