Alexander Vogt

Porosity-induced modification of the phonon spectrum of n-GaAs

Porous GaAs layers have been produced by anodic etching of (100)-oriented crystalline substrates in a solution. Scanning electron microscope images showed the formation of submicron pores, the average dimension of the remaining GaAs walls being of about 100 nm. Raman scattering by LO-phonon - plasmon coupled modes, inherent in as-grown crystals, was not observed in the porous layers. Proposed explanations are either the depletion of the GaAs skeleton due to the surface space-charge effect or the decoupling of the LO-phonon and the plasmon modes at the relative large wavevectors transferred in nanostructures. A new Raman scattering peak at , located between the bulk TO and LO frequencies, has been observed in porous layers and attributed to a surface-related phonon.

Ohmic contact formation mechanism of the PdGeAu system on n-type GaSb grown by molecular beam epitaxy

We have fabricated Pd/Ge/Au/Pt/Au ohmic contacts on n-type GaSb grown by molecular beam epitaxy. The annealed contacts show specific contact resistivities which are as low as 4.9×10−6 Ω−cm2 at an annealing temperature of 300 °C for 45 s. The resistivity is very sensitive to the annealing conditions and the thickness of the constituents. The surface remains smooth after annealing. Microstructure analysis with cross-sectional transmission electron microscopy and sputtered neutral mass spectrometry elucidates the solid phase reactions and interdiffusion of the constituents. The formation of a PdGe phase and the diffusion of Ge into GaSb seem to be the decisive and annealing-dependent processes leading to the ohmic behavior.

III–V Compound semiconductor micromachined actuators for long resonator tunable fabry-pérot detectors

Abstract Modern telecommunication demands tunable detectors that are needed for optical demultiplexing of fibre-transmitted data. The receiver therefore consists of a wavelength-selective detector sensitive around 1550 nm. Since detectors for this wavelength are typically fabricated on gallium arsenide (GaAs) or indium phosphide (InP), a monolithic integration with the filter provides additional functionality and reduces coupling problems. This article presents a long-resonator Fabry-Perot filter that has been fabricated by bulk micromachining and can be tuned by deflection of one or both of the Bragg mirrors that are realized as floating membranes. Thermal actuation of the membrane yields mechanical sensitivities up to 153 nm mW −1 under vacuum conditions and 13 nm mW −1 under normal pressure. This is high enough to tune the free spectral range with less than 5 mW.

Non-annealed ohmic contacts to p-GaSb grown by molecular beam epitaxy

Abstract We fabricated Ti/Au, Pt/Au, Pd/Au, Ni/Au, and Au non-annealed ohmic contacts on p-type GaSb grown by molecular beam epitaxy. The specific contact resistivities were as low as 2.6×10 −7 Ω cm 2 for the as-deposited contact. Annealing was performed up to 250°C to see whether the heat treatment improves the contact. Thermal stability experiments were undertaken for the Pt/Au and the Au contact. Microstructure analysis of some metal–GaSb interfaces by cross-sectional transmission electron microscopy elucidates diffusion processes taking place at room temperature.

Microstructure analysis of ohmic contacts on MBE grown n-GaSb and investigation of sub-micron contacts

We investigated the thermally induced solid state interdiffusion of Au Ge Pd and Ge Pd ohmic contacts on MBE grown n-GaSb. Furthermore, the electrical behavior of these contacts for different contact sizes down to 540 nm in diameter was compared. A specific contact resistivity as low as 4.9 × 10 6 Ωcm 2 was measured for the Au/Ge/Pd metallization. After annealing, polycrystalline AuSb 2 was observed by grazing incident X-ray diffraction (GIXD). Compared to Ge/Pd metallizations a gold top layer reduces the specific contact resistivity. The atomic structure or microstructure of the Au/Ge/Pd metallization showed a significant reduction of the thickness of amorphous Ge and led to a more spiky interface, which was observed by cross-sectional transmission clectron microscopy (TEM). Furthermore, an epitaxial regrowth of GaSb occurs, which is estimated to lead to a n - GaSb layer. The atomic microstructure has a significant effect on the current voltage (I V) characteristic up to a contact size of 950 nm in diameter, which shows a wide spread from ohmic to a more Schottky like behavior.

A GaAs pressure sensor with frequency output based on resonant tunneling diodes

We present a novel bulk semiconductor pressure sensor based on an Al/sub x/Ga/sub 1-x/As/GaAs resonant tunneling diode (RTD) with a frequency output. A relaxation oscillator is obtained with the RTD biased in the negative differential resistance (NDR) region. Pressure applied to the RTD changes the frequency of oscillation due to the shift in current-voltage characteristics. Frequency measurements have been performed on [001]-oriented RTDs with [110]-compressive uniaxial pressure. Sensitivities of up to 0.8 kHz/MPa at 113 kHz have been measured. The main feature of this sensor type is the direct frequency output obtained by using only a maximum of three components including the RTD. Using a simplified differential equation of the oscillator circuit, the pressure-dependent effects of the RTD current-voltage characteristics on the sensor output have been investigated.

Tunnelling spectroscopy of AlAs and InSb interfaces in InAs/AlSb heterostructures

MBE grown InAs/AlSb heterostructures with AlAs- and InSb-type interfaces were investigated by tunnelling spectroscopy using a scanning tunnelling microscope (STM). STM surface topography revealed a different electronic surface morphology of the thin InAs/AlSb heterostructure in the case of AlAs and InSb interfaces. Scanning tunnelling spectroscopy (STS) gives an understanding of the origin of local morphology fluctuations. STS suggests the occurrence of classical and quantum effects influencing the energy-band-structure formation in the case of these thin heterostructures.

Peculiarities of the Scanning Tunneling Microscopy Probe on Porous Gallium Phosphide

We consider scanning tunneling microscopy (STM) probe on porous GaP. Among STM effects causing image distortions, we distinguish tip effects and analyze tip shape effect, lateral effect and tip bending. We estimate maximum errors induced by these effects and perform image processing and analysis. Vital measures necessary for the STM probe on the porous matter are proposed.

Microwave noise measurements on /GaAs channels grown by molecular beam epitaxy using and

We present microwave noise measurements performed on different high electron mobility transistor channels under both darkness and illumination. Two structures of /GaAs layers have been grown with beams of and using molecular beam epitaxy. The measured room temperature, Hall mobilities and sheet carrier densities have demonstrated in both cases a good dc performance of the channels. However, the measurement of the noise temperature at 1.5 GHz has shown the sample grown with to be considerably noisier than the one grown with .