摘要:

Gallium‐implantedp+layers in Si were exposed to atomic hydrogen from a plasma. It was found that very large hydrogen concentrations, up to 7.5 times larger than the peak Ga concentration of 7×1019/cm3, segregated into thep+layer during treatment at 200 °C. The shape of the hydrogen concentration profile was similar to that of the Ga profile. Ion channeling showed that the H atoms did not occupy simple high‐symmetry sites in the lattice, and electron microscopy revealed the presence of extended {111} stacking fault defects associated with the layer of high hydrogen concentration. A mechanism to account for these findings is suggested.

ISSN:0003-6951    

DOI:10.1063/1.105964

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report the first measurement of modulation bandwidth in electron transfer quantum well modulators. A device with 1 pF capacitance provides ≳10 dB optical modulation depth at 1.537 &mgr;m wavelength with a 3 dB electrical bandwidth of 5.7 GHz. Optical pump‐probe measurements indicate that the fundamental response time is determined by the voltage‐dependent speed of carrier escape from the well.

ISSN:0003-6951    

DOI:10.1063/1.105965

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have compared ion channeling results with molecular dynamics simulations to investigate low‐temperature molecular beam homoepitaxy on silicon. We report the temperature dependence, rate dependence, and thickness dependence of films grown on Si(111). For 350 A˚ films, a transition to good crystalline quality is seen in ion channeling at growth temperatures of ≊400 °C; this is compared to ≊100 °C for (100) epitaxy. The evolution of surface microstructure leading to breakdown of epitaxial growth at low temperatures is discussed.

ISSN:0003-6951    

DOI:10.1063/1.105966

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Heteroepitaxy of GaAs on Si with a ZnSe interlayer by low‐pressure metalorganic chemical vapor deposition is reported. The structural and electrical properties of the GaAs epilayers grown on ZnSe/Si substrates were found to be superior to those of the GaAs directly on Si. The surface dislocation density of the GaAs/ZnSe/Si film can be reduced to 2×105cm−2, which is one order of magnitude lower than that of GaAs/Si. The planar Schottky diode fabricated on the GaAs/ZnSe/Si sample shows a reverse breakdown voltage as high as 30 V, whereas the diode on GaAs/Si has a breakdown voltage of about 12 V. In addition, the residual stress in the GaAs heteroepilayers calculated from photoluminescence peak shifts was 8.2×108dyn/cm2for the GaAs/ZnSe/Si structure, as compared to 2.7×109dyn/cm2for the GaAs directly on Si. This indicates that the ZnSe intermediate layer is also effective in reducing the residual stress in the GaAs film grown on Si.

ISSN:0003-6951    

DOI:10.1063/1.105967

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Epitaxial GaAs films have been grown by molecular beam epitaxy (MBE) on Si‐on‐insulator (SOI) formed by ion beam synthesis. Rutherford backscattering and channeling, x‐ray double‐crystal diffraction, and infrared reflection measurements have been used to characterize the epitaxial GaAs films. Experimental results show that the crystal quality of the GaAs films improves markedly towards the GaAs surface for thicker films where the minimum channeling yield drops to 10%. Infrared reflection spectra prove that crystalline GaAs films have been deposited on the SOI structures. Refractive index profiles of the GaAs films on SOI structures can be obtained by computer fitting the interference spectra. The results indicate that the crystal quality of these GaAs films is comparable to similar GaAs films deposited directly on Si by MBE.

ISSN:0003-6951    

DOI:10.1063/1.105968

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We report on a detailed experimental investigation of lateral tunneling between electrodes of a two‐dimensional electron gas separated by the voltage‐controlled barrier of a nanometer Schottky gate. The experimental data are modeled using the WKB method to calculate the tunneling probability of electrons through a barrier whose shape is determined from a solution of the two‐dimensional Poisson equation. This model is in excellent agreement with the experimental data over a two order of magnitude range of current.

ISSN:0003-6951    

DOI:10.1063/1.105969

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Using a novel time‐resolved optical photoluminescence imaging technique, analogous to the electrical Haynes–Shockley experiment, we have measured room‐temperature minority‐carrier transport in a series of ‘‘surface‐free’’ GaAs/Al0.3Ga0.7As double heterostructures. These measurements are only possible in ‘‘surface‐free’’ samples in which the band‐to‐band radiative recombination lifetimes are long−here up to 2.5 &mgr;s. We find minority‐carrier transport to be ‘‘diffusive,’’ with diffusion lengths of up to ∼140 &mgr;m. We also find transport in thick (≳1 &mgr;m) structures to be mediated by hole‐dominated ambipolar diffusion, whereas for thinner structures a transition from ambipolar to free‐electron‐dominated diffusion is observed. These results demonstrate that our heterostructures becomeeffectivelymodulationdopedfor GaAs thicknesses ≲1 &mgr;m.

ISSN:0003-6951    

DOI:10.1063/1.105970

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

A short‐period transient grating technique with 100 fs resolution is used to study room‐temperature perpendicular transport over nanometer dimensions in GaAs/Al0.3Ga0.7As multiple quantum wells (MQWs) whose barrier widths range from 1.4 to 15 nm. With decreasing barrier width, a transition from transport dominated by thermal over‐barrier hopping to that dominated by tunneling is observed. For the thinnest barriers, measurements are in good quantitative agreement with simple rate equations describing tunneling, and the measured grating decay rates are related to the microscopic tunneling rates. By comparison, for MQWs with thick barriers, the transport shows no barrier width dependence, and a room‐temperature over‐barrier hopping rate is extracted.

ISSN:0003-6951    

DOI:10.1063/1.105971

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Epitaxial,c‐oriented YBa2Cu3Oxthin films were deposited by dc sputtering on (11¯02)‐sapphire substrates with an intermediate buffer layer of Y‐stabilized ZrO2(YSZ), which was grown by rf magnetron sputtering. The epitaxy of the YSZ and the YBa2Cu3Oxfilms was proved by Rutherford backscattering spectrometry combined with ion channeling. The YBa2Cu3Oxfilms exhibited transition temperatures of 90 K and had critical current densities exceeding 1.2×106A/cm2at 77 K in zero magnetic field.

ISSN:0003-6951    

DOI:10.1063/1.105972

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Magnetic relaxation data have been taken on zone‐melted and sintered YBa2Cu3Oxsamples over wide temperature and magnetic field ranges. We have found that magnetic relaxation varies greatly in the samples with different microstructures and crystallographic orientations. Flux‐creep rates have been found to be reduced in the zone‐melted samples owing to large amounts of intragranular crystal defects such as edge dislocations and stacking faults. An important flux‐pinning behavior related to the pinning potential distributions has been observed in the samples. The relationship between microstructural orientation and pinning potential distributions in YBa2Cu3Oxis discussed.

ISSN:0003-6951    

DOI:10.1063/1.105973

出版商:AIP    

年代:1991

数据来源: AIP