摘要:

We have demonstrated the excitation and control of coherent cyclotron emission from a semiconductor using a THz beam containing pairs of sub-picosecond electric field pulses closely spaced in time. The source of THz radiation in these experiments is a biased coplanar stripline fabricated on semi-insulating GaAs and edge illuminated with pairs of temporally and spatially separated 70 fs pulses of near infrared light. A GaAs/AlGaAs two-dimensional electron gas was used in the experiments because of its long intraband phase relaxation time. Changes in the amplitude and phase of the cyclotron emission are observed when varying the interpulse delay and are well described within the theoretical framework of a two level system. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120167

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report the observation of highly nondegenerate four-wave mixing from a semiconductor microcavity. The phase mismatch originating from the unique relationship between a beam incidence angle and its cavity resonance frequency was minimized by using a new method where both of pump and probe beams are obliquely incident. External efficiency of 1.6&percent; was measured at 10 K for 1.5 THz frequency conversion of probe pulses by using 1 ps pump pulses of 55 pJ incident pulse energy. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120168

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Real-time measurements ofGexSi1−x/Si(001)composition and segregation dynamics in Sn/Si(001) in molecular beam epitaxy are demonstrated using parallel detection reflection electron energy loss spectroscopy. Parallel detection enables quantitative acquisition of low-loss spectra in a time of<500 &mgr;sand surface composition determination inGexSi1−x/Si(001)viaGe L2,3core loss analysis to a precision of approximately 2&percent; in time of order 1 s. Segregation and trapping kinetics of monolayer thickness Sn films during Si epitaxy on Sn-covered Si(100) has also been studied using theSn M4,5core loss. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.120136

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The Pd/Ge/Ti/Au ohmic contact to AlGaAs/InGaAs pseudomorphic high electron mobility transistor was investigated with the etch depth of an undoped GaAs/AlGaAs cap layer. The contact resistivity decreases from9.5×10−5to2.3×10−6 &OHgr; cm2when the contacts were formed on an-Al0.23Ga0.77Aslayer by removing the undoped cap layer. X-ray diffraction results show that the good ohmic contact is due to the formation ofAu2Alas well as &bgr;-AuGa. Both compounds play a role to create group-III vacancies, followed by the incorporation of Ge into group-III vacancies, namely, creation of free electron below the contact. This results in the considerable elimination of contact resistivity by lowering the effective tunneling barrier. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120169

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The surface decomposition of trisdimethylaminoarsenic (TDMAAs) on GaAs (001) has been studied employing supersonic molecular beam scattering. It was found that TDMAAs molecules adsorbed dissociatively on GaAs (001) surfaces at room temperature through a Langmuir adsorption mechanism. The initial Ga-rich(4×6)surface changed into an As-richc(4×4)surface after the injection of TDMAAs. The species such as dimethylamine and methylmethyleneimine desorbed at the surface temperatures of 150 and 230 °C, respectively, as measured by temperature-programmed desorption (TPD) spectra. The polar-angle dependence of desorption showed that the desorption of species has two maximal intensities, at the directions along surface normal and 60°, respectively. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120170

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Site-selective photoluminescence (PL) spectra obtained at 6 K from the 1540 nm4I13/2→4I15/2emissions characteristic of four distinctEr3+centers in Er-implanted films of GaN are compared with theEr3+PL excited by 325 nm above-gap pump light. Two of the site-selective 1540 nmEr3+PL spectra pumped by below-gap, trap-mediated excitation bands dominate theEr3+PL spectrum excited by above-gap light. A third broad band-excited spectrum and a fourth spectrum pumped by directEr3+4f-band absorption are apparently not strongly excited by above-gap light. These results indicate that trap-mediated excitation dominates above-gap pumping ofEr3+emission in GaN:Er, and suggest an explanation for the reduced thermal quenching ofEr3+emission in GaN. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120171

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Self-pulsation within 650 nm, AlGaInP laser diodes can be achieved via the use of a saturable absorbing, epitaxial layer within the structure. A rate equation model of this type of device is presented, which includes the process of thermally activated charge transfer from the quantum well and gain region to the absorbing layer. The results indicate that this thermal leakage mechanism saturates the absorber and hence destroys the self-pulsation at high temperatures. Comparison of the model with recently published experimental data shows good agreement and provides a consistent explanation for the loss of pulsation at temperatures in excess of 60 °C. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120172

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Cathodoluminescence at 77 K was used to study the optical properties of ion-implanted and annealed natural type IIa diamonds. The substrates were implanted at room temperature with12C+,11B+,31P+, and75As+-ions with energies of up to 350 keV and doses of up to 3×1013cm−2. After annealing at 1200°C, the cathodoluminescence spectra show a number of transitions which are induced by the radiation damage independent of the implanted ion species. Only in the B+implanted samples are there two transitions related to the implanted ion species: the 4.5 eV band and the boron bound exciton. The appearance of the bound exciton spectrum demonstrates the presence of isolated boron on substitutional lattice sites implying electrical acceptor activity. Our annealing studies indicate a minimum annealing temperature of 1000°C for the activation of the implanted boron atoms onto the acceptor states. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120173

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Infrared photothermal radiometric deep-level transient spectroscopy (PTR-DLTS) has been applied to noncontact diagnostics of ap-Si wafer. Both negative and positive peaks in the PTR-DLTS signal temperature scans have been detected. A behavior consistent with photoinjected carrier lifetime enhancement due to the thermal filling ofB+dopant levels in the band gap has been observed. The activation energies of 43 meV (negative peaks) and 60 meV (positive peaks) have been extracted from the corresponding Arrhenius plots. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.120174

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A tensile-strained five-step asymmetric coupled quantum well (FACQW) structure is proposed for large field-induced refractive index change without polarization dependence and redshift of the absorption edge. A strong exciton absorption peak is caused by electron-hole transitions between symmetric wave functions and antisymmetric wave functions with a small applied electric field. The field-induced refractive index change of strained the FACQW is larger by one order of magnitude compared to that of a rectangular quantum well and the difference in the refractive index change of TE and TM modes is under 2&percent; when the operation wavelength is not at the absorption edge. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120175

出版商:AIP    

年代:1997

数据来源: AIP