Noise in gallium nitride-based quantum well structures used for nanometer devices in the frequency range 1 HZ-3 MHZ and temperature range 77K - 324K

Document Type



Doctor of Philosophy (PhD)


Electrical Engineering

First Advisor's Name

Carolyne M Van Vliet

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Jean Andrian

Third Advisor's Name

Pierre Schmidt

Fourth Advisor's Name

Grover L. Larkins, Jr.

Date of Defense



Electronic noise has been investigated in AlxGa1-xN/GaN Modulation-Doped Field Effect Transistors (MODFETs) of submicron dimensions, grown for us by MBE (Molecular Beam Epitaxy) techniques at Virginia Commonwealth University by Dr H. Morkoç and coworkers. Some 20 devices were grown on a GaN substrate, four of which have leads bonded to source (S), drain (D), and gate (G) pads, respectively. Conduction takes place in the quasi-2D layer of the junction (xy plane) which is perpendicular to the quantum well (z-direction) of average triangular width ~3 nm. A non-doped intrinsic buffer layer of -5 nm separates the Si-doped donors in the AlxGa1-xN layer from the 2D-transistor plane, which affords a very high electron mobility, thus enabling high-speed devices. Since all contacts (S, D, and G) must reach through the AlxGa1-xN layer to connect internally to the 2D plane, parallel conduction through this layer is a feature of all modulation-doped devices. While the shunting effect may account for no more than a few percent of the current IDS, it is responsible for most excess noise, over and above thermal noise of the device.

The excess noise has been analyzed as a sum of Lorentzian spectra and 1/ƒ noise. The Lorentzian noise has been ascribed to trapping of the carriers in the AlxGa1-xN layer. A detailed, multitrapping generation-recombination noise theory is presented, which shows that an exponential relationship exists for the time constants obtained from the spectral components as a function of 1/kT. The trap depths have been obtained from Arrhenius plots of log (τT2) vs. 1000/T Comparison with previous noise results for GaAs devices shows that: a) many more trapping levels are present in these nitride-based devices; b) the traps are deeper (farther below the conduction band) than for GaAs Furthermore, the magnitude of the noise is strongly dependent on the level of depletion of the AlxGa1-xN donor layer, which can be altered by a negative or positive gate bias VGS.

Altogether, these frontier nitride-based devices are promising for bluish light optoelectronic devices and lasers; however, the noise, though well understood, indicates that the purity of the constituent layers should be greatly improved for future technological applications.



This document is currently not available here.



Rights Statement

Rights Statement

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).