, MBE) system to deposit the ferromagnetic (FM) electrodes 85 as drain and source tunneling contacts, vol.84
The 2 nm MgO is used 87 as a tunnel barrier between metals and BP to effectively 88 reduce the contact Schottky barrier height. 25 After deposition 89 and lift-off procedures ,
Finally, the 93 device was annealed at 120 C for one hour in vacuum and 94 then followed by the coverage of 10 nm MgO protection 95 layer. Figure 1(b) shows the schematic of electric characteri96 zation of BP based transistor. A drain-source bias (V ds ) was 97 applied between the two contacts to inject the current I ds 98 through the BP channel. Meanwhile, a back-gate voltage 99, nm)/Ti(10 nm) was thermally evaporated in a 92 PLASSYS MEB400s system for the large pads ,
Drain-source current-voltage (I ds 2V ds ) 103 characteristics 104 The two-terminal drain-source current-voltage charac105 teristics (I ds-V ds ) were studied at 20 K between the electro106 des E1 and E2 with negative and positive back-gate voltages 107 [Figs. 1(c) and 1(d), respectively]. From the measurement of 108 I ds ÀV ds , the back-gate voltages show an efficient modulation 109 on the I ds ,
, As soon as we applied a negative or positive 112 back-gate voltage V g , the I ds-V ds characteristics dramatically 113 change. The quasi-symmetric nonlinearity of I ds-V ds is 114 attributed to the back-to-back Schottky diode structures of 115 204 contacts, At V g ¼ 0 V, the current density is rather low (I ds <1 pA at 111 V ds ¼ 61 V)
, Co/TiO 2 /BP contacts. 24 This high I on /I off ratio provides prom
, K, the 212 I off current (at V g $ 0 V) is mainly dominated by the therm213 ionic injection through Schottky barrier, which is proportional 214 to exp(ÀqU B /k B T), 31 where k B is the Boltzmann constant and 215 U B is Schottky barrier height
, Thus, the slope of ÀqU B /k B can be extracted from a linear fit217 ting of ln(I on /I off ) versus 1/T, as shown in the insert of Fig
, Moreover, both for hole and electron transport regions, the
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