Generation-Recombination noise analysis in ungated HEMT structure to determinate the activation energy and capture cross-section of traps

Low frequency noise of ungated GaAs/AlGaAs two-dimensional electron gas (2 DEG) heterostructure grown by molecular beam epitaxy (MBE) was investigated over a wide range of temperatures from 4 K to 300 K. In the frequency range from 1 Hz to 100 KHz, noise power spectral densities (PSD) can be described as superposition of flicker noise, thermal noise and several generation-recombination (G-R) noise components. The temperature dependence of the (G-R) noise arising from the traps was used to deduce the thermal activation energies and cross sections. The present results are compared to those of the literature to identify the physico-chemical nature of traps responsible of the G-R noise.Low frequency noise of ungated GaAs/AlGaAs two-dimensional electron gas (2 DEG) heterostructure grown by molecular beam epitaxy (MBE) was investigated over a wide range of temperatures from 4 K to 300 K. In the frequency range from 1 Hz to 100 KHz, noise power spectral densities (PSD) can be described as superposition of flicker noise, thermal noise and several generation-recombination (G-R) noise components. The temperature dependence of the (G-R) noise arising from the traps was used to deduce the thermal activation energies and cross sections. The present results are compared to those of the literature to identify the physico-chemical nature of traps responsible of the G-R noise

Charge generation in metal-oxide-semiconductor capacitors during Fowler-Nordheim stress

Experimental observations are reported concerning the influence of some technological processes on the generation rate of positive oxide charge and interface states during high electric field stress. Our results on positive oxide charge generation are consistent with a model of impact ionization in silicon dioxide and we think that acoustic-phonon runaway is the controlling process for impact ionization in SiO$_2$ in films thicker than 20.0 nm at fields higher than 7 MV/cm. We have found that the positive charge is mainly due to trapped holes when the electrons are injected at the gate/SiO$_2$ interface

Ge nanocrystals formation on SiO

Ge nanocrystals (NCs) are produced by a dewetting process during annealing of an amorphous Ge layer deposited on an ultra thin SiO2 layer. We have investigated the characteristics of the resulting NCs as a function of the nominal Ge layer thickness. Thanks to transmission electron microscopy images, we have extracted both the wetting angle and the NCs aspect ratio. We found that these characteristics remain constant whatever is the nominal thickness in the range of 1.5 to 10 nm. These results suggest that NCs have reached their equilibrium shape. We also experimentally determined the evolution of the NCs with the nominal thickness of the amorphous layer and found a linear relation. These results are in agreement with mass conservation and energetical considerations. Moreover a memory effect was evidenced in all the samples by C − V measurements. At last, we demonstrate that the use of a patterned SiO2 surface improves considerably the ordering of NCs and reduces their size distribution. Such a process is promising for future integration of NCs in memory devices

Ge nanocrystals with highly uniform size distribution deposited on alumina at room temperature by pulsed laser deposition: structural, morphological, and charge trapping properties

In this work, we report on the synthesis of Ge nanocrystals (NCs) by pulsed laser deposition (PLD) at room temperature (RT) in an argon atmosphere without any further annealing process. Our results show that functional thin films of crystalline Ge nanoparticles with spherical shapes can be obtained by PLD directly on alumina layers deposited on n-doped Si (100) substrates. In addition, we also demonstrate that a uniform size distribution of NCs with an average diameter of about 3 nm and a density of 2.3x10^11 cm^-2 can be obtained by optimizing a shadow mask set-up, where a solid disk is introduced between the target and the substrate. Charge/discharge effects in Ge NCs deposited on a high-k amorphous alumina layer are also evidenced by conductive atomic force microscopy, which makes them suitable for memory applications.This work has been fully funded through the project PTDC/FIS/70194/2006 financed by the Portuguese Foundation for Science and Technology (FCT), European COST MP0901-NanoTP and COMPETE. SRCP, EMFV, and JMS are grateful for financial support through FCT grants SFRH/BD/29657/2006, SFRH/BD/45410/2008, and SFRH/BPD/64850/2009, respectively. We would like to thank David J. Barber, Augusto Lopes, Ana J. Martins, and Jose Santos for scientific discussion and technical support.European COST MP0901-NanoTPCOMPET