摘要:

Dielectric BaTiO3films were heteroepitaxially grown on Si (100) substrates in cube‐on‐cube manner by employing a conductive TiN buffer layer. An epitaxial TiN film was grown by KrF pulsed excimer laser deposition. BaTiO3film was grown epitaxially on the TiN film at a substrate temperature higher than 600 °C and in an oxygen pressure less than 1 mTorr. This epitaxial BaTiO3/TiN layer on Si was observed to have sharp interfaces and little interdiffusion of constituent atoms by secondary ion mass spectrometry. The surface of the BaTiO3film had a root‐mean‐square roughness less than 1 nm as observed by atomic force microscopy. A TiN/BaTiO3/TiN trilayer structure was formed and the dielectric property was measured for this metal‐insulator‐metal type capacitor. The BaTiO3film showed a high relative dielectric constant of 803 at the frequency of 1 MHz and a low leakage current less than 10−8A/cm2at 2 V. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113232

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The odd–even effect of the alkyl chain length of rubbed polyimide Langmuir–Blodgett (LB) films on the extrapolation length of 5CB has been successfully evaluated by measuring polar anchoring strength. The extrapolation length of 5CB for rubbed PI‐LB films with even numbers is small compared with odd numbers for alkyl chain lengths of greater than 7 carbons. The extrapolation length of 5CB on rubbed PI‐LB films with odd numbers increases gradually as the temperature increases but tends to diverge near the clearing temperature (Tc=35.3 °C). The extrapolation length diverges because of rapidly decreasing surface order nearTc. It is suggested that the polar anchoring strength on rubbed PI‐LB films with an even number is strong because of relatively high surface ordering caused by more crystalline surfaces. Finally, it is concluded that the odd–even effects of the polar anchoring strength in NLCs are strongly related to the character of the polymer and observed clearly for long alkyl chain lengths. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113233

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

La‐Sr‐Co‐O/Pb‐La‐Zr‐Ti‐O/La‐Sr‐Co‐O thin‐film capacitors have been grown in various oxygen ambients by pulsed laser deposition. As the oxygen ambient became more reducing, the capacitors developed more voltage asymmetry in hysteresis loops and a more preferred polarization state directed towards the top electrode. PLZT capacitors cooled in a fully oxidizing atmosphere (i.e., 1 atm oxygen pressure) exhibited nominally symmetric hysteresis loops and also showed little imprint both with and without fully saturating bias fields. We find that ambient oxygen pressure is an important process parameter and the imprint behavior is closely related with ambient oxygen induced effects such as oxygen vacancies, its related defect‐dipole complexes and trapping of free charges. The different imprint behavior under negative and positive bias also suggests that the dipolar‐defect complexes tend to cause imprint in PLZT capacitors. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.113234

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Electronic defects inn‐type GaN were characterized by photoemission capacitance transient spectroscopy. Conventional deep level transient spectroscopy is of limited use in semiconductors with wide band gaps (e.g., 3.4 eV for GaN at 300 K) because it utilizes thermal energy for charge emission which restricts the accessible range of bandgap energies to within ∼0.9 eV of either band edge, for practical measurement conditions. For electron photoemission to the conduction band, four deep levels were detected at optical threshold energies of approximately 0.87, 0.97, 1.25, and 1.45 eV. It is suggested that the above photodetected deep levels may participate in the 2.2 eV defect luminescence transitions, which are also demonstrated for our material. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113235

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Controlled registration of InAs clusters and selective‐area growth of InAs thin films on GaAs substrates is achieved via a combined high dose electron beam lithography/metalorganic chemical vapor deposition technique. Auger electron spectroscopy and secondary electron microscopy measurements show that growth inhibition is not a consequence of native oxide masking or processing related surface contamination, but instead is attributable to modification of the GaAs surface energy. This phenomenon is observed for a wide range of lithographic patterns and growth conditions on both (100) and (111)B orientedn‐type and semi‐insulating GaAs substrates. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113195

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Temperature dependent time‐resolved photoluminescence has been used to study the excess carrier recombination in Zn0.75Cd0.25Se/ZnSe single quantum well structures grown by molecular beam epitaxy. For temperatures <100 K radiative excitonic recombination appears to dominate, and the photoluminescence (PL) decay time follows the linear dependence on temperature over the range 50–120 K. At higher temperatures the reduction in PL efficiency and decay time indicate that nonradiative processes associated with the ZnCdSe/ZnSe interfaces dominate the recombination. The results are consistent with theoretical predictions. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113196

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied a nonlinear response of a field‐effect transistor multi &dgr;‐layer structure to an external alternating‐current signal. A specific resonance behavior of the source‐drain resistance was observed in the MHz range depending on the orientation of the magnetic field. The results are discussed within the framework of a model of electron gas heating due to the parametric resonance between the ac electrical signal and the sound wave generated by an ac electrical signal by means of the piezoelectric effect. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113197

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We suggest that a scanning tunneling microscope (STM) may be used for investigating the insulator–conductor interface, in particular SiO2/Si, at nanometer scale. For an insulating film transparent to tunneling, we estimate, using a simple model, the roughness of the interface from the STM image. It is found that the interface roughness is less than the roughness of the image surface times the ratio of effective decay lengths in the film and in vacuum. For relatively wide films, of order 10 nm, STM measurement in the field emission regime can give the interface image with 1 nm precision. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113198

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Fourier transform infrared (FTIR) absorption spectra and photoluminescence (PL) spectra for PbSe0.78Te0.22and Pb0.95Sn0.05Se0.80Te0.20layers grown by liquid phase epitaxy on (100) BaF2substrates are reported. FTIR absorption edges varied from 213 to 275 meV (between 4 and 300 K) for the ternary alloy and from 118 to 200 meV (between 10 and 300 K) for the quaternary alloy. PL energies were 174 meV at 5 keV for the ternary alloy and 100 meV at 7.1 K for the quaternary alloy. The differences between the low temperature FTIR absorption edge energies and the PL energies are attributed to the Burstein–Moss effect. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113199

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We show that piezoelectric effects can give rise to internal electric fields that modify the current–voltage characteristics of double barrier resonant tunneling devices, if suitable stresses are applied. Electric polarization fields in the direction perpendicular to the interfaces arise in heterostructures on (001)‐oriented substrates under uniaxial stress parallel to the (110) or (11¯0) orientations. We measured current–voltage characteristics of (001)‐oriented AlAs/GaAs/AlAs double barrier structures as a function of uniaxial external stress applied parallel to the (110) and the (11¯0) orientations. The substrate contact was grounded in all measurements. Under (110) stress, the resonance peaks shift to more positive voltages for both positive and negative bias. For (11¯0) stress, the peaks shift toward more negative voltages. We also calculated the current–voltage characteristics of resonant tunneling structures under uniaxial stress, taking into account stress effects on the band alignment and piezoelectric effects. We obtain satisfactory agreement between our calculations which contain no adjusted parameters and the measured data. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.113200

出版商:AIP    

年代:1995

数据来源: AIP