Air-stable luminescence silicon nanocrystals (Si-NCs) were synthesized using a novel in-flight system composed of a
Si-NC synthesis SiH4/Ar plasma and an SF6 plasma which etches and passivates the NCs. The etch plasma can
efficiently tailor the Si-NC size and the surface functionalities by tuning the gas flow rate, applied power, and pressure
of the plasma.
Si-NCs based light emitting diodes (LEDs) were fabricated by using the Si-NCs as the recombination center for
injected electron-hole pairs. Si-NCs were deposited in between two inorganic metal oxide layers, nickel oxide (NiO)
and zinc oxide (ZnO), which served as the hole transport layer (HTL) and electron transport layer (ETL), respectively.
NiO and ZnO have been chosen by considering their energy band offsets with respect to Si-NCs, and their band offsets
to the electrodes which should produce roughly comparable carrier concentrations once the contacts are forward biased,
to get charge balance at the Si-NCs. The as-prepared metal oxides were confirmed to be stoichiometric using Auger
Electron Spectroscopy (AES). Four-point probes measurements show the oxide sheet resistances in the range of 2-5×106
The as-prepared etched Si-NCs generate orange photoluminescence at a peak intensity of 650nm with a quantum
efficiency of 23%. I-V characteristics and light intensities of the Si-NCs LED without depositing the ZnO ETL have
been studied with respected to the Si-NCs thickness. LEDs made using a two minute deposition of Si-NCs
(approximately 250nm thick) showed an easily visible air-stable light emission; however, the light intensity decreased by
50% for thicker (1.5μm) Si-NC films. The LED performance was improved by using an ITO/ZnO/SiNCs/NiO/Al device
structure. The turned on voltage increased to 7V but the current saturated to 0.1A very rapidly. The Si-NCs LED EL
spectrum was collected at a bias voltage of 8.5V. The emission peaked at 653 nm for the Si-NCs LED in good
agreement with the PL results. At the highest current densities some degradation of the device was observed, otherwise
device operation was consistent and yield was good. The I-V characteristics of the Si-NC LED made using all inorganic
metal oxides showed Schottky behavior as well as good light intensity.
Using a new technique for forming cubic, single crystal silicon nanoparticles about 40 nm on a side, the authors have demonstrated a vertical flow, surround gate, Schottky barrier transistor. This approach allows the use of well known approaches to surface passivation and contact formation within the context of deposited single crystal materials for device applications. It opens the door to novel three dimensional integrated circuits and new approaches to hyper-integration. The fabrication process involves successive deposition and planarization and does not require any type of nonoptical lithography. Device characteristics show reasonable turn- off characteristics and on-current densities of more than 107 A/cm2.
Measurements of the electronic current fluctuations of free-standing hydrogenated amorphous silicon nanoparticles are described. The nanoparticles are synthesized by high-density plasma chemical vapor deposition and are deposited onto conducting substrates. An insulating matrix, either silicon oxide or silicon nitride is then grown in order to electrically isolate the particles. Electronic measurements are performed in this transverse geometry, and underneath a top electrode of area 1mm x 1mm are typically 10,000 nanoparticles with an average diameter of 150 nm in parallel. The spectral density of the current fluctuations in the a-Si:H nanoparticles is well described by a 1/f frequency dependence for frequency f, as in the case of bulk a-Si:H films. The variation of the correlation coefficients with frequency octave separation of the noise power fluctuations in bulk a-Si:H films indicates serial interactions between fluctuators. In contrast, the octave separation dependence of the correlation coefficients for the nanoparticles are very well described by an ensemble of fluctuators whose amplitudes are independently modulated in parallel.
Measurements of the second spectra that characterize the non-Gaussian statistical nature of conductance fluctuations are reported for a series of hydrogenated amorphous silicon thin films. The deposition conditions used to synthesize the films were systematically varied in order to observe the effect that differing amounts of disorder have on the noise statistics. One series of n-type films were deposited at varying substrate temperatures, another n-type series was grown at varying rf powers, and a third series of compensated films was synthesized with varying ratios of phosphine to diborane. None of these series shows any significant change in the non-Gaussian noise statistics as the long-range disorder and deposition properties are changed. Measurements of the second spectra for a film synthesized in an inductively coupled plasma thermal growth system, which yields nano-particles of ~ 150 nm in diameter, are also reported. These results are discussed in terms of models for the non-Gaussian noise properties in amorphous silicon.
In this paper we present the activities at the Center for X-ray Lithography (CXrL) that are dedicated to applying x-ray lithography to 0.25 micrometers processing. We first present the results of optimizing the parameters of the x-ray resist, AZ-PF 514, to achieve 0.25 micron features with variations of less than 10%; second, we discuss the properties of an exposure station (ES3) that feeds the in-house built aligner; third, we present the novel in-house built Two State Aligner (TSA) and its ability to achieve < 32 nm registration error; fourth, we present a developed fabrication process that produces masks with the required membrane stress, optical transparency, and mask flatness; and finally, we present the integration of all the above subprocesses by showing preliminary results from the in-progress 0.25 micrometers NMOS device run. The requirements and results of each sub-process are discussed and judged according to the 0.25 micrometers error budget goals that were initially set for 1997.