# Space Charge Effect and Resistance Switching in Doped Monocrystalline Silicones
## 3 Results
The proposed classification might be useful to explore a new type of RS device from the shape of the loop in the view of technology. Secondly, the microscopic nature of a memristor is the voltage-dependent ionic re-arrangement [7; 8; 9; 10; 11; 12; 13; 14], which is achieved mainly by the so-called filament effect. Since the hysteresis of ionic migration always exists, the memory effect holds in the whole range of the applied voltage. On the other hand, SCE-RS depends on the dynamics of carriers at a high electric field. Filling and ionization are dynamically balanced in Ohmic regime; thus, the memory effect disappears at zero voltage. Thirdly, the filament effect and its related devices have been realized in polycrystalline oxides, amorphous semiconductors, or nanowires with nanoscale devices [10; 11; 12; 13; 14; 15; 16; 17]. However, in the present work, SCE-RS is achieved in the millimeter scale monocrystalline device. In such a case, the filament effect can be ruled out absolutely. Since SCE-RS is induced by the dynamics of carriers instead of an ion filament effect, with a decrease in thermal disturbance, SCE and SCE-RS are supposed to appear at a lower electric field [18]. Figure 4 shows the temperature dependence of the normalized critical voltages measured in a doped n-Si sample 1016-1\(\#\) with \(L\) = 2 mm. In general, the critical voltages decline with a decrease in temperature. Therefore, the SCE-RS loop shows up at lower voltage. Two SCE-RS loops, measured at 30 and 50 K, are shown in the inserted figure, and the data measured at 300 K in the same voltage range are presented together for comparison. Both the lower and upper critical voltages decrease abruptly from 300 K and slightly between 150 K and 20 K. Assuming the density of states of dopants is exponentially distributed [2; 3; 4; 5; 6], the ionization suppression of dopants with shallow levels needs a lower thermal energy, and its density of states is high, resulting in the abrupt decline of the critical voltages initially. The ionization suppression of dopants with deep band sites needs higher energy, but its density of states is relatively small. Hence a slight decline in the critical voltages from 150 K to 20 K is acceptable. In the case of the ion filament effect, a memristor needs an ionic rearrangement, and the ability of ionic migration decreases at low temperatures. Thus, a higher working electric field is needed for a memristor at low temperatures, as reported by [PERSON] et al. in Si nanowires [16]. Figure 4: Temperature dependence of two critical voltages. The temperature dependence of the normalized critical voltages measured in device 1016-1\(\#\) with \(L\) = 2 mm in the range of 20 K to 300 K. Insert, two SCE-RS loops at 30 and 50 K. The data measured at 300 K is presented in the insert for comparison. Finally, Figure 5a shows the influence of a magnetic field on the I-V curve of device 0129-1# at room temperature. The inserted figure is the schematic measurement configuration. A magnetic field was applied perpendicularly to the sample surface and the direction of the current. The magnetic field suppresses the current all through the I-V curve, and its influence is more significant in the MG regime. The magnetoresistance in the MG regime reaches 20% under 2T field, which is almost 300% enhanced compared with that in Ohmic regime. It was noted that the value of magnetoresistance observed in our heavily doped samples was smaller than that of lightly doped ones in the previous reports [7; 21; 22; 23]. But their common point lies in the enhanced magnetoresistance appearing in nonlinear regimes. The suppression by the magnetic field on the I-V curve in Ohm, ETF and MG regimes is different; hence, both \(V_{\rm L}\) and \(V_{\rm U}\) may shift. However, as shown in Figure 5b, the variation of \(V_{\rm L}\) is negligible compared with the monotonic increase of \(V_{\rm U}\) under a magnetic field.