E.-H. Chen

Behavior of a new ordered structural dopant source in InAs/(001) GaP heterostructures

We report the characteristics of molecular-beam epitaxy grown InAs on highly lattice mismatched (001) GaP substrates. Strain relaxation in this system occurs at low thickness by the generation of a periodic two-dimensional square grid network of 90° misfit dislocations at the heterointerface. The very high interface dislocation density (∼1013 intersections/cm2) exerts a unique influence on the electronic properties of the system. An extended defect structure at the intersection of 90° misfit dislocations is proposed to act as an ordered structural donor source. Hall effect measurements indicate that this source is fully ionized with a constant sheet carrier concentration of 1013u2002cm−2, irrespective of the InAs layer thickness, and exhibits no freeze out at low temperatures. We have also demonstrated that the electron mobility increases significantly with InAs layer thickness, reaching values in excess of 10u2009000 cm2/Vu2009s in nominally undoped layers. The high threading dislocation density (∼1010u2002cm−2) in the ...

Temperature-dependent transport properties of InAs films grown on lattice-mismatched GaP

Hall effect and electrical resistivity measurements were carried out on undoped InAs thin films grown by molecular-beam epitaxy directly on (001)u200aGaP substrates. The large lattice mismatch between these two compounds results in a high density array of misfit dislocations at the heterointerface and threading dislocations in the InAs epilayer. The threading dislocation density varies with epilayer thickness, with the largest proportion being present near the heterointerface. This leads to variation of both the carrier concentration and electron mobility with thickness. Consequently, a multilayer analysis was used to interpret the transport data. This analysis yields a temperature-independent carrier concentration, which indicates degenerate donor levels in this narrow band-gap material. Room temperature mobilities in excess of 10u200a000 cm2/Vu200as were obtained for thick InAs layers despite dislocation densities of 1010u200acm−2. The relative insensitivity of the mobility to temperature suggests that temperature-inde...

Growth temperature dependence of transport properties of InAs epilayers grown on GaP

Undoped InAs was grown by molecular-beam epitaxy directly on GaP at a set of different substrate temperatures. Transport properties were characterized by means of Hall-effect and resistivity measurements at temperatures between 3 and 300 K. It was observed that samples grown at higher temperatures had lower carrier concentrations, consistent with a decrease of ionized defects. In addition, samples grown at higher temperatures also had higher mobility, consistent with a smaller number of scattering centers. Samples grown at higher temperatures also showed much higher sensitivity of the mobility to the measurement temperature, suggesting a drop in neutral scattering defects. Transmission electron microscopy showed that the samples grown at higher temperatures had a significantly different dislocation microstructure. The observed dislocation microstructure is consistent with the mechanisms proposed for the influence of growth temperature on the variation of carrier concentration and mobility.

Correlation of defect profiles with carrier profiles of InAs epilayers on GaP

The carrier profile for InAs films grown on GaP is modeled as a first-order approximation which assumes that 90° edge dislocation intersections and the threading dislocation intersections act as shallow donors. Due to dislocation annihilation during growth, the threading dislocation intersection density decreases as the inverse of the distance x from the InAs/GaP interface, D(x)=D0x0/(x0+x), where D0 and x0 are dislocation density at the InAs/GaP interface and the first annihilation position from the interface, respectively. The carrier profile in InAs films can be described by a similar equation that is deduced from the threading dislocation intersection profile. The calculated carrier profiles agree well with measured carrier profiles. This correlation supports our hypothesis that both the edge dislocation intersections and the threading dislocation intersections act as shallow donor sources.

Reliable contacts to two-dimensional conduction layers

For many experiments and device applications, electrical contacts to a two-dimensional conduction layer must remain reliable under repeated temperature cycling between 300 and 77 K or lower. This work introduces the use of a silicon-doped InAs contact to the AlGaAs/GaAs two-dimensional electron gas which demonstrates exceptional reliability under such temperature cycling. The noise spectrum of AlGaAs/GaAs contacted with silicon-doped InAs shows almost no dependence on bias current; this fact can be used to improve the performance of device applications such as Hall sensors. In addition, this work introduces an alternative two-dimensional conduction structure, highly mismatched InAs/GaP. InAs/GaP contacted with Ti/Au shows reliability equal to AlGaAs/GaAs contacted with silicon-doped InAs. The InAs/GaP material may be more desirable for some applications because of the lower temperature dependence of its electronic properties and potentially easier integration with silicon-based microelectronics.

Self-assembly based approaches for metal/molecule/semiconductor nanoelectronic circuits

This paper describes a technological approach which combines the nanoscale elements available from molecular devices and self-assembled molecular/nanoparticle systems with semiconductor devices which can provide the gain or bistability required for computational functionality. The architectural motivation for these configurations and experimental demonstrations of several key technologies for this hybrid approach are described.

A nanoscale ohmic contact for nanoelectronic devices

In this presentation, we report the development and characterization of low-resistance nanometer scale ohmic contacts which provide suitable characteristics for application in nanoelectronic semiconductor devices. The nanocontact structure employs a heterostructure comparable to that used in previous large-area studies of a low resistance, non-alloyed ohmic contact, namely a thin (2-10 nm) cap layer of low-temperature grown GaAs (LTG:GaAs) on a heavily doped n-type GaAs layer.