D. W. Dong

Electroluminescence studies in silicon dioxide films containing tiny silicon islands

Electroluminescence from metal‐insulator‐semiconductor structures with silicon dioxide (SiO2) layers containing varying amounts of excess silicon (Si) in the form of tiny Si precipitates have been studied in detail. Bulk insulator emission from the Si islands is shown to dominate over emission from either the SiO2 matrix material or the metallic gate material by studies of oxide or metal gate material, voltage polarity, and insulator thickness dependencies. Several distinct spectral peaks are observed in the energy range from 1.5 to 5 eV which cannot be attributed to optical interference effects. The higher‐energy peaks show a strong dependence on electric field relative to that at the lowest energy (1.7–2 eV). The entire spectral amplitude shows a strong dependence on high‐temperature annealing and excess Si content, decreasing drastically with increasing Si or decreasing annealing temperature. These results are shown to be consistent with light emission during electronic transitions between discrete ene...

Electron heating in silicon dioxide and off‐stoichiometric silicon dioxide films

Electron heating in silicon dioxide (SiO2) at electric fields ≲5 MV/cm is demonstrated using three different experimental techniques: carrier separation, electroluminescence, and vacuum emission. Gradual heating of the electronic carrier distribution is demonstrated for fields from 5 to 12 MV/cm with the average excess energy of the distribution reaching ≳4 eV with respect to the bottom of the SiO2 conduction band edge. Off‐stoichiometric SiO2 (OS‐SiO2) layers are shown to behave similarly to very thin SiO2(≲70 A in thickness) with a transition occurring from ‘‘cool’’ to ‘‘hot’’ electrons as the conduction mechanism changes from direct tunneling between silicon (Si) islands in the SiO2 matrix of the OS‐SiO2 material to Fowler‐Nordheim emission into the conduction band of the SiO2 regions. The relationship of electron heating to electron trapping, positive charge generation, interface state creation, and dielectric breakdown is treated. The importance of various scattering mechanisms for stabilizing the el...

Direct measurement of the energy distribution of hot electrons in silicon dioxide

The energy distribution of hot electrons in high‐field stressed amorphous silicon dioxide (SiO2) films have been measured using a vacuum emission technique. Electrons having average energies ≳2 eV and an energy relaxation length of λ≊32 A are observed at all fields studied (≳ 2 MV/cm). However, contrary to previous theoretical expectations, the majority of carriers in the distribution remains stable at all fields. The results are in agreement with other recent experiments (electroluminescence and carrier separation) which only measure the average energy of hot electrons in SiO2 and with recent Monte Carlo transport calculations which include scattering by both optical and acoustic phonon modes. Results for varying SiO2 thickness, metal gate thickness, oxide composition, and metal gate composition will be discussed.

Charge transport and trapping phenomena in off‐stoichiometric silicon dioxide films

The electrical characteristics of off‐stoichiometric silicon dioxide films have been investigated. The off‐stoichiometric oxide films studied had an excess atomic silicon (Si) content in the range of 1%–6%. Raman spectroscopy and photoconductivity measurements indicate that the excess Si is present as amorphous Si islands or small crystallites embedded in silicon dioxide (SiO2) forming a two‐phase material. These films differ in structure from previously reported films where dual dielectric layers of stoichiometric SiO2 and Si‐rich SiO2 with ≥13% excess atomic Si were used. These dual dielectric films were observed to produce electron injection from contacting electrodes via the Si‐rich SiO2 layer into the SiO2 at lower average electric fields. This injection mechanism was believed to be due to localized electric field enhancement near the SiO2–Si‐rich SiO2 interface caused by the curvature of the tiny Si islands in the SiO2 matrix. The current versus voltage characteristics of the off‐stoichiometric oxid...

Electrically‐alterable read‐only‐memory using Si‐rich SiO2 injectors and a floating polycrystalline silicon storage layer

Currently, electrically‐alterable read‐only‐memory (EAROM) has become increasingly important for memory and logic operations. A novel EAROM device in a field‐effect transistor (FET) configuration, which uses a floating polycrystalline silicon (poly‐Si) layer on top of thermal SiO2 and a dual electron injector structure (DEIS) between this floating poly‐Si and a control gate poly‐Si contact, is described. The DEIS stack consists of sequentially chemically vapor deposited (CVD) layers of Si‐rich SiO2 (46% atomic Si), SiO2, and Si‐rich SiO2 (46% atomic Si) between the poly‐Si layers. Electrons from either poly‐Si layer can move to the other poly‐Si layer biased at the higher voltage with moderate applied voltages. Thus, the floating poly‐Si storage layer can be charged with electrons (’’write’’ operation) or with positive charge (’’erase’’ operation) in milliseconds with negative and positive control gate voltages, respectively. The average electric fields in the intervening CVD SiO2 layer during writing and...

Observation of amorphous silicon regions in silicon‐rich silicon dioxide films

Raman scattering and optical transmission measurements have been made on chemically vapor‐deposited Si‐rich SiO2 films. The measurements show segregated regions of amorphous silicon in the as‐deposited films. Annealing the films at 1150 °C completely crystallizes the amorphous silicon. Annealing at lower temperatures produces films with both amorphous and crystalline regions.

Enhanced conduction and minimized charge trapping in electrically alterable read‐only memories using off‐stoichiometric silicon dioxide films

An electrically alterable read‐only memory using silicon dioxide and silicon‐rich silicon dioxide layers capable of being cycled ≳107 times by minimizing electron charge trapping in the SiO2 layers of the device by incorporation of small amounts of silicon is discussed in detail. Charge transfer to and from a floating polycrystalline silicon layer from a control gate electrode is accomplished by means of a modified dual‐electron‐injector‐structure stack. This modified stack has the intervening silicon dioxide layer, which is sandwiched between silicon‐rich silicon dioxide injectors, replaced by a slightly off‐stoichiometric oxide containing between 1 and 6% excess atomic silicon above the normal 33% found in silicon dioxide. The operation of the electrically alterable device structures in terms of write/erase voltages, cyclability, breakdown, and retention is related to current‐voltage characteristics obtained from capacitors. A physical model based on direct tunneling between Si islands in the off‐stoich...

A study of the electrical and luminescence characteristics of a novel Si‐based thin film electroluminescent device

The results of electrical and luminescence measurements on a new, low voltage, dc, thin film electroluminescent device structure are presented. The devices incorporate a two‐phase Si‐rich‐SiO2/SiO2 electron injector layer which provides control of current, and an active luminescent ZnS:Mn layer in which light is generated by hot electron impact excitation of the Mn2+ activator in high electric field. Separation of the processes of current control and light generation into different layers permits the effects of space charge and the average field distributions to be determined. The electroluminescence intensity is simply proportional to the average power dissipated in the ZnS:Mn layer when the average field is in the range 0.6–1.2 MV cm−1, and when field distortion due to electron trapping in the SiO2 layer is small. When the field locally in the ZnS:Mn layer exceeds ∼1.7 MV cm−1, lattice ionization competes with impact excitation of Mn2+ and the quantum efficiency falls. A simplified model assumes that in...

Attenuated total reflectance study of silicon‐rich silicon dioxide films

The infrared absorption of Si‐rich SiO2 films has been measured using the attenuated total reflection technique. Absorption lines attributed to SiOH, H2O, and SiH groups have been observed in the as‐deposited films. The concentrations of the SiOH and H2O impurities were found to be in the low 1021 cm−3 range, and the concentration of the SiH impurity was found to be 1018 cm−3. Following a 1000 C anneal 1019 cm−3 and 1016 cm−3 ranges, respectively.

Study of charge trapping as a degradation mechanism in electrically alterable read‐only memories

Charge trapping in the intervening oxide layers of electrically‐alterable read‐only memories has been studied for different device configurations incorporating a dual electron injector structure (DEIS). The degradation of the write/erase capability of these devices is associated with electron capture in neutral trapping centers present in both chemical‐vapor‐deposited and thermal oxides. Annealing the exposed DEIS stack at 1000 °C in N2 results in better cycling capability. The dominant traps in unannealed samples were found to have capture cross sections of σc0x ≊10−16−10−17 cm2, while those in annealed samples have σc0x ≊10−17−10−18 cm2.