Daniel Wallin

Electrical properties of self-assembled branched InAs nanowire junctions

We investigate electrical properties of self-assembled branched InAs nanowires. The branched nanowires are catalytically grown using chemical beam epitaxy, and three-terminal nanoelectronic devices are fabricated from the branched nanowires using electron-beam lithography. We demonstrate that, in difference from conventional macroscopic junctions, the fabricated self-assembled nanowire junction devices exhibit tunable nonlinear electrical characteristics and a signature of ballistic electron transport. As an example of applications, we demonstrate that the self-assembled three-terminal nanowire junctions can be used to implement the functions of frequency mixing, multiplication, and phase-difference detection of input electrical signals at room temperature. Our results suggest a wide range of potential applications of branched semiconductor nanostructures in nanoelectronics.

Nonlinear electrical properties of three-terminal junctions

The authors report on room-temperature electrical measurements of three-terminal junctions made from a semiconductor heterostructure. The correlation between the junction size of the devices and the voltages needed to be applied in order to observe the electrical characteristics of three-terminal ballistic junctions is studied. The authors show that the ballistic behavior of electron transport can be observed in a three-terminal junction with a junction size of a few micrometers, much larger than the mean free path of electrons in the material. The results are explained in terms of a bias-induced enhancement of the electron mean free path in the system.

Novel nanoelectronic triodes and logic devices with TBJs

In this letter, we demonstrate the realization of novel diodes, triodes, and logic gates with three-terminal ballistic junctions (TBJs) made from a semiconductor heterostructure. The approach exploits the ballistic nature of electron transport, which has emerged in the nanostructures. Importantly, we show that TBJs function as logic AND gates and can be used to construct other compound logic gates, such as NAND gates with voltage gain, when combined with a point contact (an inverter). The demonstrated devices show favorable characteristics such as low turn-on voltage in rectification and room-temperature operation.

A Novel SR Latch Device Realized by Integration of Three-Terminal Ballistic Junctions in InGaAs/InP

In this letter, a novel sequential logic device based on three-terminal ballistic junctions (TBJs) is proposed and demonstrated. Two TBJs and two in-plane gates are laterally integrated in a high-electron-mobility InGaAs/InP quantum-well material by a single-step lithography process. Electrical measurements reveal that the integrated device functions as a set-reset (SR) latch with voltage gains at room temperature. The demonstrated device provides a new and simple circuit design for SR latches in digital electronics.

Frequency mixing and phase detection functionalities of three-terminal ballistic junctions

Three-terminal ballistic junctions (TBJs) are fabricated from a high-mobility InP/In0.75Ga0.25As heterostructure by electron-beam lithography. The voltage output from the central branch is measured as a function of the voltages applied to the left and right branches of the TBJs. The measurements show that the TBJs possess an intrinsic nonlinearity. Based on this nonlinearity, a novel room-temperature functional frequency mixer and phase detector are realized. The TBJ frequency mixer and phase detector are expected to have advantages over traditional circuits in terms of simple structure, small size and high speed, and can be used as a new type of building block in nanoelectronics.

A highly tunable lateral quantum dot realized in InGaAs/InP by an etching technique

We report on the realization of a quantum dot in a modulation doped InGaAs/InP heterostructure by electron beam lithography and chemical wet etching. Using etched trench defined in-plane gates and a local top gate, the tunneling barriers, electron density, and electrostatic potential of the dot can be tuned. Electrical measurements reveal clear Coulomb blockade behavior of the electron transport through the dot and the behavior of electron tunneling through its excited states.

Detection of charge states in nanowire quantum dots using a quantum point contact

The authors demonstrate operation of a charge readout scheme for quantum dots in a semiconductor nanowire using a quantum point contact defined in a GaAs∕AlGaAs two-dimensional electron gas beneath the nanowire. The quantum dots were fabricated by epitaxial growth of InP barriers along a n-type InAs nanowire. Applying negative voltages to two split-gate electrodes aligned to the nanowire induces a quantum point contact in the two-dimensional electron gas such that charging of quantum dots in the nanowire modulates the quantum point contact transmission, thus resulting in the desired detector response.

Nanoimprint lithography for fabrication of three-terminal ballistic junctions in InP/GaInAs

We present processing technology and characterization results for InP/GaInAs two-dimensional electron gas (2DEG) three-terminal ballistic junction (TBJ) devices manufactured using nanoimprint lithography (NIL). To transfer sub-100 nm features into a high-mobility InP-based 2DEG material, we used SiO2/Si stamps made using electron beam lithography and reactive ion etching. After NIL, the resist residues are removed in oxygen plasma; this is followed by wet etching of InP/GaInAs to define the TBJ structures. Fabricated TBJ devices are characterized using scanning electron microscopy and electron transport measurements. Highly non-linear electrical characteristics as predicted by the theory (Xu H Q 2001 Appl. Phys. Lett. 78 2064) are demonstrated.

Electrical properties and logic function of multibranch junction structures

We report on room-temperature electrical measurements of multibranch junction (MBJ) devices made from a semiconductor heterostructure. We show that the MBJ devices exhibit an interesting electrical property. If the voltage output at one branch is measured as a function of the voltages inputs to all the other branches, the output voltage is determined predominately by the most negative, or the lowest, voltage applied. The property arises from the nature of the voltage-induced ballistic electron transport in the MBJ device, and can in general be observed in other nanoscale MBJ structures. We also demonstrate the realization of very compact multi-input logic gates with the MBJ structures.

A sequential logic device realized by integration of in-plane gate transistors in InGaAs/InP

An integrated nanoelectronic circuit is fabricated from a high-mobility In0.75Ga0.25As/InP heterostructure. The manufactured device comprises two double in-plane gate transistors with a current channel of 1.1 mu m in length and 100 nm in width. The two transistors are coupled to each other in a configuration that the source of one transistor is directly connected with one in-plane gate of the other transistor. Electrical measurements reveal that this device functions as an SR (set-reset) latch (a sequential logic device) with a gain of similar to 4 in the logic swing at room temperature. The demonstrated device provides a simple circuit design for SR latches.