摘要:

A magnetically driven magnetostrictive sample, which is used as the sensing element in a fiber‐optic magnetometer, is known to exhibit strain bifurcations. Standard techniques for fiber‐optic magnetostrictive magnetometers employ demodulation at a carrier frequency &ohgr;cbut, typically, the resolution is limited by 1/fnoise around &ohgr;c. We present a novel technique for the detection of low‐frequency magnetic signals which employs the frequency associated with a period doubling bifurcation &ohgr;c/2, and which avoids upconverted 1/fnoise near &ohgr;c. The signal‐to‐noise ratio of low‐frequency magnetic signals near &ohgr;c/2 remains flat in the range 0.025–10 Hz, with a resolution of 5 nT/&sqrt;Hz for a sensor using only 5 mm of fiber, limited by the phase noise of the fiber interferometer.

ISSN:0003-6951    

DOI:10.1063/1.106009

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We investigate the temperature dependence of the field‐effect (FE) conductance of thin‐film transistors on undoped polycrystalline silicon layers. The FE conductance is thermally activated at a fixed gate voltage. The conductance prefactorG0increases exponentially with the FE activation energyEa, in accordance with the Meyer–Neldel rule. Using these results, a model of exponentially decaying band tails explains the FE activation energy data. By fitting the FE activation energy data with the theory, we determine the trap distribution in polysilicon layers deposited at various pressures. The results indicate that the existence of band tails is not an intrinsic property of grain boundaries.

ISSN:0003-6951    

DOI:10.1063/1.106010

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Copper is a possible substitute for Al in very large scale integration interconnects because of its higher resistance to electromigration damage (EMD) and its lower electrical resistivity. In the present work, we report on electrical resistance measurements of the activation energy for EMD in Cu films as determined by an isothermal annealing method carried out under high vacuum conditions. Temperature measurement and control were accomplished by means of a Cu thin‐film thermistor. The activation energy for EMD of evaporated Cu films was found to be 0.79±0.02 eV.

ISSN:0003-6951    

DOI:10.1063/1.106011

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

The deposition of Si1−xGexalloy layers in an atmospheric‐pressure, chemical vapor deposition reactor has been studied by separately examining the silicon and the germanium components of the deposition rate. The overall deposition rate increases approximately linearly with GeH4partial pressure, but is relatively independent of SiH2Cl2partial pressure. The silicon component of the deposition rate increases rapidly with increasing temperature for a constant germanium content, but the germanium component changes only slowly above about 675 °C, and is probably limited by mass transport.

ISSN:0003-6951    

DOI:10.1063/1.105986

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We show in this letter that population inversion between subbands in a quantum well can be achieved through resonant interband tunneling. Two basic device configurations based on polytype heterostructures are proposed and analyzed. The estimated population inversion (n2−n1) could be as high as 3×1011/cm2with a moderate injected current density 104A/cm2under a forward bias.

ISSN:0003-6951    

DOI:10.1063/1.105987

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Both 3C‐SiC and 6H‐SiC single‐crystal films can be grown on vicinal (0001) 6H‐SiC wafers. We have found that oxidation can be a powerful diagnostic process for (1) ‘‘color mapping’’ the 3C and 6H regions of these films, (2) decorating stacking faults in the films, (3) enhancing the decoration of double positioning boundaries, and (4) decorating polishing damage. Contrary to previously published oxidation results, proper oxidation conditions can yield interference colors that provide a definitive map of the polytype distribution for both the Si face and C face of SiC films. Defects were more effectively decorated by oxidation on the Si face than on the C face.

ISSN:0003-6951    

DOI:10.1063/1.105960

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Al0.5Ga0.5As/GaAs/Al0.5Ga0.5AsNpNdouble‐heterojunction bipolar transistors have been grown simultaneously by molecular beam epitaxy on (100) and 3° off (100) towards ⟨111⟩AGaAs substrates. On the tilted substrate, the current gain is significantly higher, comparable to the maximum expected value, with a marked reduction of its dependence on current and device geometry. For 10 &mgr;m×40 &mgr;m emitter devices, maximum common emitter current gains (&bgr;) of 1630 and 725 were measured at a current density of ∼6.3 kA/cm2on the tilted and flat substrates, respectively. On the tilted substrate, both the emitter injection efficiency and base transport factor are increased. We have used compositionally graded emitter‐base (e‐b) and abrupt base‐collector (b‐c) junctions. We find that the abrupt b‐c junction does not result in an offset voltage but certainly reduces the electron collection efficiency, and hence the gain, in the region where it is forward biased. The device characteristics and the current gain on both substrates were essentially independent of temperature between 25 and 100 °C, except for a slight decrease of gain with increasing temperature.

ISSN:0003-6951    

DOI:10.1063/1.105961

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

We have measured the total soft‐x‐ray power from a transition radiator composed of a stack of 25 beryllium foils each 1.0 &mgr;m thick which were penetrated by a relativistic electron beam whose maximum power was approximately 7 kW. The maximum total soft‐x‐ray power was measured to be 15.2 mW for a 245 MeV, 37 &mgr;A electron beam. The bandwith of the radiation at the full width half maximum points was calculated to be between 0.6 and 1.6 keV. In addition, we have exposed photoresist‐coated silicon wafers at a distance of 3 m from the radiator. Exposure times of the bare resist were as short as 120 s for 5 cm2of wafer are (resist sensitivity is 55.6 mJ/cm2). The shortest time for mask/wafer exposure was 180 s for 5 cm2.

ISSN:0003-6951    

DOI:10.1063/1.105962

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

Exposure of GaAs field‐effect transistors to &agr;‐particle radiation has resulted in burnout paths from under the gate to both the source and the drain. Monte Carlo calculations show that the current response from an &agr;‐particle penetrating the center of the gate electrode at normal incidence lasts for 60 ps, about five times longer than predicted by previous hydrodynamic modeling. The thermalization of the induced electrons causes a maximum subsurface heating of the epilayer near the source and the drain when both are held at ground with a negative bias on the gate. A possible melting of the semiconductor will take place at these locations. We present here for the first time a more accurate simulation of the actual lattice heating rates obtained from electron‐phonon exchanges inside the device. Although the qualitative results support the previous hydrodynamic analysis, some important quantitative differences are noted.

ISSN:0003-6951    

DOI:10.1063/1.105963

出版商:AIP    

年代:1991

数据来源: AIP

摘要:

This letter demonstrates that recombination lifetimes in excess of 5 ms can be achieved in the oxidized magnetic Czochralski (MCZ) silicon by a combination of high‐purity crystal growth, proper cleaning and oxidation conditions. Lifetime studies were conducted at room temperature on as‐grown as well as oxidized 2000 &OHgr; cm low oxygen (∼5 ppm) MCZ silicon by an injection sensitive, contactless photoconductive decay technique with controlled injected carrier densities up to 1017cm−3. Record Shockley–Read–Hall lifetimes of 8.5 and 6.6 ms were achieved in the as‐grown and oxidized MCZ wafers, respectively. However, oxidized Czochralski (CZ) silicon with 14.2 ppm oxygen gave lifetime of only 200 &mgr;s due to much higher concentrations of as‐grown and process‐induced defects. Lifetime versus injection level analysis gave ambipolar Auger recombinationCcoefficient of 1.1×10−30(±9%) cm6 s−1before and after the oxidation in both MCZ and CZ silicon. Unlike theCcoefficient, theBcoefficient (radiative band‐to‐band + trap‐assisted Auger) in low‐oxygen MCZ silicon was found to be four times smaller than the value in high oxygen CZ silicon.  

ISSN:0003-6951    

DOI:10.1063/1.106407

出版商:AIP    

年代:1991

数据来源: AIP