Date of Graduation

12-2014

Document Type

Thesis

Degree Name

Master of Science in Microelectronics-Photonics (MS)

Degree Level

Graduate

Department

Graduate School

Advisor

Alan Mantooth

Committee Member

Gregory Salamo

Second Committee Member

Simon Ang

Third Committee Member

Ken Vickers

Keywords

GaAs, Gallium Nitride, GaN, Hall Effect, Hall Effect Sensor, HEMT

Abstract

In this work, micro-Hall devices were developed for the purpose of sensing current within a high temperature and high power environment. GaAs HEMT, InGaAs pHEMT, and GaN HEMT structures were studied. These structures were grown by molecular beam epitaxy. Processing techniques including photolithography, metallization, Si deposition, wet etching, and dry etching were studied. Electrical characterization measurements including low frequency noise, Hall effect, sensitivity, capacitance-voltage, and current-voltage were performed.

Electron mobility and sheet carrier density studies were performed for both the InGaAs pHEMT and GaAs HEMT structures. Results indicated the InGaAs pHEMT was superior and thus fabricated as the micro-Hall device. The Hall mobilities for the InGaAs QW micro-Hall device were found to be 67,300 cm2/Vs and 7,980 cm2/Vs at 80 K and 290 K respectively. The sheet density was found to be 5.3×1011 cm-2 and 4.2×1011 cm-2 at 80 K and 290 K, respectively. Deep level noise spectroscopy was performed and two active electron traps that degrade the magnetic field detection limit were discovered. The minimum detectable magnetic field of 2.5×10-9 T at 80 K and 100 kHz was recorded. A mobility decrease and an increase in carrier density were found at temperatures above 500 K, further contributing to the degradation in device performance. The Hall mobility and sheet density recorded for this device at 550 K was 1160 cm2/Vs and 4.2×1012 cm-2.

Due to the wide band gap and high peak electron drift velocity, GaN/AlGaN HEMT structures were studied as an alternative material system to the GaAs/InGaAs/AlGaAs QW structures. The GaN/AlGaN material system was optimized with respect to high electron mobility and low electron density. It was found that buffer layer thickness, AlGaN barrier thickness, and Al composition in the AlGaN layer had dramatic effects on mobility and electron sheet carrier density. Based on these findings, the GaN/Al0.21Ga0.79N/GaN structure was found most appropriate for the fabrication of the micro-Hall effect device. For this structure, Hall mobilities of 15,300 cm2/Vs and 1,400 cm2/Vs and sheet electron densities as high as 6 × 1012 cm-2 and 1.0 × 1013 cm-2 were measured at 8 K and 295 K, respectively.

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