Si1-xGex/Si resonant-cavity-enhanced photodetectors with a silicon-on-oxide reflector operating near 1.3 mu m

We report on a Si1-xGex/Si multiple quantum-well resonant-cavity-enhanced (RCE) photodetector with a silicon-on-oxide reflector as the bottom mirror operating near 1.3 mu m. The breakdown voltage of the photodetector is above 18 V and the dark current density at 5 V reverse bias is 12 pA/mu m(2). The RCE photodetector shows enhanced responsivity with a clear peak at 1.285 mu m and the peak responsivity is measured around 10.2 mA/W at a reverse bias of 5 V. The external quantum efficiency at 1.3 mu m is measured to be 3.5% under reverse bias of 16 V, which is enhanced three- to fourfold compared with that of a conventional p-i-n photodetector with a Ge content of 0.5 reported in 1995 by Huang [Appl. Phys. Lett. 67, 566 (1995)]. (C) 2000 American Institute of Physics. [S0003-6951(00)00628-8].

Raman study on residual strains in thin 3C-SiC epitaxial layers grown on Si(001)

Raman scattering measurement has been used to study the residual strains in the thin 3C-SiC/Si(001) epilayers with a variation of film thickness from 0.1 to 1.2 mu m. which were prepared by chemical vapor deposition (CVD)growth. Two methods have been exploited to figure our the residual strains and the exact LO bands. The final analyzing results show that residual strains exist in the 3C-SiC epilayers. The average stress is 1.3010 GPa, and the relative change of the lattice constant is 1.36 parts per thousand. Our measurements also show that 3C-SiC phonons are detectable even for the samples with film thickness in the range of 0.1 to 0.2 mu m. (C) 2000 Published by Elsevier Science S.A. All rights reserved.

Characteristics of circular waveguide photodetectors using SiGe/Si multiple quantum wells

We report on the fabrication of circular waveguide photodetectors with a response near 1.3 mu m wavelength using SiGe/Si multiple quantum wells. The quantum efficiency of the circular waveguide photodetector is improved when compared with that of the rib waveguide photodetector in the same wavelength at 1.3 mu m The frequency response of the photodetectors is simulated. The emciency-bandwidth product of the circular waveguide photodetectors is improved correspondingly. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

Observation of quantum-confined Stark shifts in SiGe/Si type-I multiple quantum wells

Quantum-confined Stark shifts in SiGe/Si type-I multiple quantum wells are suggested by the bias dependence of the photocurrent spectra of p-i-n photodiodes. Both Stark redshift and blueshift have been observed for the same sample in the different ranges of electric fields applied to the quantum wells. The turnaround point corresponds to a certain electric field (named "critical" field). This phenomenon was generally predicted by Austin in 1985 [Phys. Rev. B 31, 5569 (1985)] and calculated in detail for SiGe quantum structure by Kim recently [Thin Solid Films 321, 215 (1998)]. The critical electric field obtained from the photocurrent spectra is in reasonable agreement with the theoretical prediction. (C) 2000 American Institute of Physics. [S0021-8979(00)03711-7].

Photoluminescence in Si and Be directly doped self-organized InAs/GaAs quantum dots

We report on the photoluminescence in directly Si- and Be-doped self-organized InAs/GaAs quantum dots (QDs). When the doping level is low, a decrease in linewidth is observed. However, it will decrease the uniformity and photoluminescence peak intensity of QDs when the doping level is high. We relate this phenomenon to a model that takes the Si or Be atoms as the nucleation centers for the formation of QDs. (C) 2000 Elsevier Science B.V. All rights reserved.

Sputtering of ZnO buffer layer on Si for GaN blue light emitting materials

The preparation of high quality ZnO/Si substrates for the growth of GaN blue light emitting materials is considered. ZnO thin films have been deposited on Si(100) and Si(lll) substrates by conventional magnetron sputtering. Morphology, crystallinity and c-axis preferred orientation of ZnO thin films have been investigated by transmitting electron microscopy (TEM), X-ray diffraction (XRD) and X-ray rocking curve (XRC). It is proved that the ZnO thin films have perfect structure. The full-width-at-half-maximum (FWHM) of the ZnO(002) XRC of these films is about 1 degrees, while the minimum is 0.353 degrees. This result is better than the minimum FWHM (about 2 degrees) reported by other research groups. Moreover, comparison and discussion are given on film structure of ZnO/Si(100) and ZnO/Si(lll).

A study of Si1-xGex/Si quantum-well intermixing by photocurrent spectroscopy

Photocurrent spectroscopy has been used to study quantum-well intermixing in this paper. The cut-off wavelength of the photodiodes based on the implanted and annealed materials is significantly reduced, compared with that measured in annealed-only photodetectors. The bandgap of SiGe quantum well in implanted and annealed samples is blue-shifted by up to 97 meV, relative to that in annealed-only samples. (C) 2000 Elsevier Science S.A. All rights reserved.

The effect of dopant Si on the uniformity of self-organized InAs quantum dots

The photoluminescence in directly si-doped self-organized InAs quantum dots was systematically studied. With doping, a decrease in linewidth and a little blue shift in peak were observed by PL measurement. The results show that direct doping when growing InAs layer may be helpful to the formation of uniform small quantum dots. The work will be meaningful for the fabrication of self-organized InAs quantum dots semiconductor device.

Doping during low-temperature growth of materials for n-p-n Si/SiGe/Si heterojuction bipolar transistor by gas source molecular beam epitaxy

In situ doping for growth of n-p-n Si/SiGe/Si heterojuction bipolar transistor (HBT) structural materials in Si gas source molecular beam epitaxy is investigated. We studied high n-type doping kinetics in Si growth using disilane and phosphine, and p-type doping in SiGe growth using disilane, soild-Ge, and diborane with an emphasis on the effect of Ge on B incorporation. Based on these results, in situ growth of n-p-n Si/SiGe/Si HBT device structure is demonstrated with designed structural and carrier profiles, as verified from characterizations by X-ray diffraction, and spreading resistance profiling analysis. (C) 2000 Elsevier Science B.V. All rights reserved.

Structural properties of SI-GaAs grown in space

The structural properties of Semi-insulating gallium arsenide (SI-GaAs) crystal grown with power-travelling technique in space have been studied by double-crystal x-ray diffractometry and chemical etching. The quality of the crystal was first evaluated by x-ray rocking-curve method. The full width at half maximum of x-ray rocking curve in space-grown SI-GaAs is 9.4+/-0.08 are seconds. The average density of dislocations revealed by molten KOH is 2.0 X 10(4) cm(-2), and the highest density is 3.1 X 10(4) cm(-2). The stoichiometry in the single crystal grown in space is improved as well. Unfortunately, the rear of the ingot grown in space is polycrystalline owing to being out of control of power. (C) 1999 COSPAR. Published by Elsevier Science Ltd.

Properties of proton-implanted p-type Si: supports for the models explaining a novel p-n junction in Si

Proton-implanted and annealed p-type Si wafers were investigated by using both transmission electron microscopy and spreading resistivity probe. The novel pn junction [Li et al., Mat. Res. Sec. Symp, Proc. 396 (1996) 745], as obtained by using n-type Si subjected to the process as this work, was not observed in the p-type Si wafers in this work. A drop of superficial resistivity in the sample was found and is explained by the proposed models interpreting the novel pn junction. (C) 2000 Elsevier Science B.V. All rights reserved.

Mechanical alloying of Fe-Mn and Fe-Mn-Si

The ball milling of Fe-24Mn and Fe-24Mn-6Si mixed powders has been performed by the high energy ball milling technique. By employing X-ray diffraction and Mossbauer measurements, the composition evolution during the milling process has been investigated. The results indicate the formation of paramagnetic Fe-Mn or Fe-Mn-Si alloys with a metastable fee phase as final products, which imply that the Fe and Mn proceed a co-diffusion mechanism through the surface of fragmented powders. The thermal stability and composition evolution of the as-milled alloys were discussed comparing with the bulk alloy. (C) 1999 Published by Elsevier Science S.A. All rights reserved.

Effect of Si overgrowth on the structural and luminescence properties of Ge islands on Si(100)

The effect of Si overgrowth on the structural and luminescence properties of strained Ge layer grown on Si(1 0 0) is studied. Capping Si leads to the dissolution of Ge island apex and reduced island height. The structural changes in island shape, especially in chemical composition during Si overgrowth have a large effect on the PL properties. The integrated PL intensity of Ge layer increases and there are large blue shifts in peak energies after capping Si. The PL spectra from buried Ge layer are consistent with type-II band alignment in SiGe/Si. We show that the PL properties from buried Ge layer may be tailored by modifying the cap layer growth conditions as well as post-growth annealing. (C) 1999 Elsevier Science B.V. All rights reserved.

Improvement of photoluminescence of strained SiGe/Si layers on patterned Si substrate

A strained SiGe/Si superlattice structure has been grown on a patterned Si substrate and its photoluminescence has been studied. The patterned substrate is composed of pyramid-like structures. It is found that there are Ge-rich SiGe quantum wires (QWR) at the crossings of adjacent planes that form the pyramid-like structure. Photoluminescence of strained the SiGe layer grown on a planar substrate and a patterned substrate was compared. The total intensity of photoluminescence from the patterned substrate was 5.2 times larger than that from the planar substrates. The result is discussed and it is believed that this increase in photoluminescence is related to the observed QWRs. (C) 1999 Elsevier Science Ltd. All rights reserved.

Effect of Si doping on cubic GaN films grown on GaAs(100)

Epitaxial layers of cubic GaN have been grown by metalorganic vapor-phase epitaxy (MOVPE) with Si-doping carrier concentration ranging from 3 x 10(18) to 2.4 x 10(20)/cm(3). Si-doping decreased the yellow emission of GaN. However, the heavily doped n-type material has been found to induce phase transformation. As the Si-doping concentration increases, the hexagonal GaN nanoparticles increase. Judged from the linewidth of X-ray rocking curve, Si-doping increases the density of dislocations and stacking faults. Based on these observations, a model is proposed to interpret the phase transformation induced by the generated microdefects, such as dislocations and precipitates, and induced stacking faults under heavy Si-doping. (C) 1999 Elsevier Science B.V. All rights reserved.