Importance of barrier layers in thermal diodes for energy conversion

Abstract

Very high thermal to electric conversion efficiencies have been reported previously with thermal diode structures in which a thin n-type emitter layer is formed on the hot side of a thick near-intrinsic thermoelectric semiconductor. The figure of merit derived from direct measurements of electrical parameters and heat flow is increased by as much as a factor of eight. The question of what physical mechanisms are involved has been of interest since the initial observations of the effect. We have conjectured that the short-circuit current injection in these experiments is due to a second-order thermionic injection mechanism. More recently, we proposed that the open-circuit voltage comes about due to the presence of a p-type blocking layer between the emitter and the near-intrinsic bulk region. The experiments reported here show that a p-type blocking layer is required for the effect, and the dependence of conversion efficiency on the blocking layer concentration and width is studied. The results are generally consistent with calculations done so far based on a nonlocal generalized Onsager-type transport model.

Current transport and thermoelectric properties of very high power factor Fe3O4/SiO2/p-type Si(001) devices

“…A further, positive, increase of VA will attract electrons towards the Si / SiO 2 interface causing inversion and the current will then flow from the conduction band of Si(001) into the should open a gap at the Fermi energy resulting into the metal-insulator transition below T V = 120 K [17] and a reduction in the current for a specific applied voltage. From the above, we conclude that the Fe 3 O 4 / SiO 2 / p-type Si(001) heterostructure acts like a p-n junction, which is expected to limit the ohmic return current that occurs in bulk materials during charge redistribution under a temperature gradient resulting into higher thermopower as has been shown in p-n thermal diodes [18]. However, before elaborating further on the thermoelectric properties it is necessary to consider in more detail the current flow distribution in the lateral direction since this is critical in extracting the resistivity and power factor of the In addition, the temperature dependence of the longitudinal resistance exhibits a sharp drop with increasing temperature as shown in the inset of Fig.…”

“…At low temperatures, only a limited number of carriers will undergo tunneling from the Fe 3 O 4 into the Si(001) but for temperatures above 200K a larger number of electrons will cross into the underlying p-type Si(001), which in turn allows one to measure the potential difference that develops as a result of the charge redistribution in the p-type Si(001) due to the applied temperature gradient. We should note that hot carrier filtering through barriers with heights of many kT [28] or carrier injection using p-n thermal diodes [18] have been shown to yield high S and ZT although the precise physical mechanisms are not yet well understood. It is, therefore, possible that hot carrier filtering occurs due to the specific electronic structure of Fe 3 O 4 and the existence of the two spin down bands as shown in Fig.…”

Sensing Power MOSFET Junction Temperature Using Circuit Output Current Ringing Decay

“…This method has the potential to provide a reasonably accurate highbandwidth estimate of the device junction temperature. However, galvanic isolation is not achieved [6] due to the location of the diode on the semiconductor device die. Noise from the device switching can also cause problems, as the variation of the voltage based on temperature change is on the order of millivolts, while the voltage being switched may be on the order of hundreds of volts [7].…”

Monte Carlo study of the Electron Transport Properties of an Array of Si Nanocrystals

“…This is mainly due to their decreased thermal conductivity compared to the corresponding bulk material. Moreover, enhanced thermoelectric power factor has been reported in nanocrystalline materials and was attributed to the presence of energy barriers [1][2][3][4][5][6][7][8]. Here, we present Monte Carlo simulations on the transport properties of nanocrystalline Si.…”