Role of spontaneous polarization in the formation of <Emphasis Type="Italic">NH</Emphasis>-SiC/3<Emphasis Type="Italic">C</Emphasis>-SiC/<Emphasis Type="Italic">NH</Emphasis>-SiC structures based on silicon carbide polytypes

The effect of the electrostatic field caused by spontaneous polarization in hexagonal plates of a heterostructure based on NH-SiC/3C-SiC/NH-SiC silicon carbide polytypes on relative positions of energy bands is considered. It was shown that the asymmetry arising in the system is associated with the superposition of polarization and contact fields.     

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.     

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.     

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.     

3<Emphasis Type="Italic">C</Emphasis>-SiC <Emphasis Type="Italic">p-n</Emphasis> structures grown by sublimation on 6<Emphasis Type="Italic">H</Emphasis>-SiC substrates

Sublimation epitaxy in a vacuum has been employed to grow n-and p-type 3C-SiC layers on 6H-SiC substrates. Diodes have been fabricated on the basis of the p-n structure obtained, and their parameters have been studied by measuring their current-voltage and capacitance-voltage characteristics and by applying the DLTS and electroluminescence methods. It is shown that the characteristics of the diodes studied are close to those of diodes based on bulk 3C-SiC. A conclusion is made that sublimation epitaxy can be used to fabricate 3C-SiC p-n structures on substrates of other silicon carbide polytypes.     

Study of the 3<Emphasis Type="Italic">C</Emphasis>-SiC layers grown on the 15<Emphasis Type="Italic">R</Emphasis>-SiC substrates

The 3C-SiC layers grown on the 15R-SiC substrates by sublimation epitaxy in vacuum are studied. Using X-ray topography and Raman spectroscopy, it is shown that the obtained layers are of a rather high structural quality. By the data of the Raman spectroscopy and capacitance-voltage measurements, it is established that the electron concentration in the 3C-SiC layer is (4–6) × 10¹⁸ cm^?3.     

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.     

Electrical properties of <Emphasis Type="Italic">n-</Emphasis>GaN/<Emphasis Type="Italic">p</Emphasis>-SiC heterojunctions

Epitaxial GaN layers were grown by hydride vapor phase epitaxy (HVPE) on commercial (CREE Inc., USA) p⁺-6H-SiC substrates (Na ? Nd ≈ 7.8 × 10¹⁷ cm^s?3) and n⁺-6H-SiC Lely substrates with a predeposited p⁺-6H-SiC layer. A study of the electrical properties of the n-GaN/p-SiC heterostructures obtained confirmed their fairly good quality and demonstrated that the given combination of growth techniques is promising for fabrication of bipolar and FET transistors based on the n-GaN/p-SiC heterojunctions.     

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.     

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.     

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.     

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.     

<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.     

Circular polarization of the photoluminescence from a system of two-dimensional <Emphasis Type=Italic>A</Emphasis><Superscript>+</Superscript> centers in a magnetic field

A series of GaAs/AlGaAs quantum well structures with different concentrations of A ⁺ centers is studied experimentally by polarized photoluminescence spectroscopy. The spectral dependences of the circular polarization and the energy shifts in a magnetic field exhibit qualitatively different behavior for samples corresponding to the weak and strong localization conditions. The results obtained are explained in the context of a suggested model describing optical transitions between states of localized and free electrons and A ⁺ centers.     

Induced surface states of the ultrathin Ba/3<Emphasis Type="Italic">C</Emphasis>-SiC(111) interface

The electronic properties of the Ba/3C-SiC(111) nanointerface are for the first time studied by photoelectron spectroscopy with the use of synchrotron radiation in the energy range 80–450 eV. The experiments are performed in situ in ultrahigh vacuum for ultrathin Ba coatings on 3C-SiC(111) samples grown by a new method of substituting substrate atoms. It is found that the adsorption of Ba brings about the appearance of induced surface states with the binding energies 1.9, 6.2, and 7.5 eV. Evolution of the surface states and the spectra of the Si 2p and C 1s core levels shows that the Ba/3C-SiC(111) interface is formed due to charge transfer from Ba adatoms to surface Si atoms and underlying C atoms.     

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.