Noise analysis and optimization of a charge transformer, a noise-matching device for single electron transistors

Operation and noise analysis of a recently proposed noise-matching device, called a charge transformer, are presented. The charge transformer consists of N identical capacitors and 3N+13N+1 switches that enable the capacitors to be connected either in series or in parallel. The device is operated by switching back and forth between these two configurations at speeds faster than the signals that will be measured. We show that an ideal charge transformer can achieve perfect noise matching between any single-electron transistor and a high capacitance device that is under test. We also discuss how a realistic charge transformer made using switches with finite capacitance and resistance should be operated to achieve optimum noise performance. © 2003 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69743/2/JAPIAU-93-6-3364-1.pd

Charge Transport Transitions and Scaling in Disordered Arrays of Metallic Dots

We examine the charge transport through disordered arrays of metallic dots using numerical simulations. We find power law scaling in the current-voltage curves for arrays containing no voids, while for void-filled arrays charge bottlenecks form and a single scaling is absent, in agreement with recent experiments. In the void-free case we also show that the scaling exponent depends on the effective dimensionality of the system. For increasing applied drives we find a transition from 2D disordered filamentary flow near threshold to a 1D smectic flow which can be identified experimentally using characteristics in the transport curves and conduction noise.Comment: 4 pages, 4 postscript figure

Illumination and annealing characteristics of two-dimensional electron gas systems in metal-organic vapor-phase epitaxy grown AlGaN/AlN/GaN heterostructures

We studied the persistent photoconductivity (PPC) effect in AlGaN/AlN/GaN heterostructures with two different Al-compositions (x=0.15 and x=0.25). The two-dimensional electron gas formed at the AlN/GaN heterointerface was characterized by Shubnikov-de Haas and Hall measurements. Using optical illumination, we were able to increase the carrier density of the Al0.15Ga0.85N/AlN/GaN sample from 1.6x10^{12} cm^{-2} to 5.9x1012 cm^{-2}, while the electron mobility was enhanced from 9540 cm2/Vs to 21400 cm2/Vs at T = 1.6 K. The persistent photocurrent in both samples exhibited a strong dependence on illumination wavelength, being highest close to the bandgap and decreasing at longer wavelengths. The PPC effect became fairly weak for illumination wavelengths longer than 530 nm and showed a more complex response with an initial negative photoconductivity in the infrared region of the spectrum (>700 nm). The maximum PPC-efficiency for 390 nm illumination was 0.011% and 0.005% for Al0.25Ga0.75N/AlN/GaN and Al0.15Ga0.85N/AlN/GaN samples, respectively. After illumination, the carrier density could be reduced by annealing the sample. Annealing characteristics of the PPC effect were studied in the 20-280 K temperature range. We found that annealing at 280 K was not sufficient for full recovery of the carrier density. In fact, the PPC effect occurs in these samples even at room temperature. Comparing the measurement results of two samples, the Al0.25Ga0.75N/AlN/GaN sample had a larger response to illumination and displayed a smaller recovery with thermal annealing. This result suggests that the energy scales of the defect configuration-coordinate diagrams for these samples are different, depending on their Al-composition.Comment: 27 pages, 8 figure

Quantum point contact transistor with high gain and charge sensitivity

We analyze the potential performance of quantum point contact (QPC) devices in charge detection applications. For the standard QPC structure we show that the charge sensitivity is strongly dependent on gate geometry and can be close to the quantum limit, and that the gain parameter is less than one under bias conditions where the charge sensitivity is optimized. We propose a novel QPC device consisting of two split gates for defining the QPC and a third gate which can be used to filter out hot electrons that are emitted from the QPC. We show that this proposed device can have a high gain and a charge sensitivity close to that of single electron transistors. The device can be realized using high quality GaAs/AlGaAs with a two-dimensional electron gas and standard nanofabrication techniques. Unlike single electron transistors, the gain of the proposed device does not depend on the charge configuration near the active region of the device. Therefore the device can be used as an electrometer without a feedback charged locked loop and multiple devices can easily be integrated. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69765/2/JAPIAU-89-6-3453-1.pd

Energy relaxation probed by weak antilocalization measurements in GaN heterostructures

Energy relaxation and electron-phonon (e-p) interaction are investigated in wurtzite Al0.15Ga0.85N/AlN/GaN and Al0.83In0.17N/AlN/GaN heterostructures with polarization induced two-dimensional electron gases in the Bloch–Grüneisen regime. Weak antilocalization (WAL) and Shubnikov–de Haas measurements were performed on gated Hall bar structures at temperatures down to 0.3 K. We used WAL as a thermometer to measure the electron temperature Te as a function of the dc bias current. We found that the power dissipated per electron, Pe, was proportional to T4e due to piezoelectric acoustic phonon emission by hot electrons. We calculated Pe as a function of Te without any adjustable parameters for both the static and the dynamic screening cases of piezoelectric e-p coupling. In the temperature range of this experiment, the static screening case was expected to be applicable; however, our data was in better agreement with the dynamic screening case