Waveguide photonic crystals with characteristics controlled with <Emphasis Type=Italic>p</Emphasis>-<Emphasis Type=Italic>i</Emphasis>-<Emphasis Type=Italic>n</Emphasis> diodes

A one-dimensional waveguide photonic structure—specifically, a photonic crystal with a controllable frequency characteristic—is designed. The central frequency of the spectral window of the photonic crystal can be tuned by choosing the parameters of disturbance of periodicity in the photonic crystal, whereas the transmission coefficient at a particular frequency can be controlled by varying the voltage at a p-i-n diode. It is shown that the possibility exists of using the waveguide photonic crystal to design a microwave device operating in the 3-cm-wavelength region, with a transmission band of 70 MHz at a level 3 dB and the transmission coefficient controllable in the range from −1.5 to −25 dB under variations in the forward voltage bias at the p-i-n diode from zero to 700 mV.     

Study of the <Emphasis Type=Italic>p</Emphasis>-Ge-<Emphasis Type=Italic>n</Emphasis>-GaAs heterojunction under hydrostatic pressure

The current-voltage characteristic of the p-Ge-n-GaAs heterojunction is experimentally studied under hydrostatic pressure as high as 8 GPa and temperature of 300 K. The baric coefficient of the edge of the valence band of Ge is calculated using the experimental results.     

Charge-Compensated <Emphasis Type=Italic>n</Emphasis>-Type Skutterudites

Ba+Yb double-filled n-type skutterudites with a modest degree of charge compensation by Fe on the Co lattice have been synthesized and compacted by spark-plasma sintering, and their thermoelectric properties evaluated at temperatures up to 800 K. Although this approach to making n-type skutterudites seems counterintuitive, the presence of Fe leads to a reduction in the thermal conductivity while it preserves a robust Seebeck coefficient. Consequently, a high ZT in excess of 1.3 was achieved at 800 K in these Fe-containing n-type skutterudite compounds.     

Planar <Emphasis Type=Italic>n</Emphasis>-on-<Emphasis Type=Italic>p</Emphasis> HgCdTe FPAs for LWIR and VLWIR Applications

Mainly driven by space applications, mercury cadmium telluride (MCT) focal-plane arrays (FPAs) have been successfully developed for very long wavelengths (λ _CO > 14 μm at 55 K). For this purpose, the standard n-on-p technology based on MCT grown by liquid-phase epitaxy (LPE) and involving vacancy doping has been modified to extrinsic doping by a monovalent acceptor. Due to the planar diode geometry obtained by ion implantation, most of the carrier generation volume is located in the p-type region with a thickness of approximately 8 μm. According to our understanding, the Shockley–Read centers connected with the Hg vacancies are thus significantly reduced. This situation should lead to longer minority-carrier lifetimes and smaller generation rates under equilibrium conditions, therefore yielding lower dark current. We indeed observe a reduction by a factor of approximately 15 by using extrinsic doping. Recent dark current data obtained in the temperature range from 55 K to 85 K on 288 × 384 FPAs with λ _CO(60 K) = 12 μm, either intrinsically or extrinsically doped, corroborate this finding. These data, new results on a 112 × 112 pixel demonstrator array with λ _CO(55 K) = 14.4 μm, and earlier measurements are compared with Tennant’s Rule 07 established for p-on-n technology.     

A filter of <Emphasis Type=Italic>H</Emphasis><Subscript>0<Emphasis Type=Italic>n</Emphasis></Subscript> modes in a multimode rectangular waveguide

A technique is developed for calculating the electrodynamic characteristics of a filter of H _0n modes in the case of various configurations of the filter and various combinations of its mechanical and electric parameters. In numerical computations, the complete set of the filter parameters is taken into account. It is shown that the number of absorbing elements in the filter can be reduced from three to two and that, simultaneously, the quality characteristics of the filter can be improved.     

Study of the current-voltage characteristic of the <Emphasis Type=Italic>n</Emphasis>-CdS/<Emphasis Type=Italic>p</Emphasis>-CdTe heterostructure depending on temperature

Current-voltage characteristics of the n-CdS/p-CdTe heterostructure are studied at different temperatures. It is established that the forward portion of the current-voltage characteristic of these structures at low voltages (as high as 0.5 V) is described by the exponential dependence, while at high voltages (as high as 2.6 V), there is a portion of sublinear growth of the current with voltage. Experimental results are interpreted based on the theory of the effect of injection depletion. It is shown that the product of mobility of majority carriers by the concentration of deep centers increases as the temperature is increased.     

Electroluminescence in <Emphasis Type=Italic>p</Emphasis>-InAs/AlSb/InAsSb/AlSb/<Emphasis Type=Italic>p</Emphasis>(<Emphasis Type=Italic>n</Emphasis>)-GaSb type II heterostructures with deep quantum wells at the interface

Luminescent characteristics of asymmetric p-InAs/AlSb/InAsSb/AlSb/p-GaSb type II heterostructures with deep quantum wells at the heterointerface are studied. The heterostructures were grown by metalorganic vapor phase epitaxy. Intense positive and negative luminescence was observed in the range of photon energies of 0.3–0.4 eV with a forward and reverse bias, respectively. Dependences of the spectra and intensities for positive and negative luminescence on the pumping current and on the temperature are studied in the range of 77–380 K. It is established that, at a temperature higher than 75°C, intensity of negative luminescence surpasses that of positive luminescence by 60%. The suggested heterostructures can be used as lightemitting diodes (photodiodes) with switched positive and negative luminescence in the mid-IR spectral range of 3–4 μm.     

Photosensitivity of <Emphasis Type=Italic>n</Emphasis>-CdS/<Emphasis Type=Italic>p</Emphasis>-CdTe heterojunctions obtained by chemical surface deposition of CdS

A new technology of chemical surface deposition is developed, and thin CdS films (35–100 nm) on the p-CdTe substrates are obtained. Electrical and photoelectric properties of n-CdS/p-CdTe heterojunctions are studied, and it is shown that the developed method provides high efficiency of photoconversion in the range restricted by the CdTe and CdS band gaps. It is shown that the method of chemical surface deposition of CdS can be used in the design of thin-film n-CdS/p-CdTe.     

<Emphasis Type=Italic>ZT</Emphasis> Measurements Under Large Temperature Differences

All current techniques for ZT measurement are carried out under a small temperature difference, despite the fact that thermoelectric devices are likely to operate under a relatively large temperature difference. In this paper, we describe a new technique which enables ZT measurement under a large temperature difference. The principle of measurement is presented, followed by a proof-of-concept study. The results of this study show that ZT values obtained under a large temperature difference differ significantly from those obtained under small temperature differences. The technique provides a more realistic evaluation of thermoelectric materials and devices.     

Quantum wells on 3<Emphasis Type=Italic>C</Emphasis>-SiC/<Emphasis Type=Italic>NH</Emphasis>-SiC heterojunctions. Calculation of spontaneous polarization and electric field strength in experiments

The results of experiments with quantum wells on 3C-SiC/4H-SiC and 3C-SiC/6H-SiC heterojunctions obtained by various methods are reconsidered. Spontaneous polarizations, field strengths, and energies of local levels in quantum wells on 3C-SiC/NH-SiC heterojunctions were calculated within a unified model. The values obtained are in agreement with the results of all considered experiments. Heterojunction types are determined. Approximations for valence band offsets on heterojunctions between silicon carbide polytypes and the expression for calculating local levels in quantum wells on the 3C-SiC/NH-SiC heterojunction are presented. The spontaneous polarizations and field strengths induced by spontaneous polarization on 3C-SiC/4H-SiC and 3C-SiC/6H-SiC heterojunctions were calculated as 0.71 and 0.47 C/m² and 0.825 and 0.55 MV/cm, respectively.     

Thermoelectric Power and <Emphasis Type=Italic>ZT</Emphasis> in Conducting Organic Semiconductor

A recent report on poly(3,4-ethylenedioxythiophene-tosylate) (PEDOT.Tos) suggested that the thermoelectric figure of merit (ZT) could be enhanced when the percentage oxidation was chemically altered. This invokes the question of whether the carrier density or the mobility was modified. In this work, we analyzed data reported by Bibnova et al. (Nat. Mater. 10, 429, 2011) and extracted the transport parameters using three-dimensional (3D) and two-dimensional (2D) models. Our results indicate that the increase in the power factor (S ² σ) was due primarily to upward extension in the range of thermoelectric power. A changeover from lattice scattering to ionized impurity scattering in PEDOT.Tos allowed the equation governing the thermoelectric power to be valid at higher carrier densities, resulting in an increase in the power factor. ZT was also enhanced in PEDOT.Tos due to the low intrinsic thermal conductivity (~0.37 W/m K). The peak value of ZT (~0.3) was found close to the regime where the semiconductor turned “metallic,” beyond which ZT would decrease. We are of the opinion that charge-to-charge scattering (which normally would lower the power factor in highly doped semiconductors) remain subdued in PEDOT.Tos due potentially to electronic screening and a lack of long-range order. We used the reported data to compute the carrier density and mobility assuming ionized impurity scattering and found the peak power factor to occur for carrier density of ~1 × 10²⁶ m⁻³ and mobility of ~5 × 10⁻⁴ m²/V s.     

Temperature-dependent conductivity and photoconductivity of <Emphasis Type=Italic>p</Emphasis>-CuI crystals

The effect of the vacuum annealing of p-CuI crystals on their resistivity, transmittance, temperature-dependent conductivity, and photoconductivity in the visible and ultraviolet spectral regions is studied. It is shown that the conductivity and transmittance of CuI increase at low annealing temperatures and decrease, as the temperature of vacuum annealing is increased over 60 min. It is established that these systematic features are connected with the formation of intrinsic donor or acceptor defects in the CuI crystal lattice.     

Semi-insulating 4<Emphasis Type=Italic>H</Emphasis>-SiC layers formed by the implantation of high-energy (53 MeV) argon ions into <Emphasis Type=Italic>n</Emphasis>-type epitaxial films

It is shown that 9-μm-thick semi-insulating surface layers can be formed in moderately doped n-type silicon carbide (donor concentration 2 × 10¹⁶ cm^–3) via the comparatively low-dose (7 × 10¹¹ cm^–2) implantation of high-energy (53 MeV) argon ions. The free-carrier removal rate is estimated at ~10⁴ cm^–1. The resistivity of the semi-insulator is no less than 7 × 10¹² Ω cm. Analysis of the monopolar current of electron injection into the semi-insulator shows that the impurity-conductivity compensation is due to radiationinduced defects pinning the equilibrium Fermi level at a depth of 1.16 eV below the conduction-band bottom. The density of defect states at the Fermi level is 2.7 × 10¹⁶ cm² eV^–1.     

Effect of annealing on the luminescence of <Emphasis Type=Italic>p</Emphasis>-CuI crystals

The photoluminescence spectra of CuI samples containing different numbers of intrinsic defects are studied at the temperature 80 K. The samples were excited with continuous-wave (cw) and pulse optical excitation. Emission peaks related to bound and free excitons, and to the recombination of electrons at shallow and deep crystal-lattice defect levels are observed. It is found that CuI crystals subjected to high-temperature annealing contain hexagonal phase inclusions.     

Study of the influence of the sulfide and ultraviolet treatment of the <Emphasis Type=Italic>n</Emphasis>-<Emphasis Type=Italic>i</Emphasis>-GaAs surface on the parameters of ohmic contacts

The possibility of improving the parameters of AuGe/Ni- and Ge/Cu-based ohmic contacts to n-i-GaAs by modifying the preliminarily oxidized GaAs surface in a sulfide-containing solution, as well as via the effect of ultraviolet radiation generated with a KrCl excimer lamp on a chalcogenated surface, is studied. It is shown that preliminary oxidation of the n-i-GaAs surface with subsequent chalcogenation makes it possible to decrease the density of the surface states, to increase the reproducibility of the passivation of the surface, and to decrease the reduced contact resistance of the AuGe/Ni ohmic contacts by a factor of 1.5. The treatment of the chalcogenated surface of n-i-GaAs with an ultraviolet radiation with wavelength λ = 222 nm and emission power density W = 12 mW cm⁻² performed in vacuum before the deposition of metal layers of the Ge/Cu ohmic contacts makes it possible to decrease the reduced contact resistance by 25–50% andimprove the morphological characteristics of the surface of the contact area.     

Specific features of recombination in layered <Emphasis Type=Italic>a</Emphasis>-Si:H films

The absorbed light spectral composition determines the type of carrier generation: interband generation or mixed generation that also includes the generation of electrons from levels of the valence-band tail. The generation type affects the value and temperature dependence of the electron recombination rate in a-Si:H layered films. This effect is caused by a variation in the occupation of the levels of silicon dangling bonds and the valence band tail with electrons upon a change in the carrier generation type. As a result, in the case of mixed carrier generation in the investigated films with a low concentration of native dangling bonds, electron recombination in the films is slow and recombination at the levels of the valence-band tail can prevail up to room temperature.     

Valence Band Studies of <Emphasis Type=Italic>p</Emphasis>- and <Emphasis Type=Italic>n</Emphasis>-Type Ba<Subscript>8</Subscript>Ga<Subscript>16</Subscript>Ge<Subscript>30</Subscript> Using High-Resolution Photoelectron Spectroscopy

The electronic states of p- and n-type Ba₈Ga₁₆Ge₃₀ (BGG) are studied by high-resolution x-ray photoelectron spectroscopy. In BGG, three bands are resolved in the valence band region. Theoretical calculations show that the three band structures in the valence band are mainly constructed by the Ge/Ga 4s and 4p wavefunctions with little contribution from Ba 5s, 5p, and 5d. The valence band around the Fermi level region of n-type BGG is sensitive to temperature, while that of p-BGG is stable when the temperature changes. The data indicate that the endohedral Ba in p- and n-type BGG rattle with different modes due to the different hybridization with the orbitals of the framework polyhedra.