High temperature thermoelectric properties of optimized InGaN

Abstract

The effects of carrier concentration, composition, and temperature on the thermoelectric properties of high quality n-type InGaN grown by metal organic chemical vapor deposition (MOCVD) were systematically investigated. The Seebeck coefficient was found to decrease and electrical conductivity increase with increasing carrier concentration, while both were found to decrease with increasing indium composition. Additionally, thermal conductivity was found to decrease by over an order of magnitude as indium composition was increased from 0 to 19%. These trends resulted in optimum carrier concentration and indium composition of 1.1×1019 cm−3 and 17%, respectively, with a room temperature ZT of 0.04. Increasing temperature resulted in a rapidly increasing ZT, reaching a maximum value of 0.34 at 875 K. This significantly improved ZT demonstrates the potential of InGaN and other III-Nitride materials for high temperature thermoelectric applications.

Calculated thermoelectric properties of InxGa1−xN, InxAl1−xN, and AlxGa1−xN

“…ZT increases with temperature and reaches 0.85 at 1200 K for In 0.1 Ga 0.9 N. Also shown are experimental data points for In 0.17 Ga 0.83 N at a carrier density of 1.1 Â 10 19 cm À3 . 5 Seebeck coefficient and electrical conductivity are seen to match experimental values well while thermal conductivities at low temperatures are higher than experimental values, likely for the same reasons described above. Good thermal conductivity agreement is obtained at moderate to high temperatures as the relative importance of Umklapp scattering increases.…”

“…Figure 2 shows the Seebeck coefficient, electrical conductivity, thermal conductivity, and ZT calculated for In 0.1 Ga 0.9 N at 300 K, 600 K, and 900 K versus carrier density. Also shown are literature experimental data points for In 0.09 Ga 0.91 N at 300 K. 5 The Seebeck coefficient decreases and electrical conductivity increases with increasing carrier concentration while thermal conductivity remains relatively constant. An optimum carrier density at which ZT is maximized exists for each temperature and increases from 1 Â 10 19 cm À3 at 300 K to 3 Â 10 19 cm À3 at 900 K. These results are all in excellent agreement with available experimental data, providing an important validation for the calculations presented in this work.…”

“…5,20 Seebeck coefficient, electrical conductivity, and thermal conductivity are all seen to decrease near the center of the composition range. The electrical and thermal conductivities are reduced due to the additional alloy atoms scattering electrons and phonons at compositions away from the binary endpoints.…”

“…Additionally, GaN is non-toxic, an important consideration for distributed applications such as automobile waste heat recovery. 8 The potential of III-nitride materials for thermoelectric applications has motivated increasing research on the experimental properties of GaN, 9,10 InGaN, 3,5,11,12 InAlN, [13][14][15] and AlInGaN 16,17 as well as III-nitride based thermoelectric devices. 18 There have also been a few attempts to calculate and predict the properties of these materials, most notably the thermoelectric properties of GaN, 4 AlGaN, 4,19 and InGaN.…”

“…1,2 In addition to these applications, their potential suitability as a high temperature thermoelectric material has been suggested by a number of authors. [3][4][5] Thermoelectrics are capable of converting heat into electricity and have recently received significant attention for waste heat recovery applications. 6,7 The major limiting factors in their commercial deployment are high cost and relatively low efficiency.…”