In this review, the structural, mechanical, thermal, and chemical properties of substrates used for gallium nitride (GaN) epitaxy are compiled, and the properties of GaN films deposited on these substrates are reviewed. Among semiconductors, GaN is unique; most of its applications uses thin GaN films deposited on foreign substrates (materials other than GaN); that is, heteroepitaxial thin films. As a consequence of heteroepitaxy, the quality of the GaN films is very dependent on the properties of the substrate—both the inherent properties such as lattice constants and thermal expansion coefficients, and process induced properties such as surface roughness, step height and terrace width, and wetting behavior. The consequences of heteroepitaxy are discussed, including the crystallographic orientation and polarity, surface morphology, and inherent and thermally induced stress in the GaN films. Defects such as threading dislocations, inversion domains, and the unintentional incorporation of impurities into the epitaxial GaN layer resulting from heteroepitaxy are presented along with their effect on device processing and performance. A summary of the structure and lattice constants for many semiconductors, metals, metal nitrides, and oxides used or considered for GaN epitaxy is presented. The properties, synthesis, advantages and disadvantages of the six most commonly employed substrates (sapphire, 6H-SiC, Si, GaAs, LiGaO 2 , and AlN) are presented. Useful substrate properties such as lattice constants, defect densities, elastic moduli, thermal expansion coefficients, thermal conductivities, etching characteristics, and reactivities under deposition conditions are presented. Efforts to reduce the defect densities and to optimize the electrical and optical properties of the GaN epitaxial film by substrate etching, nitridation, and slight misorientation from the (0 0 0 1) crystal plane are reviewed. The requirements, the obstacles, and the results to date to produce zincblende GaN on 3C-SiC/Si(0 0 1) and GaAs are discussed. Tables summarizing measures of the GaN quality such as XRD rocking curve FWHM, photoluminescence peak position and FWHM, and electron mobilities for GaN epitaxial layers produced by MOCVD, MBE, and HVPE for each substrate are given. The initial results using GaN substrates, prepared as bulk crystals and as free-standing epitaxial films, are reviewed. Finally, the promise and the directions of research on new potential substrates, such as compliant and porous substrates are described.

Substrates for gallium nitride epitaxy

Materials for high temperature acoustic and vibration sensors: A review

Crystallographic texturing of polycrystalline ferroelectric ceramics offers a means of achieving significant enhancements in the piezoelectric response. Templated grain growth (TGG) enables the fabrication of textured ceramics with single crystal-like properties, as well as single crystals. In TGG, nucleation and growth of the desired crystal on aligned single crystal template particles results in an increased fraction of oriented material with heating. To facilitate alignment during forming, template particles must be anisometric in shape. To serve as the preferred sites for epitaxy and subsequent oriented growth of the matrix, the template particles need to be single crystal and chemically stable up to the growth temperature. Besides templating the growth process, the template particles may also serve as seed sites for phase formation of a reactive matrix. This process, referred to as Reactive TGG (RTGG), has been used to obtain highly oriented Pb(Mg1/3Nb2/3)O3-PbTiO3, Sr0.53Ba0.47Nb2O6, and (N...

Templated Grain Growth of Textured Piezoelectric Ceramics

Piezoelectric materials are used in numerous applications requiring a coupling between electrical fields and mechanical strain. Despite the technological importance of this class of materials, for only a small fraction of all inorganic compounds which display compatible crystallographic symmetry, has piezoelectricity been characterized experimentally or computationally. In this work we employ first-principles calculations based on density functional perturbation theory to compute the piezoelectric tensors for nearly a thousand compounds, thereby increasing the available data for this property by more than an order of magnitude. The results are compared to select experimental data to establish the accuracy of the calculated properties. The details of the calculations are also presented, along with a description of the format of the database developed to make these computational results publicly available. In addition, the ways in which the database can be accessed and applied in materials development efforts are described.

/pdf/a-database-to-enable-discovery-and-design-of-piezoelectric-36v4ckzqhq.pdf

A database to enable discovery and design of piezoelectric materials

Impedance and electric modulus analysis of Sm-modified Pb(Zr0.55Ti0.45)1−x/4O3 ceramics

https://iopscience.iop.org/article/10.1143/JJAP.11.904/pdf

Electrooptic and Piezoelectric Properties of La 2 Ti 2 O 7 Single Crystal

Ferroelectric Properties of Sr2Nb2O7 Single Crystal

A single crystal of lithium meta-gallate is synthesized by means of the Bridgman technique. The values of all tensor components of piezoelectric constant d, elastic compliance sE and dielectric constant eT are determined. The variations of the electromechanical coupling factor k'31 in the length-extensional mode of LiGaO2 resonators with crystallographic orientation are determined numerically by use of the values of the tensor components obtained. In order to determine the variations of the temperature coefficient of resonance frequency Tfr in the length-extensional mode of the resonators with orientation, the values of temperature coefficients both of elastic compliance and thermal expansion are measured. The maximum of k'31 is found to be 0.23, the value of Tfr being in the range from -40 to -65 ppm/°C.

Piezoelectric, Elastic and Dielectric Properties of LiGaO2

Piezoelectric ceramic composition

Perovskite solid solutions exist throughout the ternary system Pb(Mn3+ 1/2NU1/2)O3-PUTiO3 PbZrO3 and in up to 40mol% of the first component in Pb(Mn2+ 1/3Nb2/3)O3-PbTiO3-PbZrO3; at higher concentrations, a mixture of perovskite and pyrochlore phases was obtained. With Pb(Mn2+ 1/3Nb2,a)O3, ceramics showed enhanced piezoelectric activity and increased mechanical quality factor, both in comparison to the PbTiO3PbZrO3 binary and with Pb(Mn3+ 1/2Nb1/2)O3. Much improved piezoelectric properties were obtained, when manganese ions were regarded as divalent ions, in comparison with the case of trivalent ions. The difference seems to be caused by different amount of space charge generated in the ceramics, resulting from the co-existence of manganese ion and niobium ion. The amount in the former ceramics is much larger than that of the latter. The Curie point and electrical resistivity of these ceramics remain sufficiently high for practical use. (Received October 5, 1973)

Masao Takahashi

Papers

Electrooptic and Piezoelectric Properties of La 2 Ti 2 O 7 Single Crystal

Ferroelectric Properties of Sr2Nb2O7 Single Crystal

Piezoelectric, Elastic and Dielectric Properties of LiGaO2

Piezoelectric ceramic composition

Piezoelectric Properties of Ternary Ceramic Compounds Consisting Either of Pb(Mn 2+ 1/3 Nb 2/3 )O 3 or Pb(Mn 3+ 1/2 Nb 1/2 )O 3 with PbTiO 3 -PbZrO 3