The electronic band gap of single crystalline ZnGeN2 epitaxial layer grown on sapphire substrate by metal organic chemical vapor deposition has been measured by optical transmission and room temperature photoluminescence. The band gap energy is 2.99eV at room temperature, and the band gap is a direct transition type. The interference oscillations of the transmission spectra together with rutile prism coupling measurements have been used to determine the r fractive index and the dispersion characteristics of the single crystal ZnGeN2 below the band gap energy. The rutile prism coupling measurement displays the wave guide modes of the film at 6 2.8nm wavelength of the He-Ne laser, enabling determination of the film thickness and refractive index precisely at the wavelength. The refractive index of ZnGeN2 crystal is 2.35 at 6328Å wavelength. The measured refractive index dispersion curve can be fitted with the first-order Sellmeier equation n2(λ) = A + λ2/(λ2-B), using fitting parameters A=4.3 1, B=0.076.

To stimulate further research on the TI-based semiconductor alloys for long-wave infrared (LWIR) application, we carried out detailed calculations for the variation of band gaps versus lattice constants and the alloy miscibility gaps of cation-substituted pseudo-binary alloys. These results are used to identify promising TI-based LWIR alloys and the lattice-matched non-TI bearing alloys for possible substrates and passivation caps. Although all the six Tl-bearing pseudo-binary alloys studied can have a 0.1 eV band gap, none of these systems are lattice matched to a pure III-V compound. Five of these six alloys can have a non-TI-bearing lattice-matched ternary alloy as the substrate, but only two do not have a serious problem with the miscibility gap. When further considering the difficulty of incorporating TI with a large concentration, the only promising LWIR pseudo-binary alloy left is In1−xTlxAs with x≍0. 16.

We report on the metal-organic chemical vapor deposition (MOCVD) of strained layer superlattices (SLSs) of InAsSb/InAs/InPSb/InAs as well as mid-infrared optically pumped lasers grown using a high speed rotating disk reactor (RDR). The devices contain AlAsSb cladding layers and strained, type I, InAsSb/InAs/InPSb/InAs strained layer superlattice (SLS) active regions. By changing the layer thickness and composition of the SLS, we have prepared structures with low temperature (<20K) photoluminescence wavelengths ranging from 3.4 to 4.8 µm. The optical properties of the InAsSb/InPSb superlattices revealed an anomalous low energy transition that can be assigned to an antimony-rich, interfacial layer in the superlattice. This low energy transition can be eliminated by introducing a 1.Onm InAs layer between the InAsSb and InPSb layers in the superlattice. An InAsSb/InAs/InPSb/InAs SLS laser was grown on an InAs substrate with AlAs0.16Sb0.844cladding layers. A lasing threshold and spectrally narrowed laser emission were seen from 80 through 250 K, the maximum temperature where lasing occurred. The temperature dependence of the SLS laser threshold is described by a characteristic temperature, T0 = 39 K, from 80 to 200 K.

In order to overcome some of the inherent difficulties with applying conventional pyrometry to production scale rotating disc MOVPE reactors, the in-situ technique of emissivity compensated pyrometry has been applied. Due to the extreme temperature sensitivity of epitaxial processes involving InxGa1−xAs1−yPy, this material system provides the optimum proving grounds for this technology. With this temperature measurement technique, we have developed a method for measuring the temperature of the substrate during MOVPE growth in high speed rotating disc reactors that does not require any modification to the reactor hardware. Real world testing, during the growth of complex epitaxial structures involving the highly temperature sensitive InxGa1−xAs1−yPy quaternary, indicates a very strong correlation between the measured temperature of the substrate during growth, and actual epitaxial wafer measurements after growth. This temperature measurement system can be used to maintain the wavelength of the InxGa1−xAs1−yPy quaternary materials within a range of 2 nm.

Photoresponses of photovoltaic cells using ion-beam synthesized (IBS) polycrystalline p+-β-FeSi2/n-Si heterojunctions were examined in an infrared (IR) wavelength region. At room temperature, an evident photoresponse due to an internal photoemission from trap levels in β-FeSi2 with the threshold energy Φ=0.62 eV was observed at 0.6-0.87 eV. The pronounced increase of a photoresponse corresponding mostly to an interband transition in β-FeSi2 was observed at 0.87-1.1 eV. The maximum dominated by a surface recombination process appeared around ∼1.2 eV. The surface recombination rate of ∼104 cm/s was estimated. The quantum efficiency was ∼60 % in the 0.8-1.0 µm wavelength region and ∼14 % around the band-gap of βFeSi2.

The bulk crystal of silicon germanium was grown by vertical Bridgman method with germanium composition, x, varying from 0.6 to 1.0. The temperature dependent variation of the mobility is indicative of alloy scattering dominantly for the bulk wafer. Phosphorus was diffused in as-grown p-type bulk wafer at 850 °C to form pn-junction, and the diffusion coefficient of phosphorus was evaluated as a function of x. The diffusion behavior of phosphorus in silicon germanium is closely correlated with the germanium self-diffusion with changing x. For specimens with lower content x, P concentration profiles indicated “kink and tail” shape, while it was not observed for higher x. For current-voltage characteristics measurement, an ideality factor was obtained.

We report on the photoconductivity and transient in n-PbTe(Ga) epitaxial films prepared by the hot wall technique on the <11 I>-BaF2 substrates. Photoconductivity measurements performed under continuous and pulse illumination in the temperature range 4.2-300 K give the photoresponse to be composed from negative and positive parts. The experimental results are interpreted assuming the mixed valence of Ga in lead telluride.

Galvanomagnetic properties of n-Pb1−xGexTe<Ga>(O.04≤x≤O.08) single crystals have been investigated in the shielded from external background illumination chamber and under controlled illumination from infrared heat source. Low temperature activation range of the impurity conductivity on the dark curves of ρ(l/T) was revealed and attributed to the appearance of gallium-induced deep level E Ga in the gap of the alloys. It was shown that the alloys possess high infrared photosensitivity at temperatures below Tc=50%60 K, and effect of the persistent photoconductivity at helium temperatures was revealed.

A series of Pb1−xEuxTe/PbTe multi-quantum well (MQW) samples were grown on (111) cleaved BaF2substrates by molecular beam epitaxy. The Eu content was maintained at x∼0.06 and the PbTe well width was varied from 50 to 200 Å. The co/2Θ scans of the (222) Bragg reflection showed very well resolved satellite peaks for all samples indicating that sharp interfaces were obtained. The strain inside the MQW structure was obtained as a function of the PbTe well width by fitting the ω/2Θ scans to the ones calculated by dynamical theory of x-ray diffraction. The transition energies between the confined states in the conduction and valence bands of the PbTe well were determined through the infrared transmission measurement analysis.

The metal-organic chemical vapor deposition (MOCVD) technique has been successfully applied for growth of Sn-doped transparent, conducting Zn-In-O and Ga-In-O films using Sn(acac)2, In(dpm)3, Ga(dpm)3, and Zn(dpm)2, as volatile precursors. The 25 °C electrical conductivity of the as-grown films is as high as 1030 S/cm (n-type, carrier density N = 4.5 × 1020 cm−3, mobility µ = 14.3 cm2/V•s) for the Zn-In-O series and 700 S/cm (n-type, N = 8.1 × 1019 cm−3, µ = 55.2 cm2/V•s) for the Ga-In-O series. After Sn-doping, the Zn-In-O series exhibits 25 'C electrical conductivities as high as 2290 S/cm with a higher carrier mobility, while the Ga-InO series exhibits higher electrical conductivity (3280 S/cm at 25 °C) and much higher carrier density, but with diminished mobility. All films show broader optical transparency windows than that of commercial ITO films. Reductive annealing, carried out at 400-425 °C in a flowing gas mixture of H2(4%) and N2, results in increased carrier density and mobility as high as 64.6 cm2/V•s for films without Sn doping, but lowered carrier density for the Sn-doped films. X-ray diffraction, transmission electron microscopy, micro diffraction, and high-resolution X-ray analysis show that all films with good conductivity have cubic, homogeneously doped In2O3-like crystal structures.

Polycrystalline thin films of lead sulphide were deposited on glass substrates by the hot wall technique. The grain size varied from 100 to 500 A by varying the growth rate and the substrate temperature. The grain boundaries are assumed to influence the optoelectronic properties of polycrystalline films by generating potential energy relieves, estimated to reach 0.1 eV. We investigated the influence of the barrier height by introducing impurity atmospheres into the grain boundaries. Oxygen and indium were introduced into the films by diffusion from a gas phase. Conductivity was measured in the 80-300 K range. It rises with increasing temperature in oxygen doped films, indicating that conductivity is a thermal activation process. In the same time the conductivity of In doped PbS films decreases with temperature like in PbS single crystals. Photoconductivity was observed in films annealed in oxygen, which was significant up to room temperature. Carrier lifetime was found to decrease with rising temperature and be larger in films annealed in oxygen.

A model is proposed to explain the optoelectronic behavior of the polycrystalline films. It is proposed that charge accumulation near grain boundaries set up potential barriers for free carriers. The barriers increase by oxygen and decreases by indium doping. The charge carriers generated by an illumination become spatially separated at grain boundaries. This separation retards their recombination and increases their lifetime, giving rise to persistent photoconductivity and potential high photosensitivity.

Striking progress has been made in the development of thigh optical quality, large size and low absorbing single crystals of ZnGeP2, AgGaS2 and CdGeAs2. This will now enable continuously tunable infrared laser sources to be built covering the spectral region from 3.9 to 11 µm.

Electron paramagnetic resonance (EPR) as well as time-resolved and time-integrated photoluminescence (PL) are used to characterize the defect centers in ZnGeP2 bulk crystals. The samples, as-grown, electron-irradiated and annealed, reveal a strong intensity dependence of the VZn-correlated EPR-transitions. Photo-EPR experiments show that this intensity behavior is mainly caused by a recharging of the VZn centers owing to the preparation induced shift of the Fermi-level. The luminescence spectra show a broad infrared emission with peak position at 1.23 eV that exhibits features of classical donor-acceptor recombination. The hyperbolic decay characteristics, investigated in energy range from 1.2 eV up to 1.5eV, suggest that this broad emission band is related to one energetic recombination center. This recombination is interpreted to be between donor-acceptor states related to residual disorder on the cation sublattice that is retained in metastable equilibrium during the formation of the chalcopyrite structure. The emission decay behavior in the energy range from 1.2 eV up to 1.6 eV is characterized by two hyperbolic time constants, and explained as the super-composition of the decays from the broad emission center peaked at 1.2 eV and an additional donor-acceptor recombination centers at 1.4 eV.

Bulk ZnGeP2 (ZGP) crystals grown for high-power tunable mid-infrared laser systems contain large concentrations of three native defects. Using EPR, these three defects have been identified as the Zn vacancy (an acceptor), the phosphorus vacancy (a donor), and the germanium-on-zinc antisite (also a donor). We have studied the wavelength dependence of the photoinduced changes in the EPR signal intensity of the three defect centers using 633 nm and 1064 nm light. We observe a significant increase in the EPR signal under 633 nm light. The 633-nm light also produces an increase in the defect-related 1-R.m absorption band, and we have used a spectrophotometer to measure the spectral shape of the photoinduced change in absorption in this near-IR region. The 633-nm wavelength produces paramagnetic forms of both donor centers, while 1064 nm light only produces the EPR-active center. Time decays of the photoinduced EPR signals have been measured for each of the donors.

The electronic band structures were calculated for a number of chalcopyrites in both the II-IV-V2 and I-III-VI2 families using the linear muffin-tin orbital method. From these band structures, the second harmonic generation coefficients were calculated using a recently developed methodology in which a separation is made of inter- and intraband contributions. We found that the high value of d36 in CdGeAs2 is in large part due to the fact, that in this material, unlike in the other chalcopyrites, almost no compensation occurs between inter- and intraband contributions, the former one being unusually small. For the case of ZnGeP2, a detailed investigation of the band structure, reveals that it has an indirect band gap rather than a pseudodirect one. The implications of this for the interpretation of the optical spectra are discussed. Finally, for the I-III-VI2 materials, we find that the Te based materials have far higher d36 than the selenides. Combined with their potential for non-critical phase matching, this makes AgGaTe2 an interesting compound.

Inelastic light scattering by optical phonons and the temperature dependent electrical conductivity, Hall constant and photosensitivity were studied in oriented CdGeAs2 crystals grown by ultra-low gradient freeze technique from near-stoichiometric melts. Observation of the clear polarization dependence of the inelastic light scattering spectra by optical phonons combined with the absence of any dependence of the intensity and frequency shift of the observed lines with mapping measurements in 300 μm steps indicated the high optical quality and homogeneity of these single crystals. It is shown that surface-barrier structures using these single crystals may be used as wide-band detectors for natural light, as well as selective photoanalyzers for linearly polarized radiation.

Brudnyi, et al., and Zwieback, et al., have shown that introducing damage by irradiation with MeV electrons can alter the electrical and optical properties of undoped p-type CdGeAs2(CGA) crystals. Brudnyi's studies of the electrical transport properties of isochronally annealed samples demonstrated type conversion and identified at least two new centers, one a stable donor. Zwieback used multi-MeV electrons to introduce compensating donors, thereby, significantly improving the optical transparency of CGA crystals. However, at the present little is known about these centers. Therefore, we have studied these centers by observing the properties of electron-irradiated specimens using Thermal Admittance Spectroscopy (TAS) and correlated the results of these measurements with capacitance-voltage measurements and Hall effect measurements. Measurements before an after irradiation are compared. The as-grown native acceptor concentrations in our samples varied from a low in the mid 1016 cm−3to nearly 1019 cm−3. Significant changes in the electrically active states in the band gap were seen as a result of a single irradiation with 2 MeV electrons to a total dose of 5 × 105cm−2. The samples appear to respond more strongly than Brudnyi's samples. The thermal activation energies have been determined using TAS and they will be reported.

We report on the effects of fast electron irradiation on the optical absorption (α) of CdGeAs2and ZnGeP2 and on the electrical properties of CdGeAs2. In p-CdGeAs2 irradiation led to the reduction in α and an increase in the electrical resistivity. The lowest values of α (about 0.1 cm' at 5µm<λ<10µm) were obtained on irradiated crystals of p-type with the highest degree of compensation. Further accumulation of the electron dose caused conversion to n-type and deterioration of the optical transmission. In ZnGeP2 irradiation caused a decrease in a at λ>0.85 λm and increase in α at λ<0.85 μm. At λ=2.05 μm, α for the o-ray could be reduced to less than 0.08 cm−1. At higher doses, saturation in α was observed. The effects of irradiation are discussed in connection with possible mechanisms of optical absorption in CdGeAs2 and ZnGeP2.

The optical properties of TexSe(1−x) were studied for x = 0.8, 0.9, and 1.0. The results for variable temperature, polarization sensitive, spectral photoconductivity measurements on oriented single crystals, as well as the energy band gaps and their temperature dependencies are presented. In all cases, the band gap was found to increase with increasing temperature. Analytical expressions describing the temperature dependent behavior are reported. Furthermore, for the first time the characteristic two peak spectrum of tellurium was separated into its two components for incident radiation polarized parallel and perpendicular to the c-axis as a function of temperature. However, two distinct peaks were not discernible in the alloys, with or without polarization, although the signal intensity was slightly polarization dependent.

Second-harmonic generation in CdSe nanocrystals doped in indium tin oxide ( ITO ) films has been examined. The thin film samples were prepared by r.f. magnetron sputtering with ITO target on which CdSe chips were placed. The X-ray diffraction patterns of as-deposited films indicate that CdSe crystallites are precipitated in an amorphous ITO matrix, and they are preferentially oriented in the direction of (111) plane of zinc blende structure or (002) plane of wurtzite structure. The mean diameter of CdSe crystallite was estimated to be 3-5 nm using Scherrer's equation. Moreover, the CdSe crystallites grew with keeping its initial orientation when a dc voltage of 50 V/cm was applied in the direction parallel to the film surface. The application of the electric field effectively enhanced the second-harmonic intensity by two orders of magnitude compared to that of the as-deposited films. The second-order nonlinear coefficient d(2) for the electrically-treated specimen calculated on a basis of a modified Maker fringe theory is d31 = 3.0 × 10 pm/V at the wavelength of 1064 nm, which is comparable to d values reported for CdSe single crystal, d 31 = 25 pm/V at 1054 nm and d 33 =76 pm/V at 1064 nm.