Vladimir Fuflyigin

Electron beam-induced increase of electron diffusion length in p-type GaN and AlGaN/GaN superlattices

The diffusion length, L, of electrons in Mg-doped p-GaN grown by metal-organic chemical vapor deposition was found to increase linearly from 0.55 to 2.0 μm during 1500 s of electron beam irradiation. Similar trends were observed for p-type Mg-doped GaN and AlGaN/GaN superlattices grown by molecular-beam epitaxy. While the electron diffusion length in p-(Al)GaN depends on irradiation time, the diffusion length of holes in n-GaN remains unchanged, with L∼0.35 μm. We attribute the observed diffusion length change in p-(Al)GaN to an increase in the minority carrier lifetime. This increase is likely due to electron beam-induced charging of the deep metastable centers associated with Mg doping. The concentration of these centers was estimated to be ∼1018 cm−3. The minority carrier diffusion length increase in p-(Al)GaN, which occurs during electron injection, may lead to self-improvement of the bipolar transistor characteristics.

Pyroelectric properties of AlN

Pyroelectric properties of high-quality (0001)AlN films grown on (111) Si were studied. The pyroelectric coefficient p was measured using the dynamic method. The value was in the range of 6–8 μC/(m2 K), yielding a p/e figure-of-merit of 0.8–0.95. The pyroelectric coefficient was independent of temperature and applied bias. Leakage current as low as 1–2×10−9 A/cm2 was measured at 5 V on large area devices. The obtained results indicate that AlN films can be used in pyroelectric thin-film devices.

Growth of ferroelectric oxide films on n-GaN/c-sapphire structures

High-quality (Pb, La)(Ti, Zr)O3 films were grown on n-GaN. The film thickness ranged from 0.5 to 5 μm. The material was prepared by a chemical solution method with compositions of 8/65/35 and 0/52/48. The films grown on GaN buffered with a thin layer of indium in oxide were highly textured and exhibited excellent ferroelectric properties with Pr=20–26 μC/cm2. A large field-induced birefringence of 0.025 was measured in the film with a composition of 8/65/35 under a field strength of 2×105 V/cm.

Thin ferroelectric interferometer for spatial light modulations.

Thin ferroelectric interferometers (TFIs) for use as light-modulating devices were fabricated entirely with thin-film techniques on sapphire substrates. The ferroelectric layer in the TFI devices was a lead lanthanum zirconated titanate thin-film material, which can be formed from a chemical solution on highly reflective dielectric mirror surfaces. Light intensity modulation in both transmission and reflection modes was demonstrated with the fabricated devices. Experimental data and simulations show that TFI devices possess tremendous potential in spatial light modulators because of their fast-switching, low-driving voltage and readiness for integration with a variety of substrates, including silicon.

Minority electron transport anisotropy in p-type Al/sub x/Ga/sub 1-x/N/GaN superlattices

The minority electron diffusion length, L, in Mg-doped molecular beam epitaxy (MBE) grown p-type Al/sub x/Ga/sub 1-x/N/GaN superlattices with aluminum content x=0.1 and 0.2 was measured perpendicular and parallel to the superlattice planes by the electron beam induced current technique. A large anisotropy in the transport properties was observed with the effect varying from 1:3 to 1:6. We attribute an experimentally observed diffusion length anisotropy to minority electron scattering during transport across the potential barriers of the superlattice. Reference p-GaN samples were also investigated, and the diffusion length was observed to be isotropic in both MOCVD (L=0.5 /spl mu/m) and MBE (L=0.27 /spl mu/m) grown samples.

Free-standing films of PbSc0.5Ta0.5O3 for uncooled infrared detectors

Highly textured PbSc0.5Ta0.5O3 (PST) films were grown on (111) Pt/Si by the sol–gel technique. The PST films were subsequently lifted off the silicon substrate using reactive ion etching. A 40%–50% increase in dielectric constant and pyroelectric coefficient was observed for suspended films compared to those properties of the PST films on a Si substrate. Typical values of the pyroelectric coefficient were measured to be 20–45 nC/(cm2 K) for 200–300 nm thick PST films. The loss tangent values were below 0.02 (at 10 kHz), and the leakage current density was as low as 2–3×10−8 A/cm2 at 1 V bias.

Epitaxial electro-optical BaTiO3 films by single-sourcemetal–organic chemical vapour deposition

Chemical vapour deposition (CVD) is a promising process for the production of ferroelectric complex oxide films having a large electro-optical coefficient. We report the epitaxial growth of high-quality BaTiO 3 films using a single-source CVD process. A variety of epitaxial relationships have been achieved with BaTiO 3 films grown cube-on-cube on substrates of large lattice mismatched LaAlO 3 and MgO, and «001», «110» and «111» oriented SrTiO 3 . A large quadratic electro-optic coefficient was measured for CVD-prepared BaTiO 3 films. These films also have values of the optic refractive indices and second electro-optic susceptibilities close to those of bulk BaTiO 3 crystals, indicating their excellent quality.

Infrared spectroscopy of ZnSiN2 single-crystalline films on r-sapphire

This letter presents a study of optical phonon modes of single-crystalline orthorhombic ZnSiN2 semiconductor epitaxially deposited on r-sapphire. An epitaxial relationship for ZnSiN2 film was found from x-ray diffraction to be (0k0)ZnSiN2‖(10 12)Al2O3 and [100]ZnSiN2‖(1210)Al2O3. Six B1 optical modes were revealed in 400–1000 cm−1 range in s-polarized infrared reflectance spectra. This is consistent with the analysis of the phonon symmetry and selection rules presented. The frequencies of the transversal and longitudinal components, phonon damping, and oscillator strengths of the B1 phonons as well as high frequency dielectric constant e∞xx of the orthorhombic ZnSiN2 were determined.

Electro-optic effect in Ba1−xPbxTiO3 films

High quality Ba1−xPbxTiO3 (x=0–0.25) films were grown on R-Al2O3 in a wide thickness range of 0.5–3 μm. Significant improvement of the films’ crystallinity and optical quality was observed in the presence of lead oxide for the films prepared at 650–700 °C. Strong texture of (110) type was observed in these films. The material is transparent at 350–2000 nm, indicating the possibility of its application in light controlling devices at wavelengths used in optical communication: 1300 and 1500 nm. Maximum field induced relative phase shift of 0.22 rad was measured in the film with composition of Ba0.9Pb0.1TiO3 under a field strength of 3×106 V/cm.

The structural heterogeneity and optical properties in chalcogenide glass films

The microscopic structure and optical properties of glassy films prepared by vapour phase deposition process from the germanium–arsenic–selenium family of chalcogenide glasses have been studied. A number of different molecular clusters or domains that can exist in the glass structure are found to play a significant role in determining the absorption characteristics and refractive index of the glass films. Modifications of the glass structure can be described by a variation of relative concentrations of the clusters and can be effected by modifications of film chemical composition and deposition conditions. Changes in absorption spectra are directly correlated with variation in relative concentrations of the structural fragments with different electronic bandgap properties. Experimental results suggest structural heterogeneity and support validity of the cluster structural model for the chalcogenide glasses.