A. Sigurdardottir

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.

A comparative study of uniaxial pressure effects in intraband AlGaAs/GaAs and interband InAs/AlSb/GaSb resonant tunneling diodes

We report on the effects of uniaxial pressure on (001)-oriented AlGaAs/GaAs and InAs/AlSb/GaSb double barrier resonant tunneling diodes (RTDs). The current–voltage characteristics of the AlGaAs/GaAs RTDs shift asymmetrically due to stress-induced piezoelectric fields in the barriers and well structures. Although all the materials involved are piezoelectric, the interband InAs/AlSb/GaSb resonant tunneling device surprisingly shows, in contrast to the AlGaAs/GaAs one, a symmetrical behavior for the same orientation [110] of the applied pressure. We explain the observed differences considering the different tunneling paths involved in the conduction mechanism of the two heterostructure device types as well as their pressure dependencies.

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.

Interface tuning of the InAs/AlSb heterostructure-based quantum wells

This work shows the importance of interface consideration at the barrier sides for quantum well (QW)-based semiconductor structures, on the example of the InAs/AlSb heterostructure. Various interface combinations of AlAs and InSb type have been included in an InAs/AlSb double-barrier resonant-tunneling-diode structure, and the resulting transmission functions have been calculated. A systematic comparison of the resulting structures with each other and also with the traditional case without interface consideration have been made. Clear tendencies and relationships observed in the transmission characteristics of the different structures let the interface tuning emerge as a quality tool for QW-device tayloring.

Comparative investigation of interface effect on transmission function of electrons and holes in InAs/AlSb-based heterostructures

The influence of interface types in InAs/AlSb based heterostructures are considered for both electrons and holes. First calculations based on the transfer matrix method and including AlAs, InSb interface types or some of their combinations show the existence of more quantized energy hole levels than can be expected in the case when no interface effects are considered. The consideration is simplified by assuming the interfaces as individual intermediate layers formed between the InAs–quantum well and AlSb barriers. While for electrons such an intermediate layer of AlAs modifies the designed barriers or quantum wells of the heterostructure, it creates narrow barriers for holes leading to the appearance of a miniband type of energy levels.