GaAs Nanomembranes in the High Electron Mobility Transistor Technology

A 100 nm MOCVD-grown HEMT AlGaAs/InGaAs/GaAs heterostructure nanomembrane was released from the growth GaAs substrate by ELO using a 300 nm AlAs layer and transferred to sapphire. The heterostructure contained a strained 10 nm 2DEG In0.23Ga0.77As channel with a sheet electron concentration of 3.4 × 1012 cm−2 and Hall mobility of 4590 cm2V−1s−1, which was grown close to the center of the heterostructure to suppress a significant bowing of the nanomembrane both during and after separation from the growth substrate. The as-grown heterostructure and transferred nanomembranes were characterized by HRXRD, PL, SEM, and transport measurements using HEMTs. The InGaAs and AlAs layers were laterally strained: ~−1.5% and ~−0.15%. The HRXRD analysis showed the as-grown heterostructure had very good quality and smooth interfaces, and the nanomembrane had its crystalline structure and quality preserved. The PL measurement showed the nanomembrane peak was shifted by 19 meV towards higher energies with respect to that of the as-grown heterostructure. The HEMTs on the nanomembrane exhibited no degradation of the output characteristics, and the input two-terminal measurement confirmed a slightly decreased leakage current.

Scattering Mechanisms and Suppression of Bipolar Diffusion Effect in Bi2Te2.85Se0.15Ix Compounds

We investigated the anisotropic thermoelectric properties of the Bi2Te2.85Se0.15Ix (x = 0.0, 0.1, 0.3, 0.5 mol.%) compounds, synthesized by ball-milling and hot-press sintering. The electrical conductivities of the Bi2Te2.85Se0.15Ix were significantly improved by the increase of carrier concentration. The dominant electronic scattering mechanism was changed from the mixed (T ≤ 400 K) and ionization scattering (T ≥ 420 K) for pristine compound (x = 0.0) to the acoustic phonon scattering by the iodine doping. The Hall mobility was also enhanced with the increasing carrier concentration. The enhancement of Hall mobility was caused by the increase of the mean free path of the carrier from 10.8 to 17.7 nm by iodine doping, which was attributed to the reduction of point defects without the meaningful change of bandgap energy. From the electron diffraction patterns, a lattice distortion was observed in the iodine doped compounds. The modulation vector due to lattice distortion increased with increasing iodine concentration, indicating the shorter range lattice distortion in real space for the higher iodine concentration. The bipolar thermal conductivity was suppressed, and the effective masses were increased by iodine doping. It suggests that the iodine doping minimizes the ionization scattering giving rise to the suppression of the bipolar diffusion effect, due to the prohibition of the BiTe1 antisite defect, and induces the lattice distortion which decreases lattice thermal conductivity, resulting in the enhancement of thermoelectric performance.

Hall Study of Conductive Channels Formed in Germanium by Beams of High-Energy Light Ions

The implantation of the high-energy ions of H+ or He+ in germanium leads to the creation of buried conductive channels in its bulk with equal concentrations of acceptor centers. These centers are the structure defects of the crystal lattice which arise in the course of deceleration of high-energy particles. This method of introducing electrically active defects is similar to the doping of semiconductors by acceptor-type impurities. It has been established that the density of defects increases with the implantation dose till ≈5×10^15 cm−2. The further increase of the implantation dose does not affect the level of doping. In the range of applied doses (10^12–6×10^16) cm−2, the Hall mobility of holes in the formed conducting channels is practically independent of the implanted dose and is about (2-3)×10^4 cm2/Vs at 77 K. The doping ofthe germanium by high-energy ions of H+ or He+ to obtain conducting regions with high hole mobility can be used in the microelectronics technology.

Characterizations of gallium nitride films grown on epitaxial sapphire templates

High-quality GaN films were grown on AlN/c-sapphire templates by MOVPE with Hall mobility of 802 cm2/V.s and carrier concentration of 8.1x1016/cm3 at 300K have achieved. The film low dislocation density of 5x107 cm-2 and X-ray rocking curve FWHM of 101 and 250 arcsec for the (0004) and (20-24) reflections were also obtained, respectively.

Gallium nitride films grown on AlN/sapphire templates

High-quality GaN films were grown on AlN/c-sapphire templates by MOVPE with Hall mobility of 802 cm2/V.s and carrier concentration of 8.1x1016/cm3 at 300K have achieved. The film low dislocation density of 5x107 cm-2 and X-ray rocking curve FWHM of 101 and 250 arcsec for the (0004) and (20-24) reflections were also obtained, respectively.

High quality gallium nitride films grown on epitaxial AlN/sapphire templates

High-quality GaN films were grown on AlN/c-sapphire templates by MOVPE with Hall mobility of 802 cm2/V.s and carrier concentration of 8.1x1016/cm3 at 300K have achieved. The film low dislocation density of 5x107 cm-2 and X-ray rocking curve FWHM of 101 and 250 arcsec for the (0004) and (20-24) reflections were also obtained, respectively.