Electrical double layer gating in GaAs–(Al,Ga)As heterostructures using tetrabutylammonium bis(trifluoromethylsulfonyl)imide

Abstract

We report on the gating in GaAs-(Al,Ga)As heterostructures using the electrical double layer of ionic liquids. We employ tetrabutylammonium bis(trifluoromethylsulfonyl)imide for the ionic liquid, which has a melting point of 92 • C. As the 'ionic liquid' is solid at room temperature, the device operation is more stable compared to when an aqueous electrolyte is used. Hysteretic behavior appeared in the variation of the resistance when the negative gate bias exceeded ∼ −3 V, which is considered to be the electrochemical window of the ionic liquid. Temporary gate degradation occurred when the positive gate bias was larger than 8 V. We attribute these characteristics to the generation of space charge and its slow dissipation in the ionic liquid. The gating ceases to function at low temperatures with a transition range of 100-200 K due to the freezing of ions.

Element substitution from substrates in Bi2Se3, Bi2Te3and Sb2Te3overlayers deposited by hot wall epitaxy

“…Despite the large vapour pressure of P, the P resulting from the substitution may remain on the substrate surface if the generation is faster than the evaporation. Similar survival of Bi droplets was reported in [1,2] when the substitution took place for Bi 2 Se 3 and Bi 2 Te 3 .…”

“…(For comparison, the melting point of Sb 2 Te 3 is 629 °C.) Indeed, the mean bond energies were reported to be 422, 407 and 377 − kJ mol 1 for Bi 2 Se 3 , Sb 2 Te 3 and Bi 2 Te 3 , respectively [18]. That the substitution occurs in fewer cases for Bi 2 Te 3 than for Bi 2 Se 3 is, therefore, unexpected.…”

“…In hot wall epitaxy growth of chalcogenide layers, the composing elements in the layers are substituted by the atoms diffused from the substrates for some combinations of the layer and substrate materials [1][2][3][4]. For Bi 2 Se 3 [1], Bi 2 Te 3 [2] and Sb 2 Te 3 [2] layers prepared on Cu or Ag surfaces, Bi and Sb are replaced entirely by these transition metals. In contrast to the complete substitution on the Cu and Ag surfaces, the substitution is partial on Ni surfaces and no substitution takes place on Au surfaces.…”

“…It may be of considerable importance in applying the substitution phenomenon that the diffusion of the substrate atoms across the synthesized compounds can be remarkably long. The resultant compounds form in some cases objects that are of tens of micrometers in size [1,2].…”