Improvement in HgCdTe diode characteristics by low temperature post-implantation annealing

Hg_1−xCd_xTe diodes (x∼0.22) with different carrier concentrations in p type materials have been fabricated by employing an ion-implantation technique. The performances of the diodes, prior to and after low temperature postimplantation annealing, have been investigated in detail by model fitting, taking into account dark current mechanisms. Prior to the annealing process, dark currents for diodes with relatively low carrier concentrations are found to be limited by generation-recombination current and trap-assisted tunneling current, while dark currents for diodes with higher carrier concentrations are limited by band-to-band tunneling current. These dark currents in both diodes have been dramatically decreased by the low temperature annealing at 120∼150°C. From the model fitting analyses, it turned out that trap density and the density of the surface recombination center in the vicinity of the pn junction were reduced by one order of magnitude for a diode with lower carrier concentration and that the carrier concentration profile in a pn junction changed for a diode with higher carrier concentration. The improvements are explained by changes in both carrier concentration profile and pn junction position determined by interaction of interstitial Hg with Hg vacancy in the vicinity of the junction during the annealing process.     

Transient Negative Capacitance Effect in Atomic‐Layer‐Deposited Al2O3/Hf0.3Zr0.7O2 Bilayer Thin Film

The negative capacitance (NC) effect is now attracting a great deal of attention in work towards low‐power operation of field effect transistors and extremely large capacitance density in dynamic random access memory. However, to date, observation of the NC effect in dielectric/ferroelectric bilayer capacitors has been limited to the use of epitaxial ferroelectric thin films based on perovskite crystal structures, such as Pb(Zr,Ti)O₃ and BaTiO₃, which is not compatible with current complementary metal oxide semiconductor technology. This work, therefore, reports on the transient NC effect in amorphous‐Al₂O₃/polycrystalline‐Hf_0.3Zr_0.7O₂ bilayer systems prepared using atomic layer deposition. The thin film processing conditions are carefully tuned to achieve the appropriate ferroelectric performances that are a prerequisite for the examination of the transient NC effect. Capacitance enhancement is observed in a wide voltage range in 5–10 nm thick Al₂O₃/Hf_0.3Zr_0.7O₂ bilayer thin films. It is found that the capacitance of the dielectric layer plays a critical role in the determination of additional charge density induced by the NC effect. In addition, inhibition of the leakage current is important for stabilization of nonhysteretic charge–discharge behavior of the bilayers. The mean‐field approximation combined with classical Landau formalism precisely reproduces the experimental results.     

Partially Depleted Silicon-on-Ferroelectric Insulator Field Effect Transistor- Parametrization & Design Optimization for Minimum Subthreshold Swing

This paper presents the concept of a new field effect transistor based on ferroelectric insulator. The proposed design is named Partially Depleted Silicon-on-Ferroelectric Insulator Field Effect Transistor (PD-SOFFET). The design combines the concepts of negative capacitance in ferroelectric material and silicon-on-insulator (SOI) device. The structure varies from the conventional SOI technology by substituting the buried SiO₂ with a layer of ferroelectric insulator. This new material stack can extract an effective negative capacitance (NC) in the body of the device. The NC effect can provide internal signal boosting. It is demonstrated that the subthreshold swing and the threshold voltage of the proposed device can be lowered by carefully selecting the doping density, the types of the gate oxide and the thicknesses of the ferroelectric film, the silicon layer above the buried insulator and the gate oxide. Lower subthreshold swing is a prime requirement for ultra-low-power design. This paper focuses on studying several parameters to tune the subthreshold swing of the SOFFET device. We have recently introduced the concept of the new transistor, SOFFET, with ferroelectric insulator embedded inside the silicon substrate to lower the subthreshold swing. This paper investigates the impacts of different oxide materials, ferroelectric thicknesses and doping profiles on the negative capacitance inside the body of the proposed PD-SOFFET. It is observed that some emerging gate oxide materials can improve subthreshold flexibility, lower leakage and provide better control over the channel in the proposed device.     

Wavelength variation of 1.6 µm wavelength buried heterostructure GaInAsP/InP lasers due to direct modulation

Wavelength shift during the period of direct modulation (dynamic wavelength shift) for injection lasers having a BH structure has been investigated both experimentally and theoretically. A GaInAsP/InP BH laser emitting a nominal wavelength of 1.61 μm was modulated by a sinusoidal current at frequencies in the range of 0.2-2 GHz. The full width of the dynamic wavelength shift was 0.35 nm at a modulation frequency of 1.8 GHz, and a modulation depth of 63 percent at a bias current 1.14 times the threshold current. It was found that the width of the dynamic wavelength shift increases with proportion to the modulation depth, and with inverse proportion to the bias current at a frequency below 1 GHZ. The differential coefficientdn/dNof refractive indexnfor carrier densityNin the active region was measured for the purpose of the analysis. The value obtained is-1.2 times 10^{-20}cm³. The dynamic shift of the lasing wavelength was found to be characteristic of the change of the refractive index induced by the oscillation of carrier density in the active region during intensity modulation. The theoretical shift shows maximum value at a resonance-like modulation frequency. The peak height of the resonance wavelength shift is strongly affected by carrier diffusion in the transverse direction, and has a minimum value when stripe width is nearly equal to carrier diffusion length.     

Conformational Domain Wall Switch

Domain walls in ferroelectric materials have tantalizing potential in disruptive memory and reconfigurable nanoelectronics technologies. Here, a ferroelectric domain wall switch with three distinct addressable resistance states is demonstrated. The device operation hinges on fully controllable and reversible conformational changes of the domain wall. As validated by atomistic simulations consistent with the experiments, using electric field, the shape—and hence the charge state—of the domain wall and ultimately its conduction are altered. Sequential nanoscale transitions of the walls are visualized directly using stroboscopic‐piezoresponse force microscopy and Kelvin probe microscopy. Anisotropic head‐to‐head domain wall injection, stabilized by the majority carrier type of the ferroelectric, BiFeO₃, is identified as the key factor that enables conformational control.     

确定VCSEL电势及载流子自洽分布算法的研究

分别使用准Fermi能级和pn结模型决定VCSEL的有源层压降,建立了两种自洽确定VCSEL中电势及载流子分布的方法.针对电极电压变化和氧化层限制孔径变化的两种情况,在阈值附近对器件中的结电压分布、载流子浓度分布和注入有源层电流密度分布进行了计算;针对两者所得结果的差异进行了简要的分析,指出了二者的特点及适用范围.     

High Hole Mobility in Long‐Range Ordered 2D Lead Sulfide Nanocrystal Monolayer Films

Coupling between colloidal semiconductor nanocrystals (NCs) with long‐range order is critical for designing advanced nanostructures with controlled energy flow and charge carrier transport. Herein, under the premise of keeping long‐range order in 2D NC monolayer, its native organic ligands are exchanged with halogen ions in situ at the liquid–air interface to enhance the coupling between NCs. Further treatments on the films with dimethyl sulfoxide, methanol, or their mixture effectively improve carrier mobility of the devices. The devices show repeatable enhanced p‐type transport behavior with hole mobility of up to 0.224 ± 0.069 cm² V^?1 s^?1, the highest value reported for lead sulfide NC solids without annealing treatment. Thanks to accurate control over the surface of NCs as well as the structure of NC film, the ordered NC monolayer film of high hole mobility suggests great potentials for making reliable high performance devices.     

Carrier-induced energy shift in GaAs/AlGaAs multiple quantum welllaser diodes

Emission energy shift due to high carrier density at threshold in multiple quantum well (MQW) laser diodes is investigated theoretically. This energy shift is evaluated through the Schrodinger and the Poisson equations self-consistently as well as the calculation of the gain spectra with carrier-dependent lifetime broadening. The band filling and the gain broadening effects show a blue shift on the emission energy. Larger number of wells, lower barrier height, or wider well thickness, reduces the blue shift dependence on the carrier density. At high injections, this blue shift is offset by the bandgap shrinkage effect, which displays smaller influence on MQW's. While the carrier density is further increased, the transition due to the second quantized state is found in single quantum wells, however it is difficult to be observed in MQW's     

Carrier density dependence of refractive index in AlGaAs semiconductor lasers

Carrier density dependence of the refractive index in the active layers of semiconductor lasers is evaluated from the wavelength shift with increases in current by taking into account effects of the active layer temperature rise and lateral carrier and optical field distributions on the wavelength shift. The derived refractive index change due to carrier density increase is-4 times 10^{-27}m³, which is in good agreement with the theoretical value.     

Separation of local bulk and surface recombination in crystalline silicon from luminescence reabsorption

Spontaneous photoemission of crystalline silicon provides information on excess charge carrier density and thereby on electronic properties such as charge carrier recombination lifetime and series resistance. This paper is dedicated to separating bulk recombination from surface recombination in silicon solar cells and wafers by exploiting reabsorption of spontaneously emitted photons. The approach is based on a comparison between luminescence images acquired with different optical short pass filters and a comprehensive mathematical model. An algorithm to separate both front and back surface recombination velocities and minority carrier diffusion length from photoluminescence (PL) images on silicon wafers is introduced. This algorithm can likewise be used to simultaneously determine back surface recombination velocity and minority carrier diffusion length in the base of a standard crystalline silicon solar cell from electroluminescence (EL) images. The proposed method is successfully tested experimentally. Copyright © 2009 John Wiley & Sons, Ltd.     

Ultrahigh Tunability of Room Temperature Electronic Transport and Ferromagnetism in Dilute Magnetic Semiconductor and PMN‐PT Single‐Crystal‐Based Field Effect Transistors via Electric Charge Mediation

Multiferroic heterostructures composed of complex oxide thin films and ferroelectric single crystals have aroused considerable interest due to the electrically switchable strain and charge elements of oxide films by the polarization reversal of ferroelectrics. Previous studies have demonstrated that the electric‐field‐control of physical properties of such heterostructures is exclusively due to the ferroelectric domain switching‐induced lattice strain effects. Here, the first successful integration of the hexagonal ZnO:Mn dilute magnetic semiconductor thin films with high performance (111)‐oriented perovskite Pb(Mg_1/3Nb_2/3)O₃‐PbTiO₃ (PMN‐PT) single crystals is reported, and unprecedented charge‐mediated electric‐field control of both electronic transport and ferromagnetism at room temperature for PMN‐PT single crystal‐based oxide heterostructures is realized. A significant carrier concentration‐tunability of resistance and magnetization by ≈400% and ≈257% is achieved at room temperature. The electric‐field controlled bistable resistance and ferromagnetism switching at room temperature via interfacial electric charge presents a potential strategy for designing prototype devices for information storage. The results also disclose that the relative importance of the strain effect and interfacial charge effect in oxide film/ferroelectric crystal heterostructures can be tuned by appropriately adjusting the charge carrier density of oxide films.     

Coherent optical tapping using semiconductor optical amplifier

Semiconductor optical amplifiers are attractive not only as optical repeaters but also as functional devices, since carrier density modulation in amplifiers causes a nonlinear phenomenon. Utilizing the effect of the carrier density modulation on the semiconductor optical amplifier junction voltage, a coherent optical tapping is proposed for signal monitoring or control signal extraction. A 155 Mb/s FSK (frequency shift keying) signal tapping was realized with a simple configuration using heterodyne single-filter detection with -24.4 dBm sensitivity. Many applications for this coherent optical tapping are discussed, and basic characteristics for frequency-selective tapping from FDM (frequency division multiplexing) signals and optical amplifier gain control are examined     

The Impact of Carrier Transport Confinement on the Energy Transfer Between InGaN/GaN Quantum‐Well Nanorods and Colloidal Nanocrystals

The energy transfer (ET) between InGaN/GaN multiple‐quantum‐well (MQW) nanorods (NRs) and semiconductor nanocrystals (NCs) for efficient color conversion is studied. An exceptional contribution of carrier transport confinement to the ET mechanisms is observed in the proximal side‐wall coupling system, which consists of InGaN/GaN NRs and CdSe NCs. Under relatively low or high excitation, the ET rate shows different carrier‐density dependence, resulting from different electron‐hole configurations, i.e., bound excitons and free carriers. In the localized exciton regime, the ET rate decreases when increasing temperature from 20 K to 200 K. However, in the free‐carrier regime, the ET rate varies insignificantly in the same temperature range. The temperature dependence in this NR‐NC coupling system is different from that in the previously studied planar MQW‐NC coupling system. It is suggested that the carrier transport confinement in NRs is a major factor for these divergences. The highly efficient ET with efficiency up to 80% shows a promising potential of using such NR‐NC coupled structures for ET‐pumped, NC‐based, light‐emitting devices.     

Additional wavelength shift of peak gain due to inhomogeneousdistributions of carriers inside semiconductor lasers

According to the traveling wave rate equations, the carrier density inside a semiconductor laser is position dependent. This will introduce an additional wavelength shift for the radiation that experiences the largest gain. Analysis has led to the establishment of the relationship between the shift and the mean square deviation of the carrier density from its mean. Calculations show that under certain circumstances the shift may approach the order of 10^-1 nm     

Admittance spectroscopy: A powerful characterization technique for semiconductor crystals—Application to ZnTe

The admittance spectroscopy technique is shown to be a very convenient tool for analyzing majority carrier traps: energy level, capture cross section and concentrations are easily obtained without complicated mathematical treatment. The series resistance in the material underlying the Schottky or pn junction is also detected when the free carriers are freezing out. It allows to get the shallowest level energy and its compensation ratio. The method has been applied to ZnTe material analysis and the effect on the admittance of six different acceptors is demonstrated. When comparing the electrically determined ionization energy of a given impurity with its optical value the former appears as systematically lower but most of the difference can be ascribed to Poole Frenkel or impurity concentration effects.     

铁电栅材料GaN基场效应晶体管的特性

针对铁电薄膜/GaN基FET结构,利用数值方法研究了铁电栅材料自发极化强度PS变化对GaN基表面电子浓度nS和场效应晶体管转移特性Id-Vg的影响,给出了典型PS和εr值下跨导gm与Vg的关系。结果表明:零栅压下,nS在随PS(0～±59μC/cm2)变化时有4～6个数量级的提高或降低;当Vg=0.65V、PS为-26～26μC/cm2时,nS提高约4个数量级;负栅压下,nS因受引起电子耗尽的PS的影响而降低6～7个数量级,而PS未对Id-Vg产生明显影响,跨导gm在1V左右的栅偏压下达到最大值。这些结果对利用铁电极化和退极化可能改善新型器件性能的研究具有重要意义。     

Ferroelectric Phase Shifters for VHF and UHF

The analysis, construction, and performance of compact surface wave ferroelectric phase shifters suitable for operation in the100-to1000-MC frequency range are described. Although this ferroelectric loaded parallel-plane structure is a very low impedance structure, a satisfactory terminal impedance matching technique has been devised. Kilovolt level voltages are needed; but since the current required to maintain or rapidly shift phase is low, the over-all control power requirements are at least an order of magnitude less than those for comparable ferrite phase shifters. One of these room temperature operable phase shifters provided 348/spl deg/ of phase shift at 207 Mc. It had an insertion loss which varied from 3.7 to 2.2 db over a zero- to 4000-volt range of applied dc control voltage.     

温度梯度对GaN热压电pn结电学性能的影响

热感应产生的极化电势可以改变压电半导体结构内的力电物理量,这在人工智能、微机电系统(MEMS)中极具应用价值.文章针对温度梯度作用下的氮化镓(GaN)压电pn结,采用二维压电半导体多场耦合方程和精确的热电物理边界条件,数值分析了温度梯度改变对GaN热压电pn结内极化强度、电势、电场、载流子分布及电流等物理场的影响.结果表明:由于温度梯度场和极化电荷之间存在耦合,热压电pn结电学性能对温度梯度高度敏感,由温度改变产生的热感应极化电荷可以有效调节该结构的开启电压和载流子传输特性,这为操控与温度相关的智能异质结器件电流传输提供了新的方法和理论指导.     

Electrical and photoelectric properties of Si-based metal–insulator–semiconductor structures with Au nanoparticles at the insulator–semiconductor interface

It is shown that the formation of Au nanoparticles at the insulator–silicon interface in structures with a high density of surface states results in a shift of the Fermi-level pinning energy at this interface towards the valence-band ceiling in silicon and in increasing the surface-state density at energies close to the Fermi level. In this case, a band with a peak at 0.85 eV arises on the photosensivity curves of the capacitor photovoltage, which is explained by the photoemission of electrons from the formed Au-nanoparticle electron states near the valence-band ceiling in silicon.     

Recombination current measurements in the space charge region of MOS field-induced pn junctions

Electrically active defects in the device region are routinely monitored by CV measurements of reverse-biased field-induced (FI) pn junctions in MOS structures. While useful, this approach is sensitive only to near mid gap defects. Here, we demonstrate a method for interrogation of forward-biased FI pn junctions, which can reveal defect levels over a significantly wider region of the band gap. The method proposed is based on a simultaneous measurement of the gate current and the high frequency gate capacitance in non-equilibrium non-steady state in response to a linear gate voltage ramp which drives the MOS capacitor from inversion equilibrium towards accumulation. This recombination-sensitive technique enables a self-consistent determination of the forward current–voltage characteristic of the FI pn junction. It makes a wider range of important impurities, especially metallic contaminants, accessible to detection by MOS CV approaches. Since the approach satisfies the low-injection condition, the results can be directly related to the properties of the defect centres, thus facilitating defect identification and control.