摘要:

Residual stress in thin silicon dioxide films has been studied as a function of storage time. Films of varying microstructure and impurity content were deposited by plasma-enhanced chemical vapor deposition. Initially, all the films exhibited compressive stress, the magnitude of which was found to increase rapidly with time for the first few hours after deposition. For all the deposited thin films, this increasing compressive stress eventually saturates and then begins to decrease with time. The time at which the transition occurs depends on film thickness and quality, whereas, for relatively thicker films deposited under identical conditions, a saturation in compressive stress after long aging time was observed. No existing model of thin oxide films successfully explains the observed time variation of stress. In this paper, the variation of film stress as a function of storage time and film properties, such as porosity and impurity content, is discussed. Three driving forces, namely, surface reactivity, silanol buildup, and water dipole interaction, each of whose contribution varies depending on film thickness and quality, have been identified as potential mechanisms behind stress change in oxide films. A unified model consisting of these driving forces can explain the time variation of stress behavior in oxide films, irrespective of film quality and thickness. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364347

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on the thermal stability of Pt and Pd thin films on GaN up to 800 °C. We have found that for Pt thin films submicron size metal spheres form at temperatures as low as 600 °C and the film turns into discontinuous islands at 725 °C and above. Pd begins to form islands above 700 °C and areas of the film begin to delaminate due to thermally generated compressive stress. The general behavior of these films is that found for most metal films on ceramics, suggesting that metals on GaN do not react as they typically do on common elemental and compound semiconductors. This ceramic-like behavior must be considered when determining which metals may act as good electrical contacts for GaN, especially for high temperature applications or alloyed contacts. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364091

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A Si/Pd ohmic contact scheme ton-GaP(n∼5×1017cm−3) was investigated using Rutherford backscattering spectrometry, transmission electron microscopy, energy dispersive x-ray spectrometry, and the Cox–Strack measurement. Contact resistivities of∼2×10−4&OHgr;cm2are obtained for annealing temperatures ranging from 350 to 650 °C. This contact is thermally stable at 550 °C. The ohmic contact formation mechanism is rationalized in terms of the solid phase regrowth of ann+layer and the solid phase epitaxy of a Si layer. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364320

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this work, we investigate the deep levels present in ion implanted and rapid thermal annealed (RTA) InPp+-njunctions. The samples were implanted with magnesium or coimplanted with magnesium and phosphorus. These levels were characterized using deep level transient spectroscopy (DLTS) and capacitance–voltage transient technique (CVTT). Seven majority deep levels located in the upper half of the band gap were detected in the junctions by using DLTS measurements, four of which (at 0.6, 0.45, 0.425, and 0.2 eV below the conduction band) result from RTA, while the origin of the other three levels (at 0.46, 0.25, and 0.27 eV below the conduction band) can be ascribed to implantation damage. An RTA-induced origin was assigned to a minority deep level at 1.33 eV above the valence band. From CVTT measurements, several characteristics of each trap were derived. Tentative assignments have been proposed for the physical nature of all deep levels. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364348

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photocapacitance measurement is applied to investigate the stoichiometry-dependent deep levels inp-type InP crystals doped with Zn prepared by 4 h annealing at 700 °C under controlled phosphorus vapor pressure. Photocapacitance results reveal three dominant deep levels. A dominant deep level at 1.05 eV above the valence band is detected commonly before and after annealing, and the change of level densities is shown as a function of the phosphorus vapor pressure. Another two deep levels are also detected after annealing at 0.74 eV above the valence band and at 0.51 eV below the conduction band. In view of the deviation from the stoichiometric composition of InP, possible origins of these levels and their optical transition mechanism are discussed. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.364349

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In undoped bulk-grown GaAs single crystals, which show a wide variation of the resistivity, a characteristic dependence of the Hall mobility on the carrier concentration with a pronounced minimum at about1×1010 cm−3is observed. By applying a standard effective medium theory it is shown that this minimum is caused by mesoscopic nonuniformities of the charge carrier concentration and not by increased scattering rates or additional scattering mechanisms as would be the standard interpretation in the case of homogeneous samples. These nonuniformities observed by high-resolution point-contact measurements are connected with the cellular structure of dislocations. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364350

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a study of high energy electron transport in GaAs using an analytical model of the band structure. This model is based on piecewise polynomial approximation of the dispersion relation in different regions of the Brillouin zone. It accounts for the first two conduction bands and reproduces all important features of the full band structure. We have used this model to set up a Monte Carlo simulation of electron transport accounting for impact ionization. It has been shown that this “extended valley” model yields essentially the same results as the most rigorous full band Monte Carlo calculations. We have found a large influence of high energy anisotropy on electron transport. Another important result is that most impact ionization events are due to electrons in the second conduction band. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364351

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Here we report the electron migration by photo- or thermostimulation inBaFCl:Eu2+. Electrons released fromFcenters may be trapped by other defect sites to formFaggregates or another type ofFcenter and vice versa. This migration reduces the photostimulated luminescence efficiency, lowers the imaging plate sensitivity, and causes the difference between the optical absorption and photostimulation spectra of color centers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364145

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By analyzing various experimental photoluminescence (PL) and photoluminescence excitation (PLE) spectra in porous silicon (PS), we have found that the PL spectra in PS are characterized by the transitions among the quantum confined states in nanoscale Si which are influenced by the surface chemical bonds. Since the size of silicon filament is comparable to that of surface potential, its electron states are modified by the surface potential. We use a two-dimensional state-dependent surface potential to model the overlapping of surface chemical bonds, from which we obtain a new set of quantum confined states modified by the surface potential. By using these new quantum states the effective luminescence, experimental PL, and PLE spectra in porous Si are well explained. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364146

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

GaAsp-i-nstructures with very abrupt doping transitions and different lengths of the quasi-intrinsic zone have been fabricated by molecular beam epitaxy technology. For structures with ultra-thin intrinsic zones, tunnel currents were determined experimentally up to electric fields of 1.9 MV/cm, in good agreement with a modified Kane model. The difference of calculated tunnel current and measured total current in structures which also perform impact ionization is used to fit a Monte Carlo simulation program at high electric fields. Resulting idealized homogeneous-field ionization rates are given which are experimentally verified up to fields of 1.3 MV/cm. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.364147

出版商:AIP    

年代:1997

数据来源: AIP