Contains report on one research project.Joint Services Electronics Program (Contract DAAG29-78-C-0020)Joint Services Electronics Program (Contract DAAG29-80-C-0104

Kastner, Marc A.

DSpace@MIT

XVII, ELECTRONIC PROPERTIES OF INTRINSIC DEFECTSIN AMORPHOUS SILICON DIOXIDEAcademic Research StaffProf. M.A. KastnerGraduate StudentsC.M. GeeJ.H. StathisJoint Services Electronics Program (Contracts DAAG29-78-C-0020 andDAAG29-80-C-0104)Marc A. KastnerDefects in amorphous (a-) Si0 2 are thought to result in deleterious opticaland electronic effects. They may be responsible for limiting the transmission ofoptical fibers; they may be the origin of surface states at Si-Si0 2 interfaceswhich trap charge carriers; they probably cause potential fluctuations which scat-ter mobile carriers moving near the Si-Si0 2 interfaces. Both of the latter effectsseriously limit the performance of MOS devices.Many techniques have been employed to study the defects in a-Si0 2, and agreat deal is known about them. However, the electronic structure and propertiesof the intrinsic defects are not yet well established. On the other hand, muchprogress has been made in developing detailed models for intrinsic defects in nar-rower band-gap chalcogenide glasses (e.g., Se, As2S3, AsxTey etc.). The modelshave been successful in explaining Fermi-level pinning in the diamagnetic groundstate and a wide variety of excited-state properties. The model of Kastner, Adler,and Fritzsche strongly emphasizes that the nature of the defects is a result ofthe special chemical bonding in materials containing two-fold-coordinated group VIelements. Therefore, it was proposed that defects similar to those in sulfides,selenides, and tellurides would be present in oxide glasses as well.The most valuable probe of defects in semiconducting glasses has been photo-luminescence (PL). The large PL Stokes shift and linewidth provided evidence forthe strong electron-photon coupling necessary to explain the effective attractionbetween electrons (Anderson's effective negative correlation energy). We thereforePR No. 123 103(XVII. ELECTRONIC PROPERTIES OF INTRINSIC DEFECTS IN a-Si0 2)undertook a program solely under JSEP funding to study PL in a-Si0 2.The program has been very successful. After completing construction of avacuum ultraviolet spectrometer, which includes the capability of cooling samplesto low temperature in very high vacuum, we made the first observation of intrinsicdefect PL in a-Si0 2. We found that both the radiative and nonradiative mecha-nisms were very similar to those in narrower band-gap glasses. Our observationsof the temperature dependence of the PL intensity were particularly valuable forthey suggested a mechanism for the nonradiative process which appears to dominatein all the glasses.Since time-dependent spectroscopy has led to deeper insight into the radi-ative recombination mechanism in a-As2S3 , it was important to develop the capabil-ity of carrying out such experiments on a-Si0 2. During the past year, we addedto our optical system a pulsed F2 laser which emits lO-nsec pulses with 1 MWpeak power. This high power has enabled us to begin the time-resolved measure-ments. It has also allowed us to observe PL bands which we were not able to detectwith the H2 discharge lamp. The new laser has made possible a range of interest-ing experiments which we are now beginning to explore.PR No. 123 104

Electronic Properties of Intrinsic Defects in Amorphous Silicon Dioxide

http://dspace.mit.edu/bitstream/1721.1/56792/1/RLE_PR_123_XVII.pdf

Electronic Properties of Intrinsic Defects in Amorphous Silicon Dioxide

Abstract

Similar works

Full text

Available Versions

DSpace@MIT