Article:Stone, M.R., Naftaly, M., Miles, R.E. et al. (2 more Abstract-We present experimental characterization of semilarge photoconductive emitters, including their electrical/photoconductive parameters and terahertz spectra. A range of emitters were studied and fabricated on both LT-GaAs and SI-GaAs, having a variety of electrode geometries. The spatial cone of terahertz radiation was defined. The dependencies of the photocurrent and the terahertz power on the bias voltage and the laser power were determined. A Fourier-transform interferometer is used to determine the terahertz spectra and to clarify the effects of the substrate and electrode geometry.

Room-temperature electroluminescence is reported from InAsSb multiple-quantum-well light-emitting diodes. The diodes exhibited emission in the mid-infrared peaking near 4 m. The spectral dependence on injection current at 4 K was investigated and two transitions were identified, centered at 4.05 and 3.50 m, which are associated with the eigenstates of the confined holes inside the quantum well. The use of an Sb predeposition and As flux surface exposure during epitaxial growth was observed to have a major effect on the electroluminescence output.

Detailed studies are reported on the photoluminescence of InAsSb/ InAs multiple quantum wells grown by molecular beam epitaxy on InAs substrates with the Sb mole fraction ranging from 0.06 to 0.13. From 4 K photoluminescence the band alignment was determined to be staggered type II. By comparing the emission peak energies with a transition energy calculation it was found that both the conduction and valence bands of InAsSb alloy exhibit some bowing. The bowing parameters were determined to be in the ratio of 4:6. For a sample with Sb composition ϳ0.12 in the quantum well the photoluminescence emission band covers the CO 2 absorption peak making it suitable for use in sources for CO 2 detection. © 2006 American Institute of Physics. ͓DOI: 10.1063/1.2388879͔Among the family of bulk III-V compound semiconductors the InAsSb alloy system has the lowest band gap energy ͑E g = 0.145 eV at x = 0.634͒ and is thus an important material for mid-IR devices. 1,2 Heterostructures based on InAsSb alloys, such as InAs/ InAsSb, InAsSb/ InAsPSb, InAsSb/ InGaSb, and so on, have been widely applied as the active medium for mid-IR optoelectronic devices. [3][4][5][6] The InAsSb/ InAs multiple quantum well ͑MQW͒ system is appropriate for use in the active region of 3 -5 m lightemitting diodes that could be deployed in portable gas analyzers and which are important for environmental protection. 6 In this letter we report on a series of InAsSb/ InAs multiple quantum well samples grown by molecular beam epitaxy ͑MBE͒ on InAs substrates. Photoluminescence ͑PL͒ spectroscopy measurements were undertaken to investigate the dependence of emission wavelength on composition and also to gain information about the conduction band and valence band bowing parameters. The transition energies of the above-mentioned samples lie within the range of 0.2-0.4 eV ͑3-5 m͒.The InAsSb/ InAs MQW samples were grown on ͑100͒ n + -InAs substrates using a VG-V80H MBE system. Two cracker cells were used to provide the Sb and As 2 beams. A thermal effusion K cell was used to provide the In flux. An InAs buffer layer with a thickness of 100 nm was grown at 480°C. Then a seven-period InAsSb/ InAs MQW with various Sb compositions was grown at 450°C. The thickness of the InAsSb well and InAs barrier were 7 and 50 nm, respectively. In situ reflection high energy electron diffraction ͑RHEED͒ was used to monitor surface reconstruction. After growth the samples were characterized using double crystal x-ray diffraction ͑DXRD͒ and PL to study their structural and optical properties. Figure 1 shows the DXRD spectra of the InAsSb/ InAs MQW samples. During the growth of the MQWs, the in situ RHEED pattern showed a clear 4 ϫ 2 reconstruction when InAs was deposited and became slightly blurry when InAsSb was deposited. This implies a rougher growing surface when the Sb beam was incident. For samples with a higher Sb composition, only bulk lines were observed and we believe that this may result from the stress caused by lattice mismatch. However, the satellite peaks in the DXRD sp...

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Continuous-wave terahertz ͑THz͒ radiation was generated by photomixing two modes of a titanium sapphire laser. The laser was induced to oscillate on two modes by placing a Fabry-Perot etalon in the laser resonator. The frequency of terahertz radiation, which was equal to the difference frequency of the two modes, was varied by adjusting the free spectral range ͑FSR͒ of the etalon. Photomixing was performed by logarithmic spiral antennas fabricated on low-temperature-grown GaAs; and the emitted THz radiation was characterized. The THz power, measured by a Golay cell, was 1 W at 0.3 THz and 0.7 W at 0.5 THz. The THz frequency, as determined by a Fourier transform interferometer, was seen to correspond to the etalon FSR. The current-voltage characteristics of photomixers were also determined, and photocurrent modulation was observed by the autocorrelation of the laser beam.