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...

The amplitudes of terahertz radiation are measured for a series of GaAs surface intrinsic-N(+) structures with various built-in surface electric fields as the bias. As the surface field is lower than the so-called "critical electric field" related with the energy difference between the Gamma to L valley of the semiconductor, the amplitude is proportional to the product of the surface field and the number of photo-excited carriers. As the surface field exceeds the critical field, the amplitude is independent of the surface field but proportional to the product of the critical field and the number of the photo-excited carriers.

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Strained GaAsSb/GaAs quantum wells grown on GaAs substrate, which exhibit a staggered type41 band alignment, are of interest for infrared optoelectronic devices applications, because of its optical interband transitions occur at longer wavelengths than those corresponding to the fundamental band gap energies of each constituent. The quantum wells have been used successfully to fabricate laser diodes, which have emerged to be one of the candidates for 1 . 3~ laser source on GaAs substrate [l]. In this study, by using Sb monomer to deposit GaAsSb layer, we demonstrate a high quality low-threshold GaAsSb/GaAs double quantum well laser diode.

Using the Z-scan technique with 532 nm 19 ps laser pulses separated by two time intervals τ's (0.1 s and 1.0 s) sandwiching the mass diffusion time constant of the CHClO + 1,2 dichloroethane solution, we investigate short-pulse-induced solute migration in the sample by measuring its transmittance change with τ variation. Preparing the sample at two concentrations, we find that τ reduction, from 1.0 s to 0.1 s, increases its transmittance when input pulse energy ε exceeds a threshold ε, which is lower for the dilute solution than the concentrated one. At two ε's above ε for the dilute solution, τ-reduction-induced transmittance increase in the dilute solution, as compared to that in the concentrated solution, is more at the lower ε and less at the higher ε. This differs from continuous-wave-driven thermal diffusion which always causes a larger transmittance increase in the concentrated solution by inducing a larger temperature gradient. From this study, we predict that solute migration induced by short pulses at 1064 nm is one of the undesired heating effects occurring when this solution is used to simultaneously Q-switch and mode-lock Nd:YAG lasers.

The band offset of the type-ll GaAso.,Sbo.,1GaAs quantum well (Qw) is studied. We propose an extrapolation method to remove the band-bending effect and determine the flat-band transition energy of the type-I1 QW from photoluminescence (PL) measurement. Then, we compare the PL peak energies of the type-II GaAso.+bo,,/GaAs QW and the type4 Alo.,G%,7As/ GaAso.,Sbo,l QW to obtain the strained band gap energy of GaAso.7Sbo.3 and the valence-band-offset ratio of the type-ll QW. The obtained band gap energy and valence-band-offset ratio are 1.01 eV and 1.15. GaAsSbiGaAs double-quantum-well lasers were also grown and fabricated. The laser demonstrates a very low threshold current density of 210 Ncm' with an emission wavelength of 1.28pm.