Polar Properties of BeO Single Crystals

Abstract

Piezoelectric, dielectric, and pyroelectric measurements were made on hexagonal BeO crystals grown in molten lithium molybdate flux. The piezoelectric constant d33∼0.24×10−12 C/N, ε33T/ε0∼7.6, and the average free pyroelectric constant in the range −196° to 25°C is −3.4×10−10 C/cm2 °C. The sound velocity perpendicular to the polar axis is 12 000 m/sec. Although no absolute identification of crystal planes was made, it was concluded from the sign of the piezoelectric constant d33 that the oxygen side of the closely coupled Be—O layer is that of principal growth and etch. Polarity of the crystal structure is reflected in typical crystal growth habits and in characteristic etch patterns which are described.

Polarization doping of graphene on silicon carbide

“…The spontaneous polarization (which is a bulk property) leads to a polarization charge on the polar surfaces of hexagonal semiconductor compounds, such as SiC and GaN, which is usually compensated by internal charge formation due to depletion/accumulation of charge carriers or by external buildup of ionic charge on the surfaces. Only the modulation of the polarization charge at a surface upon an external perturbation can be measured [24][25][26], making the effect itself difficult to address experimentally. The existence of various SiC polytypes offers an excellent opportunity to address the question.…”

Origin of Doping in Quasi-Free-Standing Graphene on Silicon Carbide

“…It essentially leads to effective surface charges on the polar surfaces of the semiconductor compounds which are usually compensated completely or in part by internal charge formation due to depletion or accumulation of charge carriers or by external build-up of ionic charge on the surfaces. Only the modulation of the effective polarization charge at a surface upon an external perturbation like strain, temperature variation or the presence of optical phonons can be measured [11][12] [13], but not its base value. As a consequence, no experimental data are available for the polarization of any hexagonal semiconductor crystal.…”

Chemical design of a new displacive-type ferroelectric

“…and compared the results with those for other wurtzite compounds. 89 The piezoelectric coefficient (d 33 ) values for ZnO, CdSe, CdS, and BeO are 12.0, 7.84, 10.32, and 0.24 pC N −1 , respectively. Piezoelectric coefficients of wurtzite-type GaN and AlN have been reported to be 4.0 90 and 5.1 pC N −1 , 91 respectively.…”