Wide range temperature-dependent (80–630 K) study of Hall effect and the Seebeck coefficient of β -Ga2O3 single crystals

Abstract

Investigation of Seebeck coefficient in ultra-wide bandgap materials presents a challenge in measurement, nevertheless, it is essential for understanding fundamental transport mechanisms involved in electrical and thermal conduction. β-Ga2O3 is a strategic material for high power optoelectronic applications. Present work reports Seebeck coefficient measurement for single crystal Sn doped β-Ga2O3 in a wide temperature range (80-630 K). The non-monotonic trend with large magnitude and negative sign in the entire temperature range shows electrons are dominant carriers. The structural and Raman characterization confirms the single-phase and presence of low, mid, and high-frequency phonon modes, respectively. Temperature dependent (90-350 K) Hall effect measurement was carried out as supplementary study. Hall mobility showed µ T 1.12 for T<135 K and µ T −0.70 for T>220 K. Activation energies from Seebeck coefficient and conductivity analysis revealed presence of inter band conduction due to impurity defects. The room temperature Seebeck coefficient, power factor and thermal conductivity were found as 68.57 ±1.27 µV/K, 0.15 ±0.04 µW/K 2 cm and 14.2 ± 0.6 W/mK, respectively. The value of the figureof-merit for β-Ga2O3 was found to be ~ 0.01 (300 K).

β-Ga2O3: a potential high-temperature thermoelectric material

“…It is worthy to note that the increasing rate of ZT also and mobility of 90 cm 2 V À1 s À1 . 45 By using this carrier mobility and carrier concentration, our calculation gives a ZT value of 0.007 at 300 K, which is in good agreement with the results of Kumar et al This further confirms the reliability of our calculations, and a high carrier mobility and optimal carrier concentration are both necessary to achieve good thermoelectric performance. Based on the above results and discussion, it can be concluded that an elaborate tailoring of the electrical transport properties of b-Ga 2 O 3 to attain the optimal carrier concentration is the first and the most important step for high thermoelectric performance.…”

“…The room temperature mobility is 101 cm 2 V À1 s À1 . According to the study of the b-Ga 2 O 3 single crystal by Kumar et al, 45 the relationship between mobility and temperature is m e p T À0.70 when the temperature is higher than 220 K. 45 By fitting the calculated results, we get the relationship of electron mobility with temperature as m e p T À0. 67 , which shows an excellent agreement with the experimental results.…”

“…67 , which shows an excellent agreement with the experimental results. 45 It should be pointed out that some extended defects may be generated at high temperatures, which will reduce the electron mobility. However, the experimental value of the carrier mobility at room temperature in b-Ga 2 O 3 has a wide range between 90 and 300 cm 2 V À1 s À1 according to the reported data.…”

“…However, the experimental value of the carrier mobility at room temperature in b-Ga 2 O 3 has a wide range between 90 and 300 cm 2 V À1 s À1 according to the reported data. 34,45,[52][53][54] For a more comprehensive evaluation of the thermoelectric performance of b-Ga 2 O 3 , three typical mobility values at room temperature were also used in the present work, which are 90 cm 2 V À1 s À1 reported by Kumar, 45 184 cm 2 V À1 s À1 by Feng 34 and 300 cm 2 V À1 s À1 by Sasaki, 54 respectively. Wherein, the electron mobility of b-Ga 2 O 3 at different temperatures was obtained by applying the relationship between mobility and temperature m e p T À0.70 .…”

“…Wherein, the electron mobility of b-Ga 2 O 3 at different temperatures was obtained by applying the relationship between mobility and temperature m e p T À0.70 . 45 After getting electron mobilities of b-Ga 2 O 3 , the electrical conductivity along the [100] direction is shown in Fig. 5.…”