Ab initio cluster methods are used to investigate vacancy-impurity complexes in diamond. We assign the 1.682 eV, twelve-line optical band a vacancy-Si complex which has very unusual, possibly unique structure with Si atom at center of split vacancy. The method also successfully accounts for 1.945, 2.156, and 2.985 eV transitions trigonal vacancy-N defects estimates radiative lifetimes given.

The incorporation of Au during vapor-liquid-solid nanowire growth might inherently limit the performance nanowire-based devices. Here, we assess material quality Au-assisted and Au-free grown GaAs/(Al,Ga)As core-shell nanowires using photoluminescence spectroscopy. We show that at room temperature, internal quantum efficiency is systematically much lower for than ones. In contrast, optoelectronic latter comparable to state-of-the-art planar double heterostructures.

GaAs nanowires (NWs) grown by molecular-beam epitaxy may contain segments of both the zincblende (ZB) and wurtzite (WZ) phases. Depending on growth conditions, we find that optical emission such NWs occurs either predominantly above or below band gap energy ZB [E(g,ZB)]. This result is consistent with assumption [E(g,WZ)] larger than E(g,ZB) alternating WZ along wire axis establish a type II alignment, where electrons captured within recombine holes neighboring segments. Thus, corresponding...

Abstract Broadband terahertz spectroscopy enables many promising applications in science and industry alike. However, the complexity of existing systems has as yet prevented breakthrough this technology. In particular, established time-domain (TDS) schemes rely on complex femtosecond lasers optical delay lines. Here, we present a method for optoelectronic, frequency-modulated continuous-wave (FMCW) sensing, which is powerful tool broadband industrial non-destructive testing. our method,...

Continuous wave (cw) terahertz (THz) radiation has a wide array of applications, ranging from sensing to next-generation wireless communication links. Industrial applications frequently require THz systems that are broadband, highly efficient, and compact. Photomixer-based solutions hold promise in meeting these demands, offering extremely broadband operation the potential for miniaturization through photonic integration. However, current photoconductive antenna (PCA) receivers used...

Local-density-functional pseudopotential theory is used to investigate native defects in diamond, their structure, electronic, vibrational, and diffusive properties. We find the only truly stable structure for an interstitial atom be 〈100〉 split defect. This conclusion holds neutral, -1, +1, +2 charge states. analyze multiplet of this defect, finding $^{1}$${\mathit{B}}_{1}$ lowest energy. However, a Jahn-Teller distortion also possible all but state, giving considerable reductions energy...

The effects of AlGaAs shell thickness and growth time on the minority carrier lifetime in GaAs core GaAs/AlGaAs core-shell nanowires grown by metal-organic chemical vapor deposition are investigated. increases with increasing up to a certain value as result reducing tunneling probability carriers through shell, beyond which reduces due diffusion Ga-Al and/or impurities across heterointerface. Interdiffusion at heterointerface is observed directly using high-angle annular dark field scanning...

The nucleation and growth of InAs nanowires on bare Si(111) has been investigated by molecular beam epitaxy. Nontapered with high aspect ratio were grown perpendicular to the substrate without use catalyst particles, surface oxide, or other mask. takes place in In-rich areas forming spontaneously beginning process. As proceeds, local stoichiometry interface changes from As-rich, continues a vapor–solid mode. This transition As-rich conditions is correlated evolution nanowire morphology, that...

GaAs/AlxGa1−xAs core-shell nanowires were grown by metal organic chemical vapor deposition with optimized AlxGa1−xAs shell and twin-free Au-catalyzed GaAs cores. Time-resolved photoluminescence measurements carried out on single at room temperature, revealing minority carrier lifetimes of 1.02 ± 0.43 ns, comparable to self-assisted molecular beam epitaxy. The long are mainly attributed improvement the interface quality. upper limit surface recombination velocity structure is calculated be...

Semiconductor nanowires have proven a versatile platform for the realization of novel structures unachievable by traditional planar epitaxy techniques. Among these, periodic arrangement twin planes to form twinning superlattice has generated particular interest. Here we demonstrate formation in GaAs and investigate diameter dependence both morphology plane spacing. An approximately linear relationship is found between spacing nanowire diameter, which contrasts with previous results reported...

We investigate photoconductive terahertz (THz) emitters compatible with 1550 nm excitation for THz time-domain spectroscopy (TDS). The are based on rhodium (Rh) doped InGaAs grown by molecular beam epitaxy. InGaAs:Rh exhibits a unique combination of ultrashort trapping time, high electron mobility, and resistivity. made feature an emitted power 637 μW at 28 mW optical 60 kV/cm electrical bias field. In particular fiber coupled emitter, this is outstanding result. When these combined...

Rhodium (Rh)-doped In0.53Ga0.47As grown by gas-source molecular beam epitaxy is investigated as a terahertz (THz) detector antenna for optical excitation at 1550 nm. The 4d transition metal rhodium acts deep level and ultrafast trapping center. At doping concentration around 8 × 1019 cm−3, InGaAs:Rh exhibits ideal properties application THz antenna: an ultrashort carrier lifetime below 200 fs in combination with mobility of 1010 cm2/Vs. detectors fabricated from this sample show record peak...

We studied the doping with Si and Be of GaAs nanowires (NWRs) grown by molecular beam epitaxy. Regarding NW morphology, no influence was observed for but high concentrations cause a kinking tapering NWRs. investigated local vibrational modes means resonant Raman scattering to determine incorporation sites dopant atoms. For doping, both donors on Ga acceptors As have been observed. found be incorporated as an acceptor sites. However, at concentration, is also interstitial

We report resonant Raman scattering (RRS) by the TO, LO, and 2 LO modes of single wurtzite zinc-blende GaAs nanowires. The optical band gap is $1.460\phantom{\rule{0.16em}{0ex}}\mathrm{eV}\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ at room temperature, $35\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.16em}{0ex}}\mathrm{meV}$ larger than gap. measurements using incoming light polarized parallel perpendicular to wire $c$ axis allowed us investigate splitting heavy...

Continuous wave THz (cw THz) systems define the state-of-the-art in terms of spectral resolution spectroscopy. Hitherto, acquisition broadband spectra a cw system was always connected with slow operation. Therefore, high update rate applications like inline process monitoring and non-destructive testing are served by time domain spectroscopy (TDS) systems. However, no fundamental restriction prevents technology from achieving faster rates be competitive this field. In paper, we present fully...

Electromagnetic waves in the terahertz (THz) frequency range are widely used spectroscopy, imaging and sensing. However, commercial, table-top systems covering entire from 100 GHz to 10 THz not available today. Fiber-coupled spectrometers, which employ photoconductive antennas as emitters receivers, show a bandwidth limited 6.5 some suffer spectral artifacts above 4 THz. For these systems, we identify absorption polar substrate of antenna main reason for limitations. To overcome them,...

Terahertz wireless communications is an increasingly interesting research topic due to the high demand for un-allocated channels and data rates. Photonic solutions have shown great potential in this field. However, most photonics assisted THz links so far employed optoelectronics only on transmit side. Thus, full of photonic communication has not been utilized yet. Here, we introduce also receive side by using a photoconductive antenna based heterodyne detector. This allows down-conversion...

The oscillating piezoelectric field of a surface acoustic wave (SAW) is employed to transport photoexcited carriers, as well spatially control exciton recombination in GaAs-based nanowires (NWs) on subns time scale. experiments are carried out core–shell NWs transferred SAW delay line LiNbO3 crystal. Carriers generated the NW by focused laser spot acoustically second location, leading remote emission light pulses synchronized with phase. dynamics carrier transport, investigated using and...

We present photomixers made of iron doped indium gallium arsenide (InGaAs:Fe) as broadband receivers in optoelectronic continuous wave (cw) terahertz (THz) systems. InGaAs:Fe shows higher resistivity and shorter carrier lifetimes compared to the state-of-the-art low-temperature-grown material. These improved material properties translate into an frequency response lower noise level photomixers. were able measure a bandwidth 4.5 THz with peak dynamic range 112 dB at 30 mW laser excitation...

For the first time, we present photoconductive, continuous wave (cw) terahertz (THz) detectors for 1550 nm excitation based on rhodium- (Rh) doped indium gallium arsenide (InGaAs) grown by molecular beam epitaxy. Compared to iron- (Fe) material, Rh-doped InGaAs shows higher carrier mobilities with similar lifetimes. Therefore, these photoconductive antennas outperform InGaAs:Fe-based a factor of 10 in terms responsivity and noise-equivalent-power (NEP) while maintaining same bandwidth. In...

Silicon and germanium single crystals are implanted with protons. The infrared-absorption spectra of the samples contain sharp absorption lines due to excitation hydrogen-related local vibrational modes. at 743.1, 748.0, 1986.5, $1989.4{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in silicon 700.3, 705.5, 1881.8, $1883.5{\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ originate from same defect two materials. Measurements on coimplanted protons deuterons show that contains equivalent hydrogen atoms....

Devices based upon semiconductor nanowires provide many well-known advantages for next-generation photovoltaics, however, limited experimental techniques exist to determine essential electrical parameters within these devices. We present a novel application of technique two-photon induced photocurrent that provides submicrometer resolution, three-dimensional reconstruction photovoltaic parameters. This tool is used characterize two GaAs nanowire-based devices, revealing the detail current...

III-V compound semiconductor nanowires are generally characterized by the coexistence of zincblende and wurtzite structures. So far, this polytypism has impeded determination electronic properties metastable phase GaAs, which thus remain highly controversial. In an effort to obtain new insights into topic, we cross-correlate nanoscale spectral imaging near-field scanning optical microscopy with a transmission electron analysis very same polytypic GaAs nanowire dispersed onto Si wafer. Thus,...

GaAs nanowires were grown on Si(111) substrates by molecular-beam epitaxy employing Au droplets for the vapor-liquid-solid mechanism. The nucleation happens in three stages, which coincide with abundance of one different manifestations: first Au-induced lateral traces, then three-dimensional islands, and finally vertical nanowires. During deposition 7 ML no grew. By reflection high-energy electron diffraction transmission microscopy, crystal structure manifestations was examined. Traces...