Band alignment and polarization engineering inκ-Ga_(2)O_(3)/GaN ferroelectric heterojunction

Ferroelectric-semiconductor heterostructures offer an alternative strategy to manipulate polarization towards advanced devices with engineered functionality and improved performance.In this work,we report on the heteroepitaxial construction,band structure alignment and polarization engineering of the single-phasedκ-Ga_(2)O_(3)/GaN ferroelectric/polar heterojunction.A type-II band alignment is determined at theκ-Ga_(2)O_(3)/GaN polar hetero-interface,with a valence band offset of(1.74±0.1)eV and a conduction band offset of(0.29■0.1)eV.Besides the band edge discontinuity,charge dipoles induced by spontaneous polarization lead to the observed band bending with built-in potentials of 0.9 and 0.33 eV,respectively,at theκ-Ga_(2)O_(3)surface andκ-Ga_(2)O_(3)/GaN interface.The polarization switching properties of ferroelectricκ-Ga_(2)O_(3)are identified with a remanent polarization of approximately 2.7μC/cm^(2)via the direct hysteresis remanent polarization/voltage(P-V)loop measurement.These findings allow the rational design ofκ-Ga_(2)O_(3)ferroelectric/polar heterojunction for the application of power electronic devices,advanced memories and even ultra-low loss negative capacitance transistors.

Adsorption behaviour of molecular sieve and activated carbon for CO_(2) adsorption at cold temperatures

At present,insufficient works have provided insights into the application of adsorption to remove CO_(2) in flue gas below room temperatures under ambient pressure.In this work,the effects of temperature,CO_(2) partial pressure and moisture on dynamic adsorption characteristics for CO_(2) are conducted for various adsorbents.Based on our findings,lower the adsorbing temperature can drastically enhance the adsorption of carbon dioxide over molecular sieves and activated carbon.Among various adsorbents,13X molecular sieve shows highest adsorption capacity.With a concentration of 10%CO_(2) in flue gas,the specific adsorption capacity of CO_(2) over 13X molecular sieve is 0.11,2.54 and 5.38 mmol/g at 80℃,0℃ and -80℃,respectively.In addition,the partial pressure of CO_(2) also has a significant impact on the adsorption capacity.With the increment of the concentration of CO_(2) from 1%to 10% under 0℃,the specific capacity of 13X molecular sieve increases from 1.212 mmol/g to 2.538 mmol/g.Water vapor in flue gas can not only reduce the specific adsorption capacity of CO_(2) due to competing adsorption,but also increase the heat penalty of molecular sieve regeneration due to the water adsorption.An overall analysis is conducted on the energy penalty of capture 1 ton CO_(2) at various adsorption temperatures between -80℃ and 80℃,considering both the heat penalty of molecular sieve regeneration as well as the energy penalty for cooling the adsorber.It is found that the lowest energy penalty is about 2.01 GJ/ton CO_(2) when the adsorption is conducted at 0℃.