摘要:

We have deduced the spatial distribution of defects in light‐soaked hydrogenated amorphous silicon (a‐Si:H) from the thickness dependence of the areal defect density using a large number of film thicknesses, ranging from 0.05 to 8.7 &mgr;m. The light soaking was done with strong white light generated by a Xe lamp with an infrared‐cut filter and the defects were measured using electron spin resonance. The distribution of defects is found to be highly nonuniform and has an inverse power‐law formNv(x)=Ax−&agr;, whereNv(x) is the defect density at depthxmeasured from the surface, andAand &agr; (≊0.6) are constants and depend on the light‐soaking time. Our results show unambiguously that the Staebler–Wronski effect is a bulk effect, however the regions close to the surface are affected much more by light soaking than the regions deep in the bulk of the sample. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114118

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Electroluminescent devices were fabricated in SiO2films containing Ge nanocrystals formed by ion implantation and precipitation during annealing at 900 °C, and the visible room‐temperature electroluminescence and photoluminescence spectra were found to be broadly similar. The electroluminescent devices have an onset for emission in reverse bias of approximately −10 V, suggesting that the mechanism for carrier excitation may be an avalanche breakdown caused by injection of hot carriers into the oxide. The electroluminescent emission was stable for periods exceeding 6 h. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114080

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The relationship between structural defects and device performance of In0.21Ga0.79As/(Al,Ga)As high electron mobility transistors with different In0.21Ga0.79As channel thicknesses (75–300 A˚) was analyzed. Using triple axis x‐ray diffraction and transmission electron microscopy, we determined that the presence of misfit dislocations along only one of the ⟨110⟩ directions did not impair device performance. In fact, the sample with the highest cutoff frequency possessed the misfit dislocations along one ⟨110⟩ direction. However, for thicker samples, with an orthogonal array of misfit dislocations, the device parameters were significantly degraded. We also determined that x‐ray diffuse scattering correlates strongly with device performance, making this nondestructive technique useful for device performance evaluation. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114081

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A novel kind of phototransistor with high gain and sub‐&mgr;m spatial resolution is fabricated by focused laser beam‐induced Zn doping of ann‐modulation doped GaAs/Al0.4Ga0.6As quantum well structure. To produce this lateralnpn‐structure,p‐doped lines are directly written over a mesa without degrading the quality of the sample. The local Zn doping causes an effective potential barrier for electrons. Photogenerated holes reduce this barrier and amplify the thermionic electron current. Spatially resolved photocurrent measurements show typical responsivities above 103A/W and linewidths as small as 605 nm. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114082

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have observed the population of the second two‐dimensional electron subband in &dgr;‐doped Al0.48In0.52As/Ga0.47In0.53As heterostructures by Shubnikov–de Haas measurements. After illuminating the samples at low temperature, the electron density increases from 17.3 to 18.2×1011cm−2for the first subband and from 3.6 to 4.1×1011cm−2for the second subband. The population of the second subband begins when the first subband is filled at a density of 10.3×1011cm−2. The effective mass of the second subband is equal to (0.045±0.003)m0, indicating significant band nonparabolicity in the Ga0.47In0.53As well. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114083

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The reactivity of the Al/Si3N4/Si(100) system has been studied using x‐ray photoelectron spectroscopy (XPS). The Si3N4overlayer was prepared on Si(100) by N ion implantation and subsequent annealing. The deposition at 673 K of Al on a 18 A˚ Si3N4overlayer leads to the total reduction of the Si3N4overlayer and the aluminum nitridation. The reaction also takes place at room temperature (RT) but to a lesser degree. The stability of a RT formed Al/Si3N4/Si structure was examined by increasing the sample temperature up to 673 K. In this way, the near complete reduction of a 24 A˚ Si3N4overlayer was obtained. These results show the instability of the Al/Si3N4interface at moderate annealing temperatures. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114084

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

An array of transfer length measurement (TLM) structures was formed on an electrically isolated (0001)n+6H&agr;‐SiC epilayer. Then+6H&agr;‐SiC epilayer contained aninsituincorporated nitrogen concentration of 4×1019cm−3. The specific contact resistance (&rgr;c), sheet resistance (Rs), contact resistance (Rc), and transfer length (LT) were calculated from resistance (RT) versus contact spacing (d) measurements obtained from 17 TLM structures. The linear curves used for these calculations were fit to theRTversusddata by calculating the standard error of linear regression ofRTond; where, the average correlation coefficient with a straight line was 1.0000 and the average standard error of linear regression ofRTondwas 0.08 &OHgr;. The resulting average values were: &rgr;c=1.30×10−5&OHgr; cm2,Rs=14.4 &OHgr;/square,Rc=1.6 &OHgr;, andLT=9.5 &mgr;m. The (111) TiC contacts, epitaxially grown by chemical vapor deposition, were thermally and chemically stable at 1400 °C. The TiC contacts could not be scratched with a tungsten carbide scriber, nor delaminated from the 6H&agr;‐SiC substrate. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114085

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The refractive index changes have been time resolved in crystalline Ge near the direct‐band‐gap (0.8 eV, 1.55 &mgr;m) following femtosecond pulse excitation at room temperature. Measurements were made for 1.485<&lgr;<1.55 &mgr;m using degenerate pump‐probe transmission and reflection spectroscopy with 120 fs pulses from an optical parametric oscillator. Resonant excitation leads to large refractive index changes (≳10−3for 1017cm−3carrier density) dominated by band filling and carrier screening effects. Unlike the much slower recovery observed in direct gap semiconductors, the refractive index change disappears with a time constant of 230 fs due to intervalley scattering of electrons to the lower energyLvalley in this indirect‐gap semiconductor. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114086

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Insituscanning tunneling microscopy (STM) has been used to examine the etching of ann‐Si(001) electrode in 0.1 M NH4F. Cathodic polarization facilitated chemical etching of Si(001) to give {111} microfacets as a result of the tendency of Si to form a monohydride terminated surface. Time‐dependentinsituSTM atomic images were obtained to demonstrate the preferential etching at the kinks and steps. From the results of the time‐dependent imaging, local etching rates were evaluated for the specific crystallographic directions. A Si(001):H‐(1×1) square structure was also obtained, demonstrating the presence of dihydride configuration in the beginning of the etching. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114087

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The grain boundary YBa2Cu3Oy(YBCO) Josephson junctions are fabricated on (100)MgO bicrystal substrates with a misorientation angle of 24° and the microwave properties of Josephson effects are studied up to millimeter‐wave range. Strong [100]//[010] and [010]//[100] in‐plane orientations are observed at the junction interface of a YBCO film, whose microscopic geometries are discussed in connection with the observed Josephson effects. The directly observed maximum Josephson microwave self‐radiation powers from the junction at receiver frequencies offREC=22 GHz and 47 GHz are 3.2×10−12W and 5.6×10−14W, respectively. The observed characteristic voltage (Vc) is 4.4 mV, corresponding to the frequency of about 2 THz at 4.2 K. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114088

出版商:AIP    

年代:1995

数据来源: AIP