H. Mousa, K. Teker
Istanbul Sehir University,
Keywords: In-Situ doping, Silicon Carbide Nanowires, Optical properties
Summary:With the increase interest to the wideband gap (WBG) semiconductors, Silicon Carbide (SiC) is proving to be a promising candidate for fabricating nanoelectronic and optoelectronic devices such as field-effect transistors (FETs), diodes, and UV sensors. What makes SiC a good candidate compared to the other semiconductors is its ability to withstand harsh environments, high radiation resistance as well as its high breakdown field. In order to integrate any semiconductor devices for electronics and photonics, it is required to form p-type and n-type conductivity. In this work, we have investigated in-situ n-type doping of SiC nanowires (SiCNWs) by studying the electrical and photoelectrical properties of undoped and nitrogen- doped SiCNWs. The synthesis of the undoped SiC nanowires took place in a single source cold-wall RF heated MOCVD reactor on SiO2 /Si substrate at a temperature of 1100°C with Ni as a catalyst. The growth process was repeated by flowing nitrogen at a rate of 1 sccm to produce the doped- SiCNWs. In order to fabricate the single SiCNW device, dielectrophoresis was used to integrate the grown SiCNWs onto pre-patterned Au electrodes with a channel width of around 3 µm onto a highly-doped Si substrate (acting as the back gate) covered with an oxide layer. Figure 1(a) shows an SEM image of the grown SiC nanowires on a SiO2 /Si substrate. Figure 1(b) shows the aligned SiC nanowire between the Au electrodes. The transport properties were studied by sweeping gate voltage (Vg) from -30 V to 30 V at a constant source-drain voltage (Vds) of 0.01 V. Figure 2(a) shows the Ids - Vgs curve of the N-doped SiCNW device. Figure 2(b) shows the Ids - Vgs curve of the undoped SiCNW device. In comparing the Ids – Vgs curves of the N-doped and undoped SiCNW devices, the current of the N-doped SiCNW device is 2240 times higher than the undoped SiCNW device at constant Vg of 30 V. Moreover, the Ids – Vgs for the undoped device shows an ambipolar behavior with unbalanced p-branch (negative gate voltages side) and n-branch (positive gate voltages side). After doping, a significant conductance change at the n-branch was observed. The more details will be discussed in the paper. Next, the photoelectric properties of the N-doped SiCNW device were investigated by exposure to a UV light with a wavelength of 254 nm and intensity of 1.8 mW/cm2. The rise and decay times were determined to be 0.09 s and 0.06 s for the undoped SiCNW device. Nevertheless, the speed of the N-doped SiCNW device was slightly reduced under the UV light exposure. Moreover, the mechanisms of the change in conductance and speed of the device to the UV light due to nitrogen doping will be discussed in details.