Ab initio and experimental studies of polarization and polarization related fields in nitrides and nitride structures

Abstract

Spontaneous and piezoelectric polarization in the nitrides is analyzed. The slab model was designed and proved to be appropriate to obtain the spontaneous polarization in AlN, GaN and InN. The spontaneous polarization and polarization related electric fields in AlN, GaN and InN were determined using DFT slab calculations. The procedure generates single value of spontaneous polarization in the nitrides. It was shown that Berry phase polarization may be applied to determination of spontaneous polarization by appropriate addition of polarization induced electric fields. The electric fields obtained from slab model are consistent with the Berry phase results of Bernardini et al. The obtained spontaneous polarization values are: 8.69*10-3 C/m2, 1.88*10-3 C/m2, and 1.96*10-3 C/m2 for AlN, GaN and InN respectively. The related Berry phase polarization values are 8.69*10-2 C/m2, 1.92*10-2 C/m2, and 2.86*10-2 C/m2, for these three compounds, respectively. The GaN/AlN multiquantum wells (MQWs) were simulated using ab intio calculations. The obtained electric fields are in good agreement with those derived from bulk polarization values. GaN/AlN MQWs structures, obtained by MBE growth were characterized by TEM and X-ray measurements. Time dependent photoluminescence measurements were used to determine optical transition energies in these structures. The PL obtained energies are in good agreement with ab initio data confirming overall agreement between theoretical and experimental data.

Electrical Polarization in AlN/GaN Nanodisks Measured by Momentum-Resolved 4D Scanning Transmission Electron Microscopy

“…The difference to the measured value of 5.3 MV=cm can be partially explained by (plastic) strain relaxation as observed previously [17]. Similar discrepancies have been reported by Strak et al [30], where ab initio calculations gave polarization-induced fields of 7.7 MV=cm, whereas photoluminescence results yielded only 4.5 MV=cm and the evaluation of the Berry phase provided field strengths between 5 and 6.7 MV=cm [30,31]. In addition, the measurement of internal electric fields is affected by mobile screening charges due to (unintentional) doping [32] or charges generated by the electron beam [33].…”

Critical Evaluation of Various Spontaneous Polarization Models and Induced Electric Fields in III-Nitride Multi-Quantum Wells

“…The calculation method in both papers is the same, based on the Berry phase approach, but they used different reference systems. Then, in our earlier reports, we proposed a new method of calculation of the spontaneous polarization without using any reference structure [ 22 ]. Thus, three different sets of values of spontaneous polarization in III-nitrides exist.…”

Investigation of the electron-acoustic phonon interaction via the deformation and piezoelectric potentials in AlN/GaN resonant tunneling nanostructures

“…where ( ) 1 ( ), ( ) 2 ( ), ( ) 3 ( ) -are the elastic displacement vector components, defined in separate nanosystem -th layer and it is taking into account that the electric field in our case has only one nonzero component. Now using expression (10), the system of differential equations ( 9) written for separate -th layer of the nanostructure is obtained as it follows:…”

“…-∞ is the high frequency dielectric constant, and -are the frequencies of the longitudinal and transverse modes of optical phonons respectively, defined in the vicinity of a Γ-point as irreducible representations 1 ( ) and 1 ( ) [13,24,25]. Taking into account (10), (12) from the system of equations (11) we obtain:…”

“…For RTS created on the basis of Group III Nitrides an important role is played by the effects of the potential profile deformation of such nanostructures by an internal electric field, which is a consequence of the arising spontaneous and piezoelectric polarizations [7][8][9][10]. Regarding the influence of the potential associated with the piezoelectric effect, such related problem was solved only numerically [11], using the finite difference method in order to study the thermal conductivity of a single-layer GaN nanofilm.…”