摘要:

The diffusion in TiN/B–C–N multilayers during vacuum annealing at temperatures up to 1000 °C and/or 300 keV argon irradiation is studied. Changes in composition, stress field, bilayer repeat length, and interface quality are reported. The effect of stress on diffusion is proved by performing the same annealing or the same irradiation on a multilayer with and without compressive stress. During thermal annealing, demixing or phase separation is observed. On the contrary, during irradiation, mixing occurs. Both phenomena are enhanced in the presence of the stress field. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122089

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report on the properties ofBa(Mg1/3Ta2/3)O3thin films prepared by the metalorganic solution deposition technique. BulkBa(Mg1/3Ta2/3)O3ceramics have shown excellent dielectric properties at microwave frequencies; however, the high sintering temperature of bulk material is the major obstacle in their use as dielectric resonators to miniaturize microwave circuits. It was possible to obtain an ordered-perovskite phase of 0.3-&mgr;m-thickBa(Mg1/3Ta2/3)O3films with trigonal symmetry at an annealing temperature of 700 °C, which is much lower than the bulk sintering temperatures. The electrical measurements were conducted onPt/Ba(Mg1/3Ta2/3)O3/Ptcapacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 22.2 and 0.009, respectively. The dielectric constant of thin films was comparable to the typical values(&egr;r∼23.5–25)reported for bulk ceramics. The temperature coefficient of capacitance was −145 ppm/°C in the measured temperature range of 25–125 °C. The leakage current density was lower than10−7 A/cm2at an applied electric field of 0.5 MV/cm. The high dielectric constant, which is comparable to bulk, low dielectric loss, and good temperature and bias stability suggest the suitability ofBa(Mg1/3Ta2/3)O3thin films for microwave communications and integrated capacitor applications. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122090

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Real-time transmission electron microscopy (TEM) was used to directly examine the temperature dependence of electromigration-induced void and failure dynamics over the range 200–350 °C. The studies were done using submicron Al interconnects and a special sample stage, which allowed TEM observations to be recorded while heating and passing current through the sample. A novel sample design dramatically minimized any Joule heating in the runners. Our experiments directly reveal that the mechanism responsible for void and failure dynamics at temperatures <250 °C is distinctly different from that at higher temperatures. These results have implications regarding methods used for predicting electromigration reliability at use conditions from accelerated test data. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122091

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Back-illuminated GaN/AlGaN ultraviolet (UV) heterojunction photodiodes with high quantum efficiencies are demonstrated. Photovoltaic (zero bias) responsivity of 0.2 A/W at 355 nm was achieved. The improved efficiencies primarily arise from the use of AlGaN/GaN heterojunction in which photons are absorbed within thep-njunction thus eliminates carrier losses due to surface recombination and diffusion processes in previously reported homojunction devices. Very high dark impedance and large visible rejection ratio were obtained. These results indicate high quality GaN/AlGaN interface and efficient photocarrier collection in the photodiode. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122092

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Low-frequency noise in the frequency region of 20 Hz to 20 kHz is investigated in AlGaN/GaN high electron mobility transistors (HEMTs) grown on SiC substrates. The noise spectra have the form of the1/f(flicker) noise. The measured Hooge parameter is as low as 0.0001. This value is comparable with Hooge parameter values for commercial GaAs field effect transistors and approximately two orders of magnitude smaller than Hooge parameter value measured for AlGaN/GaN heterostructures grown on sapphire. The level of noise depends on the gate leakage current; the noise is much higher in devices with a high gate leakage current. The small measured values of the Hooge parameter are related to a smaller leakage current and to a better material quality of the devices on SiC substrates and to a high electron sheet density. The low levels of the1/fnoise in the AlGaN/GaN HEMTs on SiC substrates make them suitable for applications in communication systems. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122093

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

Capacitance–voltage characteristics have been measured at various frequencies and temperatures for structures containing a sheet of self-assembled InAs quantum dots in bothn-GaAsandp-GaAsmatrices. Analysis of the capacitance–voltage characteristics shows that the deposition of 1.7 ML of InAs forms quantum dots with electron levels 80 meV below the bottom of the GaAs conduction band and two heavy-hole levels at 100 and 170 meV above the top of the GaAs valence band. The carrier energy levels agree very well with the recombination energies obtained from photoluminescence spectra. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122094

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The dark current as a function of temperature and infrared absorption of thep-dopedIn0.15Ga0.85As/Al0.45Ga0.55Asmultiple quantum well structures grown by molecular beam epitaxy are investigated. The dark currentIdof the structure is found to be basically symmetrical over a voltage range from −10 to +10 V. It is about10−9 Aat a bias of 1 V at 80 K, more than two orders of magnitude lower than that reported forp-doped GaAs/AlGaAs QW structures with the same size. It is also found thatIdis proportional toT exp[−(EC–EF)/kT]at 70 K and above while at temperatures below 30 K it does not change significantly. TheEC–EFdecreases with the increase in bias in an exponential form, due likely to energy bandgap bending. A strong infrared absorption peaked at a wavelength of 10.7 &mgr;m is in excellent agreement with the estimated value of 10.4 &mgr;m. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122095

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

In this work, the band offsets at theGa0.5In0.5P/AlxGa0.5−xIn0.5Pheterojunction lattice matched to (001) GaAs was calculated over the whole range of aluminum composition fromx=0.0to 0.5 using the first-principles pseudopotential method with virtual crystal approximation. The valence band offset, VBO, varies withxasVBO=0.433x eV,while the inferred conduction band offset CBO at &Ggr; minimum (band-gap difference minus the valence band offset) varies inxasCBO&Ggr;=0.787x eV.Our results are in good agreement with the experimental data. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122096

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

We report the observation of interband exciton transitions inInSb/AlxIn1−xSbmulti-quantum-well samples. The exciton peaks are identified with the use of a simple quantum well model. The strain present in the InSb wells alters the spectrum significantly from that for unstrained III–V materials and makes it possible to use the exciton spectrum in determining the band offset. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122097

出版商:AIP    

年代:1998

数据来源: AIP

摘要:

The photoluminescence emission peak energy of GaN quantum dots was observed to shift to higher energy with decreasing quantum dot size. This effect was found to be a combination of a blueshift from the confinement-induced shift of the electronic levels and a redshift from the increased Coulomb energy induced by a compression of the exciton Bohr radius. From this observation, absolute values of the exciton binding energy as a function of quantum dot size are determined. ©1998 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.122098

出版商:AIP    

年代:1998

数据来源: AIP