IEEE Standard on Piezoelectricity

The temperature dependence of the piezotronic and piezophototronic effects in a-axis GaN nanobelts from 77 to 300 K is investigated. The piezotronic effect is enhanced by over 440% under lower temp-eratures. Two independent processes are discovered to form a competing mechanism through the investigation of the temperature dependence of the piezophototronic effect in a-axis GaN nanobelts.

Temperature Dependence of the Piezotronic and Piezophototronic Effects in a‐axis GaN Nanobelts

Coupled electro-thermo-mechanical simulation and Raman thermometry were utilized to analyze the evolution of mechanical stress in AlGaN/GaN high electron mobility transistors (HEMTs). This combined analysis was correlated with electrical step stress tests to determine the influence of mechanical stress on the degradation of actual devices under diverse bias conditions. It was found that the total stress as opposed to one dominant stress component correlated the best with the degradation of the HEMT devices. These results suggest that minimizing the total stress as opposed to the inverse piezoelectric stress in the device is necessary in order to avoid device degradation which can be accomplished through various growth methods.

The impact of mechanical stress on the degradation of AlGaN/GaN high electron mobility transistors

We present the results of experimental and theoretical studies of the surface plasmon polariton excitations in heavily doped GaN epitaxial layers. Reflection and emission of radiation in the frequency range of 2–20 THz including the Reststrahlen band were investigated for samples with grating etched on the sample surface, as well as for samples with flat surface. The reflectivity spectrum for p-polarized radiation measured for the sample with the surface-relief grating demonstrates a set of resonances associated with excitations of different surface plasmon polariton modes. Spectral peculiarities due to the diffraction effect have been also revealed. The characteristic features of the reflectivity spectrum, namely, frequencies, amplitudes, and widths of the resonance dips, are well described theoretically by a modified technique of rigorous coupled-wave analysis of Maxwell equations. The emissivity spectra of the samples were measured under epilayer temperature modulation by pulsed electric field. The emi...

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Interaction of surface plasmon polaritons in heavily doped GaN microstructures with terahertz radiation

The effect of metal electrodes on surface acoustic wave (SAW) properties in bulk semi-insulating Z-cut GaN crystal was measured for the first time. A SAW synchronous two-port resonator was used for these measurements. Such SAW parameters as velocity, electromechanical coupling coefficient, and reflection coefficient of a single reflecting strip were determined by matching the measured and calculated amplitude responses of the resonator for aluminum and gold electrodes at a frequency of about 240 MHz. It was found that for gold electrodes, the reflection coefficient of a single reflecting strip is much larger compared with that of aluminum. Changes of resonance frequency against temperature were measured in the temperature range from -20 °C to 80 °C and linear temperature coefficient of frequency of about -23 ppm/°C was obtained. Isotropic SAW properties in the propagation plane, low temperature coefficient of frequency, and possibility of integration with active devices make the bulk Z-cut GaN crystal attractive for practical applications.

Effect of Metal Electrodes on Surface Acoustic Wave Properties in Bulk Z-Cut GaN Crystal

Mass density, dielectric, elastic, and piezoelectric constants of bulk GaN crystal were determined. Mass density was obtained from the measured ratio of mass to volume of a cuboid. The dielectric constants were determined from the measured capacitances of an interdigital transducer (IDT) deposited on a Z-cut plate and from a parallel plate capacitor fabricated from this plate. The elastic and piezoelectric constants were determined by comparing the measured and calculated SAW velocities and electromechanical coupling coefficients on the Z- and X-cut plates. The following new constants were obtained: mass density p = 5986 kg/m3; relative dielectric constants (at constant strain S) e11S/e0 = 8.6 and e11S/e0 = 10.5, where e0 is a dielectric constant of free space; elastic constants (at constant electric field E) C11E = 349.7, C12E = 128.1, C13E = 129.4, C33E = 430.3, and C44E = 96.5 GPa; and piezoelectric constants e33 = 0.84, e31 = -0.47, and e15 = -0.41 C/m2.

W. Soluch

Papers

Determination of mass density, dielectric, elastic, and piezoelectric constants of bulk GaN crystal