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 energy levels associated with Si islands and/or their interface with the SiO2 host matrix material. Quantum size effects, similar to those observed in semiconductor superlattices, are proposed as one possible explanation.

Electroluminescence studies in silicon dioxide films containing tiny silicon islands

The room temperature, photoluminescent properties of manganese‐doped zinc sulfide films deposited by spray pyrolysis are reported. These films were deposited on Pyrex glass substrates at atmospheric pressure using air as a carrier gas. All films were polycrystalline with a wurtzite (hexagonal) structure. The manganese doping was achieved by mixing MnCl3 with the starting solution to deposit ZnS. The photoluminescence spectra was measured at room temperature as a function of the different deposition parameters and the Mn concentration. Besides the characteristic light emission associated with Mn impurities in a ZnS matrix, a peak associated with the self‐activated emission was also observed under certain deposition conditions (low substrate temperatures and/or long deposition times). The presence of chlorine impurities in the films is suggested to be associated with this emission. The Mn luminescence presents a quenching effect with the Mn concentration. This quenching effect is similar to the one reported on films deposited by other techniques. The light emission at this center has an activation energy of 0.71±0.05 eV with the deposition temperature. This energy is proposed to be related with the energy required by the Mn atoms to find a proper site during the growth process to form a Mn2+ center.

Luminescent properties of ZnS:Mn films deposited by spray pyrolysis

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...

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

We report the fabrication of light‐emitting diodes from the semiconducting conjugated polymer poly[2‐methoxy,5‐(2’‐ethyl‐hexyloxy)‐1,4‐phenylene‐vinylene], using doped silicon (both n and p type) as an electrode material. Light emission at low voltages is clearly demonstrated. The presence of a thin SiO2 layer at the silicon interface modifies the device characteristics compared to devices fabricated on indium‐tin‐oxide substrates. An interesting consequence of this is the ability to align the Fermi level of the silicon electrode with the lowest unoccupied molecular orbital of the polymer allowing hole injection in forward bias and electron injection in reverse bias.

Fabrication of polymer light‐emitting diodes using doped silicon electrodes

As an effort toward a goal of monolithic optoelectronics for silicon (Si) chip-to-chip connections, we have fabricated organic light emitting diodes (LED's) using either heavily N-doped silicon (Si) as a cathode or P-doped Si as an anode. A thin silicon dioxide (SiO/sub 2/) layer, thermally grown on Si before deposition of a polymer or a molecular organic layer, enhances the electron injection into the semiconducting emissive layer. Without the thin oxide layer, no light was observed from LED's made from either (2-methoxy, 5-(2'-ethyl-hexoxy)-1, 4-phenylene vinylene) (MEH-PPV) or 8-hydroxyquinoline aluminum (Alq). With the SiO/sub 2/ layer,the internal quantum efficiencies as high as 0.02% and 0.5% have been observed for MEH-PPV and Alq, respectively, and the turn-on voltages were as low as 2.5 V and 8 V, again for MEH-PPV and Alq, respectively. From the LED response time measurement, we identified RC constant and the recombination time of transport-related traps as the speed limiting factors. >

Silicon compatible organic light emitting diode

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...

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

Thin film direct-current electroluminescent devices with ZnS:Mn as the active light-emitting layer have been fabricated on Si wafers. The devices incorporate a high-efficiency electron injector layer capable of passing high current densities (>10-2A cm-2dc) through the active layer. A useful luminance of 78 fL has been achieved at 48V, significantly lower voltage than for conventional ac thin film or dc powder electroluminescent devices. The structure also includes a potential energy step at the interface between SiO 2 and ZnS due to the difference in electron affinities which offers the possibility of hot electron injection into the active layer. The unique combination of efficient cathode emission and hot injection possible in these devices suggests that a solid state analogue of the cathode ray tube may be realizable.

D. J. DiMaria

Papers

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

A new low-voltage Si-compatible electroluminescent device