摘要:

Melting and rapid solidification has been induced in amorphous Ge films by irradiation with nano- and picosecond laser pulses. The degree of structural relaxation of the rapidly solidified amorphous material has been investigated both by determining the minimum fluence required for surface melting and by means of Raman spectroscopy. The results evidence that the degree of relaxation of the rapidly solidified material is controlled by several parameters such as the duration and fluence of the laser pulse, and the thermal conductivity of the substrate, all of them affecting the supercooling prior to solidification. It is demonstrated that both relaxation and derelaxation can be induced if the above mentioned parameters are properly selected. The degree of relaxation is observed to decrease as the supercooling increases. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365803

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In the present work the effect of incident laser power on the Raman spectra of diamond isolated particles and continuous films deposited on silicon and glassy carbon (GC) substrates by the chemical vapor deposition method is investigated. It is shown that the Raman line position measured for diamond particles shifts to lower wave numbers as a function of incident laser power. These shifts were most drastic for single particles deposited on GC that were examined using a Raman microprobe. In this case the diamond peak displayed a negative shift of∼18 cm−1when the laser power output was increased from 1 to 15 mW. The laser beam diameter was∼2 &mgr;mand the diamond particle measured was 3–6 &mgr;m in diameter. Micro-Raman measurements of diamond particles deposited on a silicon substrate or continuous diamond films on GC display very small changes in the diamond Raman peak wavelength for the same laser power range. From our studies it is concluded that the negative shift of the Raman peak position is caused by laser-induced local heating of the irradiated diamond particles. The temperature under the laser spot was calculated from the intensity ratio of Stokes to anti-Stokes Raman lines measured as a function of laser power output. The Raman peak wavelength calculated for each temperature showed excellent agreement with our experimental results. The local temperature of an isolated diamond crystal on GC rises to∼1000 Kat 15 mW laser power output, whereas the temperature change of the continuous film on GC and of a single particle on silicon was in the 0–30 K range above room temperature for the same laser power output range. This difference in heating is explained on the basis of efficient heat dissipation through a large contact area between the deposited particles and the substrate surface in the case of single particles deposited on silicon or through grain boundaries in the case of the continuous film on GC. The inefficient heat dissipation from the isolated diamond particles on GC is related to the small contact area between the diamond crystals and the GC substrate as a result of etching during the deposition process and possibly to the presence of an amorphous component in the diamond crystals deposited. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365804

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have measured the temperature dependence of the electron mobility between∼200and 300 K in undoped and 0.3&percent; Fe-dopedBi12GeO20(BGO) and undopedBi12SiO20(BSO) using a time-of-flight technique. We found that mobilities calculated from the observed transit times were independent of sample thickness and applied voltage, but depended approximately exponentially on temperature. The hole current transients were very weak and featureless, and consequently we were unable to measure mobilities for holes. The measured drift mobilities varied from6.1×10−4to0.10 cm2/Vsfor undoped BGO,6.1×10−4to0.0170 cm2/Vsfor 0.3&percent; Fe-doped BGO, and∼5×10−4to0.014 cm2/Vsfor undoped BSO. Values of the microscopic mobility were estimated to be 5.9, 2.3, and1.4 cm2/Vsfor undoped, 0.3&percent; Fe-doped BGO, and undoped BSO, respectively. From the temperature dependence of the electron mobility we obtained an activation energy for the dominant trap ofEt=0.31 eVfor undoped BGO,Et=0.34 eVfor 0.3&percent; Fe-doped BGO, andEt=0.31 eVin the undoped BSO sample. These values are interpreted as the trap depth of the main traps dominating the mobility and agree well with values obtained from the analysis of thermally stimulated conductivity measurements performed previously. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365805

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A self-consistent two-carrier numerical model for steady-state current flow inn-semi-insulating-n InP structures allows the treatment of avalanche breakdown in addition to trap filling. Band-to-band impact ionization is included as a source term in the continuity equations. Carrier diffusion, nonlinear velocity field characteristics, and Shockley-Read-Hall recombination through the traps are also included, and the effects of each on the field and trapped carrier distributions are calculated. (The progress of trap filling predicted by the traditional drift-only theory is also calculated.) With impact ionization, hole accumulation near the cathode redistributes the space charge and contributes to positive feedback for avalanche breakdown. The model predictions are consistent with experimentally observed catastrophic breakdown and allow the development of design guidelines for avoiding device failure. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365806

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A systematic study of the ground-state binding energies of a hydrogenic impurity in quantum dots subjected to external electric and magnetic fields is presented. The quantum dot is modeled by superposing a lateral parabolic potential and a square-well potential and the energies are calculated via a variational approach within the effective-mass approximation. The interplay between the confinement effects due to the applied fields and the quantum-size confinements on the binding energies is analyzed. The role played by the impurity position along the well direction on the impurity energies is also discussed. We have shown that by changing the strength of the external electric and magnetic fields, a large spread in the range of the donor binding energy may be obtained, for a particular choice for the lateral confinement. The presented results could be used to tailor energy states in optoelectronic devices. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365807

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The band structure of strained Si (4–10 ML) on (001) GaAs, band lineups of the strained Si/(001)GaAs heterojunction, and confined energy levels of theSi3N4/Si/GaAsquantum well have been calculated via a pseudopotential method. It has been found that in this technically importantSi3N4/Si/(001)GaAsstructure, strained Si has a very narrow band gap (0.34 eV) at the&Dgr;⊥point in the Brillouin zone. For the strained Si/(001)GaAs heterojunction, the conduction band offsets from the&Dgr;⊥for Si to the &Ggr; valley for GaAs is 0.83 eV, and that from the&Dgr;⊥valley for Si to theXvalley for GaAs is 1.21 eV. The valence band offset is 0.25 eV. The lowest confined energy level in the conduction band of theSi3N4/Si/GaAsquantum well ranging from 4 to 10 monolayers is found to be 0.22–0.28 eV above the conduction band edge of strained Si, or 0.57–0.61 eV below the conduction band edge of GaAs, while the first confined energy level in the valence band is barely above the valence band maximum of GaAs. The accumulation and inversion take place at these confined energy levels. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365808

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The dc-current stress behavior ofMo/a-SiNxHy/Mothin-film diodes is discussed for severala-SiNxHy-plasma-deposition conditions. Current transport is governed by thermionic field emission of electrons over a reverse biased Schottky barrier. The barrier height is determined by thea-SiNxHy-plasma-deposition conditions. Therefore these back-to-back Schottky devices provide an elegant way to perform dc-current stressing at several well defined carrier densities for similar stress fields. It is shown that such experiments allow assessment of defect-state creation/anneal mechanisms ina-SiNxHy.An electron-trapping-triggered anneal mechanism accounts for the observed dependence of the defect density at the electrode injecting contact (cathode) on the hole-barrier height at the anode. Also a new microscopically detailed anneal reaction scheme is proposed. The defect-state creation/anneal mechanism is expected to be generally applicable for all silicon-rich hydrogenated amorphous silicon alloys. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365809

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Schottky barrier structure and metal-insulator-semiconductor structure have been fabricated on boron-doped diamond film samples, which were grown using the microwave enhanced chemical vapor deposition method. By measuring the capacitance-voltage(CV)spectroscopies of both structures, boron acceptor concentration of∼1017 cm−3in the diamond samples has been measured. In theCVmeasurement, the influences from interface states, non-boron deep centers, emission/capture time constant distribution of boron acceptors and diamond resistance have been considered. It shows that proper ac modulation frequency should be selected in the measurement. It also shows that, in the measurement of dopant concentration in wide gap semiconductors, theCVmeasurement of the semiconductor Schottky barrier structure is a better choice, because Ohmic contact problem can be avoided. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365810

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Fowler–Nordheim tunneling current oscillations are used to investigate two metal/oxide/Si interfaces:n+polysilicon/oxide andoxide/p-Siinterfaces on the same samples forp-Si substrate metal–oxide–semiconductor devices. Electron injection from thep-Si substrate is facilitated by the application of visible light during theI–Vmeasurement in order to create and inject sufficient carriers into theSiO2conduction band. We compare the interfaces of thermal with rapid thermal silicon oxides prepared with nitrogen. We find that these two processes yield the same quality of interfaces. An analysis of the magnitude of the current oscillations indicates that the oxide/Si interface is superior to the polysilicon/oxide interface. Oxide thicknesses are determined from the oscillations at each interface for devices fabricated on the same wafer, and the requirement of constant film thickness enables the (uncertain) value of the barrier at thep-Si injecting electrode to be approximated at 2.80±0.1 eV. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365811

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An oxide-breakdown mode induced by hot-electron injection into an oxide is reported forn-channel metal–oxide–semiconductor field-effect transistors with 6 nm thick gate oxides. The diameter of the current path formed after breakdown was estimated to be less than 10 nm based on spreading-resistance measurements. The measured charge to breakdown was102–104 C/cm2in an oxide field of 5–7 MV/cm. This value is much smaller than that extrapolated from the results of Fowler–Nordheim (FN) tunneling experiments. The charge to breakdown in the hot-electron injection method decreased as the electric field increased in a silicon substrate. This was quite different from the case with FN tunneling injection, where the oxide field plays a significant role in oxide breakdown. Good correlation between the calculated electron energy in the oxide and the electric field in the silicon substrate suggests that the difference between hot-electron injection and FN tunneling can be explained in terms of the average electron energy in the oxide. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365812

出版商:AIP    

年代:1997

数据来源: AIP