ALBERT

Notes: Interfacial microstructures of Pd/Ge/Ti/Au ohmic contact to n-type GaAs have been investigated using cross-sectional transmission electron microscopy, and the results are used to interpret the electrical properties. Annealing at 300 °C yields a contact resistance of 0.62 Ω mm and the layer structure is changed to GaAs/PdGe/Au4Ti/TiO. The ohmic contact is formed through a solid phase regrowth of GaAs heavily doped with Ge below the PdGe layer. At 380 °C, the lowest contact resistance of 0.43 Ω mm is obtained. The layer structure is changed to GaAs/(Ge–Ti)/PdGe/TiO. Spikes composed of Au and AuGa are found at the grain boundaries of the PdGe compound. The formation of AuGa at 380 °C reduces the contact resistance through the creation of more Ga vacancies at the interface of GaAs/PdGe, and the incorporation of elemental Ge. © 1996 American Institute of Physics.

Notes: Thermally stable, low-resistance PdGe-based ohmic contacts to high–low doped n-GaAs have been developed. The lowest contact resistance obtained is two times lower than that of previously reported PdGe ohmic contacts. The contacts are thermally stable even after isothermal annealing for 5 h at 400 °C under atmosphere ambient. X-ray diffraction results and Auger depth profiles show that the good PdGe-based ohmic contact is due to the formation of both AuGa and TiO compounds. The AuGa compound enhances the creation of more Ga vacancies, followed by the incorporation of Ge into Ga vacancies, and the TiO compound suppresses As outdiffusion from the GaAs substrate, respectively. © 1995 American Institute of Physics.

Notes: Fully-coherent Si0.7Ge0.3 layers were deposited on Si(001) by gas-source molecular beam epitaxy (GS-MBE) from Ge2H6/Si2H6 mixtures in order to probe the effect of steady-state hydrogen coverages θH on surface morphological evolution during the growth of compressively strained films. The layers are grown as a function of thickness t at temperatures, Ts=450–550 °C, for which strain-induced roughening is observed during solid-source MBE (SS-MBE) and deposition from hyperthermal beams. With GS-MBE, we obtain three-dimensional (3D) strain-induced growth mounds in samples deposited at Ts=550 °C for which θH is small, 0.11 monolayer (ML). However, mound formation is dramatically suppressed at 500 °C (θH=0.26 ML) and completely eliminated at 450 °C (θH=0.52 ML). We attribute these large differences in surface morphological evolution primarily to θH(Ts)-induced effects on film growth rates R, adatom diffusion rates Ds, and ascending step-crossing probabilities. GS-MBE Si0.7Ge0.3(001) growth at 450 °C remains two dimensional, with a surface width 〈w〉〈0.15 nm, at all film thicknesses t=11–80 nm, since both R and the rate of mass transport across ascending steps are low. Raising Ts to 500 °C increases R faster than Ds leading to shorter mean surface diffusion lengths and the formation of extremely shallow, rounded growth mounds for which 〈w〉 remains essentially constant at (similar, equals)0.2 nm while the in-plane coherence length 〈d〉 increases from (similar, equals)70 nm at t=14 nm to 162 nm with t=75 nm. The low ascending step crossing probability at 500 °C results in mounds that spread laterally, rather than vertically, due to preferential attachment at the mound edges. At Ts=550 °C, the ascending step crossing probability increases due to both higher thermal activation and lower hydrogen coverages. 〈w〉(t) increases by more than a factor of 10, from 0.13 nm at t=15 nm to 1.9 nm at t=105 nm, while the in-plane coherence length 〈d〉 remains constant at (similar, equals)85 nm. This leads, under the strain driving force, to the formation of self-organized 3D {105}-faceted pyramids at 550 °C which are very similar to those observed during SS-MBE. © 2002 American Institute of Physics.

Notes: Electromagnetic properties of an Ag2O doped and an undoped BiPbSrCaCuO superconductor were evaluated to investigate the effect of the pinning center on the magnetic shielding and suspension/levitation phenomena. The residual magnetization M=M+–M− increased with the dopant concentration, a maximum for 2% doping, wherein a fine uniform dispersion of Ag particles was observed. The fine Ag particles form a cluster with increasing dopant as the particles condense with each other and grow, consequently does the number of flux passing through decreases, so the magnetization M decreases. This result indicates that M is proportional to the number of magnetic flux lines passing through the sample, because the smaller the particle size the larger the ratio of the surface area to the volume. Magnetic shielding was evaluated by measuring the induced voltage in the secondary coil by placing the sample in between the primary coil. The voltage was initially set to 0.5 V, and decreased to 0.17 and 0.28 V, respectively, for the undoped and 2% Ag2O doped samples. The much less change in the induced voltage for the 2% doped sample is attributed to increased flux shielding by shielding the vortex current. Simultaneous stable levitation and suspension of 2% Ag2O doped disk samples weighing 0.3 g were observed, respectively, above (3 mm) and beneath (2 mm) a toroidal permanent magnet under a field cooled condition. The role of flux pinning is discussed to account for the phenomena by considering the hysteretic force function. © 2001 American Institute of Physics.

Notes: Si ions were implanted into 100-nm-thick SiO2 layer thermally grown on crystalline Si at an energy of 55 keV with various doses ranging from 1×1014 to 1×1017 Si/cm2 at room temperature. Si ions go through the interface between SiO2 layer and Si substrate generating defects in SiO2 layer and Si substrate as well. Defect-related phenomena were characterized by photoluminescence (PL) and electron spin resonance (ESR) measurements. The PL experiment shows that there exists a dose window for a maximum intensity of luminescence related to radiative defects, while the ESR exhibits that nonradiative defects change from E′ centers to Pb centers as the dose increases. It is considered that the intensity is controlled by the density ratio of radiative to nonradiative defects induced by ion implantation. © 2000 American Institute of Physics.

Notes: The effect of surface passivation of undoped p-CdTe(100) by (NH4)2Sx treatment was investigated by using photoluminescence (PL), photoconductivity (PC), and x-ray photoelectron spectroscopy (XPS). After sulfur treatment for 2 min, the acceptor bound exciton (A0, X) peak increases greatly in the PL spectrum, and the minority-carrier lifetime of CdTe becomes the longest value in the PC measurement. The XPS spectrum for untreated CdTe shows the additional peaks on the right side of two main Te peaks corresponding to the Te 3d core levels, and these additional peaks are related to TeO3 with binding energies of 576.2 and 586.5 eV. After sulfur treatment, while the intensities of the Te 3d core levels decreased gradually, those of the TeO3 peaks disappear. In addition, the S 2p core-level spectra for sulfur-treated CdTe show the peaks at the 161.7 and 162.8 eV, which are attributed to a CdS formation at the surface of CdTe. These results indicate the sulfur effectively dissociates the native oxides from and neutralizes the dangling bonds at the surface of CdTe. © 2000 American Institute of Physics.