Ballistic transport in nanoscale self-switching devices

Abstract

Using the Monte Carlo method, a type of semiconductor nano-device called self-switching device (SSD), which has diode-like I-V characteristics, was simulated. After analyzing the microscopic transport behavior of the carriers, we show that the ballistic effects exist in the SSDs when the channel length of the device is extremely short (~120 nm). Furthermore, we show that the ballistic effect doubles the average drift velocity of the carriers (to ~6.0×10 7 cm/s) in short-channel SSDs, which decreases the transit time. This implies that when the dimensions are decreased to nanoscale length, the SSD can operate much faster because the ballistic effect increases the operation speed of the device. Moreover, because of the ballistic transport, the energy efficiency may also be improved. During the last two decades, the dimensions of compound semiconductor devices have become smaller. Electronic devices at micrometer and nanometer scale have attracted increasing attention [1][2][3]. In 2003, using an asymmetric structure, Song et al. designed a novel device with diodelike I-V characteristics, which was called a self-switching device (SSD) [4]. The fabrication of SSD is remarkably simple, and only requires one etching step to produce the two required insulating trenches. This simplicity makes it possible to downscale the geometrical dimensions of the device to nanoscale, which increases its cut-off frequency. It has been reported that a SSD can operate at a frequency over 110 GHz at room temperature [5] and at 2.5 THz at 150 K [6]. SSDs are fabricated using modulation-doped quantum well structures such as InGaAs/InP and InGaAs/InAlAs, in which the carriers transported in the active layer form two dimensional electron gas (2DEG). After the growth of each layer, only two insulating L-shaped trenches (with a width *Corresponding author (email: stswangg@mail.sysu.edu.cn) of d and a length of L) along the direction perpendicular to the surface needed to be etched. This etching can be done using high-resolution lithography (as shown in Figure 1). Between these two trenches, there is a channel with a width of W in which the electrons are transported.When in operation, the left side is grounded and a bias voltage is applied to the right side. The diode-like I-V characteristics were simulated using the Monte Carlo method in this paper. It has been shown [4,7,8] that the electrical properties of a SSD are partially determined by its geometrical structure. Increasing either the width of the channel, W, or the trenches, d, will decrease the threshold voltage of the SSD (but not decrease it below zero). These parameters also influence the drain current when the reverse bias voltage is applied. This means that, as a switching device, the threshold voltage of a SSD is adjustable. If the geometrical parameters W, d or L are chosen properly, the threshold voltage can be set to zero.It has been suggested that SSDs have a diode-like I-V characteristics because of the field effects resulting from the charging regions near the channel [9...

The Monte Carlo Method Used in Self-Switching Device

“…The material of self-switching device usually is InGaAs/InP and InGaAs/InAlAs, which has modulation-doped quantum well structure [5]. So the carriers transported in the active layer will form two dimension gas (2DEG).…”