In order to increase agricultural productivity, several countries heavily rely on deadly insecticides, known to be toxic to
most living organisms and thus significantly affect the food chain. The most obvious impact is to human beings who
come into contact, or even consume, pesticide-exposed crops. This work hence focused on an alternative method for
insecticide detection at trace concentration under field tests. We proposed a compact Raman spectroscopy system, which
consisted of a portable Raman spectroscope, and a surface-enhanced Raman scattering (SERS) substrate, developed for
the purpose of such application, on a chip. For the selected portable Raman spectroscope, a laser diode of 785 nm for
excitation and a thermoelectric-cooled CCD spectrometer for detection were used. The affordable SERS substrates, with
a structure of distributed silver nanorods, were however fabricated by a low-energy magnetron sputtering system. Based
on an oblique-angle deposition technique, several deposition parameters, which include a deposition angle, an operating
pressure and a substrate rotation, were investigated for their immediate effects on the formation of the nanorods. Trace
concentration of organophosphorous chemical agents, including methyl parathion, chlorpyrifos, and malathion, adsorbed
on the fabricated SERS substrates were analyzed. The obtained results indicated a sensitive detection for the trace
organic analyses of the toxic chemical agents from the purposed portable SERS system.
We report the formation and growth characteristics of an interfacial misfit (IMF) array between AlSb and Si and their application to III-Sb based quantum well (QW) light-emitting devices including edge-emitting laser diodes and verticalcavity surface emitting lasers (VCSELs) monolithically grown on a Si (001) substrate. A III-Sb epi-structure is grown monolithically on the Si substrate via a thin (≅50 nm) AlSb nucleation layer. A 13% lattice mismatch between AlSb and Si is accommodated by using the IMF array. We demonstrate monolithic VCSELs grown on Si(001) substrates operating under room-temperature with optically-pumped conditions. A 3-mm pump spot size results in peak threshold excitation density of <i>I<sub>th</sub></i>= 0.1 mJ/cm<sup>2</sup> and a multimode lasing spectrum peak at 1.62 μm. Moreover, broad-area edgeemitters consisting of GaSb/AlGaSb QWs are demonstrated under pulsed conditions at 77K with a threshold current density of ≅2 kA/cm<sup>2</sup> and a maximum peak output power of ≅20 mW for a 1mm-long device. A use of 5° miscut Si substrates enables both IMF formation and suppression of an anti-phase domain, resulting in a drastic suppression of dislocation density over the III-Sb epi-layer and realization of electrically-injected laser diodes operating at 77 K. The current-voltage (I-V) characteristics indicate a diode turn-on of 0.7 V, which is consistent with a theoretical built-in potential of the laser diode. This device is characterized by a 9.1 Ω forward resistance and a leakage current density of 0.7 A/cm<sup>2</sup> at -5 V and 46.9 A/cm<sup>2</sup> at -15 V. This IMF technique will enable the realization of III-Sb based electrically injected VCSELs operating at the fiber-optic communication wavelength monolithically grown on a Si platform.
Doping of the clad layers in thin GaAs/GaInP heterostructures, displaces the band energy discontinuity, modifies
the carrier concentration in the active GaAs region and changes the quality of the hetero-interfaces. As a result,
internal and consequently external quantum efficiencies in the double heterostructure are affected. In this paper,
the interfacial quality of GaAs/GaInP heterostructure is systematically investigated by adjusting the doping
level and type (n or p) of the cladding layer. An optimum structure for laser cooling applications is proposed.
We present the growth and characterization of high quality semiconductor laser cooling material. The structure consists of GaAs passivated by InGaP which has been reported to have a longest surface recombination lifetime. GaAs was grown on 10 degree miscut GaAs substrate and sandwiched between lattice matched In<sub>0.49</sub>Ga<sub>0.51</sub>P. This structure was grown by a low-pressure metal organic chemical vapor deposition (MOCVD) system. The material was grown in the temperature range of 550 to 700 °C at 60.8 Torr. The morphology of InGaP was improved by the growth on 10 degree miscut substrate along <110> direction, which is confirmed by X-ray diffraction (XRD). The uninterrupted growth technique and GaP separation layer are employed to prevent the indium segregation and P/As intermixing at the interface between InGaP and GaAs. The effects of V/III ratio, growth temperature and material precursors on material impurities were also studied. The carrier lifetimes were measured using the time resolved photoluminescence (TRPL) technique at cryogenic temperatures. The experimental results show that the carrier lifetime was increased by 5 times with the use of TBA as arsenic source in place of AsH<sub>3</sub>. Recent results show a highest room temperature carrier lifetime of 2 &mgr;sec.
In this paper, we describe the results of using strain-compensation (SC) for closely-stacked InAs/GaAs quantum dot (QD) structures. The effects of the (In)GaP SC layers has been investigated using several methods. High-resolution x-ray diffractometry (XRD) quantifies the values of experimental strain reduction compared to calculations. Atomic force microscopy (AFM) indicates that the SC layer improves both QD uniformity and reduces defect density. Furthermore, increase in photoluminescence (PL) intensity has been observed from compensated structure. The use of Indium-flushing to dissolve large defect islands prevent further defect propagation in stacked QD active region. Room-temperature ground-state lasing at emission wavelengths of 1227-1249 nm have been realized with threshold current densities of 208-550 A/cm<sup>2</sup> for 15-20 nm spacing structures.