Fabrication and characterization of La_(2-x)Sr_xCuO _4/Nb-SrTiO_3 heterojunctions in different doped regimes

摘要

Two types of p-n junction were fabricated by depositing underdoped La _(1.9)Sr_(0.1)CuO_4 film and overdoped La _(1.8)Sr_(0.2)CuO_4 film on n-type 0.5 wt.% Nb-doped SrTiO_3 (NSTO) substrates using pulsed laser deposition technique (PLD), respectively. Current-voltage (I-V) characteristics of the La _(2-x)Sr_xCuO_4/NSTO heterojunction were measured in the temperature range from 5 K to 300 K. All I-V curves show a fine rectifying property and a visible reduction of the diffusion potential (V_d) is observed, but the behaviors of V_d are vastly different for the underdoped and overdoped regimes at temperatures below T_c. Analysis results show that the characteristics of the heterojunction are possibly affected not only by the superconducting gap of LSCO at T_c, but also by the depletion layer in the interface of LSCO/NSTO junction. The variation of the depletion layer is possibly different under the same applied bias voltages for the underdoped La_(1.9)Sr_(0.1)CuO_4/NSTO junction and overdoped La_(1.8)Sr_(0.2)CuO_4/NSTO junction due to the difference of carrier density at La_(1.9)Sr _(0.1)CuO_4 and La_(1.8)Sr_(0.2)CuO _4.