Dissertation/Thesis Abstract

Device Engineering of AlGaN/GaN HEMTs for Applications in Power-Electronic and Sensing
by Mahaboob, Isra, Ph.D., State University of New York at Albany, 2019, 265; 13885888
Abstract (Summary)

The research work presented in this Ph.D. thesis focuses on the engineering of AlGaN/GaN high electron mobility transistors (HEMTs) for the development of future device technology in power electronic and sensing applications.

For the development of HEMT based stretchable electronic platform for power electronic and sensing applications, the impact of stretchable geometry wavy patterns on the electrical performance of HEMTs was investigated. In the typical [0001] growth direction for (Al)GaN, the matrix is invariant upon rotation about the [0001] direction. Due to this in-plane rotational symmetry, similar electrical behavior was observed between stretchable and conventional geometry HEMTs. Potential of selective area epitaxy (SAE) technique for the development of low-stress stretchable geometry HEMTs was demonstrated in the current work. The dependence of Al incorporation in the AlGaN barrier, lateral/sidewall growth profile and electrical properties of SAE heterostructures on Al/Ga source ratio and mask material was investigated. Higher Al incorporation along with improvement in heterointerface quality in the SAE layers with an increase in Al to Ga ratio was observed. AlGaN composition, crystal quality and electrical properties of SAE AlGaN/GaN microstructures were shown to be affected by the choice of mask material. Further, the effect of dielectric (SiO2/SiNx) and metal (W) masks on impurity incorporation and electrical properties of SAE (Al)GaN microstructures was studied. It was shown that SAE growths under the conditions used result in highly conductive n-type material. Carrier concentrations greater than metal-nonmetal transition (MNM) level and low resistivity in the range of 0.18–0.29 mΩ-cm were observed from Hall measurements for these structures. Similar dopant and carrier concentrations were obtained from SIMS and Hall data, indicating low compensation from acceptors in the SAE growths. Our findings point towards the need for the development of stable mask materials to develop device quality SAE structures with controlled electrical properties.

AlGaN/GaN HEMTs have been extensively studied as potential candidates for bio-chemical sensing applications due to their highly sensitive detection of surface phenomena, fast response time, aqueous stability and bio-compatibility. Due to these unique chemical and electrical properties, they are well suited for development of sensor technology that can interface with living systems. To monitor reactive and transient biochemical molecules such as reactive oxygen species (ROS) in living systems, AlGaN/GaN HEMT sensor was used in the present work to detect hydrogen peroxide (H2O2) with boronate-based fluorescent probe receptor. The fluorescence from the boronate probe was a positive indicator to confirm the detection of H2O2. The real-time response of HEMT sensor to 25 μM and 12.5 μM of H2O2 was tested. The results showed that the response of the HEMT sensor matches well with the emission trend as the reaction proceeded overtime. These results demonstrate the potential of the use of AlGaN/GaN HEMT sensor for the real-time detection of reactive and transient species such as H2O2 in living cells.

For the application of AlGaN/GaN HEMTs in both power electronic and sensing systems, the complete potential is not fully utilized due to their normally-ON nature and the resultant design complexities in the rest of the system to accommodate this characteristic. In order to enhance the design capability of this device technology and to enable dynamic control of threshold voltage, the successful integration of body-diode based back-gate control in AlGaN/GaN HEMTs was demonstrated for the first time. In this configuration, p-GaN body-diode based back-gate control is used to shift the threshold voltage and dynamically modulate the ON/OFF characteristics of a normally-ON HEMT. A fourth (back-gate) terminal is connected to the p-GaN layer to control the depletion width of the body-diode, which in turn modulates the two-dimensional electron gas (2DEG) density. A positive/negative shift in the threshold voltage is measured by increasing/decreasing the depletion width below the channel. A positive back-gate bias application in the ON-state is shown to increase the 2DEG current density resulting in higher ON-current. The application of a negative back-gate bias is shown to be effective in the positive shift of the threshold voltage, in reducing the 2DEG channel current and in increasing the OFF-state break-down voltage. (Abstract shortened by Proquest.)

Indexing (document details)
Advisor: Shahedipour-Sandvik, Fatemeh
Commitee: Jones, Kenneth, Melendez, J Andres, Potyrailo, Radislav A., Tokranova, Natalya
School: State University of New York at Albany
Department: Nanoscale Science and Engineering-Nanoscale Engineering
School Location: United States -- New York
Source: DAI-B 80/11(E), Dissertation Abstracts International
Subjects: Nanotechnology, Materials science
Keywords: Body-diode, Device engineering, GaN, HEMTs, Power-electronics, Sensing
Publication Number: 13885888
ISBN: 978-1-392-28759-0
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