Dislocation scattering in a two-dimensional electron gas

A theory of scattering by charged dislocation lines in a two-dimensional electron gas (2DEG) is developed. The theory is directed towards understanding transport in AlGaN/GaN high-electron-mobility transistors (HEMT), which have a large number of line dislocations piercing through the 2DEG. The scattering time due to dislocations is derived for a 2DEG in closed form. This work identifies dislocation scattering as a mobility-limiting scattering mechanism in 2DEGs with high dislocation densities. The insensitivity of the 2DEG (as compared to bulk) to dislocation scattering is explained by the theory.Comment: 6 pages, 3 figure

Current–voltage characteristics of polar heterostructure junctions

We report calculations that show that a metal–polar semiconductor heterostructure can exhibit highly controllable nonlinear current–voltage characteristics. A change in barrier thickness can alter the characteristics from Schottky-like to ohmic in different bias regimes. The origin of these unusual effects is a large electric field (>106 V/cm)(>106 V/cm) and high sheet charge(∼1013–1014cm−2)(∼1013–1014cm−2) without doping, in the polar heterostructure. Theoretical calculation of the tunneling current density in these systems is done in this work. The results indicate that very interesting nonlinear behavior is shown by these systems, even in the undoped case. The choice of suitable compositions of the materials and thicknesses can be used to tailor devices with desired characteristics. © 2002 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71184/2/JAPIAU-91-5-2989-1.pd

Fabrication of single or multiple gate field plates

A process for fabricating single or multiple gate field plates using consecutive steps of dielectric material deposition/growth, dielectric material etch and metal evaporation on the surface of a field effect transistors. This fabrication process permits a tight control on the field plate operation since dielectric material deposition/growth is typically a well controllable process. Moreover, the dielectric material deposited on the device surface does not need to be removed from the device intrinsic regions: this essentially enables the realization of field-plated devices without the need of low-damage dielectric material dry/wet etches. Using multiple gate field plates also reduces gate resistance by multiple connections, thus improving performances of large periphery and/or sub-micron gate devices

Fabrication of single or multiple gate field plates

"This invention relates to semiconductor devices, and more particularly, to the fabrication of single or multiple gate field plates.

Examination of tunnel junctions in the AlGaN/GaN system: Consequences of polarization charge

A strong piezoelectric effect and a large spontaneous polarization allow one to incorporate a large electric field (>106 V/cm)(>106V/cm) and high sheet charge (>1013 cm−2)(>1013cm−2) without doping in the AlGaN/GaN heterostructure. Theoretical studies are done to examine how polarization effects can be exploited to design metal–AlGaN/GaN tunnel junctions. We find that with a proper choice of AlGaN thickness undoped junctions can be made with very high metal to two-dimensional electron gas tunneling. Thus, a Schottky junction can be converted to a tunnel junction without doping. The tunneling probabilities approach those produced in a system doped at ∼ 4×1019 cm−3.∼4×1019cm−3. This work suggests that very interesting tunnel junctions can be made from undoped AlGaN/GaN heterostructures. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70932/2/APPLAB-77-12-1867-1.pd

Study of charge control and gate tunneling in a ferroelectric-oxide-silicon field effect transistor: Comparison with a conventional metal-oxide-silicon structure

It is known that conventional metal-oxide-silicon (MOS) devices will have gate tunneling related problems at very thin oxide thicknesses. Various high-dielectric-constant materials are being examined to suppress the gate currents. In this article we present theoretical results of a charge control and gate tunneling model for a ferroelectric-oxide-silicon field effect transistor and compare them to results for a conventional MOS device. The potential of high polarization charge to induce inversion without doping and high dielectric constant to suppress tunneling current is explored. The model is based on a self-consistent solution of the quantum problem and includes the ferroelectric hysteresis response self-consistently. We show that the polarization charge associated with ferroelectrics can allow greater controllability of the inversion layer charge density. Also the high dielectric constant of ferroelectrics results in greatly suppressed gate current. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71117/2/JAPIAU-89-3-1856-1.pd