Date of Graduation

12-2020

Document Type

Thesis

Degree Name

Master of Science in Microelectronics-Photonics (MS)

Degree Level

Graduate

Department

Microelectronics-Photonics

Advisor/Mentor

Ware, Morgan E.

Committee Member

Chen, Zhong

Second Committee Member

Sides, Cynthia

Third Committee Member

Wise, Rick L.

Keywords

Graded InGaN; Ohmic contact; Specific contact resistance

Abstract

There is an increasing demand for high-power electronic components and optoelectronic devices with low-loss and high efficiency. III-nitride semiconductor materials have demonstrated great potential for high-power, high-frequency, and high-temperature applications because of their remarkable and wide-ranging electronic and physical properties. These material systems, including alloys of AlN, GaN, and InN, are currently being explored for their potential to develop efficient photovoltaic cells. They can potentially achieve higher efficiency because of their very high direct wide band edge, absorption coefficients, and resistance to defects. The compositionally graded Group III-nitride alloy allows access to a large range of energies by varying the bandgap. In a unique way, this change in bandgap can be achieved by grading the indium composition during growth. These graded composition alloys do not yet have well-characterized metal contact materials, so the focus here is studying low-resistance ohmic contacts on graded layers of InGaN grown on semi-insulating GaN by the use of the transmission line method. Carrier concentration and mobility are subsequently characterized in the graded films by temperature-dependent Hall-effect measurements.

The samples were grown by molecular beam epitaxy with different indium compositions at 21.5% and 28%. The growth of these samples was characterized by atomic force microscopy, x-ray diffraction, and photoluminescence. Ni/Au and Cr/Au metal contacts were deposited on InGaN semiconductor materials through electron-beam evaporation. After room temperature characterization, the samples were progressively annealed to 200 oC, 300 oC, 400 oC, and 500 oC, to study the formation and evolution of ohmic contacts. This was done by use of the transmission line method resulting in the characterization of the contact resistance, transfer length, and sheet resistance of the metal to compositionally graded film contacts. This work demonstrates that the Cr/Au contact layer has lower specific contact resistivity than Ni/Au on the n-type InGaN graded materials, for both indium concentrations.

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