摘要:

3 W cw output power has been obtained from aluminum‐free, strained‐layer double‐quantum well (DQW) InGaAs/InGaAsP/InGaP uncoated, 100‐&mgr;m‐wide stripe diode lasers (&lgr;=0.945 &mgr;m) grown by low‐pressure MOCVD on exact (100) GaAs substrates. The combination of high‐band‐gap (1.62 eV) InGaAsP confinement layers and the DQW structure provides relatively weak temperature dependence for both the threshold currentIthas well as the external differential quantum efficiency &eegr;d. Furthermore, the series electrical resistance for 100 &mgr;m×600 &mgr;m stripe‐contact devices is as low as 0.12 &OHgr;. As a result, the power conversion efficiency reaches a maximum of 40% at 8×Ith, and decreases to only 33% at the maximum power (i.e., 3 W) at 28×Ith. Low‐temperature (12 K) photoluminescence measurements of InGaAs/InGaAsP quantum‐well structures exhibit narrow linewidths (<10 meV) for material grown on exact (100) GaAs substrates, while growths on misoriented substrates exhibit linewidth broadening, as a result of ‘‘step bunching.’’ Laser structures grown on misoriented substrates exhibit increased temperature sensitivity of bothIthand &eegr;d, compared with structures grown on exact (100) substrates. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114836

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We show theoretically how the quantum‐confined Stark effect (QCSE) shifts of the E1–HH1 and E1–LH1 energy transitions can be engineered to be closely matched over the entire range of applied fields up to ±100 kV/cm using structures containing more than one strained‐layer composition within each well. In contrast, conventional quantum wells that contain a single uniform composition within each well can at best have the energy levels for the HH1 and LH1 states matched at only one field value. Furthermore, we show how the TE and TM absorption spectra are modified using multistrain‐stepped structures leading to improved polarization‐insensitive QCSE modulators. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114837

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Quasi‐single‐cycle near‐infrared light pulses with a measured spectrum extending from 7 to 15 &mgr;m have been generated, opening up new perspectives in IR spectroscopy. The method is based on the rectification of 0.8 &mgr;m 10–15 fs light pulses from a 100 MHz oscillator, using the instantaneous second‐order polarizability of bulk semiconductors such as GaAs. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114838

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Difference frequency generation in quasi‐phase‐matched LiNbO3is carried out using a Nd:YAG laser and a high power semiconductor laser. Operation at quasi‐phase‐matching degeneracy point results in an ultrawide 0.5 &mgr;m acceptance bandwidth. Crystal‐rotation‐free wavelength tuning of 4.0–4.5 &mgr;m, with 0.2 mW output power at 4.5 &mgr;m is achieved. Separately, a tuning range 3.0–5.5 &mgr;m is demonstrated with sample rotation and a Ti:Al2O3laser. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114839

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The characteristics of frequency chirp of a two section distributed feedback (DFB) laser, which is under large signal modulation, is studied while the optical intensity and optical modulation depth are fixed. It is found that the measured time‐averaged power spectrum of the laser changes from one of a predominantly negative frequency chirp (red shift) to positive chirp (blue shift) as the injection current distribution between the two sections is changed. Our theoretical calculation of frequency chirp in DFB lasers based on the Green’s function method explains the shift of the frequency chirp in the two section DFB laser. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114840

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The vertical magnetotransport properties of GaAs–AlAs superlattices have been investigated as a function of the in‐plane magnetic field orientation. Two main effects were observed: (i) the influence of the roughness anisotropy with respect to the crystallographic orientation, and (ii) the nonparabolicity of the energy in the plane of the layers. The interface fluctuations induced a modulation of the miniband transport with a period of 180°. The nonparabolic energy of the deflected electronic orbits also induced a modulation of the vertical transport but with a period of 90°. Both observed effects are in qualitative agreement with a semiclassical description of the Boltzmann transport equation. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114841

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Large second‐order nonlinear optical response has been observed in silicon carbide thin films deposited by pulsed laser ablation on sapphire and fused silica substrates; films on both substrates were uniform and optically transparent but exhibited distinct orientations. Thed33values of the sapphire‐substrate samples were determined to be 10 pm/V. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114842

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Optical emission spectroscopy and charge collector time‐of‐flight measurements have been used to study interaction of laser ablation carbon plasma with grid screens in vacuum under conditions typical for pulsed laser deposition of thin diamondlike films. The effect of velocity distribution transformation of the ion flow has been observed and studied in a variety of experimental conditions. Our results indicate that the observed phenomenon is due to interaction of two plasma flows, the initial expanding one and the fraction of that flow scattered by the substrate or the screen. Three typical modes of velocity distribution function transformation have been observed depending on the plasma density: linear attenuation of the flow density, nonlinear attenuation of the slow ‘‘tail’’ of the velocity distribution function, and nonlinear transformation of the entire velocity spectrum. The latter regime occurs when plasma is throttling through the fine mesh screen. Our observations show that the reported phenomenon may substantially affect deposited film properties. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114843

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Atomic‐scale mechanical processing of layered materials such as muscovite mica was performed using an atomic force microscope (AFM). Processing began at a certain critical load above 130 nN, and the processing depth increased discretely with load. Fracture easily occurred at the two cleavage planes of SiO4–K and K–SiO4interfaces. With a load slightly larger than the critical load, several repetitions of mechanical sliding of the tip generated a 1 nm deep groove which corresponds to the distance from the top surface of SiO4to the top surface of the next SiO4layer beneath it with the removal of residual potassium on the surface. For example, a groove with four steps of 1 nm depth was processed by step‐by‐step mechanical sliding. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114844

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The preferred orientation of polycrystalline TiN films grown by ultrahigh‐vacuum reactive‐magnetron sputter deposition on amorphous SiO2at 350 °C in pure N2discharges was controllably varied from (111) to completely (002) by varying the incident ion/metal flux ratioJi/JTifrom 1 to ≥5 with the N+2ion energyEimaintained constant at &bartil;20 eV (&bartil;10 eV per incident accelerated N). All samples were slightly over‐stoichiometric with N/Ti=1.02±0.03. Films deposited withJi/JTi=1 initially exhibit a mixed texture with competitive columnar growth which slowly evolves into a nearly complete (111) texture at film thicknesses greater than 1 &mgr;m. However, films grown withJi/JTi≥5 exhibit an essentially complete (002) preferred orientation from the earliest observable stages. The normalized XRD (002) intensity ratio in thick layers increased from &bartil;0 to 1 asJi/JTiwas varied from 1 to ≥5. Both (111) and (001) interplanar spacings remained constant as a function of film thickness yielding a lattice constant of 0.4240±0.0005 nm, equal to that of unstrained bulk TiN. Contrary to previous models, the present results establish that TiN preferred orientation can be controlled without introducing large in‐plane compressive stress and/or changes in the strain energy as a function of layer thickness. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114845

出版商:AIP    

年代:1995

数据来源: AIP