Bang Li

A single crystalline InP nanowire photodetector

Single crystalline nanowires are critical for achieving high-responsivity, high-speed, and low-noise nanoscale photodetectors. Here, we report a metal-semiconductor-metal photodetector based on a single crystalline InP nanowire. The nanowires are grown by a self-catalyzed method and exhibit stacking-fault-free zinc blende crystal structure. The nanowire exhibits a typical n-type semiconductor property and shows a low room temperature dark current of several hundred pA at moderate biases. A photoresponsivity of 6.8 A/W is obtained at a laser power density of 0.2 mW/cm2. This work demonstrates that single crystalline InP nanowires are good candidates for future optoelectronic device applications.

Self-catalyzed Growth of InAs Nanowires on InP Substrate

We report on the self-catalyzed growth of InAs nanowires on InP substrate by metal-organic chemical vapor deposition. At a moderate V/III ratio, tapered nanowires are obtained, suggesting a strong surface diffusion effect. Dense twin faults are observed perpendicular to the nanowire growth direction due to the fluctuation of In atoms in the droplet originating from the surface diffusion effect. At a lower V/III ratio, the nanowires exhibit kinking, which is associated with a high adhesion due to a large sticking coefficient of TMIn. The twin faults are dramatically suppressed and even completely eliminated in the NW branch after kinking, which is attributed to a stable In supply with a negligible diffusion effect. This work provides a method for the fabrication of defect-free InAs nanowires.

Controllable photoresponse behavior in a single InAs nanowire phototransistor

We demonstrate a single InAs nanowire phototransistor with controllable photoresponse behavior. The device is based on a top-gated nanowire field effect transistor with an electron mobility of 5790 cm2 V−1 s−1. In the absence of gate voltage, negative and positive photoresponses are observed under low and high illumination, respectively. By applying a relatively high negative/positive gate voltage, pure positive/negative photoresponse is obtained, respectively. The controllable photoresponse is attributed to a gate-voltage-induced barrier height modulation between the trap state energy level in the photogating layer and the conduction band of nanowire. The device is promising for optoelectronic applications.

Mimicking synaptic functionality with an InAs nanowire phototransistor

We demonstrate a nanowire (NW) phototransistor with synaptic behavior based on inherent persistent photoconductivity. The device is comprised of a single crystalline InAs NW, covered by a native indium oxide layer acting as the photogating layer (PGL). In the negative photoresponse range, the device mimics synaptic neuromorphic behaviors of short-term plasticity, long-term plasticity (LTP), and paired-pulse facilitation. Moreover, the transition from short-term to LTP is observed as the stimulus intensity increases, behaving in accord with the feature of cooperativity. The synaptic behaviors of the device are attributed to the photo-generated electrons trapped/detrapped in the PGL. This NW-based photonic synaptic device would find promising applications in neuromorphic systems and networks.

Modulating photoelectric performance of graphene/gallium arsenide nanowire photodetectors by applying gate voltage

Here, the authors demonstrate that the performance of graphene/gallium arsenide nanowire photodetectors could be modulated by applying gate voltage on graphene. The current–voltage curves under illumination continuously shift downward when an increasing negative gate voltage is applied, while they shift upward when an increasing positive gate voltage is applied, suggesting the modulation effect of gate voltage on the Schottky barrier height. Under a small negative gate voltage of 0.06 V, the dark current, on/off ratio, responsivity, and detectivity are dramatically improved from 6.1 to 0.22 nA, 13 to 2094, 57.1 to 351.2 mA/W, and 2.2 × 108 to 7.2 × 109 cm Hz1/2/W, respectively, due to the enhancement of the Schottky barrier height. This work provides an effective way for modulating the graphene/nanowire junction properties and enabling high performance photodetectors.Here, the authors demonstrate that the performance of graphene/gallium arsenide nanowire photodetectors could be modulated by applying gate voltage on graphene. The current–voltage curves under illumination continuously shift downward when an increasing negative gate voltage is applied, while they shift upward when an increasing positive gate voltage is applied, suggesting the modulation effect of gate voltage on the Schottky barrier height. Under a small negative gate voltage of 0.06 V, the dark current, on/off ratio, responsivity, and detectivity are dramatically improved from 6.1 to 0.22 nA, 13 to 2094, 57.1 to 351.2 mA/W, and 2.2 × 108 to 7.2 × 109 cm Hz1/2/W, respectively, due to the enhancement of the Schottky barrier height. This work provides an effective way for modulating the graphene/nanowire junction properties and enabling high performance photodetectors.

Fabrication and Characterization of An Ohmic GaAs Nanowire Photodetector

We have fabricated a single GaAs nanowire photodetector, which has an extremely low conduction current in dark and shows resistor-like linear conduction behavior under illumination. A highest responsibility was obtained as 1.58×10-3 A/W.