Highly transparent low capacitance plasma enhanced atomic layer deposition Al2O3-HfO2 tunnel junction engineering

Abstract : The development of metallic single electron transistor (SET) depends on the downscaling and the electrical properties of its tunnel junctions. These tunnel junctions should insure high tunnel current levels, low thermionic current, and low capacitance. The authors use atomic layer deposition to fabricate Al2O3 and HfO2 thin layers. Tunnel barrier engineering allows the achievement of low capacitance Al2O3 and HfO2 tunnel junctions using optimized annealing and plasma exposure conditions. Different stacks were designed and fabricated to increase the transparency of the tunnel junction while minimizing thermionic current. This tunnel junction is meant to be integrated in SET to enhance its electrical properties (e.g., operating temperature, ION/IOFF ratio)

Interface traps effect on the charge transport mechanisms in metal oxide semiconductor structures based on silicon nanocrystals

International audienceThe transport phenomena in Metal-Oxide-Semiconductor (MOS) structures having silicon nanocrystals (Si-NCs) inside the dielectric layer has been investigated by high frequency Capacitance-Voltage (C-V) method and the Deep-Level Transient Spectroscopy (DLTS). For the reference samples without Si-NCs, we observe a slow electron trap for a large temperature range, which is probably a response of a series electron traps having a very close energy levels. A clear series of electron traps are evidenced in DLTS spectrum for MOS samples with Si-NCs. Their activation energies are comprised between 0.28 eV and 0.45 eV. Moreover, we observe in this DLTS spectrum, a single peak that appears at low temperature which we attributed to Si-NCs response. In MOS structure without Si-NCs, the conduction mechanism is dominated by the thermionic fast emission/capture of charge carriers from the highly doped polysilicon layer to Si-substrate through interface trap-states. However, at low temperature, the tunneling of charge carriers from highly Poly-Si to Si-substrate trough the trapping/detrapping mechanism in the Si-NCs contributed to the conduction mechanism for MOS with Si-NCs. These results are helpful to understand the principle of charge transport of MOS structures having a Si-NCs in the SiOx = 1.5 oxide matrix

Concept of new photodetector based on single electron transistor for single charge detection

In this paper, we present a model proposition of photo-SET (single electron photo-detector) aiming at detecting one by one electrons. In the first part of this work, we present the two blocs of the proposed photo-SET (reading and detection blocs). The device structure presented is consisting of two SETs capacitively coupled. In this model, the first SET (SET1) is supposed to read the charge whereas the detection bloc is represented by the second SET (SET2). In the second part, we investigate the effects of photoexcitation on Id-Vg curves and we present results obtained on the output photo-SET characteristics after variation of power illumination and response time

Study of photogenerated traps in nanopixels by random telegraph signal and low frequency noise

In this work, we present noise analysis in a Single Electron Photo-detector (photo-SET or nanopixel) able to detect one by one electron. We perform the power spectral densities (PSD) of random telegraph signals (RTSs) measured in the dark conditions and under light illumination. Photoinduced RTS can be attributed to the charging of a dot near the current path. From these results, photogenerated traps were identified. It is also found that RTS fluctuations depend on the light wavelength

Charging effects in Ge nanocrystals embedded in SiO/sub 2/ matrix for non volatile memory applications

International audienc

Study of the kink effect in AlInAs/GaInAs/InP composite channel HFETs

A detailed study is presented on AlInAs/InGaAs/InP composite channels. These devices combine the advantages of high mobility at low voltages and high electric field operations thanks to the use of a composite channel formed by a thin InGaAs layer and a doped InP subchannel. Due to the very low gate leakage currents, it has been possible to precisely study the impact ionization contributions as a function of the temperature. Surprisingly, it is not possible from our measurements to correlate the kink effect observed in the devices with the impact ionization phenomenon. Therefore, a detailed study of the AlInAs deep traps, and the deep levels detected in the devices has been performed using DLTS, CTS, drain lag, and low frequency noise measurements. The observation of the kink effect in our HFETs has been clearly connected to an electron trap located in the AlInAs layers. In order to confirm this result, the optical properties of this deep trap have been studied by I-V measurements under optical excitation for HFETs, and by DLOS on bulk AlInAs. Our measurements show that the same defect is observed in AlInAs and in the HFETs and that it is possible to suppress the kink effect by an optical ionization of this electron trap. Finally, our electro-optical study shows the direct correlation between deep traps in the AlInAs barrier layers and the kink effect in these devices

Effect of annealing time on the performance of tin oxide thin films ultraviolet photodetectors

International audienceTin oxide SnO2 thin films were deposited by sol gel method on glass substrates. The as-deposited thin films were then annealed at 550 °C for different time durations (15, 30, 60 and 120 min). Structural and morphological investigations were carried out on all samples by X-ray diffraction method and atomic force microscopy while optical properties were obtained with UV–Visible spectrophotometer. XRD patterns reveals that the samples possess polycrystalline with rutile structure of SnO2 without any secondary phase. AFM image showed that SnO2 thin films having a smooth surface morphology. The optical properties in the visible range showed that the deposited layers have a high transmission factor. The optical band gap energy varies in the range of 3.61–3.73 eV. Finally, ultraviolet (UV) detection properties of samples as an active layer in UV photodetector devices were investigated. Current-voltage characteristics of the SnO2 thin films are performed under dark and light environment, which show low dark current of 22.9 nA with a linear behavior and high current ration > 104 under 2 V applied voltage and 120 min as annealing time. Whereas, high photocurrent is observed for samples annealing for 30 min. Moreover, the transient photoresponse of the fabricated device is reported under different annealing times

On the saturation mechanism in the Ge nanocrystals-based non-volatile memory

International audienc

Electrical study of Ge-nanocrystal-based metal-oxide-semiconductor structures for p-type nonvolatile memory applications

International audienc

Strained Si1-xGex/Si Dots and Wires Grown by Selective Epitaxy

Selective epitaxial growth of Si1-xGex was studied with the aim to fabricate quantum wires and dots. The selective deposition was performed by low pressure chemicd vapor deposition with dichlorosilane and germane as precursors, at 0.1 Torr and 700°C in a radiation heated, cold wall, high vacuum, quartz reactor. Dislocation free strained dots and wires could be grown much thicker than the critical thickness for unpatterned area, because the critical thickness by formation of misfit dislocations increases when the window dimension is reduced. For x up to 20% it was found that for 10x10µm2 dots the critical thickness increases by more than 4 times. The tendency of facet formation was exploited to realize laterally confined multiple quantum well dots and wires with size down to 50 nm. Besides the emission from the (100) quantum well layers excintonic emissions from quantum well layers from flat {110} facets and from islands in the (100) and {311}facets were detected. All dots and wires luminecse stronly down to the lowest achieved dimension of 50 nm, the integral intensity exceeding that from the substrate