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# Introduction

Nanowires (NW) are being extensively studied due to their potential for novel electronic, photonic, thermal, electrochemical and mechanical properties.(Yang 2010) (Dasgupta 2014) (Li 2006) There does not seem to be a limit to the innovative electronic designs that are being created to test the limits of these properties. This article reviews the most recent electronics that have been designed using Gallium Arsenide (GaAs) nanowires. Within the last 5 years Gallium Arsenic (GaAs) nanowires have been explored for a myriad of possible devices including, transistors, photo-detectors, LED, solar cells, nanolasers, thermoelectric and piezoelectric devices.

# Transistors

Transistors are at the heart of any electronic device. Of course, in order to make smaller devices the transistors must scale accordingly. NW’s small dimensions naturally make it a candidate for transistor fabrication. In particular GaAs NW are of interest due to having high charge carrier mobility, a desirable trait for devices such as microchips, which has historically been dominated by Si technology. Miao and coworkers have recently done record breaking work by creating GaAs NW arrays in planar (as opposed to typical vertical) form for T-gated high electron mobility transistors (HEMTs).(Miao 2014) A 1.5x1.5 $$cm^2$$ chip with 115 planar HEMTS was fabricated and characterized in terms of its DC current-voltage characteristics and radio frequency (RF) performance. Growth methods included etching alignment markers on a GaAs substrate with iductively coupled plasma, depositing Au seeds (100nm diameter and 300nm seperation distance) and VLS growth.(Miao 2013) Characterization testing found $$\frac{f_t}{f_{max}}=\frac{33}{75}GHz$$ and $$\frac{I_{on}}{I^{off}}=10^4$$. The GaAs NW chip greatly outperfroms other current NW, carbon nanotube, or graphene Field Effect Transistors (FET) (Figure \ref{fig:best}). (Miao 2014)

\label{fig:best} A log-linear plot of DC performance vs RF performance. The GaAs NW perform orders of magnitude better than previous fabrications. Gate length (L_G) Figure 5 from reference (Miao 2014)

GaAs NW FET have been demonstrated for detection of biological electrical activity, such as electrical activity produced by skeletal muscles and recorded as electromyogram (EMG).(Imai 2014) The stochastic resonance, a phenomenon in which a system’s response to weak signals increases by the addition of noise, was taken advantage of along with a technique of parallel summing network in order to detect the EMG in a human forearm.(Imai 2014)

# Photodectors and Sensors

Spectrosocopy and imaging are important to provide insight into analysis, and characterization of a chemical physical processes. (Dai 2014)Furthermore, optical data links, such as vertical cavity surface emitting lasers, rely on photodectors on the receiving end to be sensitive enough to detect different frequencies of light.(Seyedi 2014) Therefore improvements of photodectors and other sensors are always desired.

Peng and coworkers developed single GaAs nanowires as microscopic coherent THz sensors.(Peng 2015) These single GaAs nanowire detectors were fabricated using a direct laster lithographic technique and were even used as a spectrometer to measure the transmission spectrum of a 290 GHz low pass filter.

Dai and coworkers have developed a nanowire photodetector using a GaAs core and AlGaAs shell nanowires.(Dai 2014) In typical III-V NW the large density of surface states pin the surface fermi energy, limiting carrier mobility. These surface states were “passivated” by placing a “shell” on top. The GaAsAl shell and GaAs are found to be significantly more sensitive as a photodetector than the GaAs nanowire alone. Low dark current and high photoresponsivity was found in the range of 300-890 nm.

Seyedi and coworks also demonstrated the power of GaAs core and AlGaAs shell NW. They explain how NW based photodectors have detection limits based on active area diameter and GaAs nanowires have large active areas. A bandwidth sensitivity of several GHz was found for the NW.(Seyedi 2014)