Design and characterization of self-switching diode and planar barrier diode as high-frequency rectifiers

The development of high-speed rectifying devices has become one of major research areas which can be utilized in many applications, including radio-frequency (RF) and detection systems. Examples of these devices are Schottky diode and planar-doped barrier diode. However, all these excellent devices require a very challenging in fabrication process due to their complex structures and a precise doping concentration for each critical layers which are relatively high cost. The prospects of using electronic devices with planar structure are therefore become increasingly promising. These planar devices provide additional advantages of being not only simple but also able to operate at high frequencies. As such, in this research work, the feasibility of utilizing two silicon-based planar nanodevices of self-switching diode (SSD) and planar barrier diode (PBD) for microwave and terahertz rectification has been demonstrated using simulations. SSD has recently been demonstrated as room-temperature rectifiers operating at terahertz frequencies. In this research work, the rectifying performance of SSD is evaluated using a parameter known as the curvature coefficient, derived from the current-voltage (I-V) characteristic of the device. The effects of varying the geometrical structure and the insulator dielectric relative permittivity (from 1 – 9.3) of SSD on the curvature coefficient of the device are studied and analyzed by means of a two-dimensional device simulator. The simulations are also performed under temperature range of 250 – 500 K. The results show that the highest cut-off frequency attained in this research work is approximately 19 GHz, operating at unbiased condition. By implementing similar simulation settings used in demonstrating siliconbased SSDs, a new unipolar planar nanodiode as a rectifier is introduced and developed in this research work. This new device is referred as PBD which has a funnel-shaped geometrical channel that allows current to flow across the device. At zero bias, the nonuniform depletion region, developed at the neck of the funnel-shape channel due to surface charges at semiconductor/insulator interface, is predicted to create an energy barrier along the channel with asymmetrical profile. An external voltage applied across a PBD is expected to produce different height of the energy barrier depending either the voltage given is positive or negative. As a result, a nonlinear I-V characteristic is realized which can be utilized in signal rectification. This operating principle of PBD has been demonstrated and validated in the simulations of this research work. It has also been described using thermionic emission theory which may govern the flow of current across the device. Similar to SSD, the rectification performance of PBD is characterized and evaluated based on the curvature coefficient and cut-off frequency of the device. By varying the geometrical design and insulator dielectric relative permittivity (from 1-9.3) of PBD, curvature coefficient of the device can be optimized in order to improve the rectification performance. The highest cut-off frequency obtained in the simulation of this work is approximately 0.8 THz. Both SSD and PBD have a planar architecture that can therefore be realized in a single lithography step which makes the whole fabrication process of the devices simpler, faster and at lower cost when compared with other conventional electronic devices.