摘要:

InAs nanocrystal quantum dots have been prepared via colloidal chemical synthesis using the reaction of InCl3and As[Si(CH3)3]3. Sizes ranging from 25 to 60 A˚ in diameter are produced and isolated with size distributions of ±10%–15% in diameter. The nanocrystals are crystalline and generally spherical with surfaces passivated by trioctylphosphine giving them solubility in common organic solvents. The dots have been structurally characterized by transmission electron microscopy (TEM) and powder x‐ray diffraction (XRD) and the optical absorption and emission have been examined. Quantum confinement effects are evident with absorption onsets well to the blue of the bulk band gap and size dependent absorption and emission features. The emission is dominated by band edge luminescence. These quantum dots are particularly interesting as they provide an opportunity to make important comparisons with comparably sized InAs quantum dots synthesized by molecular beam epitaxy techniques. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117605

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Negative differential conductance based on lateral band‐to‐band tunneling is demonstrated in a three‐terminal silicon tunneling device. The device is fabricated with the current silicon ultra‐large scale integration (Si ULSI) process, taking care of the field isolation to reduce the excess tunneling current that flows over some intermediate states. It is observed that the forward biased band‐to‐band tunneling current is largely controlled by the gate bias which modulates the tunneling barrier width. The three‐terminal Si tunneling device is promising as the post complementary metal–oxide‐semiconductor device in future Si ULSI. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117606

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We report record high breakdown voltages up to 340 and 230 V realized on unintentionally doped (1.5 &mgr;m gate length) and Si doped (1 &mgr;m gate length) AlGaN/GaN modulation doped field effect transistors (MODFETs), respectively. The devices also have large transconductances up to 140 mS/mm and a full channel current of 150–400 mA/mm. The Si doped MODFET sample demonstrated a very high room temperature mobility of 1500 cm2/Vs. With these specifications, GaN field effect transistors as microwave power devices are practical. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117607

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Arsenic precipitation from a thin, 100‐nm surface layer of GaAs grown at low temperature (LT) by molecular beam epitaxy is investigated. The precipitate depth distribution is examined for different rapid thermal annealing cycles. It is found that the precipitate distribution can tail a long distance into the underlying stoichiometric GaAs layer, depending on the peak annealing temperature. The distribution for an 800 °C anneal is virtually unaffected by a prior low temperature ‘‘soak’’ at 600 °C, thus showing that the precipitation is insensitive to the initial point defect concentrations in this temperature range. The relevance of these results to the precipitation process and to the use of thin LT layers in device applications is discussed. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117608

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

SiGe quantum wells were grown at 525 °C using a commercially available, ultrahigh vacuum–chemical vapor deposition system, in which the purity of the material and quality of interfaces have already been demonstrated. Changes in photoluminescence line energies are monitored and the extent of interdiffusion in the wells during annealing is calculated. A strong initial enhancement of the diffusivity is observed in as‐grown material. Material annealed using a two‐step process in which strain and Ge peak concentrations are unchanged after the first (low temperature) step, shows a much lower interdiffusion during the second step. It is argued that strain alone cannot explain the enhanced interdiffusion, which is, thus, attributed to grown‐in, nonequilibrium point defects. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117609

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Electric field‐enhanced degradation has been observed in amorphous silicon solar cells exposed to intense illumination (45–60 suns) at elevated temperatures (≳160 °C). The front tin oxide contacts of bothp–i–nandn–i–pcells darken significantly when a strong reverse bias is applied at elevated temperatures and under intense illumination. Compositional profiles of the cells show that a strong reverse bias causes a depletion of hydrogen near the contacts. These results are interpreted in terms of proton motion near thep/iinterface ofp–i–ncells and negative hydrogen ion motion near thei/ninterface. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117610

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We present a Monte Carlo investigation of noise and velocity fluctuations in Si at 300 K under full degenerate conditions. The presence of the Pauli principle is found to strongly modify the shape of the correlation functions: at low electric fields, the time decay decreases due to the shortening of momentum relaxation time and the variance evidences nonparabolicity effects. At increasing electric fields, the correlation function exhibits a negative part that can be associated with ballistic carriers crossing the velocity space from negative to positive values of the Fermi velocity without scattering. A microscopic analysis in terms of diagonal and off‐diagonal contributions to the velocity correlation confirms this interpretation. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117611

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The nature of the defects in sputter‐deposited GeO2:SiO2thin films and their relationship to charge trapping and enhanced photosensitivity have been studied using electron paramagnetic resonance, capacitance–voltage, and optical bleaching and absorption spectroscopies. We find a good qualitative agreement between the density ofisolatedGe dangling bonds measured magnetically, the density of charge trapping sites measured electrically, and the density of absorbing centers measured optically. Collectively, all observations can be modeled by assuming that a change in spin state and charge state of isolated paramagnetic neutral Ge dangling bonds, to form either diamagnetic positively or negatively charged Ge sites, are largely responsible for the charge trapping and photosensitivity in these thin films. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117612

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A growth process has been investigated for the epitaxial growth of silicon carbide. The technique can simply be described as chemical vapor deposition (CVD) at high temperatures, hence the name high temperature CVD (HTCVD). The growth process however, differs greatly from that of the CVD process due to the significant sublimation and etch rates at the extreme growth temperatures (1800–2300°C). The grown rates obtained with the HTCVD are in the order of several tens of &mgr;m/h to 0.5 mm/h. The purity and crystallinity of the growth layers are outstanding showing strong free exciton related photoluminescence. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.117613

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Aninsitulaser reflectometer is used to determine the surface roughness of III–V laser heterostructure as it etches in an electron cyclotron resonance etcher. A stochastic model links the reflectometer signals with the fluctuations of the surface height and slope, and with the size of the illuminated surface area. This technique is valuable for improving the quality of optical waveguides etched in III–V heterostructure, and the electrical contacts for optoelectronic devices. ©1996 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.116907

出版商:AIP    

年代:1996

数据来源: AIP