Forming Low-Resistance p-Type Layers in Ga1 – xAlxN/GaN Heterostructures

Semiconductors - A technique for fabricating a GaN-based functional heterostructure is proposed, which allows the growth of n-type GaN and InxGa1 – xN layers and р-type GaN and...     

Predicting the Conditions for the Vapor-Phase Epitaxy of the III–V Compounds

Semiconductors - Chloride-hydride epitaxy is the main vapor-phase technique for forming layers of functional homostructures and heterostructures for microelectronics and optoelectronics. At...     

Temperature Coefficient of Movement of the Resonance Level of Iron in Pb1 – x – ySnxFeyTe Alloys

Semiconductors - The phase and elemental composition and the temperature dependences of the resistivity and Hall coefficient (temperature range 4.2 K ≤ T ≤ 300 K, magnetic fields B...     

Synthesis and Thermoelectric Properties of an Sn1 – xPbxSb4Te8 Solid Solution Doped with Bismuth

Semiconductors - The thermoelectric properties of a solid solution of Sn1 – xPbxSb4Te8 and Sn1 – xPbxSb4 – yBiyTe8...     

MOS-Hydride Epitaxy Growth of InGaAs/GaAs Submonolayer Quantum Dots for the Excitation of Surface Plasmon–Polaritons

Semiconductors - The properties of InGaAs/GaAs quantum dots (QDs) grown by MOS-hydride migration-stimulated epitaxy at a reduced pressure using submonolayer deposition are investigated. The...     

A genetic algorithm with chromosome-repairing for min − # and min − ε polygonal approximation of digital curves

A genetic algorithm for solving min ? ε polygonal approximation and min ? # polygonal approximation is proposed in this paper. It combines traditional split-and-merge techniques with a novel chromosome-repairing scheme to cope with constraints. Due to this combination of techniques we call our new method SMCR. In this new scheme an infeasible solution cannot only be easily transformed into a feasible one, but also be optimized. The experimental results show that the proposed SMCR has higher performance than the other GA-based methods and some non-GA-based methods.     

Economic and system impact of hybrid Raman–EDFA amplification in a 40 × 40 Gbps optical transmission network with DPSK modulation

Demands of modern high-bandwidth services drive the need to constantly improve existing optical amplification technology beyond its current bounds. In this paper, we demonstrate a hybrid broadband amplification scheme which is capable of improving the system performance of a wavelength-division-multiplexed (WDM) network. We present the study of optical signals with differential-phase-shift keying (DPSK) modulation at 40 Gbps and its transmission in a 50-GHz spaced, 40-channel WDM system over an 80-km link with hybrid optical amplification. A comparison of the system and cost impacts of a Raman-only amplification scheme with two hybrid Raman–erbium doped fiber amplifier schemes (Hybrids I and II) is performed. It is shown that one of the proposed hybrid schemes (Hybrid II) outperforms the other by (i) improving the tolerance to signal input power by 17 dB and (ii) increasing the system reach by 55 km for input signal power of 5 dBm, for a bit error rate (BER) performance of 10⁻¹².     

Erratum to: First-Principles Investigation of Electronic Properties of GaAsxSb1 – x Ternary Alloys

Semiconductors - erratum     

Band offsets at interfaces of (1 0 0)InxGa1−xAs (0 ⩽ x ⩽ 0.53) with Al2O3 and HfO2

The electron energy band alignment at interfaces of In_xGa_1?xAs (0 ? x ? 0.53) with atomic-layer deposited insulators Al₂O₃ and HfO₂ is characterized using combined measurements of internal photoemission of electrons and photoconductivity. The measured energy of the In_xGa_1?xAs valence band top is found to be only marginally influenced by the semiconductor composition. This result suggests that the observed bandgap narrowing from 1.42 to 0.75 eV when the In content increases from 0 to 0.53 occurs mostly through downshift of the semiconductor conduction band bottom. Electron states originating from the interfacial oxidation of In_xGa_1?xAs lead to reduction of the electron barrier at the semiconductor/oxide interface.     

Coexistence conditions of LTE-advanced at 3400–3600 MHz with TVRO at 3625–4200 MHz in Brazil

In Brazil, the 3625–4200 MHz frequency band (C-band) is widely used by TV receive-only (TVRO) application in the fixed satellite service (FSS). The 3400–3600 MHz adjacent band can be used by International Mobile Telecommunications (IMT) systems, but many low noise block downconverters (LNB) of TVRO sold in Brazil have not a C-band filter. Thus, it is likely that the low cost LNB used in TVRO receivers would be overloaded by the IMT-systems emissions within the LNB wideband receiver, even the IMT stations operating accordingly to international standards. This paper shows that both systems can coexist harmoniously depending on the characteristics of the IMT system and on the FSS receiver specifications.

     

Atomistic model structure of the Ge(1 0 0)–GeO2 interface

An atomistic model of the Ge–GeO₂ interface has been generated through first-principle methods based on density functional theory. The interface model consists of amorphous GeO₂ connected to crystalline Ge through a substoichiometric oxide region showing regular structural parameters. Structural and electronic properties are compared to available experimental data and studied as they evolve across the Ge–GeO₂ interface.     

A 0.1–1 GHz low power RF receiver front-end with noise cancellation technique for WSN applications

A low power 0.1–1 GHz RF receiver front-end composed of noise-cancelling trans-conductor stage and I/Q switch stage was presented in this paper. The RF receiver front-end chip was fabricated in 0.18 µm RF CMOS. Measurement results show the receiver front-end has a conversion gain of 28.1 dB at high gain mode, and the single-sideband (SSB) noise figure is 6.2 dB. In the low gain mode, the conversion gain of the receiver front-end is 15.5 dB and the IP1dB is −12 dBm. In this design, low power consumption and low cost is achieved by current-reuse and inductor-less topology. The receiver front-end consumes only 5.2 mW from a 1.8 V DC supply and the chip size of the core circuit is 0.12 mm².     

Comparative study of low-frequency noise in 0.18 μm and 0.35 μm gate-length nMOSFETs with gate area of 1.1 μm2

We analyzed the noise characteristics of 0.18 μm and 0.35 μm nMOSFETs with a gate area of 1.1 μm² in the frequency range of 1 Hz to 100 kHz. Both two- and four-finger devices were investigated and analyzed. The experimental results show that the noise of 0.35 μm gate-length nMOSFET possesses lower 1/f component than the 0.18 μm one, whereas the four-finger devices reveal less 1/f noise than those of with two-finger ones. Furthermore, we used time domain measurement of drain current and also the statistical analysis of wafer level on the random telegraph signals (RTS) tests, and the results showed that RTS noise is higher in devices with a 0.35 μm gate-length, and devices with a smaller gate finger width produce more RTS noise than devices with a larger gate finger width.     

Effects of geometry,applied hydrostatic pressure and magnetic field on the electron–hole transition energy in a GaAs–Ga1−xAlxAs pillbox immersed in a system of Ga1−yAlyAs

In this work, we study the behavior of the electron–hole transition energy in a GaAs–Ga_1?xAl_xAs pillbox immersed in a system of Ga_1?yAl_yAs as a function of thickness of the ladder barrier potential for a fixed length of the pillbox, length of the pillbox, thickness of the ladder barriers and pillbox position in the host of Ga_1?yAl_yAs. The behavior of the electron–hole transition energy as a function of an applied hydrostatic pressure and an applied magnetic field is also studied. For both electron and hole we found that in the strong confinement regime (L?10 Å) energy of the ground state as function of the position of the pillbox relative to the ladder barrier potential presents a behavior similar to the binding energy of a hydrogenic impurity in quantum wells, quantum wires and quantum dots [L. Esaki, R. Tsu, IBM J. Res. Dev. 14 (1970) 61; G. Bastard, Phys. Rev. B 24 (1981) 4714; N. Porras-Montenegro, J. López-Gondar, L.E. Oliveira, Phys. Rev. B 43 (1991) 1824]. Electron–heavy hole transition energies increase with the applied magnetic field. Also, we have found that these transition energies, as a function of the applied hydrostatic pressure, present an excellent agreement with experimental reports by Venkateswaran et al. [phys. Rev. B 33 (1986) 8416].     

Modeling of Ga1−xInxAs1−y−zNySbz/GaAs quantum well properties for near-infrared lasers

The aim of this work is to model the properties of GaInAsNSb/GaAs compressively strained structures. Indeed, Ga_1?xIn_xAs_1?y?zN_ySb_z has been found to be a potentially superior material to GaInAsN for long wavelength laser dedicated to optical fiber communications. Furthermore, this material can be grown on GaAs substrate while having a bandgap smaller than that of GaInNAs. The influence of nitrogen and antimony on the bandgap and the transition energy is explored. Also, the effect of these two elements on the optical gain and threshold current density is investigated. For example, a structure composed of one 7.5 nm thick quantum well of material with In=30%, N=3.5%, Sb=1% composition exhibits a threshold current density of 339.8 A/cm² and an emission wavelength of 1.5365 μm (at T=300 K). It can be shown that increasing the concentration of indium to 35% with a concentration of nitrogen and antimony, of 2.5% and 1%, respectively, results in a decrease of the threshold current density down to 253.7 A/cm² for a two well structure. Same structure incorporating five wells shows a threshold current density as low as 221.4 A/cm² for T=300 K, which agrees well with the reported experimental results.     

Device characteristics of AlGaN/GaN MIS–HEMTs with high-k HfxZr1−xO2 (x = 0.66, 0.47, 0.15) insulator layer

This study investigates the characteristics of AlGaN/GaN MIS–HEMTs with Hf_xZr_1−xO₂ (x = 0.66, 0.47, and 0.15) high-k films as gate dielectrics. Sputtered Hf_xZr_1−xO₂ with a dielectric constant of 20–30 and a bandgap of 5.2–5.71 eV was produced. By increasing the Zr content of HfZrO₂, the V_TH shifted from −1.8 V to −1.1 V. The highest Hf content at this study reduced the gate leakage by approximately one order of magnitude below that of those Zr-dominated HFETs. The maximum I_DS currents were 474 mA/mm, 542 mA/mm, and 330 mA/mm for Hf content of 66%, 47%, 15% at V_GS = 3 V, respectively.     

Comparison of Continuously- and Step-Graded ZnS y Se1−y /GaAs (001) Metamorphic Buffer Layers

The design of metamorphic buffer layers for semiconductor devices with reduced defect densities requires control of lattice relaxation and dislocation dynamics. Graded layers are beneficial for the design of these buffers because they reduce the threading dislocation density by (1) allowing the distribution of the misfit dislocations throughout the buffer layer therefore reducing pinning interactions, and (2) enhancing mobility from the high built-in surface strain which helps to sweep out threading arms. In this work, we considered heterostructures involving a linearly-graded (type A) or step-graded (type B) buffer grown on a GaAs (001) substrate. For each structure type, we studied the equilibrium configuration and the kinetically-limited lattice relaxation and non-equilibrium threading dislocations by utilizing a dislocation dynamics model. In this work, we have also considered heterostructures involving a constant composition ZnS _y Se_1?y device layer grown on top of a GaAs (001) substrate with an intermediate buffer layer of linearly-graded (type C) or step-graded (type D) ZnS _y Se_1?y . For each structure type, we studied the requirements on the thickness and compositional profile in the buffer layer for the elimination of all mobile threading dislocations from the device layer by the dislocation compensation mechanism.     

Design of S-Graded Buffer Layers for Metamorphic ZnS y Se1−y /GaAs (001) Semiconductor Devices

We present design equations for error function (or “S-graded”) graded buffers for use in accommodating lattice mismatch of heteroepitaxial semiconductor devices. In an S-graded metamorphic buffer layer the composition and lattice mismatch profiles follow a normal cumulative distribution function. Minimum-energy calculations suggest that the S-graded profile may be beneficial for control of defect densities in lattice-mismatched devices because they have several characteristics which enhance the mobility and glide velocities of dislocations, thereby promoting long misfit segments with relatively few threading arms. First, there is a misfit-dislocation-free zone (MDFZ) adjacent to the interface, which avoids dislocation pinning defects associated with substrate defects. Second, there is another MDFZ near the surface, which reduces pinning interactions near the device layer which will be grown on top. Third, there is a large built-in strain in the top MDFZ, which enhances the glide of dislocations to sweep out threading arms. In this paper we present approximate design equations for the widths of the MDFZs, the built-in strain, and the peak misfit dislocation density for a general S-graded semiconductor with diamond or zincblende crystal structure and (001) orientation, and show that these design equations are in fair agreement with detailed numerical energy-minimization calculations for ZnS _y Se_1?y /GaAs (001) heterostructures.     

Impurity states in a spherical GaAs–Ga1-x AlxAs quantum dots: Effects of hydrostatic pressure

We calculated the binding energies of shallow donors and acceptors in a spherical GaAs–Ga${}_{1-x}$Al${}_x$As quantum dot under isotropic hydrostatic pressure for both a finite and an infinitely high barrier. We use a variational approach within the effective mass approximation. The binding energy is computed as a function of hydrostatic pressure, the dot sizes and the impurity position. The results show that the impurity binding energy increases with the pressure for any position of the impurity. We have also found that the binding energy depends on the location of the impurity and the pressure effects are less pronounced for impurities on the edge.