Infrared Nonlinear Optics

Contains reports on four research projects.DARPA/Universities Research Initiative (Contract NOOO14-46-K-0760)SDI/IST managed by the Naval Research Laboratory (Contract N00014-87-K-2031

Infrared Nonlinear Optics

Contains reports on six research projects.Defense Advanced Research Projects Agency Universities Research Initiative (Contract N00014-46-K-0760)Strategic Defense Initiative/Innovative Science & Technology, managed by the U.S. Naval Research Laboratory (Contract N00014-87-K-2031)National Science Foundation (Grant EET-87-18417

Low-temperature photoluminescence in In-doped CdMnTe/CdTe quantum wells and superlattices

Multiple quantum wells and superlattices of CdMnTe/CdTe were grown epitaxially on ZnCdTe using Pulsed Laser Evaporation and Epitaxy for Cd.85Mn.15Te doped with indium and high purity CdTe targets. Photoluminescence was measured in the 4-80 K temperature range. The use of different excitation wavelengths (488 nm and 623 nm) led to depth studies of the structures. In order to determine the degree of indium incorporation in the wells, the results from the multiple layer structures were compared with the photoluminescence from single layers deposited under similar conditions.NRC publication: Ye

Infrared reflectance and transmission spectra in II-VI alloys and superlattices

Room temperature measurements of the far-infrared (FIR) reflectance spectra are reported for the polar optical phonons in a series of bulk Cd[subscript x]Zn[subscript 1−x]Te (0 ≤ x ≤ 1) and CdSe[subscript x]Te[subscript 1−x] (0 < x ≤ 0.35) crystals grown by Bridgman technique. The composition-dependent spectra exhibited many fundamental aspects of lattice vibrations, while the results of long-wavelength optical modes for the end member binary compounds displayed phonon values in good agreement with the existing inelastic neutron scattering and/or Raman spectroscopy data. Using a standard methodology of multilayer optics with effective-medium dielectric tensors, we simulated the FIR transmission and reflectivity spectra at oblique incidence (Berreman's effect) in many II-VI free-standing thin films, epilayers and superlattices. Berreman's approach provided us with a strong basis for analyzing the infrared experimental data and offered an effective means of estimating the zone-center transverse and longitudinal optical (ω[subscript TO], ω[subscript LO]) phonon frequencies in polar-semiconductor thin films and heterostructure materials of increasing technological importance.Indiana University of Pennsylvania. Graduate School (Innovation Grant)National Science Council (China) (Grant No. NSC 98-2221-E-002-015-MY3)National Science Council (China) (Grant No. NSC 98-3114-E-005-002-CC2

Structural and dynamical properties of Bridgman-grown CdSe[subscript x]Te[subscript 1−x] (0<x≤0.35) ternary alloys

Measurements of the Raman scattering and extended x-ray-absorption fine-structure (EXAFS) spectroscopy are reported on a series of Bridgman-grown zinc-blende CdTe[subscript 1−x]Se[subscript x] (0.35 ≥ x > 0.05) ternary alloys to empathize their lattice dynamical and structural properties. Low-temperature Raman spectra have revealed the classic CdTe-like (TO[subscript 1], LO[subscript 1]) and CdSe-like (TO[subscript 2], LO[subscript 2]) pairs of optical phonons. The composition-dependent peak positions of the LO[subscript 2] modes exhibited shifts towards the higher-energy side, while those of the LO[subscript 1] phonon frequencies have unveiled the slight redshifts. Detailed analyses of EXAFS data by using the first-principles bond orbital model have enabled us to estimate both the lattice relaxations and nearest-neighbor radial force constants around the Se/Te atoms in the CdTe/CdSe matrix. These results are methodically integrated in the “average t-matrix” formalism within the Green's-function theory for defining the impurity perturbations to comprehend the composition-dependent optical phonons in CdTe[subscript 1−x]Se[subscript x] alloys. Based on our comprehensive calculations of impurity modes in the low-composition regime x → 0, we have assigned the weak phonon feature observed near ∼175 cm[superscript −1] in the low-temperature infrared reflectivity spectroscopy study to a Se[subscript Te] localized vibrational mode

Amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] for long wavelength infrared detection

The structural, electronic, and optical properties of amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films deposited on Corning glass, Al[subscript 2]O[subscript 3] CdZnTe, SiO[subscript 2]-Si, and CaF2 substrates by Radio Frequency (RF) magnetron sputtering have been studied as they relate to Mid and Long Wavelength Infrared (MWIR and LWIR) detection. Depositions at elevated substrate temperature and pressure of <10mTorr Ar show an emergence of crystalline grains with strong X-ray diffraction peaks at the (111) and (220) orientations. Electronically the amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films deposited at 300K show hopping conduction with resistance in InSb ranging from 44 to 1.1E8 Ω-cm at 300K and 84K respectively. Optical analysis using Fourier transform infrared spectroscopy (FTIR) show the absorption of these films has an absorption tail, the equation of which differing activation energies in InSb and InAs0.3Sb0.7. Amorphous InSb and InAs[subscript 0.3]Sb[subscript 0.7] films showed thermal responsivity in excess of 100V/W for 6μm thick films held at 233K. The maxima and minima of the responsivity are shown to correspond to the interference fringes in the film. The response is highly substrate dependent and compares favorably to other thermal detectors

Room-temperature oxygen sensitization in highly textured, nanocrystalline PbTe films: A mechanistic study

In this paper, we report large mid-wave infrared photoconductivity in highly textured, nanocrystalline PbTe films thermally evaporated on Si at room temperature. Responsivity as high as 25 V/W is measured at the 3.5 μm wavelength. The large photoconductivity is attributed to the oxygen incorporation in the films by diffusion. Carrier concentration as low as 10[superscript 17] cm[superscript −3] is identified to be the consequence of Fermi level pinning induced by the diffused oxygen. The successful demonstration of IR-sensitive PbTe films without the need for high-temperature processing presents an important step toward monolithic integration of mid-wave PbTe infrared detectors on Si read-out integrated circuits (ROICs)