Electrically triggered resistance switching phenomenon in metal oxide was extensively explored for the promising potential as an emerging nonvolatile memory. Prototype chips of large-scale array based on metal oxide memory are currently under development in industry. This chapter reviews the recent research progress of metal oxide memory specifically focusing on the following topics: (1) the underlying physics of resistance switching in metal oxides, including the experimental evidences of the filamentary conduction and oxygen ion/vacancy migration involved switching mechanism; (2) state-of-the-art device characteristics and the key performance metrics such as resistance ratio, scalability, power consumption, switching speed, reliability, and uniformity; and (3) device cell structure design considerations for integration into large-scale high-density crossbar memory arrays. Challenges and strategies for future optimization of metal oxide resistive switching memory technology were discussed.

Metal Oxide Resistive Switching Memory

A novel wavelength tuning technique, applicable to shallow junction surface-emitting LED's, is shown to exhibit wavelength changes on the order of 50 nm, depending on current and gas environment, the tuning technique is external and is continuous, repeatable, reversible, controllable, and apparently nondestructive. Thermal and pressure changes in E g do not appear to be dominant mechanisms. The dominant mechanism is suspected to involve surface effects, such as desorption of adsorbed gases, which depend upon self-heating in vacuo. The one-to-one relationship between diode voltage and peak emission wavelength suggests photon-assisted tunneling as the tuning mechanism although surface band-bending changes may play some role. Surface effects alone, such as generated by UV illumination, are shown to yield noticeable LED wavelength shift, while bulk heating with red light of much higher average irradiance does not. This technique is, in principle a general technique independent of semiconductor material. The results described here should also have implications for optical-fiber communication, gas detection and identification, and space applications.

Wavelength tuning of GaAs LED's through surface effects

Ce memoire presente les resultats de travaux portant sur l’analyse de la fiabilite de diodes laser de pompe emettant a 980 nm et de photodiodes InGaAs pour des applications spatiales. La severite de l’environnement spatial (vide, radiations, contraintes thermomecaniques) impose d’evaluer la robustesse de ces deux technologies qui ont ete specialement concues pour des applications de telecommunications sous-marines. L’objectif de ce memoire est donc de proposer une methodologie d’evaluation de la fiabilite en s’appuyant la caracterisation electro-optique, l’analyse physico-chimique et la modelisation. Les diodes laser ont ete vieillies sous ultravide (pression de 10-7 mbar) pendant 5000h sous 800 mA et 60°C. Certains composants, dont l’hermeticite du boitier a ete volontairement rompue, ont presente des defaillances de type COD (Catastrophic Optical Damage). Les caracteristiques des composants, dont le boitier est reste hermetique, n’ont cependant pas derive. Apres avoir modelise les caracteristiques electriques du composant, mene des analyses physiques (AFM, MEB, MET, cathodoluminescence et ToF-SIMS) et calcule la variation de la pression a l’interieur du boitier, nous avons estime la duree de vie du composant fonctionnant sous ultravide a 26 ans.Les photodiodes ont ete irradiees par des protons d’energie comprise entre 30 et 190 MeV sous une fluence comprise entre 5.1010 et 1012 p/cm², entrainant une augmentation du courant d’obscurite de trois decades. La modelisation du courant d’obscurite a permis d’estimer la duree de vie du composant en environnement spatial a 15 ans.Ces travaux ont egalement contribue a mettre en evidence des mecanismes de degradation peu documentes (COD sous vide, difficulte d’ajustement avec le NIEL, degradation du reseau de Bragg expose aux rayonnements ionisants), ce qui permet de mieux apprehender le comportement des diodes laser et des photodiodes exposees a l’environnement spatial.

Evaluation de la fiabilité de composants optoélectroniques pour des applications spatiales : apport des caractérisations et des modélisations électro-optiques

It is shown that a semiconductor laser driven by short electrical current pulses represents a high‐speed gate for external optical signals. Based on this finding a novel sampling technique for the detection of light pulses is demonstrated. Conventional semiconductor lasers can be used as sampling gates in a cross correlation arrangement. The time resolution is observed to be better than 10 ps under appropriate injection conditions of the sampling laser. Computer simulations of the sampling system are carried out in the framework of the rate equation model. The theoretical predictions on the time response and the dynamics of the sampling system agree with the experimental observations.

Picosecond optical sampling by semiconductor lasers

Surface effects stemming simply from photodiode operation in vacuum environment are seen to improve quantum efficiency significantly. This is attributed to desorption of surface impurities and consequent reduction of surface recombination and Debye length. Effective depletion layer width, because of junction shallowness, can also be noticeably affected by changes in surface potential and free charge redistribution stemming from desorption of surface impurities. Quantum efficiency enhancement here in vacuum is greatest at visible wavelengths, thus suggesting application in solar cell technology, particularly since I sc , V oc , and fill factor are all increased in vacuum.

Significant photodiode quantum efficiency improvement and spectral response alteration through surface effects in vacuum

Wavelength tuning via shallow junction GaAs LED's as a result of gamma irradiation is increased significantly when the irradiated LED's are operated in vacuum. Vacuum operation is seen to be essentially equivalent to increased gamma ray dosage for low irradiation levels as a result of desorptive processes common to both phenomena. They give rise to decreased nonradiative and increased radiative components of surface recombination photon emission. It is this spectrum which is shifted according to changes in surface potential and forward voltage deriving from alterations in surface state populations. A mathematical model is developed to relate wavelength tuning with surface potential and forward voltage shift. This technique is, in principle, a general technique independent of semiconductor material. It suggests the possibility of wavelength tuning via surface band-bending changes deriving from surface electric field changes, as is done with MIS devices. Examination of irradiated diode properties in vacuum and under pressure permits greater insight into the basic nature of surface phenomena long suspected to play a significant role in the diode electronic property changes brought about by nuclear irradiation.

Gamma ray irradiated LED's: Surface emission and significant wavelength tuning via surface states

Alterations of device characteristics as a result of γ-ray irradiation of shallow-junction surface emitting devices are different from those of deep-junction devices with respect to LED emission intensity reduction, I-V curve, line shape, and spectral shift. In particular, much larger spectral shifts in the opposite direction-toward longer wavelengths-are reported here than those found in the literature for deep-junction devices. A qualitative model based upon photochemical doping and changes in surface band bending is proposed to explain these phenomena. Changes in surface emitting shallow-junction optical radiation source device characteristics brought about by γ-ray irradiation are desirable ones for utilization in most optical fiber communication systems. These changes include linewidth narrowing, decreased time response, and decreased material dispersion because of the emission wavelength change.

Spectral tuning and linewidth narrowing of shallow-junction surface emitting GaAs LED&#769;s through &#947;-ray irradiation

Various Si and Ge rectifier diodes are tested at frequent intervals of γ‐radiation doses for changes in ideality factor η and minority carrier lifetime τ. Although both parameters are well known to decrease with dosage, here they are probably for the first time measured to also subsequently increase, decrease, increase, etc., at higher dosages. Examination of diodes in vacuum prior to and following even modest irradiation levels indicates experimentally that noticeable changes in surface properties have been induced by the irradiation. Such experimental techniques permit greater insight into the basic structure of surface phenomena long suspected to play a significant role in diode changes brought about by nuclear irradiation. Utilization of such surface changes leads to a broad general concept to explain the reversals and changes in the dosage dependences of η and τ in terms of bulk versus surface effects.

I. Hirsh

Papers

Wavelength tuning of GaAs LED's through surface effects

Significant photodiode quantum efficiency improvement and spectral response alteration through surface effects in vacuum

Gamma ray irradiated LED's: Surface emission and significant wavelength tuning via surface states

Spectral tuning and linewidth narrowing of shallow-junction surface emitting GaAs LED́s through γ-ray irradiation

A simple qualitative model of surface versus bulk effects in gamma-ray irradiated p-n diodes

I. Hirsh

Papers

Wavelength tuning of GaAs LED's through surface effects

Significant photodiode quantum efficiency improvement and spectral response alteration through surface effects in vacuum

Gamma ray irradiated LED's: Surface emission and significant wavelength tuning via surface states

Spectral tuning and linewidth narrowing of shallow-junction surface emitting GaAs LED&#769;s through &#947;-ray irradiation

A simple qualitative model of surface versus bulk effects in gamma-ray irradiated p-n diodes

Spectral tuning and linewidth narrowing of shallow-junction surface emitting GaAs LED́s through γ-ray irradiation