Dissertation Defense, Hua Tong

Title: Thermoelectric Characteristics and Measurements of Ternary III-Nitride Semiconductors

Date: Monday, August 16th, 2010

Time: 1:00 pm to 3:00pm

Location: Neville Hall 3 (NV003)

Abstract:

Significant attentions have been paid to thermoelectrics recently due to increased efficiency requirements for renewable power sources as well as for solid state cooling. The thermoelectric power generation can recycle energy from the surplus waste heats which account for more than 60% of all U.S. energy lost from power plants, industrial processes and vehicles. Solid state cooling can actively cool devices when they are becoming increasingly more important for high density integration and high power devices.

In this dissertation, the ternary III-Nitride semiconductors for thermoelectricity are investigated theoretically and experimentally. The scatterings of carriers and phonons are modeled to simulate the thermoelectric characteristics of III-Nitride alloys. The simulation gives good results in predicting the thermoelectric properties, such as the lattice and electronic thermal conductivity, electrical conductivity, Seebeck coefficients, the figure of merit (z*T), and the trend for various temperature, carrier concentration and alloy composition. The research works also include material growth using in-house metalorganic vapor phase epitaxy (MOVPE) system, device design and fabrication, and thermoelectric characterizations. To measure the thermal conductivity of InN and GaN epi-layer, a 2D multilayer thermal diffusion model was developed and extended slope technique of 3ω method is proposed for accurate data reduction. The measurements of Seebeck coefficient, electrical conductivity and thermal conductivity for thin film layer achieve the power factor and the thermoelectric figure of merit (z*T).

The proposed extended slope technique of 3ω method based on the 2D multilayer thermal diffusion model is in the most general configuration to extract the thermal conductivity of thin films. The thermal conductivity measurements of MOVPE-grown AlInN and pulsed-MOVPE grown InN alloys represent the first measurements of the single crystalline material reported in literature. The measurement of the thermoelectric figure of merits for AlInN alloy leads to the record high z*T value, which represents the best reported value for nitride-based material systems and the first identification of MOVPE-grown AlInN as excellent material for thermoelectric material system.

Committee Members:

Prof. Nelson Tansu (Ph.D. Advisor)

Prof. Yujie Ding

Prof. Alastair D. McAulay

Dr. Juan A. Herbsommer

Dr. Ronald A. Arif