Scandium-doped wurtzite nitrides such as (Al, Sc)N and (Ga, Sc)N have recently attracted considerable attention due to their enhanced piezoelectric properties and the emergence of ferroelectric behavior. (Al, Sc)N has already been widely adopted in commercial high-frequency filters for smartphones, owing to its outstanding piezoelectric performance. Moreover, the discovery of ferroelectricity in both (Al, Sc)N and (Ga, Sc)N has spurred research into their potential applications in memory devices and GaN-based transistors. This review summarizes the mechanisms underlying the piezoelectric and ferroelectric properties of scandium-doped wurtzite nitrides, drawing on existing experimental and theoretical studies. It also provides perspectives on recent advances in device integration and discusses the future potential of these materials for next-generation electronics.

  Group-III nitride semiconductors such as gallium nitride (GaN) have been investigated for various applications such as short wavelength light emitting devices and power devices due to their excellent material properties such as wide band-gap. We have proposed a neutron semiconductor detector using BGaN as a new possibility using such group-III nitride semiconductors. Boron (B) atoms have a large neutron capture cross section, which allows neutrons to be captured in semiconductors and thus has potential applications as a neutron imaging sensor. In this paper, we present the concept, principle of operation, and research progress of such a novel neutron sensing device. In particular, the development of a thick BGaN film growth technique with suppressed gas phase reaction and the detection of neutron capture signals achieve by thick BGaN diodes is presented.

  Hexagonal boron nitride (hBN) is a semiconductor that crystallizes in layers of a two-dimensional honeycomb structure composed of sp²-bonded B and N, namely monolayer BN (mBN), which are connected by out-of-plane π bond with a stacking sequence AA'. Since hBN exhibits high quantum efficiency (QE) near-band-edge emission at around 5.77 eV (215 nm) in spite of the indirect bandgap, hBN has attracted attention as a novel deep-ultraviolet (DUV) light-emitting material. Recently, syntheses and characterizations of layered BN polytypes such as AB-stacked graphitic BN (bBN), ABC-stacked rhombohedral BN (rBN), and even mBN have been reported, which included important information with respect to both scientific research and the practical use. In this article, the results of steady-state, temporary resolved, and spatially resolved luminescence measurements on hBN microcrystals and rBN epilayers containing bBN segments are shown to explore the superiority of hBN polytypes. Similar to the case of hBN, rBN and bBN exhibit excellent light-emitting performances in spite of principally indirect bandgap, including the retrograde thermal quenching behavior.

  Boron nitride (BN) has several polymorphs with different bonding states and crystal structures. Among them, sp³-bonded cubic boron nitride (c-BN) is a promising ultrawide-bandgap semiconductor for high-power electron device applications due to its large bandgap energy of 6.25 eV and high breakdown field of ~17.5 MV/cm. However, the epitaxial growth of c-BN has been challenging because it is a metastable phase. Recently, we have successfully achieved the epitaxial growth of c-BN layers on diamond substrates by developing an ion-beam-assisted MBE with independent boron, nitrogen radical and Ar⁺ ion sources. In this article, we first introduce the physical properties of c-BN, then describe our ion-beam-assisted MBE technology for phase-pure c-BN epitaxial growth and discuss the growth mechanism based on the established growth phase diagram. Finally, we present n-type conductivity control of c-BN with in-situ Si doping and discuss the carrier scattering mechanisms.

  The critical point at which vacancy (C_V) and interstitial Si atom (C_I) concentrations have minimum values is generally used to obtain a high-quality Si single ingot by the Czochralski (Cz) method. But the growth method is not stable at the view point of obtaining the minimum limit of remained C_V and C_I concentrations. The reason why the critical point varies depending on temperature is that each critical point exactly corresponds to each cross point (Cp) of the C_V and C_I concentration curves. To obtain the minimum limit of the C_V and C_I concentrations, Nakajima has implemented the Cp=0 control at which the C_V and C_I concentrations have practically minimum limit values (C_V = C_I = 0) because the pair annihilation is finished at the Cp = 0. The Cp = 0 point is fully compatible to the perfect critical point where both C_V and C_I are practically zero.