Effects of alternating current voltage amplitude and oxide capacitance on mid-gap interface state defect density extractions in In0.53Ga 0.47As capacitors

This work looks at the effect on mid-gap interface state defect density estimates for In0.53Ga0.47As semiconductor capacitors when different AC voltage amplitudes are selected for a fixed voltage bias step size (100 mV) during room temperature only electrical characterization. Results are presented for Au/Ni/Al2O3/In0.53Ga0.47As/InP metal–oxide–semiconductor capacitors with (1) n-type and p-type semiconductors, (2) different Al2O3 thicknesses, (3) different In0.53Ga0.47As surface passivation concentrations of ammonium sulphide, and (4) different transfer times to the atomic layer deposition chamber after passivation treatment on the semiconductor surface—thereby demonstrating a cross-section of device characteristics. The authors set out to determine the importance of the AC voltage amplitude selection on the interface state defect density extractions and whether this selection has a combined effect with the oxide capacitance. These capacitors are prototypical of the type of gate oxide material stacks that could form equivalent metal–oxide–semiconductor field-effect transistors beyond the 32 nm technology node. The authors do not attempt to achieve the best scaled equivalent oxide thickness in this work, as our focus is on accurately extracting device properties that will allow the investigation and reduction of interface state defect densities at the high-k/III–V semiconductor interface. The operating voltage for future devices will be reduced, potentially leading to an associated reduction in the AC voltage amplitude, which will force a decrease in the signal-to-noise ratio of electrical responses and could therefore result in less accurate impedance measurements. A concern thus arises regarding the accuracy of the electrical property extractions using such impedance measurements for future devices, particularly in relation to the mid-gap interface state defect density estimated from the conductance method and from the combined high–low frequency capacitance–voltage method. The authors apply a fixed voltage step of 100 mV for all voltage sweep measurements at each AC frequency. Each of these measurements is repeated 15 times for the equidistant AC voltage amplitudes between 10 mV and 150 mV. This provides the desired AC voltage amplitude to step size ratios from 1:10 to 3:2. Our results indicate that, although the selection of the oxide capacitance is important both to the success and accuracy of the extraction method, the mid-gap interface state defect density extractions are not overly sensitive to the AC voltage amplitude employed regardless of what oxide capacitance is used in the extractions, particularly in the range from 50% below the voltage sweep step size to 50% above it. Therefore, the use of larger AC voltage amplitudes in this range to achieve a better signal-to-noise ratio during impedance measurements for future low operating voltage devices will not distort the extracted interface state defect density.

Experimental analysis of novel telecom source materials and devices

Incumbent telecommunication lasers emitting at 1.5 µm are fabricated on InP substrates and consist of multiple strained quantum well layers of the ternary alloy InGaAs, with barriers of InGaAsP or InGaAlAs. These lasers have been seen to exhibit very strong temperature dependence of the threshold current. This strong temperature dependence leads to a situation where external cooling equipment is required to stabilise the optical output power of these lasers. This results in a significant increase in the energy bill associated with telecommunications, as well as a large increase in equipment budgets. If the exponential growth trend of end user bandwidth demand associated with the internet continues, these inefficient lasers could see the telecommunications industry become the dominant consumer of world energy. For this reason there is strong interest in developing new, much more efficient telecommunication lasers. One avenue being investigated is the development of quantum dot lasers on InP. The confinement experienced in these low dimensional structures leads to a strong perturbation of the density of states at the band edge, and has been predicted to result in reduced temperature dependence of the threshold current in these devices. The growth of these structures is difficult due to the large lattice mismatch between InP and InAs; however, recently quantum dots elongated in one dimension, known as quantum dashes, have been demonstrated. Chapter 4 of this thesis provides an experimental analysis of one of these quantum dash lasers emitting at 1.5 µm along with a numerical investigation of threshold dynamics present in this device. Another avenue being explored to increase the efficiency of telecommunications lasers is bandstructure engineering of GaAs-based materials to emit at 1.5 µm. The cause of the strong temperature sensitivity in InP-based quantum well structures has been shown to be CHSH Auger recombination. Calculations have shown and experiments have verified that the addition of bismuth to GaAs strongly reduces the bandgap and increases the spin orbit splitting energy of the alloy GaAs1−xBix. This leads to a bandstructure condition at x = 10 % where not only is 1.5 µm emission achieved on GaAs-based material, but also the bandstructure of the material can naturally suppress the costly CHSH Auger recombination which plagues InP-based quantum-well-based material. It has been predicted that telecommunications lasers based on this material system should operate in the absence of external cooling equipment and offer electrical and optical benefits over the incumbent lasers. Chapters 5, 6, and 7 provide a first analysis of several aspects of this material system relevant to the development of high bismuth content telecommunication lasers.

Exploring several nonconventional interactions of ice-binding proteins

Traditionally, ice-binding proteins (IBPs), also known as antifreeze proteins (AFPs), have been defined by two universal activities: ice recrystallization inhibition and thermal hysteresis. However, there remains the possibility IBPs have other complementary functions given the diversity found within this protein group. This thesis explores some of these in both natural and applied settings, in the hopes of furthering our understanding of this remarkable group of proteins. Plant IBPs could function as part of a defensive strategy against ice nucleators produced by certain pathogens. To assess this hypothesis, recombinant IBPs from perennial ryegrass and purple false brome were combined with the ice nucleation protein (INP) from the plant pathogen, Pseudomonas syringae. Strikingly, the plant proteins depressed the freezing point of the bacterial INP, while a fish AFP could not, nor did the INPs have any effect on IBP activity. Thus, the interaction between these two different proteins suggests a role in plant defensive strategies against pathogenic bacteria as another IBP function. In addition, the potential use of hyperactive insect IBPs in organ preservation was investigated. Current kidney preservation techniques involve storing the organ at 4 °C for a maximum of 24 h prior to transplantation. Extending this “safe” time would have profound effects on renal transplants, however, ischemic injury is prevalent when storage periods are prolonged. Experiments described here allowed subzero preservation for 72 h with the addition of a beetle IBP to CryoStasis® solution. Kidneys stored using the traditional technique for 24 h and the method developed here for 72 h showed similar levels of biomarker enzymes, underscoring the potential utility of insect IBPs for future transplant purposes. Finally, IBP function in the freeze-tolerant gall fly, Eurosta solidaginis, was examined. Larvae representing the mid-autumn stage displayed ice-binding activity, suggesting an IBP is being expressed, possibly as a protective measure against freezing damage when fall temperatures can unpredictably drop. IBP activity was also observed in the larvae’s host plant, Solidago spp. Mass spectrometry analysis of ice-affinity purified plant extracts provided three candidate pathogenesis-related proteins that could be responsible for the detected activity, further demonstrating additional functions of IBPs.

Piezo force microscopy and peakforce tuna measurements of III-V semiconductor nanowires

GaN, InP and GaAs nanowires were investigated for piezoelectric response. Nanowires and structures based on them can find wide applications in areas purposes such as nanogenarators, nanodrives, Solar cells and other perspective areas. Experemental measurements were carried out on AFM Bruker multimode 8 and data was handled with Nanoscope software. AFM techniques permitted not only to visualize the surface topography, but also to show distribution of piezoresponse and allowed to calculate its properties. The calculated values are in the same range as published by other authors.

Investigation of the Nucleation and Growth of Colloidal Indium Phosphide: from Molecular Precursors to Semiconductor Nanocrystals through In37P20(O2CR)51 as a Magic-Size Intermediate

Thesis (Ph.D.)--University of Washington, 2016-06

Material characterization and process development for indium-arsenide / indium-gallium-antimonide channel, high electron mobility transistors for low power, high speed applications

Efforts to push the performance of transistors for millimeter-wave and microwave applications have borne fruit through device size scaling and the use of novel material systems. III-V semiconductors and their alloys hold a distinct advantage over silicon because they have much higher electron mobility which is a prerequisite for high frequency operation. InGaAs/InP pseudomorphic heterojunction bipolar transistors (HBTs) have demonstrated fT of 765 GHz at room temperature and InP based high electron mobility transistors (HEMTs) have demonstrated fMax of 1.2 THz. The 6.1 A lattice family of InAs, GaSb, AlSb covers a wide variety of band gaps and is an attractive future material system for high speed device development. Extremely high electron mobilities ~ 30,000 cm^2 V^-1s^-1 have been achieved in modulation doped InAs-AlSb structures. The work described in this thesis involves material characterization and process development for HEMT fabrication on this material system.

A functional specification and validation model for networks on chip in the ACL2 logic

International audience

From Hardware Processes to asynchronous circuits via petri nets: An Application to Arbiter Design

International audience

Asynchronus design for improved EMC behavior of ICs

International audience

An 8x8 thermopile based uncooled infrared sensor

International audience

Dynamically balanced and plausible trajectory planning for human-like characters

International audience

Optimisation of digitally coded test vectors for mixed-signal components

International audience

Early analysis of fault-attack effects for cryptographic hardware

International audience

Definition of Model-based diagnosis problems with Altarica

International audience

Utilisation d'une méthode de correction de retards pour la vérification d'un assemblage de fonctions RTL par rapport à un assemblage de fonctions au niveau fonctionnel

National audience