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.     

Study of the intermediate layer at the <Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>-CdS/<Emphasis Type="Italic">p</Emphasis>-CdTe interface

The effect of production conditions and subsequent stimulation by ultrasonic irradiation on the formation of a solid solution at the n-CdS/p-CdTe interface in solar cells has been investigated. The phase composition of the solid-solution transient layer was investigated by a nondestructive photoelectric method (measurement of the spectral distribution of photosensitivity in the gate and photodiode modes). It is shown that the phase composition and thickness of the intermediate CdTe_1?x S _x layer depend strongly on the heterostructure formation conditions.     

Mechanisms of charge transport in anisotype <Emphasis Type="Italic">n</Emphasis>-TiO<Subscript>2</Subscript>/<Emphasis Type="Italic">p</Emphasis>-CdTe heterojunctions

Surface-barrier anisotype n-TiO₂/p-CdTe heterojunctions are fabricated by depositing thin titanium-dioxide films on a freshly cleaved surface of single-crystalline cadmium-telluride wafers by reactive magnetron sputtering. It is established that the electric current through the heterojunctions under investigation is formed by generation-recombination processes in the space-charge region via a deep energy level and tunneling through the potential barrier. The depth and nature of the impurity centers involved in the charge transport are determined.     

Electrical Characteristics of <Emphasis Type="Italic">n</Emphasis>-ZnO/<Emphasis Type="Italic">p</Emphasis>-Si Heterojunction Diodes Grown by Pulsed Laser Deposition at Different Oxygen Pressures

Heterojunction diodes of n-type ZnO/p-type silicon (100) were fabricated by pulsed laser deposition of ZnO films on p-Si substrates in oxygen ambient at different pressures. These heterojunctions were found to be rectifying with a maximum forward-to-reverse current ratio of about 1,000 in the applied voltage range of −5 V to +5 V. The turn-on voltage of the heterojunctions was found to depend on the ambient oxygen pressure during the growth of the ZnO film. The current density–voltage characteristics and the variation of the series resistance of the n-ZnO/p-Si heterojunctions were found to be in line with the Anderson model and Burstein-Moss (BM) shift.     

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.     

Effect of different chemical treatments of surface on the height of Al-<Emphasis Type="Italic">p</Emphasis>-SiGe and Au-<Emphasis Type="Italic">n</Emphasis>-SiGe barriers

The effect of different chemical treatments on the properties of Au-n-SiGe and Al-p-SiGe Schottky barriers has been investigated. Etching under different conditions was used to prepare surfaces with different densities of surface states (D _ss). It is shown that the barrier height in the structures under study correlates with the D _ss value and germanium content in the Si_{1 − x} Ge _x alloy.     

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.     

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.     

Epitaxial Growth and Device Design Optimization of Full-Vertical GaN <Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">i</Emphasis>-<Emphasis Type="Italic">n</Emphasis> Rectifiers

The optimization of growth parameters, epitaxial structure, and device design for full-vertical gallium nitride (GaN) p-i-n rectifiers grown on n-type 6H-SiC substrates employing AlGaN:Si conducting buffer layers have been studied. The Al _x Ga_1−x N:Si (x = ~0.1) nucleation layer is calibrated to be capable of acting as a good buffer layer for subsequent GaN growth as well as to provide excellent electrical properties. Two types of full-vertical devices were fabricated and compared: one without any current guiding and the other with the current guiding in the p-layer. The reverse breakdown voltage for rectifiers with a relatively thin 2.5-μm-thick i-region without p-current guiding was found to be over −330 V, while one with p-current guiding was measured to be over −400 V. Devices with p-current guiding structures exhibit reduced reverse leakage current by an order of magnitude >4 at −100 V.     

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.     

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.     

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.     

Effect of High-Density Plasma Process Parameters on Carrier Transport Properties in <Emphasis Type="Italic">p</Emphasis>-to-<Emphasis Type="Italic">n</Emphasis> Type Converted Hg<Subscript>0.7</Subscript>Cd<Subscript>0.3</Subscript>Te Layer

Exposure of p-type HgCdTe material to Ar/H₂-based plasma is known to result in p-to-n conductivity-type conversion. While this phenomenon is generally undesirable when aiming to perform physical etching for device delineation and electrical isolation, it can be used in a novel process for formation of n-on-p junctions. The properties of this n-type converted material are dependent on the condition of the plasma to which it is exposed. This paper investigates the effect of varying the plasma process parameters in an inductively coupled plasma reactive ion etching (ICPRIE) tool on the carrier transport properties of the p-to-n type converted material. Quantitative mobility spectrum analysis of variable-field Hall and resistivity data has been used to extract the carrier transport properties. In the parameter space investigated, the n-type converted layer carrier transport properties and depth have been found to be most sensitive to the plasma process pressure and temperature. The levels of both RIE and ICP power have also been found to have a significant influence.     

Electric properties of (SiC)<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>(AlN)<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/SiC anisotropic heterostructures

The heterostructures of p-(SiC)_{1 − x} (AlN) _x / _n -6H-SiC are synthesized by means of sublimation epitaxy of (SiC)_{1 − x} (AlN) semiconductor solid solutions at 6H-SiC substrates. The results of the investigation of the concentration and temperature dependences on current-voltage characteristics (CVCs) are presented. It is revealed that due to the high potential barriers the forward current is caused by the tunneling and recombination processes of charge carriers via states at the boundary surface.     

A Scanning Probe Microscopy Study of Cd<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te

The effects of several ex vacuo methods used in the surface preparation of Cd_1−x Zn _x Te (CZT) have been studied using noncontact atomic force microscopy, scanning tunneling microscopy, and scanning tunneling spectroscopy. Preparation techniques include mechanical lapping, hydroplane bromine-methanol polishing, and in vacuo annealing. The morphology, electrical homogeneity, and local density of states (LDOS) have been studied for each preparation method. Impurities and oxides quickly form on the surface after each preparation method. Annealing in ultrahigh vacuum causes the surface electronic structure to become inhomogeneous whilst the LDOS suggests a compositional change from an oxide surface to p-type CZT.     

AUTOCORRELATIONS OF l-SEQUENCES WITH CERTAIN SHIFTS

In this paper, the autocorrelations of maximal period Feedback with Carry Shift Register sequences （l-sequences） are discussed. For an l-sequence a with connection integer q = p^e（e ≥ 2） and period T = p^t-1（p- 1）, and for any integer i, 1 ≤ i ≤ e/2, by calculating the number of certain sets, it is shown that the autocorrelation of a with shift τ= kT/2p^i is Ca（τ） =（-1）^k-1 T/p^2i-1, where 1 ≤ k ≤ 2p^i - 1, and gcd（k,2p^i） = 1. This result shows there do exist some shifts such that the autocorrelations of l-sequences are high although most autocorrelations are low. Such result also holds for the decimations of l-sequences.     

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.     

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.     

Magneto-Transport Characterization of <Emphasis Type="Italic">p-</Emphasis>Type HgCdTe

The electrical properties of semiconductor materials have conventionally been extracted via Hall measurements performed at a single magnetic field. When applied to a semiconductor such as HgCdTe with mixed conduction characteristics, the values obtained from the Hall measurement represent only an averaged contribution of all carriers present in the sample. In this study, the transport properties of a liquid-phase epitaxially (LPE) grown p-type HgCdTe were determined. Variable magnetic field and temperature Hall and resistivity measurements were employed in conjunction with the improved-quantitative mobility spectrum analysis (iQMSA) algorithm to extract the concentrations and mobilities of all carriers present in the material. A comparison study was made between a van der Pauw Greek cross and a standard Hall bar structure on the same material. A disparity in the transport property of the sample was observed when both structures were measured within a few days of each other. Through iQMSA analysis, the discrepancy is seen to be attributed to the formation of an n-type skin inversion layer within a week after processing.     

The generation-recombination mechanism of charge transport in a thin-film CdS/CdTe heterojunction

An n-CdS/p-CdTe heterostructure is studied. The heterostructure is obtained using the sequential growth of CdS and CdTe layers by electrochemical deposition and closed-space sublimation, respectively. The measured current-voltage characteristics are interpreted in the context of the Sah-Noyce-Shokley generation-recombination model for the depletion layer of a diode structure. The theory quantitatively agrees with the experimental results.