摘要:

Photoluminescence investigations on undopedn‐type GaN layers grown on 6H‐SiC and sapphire reveal the presence of residual acceptors with a binding energy of 230 meV. Their presence in high temperature vapor phase epitaxy grown layers is strongly correlated with the graphite susceptor containing the Ga. Mg as a contamination can be ruled out. In metal organic vapor phase epitaxially grown layers, the metal organic are probably the source of the carbon contamination. It is concluded that carbon on nitrogen sites introduces the most shallow acceptor in GaN. The experimental observations are supported by an estimate of the acceptor binding energy using effective‐mass‐theory. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114403

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We describe a method of lateral band gap modulation by creating steep lateral strain gradients in multiquantum (MQW) structures on InP. The strain modulation is obtained by controlled elastic relaxation of micromachined free‐standing strained MQW stacks. Large lateral energy modulation is achieved, suitable for lateral optical mode confinement and lateral quantum confinement of excitons. It is pointed out that this technology can be applied in monolithic integration of semiconductor optical devices. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114404

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

A non‐linear superconducting transmission line has been successfully employed in heterodyne detection of sub‐millimeter waves. In our experiments an Nb/Al/AlOx/Nb tunnel junction, measuring 0.15×40 &mgr;m, with a critical current density of about 2500 A/cm2is used as a distributed mixer element. We have demonstrated that quantum limited sensitivity can be achieved with this type of device. At 460 GHz, aY‐factor of 2.5 has been recorded, corresponding to a double‐side‐band receiver noise temperature of 80 K. The double‐side‐band conversion loss is about 1 dB and the mixer noise temperature is estimated to be 18(±10) K. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114405

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Flicker noise inc‐axis oriented long YBCO bicrystal grain boundary junctions was characterized as a function of temperature, biasing conditions, and magnetic field applied perpendicular to thea–bplane over a wide range of temperatures from 15 K to over 70 K. Aperiodic variations, as a function of magnetic field, were observed in both the junction voltages,VJ, and the flicker noise magnitude under constant current bias as the magnetic field was scanned from 0 to 8 G. The noise magnitudes were found to peak at the minima ofVJ. Analyses of the field dependencies of the magnitudes and the functional form of the voltage noise power spectra show that the noise did not arise from thermally activated flux motion. Based on the dependencies of the noise power spectra on the bias current and the dynamic resistance of the junction, we conclude that the noise originates from the fluctuations of the critical current of the devices most likely due to trapping of carriers or defect motion within the grain boundary. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114522

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The conversion of semiconductive SrCuO2‘‘infinite layer’’ epitaxial films into a metallic and superconducting (Tc&bartil;30 K) oxycarbonate phase related to Sr2CuO2(CO3) has been induced by thermal processing in oxidizing ambient containing a small amount of CO2. Ion beam analysis using the resonant12C(p,p)12C elastic backscattering cross section for protons incident at 1.73 MeV confirms the presence of substitutional C in the converted perovskite lattice. Comparison of the threshold CO2partial pressure with thermodynamic stability data for SrCO3suggests that the conversion is initiated by the high affinity of Sr(O) for CO2. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114523

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The low frequency current–voltage characteristics of YBa2Cu3O7–SrRuO3–YBa2Cu3O7Josephson junctions show an increasing resistance and phase shift in fields of 0 to 8 T. A critical current is also evident up to 8 T. Data are analyzed in terms of field‐induced perturbations of the current paths through the junction. Results indicate a highly inhomogeneous interface where the mean width of spatial variations in both normal and supercurrent is of order 50 to 100 A˚. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114524

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Large area (0.8 cm2) single‐crystal films ∼1 &mgr;m thick of Ni–Cu alloy have been electrodeposited directly onto (100)n‐type GaAs. The epitaxial relationship was found to be (001) Ni–Cu parallel to (001) GaAs and [110] Ni–Cu parallel to [100] GaAs. Magnetic measurements show the films to be ferromagnetic. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114525

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

CO has been detected down to 500 parts per trillion by volume using infrared excitation of CO dissolved in liquid Ar solution with laser induced fluorescence detection. The feasibility of theinsitudetection of trace concentrations of atmospheric and industrial pollutants dissolved in liquid air is discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114526

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We have studied nucleation and growth characteristics of diamond on nickel with AlN buffer layers. The diamond deposits on partially filled 3‐dshell transition metals such as Ni, Fe, and Co usually result in the formation of interposing graphite layers which cause poor adhesion of diamond overlayers. To minimize and preferably eliminate the formation of the interposing graphite layer, we coated nickel substrate with ∼1000 A˚ thick AlN layer by using pulsed laser deposition and subsequently, subjected them to diamond deposition by hot filament chemical vapor deposition method. It is found that the aluminum nitride layer plays a crucial role in limiting carbon diffusion and inhibiting the formation of graphitic carbon and simultaneously enhancing the nucleation and adhesion of diamond phase. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114527

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Laser ablation of a BiSrCaCuO target is performed both in vacuum and in an oxygen pressure of 0.1 mbar. Two substrates are located in the chamber in order to study the role of re‐emission processes from the growing film and/or the scattering of the ablated species by an oxygen atmosphere. The results indicate that re‐emission processes from the growing film are very weak (they may affect up to 1% of the deposited material at most) and are not related to the re‐sputtering of the growing film. Films grown in vacuum are found to have the correct cation composition, whereas those grown in an oxygen environment show significant variations which are clearly related to gas scattering processes. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114528

出版商:AIP    

年代:1995

数据来源: AIP