The magneto resistance of a narrow single quantum well is spectacularly different from the usual behavior. At filling factors 2 3 and 3 5 we observe large and sharp maxima in the longitudinal resistance instead of the expected minima. The peak value of the resistance exceeds those of the surrounding magnetic field regions by a factor of up to three. The formation of the maxima takes place on very large time scales which suggests a close relation with nuclear spins. We discuss the properties of the observed maxima due to a formation of domains of different electronic states.

Two dimensional electron gases in narrow GaAs quantum wells show huge longitudinal resistance (HLR) values at certain fractional filling factors. Applying an RF field with frequencies corresponding to the nuclear spin splittings of 69 Ga, 71 Ga and 75 As leads to a substantial decreases of the HLR establishing a novel type of resistively detected NMR. These resonances are split into four sub lines each. Neither the number of sub lines nor the size of the splitting can be explained by established interaction mechanisms.Two-dimensional electron gases (2DEGs) with very high mobilities of the electrons can be formed in quantum wells and heterostructures based on the GaAs/Al x Ga 1−x As system. If such a 2DEG is subjected to an intense perpendicular magnetic field at very low temperatures, it shows the integer [1] and the fractional [2] quantum Hall effects at integer and fractional filling factors of one or more Landau levels. The signature of both types of quantum Hall effects is the quantization of the Hall resistance and the vanishing of the longitudinal resistance. Recently, however, huge longitudinal resistance maxima (HLR) have been observed at fractional filling factors between 1 2 and 1 [3]. The HLR is only found in samples which have a reduced well thickness (15 nm, [4]) as compared to the conventional ones. As an example, figure 1 shows longitudinal resistance measurements on a sample similar to the one used in [3] for two different carrier densities (dotted and dashed line) at a temperature of 0.35 K. Here, the magnetic field is swept at a rate of 0.7 T/min and the applied source drain current is 100 nA. The width of the sample is 80 µm and the voltage probes are 80 µm apart. For both carrier densities a very regular behavior is seen. At integer filling factors the resistance vanishes completely and at filling factor ν = 2 3 one finds a clear minimum. However, if the sweep rate of the magnetic field is drastically reduced to 0.002 T/min, a huge maximum in the longitudinal resistance (solid lines) is observed at ν = 2 3 for both carrier densities. The size of the HLR is maximal at a current density of approximately 0.6 mA/m. The HLR vanishes in tilted magnetic fields, indicating that the electron spin polarization plays an important role for the HLR. Similar maxima are also reported at other fractional filling factors [3], but in this paper we want to concentrate on the HLR at ν = 2 3 at 0.35K. The HLR develops with a time constant of about 15 min. These very long times are typical for relaxation effects of the nuclear spin system [5,6]. The only direct way to demonstrate an involvement of the nuclear spins in the HLR is a nuclear magnetic resonance (NMR) [7][8][9][10] experiment, because it allows direct modification of the nuclear polarization. In this Letter we report on experiments where radio frequency is irradiated on a sample in the HLR state and a drastic reduction of the resistance values is observed whenever the nuclei are in resonance. This is to our knowledge the clearest form of a resistively ...

Thick poly-SiGe layers, deposited by plasma-enhanced chemical vapor deposition (PECVD), are very promising structural layers for use in microaccelerometers, microgyroscopes or for thin-film encapsulation, especially for applications where the thermal budget is limited. In this work it is shown for the first time that these layers are an attractive alternative to low-pressure CVD (LPCVD) poly-Si or poly-SiGe because of their high growth rate (100-200 nm/min) and low deposition temperature (520 C-590 C). The combination of both of these features is impossible to achieve with either LPCVD SiGe (2-30 nm/min growth rate) or LPCVD poly-Si (annealing temperature higher than 900 C to achieve structural layer having low tensile stress). Additional advantages are that no nucleation layer is needed (deposition directly on SiO 2 is possible) and that the as-deposited layers are polycrystalline. No stress or dopant activation anneal of the structural layer is needed since in situ phosphorus doping gives an as-deposited tensile stress down to 20 MPa, and a resistivity of 10 m-cm to 30 m-cm. With in situ boron doping, resistivities down to 0.6 m-cm are possible. The use of these films as an encapsulation layer above an accelerometer is shown.[958]

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This paper describes a monolithically integrated ω z -gyroscope fabricated in a surface-micromaching technology. As functional structure, a 10 µm thick Silicon-Germanium layer is processed above a standard high voltage 0.35 µm CMOS-ASIC. Drive and Sense of the in plane double wing gyroscope is fully capacitively. Measurement of movement is also done fully capacitively in continuous-time baseband sensing. For characterization, the gyroscope chip is mounted on a breadboard with auxiliary circuits. A noise floor of 0.01 °/s/sqrt(Hz) for operation at 3 mBar is achieved.