Characteristics of a GaAs spontaneous infrared source with 40 percent efficiency

The external quantum efficiency of a forward-biased GaAs p-n junction device selected for high efficiency measures 40.5, 32, and 7.3 percent at 20, 77, and 295°K, respectively. The optical exit path is through bulk material doped to a 10¹⁷donors/cm²level. The infrared emission is measured directly with a silicon solar cell. The effective transmissivity of the GaAs bulk device material is measured to be 42 and 8.3 percent at 77 and 295°K, respectively. The corresponding values for the internal quantum efficiency are 76 and 88 percent. The primary optical rise time measured for high level current pulsing conditions is 0.6 and 1.6 ns at 77 and 295°K, respectively.     

Effect of doping on the reliability of GaAs multiple quantum wellavalanche photodiodes

The effect of various doping methods on the reliability of gallium arsenide/aluminum gallium (GaAs/AlGaAs) multiple quantum well (MQW) photodiode (APD) structures fabricated by molecular beam epitaxy is investigated. Reliability is examined by accelerated life tests by monitoring dark current and breakdown voltage. Median device lifetime and the activation energy of the degradation mechanism are computed for undoped, doped-barrier, and doped-well APD structures. Lifetimes for each device structure are examined via a statistically designed experiment. Analysis of variance (ANOVA) shows that dark current is affected primarily by device diameter, temperature and stressing time, and breakdown voltage depends on the diameter, stressing time, and APD type. It is concluded that the undoped APD has the highest reliability, followed by the doped-well and doped-barrier devices, respectively. To determine the source of the degradation mechanism for each device structure, failure analysis using the electron-beam induced current method is performed. This analysis reveals some degree of device degradation caused by ionic impurities in the passivation layer, and energy-dispersive spectrometry subsequently verifies the presence of ionic sodium as the primary contaminant. However since all device structures are similarly passivated, sodium contamination alone does not account for the observed variation between the differently doped APD's. This effect is explained by dopant migration during stressing, which is verified by free carrier concentration measurements using the capacitance-voltage (C-V) technique     

Enhanced Field Ionization Enabled by Metal Induced Surface States on Semiconductor Nanotips

Recent progress in the realization of material structures with quantum confinement and high surface to volume ratio in nanoscale interwoven metal and semiconductor building blocks offers a strong potential to build highly functional nanodevices. Ultra‐sharp tips with distinct material dependent properties of metal and semiconductor exhibit important functionalities in devices including gas ionization sensors, field emission devices, and ion‐mobility spectrometry. Herein, a dramatically enhanced field ionization process and a device based on charged particle beams for which the geometrical and surface properties of the constituent semiconductor nanotips are engineered with controlled introduction of metallic impurities to realize close to three orders of magnitude reduction in the ionization electric‐field strength are described. Experimentally observed low voltage field ionization phenomenon is explained using the geometrical field enhancement, surface states induced by controlled introduction of metallic impurities, and polarizabilities of gas particles at the nanotips. The nanotips are employed to design field ionization gas sensors whose nanoscale pristine semiconductor tips are controllably decorated with atomic metal impurities to boost the electron tunneling properties under extremely low bias voltages. These devices also outperform their solid‐state macroscopic counterparts in terms of simplicity of their construction and higher selectivity.     

Infrared photoconductivity via deep copper acceptors insilicon-doped, copper-compensated gallium arsenide photoconductiveswitches

Silicon-doped, copper-compensated, semi-insulated gallium arsenide of various doping parameters was studied with respect to infrared photoconductivity. This material is used as a photoconductive switch, the bistable optically controlled semiconductor switch (BOSS). One limitation was the relatively low conductivity of the device during the on-state. Typically, silicon-doped gallium arsenide is converted to semi-insulating gallium arsenide by the thermal diffusion of copper into the GaAs:Si. It is shown that variation of the diffusion parameters can improve the on-state conductivity by the enhancement of the concentration of a copper center known as Cu_B. The conductivity of the device 150 ns after irradiation from a 20-ns FWHM laser pulse (λ=1.1 μm) is recorded for various incident energies. This on-state conductivity saturates at a value that is predicted by the densities of the copper levels and the mobility     

Auger recombination-enhanced hot carrier degradation in nMOSFETs with a forward substrate bias

Enhanced hot carrier degradation in nMOSFETs with a forward substrate bias is observed. The degradation cannot be explained by conventional channel hot electron effects. Instead, an Auger recombination-assisted hot electron process is proposed. In the process, holes are injected from the forward-biased substrate and provide for Auger recombination with electrons in the channel, thus substantially increasing channel hot electron energy. Measured hot electron gate current and the light emission spectrum provide evidence that the high-energy tail of channel electrons is increased with a positive substrate bias. The drain current degradation is about ten times more serious in forward-biased substrate mode than in standard mode. The Auger-enhanced degradation exhibits positive temperature dependence and may appear to be a severe reliability issue in high temperature operation condition.     

New semiconductor active device: the conductivity-controlled transistor

A new semiconductor 3-terminal device has been realised in which a majority-carrier current, flowing in a N+-N-N+ structure, is controlled by a minority-carrier current supplied by a forward-biased P+-N junction. The properties of this device are presented and discussed in terms of a physical model.     

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.     

Leakage current in single electron device due to implanted gallium dopants by focus ion beam

Focus ion beam (FIB) technology has been employed to fabricate quantum dot based devices such as the single electron transistor (SET) on a silicon substrate with Cr/Au/Al₂O₃ film stack. It was discovered that the dwell time of FIB gallium beam on an area impacted the dosage of gallium ions implanted into the insulating substrate, creating a highly doped region which could lead to device leakage current. This work focus on the potential electron transport possible when an over-dosed gallium rich Al₂O₃ layer will lead to leakage current between otherwise electrically isolated contact pads. Using the Keithley 4200 semiconductor parametric analyzer (SPA) and the energy dispersive X-ray spectrometer (EDS) analysis; we demonstrate the detrimental effect of leakage current in the range of pA, observed between drain/source electrodes due to the high dose of gallium implanted into the insulating Al₂O₃. The optimized FIB etching parameters to produce a high quality of device functionality with no leakage current is also demonstrated.     

Simulated solar cell device of CuGaSe2 by using CdS,ZnS and ZnSe buffer layers

We have performed ab-initio calculations for the structural, electronic, optical, elastic and thermal properties of the copper gallium chalcopyrite (CuGaSe₂). The Full Potential Linearized Augmented Plane Wave (FP-LAPW) method is used to find the equilibrium structural parameters and to compute the full elastic tensors. We have reported electronic and optical properties with the recently developed density functional of Tran and Blaha. Furthermore, optical features such as dielectric functions, refractive indices, extinction coefficient, optical reflectivity, absorption coefficients, optical conductivities, are calculated for photon energies up to 30 eV. The thermodynamical properties such as thermal expansion, heat capacity, Debye temperature, entropy and Grüneisen parameter, bulk modulus and hardness are calculated employing the quasi-harmonic Debye model at different temperatures (0–1200 K) and pressures (0–8 GPa) and the silent results are interpreted. To check the potentiality of CuGaSe₂ as future solar cell material, device modeling and simulation studies have been carried out with a variety of buffer layers over CuGaSe₂ absorption layer. The band diagram and J/V curves are analyzed and device performance parameters i.e. efficiency, open circuit voltage, short circuit current, quantum efficiency are calculated for CdS, ZnS and ZnSe buffer layers. Simulation results for CuGaSe₂ thin layer solar cell show the maximum efficiency (15.8%) with ZnSe as the buffer layer. Most of the investigated parameters are reported for the first time.     

Amplitude modulators based on the Stark effect

Amplitude modulators are basic devices for long distance optical communication. Their development started using the electro-absorption of bulk material, called the Franz-Keldysh effect. High frequency applications required larger absorption changes with electric field, therefore, attention has been shifted to multiple quantum well structures where the quantum confined Stark effect (QCSE) could improve device performance at high bit rates. However, if the amplitude modulators based on the QCSE are expected to be used in the next multigigabit long-haul fiber transmission systems, the multiple quantum well structure should be optimized taking into consideration parameters such as insertion loss, contrast ratio, chirp, polarization independence, operation voltage and wavelength. Much work has been done in several III-V semiconductor systems. The results of a detailed optimization for InGaAs/InAlAs multiple quantum well structures are presented, as an example.     

Quantifying the impact of homogeneous metal contamination usingtest structure metrology and device modeling

Deposition of metallic impurities from HF process solutions has been investigated experimentally and explained theoretically in a qualitative manner. The depositions are shown to be electrochemical in nature in that an oxidation reduction reaction results in metal ions in solution depositing on the wafer as elements with an oxidation state of 0. The theory is only qualitative in that it can only predict which metals will deposit, not how much. Experimentally, simple transmission equations can be determined which relate metallic contamination levels on Si wafer surfaces (atoms/cm²) to metal concentration in the solution (ppb). Simple test structures have been fabricated with known amounts of iron and copper contamination in the pregate oxide clean of a 1.25 μm CMOS process. Device measurements indicate device degradation in the case of copper, confirming deposition studies that copper deposits from HF solutions. Iron contaminated wafers show no contamination related device effects, in support of theoretical predictions and deposition studies indicating iron does not deposit from HF solutions. The importance and potential usefulness of test structures as homogeneous contamination monitors is illustrated through device modeling of the contamination effects observed in the test structures that can then be used to estimate the effects of such contamination on ULSI circuit performance     

Photoconductive properties of organic-inorganic Ag/p-CuPc/n-GaAs/Ag cell

A thin film of copper phthalocyanine(CuPc),a p-type semiconductor,was deposited by thermal evaporation in vacuum on an n-type gallium arsenide(GaAs) single-crystal semiconductor substrate.Then semitransparent Ag thin film was deposited onto the CuPc film also by thermal evaporation to fabricate the Ag/p-CuPc /n-GaAs/Ag cell.Photoconduction of the cell was measured in photoresistive and photodiode modes of operation. It was observed that with an increase in illumination,the photoresistance decreased in reverse bias while it increased in forward bias.The photocurrent was increased in reverse bias operation.In forward bias operation with an increase in illumination,the photocurrent showed a different behavior depending on the voltage applied.     

Gain saturation in traveling-wave semiconductor optical amplifiers

The gain saturation behavior of semiconductor traveling-wave optical amplifiers has been analyzed using a model that includes the specific dependence of gain on carrier concentration. Under the condition of a specific gain at a particular current, it is found that the saturation power strongly depends on the choice between quantum well (QW) or bulk amplifying medium but weakly on the detailed design of the device such as the number of QW's or the thickness of the bulk layer. The higher saturation power of the QW-based amplifier is caused by its logarithmic gain-current relation rather than its low optical confinement factor. Also, when the unsaturated device gain is specified, the designed saturation power can be obtained with the lowest drive current by using the highest optical confinement     

Enhancement of n‐Type Organic Field‐Effect Transistor Performances through Surface Doping with Aminosilanes

Dopants, i.e., electronically active impurities, are added to organic semiconductor materials to control the material's Fermi level and conductivity, to improve injection at the device contacts, or to fill trap states in the active device layers and interfaces. In contrast to bulk doping as achieved by blending or co‐deposition of dopant and semiconductor, surface doping has a lower propensity to introduce additional traps or scattering centers or to even alter the layer morphology relative to the undoped active material layers. In this study, the electrical effects of a very simple, post‐device‐fabrication surface doping process involving various amine group–containing alkoxysilanes on the performance of organic field‐effect transistors (OFETs) made from the well‐known n‐type materials PTCDI‐C8 and N2200 are researched. It is demonstrated that OFETs doped in such a way generally show enhanced characteristics (up to 10 times mobility increase and a significant reduction in threshold voltage) without any adverse effects on the devices' on/off ratio. It is also shown that the efficiency of the doping process is linked to the number of amine groups.     

Broadband enhancement of coaxial heterogeneous gallium arsenide single‐nanowire solar cells

Coaxial gallium arsenide single‐nanowire solar cells with multiple electrically and optically functional nanoshells are presented in this paper. Both optical absorption and light‐conversion characteristics are extensively examined by performing a comprehensive device‐oriented simulation. It is found that a window layer with a large semiconductor bandgap is necessary for the nanowire gallium arsenide solar cells, which allow internal quantum efficiency ~100% in ~75% of the absorption band of gallium arsenide. Results also reveal the role of nanofocusing effect in enhancing the performance of nanowire devices that show both absorption and external quantum efficiencies over 100% under resonances. A dielectric cladding shell is introduced and optimized, which enhances the nanofocusing effect and leads to extraordinary enhancement of both absorption and light‐conversion capabilities in a very broad band. This design contributes a short‐circuit current density increased by 2.4 times and an open‐circuit voltage over 1.1 V. Copyright © 2014 John Wiley & Sons, Ltd.     

Linear applications of p-n-p-n tetrode

If a four-terminal p-n-p-n device is connected in such a way that its center junction is reversed-biased and the other two junctions are forward-biased, the device can operate as a small-signal semiconductor tetrode amplifier. This capability is demonstrated in this paper by investigating the following linear circuit applications; a controllable-gain amplifier, a signal multiplier, an amplitude modulator, and a voltage-controlled adjustable negative resistance.     

Thermally isolated MOSFET for gas sensing application

This work reports on thermally isolated electronic components for gas sensing applications. The device is composed of an array of 4 MOSFETs, a diode and a semiconductor resistor integrated on a micro-hotplate, which is fabricated using bulk micromachining of silicon. The thermal efficiency of the device is 2°C/mW with a thermal constant less than 100 ms. Holes are made in the passivation film over the gates of the MOSFET and gas sensitive films deposited on top of the gate insulator. The low thermal mass device realized allows new modes of operation for MOSFET gas sensors such as a combination of the field and thermal effects and a pulsed temperature mode of operation     

Ga2O3功率器件研究现状和发展趋势

氧化镓(Ga2O3)超宽禁带半导体材料在高频大功率器件领域具有巨大的应用潜力和前景,近几年已成为国内外研发的热点.概述了Ga2O3半导体材料在功率器件应用领域的特性优势和不足,重点介绍了日本、美国和国内的Ga2O3功率半导体器件的研发现状.详细介绍了目前Ga2O3肖特基势垒二极管(SBD)、Ga2O3金属氧化物半导体场效应晶体管(MOSFET)以及新型Ga2O3功率器件的最新研究成果.归纳出提高Ga2O3单晶和外延材料质量、优化Ga2O3功率器件结构和制造工艺是Ga2O3功率器件未来的主要发展趋势,高功率、高效率、高可靠性和低成本是Ga2O3功率器件未来的主要发展目标.最后总结了我国与美国、日本在Ga2O3功率半导体领域的技术发展差距,以及对未来我国在Ga2O3功率半导体技术方面的发展提出了建议.     

Transient annealing of indium phosphide

Thermal treatment of semiconductor samples in the range ∼ 650 to 900°C is an integral part of planar device processing for the activation of implanted ion species. This letter describes a rapid annealing procedure for the short-term treatment of such implants, which from data obtained on InP is seen to result in high activation efficiencies and mobilities ∼ 85 percent and 2600 cm²/V.s, respectively, while at the same time minimizing surface degradation and bulk impurity redistribution.     

Electron microscopy of GaAs Structures with InAs and as quantum dots

An electron-microscopy study of GaAs structures, grown by molecular-beam epitaxy, containing two coupled layers of InAs semiconductor quantum dots (QDs) overgrown with a thin buffer GaAs layer and a layer of low-temperature-grown gallium arsenide has been performed. In subsequent annealing, an array of As nanoinclusions (metallic QDs) was formed in the low-temperature-grown GaAs layer. The variation in the microstructure of the samples during temperature and annealing conditions was examined. It was found that, at comparatively low annealing temperatures (400–500°C), the formation of the As metallic QDs array weakly depends on whether InAs semiconductor QDs are present in the preceding layers or not. In this case, the As metallic QDs have a characteristic size of about 2–3 nm upon annealing at 400°C and 4–5 nm upon annealing at 500°C for 15 min. Annealing at 600°C for 15 min in the growth setup leads to a coarsening of the As metallic QDs to 8–9 nm and to the formation of groups of such QDs in the area of the low-temperature-grown GaAs which is directly adjacent to the buffer layer separating the InAs semiconductor QDs. A more prolonged annealing at an elevated temperature (760°C) in an atmosphere of hydrogen causes a further increase in the As metallic QDs’ size to 20–25 nm and their spatial displacement into the region between the coupled InAs semiconductor QDs.