摘要:

Recently it has been shown that perturbation of an already operating semiconductor laser with an additional pump pulse may lead to an unusual ultrafast switch-off. This effect is due to transient carrier heating. Subsequent carrier cooling allows for switch-on after about two picoseconds. In vertical cavity lasers containing only a few quantum wells as the active medium, the recovery, however, is limited by the comparatively low gain in the cavity. Here we demonstrate experimentally that both switch-off and switch-on can exhibit subpicosecond time constants if a bulk semiconductor is used as the active medium. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118223

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a study of the room temperature electromodulation properties of CdHgTe heterostructures as a base component for a photorefractive device operating at 1.5 &mgr;m. We reach absorption modulation as high as 200&percent;, in the near-gap transparent region of the spectrum, by application of a reverse bias of the order of 100 kV/cm. We observe the transition from the Franz–Keldysh effect in 200 Å wide wells to the quantum confined Stark effect in 90 Å wells. The calculated diffraction efficiency in a suitable photorefractive device would be of the order of8×10−4in both cases. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118297

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A high strain two-stack, two-color, InGaAs/AlGaAs and AlGaAs/GaAs quantum well infrared photodetector for midwavelength infrared (MWIR) and long wavelength infrared (LWIR) detection has been demonstrated. Each stack is designed to have detection in one of the two atmospheric windows, 3–5 &mgr;m and 8–12 &mgr;m, respectively. The MWIR stack has employed 35&percent; of indium in the InGaAs well, which not only achieved peak wavelength at 4.3 &mgr;m, but also obtained very high peak responsivity ofRp=0.65A/W, using 45° light coupling. Normal incidence without grating coupling also has high responsivity with 40&percent;–50&percent; in the MWIR stack and 35&percent;–45&percent; in the LWIR stack, respectively, compared with the 45° incidence. Despite the large in-plane compressive strain induced by the high indium concentration, the device is highly uniform and has very low dark current in the MWIR stack. The background limited temperature is 125 K for the MWIR stack with a cutoff wavelength&lgr;c=4.6&mgr;m, and is 70 K for the LWIR stack with&lgr;c=10&mgr;m. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118298

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigate the hole perpendicular transport properties in semiconductor superlattices (SLs) by using the extended Lei–Ting balance equation theory for an arbitrary energy band including hole-impurity, hole-polar-optic-phonon, and hole-nonpolar-optic-phonon scatterings. Effects of heavy-hole–light-hole mixing are taken into account by means of the approximate dispersion relation suggested by O. E. Raichev [Phys. Rev. B50, 5382 (1994)]. Numerical calculations show that the complex hole energy spectrum causes a breakdown of the negative differential conductance for the hot-hole perpendicular transport in SLs in contrast with the results corresponding to a simplified electronlike energy spectrum. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118299

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Germanium thin films have been epitaxially regrown on (001) GaAs byin situthermal pulse annealing of evaporated amorphous germanium under<102Watt/cm2broad-band irradiation in high vacuum. Epitaxial regrowth was found to occur only when the duration of the thermal pulse(te)was greater than a critical valuetc(≃3.20 s). The crystal quality of the resultant film was examined by high resolution x-ray diffraction technique (HRXRD) and grazing-incidence x-ray diffraction technique (GIXRD). All rocking curves were found to have a full width at half-maximum of about 0.02°. Both HRXRD and GIXRD confirmed the Ge overlayer was grown epitaxially as well as pseudomorphically on the substrate. Scanning electron microscopy and atomic force microscopy revealed the very different surface morphologies resulting from differentte.Forte<tc,columnar germanium grains with a four-fold symmetry and a high uniformity in size were found, while forte⩾tc,epitaxial regrowth was observed. It is suggested that epitaxial regrowth takes place via a temporary formation of liquid phase Ge. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.119071

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The continuous-wave operation of InGaN multi-quantum-well-structure laser diodes (LDs) was demonstrated at room temperature with a lifetime of 24–40 min. The threshold current and the voltage of the LDs were 80 mA and 6.5 V, respectively. The laser emission was a fundamental single-mode emission with a peak wavelength of 400.23 nm and a full width at half-maximum of 0.002 nm. The beam full width at half-power values for the parallel and the perpendicular near-field patterns were 1.6 and 0.8 &mgr;m, respectively. Those of the far-field patterns were 6.8° and 33.6°, respectively. The carrier lifetime and the threshold carrier density were estimated to be 5 ns and1×1020/cm3,respectively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118300

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have studied the potential induced by lateral surface superlattices deposited on a GaAs/AlGaAs heterostructure as a function of bias and orientation of the gates. By using the gates to null the total potential, we extracted the contribution to this potential in the absence of gate bias. Its angular dependence shows that it is dominated by strain from the gates coupled to the electrons by the piezoelectric effect. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118301

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A study of the effects of C and Ge additions on the Cu catalyzed oxidation of Si has been performed. It was found that the addition of Ge alone resulted in a marked slowdown in the rate of oxygen incorporation; during the first three days of the experiment the rate of oxygen incorporation was 25 times higher in the Si reference sample. The Ge was incorporated into the oxide. Small amounts of C added to the SiGe compound have a more pronounced effect. Carbon concentrations of less than 2&percent; prevent oxidation of SiGeC for periods of at least one month. Copper enhanced oxidation of Si(100) has produced oxides of several hundred nanometers in under one month. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118302

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The&agr;-HgI2/CdTe:Geheterostructures have been studied by cathodoluminescence (CL) in the scanning electron microscope. The&agr;-HgI2expitaxial growth was shown to cause an enhancement of the CL intensity in a layer of the substrate extending up to about 500 &mgr;m from the&agr;-HgI2/CdTe:Geinterface. CL spectra of the layer reveal the appearance of a band related to tellurium vacancies as well as the decrease of the emission attributed to defect complexes involving Ge. The data obtained indicate that Ge-impurity gettering andVTegeneration at the interface take place during&agr;-HgI2epitaxial growth. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118237

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The origin of the leakage current in low-pressure chemically vapor deposited polycrystalline silicon (polysilicon) thin-film transistors is investigated by low-frequency noise measurements. The leakage current depends on the structure of the polysilicon layer. When the grain size is relatively large (about 120 nm), the noise spectra show a pure1/fbehavior caused by carrier fluctuation within the space charge region of the drain junction. For smaller grain size (about 50 nm), the observed1/f1.5spectra are attributed to thermal noise of the bulk polysilicon film. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.118239

出版商:AIP    

年代:1997

数据来源: AIP