The object of the present invention is to provide a sputtering target for a gallium nitride thin film, which has a low oxygen content, a high density and a low resistivity.

A gallium nitride powder having powder physical properties of a low oxygen content and a high bulk density is used and hot pressing is conducted at high temperature in high vacuum to prepare a gallium nitride sintered body having a low oxygen content, a high density and a low resistivity.

In wireless communications, many radio frequency bands are used. For each frequency band, there are two frequencies one for transmit and the other for receive. As the band widths are small and separation between adjacent bands is also small, many band pass filters with different band pass frequencies are required for each communication unit such as mobile handset. The present invention provides frequency tunable film bulk acoustic resonators (FBAR) with different structures. Thin film biasing resistors are integrated into the FBAR structure for DC biasing and RF isolation. A plurality of the present tunable FBARs are connected to form microwave filters with tunable bandpass frequencies and oscillators with selectable resonating frequencies by varying DC biasing voltages to the resonators.

A semiconductor epitaxial structure is provided. The semiconductor epitaxial structure includes a substrate, a doped semiconductor epitaxial layer, and a carbon nanotube layer. The doped semiconductor epitaxial layer is located on the substrate. The carbon nanotube layer is located between the substrate and the doped semiconductor epitaxial layer. The carbon nanotube layer can be a carbon nanotube film drawn from a carbon nanotube array and including a number of successive and oriented carbon nanotubes joined end-to-end by van der Waals attractive force therebetween.

For a Periodic Table Group 13 metal nitride semiconductor crystal obtained by epitaxial growth on the main surface of a base substrate that has a nonpolar plane and/or a semipolar plane as its main surface, an object of the present invention is to provide a high-quality semiconductor crystal that has a low absorption coefficient, is favorable for a device, and is controlled dopant concentration in the crystal, and to provide a production method that can produce the semiconductor crystal. A high-quality Periodic Table Group 13 metal nitride semiconductor crystal that has a precisely controlled dopant concentration within the crystal and a low absorption coefficient and that is thus favorable for a device, can be provided by inhibiting oxygen doping caused by impurity oxygen and having the Si concentration higher than the O concentration.

The present invention is directed to crystalline solids having an empirical formula of M.sub.2A.sub.2X, wherein M is at least one Group IIIB, IVB, VB, or VIB metal, preferably Cr, Hf, Sc, Ti, Mo, Nb, Ta, V, Zr, or a combination thereof; wherein A is Al, Ga, Ge, In, Pb, or Sn, or a combination thereof; and each X is C.sub.xN.sub.y, where x+y=1. In some particular embodiments, the crystalline composition has a unit cell stoichiometry of Mo.sub.2Ga.sub.2C.

[Object] To provide a production method capable of producing a gallium nitride crystal at a lower pressure. [Solution] Provided is a method for producing a gallium nitride crystal, the method including a step of heating metal gallium and iron nitride in a nitrogen atmosphere at least to a reaction temperature at which the metal gallium and the iron nitride react.

Provided is a high-pressure reactor suitable for a high-pressure process using supercritical ammonia grow bulk crystal of group III nitride having lateral dimension larger than 2 inches or to form various transition metal nitrides. The reactor has nutrient distributed along the reactor's longitudinal axis and seed material positioned at the reactor's inner wall and along the reactor's longitudinal axis. Nutrient diffuses through supercritical ammonia from the reactor's longitudinal axis and deposits on the seed material positioned by the reactor's inner wall. Both the nutrient and seed material are heated by the same heater. Material growth can primarily be due to material diffusion through supercritical ammonia. This configuration and methodology reduce convective movement of supercritical ammonia due to temperature differential, providing a more quiescent environment in which group III nitride or transition metal nitride is formed.

A powder of gallium nitride has an oxygen content of 0.5 at or less. A green body formed by charging 8 g of the powder into a rectangular cuboidal die having a size of 10 mm40 mm and uniaxially pressing the powder at a pressure of 100 MPa has an electrical resistivity of 1.010.sup.7 .Math.cm or less.

In one instance, the invention provides a group III nitride crystal having a first side exposing nitrogen polar c-plane of single crystalline or highly oriented polycrystalline group III nitride and a second side exposing group III polar surface, polycrystalline phase, or amorphous phase of group III nitride. Such structure is useful as a seed crystal for ammonothermal growth of bulk group III nitride crystals. The invention also discloses the method of fabricating such crystal. The invention also discloses the method of fabricating a bulk crystal of group III nitride by ammonothermal method using such crystal.

In one instance, the invention provides a group III nitride crystal having a first side exposing nitrogen polar c-plane of single crystalline or highly oriented polycrystalline group III nitride and a second side exposing group III polar surface, polycrystalline phase, or amorphous phase of group III nitride. Such structure is useful as a seed crystal for ammonothermal growth of bulk group III nitride crystals. The invention also discloses the method of fabricating such crystal. The invention also discloses the method of fabricating a bulk crystal of group III nitride by ammonothermal method using such crystal.