Effect of the variation of temperature on the structural and optical properties of ZnO thin films prepared on Si (111) substrates using PLD

ZnO thin films were prepared on Si (1 11) substrates at various temperatures from 250 to 700 degrees C using pulsed laser deposition (PLD) technique in order to investigate the structural and optical properties of the films. The structural and morphological properties of the films were investigated by XRD and SEM measurements, respectively. The quality of the films was improved with the increase of the temperature. By XRD patterns the FWHMs of the (0 0 2) peaks of the ZnO films became narrower when the temperatures were above 500 degrees C. The FWHMs of the peaks of (0 0 2) of the films were as narrow as about 0. 19 degrees when films were grown at 650 and 700 degrees C. This indicates the superior crystallinity of the films. The optical properties of the films were studied by photoluminescence spectra using a 325 nm He-Cd laser. The two strongest UV peaks were found at 377.9 nm from ZnO films grown at 650 and 700 degrees C. This result is consistent with that of the XRD investigation. Broad bands in visible region from 450 to 550 nm were also observed. Our works suggest that UV emissions have close relations with not only the crystallinity but also the stoichiometry of the ZnO films. (c) 2005 Elsevier Ltd. All rights reserved.

Correlation between Er3+ emission and Si clusters in Erbium-doped a-SiOx : H films

Erbium-doped hydrogenated amorphous silicon suboxide films containing silicon clusters (a-SiOx:H) were prepared. The samples exhibited photoluminescence (PL) peaks at around 750nm and 1.54 mu m, which could be assigned to the electron-hole recombination in silicon clusters and the intra-4f transition in Er3+, respectively. We compared annealing behaviors of Si clusters and Er3+ emission and found that Si clusters emission depends strongly upon crystallinity of Si clusters, whereas Er3+ emission is not sensitive to whether it is Si nanocrystals (nc-Si) or amorphous Si (a-Si) clusters. The erbium-doped a-SiOx:H films containing either a-Si clusters or nc-Si have the same kind of Er3+ -emitting centers. Based on these results, it is concluded that a-Si clusters can play the same role on Er3+ excitation as nc-Si. (c) 2004 Elsevier B.V. All rights reserved.

An improvement on Si-etching tetramethyl ammonium hydroxide solution

An optimal concentration of the etching solution for deep etching of silicon, including 3% tetramethyl ammonium hydroxide and 0.3% (NH4)(2)S2O8, was achieved in this paper. For this etching solution, the etching rates of silicon and silicon dioxide were about 1.1 mu m(.)min(-1) and 0.5 nm(.)min(-1), respectively. The etching ratio between (100) and (111) planes was about 34:1, and the etched surface was very smooth.

Comparison of the properties of GaN grown on complex Si-based structures

With the aim of investigating the possible integration of optoelectronic devices, epitaxial GaN layers have been grown on Si(Ill) semiconductor-on-insulator (SOI) and on Si/CoSi2/Si(111) using metalorganic chemical vapor deposition. The samples are found to possess a highly oriented wurtzite structure, a uniform thickness, and abrupt interfaces. The epitaxial orientation is determined as GaN(0001)//Si(111), GaN[1120]//Si[110], and GaN[1010]//Si[112], and the GaN layer is tensilely strained in the direction parallel to the interface. According to Rutherford backscattering/channeling spectrometry and (0002) rocking curves, the crystalline quality of GaN on Si(111) SOI is better than that of GaN on silicide. Room-temperature photoluminescence of GaN/SOI reveals a strong near-band-edge emission at 368 nm (3.37 eV) with a full width at half-maximum of 59 meV. (c) 2005 American Institute of Physics.

Demonstration of low-cost Si-based tunable long-wavelength resonant-cavity-enhanced photodetectors

A simple process for fabricating low-cost Si-based continuously tunable long-wavelength resonant-cavity-enhanced (RCE) photodetectors has been investigated. High-contrast SiO2/Si(Deltan similar to2) was employed as mirrors to eliminate the need to grow thick epitaxial distributed Bragg reflectors. Such high-reflectivity SiO2/Si mirrors were deposited on the as-grown InGaAs epitaxy layers, and then were bonded to silicon substrates at a low temperature of 350 C without any special treatment on bonding surfaces, employing silicate gel as the bonding medium. The cost is thus decreased. A thermally tunable Si-based InGaAs RCE photodetector operating at 1.3-1.6 mum was obtained, with a quantum efficiency of about 44% at the resonant wavelength of 1476 nm and a tuning range of 14.5 nm. It demonstrates a great potential for industry processes. (C) 2005 American Institute of Physics.

In situ doping control for growth of n-p-n Si/SiGe/Si heterojunction bipolar transistor by gas source molecular beam epitaxy

N-p-n Si/SiGe/Si heterostructures have been grown by a disilane (Si2H6) gas and Ge solid sources molecular beam epitaxy system using phosphine (PH3) and diborane (B2H6) as n- and p-type in situ doping sources, respectively. Adopting an in situ doping control technology, the influence of background B dopant on the growth of n-Si emitter layer was reduced, and an abrupt B dopant distribution from SiGe base to Si emitter layer was obtained. Besides, higher n-type doping in the surface region of emitter to reduce the emitter resist can be realized, and it did not result in the drop of growth rate of Si emitter layer in this technology. (C) 2004 Elsevier B.V. All rights reserved.

Investigation of Mn-implanted n-Si by low-energy ion beam deposition

Mn ions were implanted to n-type Si(0 0 1) single crystal by low-energy ion beam deposition technique with an energy of 1000 eV and a dose of 7.5 x 10(17) cm(-2). The samples were held at room temperature and at 300degreesC during implantation. Auger electron spectroscopy depth profiles of samples indicate that the Mn ions reach deeper in the sample implanted at 300degreesC than in the sample implanted at room temperature. X-ray diffraction measurements show that the structure of the sample implanted at room temperature is amorphous while that of the sample implanted at 300degreesC is crystallized. There are no new phases found except silicon both in the two samples. Atomic force microscopy images of samples indicate that the sample implanted at 300degreesC has island-like humps that cover the sample surface while there is no such kind of characteristic in the sample implanted at room temperature. The magnetic properties of samples were investigated by alternating gradient magnetometer (AGM). The sample implanted at 300degreesC shows ferromagnetic behavior at room temperature. (C) 2004 Elsevier BN. All rights reserved.

Crack-free InAlGaN quaternary alloy films grown on Si(111) substrate by metalorganic chemical vapor deposition

Crack-free In0.08Al0.25Ga0.67N quaternary films, with and without thick (> 1.5 mum) high-temperature-GaN (HTGaN) interlayer, have been grown on Si(1 1 1) substrates by a low-pressure metalorganic chemical vapor deposition (MOCVD) system. Mole fractions of In and Al in quaternary alloy layers are determined by Energy dispersive spectroscopy (EDS) and Rutherford backscattering spectrometry (RBS), which are recorded as similar to8% and similar to25-27%, respectively. High-resolution X-ray diffraction (HRXRD) and room temperature photoluminescence (RT-PL) results evidence the film's single crystal structure and the existence of local In- and/or Al-rich regions. Compared with GaN film grwon on Si(1 1 1) substrate, no crack is observed in the quaternary ones. Two explanations are proposed. First, mismatch-induced strain is relaxed significantly due to gradual changes of In concentration. Second, the weak In-N bond is likely to break when the sample is cooled down to the room temperature, which is expected to favor the releasing of thermal stress. (C) 2004 Elsevier B.V. All rights reserved.

Depth distribution of the strain in the GaN layer with low-temperature AlN interlayer on Si(111) substrate studied by Rutherford backscattering/channeling

The depth distribution of the strain-related tetragonal distortion e(T) in the GaN epilayer with low-temperature AlN interlayer (LT-AlN IL) on Si(111) substrate is investigated by Rutherford backscattering and channeling. The samples with the LT-AlN IL of 8 and 16 nm thickness are studied, which are also compared with the sample without the LT-AlN IL. For the sample with 16-nm-thick LT-AlN IL, it is found that there exists a step-down of e(T) of about 0.1% in the strain distribution. Meanwhile, the angular scan around the normal GaN <0001> axis shows a tilt difference about 0.01degrees between the two parts of GaN separated by the LT-AlN IL, which means that these two GaN layers are partially decoupled by the AlN interlayer. However, for the sample with 8-nm-thick LT-AlN IL, neither step-down of e(T) nor the decoupling phenomenon is found. The 0.01degrees decoupled angle in the sample with 16-nm-thick LT-AlN IL confirms the relaxation of the LT-AlN IL. Thus the step-down of e(T) should result from the compressive strain compensation brought by the relaxed AlN interlayer. It is concluded that the strain compensation effect will occur only when the thickness of the LT-AlN IL is beyond a critical thickness. (C) 2004 American Institute of Physics.

Chemical trends of defect formation in Si quantum dots: The case of group-III and group-V dopants

Using first-principles methods, we have systematically calculated the defect formation energies and transition energy levels of group-III and group-V impurities doped in H passivated Si quantum dots (QDs) as functions of the QD size. The general chemical trends found in the QDs are similar to that found in bulk Si. We show that defect formation energy and transition energy level increase when the size of the QD decreases; thus, doping in small Si QDs becomes more difficult. B-Si has the lowest acceptor transition energy level, and it is more stable near the surface than at the center of the H passivated Si QD. On the other hand, P-Si has the smallest donor ionization energy, and it prefers to stay at the interior of the H passivated Si QD. We explained the general chemical trends and the dependence on the QD size in terms of the atomic chemical potentials and quantum confinement effects.

Energy band design for Si/SiGe quantum cascade laser

This paper introduces in detail the working principle of Si/SiGe Quantum cascade laser(QCL). Appropriate parameters are used to calculate the hole subband structure of Si/Si1-xGex quantum well using a six-band k center dot p method. The dispersion relation and energy band for different layer thickness and compositions are investigated. Meanwhile, the energy separations between hole subbands in Si/Si1-xGex/Si quantum wells are also analyzed. Finally the calculated results are used for the Si/SiGe QCL design, which will be beneficial to the structure optimization of Si/SiGe QCL.

Observations on subband electron properties in In0.65Ga0.35As/In0.52Al0.48As MM-HEMT with Si delta-doped on the barriers

Magneto-transport measurements have been carried out on a Si delta-doped In0.65Ga0.35As/In0.52Al0.48As metamorphic high-electron-mobility transistor with InP substrate in a temperature range between 1.5 and 60 K under magnetic field up to 13 T. We studied the Shubnikov-de Haas (SdH) effect and the Hall effect for the In0.65Ga0.35As/In0.52Al0.48As single quantum well occupied by two subbands and obtained the electron concentration and energy levels respectively. We solve the Schrodinger-Kohn-Sham equation in conjunction with the Poisson equation self-consistently and obtain the configuration of conduction band, the distribution of carriers concentration, the energy level of every subband and the Fermi energy. The calculational results are well consistent with the results of experiments. Both experimental and calculational results indicate that almost all of the delta-doped electrons transfer into the quantum well in the temperature range between 1.5 and 60 K.

Investigation of Ge-Si atomic interdiffusion in Ge nano-dots multilayer structure by double crystal X-ray diffraction

The fluctuations of the strained layer in a superlattice or quantum well can broaden the width of satellite peaks in double crystal X-ray diffraction (DCXRD) pattern. It is found that the width of the 0(th) peak is directly proportional to the fluctuation of the strained layer if the other related facts are ignored. By this method, the Ge-Si atomic interdiffusion in Ge nano-dots and wetting layers has been investigated by DCXRD. It is found that thermal annealing can activate Ge-Si atomic interdiffusion and the interdiffusion in the nano-dots area is much stronger than that in the wetting layer area. Therefore the fluctuation of the Ge layer decreases and the distribution of Ge atoms becomes homogeneous in the horizontal Ge (GeSi actually) layer, which make the width of the 0(th) peak narrow after annealing.

A base-emitter self-aligned multi-finger Si1-xGex/Si power heterojunction bipolar transistor

With a crystal orientation dependent on the etch rate of Si in KOH-based solution, a base-emitter self-aligned large-area multi-linger configuration power SiGe heterojunction bipolar transistor (HBT) device (with an emitter area of about 880 mu m(2)) is fabricated with 2 mu m double-mesa technology. The maximum dc current gain is 226.1. The collector-emitter junction breakdown voltage BVCEO is 10 V and the collector-base junction breakdown voltage BVCBO is 16 V with collector doping concentration of 1 x 10(17) cm(-3) and thickness of 400 nm. The device exhibited a maximum oscillation frequency f(max) of 35.5 GHz and a cut-off frequency f(T) of 24.9 GHz at a dc bias point of I-C = 70 mA and the voltage between collector and emitter is V-CE = 3 V. Load pull measurements in class-A operation of the SiGe HBT are performed at 1.9 GHz with input power ranging from 0 dBm to 21 dBm. A maximum output power of 29.9 dBm (about 977 mW) is obtained at an input power of 18.5 dBm with a gain of 11.47 dB. Compared to a non-self-aligned SiGe HBT with the same heterostructure and process, f(max) and f(T) are improved by about 83.9% and 38.3%, respectively.

Pseudospin in Si delta-doped InAlAs/InGaAs/InAlAs single quantum well

Magneto-transport measurements have been carried out on double/single-barrier-doped In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum well samples from 1.5 to 60 K in an applied magnetic field up to 13 T. Beating Shubnikov-de Haas oscillation is observed for the symmetrically double-barrier-doped sample and demonstrated due to a symmetric state and an antisymmetric state confined in two coupled self-consistent potential wells in the single quantum well. The energy separation between the symmetric and the antisymmetric states for the double-barrier-doped sample is extracted from experimental data, which is consistent with calculation. For the single-barrier-doped sample, only beating related to magneto-intersubband scattering shows up. The pesudospin property of the symmetrically double-barrier-doped single quantum well shows that it is a good candidate for fabricating quantum transistors. (c) 2007 Elsevier Ltd. All rights reserved.